Direct correlation between surface integrity and fatigue limit of surface cold worked chromium-nickel austenitic stainless steels

Abstract

Abstract Direct correlations were established between basic surface integrity (SI) characteristics (roughness, microhardness, residual stresses) obtained as a result of surface cold working (SCW) and bending fatigue limit of chromium-nickel austenitic stainless steels (CNASS). The results of experimental tests and optimization of the SCW process, implemented via hardening diamond burnishing (DB), are presented. When the requirement for the corresponding component is a high fatigue limit, the information obtained will help the researcher to find the inverse correlation between SI and finishing so that when the SCW process is implementing by another method, the same high fatigue limit can be achieved. Five roughness parameters that are functionally significant indicators of fatigue behavior, microhardness, and surface residual axial and hoop stresses form the vector of objective functions. The governing factors are the burnishing force and the number of passes. The fatigue limit was obtained by the accelerated Locati’s method. The models of the corresponding SI characteristics and the fatigue limit were obtained by a planned experiment and regression analyses. Direct correlations between SI characteristics and the fatigue limit were obtained by eliminating the variables in the corresponding pairs of models. The change trends of the microhardness and fatigue limit were found to be identical, i.e., the fatigue limit of CNASS can be controlled via inexpensively measured SI characteristics such as roughness parameters and surface microhardness. In other words, any static coldworking process can be optimized without carrying out fatigue tests by choosing these SI characteristics as objective functions and seeking a compromise optimal solution that simultaneously achieves high values of the microhardness and skewness and a low value of the roughness parameter Ra. Given the direct correlation between the microhardness and the fatigue limit, the compromise optimal solution maximizes the fatigue limit while satisfying the particular roughness requirements. The multi-objective optimization performed and comparisons made prove the effectiveness of the proposed approach.