Novel Thermal Processing of Dual Phase Steels: II – Work Hardening and Fracture Mechanisms

The volume fraction, scale and distribution of the non-ferritic phases (NFP) in the microstructure of a series of dual phase steels were varied by novel thermal processing. The effects of these microstructural modifications on uniaxial tensile properties are reported. By refining the scale of both the ferrite grains and the NFP particles, the fracture strain was increased significantly with minimal reduction in uniform strain. The fracture damage mechanisms are decohesion of NFP particles at 293 K (ductile failure) and cleavage micro-cracking of ferrite grains at 77 K (brittle failure). Recommendations are made for microstructural design of DP steels for specific applications.