Enhancement of strength-ductility trade-off in a 2000 MPa grade press-hardened steel via refined martensite with stable high-density cementite

Abstract

High-strength press-hardened steels (PHSs) are characterized by a martensite structure of high strength and adequate ductility. Strengthening PHSs with high C contents is usually accompanied by a loss of ductility and toughness. To overcome this inherent strength–ductility trade-off dilemma, we propose a novel strategy to achieve outstanding mechanical performance by introducing stable high-density Cr-rich cementite, which refines the martensite structure via Zenner pinning effect in a novel 2000 MPa grade PHS. Specifically, a high tensile strength of 2085 MPa with an appreciable total elongation of 10.1% is achieved in the novel PHS, which is far superior to commercial 22MnB5 steel (1519 MPa and 10%). The strength increase is predominantly induced by a high density of dislocations and cementite in the novel PHS, while the good ductility is attributed to the refined martensite structure coordinating plastic deformation and the enhanced work-hardening ability and dislocation storage capability mediated by massive cementite. The work can lay foundations for designing high-strength PHSs with good ductility.

Keywords

• Press-hardened steels
• Microstructural refinement
• Mechanical properties
• Cementite
• Work hardening