Martensitic (MS) Steel

To create MS steels, the austenite that exists during hot-rolling or annealing is transformed almost entirely to martensite during quenching on the run-out table or in the cooling section of the continuous annealing line. The MS steels are characterized by a martensitic matrix containing small amounts of ferrite and/or bainite. Within the group of multiphase steels, MS steels show the highest tensile strength level. This structure also can be developed with post-forming heat treatment. MS steels provide the highest strengths, up to 1700 MPa ultimate tensile strength. MS steels are often subjected to post-quench tempering to improve ductility, and can provide adequate formability even at extremely high strengths. Engineering and true stress-strain curves for MS steel grades are located in AHSS Application Guidelines Figure 2-9E.

Adding carbon to MS steels increases hardenability and strengthens the martensite. Manganese, silicon, chromium, molybdenum, boron, vanadium, and nickel are also used in various combinations to increase hardenability. MS steels are produced from the austenite phase by rapid quenching to transform most of the austenite to martensite. CP steels also follow a similar cooling pattern, but the chemistry of MS steel is adjusted to produce less retained austenite and form fine precipitates to strengthen the martensite and bainite phases.