Unveiling the effects of Ti microalloying and thermomechanical processing on recrystallization behavior and mechanical properties of type 316 stainless steel

Abstract

For the titanium-stabilized austenitic stainless steels, the interaction of precipitation due to the addition of Ti and the recrystallization process is an important aspect of grain refinement, which needs more systematic investigations. Accordingly, in the present work, the effects of Ti microalloying and thermomechanical processing on the recrystallization behavior and mechanical properties of type 316 stainless steel were investigated. It was revealed that the strain-induced α′-martensitic transformation in these metastable alloys is sensitive to the presence of Ti and C in solid solution or their presence as TiC carbides in the aged condition, as well as the temperature of rolling and reduction in thickness. During annealing, the reversion of deformation-induced α′-martensite to austenite and primary recrystallization resulted in the formation of fine-grained equiaxed microstructures, where the precipitation of TiC and sigma-phase was found to be important in the retardation of recrystallization and grain growth (by Zener pinning mechanism) as well as refining the grain size. Annealing the cold rolled 316Ti stainless steel at 800 °C led to a fine grain size of ∼2.5 μm with the precipitation of sigma-phase; while annealing at 900 °C resulted in a coarser grain size of 4 μm but without the presence of the unfavorable sigma-phase. The yield stress of 476 MPa, ultimate tensile strength of 805 MPa, and total elongation of 68 % were obtained for the latter, revealing the merits of Ti addition and thermomechanical processing for the improvement of mechanical properties.

Keywords

• Austenitic stainless steels
• Precipitation
• Grain refinement
• Mechanical properties
• Transformation-induced plasticity