EBSP analysis of modified 9Cr-1Mo martensitic steel

In order to clarify the structure change of 9Cr-1Mo tempered martensitic steel during the high temperature creep, the structures deformed were observed by SEM-OIM and TEM method. It was found that initial block and packet structures were equi-axed. These structures were very stable during creep, but just before rupture changed to elongate grain. From an analysis of the grain boundary, ∑ 3(rotation angle 70.5°), near ∑11(rotation angle 50.5°) and small angle(rotation angle 10°) boundaries existed in the martensite. This result agrees with the result predicted with K-S orientation relationship. It was also found that the density of ∑3 boundary or near ∑11 boundary decreased during high temperature creep. But, it was found that the density of ∑3 boundary decreased, and that of near ∑11 and small angle boundaries increased during the high temperature deformation. In initial structure, relative frequency of 〈110〉 common axis(Block boundary) is largest to compare with other axes. But, just before the rupture, relative frequency of 〈110〉(Block boundary) suddenly decreased and 〈123〉 and 〈233〉(not Block or Packet boundaries) increased.