| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1991: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1990: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
In multi-pass weldments of austenitic metallic materials, microcracking is frequently observed. In this study, to clarify mechanism of microcracking occurring in austenitic stainless steel multilayer weldments, relation between microcracking and welding conditions were investigated. And also effect of relation between misorientation and structure of grain boundary in 1st layer of weldments on micro-cracking was studied.
Microcracking occur along grain boundaries in the region of 1st layer which locate vicinity of 2nd layer of the welds. As microstructure of weldment is fully austenitic, cracking is very enhanced, and lower welding speed of 2nd layer increase microcracking tendency in 1st layer of weldments.
Judging from the observations of fracture surface of microcrack by SEM, cracking occur due to liquation and ductility-dip of grain boundaries.
In general, pronounced microcracking tendency in 1st layer of weldments due to following run is observed at grain boundary having large misorientation. It seemthat more segregation of impurity elements, such as S and P, occur at grain boundary having large misorientation cause microcracking. Nevertheless, the segregation at grain boundary observed by CMA and EPMA methods could not be found. It may be concluded that segregational grain boundary could not detect by reason of its narrow width.
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