Improvement of Fatigue Resistance and Fracture Toughness of Thermally Aged Duplex Stainless Steel by Laser Shock Peening

摘要

Duplex stainless steels (DSSs) offer high strength compared to common austenitic stainless steels; however, when this steel type is exposed to high temperature, the precipitation of sigma phase due to its fast formation kinetics may affect significantly the mechanical properties of the alloy. In this research, the feasibility of using laser shock peening (LSP) to reduce the negative effects of sigma phase precipitation on the mechanical properties of samples with thermal aging is studied. The LSP treatment was performed using a Nd:YAG pulsed laser operating at 10?Hz. The LSP setup was the waterjet arrangement without sample coating. The tensile, yield strength, fatigue crack growth, fracture toughness and hardness of samples aged at 750?°C for different holding times were determined. In order to assess the effect of LSP on fatigue crack growth and fracture behavior, another set of thermally aged compact tension specimens with pre-crack was LSP-treated on both faces and then fatigue loading was applied. Experimental results demonstrate that, while thermal aging accelerates fatigue crack growth of DSS samples, LSP significantly reduces the effect of thermal aging, by reducing the fatigue crack growth rate and increasing the fracture toughness of DSS aged samples.