Characterization of γ′-Fe4N precipitates in a compound layer formed by austenitic nitrocarburizing treatment

The precipitation of γ′-Fe4N phase from the ε-matrix in a quenched and aged compound layer of 0.2%C steel formed by austenitic nitrocarburizing treatment has been investigated through transmission electron microscopy. The orientation relationship between the γ′ phase and the ε matrix is determined to be “0001”ε // “111”γ′ and 〈12̄10〉ε // 〈011〉γ′. The γ′ precipitates appearing in thin plates in the “0001” planes of ε matrix are sometimes observed to be 180 ° related to each other. The mechanism of age-hardening in the compound layer is also discussed.