Effects of heat treatment on microstructures and mechanical properties of a high strength steel for cold forming

The main emphasis of the present study has been placed on understanding the effects of heat-treatment (austenitizing and isothermal treatment) on the microstructures and mechanical properties of a 0.20C-0.25Si-2.0Mn high strength steel for cold forming. The steel was austenitized, and isothermally treated at bainitic region followed by air cooling. Microstructural observation, tensile tests, and Charpy impact tests were conducted. The mechanical properties and microstructures of the steel were changed by heat-treatment conditions. The size of prior austenite increased with increasing austenitizing temperature, resulting in decrease of impact toughness. Microstructure was changed from bainite + pearlite to martensite + bainite with decreasing isothermal treatment temperature, and yield or tensile strength, yield ratio, and reduction of area were increased. From the results of the present study, it is confirmed that it is possible to develop a new C-Si-Mn high strength steel for cold forming through optimization of heat treatment