A temperature-raising bainite forming process

摘要

The present invention has been made with a view to providing a temperature-raising bainite forming process for a steel material capable of reducing the time required for the thermal treatment and the cycle time of a thermal treatment device without necessitating any special means for handling the steel material. According to the present invention, the steel material is heated to a temperature higher than the austenitic transformation point, and quenched temporarily to an intermediate point temperature higher than the martensitic transformation point. Then, the temperature of the steel material is again raised towards the range corresponding to bainitic transformation to form a bainitic structure. Then, the step of raising the temperature is discontinued before the temperature corresponding to the austenitic transformation point is reached, and the steel material is quenched subsequently. In the above-described steps of heating and raising the temperature towards the range corresponding to bainitic transformation, only the portion to be treated by the bainite forming process is irradiated locally with a high-density energy beam. <IMAGE>