Kawasaki Steel Corporation

Yoshio Yamazaki

Susumu Satoh

Toshiyuki Kato

Hideo Abe

Susumu Okada

Keiji Nishimura

Osamu Furukimi

Saiji Matsuoka

Takashi Obara

Masahiko Morita

Tetsuya Kiyasu

Disclosed are bake-hardenable sheet steel with good anti-aging property and a method for producing it. While controlling its C, P, S and N contents, the chemical composition of the sheet steel is defined to comprise not larger than 1.0% of Si, not larger than 3.0% of Mn, from 0.01 to 0.20% of Al and from 0.001 to 0.2% of Ti, in terms of % by weight. The value A (&equals;(AI,&minus;AI)/AI,) of the sheet steel is defined to be not smaller than 0.4 and the value AI,thereof to be not smaller than 30; or the ratio of the mean misorientation, M (degree), to the mean grain size, G (&mgr;m), M/G, of the sheet steel is defined to be not smaller than 0.8. The steel may additionally contain from 0.001 to 0.2% of Nb and/or from 0.0001 to 0.0080% of B. While controlling its Si, Mn, S, Al and N contents, the chemical composition of a steel slab is defined to comprise from 0.005 to 0.02% of C, not larger than 0.05% of P and from 0.025 to 0.19% of Nb, with satisfying the condition of 0.7&times;(C/12)&lE;Nb/93&lE;1.2&times;(C/12) (where C indicates the C content (wt. %), and Nb indicates the Nb content (wt. %)). To produce bake-hardenable sheet steel from it, the slab is heated, hot-rolled at a finishing delivery temperature of from 960 to 650&deg; C., coiled at a temperature of from 750 to 400&deg; C., then cold-rolled to a reduction of from 50 to 95%, and thereafter annealed for recrystallization at a temperature of from 750 to 920&deg; C. The slab may additionally contain B and/or Ti. The invention stably produces bake-hardenable sheet steel on an industrial scale.

Coated seizure-hardening type cold-rolled steel sheet having excellent aging resistance and method of production thereof

A formable thin steel sheet such as hot rolled sheet, cold rolled sheet or surface treated sheet comprises not more than 0.003 wt % of C, not more than 1.0 wt % of Si, not more than 1.0 wt % of Mn, not more than 0.15 wt % of P, not more than 0.020 wt % of S, not more than 0.0045 wt % of O, not more than 0.0020 wt % of N, not more than 0.15 wt % of Al provided that a ratio of Al/N is not less than 30, and the balance being Fe and inevitable impurities, and has not only improved formability for press forming, deep drawing or the like but also improved fatigue resistance as a welded joint.

Method of producing formable thin steel sheets

A formable thin steel sheet such as hot rolled sheet, cold rolled sheet or surface treated sheet comprises not more than 0.003 wt. % of C, not more than 1.0 wt % of Si, not more than 1.0 wt % of Mn, not more than 0.15 wt % of P, not more than 0.020 wt % of S, not more than 0.0045 wt % of O, not more than 0.0020 wt % of N, not more than 0.15 wt % of Al provided that a ratio of Al/N is not less than 30, and the balance being Fe and inevitable impurities, and has not only improved formability for press forming, deep drawing or the like but also improved fatigue resistance as a welded joint.

Formable thin steel sheets

Growing community of inventors

Chiba, Japan

Yoshio Yamazaki