WARM ROLLING METHOD

摘要

A multi-directional warm-rolling method for manufacturing a superfine grain steel material with a superfine crystal grain structure of 3 mum or smaller in average grain size. When rolling of two passes or more is performed for a steel material in the rolling temperature range of 350 to 800°C, a rolling by an oval shape hole die and a rolling by the other shape hole die are performed at least one time so that a large amount of strain can be introduced into the material by a simple means with less section reduction rate and less number of passes. Steel materials having the superfine crystal grain structure and excellent strength and ductility can be manufactured by this method.