Hot deformation behavior and 3D processing map of super austenitic stainless steel containing 7Mo–0.46N–0.02Ce: Effect of the solidification direction orientation of columnar crystal to loading direction

Abstract

In the present paper, hot compression tests on a super austenitic stainless steel (SASS) containing 7Mo–0.46N–0.02Ce were performed at temperatures of 900 °C-1200 °C and strain rates of 0.01–10 s−1. The effect of angle between solidification direction of columnar crystal and loading direction (0°, 30°, 60°, and 90°) on the flow behavior and microstructure evolution of SASS was studied. Results showed that, samples with different columnar crystal characteristics and test conditions displayed various flow behaviors due to the difference in dynamic restoration softening mechanism, flow localization, and shear band formation. With the decrease of the angle between the solidification direction of columnar crystal and loading direction, the deformation activation energy (Q) and the ln Z value of SASS decreased at the true strain of 0.7. It indicates that dynamic recovery (DRV) and dynamic recrystallization (DRX) are more likely to happen in the samples with low angles. The location and range of high efficiency of power dissipation (η) region and instability region of the samples differed much with different columnar crystal characteristics. This means obviously different hot workability and microstructure evolution behaviors. At the true strain of 0.7, no negative η-value region was observed in the 0° sample, and the range of instability region was relatively small. On the whole, SASS presented the optimum hot workability when the angle between the solidification direction of columnar crystal and loading direction was 0°.

Keywords

• Super austenitic stainless steel
• Columnar crystal
• Constitutive model
• 3D processing map
• Finite element simulation