Presentation EVALUATIONION OF HOT CRACK SUSCEPTIBILITY IN MULTI-PASS WELDS OF REDUCED ACTIVATION FERRITIC/MARTENSITIC STEEL F82H USING LONGITUDINAL VARESTRAINT TEST

Kiyoku, R.  ,  Fujiwara, M.  ,  加藤, 太一朗  ,  廣瀬, 貴規  ,  谷川, 博康  ,  Mori, H.

2017-11-06
Description
To develop the blanket modules set on the inner wall of fusion reactors, it’s necessary to establish the welding methods and conditions for each joint shapes and plates’ thickness. As welding for thicker plates of reduced activation ferritic/martensitic steel F82H, multi-pass welding will be adopted to the joints. In such a case, hot cracking is concerned in welds reheated by following weld passes. Therefore, to make sure these crack susceptibilities, the longitudinal Varestraint test with double-bead and triple-bead types were adopted to evaluate the ductility-dip crack susceptibility in weld metal during multi-pass welding. In these test, the first bead had been reheated by following weld passes and the predetermined strain was loaded to test coupons at the instance of arc turned out. After the test, number of cracks and total crack length were measured, to make the hot cracking susceptibility clear quantitatively.Figure 1 shows a surface appearance of reheated weld beads in coupons after the Varestraitnt test. Small cracks were observed in weld metal reheated by following weld passes. Their sizes were less than about 0.2mm. These cracks mainly propagated at columnar grain boundaries in weld metal detached from the fusion line. That is, these cracks were perceived as ductility-dip cracks, due to their morphologies and observed area. Total crack length measured in reheated weld metal are demonstrated in Fig. 2. The crack susceptibility was raised with the number of reheating, as compared with Fig. 2 (a) and (b). Such a tendency was remarkable in the weld metal of the steel with higher Ta content. In addition, compared between F82H steel and 9Cr-1Mo steel, the crack susceptibility in BA07 (0.04%Ta) is almost same as that in 9Cr-1Mo steel. In contrast, when Ta content in F82H is higher such as T12 (0.12%Ta), the crack susceptibility become higher than that of the Cr-Mo steel. Therefore, when multi-pass welding is conducted for the F82H steels with high Ta contents, it should be considered to control welding conditions for prevention of hot cracking in weld metal as well as high strength martensitic steels.
18th International Conference on Fusion Reactor Materials

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