process for producing extra high tensile steel having excellent stress corrosion cracking resistance

摘要

An extra high tensile steel having an excellent stress corrosion cracking resistance in sea water and a yield strength of 1080 MPa or more is provided.;A slab comprising, in terms of % by weight, 0.04 to 0.09% of C, 0.01 to 0.10% of Si, 0.05 to 0.65% of Mn, 8.0 to 11.0% of Ni, 0.5 to 1.5% of Mo, 0.2 to 1.5% of Cr, 0.02 to 0.20% of V and 0.01 to 0.08% of Al with the balance consisting of iron and unavoidable impurities is heated to a temperature between 1000°C and 1250°C, hot-rolled at a temperature of Ar' point or above, air-cooled, reheated at a rate of 120°C/min or less to a temperature region of from (Ac3 point - 40°C) to (Ac3 point + 40°C), quenched and subsequently tempered at a temperature of the Ac1 point or below.