X-ray Residual Stress Analysis of Nitrided Low Alloyed Steels

Abstract

Abstract Residual stress analyses were performed on nitrided, low alloy steels by varying the measuring conditions. The measurements were carried out in the compound layer on ∊-Fe2–3N and γ′-Fe4N as well as in the diffusion layer on α-Fe. By considering different criteria, tensile residual stresses of up to 300 MPa produced, {111}-interference, for ∊-Fe2–3N using CuKα radiation on the specimen's surface. After removing 5 μm from the surface, compressive residual stresses occur in this phase. On employing the CrKα and CuKα radiation, relatively high compressive stresses are obtained of up to above −1000 MPa for γ′-Fe4N. For measurements using CrKα radiation, compressive residual stresses result in the diffusion layer for α-Fe, which have a maximum value below the surface. Here, the measurements of the {211}-interference give lower residual stress magnitudes than measurements of the {110}- and {200}-interferences. By verifying the phase superpositions, the linear distributions of line positions or the comparable loading stress analysis using XRD or strain gauges, the results determined at the {211}-interference appear to be realistic. Attention should be paid to the high penetration depth of CrKα radiation. Here, no gradients of the investigated stress states may exist which are too large. The steel possessing a higher content of nitride forming elements such as Al, for example, mainly exhibit the highest compressive residual stresses. In the diffusion layer of 34CrAlNi7-10, maximum compressive residual stresses of −800 MPa result at {211}-interference in α-Fe.