Influence of the microstructure on the residual stresses of nitrided iron–chromium alloys

Different iron–chromium alloys (4, 8, 13 and 20 wt.%Cr) were nitrided in a NH3/H2 gas mixture at 580 °C for various times. The nitrided microstructure was characterized by X-ray diffraction, light microscopy and hardness measurements. Composition depth profiles of the nitrided zone were determined by electron-probe microanalysis. Residual stress–depth profiles of the nitrided specimens were measured using the (X-ray) diffraction sin2 ψ method in combination with cumulative sublayer removals and correction for corresponding stress relaxations. Unusual, nonmonotonous changes of stress with depth could be related to the microstructure of the nitrided zone. A model description of the evolution of the residual stress as function of depth and nitriding time was given.