Effect of Pre-Modification by Water Jet Blasting Prior to Nitriding Vein-Like Precipitates in the Composite Diffusion Layer of M50NiL Steel

In this study, M50NiL steel was carburized (C), nitrided (N), and compound-carburized then nitrided (C + N). Vein-like grain boundaries (VLGBs) were observed in the diffusion layers of both the N and C + N states due to the limited opportunity for diffusion. Transmission electron microscopy (TEM) observation revealed that the VLGB organization differed in the N and C + N states. The VLGB organization consisted mainly of Fe4N in the N state and Fe3C and Fe4N in the C + N state. When the C state was pre-modified by a 200 MPa water jet and then nitrided (C + 200P + N), the increase in dislocation density resulted in a dislocation entanglement phenomenon that split the grains to form subcrystals. The increases in grain boundaries and dislocation density promoted the diffusion of atoms, and thus the VLGB structure was not observed in the diffusion layer of the C + 200P + N state.