Microstructure, crystallographic texture and strain hardening behavior in hot tensile tests of UNS S32304 Lean Duplex stainless steel

Abstract

Duplex stainless steels can be used for applications in the nuclear industry endorsing its choice as an external shield for Type B packages. The microstructure, crystallographic texture, and the strain hardening behavior of UNS S32304 duplex stainless steel was investigated in hot tensile tests by Electron Backscattering Diffraction technique. Interrupted hot tensile tests with strain rates ε˙ = 10−2 s−1 and ε˙ = 10−1 s−1 were carried out at 700 °C using a Thermomechanical Physical simulator. The α parameter of gamma distribution was associated for the first time with strain in ferrite and austenite phases through the Grain Orientation Spread parameter (GOS). The ferrite phase did not show the dynamic equilibrium between the stored energy and recovery rates. The average GOS in the ferrite phase was larger for ε˙ = 10−1 s−1 due to a smaller time available for dislocation annihilation and rearrangement in dynamic recovery. The grain rotation sequence → - → was found in ferrite phase. In the austenite phase, the dynamic recrystallization was not observed and the and fiber textures parallel to the tensile direction were strengthened. The austenite → ferrite phase transformation occurred during the hot tensile tests and showed the Kurdjumov-Sachs orientation relationship. The modified Crussard-Jaoul analysis showed six-strain hardening stages which were associated with the average GOS and austenite → ferrite phase transformation.

Keywords

• Lean Duplex stainless steel
• Dynamic recovery
• Phase transformation
• Crystallographic texture
• Strain hardening behavior