Kabushiki Kaisha Kobe Seiko Sho

Hiromi Hori

Masatoshi Sudo

Ichiro Tsukatani

Zenichi Shibata

Akinori Ohtomo

Takafusa Iwai

Denei Takai

There are described a high strength steel plate having a low yield ratio and improved strength-elongation balance and stretch flangeability, and a method for producing same, the steel plate containing 0.01-0.2% of C, 0.3-2.5% of Mn and 0.01-1.8% of Si and having a tripple phase of polygonal ferrite, bainite and martensite, the area ratios of the bainite and martensite phases being 4-45% and 1-15%, respectively, and the area ratio of the bainite phase being greater than that of the martensite phase.

High strength steel plate and method for manufacturing same

A cold-rolled high strength steel plate with excellent formability and baking hardenability, has the composition (% by weight) 0.2-0.15% of C, 0.02-0.7% of Mn, 0.01-0.1% of Al and 0.002-0.01% of N, optionally at least one element selected from the group consisting of 0.01-0.8% of Si, 0.01-0.1% of P, 0.0002-0.005% of B and 0.01-0.5% of V, and a microstructure comprising ferrite containing 2-30% of bainite and less than 8% of martensite. The steel plate is produced by hot and cold rolling steel of the defined composition followed by rapidly heating to a temperature between the Ac.sub.1 and Ac.sub.3 transformation points, holding at this temperature for less than 5 minutes, and quenching to a temperature below 500.degree. C. at a cooling rate between 50.degree. and 500.degree. C./sec.

Cold-rolled high strength steel plate with composite steel structure of

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Akashi, Japan

Hiromi Hori