Jfe Steel Corporation

Keita Yonetsu

Hideyuki Takahashi

Kohei Hasegawa

Hiroki Nakamaru

Junichiro Hirasawa

Naoto Yoshimi

Masato Sasaki

Hideyuki Tsurumaru

A method for the manufacturing of high strength cold rolled steel sheets includes continuously annealing a cold rolled steel sheet that has a composition containing C: 0.05-0.3% mass, Si: 0.6-3.0% mass, Mn: 1.0-3.0% mass, P: &#x2266;0.1% mass, S: &#x2266;0.02% mass, Al: 0.01-1% mass, N: &#x2266;0.01% mass, and Fe and inevitable impurities: balance, in a manner such that the cold rolled steel sheet is heated in a furnace using an oxidizing burner to a steel sheet temperature of &#x2267;700&#xb0; C., then soak-annealed in a reducing atmosphere furnace at 750-900&#xb0; C., then cooled so the average cooling rate between 500&#xb0; C. and 100&#xb0; C. is &#x2267;50&#xb0; C./s. High-Si cold rolled steel sheets with high strength and good phosphatability while containing Si&#x2267;0.6% are obtained without controlling conditions so as to increase the dew point in the reducing atmosphere in the soaking furnace or to increase the vapor hydrogen partial pressure ratio.

Method for manufacturing of high strength cold rolled steel sheet of excellent phosphatability

Growing community of inventors

Okayama, Japan

Keita Yonetsu