Abstract
The results of a study on the combined nitrocarburising and laser beam hardening of 50Cr V4 steel are presented. A normalising or hardening and tempering pretreatment was applied before nitrocarburising for 4 or 8 h at 843 K. Surface and cross-sectional microstructure, layer morphology, concentration-depth profiles for carbon, nitrogen, and oxygen, and hardness-depth profiles are presented. A ttempts to correlate laser beam power, traverse speed, and degree of defocusing with the microstructures and hardness profiles obtained are described and the microstructural transformations occurring during laser treatment are discussed. Optimum hardening was obtained when the compound zone has either just or almost been transformed completely, when any porosity present has yet to coagulate to fornz larger cavities, when fine martensite coupled with retained austenite exists near to the surface, when fine, lathlike martensite is found in the diffusion layer, and when nitrogen and carbon are found at levels below those of the compound layer but higher than those of the diffusion layer, across a region wider than the original compound layer. Recommendations for transferring this combined hardening treatment to industrial practice are given.
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