Hot workability optimization of W400 non-oriented silicon steel

Abstract

Isothermal compression tests of W400 non-oriented silicon steel are performed at 0.01 to 10 s−1 and 850 to 1150 °C on a Gleeble thermo-mechanical simulator. Each stress-strain curve shows monotonous but slow increase of flow stress blessed with increasing strain. By introducing temperature into the strain rate exponent in Z parameter and proposing the temperature boundary principle, a revised constitutive pattern is built with a view to quantify flow stress versus temperature and strain rate accurately. Numerous sub-grains and sub-grain boundaries (GBs) are detected in the deformed grains, confirming the distortion energy to be reduced by dynamic recovery and thus slowing down the monotonous increase of flow stresses. Unusual discontinuous dynamic recrystallization is activated when strain rate and temperature is relatively higher, as confirmed by the random orientations of recrystallized grains. Analyses of GB shape and intergranular misorientation prove that local strain due to weak dynamic recovery leads to GB bulging and sub-GB formation, and thus activates the unusual discontinuous dynamic recrystallization. The distribution maps of strain rate sensitivity coefficient are constructed when the strain are 0.2–0.8. Based on high strain rate sensitivity coefficient, low deformation resistance and high GB stability, workability parameters are optimized as: temperature 1000–1150 °C, strain rate 0.01 to 10−0.5 s−1 and strain ≤0.6.