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- 주제어 : preheat/interpass temperature (검색결과 3 건)
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해양플랜트용 YP 690 MPa급강 다층 용접부의 재열 균열 특성 평가
신용택,조영주 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.8
This study evaluated the relationship between reheat cracking that occurs in the reheated weld zone formed by subsequent multi-pass welding and the preheat/interpass temperature. The multi-pass weldment was YP 690 MPa high-strength steel, which is used in mobile offshore platform units. The welding process was flux-cored arc welding (FCAW), which coupons were constrained by welding to simulate an actual constraint condition. Three preheat/interpass temperature ranges were employed. The characteristics of the weldment subjected to preheat/interpass temperatures higher than 80°C satisfied the relevant specifications. In the bending testing, a weldment subjected to a preheat/interpass temperature range of 50-60 °C was fractured. The results demonstrated reheat cracking in the reheated weld zone in multi-pass weldments. Reheating cracking (RHC) was initiated at carbides precipitated along the grain boundaries, induced by multipass heating; some cracks were arrested in the reheated zone and the others propagated to the columnar weld metal. The hardness of the cracked specimens was higher than that of the specimen subjected to a higher preheat/interpass temperature, confirming that a susceptible microstructure had formed due to the faster cooling rates. In the analysis of weld residual stress, the specimen with the lower preheating/interpass temperature range showed higher tensile residual stress than that of high preheating/interpass temperature range. Therefore RHC in the reheated zone of the weldment was mainly affected by grain boundary carbides, a higher hardness, and residual stresses. Based on the above discussion, the mechanism of RHC and assessment of structural integrity is presented.
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다층용접한 저합금 용접금속의 강도와 인성에 미치는 입열량 및 예열/패스간 온도의 영향
방국수(Kook-soo Bang),정호신(Ho-shin Jung),박찬(Chan Park) 한국해양공학회 2015 韓國海洋工學會誌 Vol.29 No.6
The effects of the heat input and preheat/interpass temperatures on the tensile strength and impact toughness of multipass welded weld metal were investigated and interpreted in terms of the recovery of the alloying elements and microstructure. Increases in both the heat input and preheat/interpass temperatures decreased the tensile strength of the weld metal. A lower recovery of alloying elements, especially Mn and Si, and smaller area fraction of acicular ferrite in the weld metal were observed in higher heat input welding, resulting in a lower tensile strength. In contrast, only a microstructure difference was observed at a higher preheat/interpass temperature. The impact toughness of the weld metal gradually increased with an increase in the heat input because of the lower tensile strength. However, it decreased again when the heat input was larger than 45 kJ/cm because of the much smaller area fraction of acicular ferrite. No effect of the preheat/interpass temperature on the impact toughness was observed. The formation of a weld metal heat-affect zone showed little effect on the impact toughness of the weld metal in this experiment.
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SM570 QT강 다층용접부에서 저온 균열방비를 위한 예열온도에 대한 연구
고진현,김건형 한국기술교육대학교 2006 論文集 Vol.13 No.1
A preheat temperature to prevent the cold cracking of SM570 QT structural steel weldments made by depositing multiple weld passes in the V-groove with FCAW was evaluated. The diffusible hydrogen content in the deposited weld metals increased linearly with increasing the hydrogen content in the shielding gas. It was confirmed that the cold cracking occurred in the weld specimens with preheat temperature at 50℃ and shielding gas of Ar+20%CO_(2) regardless of hydrogen content. On the other hand, the cracking did not occur in the wledments made with preheat and interpass temperatures at 75℃ and 100℃. Based on this study, it is suggested that the minimum preheat temperature to avoid the cold cracking for SM570 QT steel weld metal is 75℃.
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