Welding Inspection & Metallurgy API ICP Self Study Notes

The strain energy involved in the martensitic reaction is enormous and a large
undercooling is necessary. In low and medium carbon alloys, the martensite
tends to form in lath shaped crystals that are generally too fine to resolve in
the light microscope. In high carbon steels, plate martensite forms. For certain
steels, the rapid cooling necessary to produce a martensitic structure (e.g.
water or brine baths) introduces large surface tensile stresses and may cause
quench cracking. However, when medium carbon steels are alloyed with
elements such as nickel, chromium and molybdenum, the development of
equilibrium phases is suppressed and martensite can be formed with less
drastic cooling, such as oil quenching.