Microstructural Characterization of Martensite Formed in High-carbon Steel Based on Rodrigues-Frank Space

抄録

In order to characterize martensite microstructure in more detail, the orientation analysis based on Rodrigues-Frank (R-F) space was applied for the composite microstructure consisting of different types of martensite, retained austenite, and undissolved carbide in Cr-containing high-carbon steels. Martensite variants was separated more clearly in the R-F space, and consequently individual martensite blocks characterized by identical variant could be identified accurately in the real space. As a result, fine lath martensite and coarse plate martensite was separated by the critical block length, which is defined with a crystallinity evaluated by electron backscatter diffractometry. Furthermore, in addition to butterfly shaped plate blocks formed within an austenite grain (Type-I) and single block growing along austenite grain boundaries (Type-II), twin blocks pair growing from austenite grain boundaries to inside the grain (Type-III) could be observed as characteristic plate martensite formed in high-carbon steels. The orientation relationship of twin blocks with respect to prior austenite was changed simultaneously from near Nishiyama-Wasserman to Kurdjumov-Sachs in the growth stage. These characteristics of twin pair of Type-III is expected to be effective to reduce the increase of both strain and interfacial energies during martensitic transformation.