Developing high-strength, ductile Ni-free Fe–Cr–Mn–C–N stainless steels by interstitial-alloying and thermomechanical processing

Abstract

Microstructures and mechanical properties of a new grade of Fe–18Cr–12Mn–CN (wt%) austenitic stainless steels interstitial-alloyed with 0.3–0.48 wt% C + N at 0.22–1.06 C/N ratios were investigated after thermomechanical processing. Appropriate thermomechanical treatment was designed to obtain good combination of strength and elongation. The developed steel possessed ultimate tensile strength of 1 GPa, yield strength of 450 MPa, and elongation up to 83%. It was found that strength and ductility of the studied steels were affected by strain-hardening behavior and decreasing the strain-hardening rate resulted in lower ultimate tensile strength. Addition of C to N-containing Ni-free steels deteriorated mechanical properties. The best combination of strength and elongation was obtained in steel with lowest C + N (0.3 wt%) and C/N ratio (0.22). Keywords: Ni-free austenitic stainless steel, Interstitial-alloying, Nitrogen, Ultrahigh strength steel, Thermomechanical processing