低合金鋼の再加熱割れ感受性に及ぼす希土類元素の添加効果

Abstract

The purpose of this work is to reveal beneficial effects of rare earth metals (REM) additions on reheat cracking susceptibilities of lCr-0.5Mo and HT80 weldments. Reheat cracking susceptibilities of 1Cr-0.5 Mo steel containing 0 to 0.37 wt% REM and HT80 steel containing 0 to 0.1 wt% REM have been examined at 600°C by a hot tensile test and a small-sized y-slit crack test. Hot ductilities at 600°C of these steels were improved approximately from 10 to 80% with an increase of REM content. Moreover, any reheat cracking did not occur in lCr-0.5Mo steel weldment by adding 0.02 to 0.13 wt% REM. On the other hand, both steels containing more than 0.1 wt% REM were susceptible to liquation cracking. Therefore, the reasonable range of REM content for preventing reheat cracking was approximately from 0.02 to 0.05 wt% in lCr-0.5Mo steel. The reason why REM improved reheat cracking sucseptibilities of these steels was reducing of grain boundary segregation of impurity elements such as P, S etc. on account of scavenging effect of REM.