BAINITE FORMATION AT LOW TEMPRATURES IN A HIGH C-Si STEEL AND ITS MECHANICAL BEHAVIOR

摘要

A significant amount of stabilized austenite can be obtained in high carbon steels containing high amounts of Mn and Si (1.5-2%). At relatively low temperatures the bainite plates formed are extremely thin, making the material very strong. In this study, the influence of the thermal cycle of austempering on the mechanical behavior of a spring steel (0,56%C-1,43%Si-0,58%Mn-0,47%Cr), with TRIP effect, was investigated. The thermal cycle consisted of heating two groups of hot-rolled steel at austenite field, at 900°C for 300 s, and quickly transferring it to a metallic bath maintained at 220°C 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 levei of strength and ductility is due to a mixture of martensite and very fine bainite formation.