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탄소강 모재의 기계적 특성과 미세조직에 미치는 용접후열처리 온도의 영향
강용준(Yongjoon Kang),오창영(Chang-Young Oh),이승건(Seung-Gun Lee),이상훈(Sanghoon Lee),강성식(Sung-Sik Kang) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.6
The effect of post-weld heat treatment (PWHT) on the mechanical properties and microstructure of carbon steel base metal was investigated. MDF A 105, 106-B, 216-WCB, 516-415, and 516-485 carbon steels were employed, and the steels were each subjected to heat treatment with holding temperatures of 610, 650, 690, and 730 ℃ for 8 hours for the simulation of PWHT. The tensile strength and impact toughness of the steels showed a tendency to decrease with increasing holding temperature; this behavior was mainly attributed to the spheroidization of cementite in pearlite and the precipitation of cementite at grain boundaries.
원자로 압력용기용 저합금강 용접 열영향부의 기계적 특성과 미세조직에 미치는 용접후열처리 온도의 영향
강용준(Yongjoon Kang),박소영(So-Young Park),오창영(Chang-Young Oh),이승건(Seung-Gun Lee),강성식(Sung-Sik Kang) 대한용접·접합학회 2020 대한용접·접합학회지 Vol.38 No.1
The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of P-No. 3 low-alloy steel was investigated by taking into account the changes in microstructure. SA-508 Gr. 3 Cl. 1 forged steel was employed, and the specimens taken from the steel were thermally cycled using a Gleeble simulator to simulate coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), intercritical HAZ (ICHAZ), and subcritical HAZ (SCHAZ). The respective base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730℃ for 8 hours. Before the heat treatment, the ICHAZ, FGHAZ and CGHAZ exhibited high hardness and poor impact toughness. However, when the PWHT was applied, the hardness decreased and the impact toughness improved; the impact toughness was highly dependent on the PWHT temperature. The impact toughness of the ICHAZ and FGHAZ increased significantly when the PWHT temperature was 650℃ or below, while that of CGHAZ improved significantly when the PWHT temperature was 650℃ or higher. The microstructural changes due to the PWHT were observed by scanning electron microscopy and correlated with the mechanical properties.r composed of iron-based composition system had similar characteristics to the material to be repaired.
1 GPa 급 고강도강 다층 용접금속의 저온 충격인성에 미치는 미세조직의 영향
강용준(Yongjoon Kang),이창희(Changhee Lee) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.3
A 1 GPa class weld metal was prepared by multi-pass welding using a prototype flux-cored wire, and the correlation between microstructure and low-temperature impact toughness of the weld metal was investigated. The microstructure of the as-deposited columnar region and the equiaxed region reheated by subsequent welding passes was observed, and it was found that low-temperature transformation products such as bainite and martensite mainly developed in both regions. Since the prior austenite grains were coarse in the columnar region, the effective grain size of the final microstructure could be large; in this case, it was confirmed that the low-temperature impact toughness of the weld metal was very low. However, in the weld metal used in this study, acicular ferrite was formed inside the grains of the columnar region; the effective grain size and grain boundary misorientation distribution of the final microstructure were similar to those of the equiaxed region, and a good low-temperature impact toughness of the weld metal was obtained.
고강도강 다층 용접금속 재가열부의 미세조직 및 기계적 특성
강용준(Yongjoon Kang),박기태(Gitae Park),정성훈(Seonghoon Jeong),이창희(Changhee Lee) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.6
A large fraction of reheated weld metal is formed during multi-pass welding, which significantly affects the reliability and stability of the welded structures. In this study, the effect of reheating on the mechanical properties and microstructure of high-strength steel welds during multi-pass welding was investigated. Two kinds of high-strength steel welds with different hardenabilities, i.e., welds L (low hardenability) and H (high hardenability), were produced by single-pass, bead-in-groove welding, and both welds were thermally cycled to various peak temperatures to simulate the reheated welds using a Gleeble simulator. In as-welded weld L, acicular ferrite developed extensively in the grain interior, while grain boundary ferrite and Widmanstätten ferrite formed along the prior austenite grain boundaries. The microstructure of as-welded weld H consisted mainly of bainite, with some acicular ferrite and coalesced bainite. The microstructural changes due to thermal cycling were observed by scanning electron microscopy and correlated with the mechanical properties.