Modified Mechanical Surface Treatment for Optimized Fatigue Performance of Martensitic Stainless Steel AISI 420

Abstract

Mechanical surface treatments, deep rolling or shot peening can enhance the fatigue performance of metallic materials because near-surface compressive residual stresses and work hardening states can inhibit or retard crack initiation and propagation. Thus, the stability of compressive residual stresses and work hardening states during fatigue is very important. However, generated compressive residual stresses and work hardening layers can be relaxed because of dislocation movements, rearrangements and annihilations. The strain ageing concept is one of the ways to pin or obstruct dislocations by solute atoms (called the Cottrell cloud) as a consequence of high stability of near-surface residual stresses and work hardening states. In this research, the conventional deep rolling and its modifications, high temperature deep rolling and deep rolling followed by appropriate annealing were performed on martensitic stainless steel AISI 420. Fatigue tests were performed using a rotary bending fatigue machine to evaluate fatigue performance as well as the strain ageing effects. It was found that the conventional deep rolling could enhance the fatigue performance through generated compressive residual stresses and work hardening layers at the surface, and near-surface regions. The modified deep rolled (high temperature deep rolling and deep rolling followed by annealing) conditions exhibited a greater fatigue lifetime and performance than those of the conventional deep rolling, although some residual stress and work hardening relaxations were observed after the modified deep rolling processes.