Molybdenum in Steels

Molybdenum in Steels Molybdenum (Mo) (atomic number 42 and atomic weight 95.95) has a density of 10.22 gm/cc. Melting point of Mo is 2610 deg C and boiling point is 5560 deg C. The phase diagram of the iron molybdenum (Fe-Mo) binary system is at Fig 1. Fig 1 Iron molybdenum binary system Mo is normally referred in short as ‘moly’.  It has many important uses in alloy steels, stainless steels, alloy cast irons and super alloys. It is a powerful hardenability agent and is a constituent of many heat treatable alloy steels. Mo retards softening at higher temperatures. Hence it is used in boiler and pressure vessel steels, as well as several grades of high speed and other tool steels. Mo improves the corrosion resistance of stainless steels. In HSLA (high speed low alloy) steels, it produces acicular ferrite structures. Mo is the basis for many of the as-rolled DP (dual phase) steels used in automotive applications. While Mo may often be used interchangeably with chromium (Cr) and vanadium (V), in many cases the properties it imparts are unique. Due to it, the use of Mo has increased considerably over the past several decades. Available forms Mo is supplied as ferro-molybdenum (Fe-Mo) and as molybdic oxide (MoO3). Fe – Mo contains a minimum of 60 % Mo. Silicon (Si) and copper (Cu) may be present in quantities up to 1 % each. It is relatively expensive and is sparingly used for addition. Technical MoO3 has a minimum of 57 % Mo. SiO2 is the main impurity, but it may also contain small amounts of Cu, sulfur (S), and phosphorus (P). MoO3 is supplied either in cans or as briquettes. MoO3 briquettes may also contain some amount of carbon (C). Considerable quantity of Mo is recovered...