High-Temperature, High-Cycle Fatigue Properties of Cr-Mo Alloy Steel Plates for Pressure Vessels

Abstract

In order to clarify high-temperature, high-cycle fatigue properties of Cr-Mo alloy steel plates used for pressure vessels, rotating bending fatigue tests were carried out on three kinds of steels, JIS SCMV 2 (1 Cr-0.5 Mo), SCMV 3 (1.25 Cr-0.5 Mo) and SCMV 4 (2.25 Cr-1 Mo), at room temperature, 400, 500 and 600°C with a frequency of 7500 cycles/min, and the fatigue strength at 10⁸ cycles was obtained.
The conclusions obtained were as follows:
(1) No specimen failed in the vicinity of 10⁸ cycles and the endurance limit was found at room temperature. The number of cycles to failure increased up to 10⁸ cycles with decreasing stress amplitude at elevated temperatures.
(2) For the steel of SCMV 2, the fatigue strength at 400°C was larger than that at room temperature, but it decreased with increasing test temperature above 400°C. For the steels of SCMV 3 and 4, the fatigue strength decreased with increasing temperature.
(3) For the steels of SCMV 2 and 3, the ratio of fatigue strength at 10⁸ cycles to 0.2% proof stress was larger than unity at 400 and 500°C.
(4) The coaxing effect was observed a little at room temperature but not at elevated temperatures.
(5) The above phenomena observed at elevated temperatures can be explained qualitatively by the strengthening mechanism due to chemical interactions between interstitial atoms (C or N) and substitutional atoms (Cr or Mo).