| 摘要 |
PURPOSE:To improve toughness while maintaining high strength by direct hardening and tempering treatments by decreasing the content of C in an Ni-contg. low temp. steel and adding a small amt. of Mo thereto. CONSTITUTION:The Ni-contg. low-carbon steel contg., by weight %, 0.005-0.03% C, 0.05-0.9% Si, 0.3-2.0% Mn, 6.5-12.0% Ni, 0.02-1.0% Mo and 0.01-0.10% Al, or at least one kind of <0.05% Nb and <0.07% V as precipitation hardening components and at least one kind of <1.0% Cu and <1.0% Cr and further contg. <0.05% Ti as hardenability improving components is hot rolled at >=950 deg.C temp. and is cooled at >=5 deg.C/sec cooling rate down to a room temp. immediately after hot rolling, then the steel is hardened. The hardened steel plate is heated to a 450-620 deg.C temp. region and is then tempered by air cooling or water cooling. The steel material for a vessel for storing, transporting, etc., of LNG which has excellent strength and toughness at a cryogenic temp. is obtd. |
