7.5Ni-4Co系超強力鋼NT150-4鋼の開発

概要

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Daido Steel has supplied 7.5Ni-4Co grade steel for rocket casing, manifold and so forth and has recently marketed a higher strength version, NT150-4, through the optimization in chemical composition and heat treatment. This paper reviews the development program to elucidate the effects of alloying elements such as Cr, Mo, etc. and also hardening/tempering on mechanical properties.The new steel, NT150-4, contains 0.20C, 7.5Ni, 4Co, 2Cr, 2Mo and 0.1V. It was melted and refined by air arc and then ladle furnaces and teemed into 15 ton ingots. The hot-rolled plate 20mm thick was austenitized at 850°C, hardened by air cooling and tempered at 530°C. Its typical 0.2% Y.S., U.T.S. and KIC were 141kgf/mm2, 164kgf/mm2 and 367kgf/mm3/2 respectively.NT150-4 is applied to the motor casing for solid rocket booster of H II rocket.
大同特殊鋼株式会社の論文