High strength low carbon hot rolled δ-ferritic steel: microstructure and mechanical properties

Abstract

The present study concerns the development of high strength low carbon hot rolled bainitic and martensitic δ transformation induced plasticity steels. Equilibrium and para-equilibrium phase evolution have been examined by carrying out thermodynamic calculation using MT-DATA software. Microanalysis demonstrates that both manganese and aluminium partition between liquid and solid phases. Isothermal treatment and tempering at 350°C for bainitic and martensitic microstructures respectively have yielded the best combination of strength and ductility. All the steels have exhibited the continuous yielding behaviour and favourable ratio of yield and tensile strength, which are desirable for formability. The annealed steel has yielded a high level of tensile strength with the static toughness value in between the conventional transformation induced plasticity assisted and dual phase steels.

Keywords:

• MT-DATA
• Allotriomorphic ferrite
• δ-ferrite
• Pearlite
• Para-equilibrium

SKG would like to express his sincere thanks to Dr H. L. Yi, GIFT, POSTECH, Korea, for rendering his help in MT-DATA calculations. PPC is grateful to Tata Steel, Jamshedpur, India, for funding the research.