Excellent low temperature superplasticity and its deformation mechanism in nano/ultrafine grained Fe–17Cr–6Ni stainless steel

Abstract

Superplastic deformation typically occurs in non-ferrous metals at high temperatures, which results in severe surface oxidation and high energy consumption. In this study, we designed and manufactured a nano/ultrafine-grained stainless steel with a dual-phase microstructure that exhibits excellent low-temperature superplastic deformation capability. A maximum tensile elongation of approximately 500% was achieved when the tensile test was conducted at 700 °C with an initial strain rate of 5 × 10⁻⁴ s⁻1. Even after a 500% tensile elongation, the austenite grains in the gauge section of the tensile specimen still maintained an equiaxed grain shape, and the texture also weakened significantly, indicating that grain boundary sliding and grain rotation dominated the deformation process during superplastic flow. The outstanding superplasticity is mainly attributed to the dual-phase microstructure composed of nano/ultrafine austenite grains and martensite.

Keywords

• Nano/ultrafine grained steel
• Reverse phase transformation
• Low temperature superplastic deformation
• Grain boundary sliding
• Grain rotation
• Texture