The formation of MS steels involves transformation of most of the austenite structure existing during the annealing or hot-rolling process to the martensite structure by rapid quenching in the cooling stage of the continuous annealing line or on the run-out table. The characteristic structure of the MS steels involves a martensitic matrix consisting of bainite and/or ferrite in small quantities (Figure 1).
Figure 1. Microstructure for MS 950/1200
Key Properties of MS Steels
MS steels exhibit optimal tensile strength within the category of multiphase steels. The post-forming heat treatment process can also be used to develop these steels. The ultimate tensile strength of MS steels is 1700 MPa (Figure 2). MS steels’ ductility can be improved by subjecting them to post-quench tempering, and their formability is adequate even at very high strengths.
Figure 2. The tensile strength-elongation graph of MS steels
The addition of carbon increases the hardenability of MS steels and improves the strength of the martensite. Hardenability can also be increased using different combinations of nickel, vanadium, boron, molybdenum, chromium, silicon, and manganese.
The following table provides current production grades of MS steels and corresponding example automotive applications:
||Cross-members, side intrusion beams, bumper beams, bumper reinforcements
||Rocker outer, side intrusion beams, bumper beams, bumper reinforcements
||Side intrusion beams, bumper beams, bumper reinforcements
Download the Advanced High-Strength Steels Applications Guidelines free here, to learn more about the metallurgy, forming and joining of these new steels.
This information has been sourced, reviewed and adapted from materials provided by WorldAutoSteel (World Auto Steel).
For more information on this source, please visit WorldAutoSteel (World Auto Steel).