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Journal article

Crystallographic analysis of martensite in 0.2C-2.0Mn-1.5Si-0.6Cr steel by EBSD

The crystallography of martensite formed in 0.2C-2.0Mn-1.5Si-0.6Cr steel was studied using the EBSD technique. The results showed that the observed orientation relationship was closer to the Nishiyama- Wassermann (N-W) than to the Kurdjumov-Sachs (K-S) orientation relationship (OR). The microstructure of martensite consisted of parallel laths forming morphological packet-like structures. Typically, there were three different lath orientations in a morphological packet consisting of three specific N-W OR variants sharing the same {111} austenite plane. A packet of martensite laths with common {111} austenite plane was termed as a crystallographic packet. Generally, the crystallographic packet size corresponded to the morphological packet size, but occasionally the morphological packet was found to consist of two or more crystallographic packets. Therefore, the crystallographic packet size appeared to be finer than the morphological packet size. The relative orientation between the variants in crystallographic packets was found to be near 60°/<110>. This appears to explain the strong peak observed near 60° in the grain boundary misorientation distribution. Martensite also contained a high fraction of boundaries with their misorientation in the range 2.5-8°. Typically these boundaries were found to be located inside the martensite laths forming lath-like sub-grains, whose long axes were parallel with the long axis of the martensite laths.

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