• Journal of Welding and Joining
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• 제28권3호
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• pp.65-72
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• 2010

Some structural members of large-scale marine vessels such as large-scale offshore structures and very large container ships are assembled by very thick plates of which thickness exceeds 60mm. Also, high-tensile steels have been selected to meet the required structural strength and fatigue strength. Generally, multi-pass welding method such as FCA(Flux-Core Arc) welding has been used to join the thick plates. Considering the welding residual stresses, fatigue strength of the welded joints of thick plates should be assured since the residual stress influences the fatigue strength. This paper presents a numerical procedure to investigate the residual stress of structure joined by multi-pass FCA welding so that it can be incorporated into the fatigue strength assessment considering the effect of welding residual stress. The residual stress distribution is also measured by X-Ray diffraction method. The residual stress obtained by the computational model also has been compared with that of experiment. The results of FEA are in very good agreement with the experimental measurements.

• 대한금속재료학회지
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• 제48권11호
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• pp.1021-1027
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• 2010

The charpy impact property was lower at the surface and middle regions than that at the root region in metal welded by Tandem EGW of 82 mm thick EH40-TM steel plates. Temperature distribution in the weld sample and the heating/cooling temperature throughout the various regions in the weld metal were estimated by the commercial weld simulation program SYSWELD. The microstructure of the weld metal consisted of acicular ferrite and grain boundary ferrite. Grain boundary ferrite in the acicular ferrite matrix was found more in the surface and middle regions than in the root region, and the acicular ferrite was also coarser in the surface and middle regions where the impact toughness was lower and the input temperature was higher. Our results indicated that the impact toughness property was related to the microstructure morphology, the distribution of grain boundary ferrite, and the acicular ferrite.

• Journal of Welding and Joining
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• 제33권5호
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• pp.35-40
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• 2015

Characterization of microstructures and mechanical properties of 83mm thickness EH36-TM welds produced by the combined flux cored arc (FCA) and electro gas (EG) welding processes has been studied with the two different groove conditions, single-V (SV) and double-V (DV) bevels. The welding consumables used for FCA and EG welding processes were ASME/AWS A5.29 (E81T1-K2) and A5.26 (EG72T), respectively. Experimental results showed that all the mechanical properties of welds such as tensile property, CVN toughness and Vickers hardness met IACS requirements. The tensile strength of EG welded plates were reduced by approximately 4% (DV: 3.8%, SV: 4.2%) compared to the base metal. The hardness value of SV-beveled weld metal was slightly lower than that of DV-beveled one. There were no significant differences as per welding groove conditions except for the weld metal. In addition, at the fusion line, the toughness of SV condition was 20J lower and the weld metal was 40J lower than DV condition, respectively. On the basis of microstructural analysis, grain boundary ferrite (GBF) structures for SV condition were 2 times higher volume fraction than for DV condition and their packet sizes were coarsened to almost double. It was thus suggested that the GBF volume fractions and packet sizes in the weld metal of EH36-TM steel plates are the most important factors affecting the mechanical properties of the combined FCA and EG welded joint. Nevertheless, all the results of welds with both DV and SV conditions were found to be excellent.