Kabushiki Kaisha Kobe Seiko Sho

Yamakawa Industrial Co.

Satoru Nito

Ichiro Kokubo

Takuo Hosoda

Tsunahiro Yamakawa

Hiroyoshi Yamakawa

Masakatsu Hata

Steel containing, on a weight percent basis, 0.01 to 0.15% of carbon, 0.05 to 0.50% of silicon, 0.20 to 1.0% of manganese, 0.01 to 0.1% of aluminum, 0.3 to 2.0% of copper, 0.1 to 2.0% of nickel, 0.015 to 0.1% of niobium and 0.0005 to 0.0050% of calcium, the balance of its composition being iron and unavoidable impurities, is heated to a temperature of 1100.degree. C. to 1250.degree. C., and hot rolled. The hot-rolled steel is coiled at a temperature of 350.degree. C. to 500.degree. C. to prepare a hot-rolled steel sheet having a tensile strength not exceeding 65 kgf/mm.sup.2. The sheet is cold worked until a working strain of at least 15% is set up. The cold-worked product is heated at a temperature of 400.degree. C. to 550.degree. C. for 0.5 to three hours to yield a part having a tensile strength of at least 80 kgf/mm.sup.2 for an automobile, particularly its automatic transmission system.

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Fuji, Japan

Satoru Nito