Time-dependent deformation of low carbon steel at elevated temperatures

This paper focuses on the microstructure and deformation properties of structural steel at elevated temperatures. The amounts and morphology of carbides present were monitored as a function of thermal exposure parameters. It was observed that as the temperature approaches the ferrite-austenite phase transformation (727 °C), considerable diffusion of cementite plates and abnormal grain growth occurs. A viscoplastic constitutive model has been employed to simulate the flow behavior of the steel. Monotonic and cyclic tests were carried out to determine the kinematic and isotropic hardening parameters required for full identification of the model variables. Results of the model were compared with those obtained experimentally. The material parameters were shown to be sensitive to the microstructure and temperature. Variation in carbide amounts and morphology in the post thermal exposed specimens result in differences in the kinematic hardening, as compared to the as received material. Furthermore, the temperature sensitivity of the isotropic hardening is indicated by the presence a cyclic hardening/softening transition in the temperatures 600–700 °C. Validity of the model in capturing time dependent behavior of the structural steel is examined using a sequentially coupled thermal-stress finite element analysis of single steel beam. Results of this simulation are discussed in terms of effects of temperature and strain-rate sensitivity on the materialʹs viscoplastic deformation response.