Enhanced strength and ductility of the low-carbon steel with heterogeneous lamellar dual-phase structure produced by cyclic intercritical rolling

Abstract

Steels with outstanding mechanical properties are desired in industrial applications. Martensitic structure significantly increases the strength in low-carbon steels, but usually sacrifices their ductility. In order to improve the combination of strength and ductility, a full martensitic steel was further processed by cyclic intercritical rolling to produce a novel heterogeneous lamellar structured dual-phase (HLSDP) structure. This processing route constructs a small amount of lamellar ferrite surrounded by high volume fraction of refined martensite, which is a promising heterostructure for hetero-deformation induced (HDI) hardening. The HLSDP steel shows a simultaneously improved strength and ductility (ultimate tensile strength, UTS: 1.85 GPa; uniform elongation, UE: 5.6%), comparing to the lath martensite steel (UTS: 1.68 GPa and UE: 4.1%). The superior tensile properties of HLSDP steel are attributed to the higher strain hardening ability, which is related to the significant HDI hardening. Due to the deformation incompatibility between the soft zone (ferrite) and hard zone (martensite), strain partitioning is occurred during plastic deformation. In addition, micro digital image correlation (μ-DIC) analysis reveals the evolution of strain field during deformation. A significant strain gradient is produced near the interface of ferrite and martensite in the HLSDP steel.

Keywords

• Heterostructured materials
• Strengthening and toughening
• Dual-phase steel
• Martensite
• HDI hardening
• Strain partitioning