Ductility
Ductility can be quantified by the fracture strain formula_1, which is the engineering strain at which a test specimen fractures during a uniaxial tensile test. Another commonly used measure is the reduction of area at fracture formula_2. The ductility of steel varies depending on the alloying constituents. Increasing the levels of carbon decreases ductility. Many plastics and amorphous solids, such as Play-Doh, are also malleable.
The most ductile metal is platinum and the most malleable metal is gold.
Refractory metals
Molybdenum is the most commonly used of the refractory metals. Its most important use is as a strengthening alloy of steel. Structural tubing and piping often contains molybdenum, as do many stainless steels. Its strength at high temperatures, resistance to wear and low coefficient of friction are all properties which make it invaluable as an alloying compound. Its excellent anti-friction properties lead to its incorporation in greases and oils where reliability and performance are critical. Automotive constant-velocity joints use grease containing molybdenum. The compound sticks readily to metal and forms a very hard, friction resistant coating. Most of the world's molybdenum ore can be found in China, the USA, Chile and Canada.