Temperature dependence of tensile deformation behavior and strain hardening of lean duplex stainless steels

Abstract

Two lean duplex stainless steels with different manganese contents (4 and 8 wt.%) were deformed in the tensile mode in the temperature range of 25–300 °C. The deformation-induced martensitic transformation was characterized as the main austenite deformation mechanism of 4Mn steel at room temperature. In contrast, the strain hardening behavior of 8Mn steel was regulated by the cooperation of twinning induced plasticity and transformation induced plasticity. This was justified considering the lower austenite fraction and austenite stability in 4Mn compared to the steel containing a higher manganese content. Mechanical properties such as ultimate tensile strength and uniform elongation in both steels were significantly changed as the deformation temperature was increased. Differences in chemical composition and deformation temperature led to changing deformation mode due to strain partitioning between austenite and ferrite, austenite stability, and stacking fault energy. The most important factors influencing the mechanical properties are austenite stability and stacking fault energy at elevated temperatures. It was observed that as the austenite stability increases, martensitic transformation occurs directly from austenite grain and annealing twin boundaries but does not significantly improve strength and ductility. The strain partitioning between austenite and ferrite could provide a proper condition for strain-induced martensite transformation and deformation twinning, thereby enhanced mechanical properties at elevated temperatures.

Keywords

• Transformation induced plasticity
• Twinning induced plasticity
• Lean duplex stainless steel
• Thermomechanical processing