| 摘要 |
<p>PURPOSE:To produce an ultrahigh tensile strength hot rolled steel sheet excellent in degree of flatness by cooling a slab of steel with specific composition at respectively specified hot roll finishing temp., cooling starting temp., and cooling velocity, and then coiling this coil at a specific temp. CONSTITUTION:A slab of a steel which has a composition consisting of, by weight, 0.05-0.20% C, 1.5-3.5% Mn, 0.01-0.1% Al, <=0.5% Si, <=0.05% P, <=50ppm S, 80ppm N, <=80ppm O, and the balance iron with inevitable impurities and satisfying (Si+P)<=0.35% and (S+N+O)<=100ppm is used as a stock. Cooling is started under the conditions satisfying <=950 deg.C hot roll finishing temp. and >=800 deg.C cooling starting temp. Then, cooling is done at >=20 deg.C/s cooling rate, followed by coiling at <=400 deg.C. By this method, the ultrahigh tensile strength hot rolled steel sheet suitable for high-strength member, such as automobile bumper and door guard bar, can be produced.</p> |
