13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- (a) Base metal (c) HAZ at 0.5mm from fusion boundary (b) HAZ at 1.5mm from fusion boundary Grain boundary map Grain boundary map Grain boundary map 100μm 100μm 100μm EBSP EBSP EBSP Figure 3. Creep test specimen for the dissimilar welds Figure 4. EBSP images and grain boundary mapping (15-48˚) for the base metal and HAZ of the high B-9Cr steel in the MARBN10 steel-Alloy 263 weld joint 3. Results and discussion 3.1. Microstructures of HAZ in the dissimilar welds Figure 4 shows the EBSP (electron backscattered pattern) images and grain boundary maps of the base metal and HAZ of the high B-9Cr steel in the dissimilar welds between MARBN10 steel and Alloy 263. In the grain boundary map, grain boundaries with misorientation from 15 ˚ to 48 ˚ were drawn and their length was measured. We have reported that the fine-grained structures were not formed in HAZ of weld joints for the 9Cr-3W-3Co-VNb steel with boron and low nitrogen [1, 2]. The base metal of the present steel shows the tempered martensitic structures having the grain boundary length of 2.07 cm and KAM of 1.83 (Fig. 4(a)). The micro Vickers hardness of the
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