A Dual-Phase Press-Hardening Steel with Improved Mechanical Properties and Superior Oxidation Resistance

A dual-phase steel (martensite and ferrite) was designed and manufactured for the hot-forming application in automobile. When the quenching from an intercritical temperature of 825 degrees C produced about 19 pct fraction of ferrite grains and 80 pct martensite in this steel, such a dual-phase microstructure could ensure that both uniform and post-uniform elongations are decent sufficiently without deteriorating strength, i.e., achieving the best mechanical combination of 1762 MPa ultimate tensile strength (UTS) and 11.2 pct total elongation (TE), which is far better than 22MnB5. The straining behavior of ferrite and martensite during deformation is then discussed on the basis of microstructural parameters. Moreover, much thinner oxide layer, less than 1.6 mu m thickness, was formed on the steel after the hot forming than that on 22MnB5, because much lower soaking temperature was employed to produce the dual phase in this steel and the denser/thicker Si/Cr-rich oxide band formed at the bottom of layer, both could greatly reduce the oxidization during hot forming.