Effect of frequency and biofuel E85 on very high cycle fatigue behaviour of the high strength steel X90CrMoV18

• In all cases fatigue failure was initiated at primary chromium carbides.
• The fatigue tests in air exhibit a multiple-step S–N curve.
• The frequency effect in air was small.
• Even at 109 cycles no fatigue limit for internal carbide failure was observed.
• Fatigue strength in biofuel is significantly reduced.

In this contribution very high cycle fatigue properties of the martensitic stainless 18% chromium steel X90CrMoV18 (DIN 1.4112, AISI Type 440B) in air and biofuel with 85% ethanol are presented. They were gained on notched specimens which were loaded at a stress ratio of R = 0.1 under differing load frequencies. In all cases, fatigue failure occurred at primary chromium carbides. In addition to conventional fatigue testing, ultrasonic fatigue tests were carried out. It is shown that any frequency effect in air was very small. Although long-term exposure tests in biofuel without mechanical load showed no visible corrosion marks, fatigue strength in biofuel was significantly reduced.