Sumitomo Metal Industries, Inc.

Seiichi Watanabe

Hiroo Ohtani

Yoshiro Matsumoto

Toshiji Takigawa

Tatsuro Kunitake

Chromium-molybdenum structural steels which have high tensile strength, low susceptability to temper embrittlement, high hydrogen attack resistivity and high temperature ductility and which can be formed into very thick steel plates comprise 0.05 to 0.20% of C, 0 to 0.15% of Si, 0.46 to 1.00% of Mn, 2.00 to 3.50% of Cr, 0.80 to 1.20% of Mo, 0.00015 to 0.0015% of B, 0.005 to 0.070% of Sol. Al and inevitably entrained impurities, the balance to make up 100% of Fe. Preferably the inevitably entrained impurities of nitrogen and phosphorus are below 0.0060% of N and 0.0010% of P.

Method of making steels which are useful in fabricating pressure vessels

Chromium-molybdenum steels which have high strengths, good hydrogen attack resistivities, good high-temperature ductilities and high creep rupture strength, and which, when formed into steel plates, welded and given a high-temperature strain relief annealing treatment will acquire high resistivity to creep damage, comprises 0.11 to 0.17% of C, 0.50 to 1.20% of Si, 0.46 to 1.00% of Mn, 1.00 to 1.50% of Cr, 0.45 to 0.65% of Mo, 0.00015 to 0.0015% of B, 0.010 to 0.100% of Sol. Al and inevitably entrained impurities, the balance to make up 100% of Fe. Preferably the inevitable nitrogen and phosphorus impurities are kept below 0.0060% of N and 0.010% of P.

Steels which are useful in fabricating pressure vessels

A heavy thick steel casting having high mechanical strength with a tensile strength of 80 kg/mm.sup.2 or more, excellent impact properties with a vE.sub.O value of more than 8 kg-m/cm.sup.2 and improved weldability, and also a method of manufacturing the same. In the method, steel containing boron as an essential component and with a Ceq value corresponding to the maximum thickness of the product is cast. The casting is solidified in air, then heated to a temperature of 930.degree. to 1,050.degree. C. for one hour or more, followed by air cooling. Thereafter, the casting is quenched and tempered to thereby impart the casting with the desired characteristics.

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Amagasaki, Japan

Seiichi Watanabe