1. Field of the Invention
The present invention imparts to composition of materials intended for metallurgical treatments and constituted by a polyphase mixture of a cryogenic fluid and at least one additional constituent in the form of particles, pre-determined properties for the purpose of said treatments, for example to give it lubricating properties or to render it absorbent or reflecting with respect to the radiation emitted by metals at high temperature.
Cryogenic fluids, and in particular liquefied gases are utilized for various metallurgical treatments.
2. Description of the Prior Art
It is known to utilize certain liquefied inert gases such as nitrogen and argon for the protection of metal or alloys molten, by covering the free or exposed surface of the metal or alloy with a film of liquefied gas in order to isolate it from the atmosphere. As a result of the phenomenon of calefaction, there is formed in the film a gaseous lower layer in direct contact with the metal and a liquid upper layer superimposed on the said gaseous layer, this double layer ensuring the protection of the metal by eliminating all contact with oxygen or water vapour contained in atmospheric air, and in consequence preventing any possibility of chemical reaction likely to pollute the said metal.
While insulation with respect to atmospheric air is one of the conditions sought for, it is generally not the only one. In fact, it is frequently important, during continuous or non-continuous pouring, to limit the heat losses to the maximum extent, that is to say to limit the cooling of the metal in fusion. In the case of continuous pouring, especially of steel or non-ferrous metals into an ingot-mould, it is furthermore essential to facilitate the downward movement of the metallic mass which solidifies in contact with the walls of the ingot-mould by lubricating it.
Studies which have been carried out in these fields have shown that the use of known cryogenic fluids, in particular liquefied inert gases such as this was carried out up to the present time, did not make it possible to satisfy completely these last two conditions.
These gases are in effect transparent to the radiation emitted by the metal at high temperature, so that this latter loses a substantial part of its heat and cools down relatively quickly, while they do not on the other hand have any lubricating action in themselves.
Furthermore, it is known to utilize, for the cooling of metals, mixtures composed of a cryogenic fluid, for example liquid nitrogen, and of a divided solid additive having particle sizes greater than 5/100ths mm., and being as much as several millimeters The function of these relatively large particles is to pass through the gaseous layer which is formed by calefaction on contact with the metal in such manner as to melt and absorb the latent heat of fusion.
This cooling technique excludes the utilization of too-fine particles, especially of particles less than 5/100ths mm., since they are conveyed through the gaseous space without reaching the metal, and in consequence the desired result cannot be obtained.
One of the objects of the present invention is generally to improve heat treatments utilizing cryogenic fluids by giving these fluids definite new properties which enable them to satisfy specific conditions required according to the nature of these treatments.
The invention has especially for its object to obtain compositions of materials formed by a cryogenic fluid at at least one additional constituent in the form of particles which, contrary to the compositions of this type at present known and contrary to liquefied gases utilized alone, may be capable of reducing the radiation losses of the metal in fusion and/or facilitating the downward movement of the solidified metal into the ingot-moulds.