Microstructural evolution of SA508 grade 3 steel during hot deformation

SA508 grade 3 steel is widely used in the manufacture of large-scale forged components for nuclear reactor applications. Numerical models have already been established to simulate industrial forging process of grade 3 steel; however, limited information is available on the microstructural evolution of this steel during hot forging operation. This work focuses on the flow behavior and related microstructural evolution in grade 3 steel with detailed analysis on the interfacial friction, texture and hardness evolution. Uniaxial hot compression tests were conducted over a range of test temperatures (880-1130 °C) and true strain rates (0.001-1/s), representative of the industrial hot forging conditions. Two different deformation mechanisms, MDRX at the lowest forging temperature and DRV along with DRX at the highest forging temperature, were observed showing marked impact on the final microstructure and hardness. A random fiber-type weak deformation texture was observed irrespective of the test temperatures and strain rates used. The microstructural changes from the as-received to the various deformed conditions were quantified. The quantitative data are the key to obtain accurate parameters for DRV and DRX processes that affect the accuracy of the mathematical models.