RISS 검색 - 국내학술지논문 상세보기

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다국어 초록 (Multilingual Abstract)

In this study, the influence of heat input and post-seam annealing (PSA) temperature on themicrostructure and impact toughness of electric resistance welded (ERWed) API X70 steel pipe wasinvestigated. The ERW seam welds of pipes were fabricated with low, moderate, and high heat inputs, andfollowed by the PSA process at 950 oC. Regardless of heat input, the API X70 steel pipe exhibited goodweldability, resulting in similar microstructure factors, i.e., metal flow angle (~70o), bondline width (~22μm), and ferrite grain size (~4.4 μm). Although (Mn, Si)-rich oxide penetrators which are known to impairimpact toughness were observed at the bondline, the area fraction was estimated to be as low as 0.011%in all the ERW seam welds. The impact toughness was not affected by these penetrators because of theirminimal fraction, leading to ductile fracture at -20 oC. However, different PSA temperatures (870, 950, and1040 oC) resulted in the different grain sizes of the seam welds. The ERW seam weld annealed at 1040oC (PSA1040) exhibited the largest ferrite grain size near the bondline, whilst the smallest grain size wasfound in the ERW weld annealed at 870 oC (PSA870). In spite of having the smallest grain size, PSA870exhibited the lowest impact toughness value, showing brittle fracture at –20 oC. It was observed that thedifference in residual stresses was not macroscopically detectable by the hole drilling method. The kernelaverage misorientation (KAM) maps indicated that the highest level of residual stress was observed nearthe bondline of PSA870, as evidenced by a high density of dislocations. This study provides instructiveresults, indicating that the impact toughness of ERW seam welds are significantly more affected by residualstresses than by the grain refinement effect.