At what temperature does steel melt?
Tungsten
Of all metals in pure form, tungsten has the highest melting point (3422 °C, 6192 °F), lowest vapor pressure (at temperatures above 1650 °C, 3000 °F), and the highest tensile strength. Although carbon remains solid at higher temperatures than tungsten, carbon sublimes at atmospheric pressure instead of melting, so it has no melting point. Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and tensile strength of tungsten originate from strong covalent bonds formed between tungsten atoms by the 5d electrons.
Alloying small quantities of tungsten with steel greatly increases its toughness.
Steel
Crucible steel is steel that has been melted in a crucible rather than having been forged, with the result that it is more homogeneous. Most previous furnaces could not reach high enough temperatures to melt the steel. The early modern crucible steel industry resulted from the invention of Benjamin Huntsman in the 1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast (usually) into ingots.
Allotropes of iron
As it cools to 770 °C (1,418 °F), the Curie point (T), the iron is a fairly soft metal and becomes ferromagnetic. As iron passes below the Curie temperature, no structural change occurs, but the magnetic properties as the magnetic domains become aligned. This form of iron is stable form at room temperature. α-Fe can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form termed ε-iron, which crystallizes in a hexagonal close-packed (hcp) structure.
Red-short carbon steel
When the steel is heated up and worked, the mechanical energy added to the workpiece increases the temperature further. The iron sulfide (FeS) or iron/iron sulfide alloy (which has an even lower melting point) begins to melt, and the steel starts to separate at the grain boundaries. Steelmakers add manganese (Mn) to the steel when it is produced, to form manganese sulfide (MnS). Manganese sulfide inclusions have a higher melting point and do not concentrate at the grain boundaries. Thus, when the steel is later heated up and worked, the melting at the grain boundaries does not occur.
Lightbulb socket
The lampholder must be located far enough from the filament that the metals with the lowest melting point will remain solid. Historically this metal was a tin/lead solder whose melting point might be as low as 180 °C (360 °F). Due to the thermal changes from ambient temperature to full operating temperature, the design of a socket must allow for a considerable amount of expansion and contraction. Spring elements are required to accommodate these dimensional changes. However, the temperature at which a metal loses its spring is far below the melting point. This is why some older sockets that no longer work can be restored by prying up the base spring slightly.
Structural steel
The lowest temperature at which a plain carbon steel can begin to melt, its solidus, is . Steel never turns into a liquid below this temperature. Pure Iron ('Steel' with 0% Carbon) starts to melt at , and is completely liquid upon reaching . Steel with 2.1% Carbon by weight begins melting at , and is completely molten upon reaching . 'Steel' with more than 2.1% Carbon is no longer Steel, but is known as Cast iron.
Tempering (metallurgy)
Precise control of time and temperature during the tempering process is crucial to achieve the desired balance of physical properties. Low tempering temperatures may only relieve the internal stresses, decreasing brittleness while maintaining a majority of the hardness. Higher tempering temperatures tend to produce a greater reduction in the hardness, sacrificing some yield strength and tensile strength for an increase in elasticity and plasticity. However, in some low alloy steels, containing other elements like chromium and molybdenum, tempering at low temperatures may produce an increase in hardness, while at higher temperatures the hardness will decrease. Many steels with high concentrations of these alloying elements behave like precipitation hardening alloys, which produces the opposite effects under the conditions found in quenching and tempering, and are referred to as maraging steels.
Steel
Iron is commonly found in the Earth's crust in the form of an ore, usually an iron oxide, such as magnetite or hematite. Iron is extracted from iron ore by removing the oxygen through its combination with a preferred chemical partner such as carbon which is then lost to the atmosphere as carbon dioxide. This process, known as smelting, was first applied to metals with lower melting points, such as tin, which melts at about , and copper, which melts at about , and the combination, bronze, which has a melting point lower than . In comparison, cast iron melts at about . Small quantities of iron were smelted in ancient times, in the solid state, by heating the ore in a charcoal fire and then welding the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon content could be controlled by moving it around in the fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily.
Mushet steel
In 1899 and 1900, Taylor and Maunsel White were experimenting with hardening processes for Mushet steel and other self-hardening steels. They discovered if the steel is heated to near its melting point it creates a more durable metal. The metal will retain its hardness up to a red heat. This type of hardened self-hardening steel was the first high speed steel.
Vanadium
Vanadium is a medium-hard, ductile, steel-blue metal. It is electrically conductive and thermally insulating. Some sources describe vanadium as "soft", perhaps because it is ductile, malleable, and not brittle. Vanadium is harder than most metals and steels (see Hardnesses of the elements (data page) and iron). It has good resistance to corrosion and it is stable against alkalis and sulfuric and hydrochloric acids. It is oxidized in air at about 933 K (660 °C, 1220 °F), although an oxide passivation layer forms even at room temperature.
Tin
Tin is a soft, malleable, ductile and highly crystalline silvery-white metal. When a bar of tin is bent, a crackling sound known as the "tin cry" can be heard from the twinning of the crystals. Tin melts at low temperatures of about , the lowest in group 14. The melting point is further lowered to for 11 nm particles.
β-tin (the metallic form, or white tin, BCT structure), which is stable at and above room temperature, is malleable. In contrast, α-tin (nonmetallic form, or gray tin), which is stable below , is brittle. α-tin has a diamond cubic crystal structure, similar to diamond, silicon or germanium. α-tin has no metallic properties at all because its atoms form a covalent structure in which electrons cannot move freely. It is a dull-gray powdery material with no common uses other than a few specialized semiconductor applications. These two allotropes, α-tin and β-tin, are more commonly known as "gray tin" and "white tin", respectively. Two more allotropes, γ and σ, exist at temperatures above   and pressures above several GPa. In cold conditions, β-tin tends to transform spontaneously into α-tin, a phenomenon known as "tin pest". Although the α-β transformation temperature is nominally , impurities (e.g. Al, Zn, etc.) lower the transition temperature well below and, on the addition of antimony or bismuth, the transformation might not occur at all, increasing the durability of the tin.
Blacksmith
Another major difference between bronze and iron fabrication techniques is that bronze "can" be melted. The melting point of iron is much higher than that of bronze. In the western (Europe & the Mideast) tradition, the technology to make fires hot enough to melt iron did not arise until the 16th century, when smelting operations grew large enough to require overly large bellows. These produced blast-furnace temperatures high enough to melt partially refined ores, resulting in "cast iron". Thus cast iron frying pans and cookware did not become possible in Europe until 3000 years after the introduction of iron smelting. China, in a separate developmental tradition, was producing cast iron at least 1000 years before this.
Argentium sterling silver
Traditional sterling silver has a solidus melting temperature of 802°C (1475°F) and a liquidus flow point of 899°C (1650°F). Argentium 935 silver has a solidus of 803°C (1477°F) and a liquidus of 903°C (1657°F), while Argentium 960 has a solidus of 905°C (1661°F) and a liquidus of 925°C (1697°F).
Pnictogen
Nitrogen's melting point is −210 °C and its boiling point is −196 °C. Phosphorus has a melting point of 44 °C and a boiling point of 280 °C. Arsenic is one of only two elements to sublimate at standard pressure; it does this at 603 °C. Antimony's melting point is 631 °C and its boiling point is 1587 °C. Bismuth's melting point is 271 °C and its boiling point is 1564 °C.
Terne
Until the year 2012 lead had been replaced with the metal zinc and was used in the ratio of 50% tin and 50% zinc. This alloy had a low melting point of approximately 360 degrees Fahrenheit but is no longer available. Today terne coated metal is coated with 99.9% tin, instead of hot-dipping, a more consistent galvanic deposition process is applied. Additionally the substrate has been changed from steel to stainless steel, benefitting from the corrosion resistance of stainless steel alloys. The pure tin alloy makes soldering easier, as the melting point is homogenised and doesn't need to match the melting point of two metals with different melting temperatures.
Heat treating
Similarly, a hypoeutectoid alloy has two critical temperatures, called "arrests." Between these two temperatures, the alloy will exist partly as the solution and partly as a separate crystallizing phase, called the "proeutectoid phase." These two temperatures are called the upper (A) and lower (A) transformation temperatures. As the solution cools from the upper transformation temperature toward an insoluble state, the excess base metal will often be forced to "crystallize-out," becoming the proeutectoid. This will occur until the remaining concentration of solutes reaches the eutectoid level, which will then crystallize as a separate microstructure.
Britannia metal
Britannia metal is usually spun rather than cast, and melts at 255 degrees Celsius.
Alloy
While the high strength of steel results when diffusion and precipitation is prevented (forming martinsite), most heat-treatable alloys are precipitation hardening alloys, that depend on the diffusion of alloying elements to achieve their strength. When heated to form a solution and then cooled quickly, these alloys become much softer than normal, during the diffusionless transformation, but then harden as they age. The solutes in these alloys will precipitate over time, forming intermetallic phases, which are difficult to discern from the base metal. Unlike steel, in which the solid solution separates into different crystal phases (carbide and ferrite), precipitation hardening alloys form different phases within the same crystal. These intermetallic alloys appear homogeneous in crystal structure, but tend to behave heterogeneously, becoming hard and somewhat brittle.
Hot plate welding
With high-temperature hot plate welding, an uncoated hot plate is heated to between 300 and 400 °C, as the PTFE coating degrades at high temperatures. The high temperature decreases the viscosity of the melt, so it can peel off from the hot plate when removing the parts. This can be accompanied during the change-over phase by rapid movement of the parts from the hot plate; this prevents stringing of the melted plastic due to its viscoelastic properties. Any residual material on the hot plate's surface is usually either oxidized away or mechanically removed. With some thermoplastics, the residual material cannot be easily removed and accumulates over time. The hot plates may need to be removed and cleaned between cycles. With the higher temperatures, the matching and heating phases are shortened from those of conventional hot plate welding. However, reduced weld strength from thermal degradation of the plastic can still occur, though most of the degraded material is forced out by the flow of melted material. High-temperature hot plate welding is known to perform well for:
Heat treating
The diffusion transformation is very time-dependent. Cooling a metal will usually suppress the precipitation to a much lower temperature. Austenite, for example, usually only exists above the upper critical temperature. However, if the austenite is cooled quickly enough, the transformation may be suppressed for hundreds of degrees below the lower critical temperature. Such austenite is highly unstable and, if given enough time, will precipitate into various microstructures of ferrite and cementite. The cooling rate can be used to control the rate of grain growth or can even be used to produce partially martensitic microstructures. However, the martensite transformation is time-independent. If the alloy is cooled to the martensite transformation (M) temperature before other microstructures can fully form, the transformation will usually occur at just under the speed of sound.
Superheated water
Superheated water can be more corrosive than water at ordinary temperatures, and at temperatures above 300 °C special corrosion resistant alloys may be required, depending on other dissolved components. Continuous use of carbon steel pipes for 20 years at 282 °C has been reported without significant corrosion,
and stainless steel cells showed only slight deterioration after 40–50 uses at temperatures up to 350 °C.
The degree of corrosion that can be tolerated depends on the use, and even corrosion resistant alloys can fail eventually. Corrosion of an Inconel U-tube in a heat exchanger was blamed for an accident at a nuclear power station.
Therefore, for occasional or experimental use, ordinary grades of stainless steel are probably adequate with continuous monitoring, but for critical applications and difficult to service parts, extra care needs to be taken in materials selection.
Spin casting
A melting furnace is necessary only when spin casting metal. The metal must be molten prior to introduction into the mold. It is necessary for a spin casting furnace to have a temperature controller, as there is an optimal range for each metal. For example, a particular zinc alloy is typically cast between 775 and 800 °F, whereas it actually melts much lower around 500 °F. If the metal is introduced to the mold at a higher temperature (in this case, above 800 °F), it will wear the silicone prematurely, shortening the mold life. If the metal is introduced at significantly lower temperatures (below 775 °F), its solidification time will similarly be shortened resulting in incomplete or low quality castings. Spin casting metal requires a furnace with fine temperature control, and knowledge of proper casting temperature.
Maraging steel
The steel is first annealed at approximately for 15–30 minutes for thin sections and for 1 hour per 25 mm thickness for heavy sections, to ensure formation of a fully austenitized structure. This is followed by air cooling or quenching to room temperature to form a soft, heavily dislocated iron-nickel lath (untwinned) martensite. Subsequent aging (precipitation hardening) of the more common alloys for approximately 3 hours at a temperature of 480 to 500 °C produces a fine dispersion of Ni(X,Y) intermetallic phases along dislocations left by martensitic transformation, where X and Y are solute elements added for such precipitation. Overaging leads to a reduction in stability of the primary, metastable, coherent precipitates, leading to their dissolution and replacement with semi-coherent Laves phases such as FeNi/FeMo. Further excessive heat-treatment brings about the decomposition of the martensite and reversion to austenite.
Kevlar
Kevlar maintains its strength and resilience down to cryogenic temperatures (−196 °C); in fact, it is slightly stronger at low temperatures. At higher temperatures the tensile strength is immediately reduced by about 10–20%, and after some hours the strength progressively reduces further. For example: enduring 160 °C (320 °F) for 500 hours, reduces strength by about 10%; and enduring 260 °C (500 °F) for 70 hours, reduces strength by about 50%.
Allotropes of iron
β-Fe and the A critical temperature are important in induction heating of steel, such as for surface-hardening heat treatments. Steel is typically austenitized at 900–1000 °C before it is quenched and tempered. The high-frequency alternating magnetic field of induction heating heats the steel by two mechanisms below the Curie temperature: resistance or Joule (IR) heating and ferromagnetic hysteresis losses. Above the A, the hysteresis mechanism disappears and the required amount of energy per degree of temperature increase is substantially larger than below A. Load-matching circuits may be needed to vary the impedance in the induction power source to compensate for the change.
Aluminized steel
Aluminized steel is steel that has been hot-dip coated on both sides with aluminium-silicon alloy. This process assures a tight metallurgical bond between the steel sheet and its aluminium coating, producing a material with a unique combination of properties possessed neither by steel nor by aluminium alone. Aluminized steel shows a better behavior against corrosion and keeps the properties of the base material steel for temperature lower than . For example, it is commonly used for heat exchangers in residential furnaces, commercial rooftop HVAC units, automotive mufflers, ovens, kitchen ranges, water heaters, fireplaces, barbecue burners, and baking pans. This steel is very useful for heating things up because it transfers heat faster than most other steels.
Niobium
The metal takes on a bluish tinge when exposed to air at room temperature for extended periods. Despite a high melting point in elemental form (2,468 °C), it has a lower density than other refractory metals. Furthermore, it is corrosion-resistant, exhibits superconductivity properties, and forms dielectric oxide layers.
Solder
In specific proportions, some alloys can become eutectic — that is, their melting point is the same as their freezing point, and the alloy's melting point is lower than that of either component. Non-eutectic alloys have markedly different "solidus" and "liquidus" temperatures, and within that range they exist as a paste of solid particles in a melt of the lower-melting phase. In electrical work, if the joint is disturbed in the pasty state before it has solidified totally, a poor electrical connection may result; use of eutectic solder reduces this problem. The pasty state of a non-eutectic solder can be exploited in plumbing, as it allows molding of the solder during cooling, e.g. for ensuring watertight joint of pipes, resulting in a so-called "wiped joint".
Bonding in solids
Solids with purely metallic bonding are characteristically ductile and, in their pure forms, have low strength; melting points can be very low ("e.g.," Mercury melts at 234 K (−39 °C). These properties are consequences of the non-directional and non-polar nature of metallic bonding, which allows atoms (and planes of atoms in a crystal lattice) to move past one another without disrupting their bonding interactions. Metals can be strengthened by introducing crystal defects (for example, by alloying) that interfere with the motion of dislocations that mediate plastic deformation. Further, some transition metals exhibit directional bonding in addition to metallic bonding; this increases shear strength and reduces ductility, imparting some of the characteristics of a covalent solid (an intermediate case below).
Tempering (metallurgy)
One-step embrittlement usually occurs in carbon steel at temperatures between and , and was historically referred to as "500 degree [Fahrenheit] embrittlement." This embrittlement occurs due to the precipitation of Widmanstatten needles or plates, made of cementite, in the interlath boundaries of the martensite. Impurities such as phosphorus, or alloying agents like manganese, may increase the embrittlement, or alter the temperature at which it occurs. This type of embrittlement is permanent, and can only be relieved by heating above the upper critical temperature and then quenching again. However, these microstructures usually require an hour or more to form, so are usually not a problem in the blacksmith-method of tempering.
Forging temperature
Forging temperature is the temperature at which a metal becomes substantially more soft, but is lower than the melting temperature. Bringing a metal to its forging temperature allows the metal's shape to be changed by applying a relatively small force, without creating cracks. The forging temperature of an alloy will lie between the temperatures of its component metals. For most metals, forging temperature will be approximately 70% of the melting temperature in kelvins.
Creep (deformation)
The temperature range in which creep deformation may occur differs in various materials. Lead can creep at room temperature and tungsten requires a temperature in the thousands of degrees before creep deformation can occur, while ice will creep at temperatures near 0 °C (32 °F). As a general guideline, the effects of creep deformation generally become noticeable at approximately 35% of the melting point for metals and at 45% of melting point for ceramics. Virtually any material will creep upon approaching its melting temperature. Since the creep minimum temperature is related to the melting point, creep can be seen at relatively low temperatures for some materials. Plastics and low-melting-temperature metals, including many solders, can begin to creep at room temperature, as can be seen markedly in old lead hot-water pipes. Glacier flow is an example of creep processes in ice.
Magnetism and temperature
A magnet of ordinary carbon steel has its magnetic moment temporarily increased by cooling, that is, after it has been brought to a permanent magnetic condition ( aged ). The effect of the first immersion of such a magnet in liquid air is a large diminution in its magnetic moment, which decreases still further when it is allowed to warm up to ordinary temperatures. A second cooling, however, increases the magnetic moment, which is again decreased by warming, and after a few repetitions of this cycle of cooling and heating the steel is brought into a condition such that its magnetic moment at the temperature of liquid air is greater by a constant percentage than it is at the ordinary temperature of the air. The increase of magnetic moment seems then to have reached a limit, because on further cooling to the temperature of liquid hydrogen hardly any further increase is observed. The percentage differs with the composition of the steel and with its physical condition. It is greater, for example, with a specimen tempered very soft than it is with another specimen of the same steel tempered glass hard.
Process duct work
Ducts are usually designed as if the duct plate and stiffener temperatures match the internal duct gas temperatures. For mild carbon steels (ASTM A36) temperatures, the design yield stress ratio at 300°F is 84% of room temperature stress. At 500°F, the design yield stress ratio is 77% of room temperature stress. At 700°F, the design yield stress ratio is about 71% of room temperature stress. Temperatures above 800°F may cause mild carbon steel to warp. This is because, in this temperature range, the crystal lattice structure of mild carbon steel changes with temperatures above about 800 degrees F (reference, US Steel Plate, elevated temperature steel).
Hydrogen embrittlement
Although hydrogen atoms embrittle a variety of substances, including steel, aluminium (at high temperatures only), and titanium, however these metals are still affected in high concentrations, hydrogen embrittlement of high-strength steel is of the most importance. Austempered iron is also susceptible, though austempered steel (and possibly other austempered metals) display increased resistance to hydrogen embrittlement. Steel with an ultimate tensile strength of less than 1000 MPa (~145,000 psi) or hardness of less than 23 HRC is not generally considered susceptible to hydrogen embrittlement. In tensile tests carried out on several structural metals under high-pressure molecular hydrogen environment, it has been shown that austenitic stainless steels, aluminium (including alloys), copper (including alloys, e.g. beryllium copper) are not susceptible to hydrogen embrittlement along with a few other metals. As an example of severe hydrogen embrittlement, the elongation at failure of 17-4PH precipitation hardened stainless steel was measured to drop from 17% to only 1.7% when smooth specimens were exposed to high-pressure hydrogen.
High-speed steel
In 1899 and 1900, Frederick Winslow Taylor and Maunsel White, working with a team of assistants at the Bethlehem Steel Company at Bethlehem, Pennsylvania, US, performed a series of experiments with the heat treating of existing high-quality tool steels, such as Mushet steel, heating them to much higher temperatures than were typically considered desirable in the industry. Their experiments were characterised by a scientific empiricism in that many different combinations were made and tested, with no regard for conventional wisdom or alchemic recipes, and with detailed records kept of each batch. The end result was a heat treatment process that transformed existing alloys into a new kind of steel that could retain its hardness at higher temperatures, allowing much higher speeds and rate of cutting when machining.
Arc welding
Knifeline attack (KLA) is another kind of corrosion affecting welds, impacting steels stabilized by niobium. Niobium and niobium carbide dissolves in steel at very high temperatures. At some cooling regimes, niobium carbide does not precipitate, and the steel then behaves like unstabilized steel, forming chromium carbide instead. This affects only a thin zone several millimeters wide in the very vicinity of the weld, making it difficult to spot and increasing the corrosion speed. Structures made of such steels have to be heated in a whole to about , when the chromium carbide dissolves and niobium carbide forms. The cooling rate after this treatment is not important.
Maraging steel
Maraging steel's strength and malleability in the pre-aged stage allows it to be formed into thinner rocket and missile skins than other steels, reducing weight for a given strength. Maraging steels have very stable properties and, even after overaging due to excessive temperature, only soften slightly. These alloys retain their properties at mildly elevated operating temperatures and have maximum service temperatures of over . They are suitable for engine components, such as crankshafts and gears, and the firing pins of automatic weapons that cycle from hot to cool repeatedly while under substantial load. Their uniform expansion and easy machinability before aging make maraging steel useful in high-wear components of assembly lines and dies. Other ultra-high-strength steels, such as AerMet alloys, are not as machinable because of their carbide content.
Allotropes of iron
Beta iron (β-Fe) are obsolete terms for the paramagnetic allotrope of iron. The primary phase of low-carbon or mild steel and most cast irons at room temperature is ferromagnetic α-Fe. As iron or steel is heated above the critical temperature A or Curie temperature of 771 °C (1044K or 1420 °F), the random thermal agitation of the atoms exceeds the oriented magnetic moment of the unpaired electron spins. The A forms the low-temperature boundary of the beta iron field in the phase diagram in Figure 1. β-Fe is crystallographically identical to α-Fe, except for magnetic domains and the expanded body-centered cubic lattice parameter as a function of temperature, and is therefore of only minor importance in steel heat treating. For this reason, the beta "phase" is not usually considered a distinct phase but merely the high-temperature end of the alpha phase field.
Gallium
The melting point of gallium, at 302.9146 K (29.7646 °C, 85.5763 °F), is just above room temperature, and is approximately the same as the average summer daytime temperatures in Earth's mid-latitudes. This melting point (mp) is one of the formal temperature reference points in the International Temperature Scale of 1990 (ITS-90) established by the International Bureau of Weights and Measures (BIPM). The triple point of gallium, 302.9166 K (29.7666 °C, 85.5799 °F), is used by the US National Institute of Standards and Technology (NIST) in preference to the melting point.
Agar
Agar exhibits hysteresis, melting at 85 °C (358 K, 185 °F) and solidifying from 32–40 °C (305–313 K, 90–104 °F). This property lends a suitable balance between easy melting and good gel stability at relatively high temperatures. Since many scientific applications require incubation at temperatures close to human body temperature (37 °C), agar is more appropriate than other solidifying agents that melt at this temperature, such as gelatin.
Wrought iron
In 1925, James Aston of the United States developed a process for manufacturing wrought iron quickly and economically. It involved taking molten steel from a Bessemer converter and pouring it into cooler liquid slag. The temperature of the steel is about 1500 °C and the liquid slag is maintained at approximately 1200 °C. The molten steel contains a large amount of dissolved gases so when the liquid steel hit the cooler surfaces of the liquid slag the gases were liberated. The molten steel then froze to yield a spongy mass having a temperature of about 1370 °C. The spongy mass would then be finished by being shingled and rolled as described under puddling (above). Three to four tons could be converted per batch with the method.
Freezing
For most substances, the melting and freezing points are the same temperature; however, certain substances possess differing solid–liquid transition temperatures. For example, agar displays a hysteresis in its melting point and freezing point. It melts at 85 °C (185 °F) and solidifies from 32 °C to 40 °C (89.6 °F to 104 °F).
Pressure melting point
The pressure melting point is the temperature at which ice melts at a given pressure. The pressure melting point is nearly a constant 0 °C at pressures above the triple point at 611.7 Pa, where water can exist in only the solid or liquid phases, through atmospheric pressure (100 kPa) until about 10 MPa. With increasing pressure above 10 MPa, the pressure melting point decreases to a minimum of −21.9 °C at 209.9 MPa. Thereafter, the pressure melting point rises rapidly with pressure, passing back through 0 °C at 632.4 MPa.
Tempering (metallurgy)
Because few methods of precisely measuring temperature existed until modern times, temperature was usually judged by watching the tempering colors of the metal. Tempering often consisted of heating above a charcoal or coal forge, or by fire, so holding the work at exactly the right temperature for the correct amount of time was usually not possible. Tempering was usually performed by slowly, evenly overheating the metal, as judged by the color, and then immediately cooling, either in open air or by immersing in water. This produced much the same effect as heating at the proper temperature for the right amount of time, and avoided embrittlement by tempering within a short time period. However, although tempering-color guides exist, this method of tempering usually requires a good amount of practice to perfect, because the final outcome depends on many factors, including the composition of the steel, the speed at which it was heated, the type of heat source (oxidizing or carburizing), the cooling rate, oil films or impurities on the surface, and many other circumstances which vary from smith to smith or even from job to job. The thickness of the steel also plays a role. With thicker items, it becomes easier to heat only the surface to the right temperature, before the heat can penetrate through. However, very thick items may not be able to harden all the way through during quenching.
Tool steel
This series includes an O1 type, an O2 type, an O6 type and an O7 type. All steels in this group are typically hardened at 800°C, oil quenched, then tempered at <200°C.
Ice
To melt ice means breaking the hydrogen bonds between the water molecules. The ordering of the molecules in the solid breaks down to a less ordered state and the solid melts to become a liquid. This is achieved by increasing the internal energy of the ice beyond the melting point. When ice melts it absorbs as much energy as would be required to heat an equivalent amount of water by 80 °C. While melting, the temperature of the ice surface remains constant at 0 °C. The velocity of the melting process depends on the efficiency of the energy exchange process. An ice surface in fresh water melts solely by free convection with a velocity that depends linearly on the water temperature, "T", when "T" is less than 3.98 °C, and superlinearly when "T" is equal to or greater than 3.98 °C, with the rate being proportional to (T − 3.98 °C), with "α" =  for "T" much greater than 8 °C, and α =  for in between temperatures "T".
Type metal
Dross must be processed at specialized companies, in order to extract the pure metals in conditions that would prevent environmental pollution and remain economically feasible.Pure metal melts and solidifies in a simple manner at a specific temperature. This is not the case with alloys. There we find a range of temperatures with all kinds of different events. The melting temperature of all mixtures is considerably lower than the pure components.
Tempering (metallurgy)
Steel that has been arc welded, gas welded, or welded in any other manner besides forge welded, is affected in a localized area by the heat from the welding process. This localized area, called the heat-affected zone (HAZ), consists of steel that varies considerably in hardness, from normalized steel to steel nearly as hard as quenched steel near the edge of this heat-affected zone. Thermal contraction from the uneven heating, solidification and cooling creates internal stresses in the metal, both within and surrounding the weld. Tempering is sometimes used in place of stress relieving (even heating and cooling of the entire object to just below the A temperature) to both reduce the internal stresses and to decrease the brittleness around the weld. Localized tempering is often used on welds when the construction is too large, intricate, or otherwise too inconvenient to heat the entire object evenly. Tempering temperatures for this purpose are generally around and .
History of metallurgy in China
Around 500 BC, metalworkers in the southern state of Wu achieved a temperature of up to 1130 °C, hot enough to use hearth as a blast furnace. At this temperature, iron combines with 4.3% carbon and melts. As a liquid, iron can be cast into molds, a method far less laborious than individually forging each piece of iron from a bloom.
Welding
A reduction in fracture toughness may also be attributed to the embrittlement effect of impurities, or for body-centred cubic metals, from a reduction in temperature. Metals and in particular steels have a transitional temperature range where above this range the metal has acceptable notch-ductility while below this range the material becomes brittle. Within the range, the materials behavior is unpredictable. The reduction in fracture toughness is accompanied by a change in the fracture appearance. When above the transition, the fracture is primarily due to micro-void coalescence, which results in the fracture appearing fibrous. When the temperatures falls the fracture will show signs of cleavage facets. These two appearances are visible by the naked eye. Brittle fracture in steel plates may appear as chevron markings under the microscope. These arrow-like ridges on the crack surface point towards the origin of the fracture.
Differential heat treatment
Before the yellow or "light-straw" color reaches the edge, the smith removes the heat. The heat will continue to conduct, moving the colors toward the edge for a short time after the heat is removed. When the light-straw color reaches the edge, the smith will usually dip the steel in water, to stop the process. This will generally produce a very hard edge, around HRc58-60 on the Rockwell scale, but will leave the opposite end of the tool much softer. The hardness of the cutting edge is generally controlled by the chosen color, but will also be affected primarily by the carbon content in the steel, plus a variety of other factors. The exact hardness of the soft end depends on many factors, but the main one is the speed at which the steel was heated, or how far the colors spread out. The light-straw color is very hard, brittle steel, but the light-blue is softer and very springy. Beyond the blue color, when the steel turns grey, it is more likely to be very malleable, which is usually undesirable in a chisel. If the steel is too soft it can bend or mushroom, plastically deforming under the force of the hammer.
Aluminium nitride
Aluminium nitride is stable at high temperatures in inert atmospheres and melts about 2200 °C. In a vacuum, AlN decomposes at ~1800 °C. In the air, surface oxidation occurs above 700 °C, and even at room temperature, surface oxide layers of 5-10 nm have been detected. This oxide layer protects the material up to 1370 °C. Above this temperature bulk oxidation occurs. Aluminium nitride is stable in hydrogen and carbon dioxide atmospheres up to 980 °C.
Forging
Isothermal forging is a process by which the materials and the die are heated to the same temperature ("iso-" meaning "equal"). Adiabatic heating is used to assist in the deformation of the material, meaning the strain rates are highly controlled. Commonly used for forging aluminum, which has a lower forging temperature than steels. Forging temperatures for Aluminum are around 800 °F, while steels and super alloys can be 1700-2300 °F.
Metallic bonding
Otherwise, metallic bonding can be very strong, even in molten metals, such as Gallium. Even though gallium will melt from the heat of one's hand just above room temperature, its boiling point is not far from that of copper. Molten gallium is, therefore, a very nonvolatile liquid thanks to its strong metallic bonding.
Red-short carbon steel
Iron or steel, when heated to above 900 °F (460 °C), glows with a red color. The color of any heated object changes predictably (due to black body radiation) from dull red through orange and yellow to white, and can be a useful indicator of its temperature. Good quality iron or steel at and above this temperature becomes increasingly malleable and plastic. Iron or steel having too much sulfur, on the other hand, becomes crumbly and brittle. This is due to the sulfur forming iron sulfide/iron mixtures in the grain boundaries of the metal which have a lower melting point than the steel.
Tempering (metallurgy)
In metallurgy, one may encounter many terms that have very specific meanings within the field, but may seem rather vague when viewed from outside. Terms such as "hardness," "impact resistance," "toughness," and "strength" can carry many different connotations, making it sometimes difficult to discern the specific meaning. Some of the terms encountered, and their specific definitions are:Very few metals react to heat treatment in the same manner, or to the same extent, that carbon steel does, and carbon-steel heat-treating behavior can vary radically depending on alloying elements. Steel can be softened to a very malleable state through annealing, or it can be hardened to a state nearly as rigid and brittle as glass by quenching. However, in its hardened state, steel is usually far too brittle, lacking the fracture toughness to be useful for most applications. Tempering is a method used to decrease the hardness, thereby increasing the ductility of the quenched steel, to impart some springiness and malleability to the metal. This allows the metal to bend before breaking. Depending on how much temper is imparted to the steel, it may bend elastically (the steel returns to its original shape once the load is removed), or it may bend plastically (the steel does not return to its original shape, resulting in permanent deformation), before fracturing. Tempering is used to precisely balance the mechanical properties of the metal, such as shear strength, yield strength, hardness, ductility and tensile strength, to achieve any number of a combination of properties, making the steel useful for a wide variety of applications. Tools such as hammers and wrenches require good resistance to abrasion, impact resistance, and resistance to deformation. Springs do not require as much wear resistance, but must deform elastically without breaking. Automotive parts tend to be a little less strong, but need to deform plastically before breaking.
Allotropes of iron
As molten iron cools down, it solidifies at 1,538 °C (2,800 °F) into its δ allotrope, which has a body-centered cubic (BCC) crystal structure. δ-iron can dissolve as much as 0.08% of carbon by mass at 1,475 °C.
Transition temperature
Transition temperature is the temperature at which a material changes from one crystal state (allotrope) to another. More formally, it is the temperature at which two crystalline forms of a substance can co-exist in equilibrium. For example, when rhombic sulfur is heated above 95.6 °C it changes form into monoclinic sulfur. When cooled below 95.6 °C it reverts to rhombic sulfur. At 95.6 °C the two forms can co-exist.
Galvannealed
Production of galvannealed sheet steel begins with hot dip galvanization of sheet steel. After passing through the galvanizing zinc bath the sheet steel passes through air knives to remove excess zinc, and is then heated in an annealing furnace for several seconds causing iron and zinc layers to diffuse into one another causing the formation of zinc-iron alloy layers at the surface. The annealing step is performed with the strip still hot after the galvanizing step, with the zinc still liquid. The galvanising bath contains slightly over 0.1% aluminium, added to form a layer bonding between the iron and coated zinc. Annealing temperatures are around 500 to 565 °C. Pre-1990 annealing lines used gas-fired heating; post-1990s the use of induction furnaces became common.
Azide
Azide salts can decompose with release of nitrogen gas as discussed under Applications. The decomposition temperatures of the alkali metal azides are: NaN (275 °C), KN (355 °C), RbN (395 °C), and CsN (390 °C). This method is used to produce ultrapure alkali metals.
Silicon
Silicon crystallises in a giant covalent structure at standard conditions, specifically in a [[diamond cubic]] lattice. It thus has a high melting point of 1414 °C, as a lot of energy is required to break the strong covalent bonds and melt the solid. It is not known to have any allotropes at standard pressure, but several other crystal structures are known at higher pressures. The general trend is one of increasing [[coordination number]] with pressure, culminating in a [[hexagonal close-packed]] allotrope at about 40 [[gigapascal]]s known as Si–VII (the standard modification being Si–I). Silicon boils at 3265 °C: this, while high, is still lower than the temperature at which its lighter congener [[carbon]] sublimes (3642 °C) and silicon similarly has a lower [[heat of vaporisation]] than carbon, consistent with the fact that the Si–Si bond is weaker than the C–C bond.
Liquid metal
A few elemental metals are liquid at or near room temperature. The most well known is mercury(Hg), which is molten above −38.8 °C (234.3 K, −37.9 °F). Others include caesium(Cs), which has a melting point of 28.5 °C (83.3 °F), rubidium (Rb)(39 °C [102 °F]), francium (Fr)(estimated at 27 °C [81 °F]), and gallium (Ga)(30 °C [86 °F]).
Gallium
The melting point of gallium allows it to melt in the human hand, and then refreeze if removed. The liquid metal has a strong tendency to supercool below its melting point/freezing point: Ga nanoparticles can be kept in the liquid state below 90 K. Seeding with a crystal helps to initiate freezing. Gallium is one of the four non-radioactive metals (with caesium, rubidium, and mercury) that are known to be liquid at, or near, normal room temperature. Of the four, gallium is the only one that is neither highly reactive (rubidium and caesium) nor highly toxic (mercury) and can therefore be used in metal-in-glass high-temperature thermometers. It is also notable for having one of the largest liquid ranges for a metal, and for having (unlike mercury) a low vapor pressure at high temperatures. Gallium's boiling point, 2673 K, is more than eight times higher than its melting point on the absolute scale, the greatest ratio between melting point and boiling point of any element. Unlike mercury, liquid gallium metal wets glass and skin, along with most other materials (with the exceptions of quartz, graphite, and Teflon), making it mechanically more difficult to handle even though it is substantially less toxic and requires far fewer precautions. Gallium painted onto glass is a brilliant mirror. For this reason as well as the metal contamination and freezing-expansion problems, samples of gallium metal are usually supplied in polyethylene packets within other containers.
Gallium does not crystallize in any of the simple crystal structures. The stable phase under normal conditions is orthorhombic with 8 atoms in the conventional unit cell. Within a unit cell, each atom has only one nearest neighbor (at a distance of 244 pm). The remaining six unit cell neighbors are spaced 27, 30 and 39 pm farther away, and they are grouped in pairs with the same distance. Many stable and metastable phases are found as function of temperature and pressure.
Forging
Depending on the forming temperature steel forging can be divided into:For industrial processes steel alloys are primarily forged in hot condition. Brass, bronze, copper, precious metals and their alloys are manufactured by cold forging processes, while each metal requires a different forging temperature.Due to the narrow temperature range and high thermal conductivity, aluminium forging can only be realized in a particular process window. To provide good forming conditions a homogeneous temperature distribution in the entire workpiece is necessary. Therefore, the control of the tool temperature has a major influence to the process. For example, by optimizing the preform geometries the local effective strains can be influenced to reduce local overheating for a more homogeneous temperature distribution.
Cast iron
Carbon (C) ranging from 1.8 to 4 wt%, and silicon (Si) 1–3 wt% are the main alloying elements of cast iron. Iron alloys with lower carbon content (~0.8%) are known as steel. While this technically makes the Fe–C–Si system ternary, the principle of cast iron solidification can be understood from the simpler binary iron–carbon phase diagram. Since the compositions of most cast irons are around the eutectic point (lowest liquid point) of the iron–carbon system, the melting temperatures usually range from , which is about lower than the melting point of pure iron of .
Iron
The melting point of iron is experimentally well defined for pressures less than 50 GPa. For greater pressures, studies put the γ-ε-liquid triple point at pressures that differ by tens of gigapascals and 1000 K in the melting point. Generally speaking, molecular dynamics computer simulations of iron melting and shock wave experiments suggest higher melting points and a much steeper slope of the melting curve than static experiments carried out in diamond anvil cells. The melting and boiling points of iron, along with its enthalpy of atomization, are lower than those of the earlier 3d elements from scandium to chromium, showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and more into the inert core by the nucleus; however, they are higher than the values for the previous element manganese because that element has a half-filled 3d subshell and consequently its d-electrons are not easily delocalized. This same trend appears for ruthenium but not osmium.
Melting-point depression
The melting temperature of a bulk material is not dependent on its size. However, as the dimensions of a material decrease towards the atomic scale, the melting temperature scales with the material dimensions. The decrease in melting temperature can be on the order of tens to hundreds of degrees for metals with nanometer dimensions.
Magnetism and temperature
Aluminium steels show the same kind of phenomena as carbon ones, and the same may be said of chrome steels in the permanent condition, though the effect of the first cooling with them is a slight increase of magnetic moment. Nickel steels present some curious phenomena. When containing small percentages of nickel (e.g. 084 or 3-82), they behave under changes of temperature much like carbon steel. With a sample containing 7.65%, the phenomena after the permanent state had been reached were similar, but the first cooling produced a slight increase in magnetic moment. But steels containing 18-64 and 29% of nickel behaved very differently. The result of the first cooling was a reduction of the magnetic moment, to the extent of nearly 50% in the case of the former. Warming again brought about an increase, and the final condition was that at the barometric pressure of liquid air the magnetic moment was always less than at ordinary temperatures. This anomaly is all the more remarkable in that the behaviour of pure nickel is normal, as also appears to be generally the case with soft and hard iron. Silicon, tungsten and manganese steels are also substantially normal in their behaviour, although there are considerable differences in the magnitudes of the variations they display.
Group 12 element
Zinc is somewhat less dense than iron and has a hexagonal crystal structure.
The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C. Above 210 °C, the metal becomes brittle again and can be pulverized by beating. Zinc is a fair conductor of electricity. For a metal, zinc has relatively low melting (419.5 °C, 787.1 F) and boiling points (907 °C). Cadmium is similar in many respects to zinc but forms complex compounds. Unlike other metals, cadmium is resistant to corrosion and as a result it is used as a protective layer when deposited on other metals. As a bulk metal, cadmium is insoluble in water and is not flammable; however, in its powdered form it may burn and release toxic fumes. Mercury has an exceptionally low melting temperature for a d-block metal. A complete explanation of this fact requires a deep excursion into quantum physics, but it can be summarized as follows: mercury has a unique electronic configuration where electrons fill up all the available 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d and 6s subshells. As such configuration strongly resists removal of an electron, mercury behaves similarly to noble gas elements, which form weak bonds and thus easily melting solids. The stability of the 6s shell is due to the presence of a filled 4f shell. An f shell poorly screens the nuclear charge that increases the attractive Coulomb interaction of the 6s shell and the nucleus (see lanthanide contraction). The absence of a filled inner f shell is the reason for the somewhat higher melting temperature of cadmium and zinc, although both these metals still melt easily and, in addition, have unusually low boiling points. Gold has atoms with one less 6s electron than mercury. Those electrons are more easily removed and are shared between the gold atoms forming relatively strong metallic bonds.
Eglin steel
The material has to undergo heat treatment involving normalization, quenching and tempering to develop the required austenitic microstructure, with subsequent tempering. Test plates were 1 inch. First they were normalized. They were charged in a furnace at 500F. Heated at 125F per hour to 1625–1725F. Held at 1750F for an hour per inch of section size, and then air-cooled to room temperature. Next the samples were austenized by repeating the process up to 1700F, and held for an hour per inch of section size, then oil quenched to below 125F. Finally, they were tempered by in an oven that started below 500F, increased at 100F per hour per inch of section size, and allowed to air-cool to room temperature.
Tin pest
At 13.2 °C (about 56 °F) and below, pure tin transforms from the silvery, ductile metallic allotrope of β-form "white tin" to the brittle, nonmetallic, α-form "grey tin" with a diamond cubic structure. The transformation is slow to initiate due to a high activation energy but the presence of germanium (or crystal structures of similar form and size) or very low temperatures of roughly −30 °C aids the initiation. There is also a large volume increase of about 27% associated with the phase change to the nonmetallic low temperature allotrope. This frequently makes tin objects (like buttons) decompose into powder during the transformation, hence the name "tin pest".
Bluing (steel)
Bluing may be applied, for example, by immersing the steel parts to be blued in a solution of potassium nitrate, sodium hydroxide, and water heated to the boiling point, 275 °F to 310 °F (135 °C to 154 °C) depending on the recipe. Similarly, stainless steel parts may be immersed in a mixture of nitrates and chromates, similarly heated. Either of these two methods are called "hot bluing". There are many other methods of hot bluing. Hot bluing is the current standard in gun bluing, as both it and rust bluing provide the most permanent degree of rust-resistance and cosmetic protection of exposed gun metal.
Stainless steel
At elevated temperatures all metals react with hot gases. The most common high temperature gaseous mixture is air, and oxygen is the most reactive component of air. Carbon steel is limited to ~ in air. Chromium in stainless steel reacts with oxygen to form a chromium oxide scale which reduces oxygen diffusion into the material. The minimum 10.5% chromium in stainless steels provides resistance to ~, while 26% chromium provides resistance up to ~. Type 304, the most common grade of stainless steel with 18% chromium is resistant to ~. Other gases such as sulfur dioxide, hydrogen sulfide, carbon monoxide, chlorine, etc. also attack stainless steel. Resistance to other gases is dependent on the type of gas, the temperature and the alloying content of the stainless steel.
Superalloy
In general, high temperature materials are needed for energy conversion and energy production applications. Maximum energy conversion efficiency is desired in these energy applications, which can be achieved by increasing operating temperatures, as described by the Carnot cycle. Operating temperatures are limited by the performance of today’s superalloys, and currently, most applications operate at around 1000C-1400 C. Energy applications and their superalloy components include:
Alumina-forming stainless steels can be processed via melting and ladle casting, similar to the production of more common steels. Unlike vacuum casting processes, ladle casting is much more inexpensive. In addition, alumina-forming stainless steel has been shown to be weldable and has potential for use in high performance automotive applications, such as for high temperature exhaust piping and in heat capture and reuse.
Window shutter hardware
Tempering - as mentioned above, steel can be hardened. When heated to red-hot, the iron and carbon in the steel arrange themselves into a lattice network. When quickly quenched, the lattice is frozen in place and forms a rigid structure; the more carbon, the greater the rigidity. When quenched, the steel is as hard as it will become. The harder the steel, the more brittle it is. A file is absolutely hard. It will cut lots of mild steel because it is so much harder - but put a file in a vise and hit it with a hammer and the file will readily snap in half. Same with a drill bit, cock the drill and the bit will easily snap. Tempering is a process of controlled heating of hardened steel that will relax the lattice within the iron and carbon, thereby softening the steel. The higher the temperature, the softer the steel becomes. A chisel for steel is tempered at a high temperature - softened enough so it won't snap, but still harder than the steel it will cut. A clean piece of steel will turn a very specific color based on the temperature to which it is raised. Heat one end of a piece of steel in a fire and you can easily see bands of color move up the steel coincidental with the heat migrating up the piece. It begins as a very light yellow, turns to a darker straw color, through red and on to purple. Blacksmiths have always used these colors to identify the temperature of the steel and thus control the temper (hardness) of the work piece. Spring steel is often a pretty bluish-purple color - because it's tempered to 750* and that's the associated color - soft enough to bend, but hard enough to retain “memory” and spring back to its original shape.
Carbon
Carbon sublimes in a carbon arc, which has a temperature of about 5800 K (5,530 °C or 9,980 °F). Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest-melting-point metals such as tungsten or rhenium. Although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper, which are weaker reducing agents at room temperature.
Shot welding
The E. G. Budd Company of Philadelphia recognized the important metallurgical characteristics of 18/8 stainless steel (known today as SAE 304 austenitic stainless steel) and developed a spot welding process to take advantage of the oxidized layer on the surface of stainless steel. Heat treating the 18-8 stainless steel leaves the metal with non-magnetic and ductile properties. Repeatedly reheating the metal to 1000–1100 °C impairs the mechanical and chemical properties of the metal. The metal becomes susceptible to corrosion due to carbide precipitation, and loses fatigue resistance. The important factor in controlling the metal's properties is the dwell time at those temperatures. Using a controlled time element and recorder, a power supply with smooth current, and very brief high currents, a satisfactory spot weld may be produced.
Hysteresis
Hysteresis manifests itself in state transitions when melting temperature and freezing temperature do not agree. For example, agar melts at 85 °C and solidifies from 32 to 40 °C. This is to say that once agar is melted at 85 °C, it retains a liquid state until cooled to 40 °C. Therefore, from the temperatures of 40 to 85 °C, agar can be either solid or liquid, depending on which state it was before.
Refractory metals
Tungsten was discovered in 1781 by the Swedish chemist, Carl Wilhelm Scheele. Tungsten has the highest melting point of all metals, at .
Calcium
Calcium metal melts at 842 °C and boils at 1494 °C; these values are higher than those for magnesium and strontium, the neighbouring group 2 metals. It crystallises in the face-centered cubic arrangement like strontium; above 450 °C, it changes to an anisotropic hexagonal close-packed arrangement like magnesium. Its density of 1.55 g/cm is the lowest in its group. Calcium is harder than lead but can be cut with a knife with effort. While calcium is a poorer conductor of electricity than copper or aluminium by volume, it is a better conductor by mass than both due to its very low density. While calcium is infeasible as a conductor for most terrestrial applications as it reacts quickly with atmospheric oxygen, its use as such in space has been considered.
Exothermic welding
Typically, the ends of the rails are cleaned, aligned flat and true, and spaced apart . This gap between rail ends for welding is to ensure consistent results in the pouring of the molten steel into the weld mold. In the event of a welding failure, the rail ends can be cropped to a gap, removing the melted and damaged rail ends, and a new weld attempted with a special mould and larger thermite charge. A two or three piece hardened sand mould is clamped around the rail ends, and a torch of suitable heat capacity is used to preheat the ends of the rail and the interior of the mould. The proper amount of thermite with alloying metal is placed in a refractory crucible, and when the rails have reached a sufficient temperature, the thermite is ignited and allowed to react to completion (allowing time for any alloying metal to fully melt and mix, yielding the desired molten steel or alloy). The reaction crucible is then tapped at the bottom. Modern crucibles have a self-tapping thimble in the pouring nozzle. The molten steel flows into the mould, fusing with the rail ends and forming the weld. The slag, being lighter than the steel flows last from the crucible and overflows the mould into a steel catch basin, to be disposed of after cooling. The entire setup is allowed to cool. The mould is removed and the weld is cleaned by hot chiselling and grinding to produce a smooth joint. Typical time from start of the work until a train can run over the rail is approximately 45 minutes to more than an hour, depending on the rail size and ambient temperature. In any case, the rail steel must be cooled to less than before it can sustain the weight of rail locomotives.
Forge welding
When steel is heated to an austenizing temperature, the carbon begins to diffuse through the iron. The higher the temperature; the greater the rate of diffusion. At such high temperatures, carbon readily combines with oxygen to form carbon dioxide, so the carbon can easily diffuse out of the steel and into the surrounding air. By the end of a blacksmithing job, the steel will be of a lower carbon content than it was prior to heating. Therefore, most blacksmithing operations are done as quickly as possible to reduce decarburization, preventing the steel from becoming too soft.
Alloy
The base metal iron of the iron-carbon alloy known as steel, undergoes a change in the arrangement (allotropy) of the atoms of its crystal matrix at a certain temperature (usually between and , depending on carbon content). This allows the smaller carbon atoms to enter the interstices of the iron crystal. When this diffusion happens, the carbon atoms are said to be in "solution" in the iron, forming a particular single, homogeneous, crystalline phase called austenite. If the steel is cooled slowly, the carbon can diffuse out of the iron and it will gradually revert to its low temperature allotrope. During slow cooling, the carbon atoms will no longer be as soluble with the iron, and will be forced to precipitate out of solution, nucleating into a more concentrated form of iron carbide (FeC) in the spaces between the pure iron crystals. The steel then becomes heterogeneous, as it is formed of two phases, the iron-carbon phase called cementite (or carbide), and pure iron ferrite. Such a heat treatment produces a steel that is rather soft. If the steel is cooled quickly, however, the carbon atoms will not have time to diffuse and precipitate out as carbide, but will be trapped within the iron crystals. When rapidly cooled, a diffusionless (martensite) transformation occurs, in which the carbon atoms become trapped in solution. This causes the iron crystals to deform as the crystal structure tries to change to its low temperature state, leaving those crystals very hard but much less ductile (more brittle).
Forge welding
A primary requirement for forge welding is that both weld surfaces need to be heated to the same temperature and welded before they cool too much. When steel reaches the proper temperature, it begins to weld very readily, so a thin rod or nail heated to the same temperature will tend to stick at first contact, requiring it to be bent or twisted loose. One of the simplest ways to tell if iron or steel is hot enough is to stick a magnet to it. When iron crosses the A critical temperature, it begins to change into the allotrope called gamma iron. When this happens, the steel or iron becomes non-magnetic. In steel, the carbon begins to mix with gamma iron at the A temperature, forming a solid solution called austenite. When it crosses the A critical temperature, it changes into delta iron, which is magnetic. Therefore, a blacksmith can tell when the welding temperature is reached by placing a magnet in contact with the metal. When red or orange-hot, a magnet will not stick to the metal, but when the welding temperature is crossed, the magnet will again stick to it. The steel may take on a glossy or wet appearance at the welding temperature. Care must be taken to avoid overheating the metal to the point that it gives off sparks from rapid oxidation (burning), or else the weld will be poor and brittle.
Iron
As molten iron cools past its freezing point of 1538 °C, it crystallizes into its δ allotrope, which has a body-centered cubic (bcc) crystal structure. As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered cubic (fcc) crystal structure, or austenite. At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope. Finally, at 770 °C (the Curie point, T) iron's magnetic ordering changes from paramagnetic to ferromagnetic. As it passes through the Curie temperature, iron does not change its structure, but "magnetic domains" appear, where each domain contains iron atoms with a particular electronic spin. In unmagnetized iron, all the electronic spins of the atoms within one domain have the same axis orientation; however, the electrons of neighboring domains have other orientations with the result of mutual cancellation and no magnetic field. In magnetized iron, the electronic spins of the domains are aligned and the magnetic effects are reinforced. Although each domain contains billions of atoms, they are very small, about 10 micrometres across. This happens because the two unpaired electrons on each iron atom are in the d and d orbitals, which do not point directly at the nearest neighbors in the body-centered cubic lattice and therefore do not participate in metallic bonding; thus, they can interact magnetically with each other so that their spins align.
Electrical steel
This material is a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal at a rate of about one megakelvin per second, so fast that crystals do not form. Amorphous steel is limited to foils of about 50 µm thickness. It has poorer mechanical properties and as of 2010 it costs about twice as much as conventional steel, making it cost-effective only for some distribution-type transformers. Transformers with amorphous steel cores can have core losses of one-third that of conventional electrical steels.
Blacksmith
When iron ore is smelted into usable metal, a certain amount of carbon is usually alloyed with the iron. (Charcoal is almost pure carbon.) The amount of carbon significantly affects the properties of the metal. If the carbon content is over 2%, the metal is called cast iron, because it has a relatively low melting point and is easily cast. It is quite brittle, however, and cannot be forged so therefore not used for blacksmithing. If the carbon content is between 0.25% and 2%, the resulting metal is tool grade steel, which can be heat treated as discussed above. When the carbon content is below 0.25%, the metal is either "wrought iron (wrought iron is not smelted and cannot come from this process) " or "mild steel." The terms are never interchangeable. In preindustrial times, the material of choice for blacksmiths was wrought iron. This iron had a very low carbon content, and also included up to 5% of glassy iron silicate slag in the form of numerous very fine stringers. This slag content made the iron very tough, gave it considerable resistance to rusting, and allowed it to be more easily "forge welded," a process in which the blacksmith permanently joins two pieces of iron, or a piece of iron and a piece of steel, by heating them nearly to a white heat and hammering them together. Forge welding is more difficult with modern mild steel, because it welds in a narrower temperature band. The fibrous nature of wrought iron required knowledge and skill to properly form any tool which would be subject to stress. Modern steel is produced using either the blast furnace or arc furnaces. Wrought iron was produced by a labor-intensive process called "puddling", so this material is now a difficult-to-find specialty product. Modern blacksmiths generally substitute mild steel for making objects traditionally of wrought iron. Sometimes they use electrolytic-process pure iron.
Nisil
Nisil melts at 1341 - 1420 °C, has a density of 8.58 g/cm³, and electrical resistivity of 0.365 Ω⋅mm/m at 20 °C.
Cupellation
Lead melts at 327°C, lead oxide at 888°C and silver melts at 960°C. To separate the silver, the alloy is melted again at the high temperature of 960°C to 1000°C in an oxidizing environment. The lead oxidises to lead monoxide, then known as litharge, which captures the oxygen from the other metals present. The liquid lead oxide is removed or absorbed by capillary action into the hearth linings. This chemical reaction may be viewed as:
Tungsten
The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the elements discovered, melting at 3422 °C (6192 °F, 3695 K). It also has the highest boiling point, at 5930 °C (10706 °F, 6203 K). Its density is 19.3 times that of water, comparable to that of uranium and gold, and much higher (about 1.7 times) than that of lead. Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work. However, pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw.
Metalloid
Arsenic is a grey, metallic looking solid. It has a density of 5.727 g/cm and is brittle, and moderately hard (more than aluminium; less than iron). It is stable in dry air but develops a golden bronze patina in moist air, which blackens on further exposure. Arsenic is attacked by nitric acid and concentrated sulfuric acid. It reacts with fused caustic soda to give the arsenate NaAsO and hydrogen gas. Arsenic sublimes at 615 °C. The vapour is lemon-yellow and smells like garlic. Arsenic only melts under a pressure of 38.6 atm, at 817 °C. It is a semimetal with an electrical conductivity of around 3.9 × 10 S•cm and a band overlap of 0.5 eV. Liquid arsenic is a semiconductor with a band gap of 0.15 eV.
Fermi gas
where "m" is the electron mass. This Fermi energy corresponds to a Fermi temperature of the order of 10 kelvins, much higher than the temperature of the sun surface. Any metal will boil before reaching this temperature under atmospheric pressure. Thus for any practical purpose a metal, can be considered as a Fermi gas at zero temperature as a first approximation (normal temperatures are small compared to "T").
Helko
In accordance with DIN directions, the hardness of Helko edges is between 47-56 HRC (Rockwell) up to 30 millimeters from the cutting edge, while the eye is generally left unhardened to prevent cracks in the steel. During the manufacturing process, the axe heads are hardened and cooled down in an oil bath prior to being heated to around 400° Celsius. This relieves strain on the surface of the steel after hardening, and provides the correct level of hardness. Unlike many axes which are cooled in a water bath, Helko tools are cooled in lukewarm oil to avoid small chinks in the material. Afterwards, the tools are sandblasted to remove oil residue from the surface prior to grinding and painting.
Zinc
Zinc is a bluish-white, lustrous, diamagnetic metal, though most common commercial grades of the metal have a dull finish. It is somewhat less dense than iron and has a hexagonal crystal structure, with a distorted form of hexagonal close packing, in which each atom has six nearest neighbors (at 265.9 pm) in its own plane and six others at a greater distance of 290.6 pm. The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C. Above 210 °C, the metal becomes brittle again and can be pulverized by beating. Zinc is a fair conductor of electricity. For a metal, zinc has relatively low melting (419.5 °C) and boiling points (907 °C). The melting point is the lowest of all the d-block metals aside from mercury and cadmium; for this, among other reasons, zinc, cadmium, and mercury are often not considered to be transition metals like the rest of the d-block metals are.
Carbon steel
The purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield strength, or impact resistance. Note that the electrical and thermal conductivity are only slightly altered. As with most strengthening techniques for steel, Young's modulus (elasticity) is unaffected. All treatments of steel trade ductility for increased strength and vice versa. Iron has a higher solubility for carbon in the austenite phase; therefore all heat treatments, except spheroidizing and process annealing, start by heating the steel to a temperature at which the austenitic phase can exist. The steel is then quenched (heat drawn out) at a moderate to low rate allowing carbon to diffuse out of the austenite forming iron-carbide (cementite) and leaving ferrite, or at a high rate, trapping the carbon within the iron thus forming martensite. The rate at which the steel is cooled through the eutectoid temperature (about 727°C) affects the rate at which carbon diffuses out of austenite and forms cementite. Generally speaking, cooling swiftly will leave iron carbide finely dispersed and produce a fine grained pearlite and cooling slowly will give a coarser pearlite. Cooling a hypoeutectoid steel (less than 0.77 wt% C) results in a lamellar-pearlitic structure of iron carbide layers with α-ferrite (nearly pure iron) between. If it is hypereutectoid steel (more than 0.77 wt% C) then the structure is full pearlite with small grains (larger than the pearlite lamella) of cementite formed on the grain boundaries. A eutectoid steel (0.77% carbon) will have a pearlite structure throughout the grains with no cementite at the boundaries. The relative amounts of constituents are found using the lever rule. The following is a list of the types of heat treatments possible:Case hardening processes harden only the exterior of the steel part, creating a hard, wear resistant skin (the "case") but preserving a tough and ductile interior. Carbon steels are not very hardenable meaning they can not be hardened throughout thick sections. Alloy steels have a better hardenability, so they can be through-hardened and do not require case hardening. This property of carbon steel can be beneficial, because it gives the surface good wear characteristics but leaves the core tough.
Homologous temperature
Additionally, for a given fixed homologous temperature, two materials with different melting points would have similar diffusion-dependent deformation behaviour. For example, solder (T = 456 K) at 115 °C would have comparable mechanical properties to copper (T = 1358 K) at 881 °C, because they would both be at 0.85T despite being at different absolute temperatures.
Aluminized steel
Both Type 1 and Type 2 show excellent high reflectivity characteristics. At temperatures up to , aluminized steel reflects up to 80% of heat projected onto it. Aluminized steel has the ability to maintain its strength at temperatures up to . Although stainless steel is the stronger of the two, aluminized steel has a greater electrostatic surface, and can therefore reflect heat better.
Mercury (element)
It has a freezing point of −38.83 °C and a boiling point of 356.73 °C, both the lowest of any stable metal, although preliminary experiments on copernicium and flerovium have indicated that they have even lower boiling points (copernicium being the element below mercury in the periodic table, following the trend of decreasing boiling points down group 12). Upon freezing, the volume of mercury decreases by 3.59% and its density changes from 13.69 g/cm when liquid to 14.184 g/cm when solid. The coefficient of volume expansion is 181.59 × 10 at 0 °C, 181.71 × 10 at 20 °C and 182.50 × 10 at 100 °C (per °C). Solid mercury is malleable and ductile and can be cut with a knife.
Yield strength anomaly
Precipitation hardening superalloys exhibit yield strength anomaly over a considerable temperature range. For these materials, the yield strength shows little variation between room temperature and several hundred degrees Celsius. Eventually, a maximum yield strength is reached. For ordered intermetallics, this is usually the case at roughly 50% of the absolute melting temperature. For even higher temperatures, the yield strength decreases and, eventually, drops to zero when reaching the melting temperature, where the solid material transforms into a fluid.
Cryochemistry
As a material cools, the relative motion of its component molecules/atoms decreases - its temperature decreases. Cooling can continue until all motion ceases, and its kinetic energy, or energy of motion, disappears. This condition is known as absolute zero and it forms the basis for the Kelvin temperature scale, which measures the temperature above absolute zero. Zero degrees Celsius (°C) coincides with 273 Kelvin.