Production of seamless steel pipe for 80kg/mm2 class structure having excellent toughness of weld zone

TLDR: In this paper, a seamless steel pipe for 80kg/mm is produced by hot rolling a steel contg. class structure having excellent toughness in weld zone by hot-rolling steel specific ratios of C, Si, Mn, Cr, Mo, Cu, Al, N, B, and subjecting the steel to cooling, heating, hardening and tempering under specific conditions.

Abstract: PURPOSE:To produce a seamless steel pipe for 80kg/mm. class structure having excellent toughness in weld zone by hot-rolling steel contg. specific ratios of C, Si, Mn, Cr, Mo, Cu, Al, N, B, and subjecting the steel to cooling, heating, hardening and tempering under specific conditions. CONSTITUTION:Steel contg. 0.07-0.16 % c, 0.1-1.0% Si, 0.5-1.5% Mn, <=0.30% Cr, 0.1-0.7% Mo, <=0.30% Cu, 0.07-0.11% Al, 0.0020-0.0040% N, and 0.0005- 0.0020% B, and consisting of the balance Fe with unavoidable impurities is formed by hot rolling. After the hot rolled plate is cooled down to temp. lower than the Ar 1, the same is heated and hardened at 1-30 deg.C/sec. heating rate at 850-1,000 deg.C, and is then tempered to temp. lower than Ac 1 point. If necessary, 0.2-1.5% Ni can be contained and the P contained as unavoidable impurities is preferably kept at <=0.020% and S at <=0.010%.