HIGH-STRENGTH THICK-WALLED ELECTRIC-RESISTANCE-WELDED STEEL PIPE HAVING EXCELLENT LOW-TEMPERATURE TOUGHNESS AND METHOD FOR MANUFACTURING SAME

摘要

has a yield strength of 400 above, and an object thereof is to provide both the low-temperature toughness and HIC resistance excellent high-strength steel pipe huyuk jeonbong. In mass%, C: 0.025 ~ 0.084%, Si: 0.10 ~ 0.30%, Mn: containing 0.70 ~ 1.80%, and P, S, adjusting the Al, N, O content and, further Nb: 0.001 ~ 0.065% , V: 0.001 ~ 0.065%, Ti: 0.001 ~ 0.033%, Ca: after the containing 0.0001 ~ 0.0035%, and further Pcm is held by a steel material satisfying the below 0.20, heated to a temperature range of 1200 ~ 1280 , the non-recrystallized temperature subjected to hot rolling to a reduction ratio in reverse more than 20% and, after the end of hot rolling, 7 ~ 49 cooling stop temperature at a cooling rate of the / s: cooled to below 630 , more than 400 a hot-rolled rolled at less than 600 pulpit, and that is a hot-rolled steel strip with jeonbong pipe and roll forming, jeonbong welding, and add to the jeonbong steel pipe welds, the total thickness heated to within the range of 800 ~ 1150 , then 7 to a heat treatment is carried out to cool to below 630 at an average cooling rate of 49 / s. Thus, the base metal and weld all jeonbong, the toughness and HIC resistance are both excellent high-strength steel pipe huyuk jeonbong. ;