Flow stress property of a hardened steel at elevated temperatures with tempering effect

The flow stress property of materials is a key for the successful modeling and analysis of any thermo-mechanical processes. For hardened steels in manufacturing processes such as heat treatment, grinding, and hard machining, their martensitic structures are often changed due to tempering at elevated temperatures, and thus their flow stress property changes accordingly. To reveal the tempering effect, tensile tests at elevated temperatures with various soaking times and heat treatment experiments are performed on hardened AISI 52100 steel. It is found that, at the same temperature level the flow stress is smaller for the specimens that received stronger tempering, and the decrease of strength due to tempering effect becomes more pronounced at high temperatures. Furthermore, the tempering effect is modeled and expressed as a function of thermal history and material hardness. The modeling results agree with the experiment reasonably well. Based on the model, the tempering effect on flow stress can be separated from the softening effect due to temperature rise, and both effects can be studied individually.