1995 年 35 巻 7 号 p. 914-919
Hot ductility and precipitation behavior of titanium-bearing and titanium-free low carbon and ultra low carbon steels have been investigated by an elevated temperature tensile test and quantitative analysis of Ti, Mn and S precipitates. In the steel without titanium, the main precipitate was MnS in austenite. The amount of Mn precipitates increases as temperature is lowered until a saturation level. The dectile brittle transition temperrature can be evaluated by the Mn/S ratio. Ductility can be improved by holding at 1100°C or cooling-reheating process. On the other hand, in the titanium-bearing steel, the amount of Mn precipitates was very small due to Ti precipitated in austenite. The ductile-brittle transition temperature corresponds to the amount of Ti4C2S2 precipitated, and the ductility cannot be improved by holding at 1100°C or cooling-reheating process.
