Improving the ductility of ultrahigh strength lath martensite through heterogeneous carbon distribution

Abstract

This investigation aims to improve the ductility of ultrahigh strength (>2 GPa) press hardening steels (PHS) by exploiting the heterogeneous carbon distribution in lath martensite. The proposed strategy is demonstrated in a medium carbon PHS with a lath martensite microstructure produced by quenching austenite. It is found that by enhancing auto-tempering, the solute carbon content in the coarse laths formed earlier during martensitic transformation can be reduced, leading to the softening and ductilizing of these laths. The softened coarse laths of small volume fraction provide significant improvement in the post-uniform elongation (PUE) without compromising the ultrahigh strength of lath martensite. The remarkable improvement in the PUE of ultrastrong lath martensite achieved by exploiting heterogeneous carbon distribution is expected to be instructive for the development of ultrahigh strength PHS with good ductility and fracture toughness.

Keywords

• Lath martensite
• Carbon distribution
• Ductility
• Ultrahigh strength
• Martensitic transformation