Fatigue strength assessment of duplex and super-duplex stainless steels by 4R method

Duplex and super-duplex stainless steels are increasingly used in applications where good fatigue strength is demanded in addition to corrosion resistance. In this research work, the fatigue strength of duplex and super-duplex steels was investigated experimentally, using standard fatigue strength assessment methods, and theoretically, using conventional design methods and a novel effective notch stress-based procedure, the 4R method. The experimental tests included testing of welded joints with and without post-weld treatment. The experimental results were compared with the 4R method. The test results indicated good fatigue strength properties for both materials in the as-welded (ASW) condition, and post-weld treatment by high frequency impact (HFMI)-treatment improved the fatigue resistance at low stress ratios. No improvement, however, was found in the case of high mean stress of the applied load. The results obtained by the theoretical investigation agreed quite well with the experimental results.