Microstructure and crystallography of 20MnCr5 steel tempered at different conditions

The microstructure and crystallography of 20MnCr5 steel tempered at 180 A degrees C for 2 h were examined by electron back scattered diffraction (EBSD) in a field-emission scanning electron microscope. The crystallographic features of martensite in a prior austenite grain area were studied by pole figures (PFs). Compared to the theoretical PFs calculated with Kurdjumow-Sachs (K-S) and Nishiyama-Wassermann (N-W) orientation relationships (ORs), it is shown that both of the ORs exist in the investigated specimens. Misorientations distribution and the result of transmission electron microscope analysis indicating that [011]/54.7A degrees lath boundary existed in the microstructure also prove the coexistence of K-S and N-W ORs. When the steels were further tempered at 350 A degrees C/20 min or 500 A degrees C/20 min, the length of boundaries in equal areas decreased and the crystallographic features still fulfill the coexistence of K-S and N-W ORs.