片条状富N奥氏体组织及形成机理

he microstructure of composite diffusion layer of the nitrided and chromized low-carbon steel (steel 20) was investigated using TEM. It was found that laths of Austenite with high N (γN) precipitated from α- Ferrite in the deep diffusion layer. These γN lath always grew to form twins along an orientation, and the characteristic of γN lath is two crystallines back to back. The first, γN laths were ture twins{111}, and γN and α kept the accurate K-S relationship, and each γN and α formed sharp and smooth interface of {335}γN//{341}α, habit plane{335}. The second, γN laths were pseudo-twins{111}, and there were micro-twins {111} appeared in each γN. Localized lattice deformation (relaxation) seemed to have occurred at the interfaces of the second type of γN due to the formation of micro-twins within the twin components, which made the orientation relationship (OR) between each of the γN and the α-matrix deviated from the accurate K-S OR, and the OR between two γN twin components deviated from the genuine {111} twin relationship. In addition, the γN /α interface of the second type of γN was not as sharp and smooth as that of the first one.