Effect of Temper-bead Thermal Cycle on Toughness of Weld ICCGHAZ of Low Alloy Steel SQV-2A

抄録

In order to examine HAZ properties of SQV-2A steel welded by the temper-bead technique, the effect of temper-bead thermal cycle on the toughness has been investigated for the simulated ICCGHAZ (intercritically reheated coarse-grained HAZ). The simulated ICCGHAZ specimen was produced by applying double thermal cycle consisting of first thermal cycle with a peak temperature of 1623 K and subsequent second thermal cycle with various peak temperatures T_p2 involving A_c1 and A_c3 temperatures. At T_p2 from 973 to 1003 K, serious embrittlement of the ICCGHAZ occurred which could be attributed to the formation of coarse necklace-like M-A constituent along the prior austenite grain boundary region and fine elongated M-A constituent within the prior austenite grain. When the cooling rate of the second thermal cycle was slow, serious embrittlement was also observed at T_p2 from 1073 to 1100 K, and this could be attributed to the formation of upper bainite in the reaustenitized area during the second thermal cycle. The temper-bead (third) thermal cycle with a peak temperature of 673 K could improve significantly the toughness of ICCGHAZ embrittled at T_p2 from 973 to 1003 K. However, the temper-bead thermal cycle was not effective in improving the toughness of the ICCGHAZ embrittled at T_p2 from 1073 to 1100 K in case of slow cooling rate.