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저합금 고장력강 용접열영향부의 S . R . 귀열 발생 기구에 관한 연구
이종섭,김태웅,장래웅,엄기원 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.3
This study was carried out to investigate the mechanism of S. R. cracking in HAZ of high strength low alloy steel. Among 3 commercial high strength steels, steel A (HT80), which is equivalent to ASTM A514 Gr.F. was most susceptible to S. R cracking whereas steel C(HT60) showed no crack in oblique Y-groove test even in high restraint. The cause of S. R cracking along the coarsened austenite grain boundary was secondary hardening phenomenon and impurity segregation to the prior austenite grain boundary. The crack susceptibility was reduced as increasing heat input due to the weakening of secondary hardening.
김기철,윤의박,허보녕,엄기원,고광필,남태운 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.2
The microstructure and the fracture toughness of the weld-heat-affected zone of a ductile cast iron haute been investigated with a thermal cycle simulator to simulate the actual welding process. The matrix structure of the heat-affected zone transformed to martensite, mixture of martensite and pearlite, pearlite, and pearlite including small amount of ferrite, in turn, wish increasing cooling time from 800℃ to 500℃. The use of a proper preheat temperature prevented the formation of martensite. The welding condition for this involved a preheat temperature of 200℃ and a heat input of 30 KJ/㎝. Also, a post-weld-heat treatment of 675℃ for 2 hours was effective in reducing the hardness of ductile cast iron weldments by eliminating mariensite. The secondary graphite formed due to martensite decomposition at that title. An instrumented Charpy impact test has been carried out on a welded and post-weld-heat-treated ductile cast irons, respectively. Results showed that the dynamic fracture toughness increased slightly with higher preheat temperature and heat input. The post-weld-heat treatment improved the dynamic fracture toughness of the weldments to three times that of the as-welded condition.