PREPARATION OF LOW ALLOYED HIGH TENSILE STEEL EXCELLENT IN SULFIDE STRESS CORROSION CRACKING RESISTANCE

摘要

PURPOSE:To obtain the titled alloyed steel, by a method wherein steel mainly containing C, Si, Mn, Al, Mo, P and S is heated to an austenite temp. and the heated steel is cooled at a specific cooling speed in a predetermined temp. range and succeedingly passed through a temp. region set to a specific condition. CONSTITUTION:Steel containing, on a wt. basis, 0.05-0.35C, 0.01-1.0Si, 0.15- 2.0Mn, 0.005-0.1Al, 0.05-1.0Mo, 0.025 or less P and 0.020 or less S is prepared. In this case, one or more of 0.05-1.0Cr, 0.005-0.1Nb, 0.005-0.05Ti, 0.0002- 0.0020B, 0.0005-0.01Ca and 0.001-0.02REM are further contained in the aforementioned components. This steel is heated to an austenite temp. region and the heated steel is cooled at a cooling speed of 2 deg.C/sec or more in a temp. range of 800-500 deg.C to suppress the precipitation of pro-eutectoid ferrite. Succeedingly, this steel is passed through a temp. range of 500-300 deg.C so as to take a time of 60-1,800sec to obtain objective low alloyed high tensile steel excellent in sulfide stress corrosion cracking resistance.