Flow stress of duplex stainless steel by inverse analysis with dynamic recovery and recrystallization model

Abstract

To obtain the flow stress in duplex stainless steel, a duplex flow model is proposed that applies a rule of mixtures with the relationship between the volume fractions of austenite and ferrite. The model includes the saturated stress ratio λ and the volume fractions of austenite and ferrite at various temperatures. It considers the mechanical deformation and microstructural evolution with dynamic recrystallization (DRX) and dynamic recovery (DRV) of the two phases during hot working. To confirm the validity of the proposed model and new inverse analysis method, hot compression experiments were performed at deformation temperatures of 1 050, 1 150, and 1 250°C and strain rates of 0.1, 1, and 10 s-1with SUS329J4L, which is an austenite-ferrite duplex stainless steel. According to the flow curves, the softening rate from the peak stress was steeper with decreasing temperature from 1 250 to 1 050°C, corresponding to estimated austenite volume fractions from 33% (1 250°C) to 61% (1 050°C). Microstructural heterogeneity between DRX in the austenite and DRV in the ferrite was observed at deformation temperatures from 1 050 to 1 250°C, confirming that a clearly different restoration mechanism occurred in the two phases.