Effect of different compound layer and base material microstructures on microstrain and domain size of nitrided steel

Abstract

The inhomogenous microstrains in thermochemically treated materials can be described by calculating average crystallite size (dolnain size) limited by lattice defects and the root mean squared lattice strains in the domain using XRD analysis. When nitriding under different process parameters, specimens were removed from the experiment after different nitriding times in order to investigate the domain sizes and the mean squared lattice strains in the compound layer as a function of nitriding time. Studies of depth profiles from the compound layer were of special interest. The nitriding potential K_N, a characteristic value for the composition of the nitriding atmosphere and the formation of nitride phases, was varied from 0·5 to 0·7 at temperatures of 540 and 575°C in order to form γ nitride. Because of the low penetration depth in ferritic materials, Cu K_α radiation was used to obtain information close to the surface layers only. To obtain depth profiles of the examined specimens, thin material layers were removed in increments of 0.5, 1, or 2 μm by a sputtering process and the line profiles of the exposed surfaces were measured. Specimens were evaluated according to the methods of Warren and Averbach. Microstrain and domain size results show characteristic distributions with higher micros train values at the surface and at the compound layer/diffusion zone interface. These results can be correlated to the nitrogen and carbon contents in the compound layer. The dependence of microstructural properties on the various nitriding parameters is not significant.