Nippon Steel Corporation

Nagayasu Takemoto

Takashi Furukawa

Michio Endo

Kunio Watanabe

Kunishige Kaneko

Itaru Imabayashi

Mamoru Tashiro

A process for producing a low yield ratio, high strength two-phase steel sheet comprising hot rolling a steel composition containing 0.03 to 0.13% C, 0.8 to 1.7% Mn, not more than 0.1% Al, not more than 2.0% Si and not more than 0.5% Cr with a finishing temperature ranging from 750.degree. C. to 890.degree. C., rapidly cooling the strip to a temperature not higher than 230.degree. C., and coiling the strip at a temperature not higher than 230.degree. C. with the temperature variation during the period between the start and end of the coiling being no more than 100 degrees C. The Si content is limited to 1% or less for applications where paintability is of primary importance, and is limited to a range of from 1 to 2% for applications where the ductility is of primary importance. The process effects improvements in the artificial ageing property after working which improvement is uniform throughout the whole length of a coiled strip. The product obtained by the process is also described.

Process for producing low yield ratio, high strength two-phase steel

A method for producing a low alloy hot rolled steel strip or sheet comprising hot rolling a steel slab at a finishing temperature not higher than the Ar.sub.3 transformation temperature plus 60.degree. C. and cooling and coiling the hot rolled strip at a temperature not higher than 500.degree. C. The steel slab contains not more than 0.20% carbon, 0.50 to 2.50% manganese and 0.05 to 1.0% chromium and optionally contains not more than 1.0% silicon, the balance being iron and unavoidable impurities. The resultant strip or sheet has a high tensile strength of not less than 40 kg/mm.sup.2, a low yeild ratio of not more than 70% and an excellent total elongation of not less than 25%.

Method for producing low alloy hot rolled steel strip or sheet having

Growing community of inventors

Toyoake, Japan

Nagayasu Takemoto