Bainite Formation at Low Temperatures in High C-Si Steel and its Mechanical Behavior

Abstract

Abstract A significant amount of stabilized austenite can be obtained in high carbon steel containing high amounts of manganese and silicon (1.5–2%). At relatively low temperatures the bainite plates formed are extremely thin; as a result the material becomes very strong. In this study, the influence of austempering on the mechanical behavior of a spring steel 0.56C-1.43Si-0.58Mn-0.47Cr (wt.%), with TRIP effect, was investigated. The thermal cycle consisted of heating two groups of hot-rolled steel at the austenite field of 900°C for 300 s, and transferring it to a metallic bath maintained at 220 or 270°C, respectively, for different isothermal treatment times. The samples were then tested in tension, and their microstructures were examined by optical and scanning electron microscopy. According to the results, the samples treated at 220°C showed higher elongation, yield point, and tensile strength than those maintained at 270°C. The high level of strength and ductility is due to a mixture of martensite and very fine bainite formation.