A new orientation relationship between cementite and austenite and coexistence of pseudo-primary and secondary dislocations in the habit plane

Abstract

A new orientation relationship (OR) is found between Widmanstätten cementite precipitates and the austenite matrix in a 1.3C-14Mn steel. The associated habit plane (HP) and the dislocations in the HP have been investigated with transmission electron microscopy. The HP is parallel to in cementite, and it is parallel to in austenite. Three groups of interfacial dislocations are observed in the HP, with limited quantitative experimental data. The line directions, the spacing and the Burgers vectors of two sets of dislocations have been calculated based on a misfit analysis, which combines the CSL/DSC/O-lattice theories, row matching and good matching site (GMS) mappings. The calculated results are in reasonable agreement with the experimental results. The dislocations ‘Coarse 1’ and ‘Fine 1’ are in the same direction as the matching rows, i.e. . ‘Coarse 1’ dislocations are secondary dislocations with a Burgers vector of , and ‘Fine 1’ dislocations are pseudo-primary dislocations with a plausible Burgers vector of . The reason why the fraction of the new OR is much less than that of the dominant Pitsch OR has been discussed in terms of the degree of matching in the HPs.

Keywords:

• Cementite
• austenite
• orientation relationship
• habit plane
• dislocation

Acknowledgement

The authors wish to express thanks to Professor Zhang-zhi Shi and Mr. Zhi-peng Sun for their helpful suggestions and discussions.