“12 Chrome Moly Van” steels are a series of martensitic stainless steels designed for use at moderately high temperatures. 1.4923 is a typical grade in this series. The dominant application is steam power generating plant.
Approximate Composition – 12% Cr, 0.5% Ni, 1.0% Mo, 0.30% V(vanadium), 0.20% C (approximate EN composition, no comparable ASTM grade).
This grade combines the following characteristics:
- Moderate strength – 800 MPa UTS, 600 MPa 0.2% PS at room temperature
- Moderate high temperature strength – 280 MPa 0.2% PS at 550°C
- Good creep strength – 137 MPa rupture stress at 550°C at 100000 hours
- Moderate toughness – typically 50 J at room temperature
- Basic corrosion resistance
- Weldable with care. Requires pre and post weld heat treatment
The 12% CrMoV series of steels can be regarded as a development of the original Harry Brearley cutlery grade. By adding nickel, molybdenum and vanadium to the basic 12% Cr grade, the strength is improved especially at high temperature. The key property is creep strength. Creep is the phenomenon where a material continues to deform with time under stress. For steels it is important to take account of creep above about 450°C. Typical steam temperatures for power generation are approximately 550°C which explains the extensive use of these grades in this application sector. Further enhancements of the 12% CrMoV grades have been developed with additions of tungsten, cobalt, niobium and nitrogen. These have often been known by brand names such as FV 448, FV 535, Jethete M152.
Applications which illustrate these features include:
Pressure equipment, high temperature bolting, steam turbines, nuclear reactors, gas turbines, petroleum refining.