| 摘要 |
<p>PURPOSE:To mass-produce a steel tube having a uniform superfine structure by performing rolling by means of a stretch reducing mill while specifying stretching ratio and temp. region and utilizing the temp. increase by plastic working, inversely transforming a structure from ferritic phase to austenitic phase, and then carrying out cooling. CONSTITUTION:A 'thin-walled and hollowed-shaped hollow shell having a structure in which at least a part is composed of ferrite' is rolled by means of a stretch reducing mill while properly selecting heating temp. and regulating stretching ratio to >=1.5. Stretch-reducing is carried out while exerting temp. rise from a temp. region not higher than the Ac1 point up to a temp. region not lower than the Ac3 point by utilizing the temp. increase by plastic working, and the whole structure consisting of ferrite is temporarily subjected to inverse transformation into austenite, followed by cooling. By this method, the hot rolled seamless steel tube having a superfine structure (<=10 or <=5mu ferrite grain size) and also having superior strength, toughness, ductility, corrosion resistance, etc., can stably be produced.</p> |
