The Effect of Atmosphere on the Frequency Effect in the High Temperature Fatigue of a Carbon Steel

The atmospheric effect on the frequency effect was studied in the high temperature fatigue of a carbon steel by using dried town gas as an inert environment. At 550°C, the fatigue strength was higher in gas than in air in the long life test under low stress levels owing to the reduction of corrosion fatigue effects by high temperature oxidation. At 400°C, the effect of gas was hardly found on fatigue strengths. Considerations were made on the frequency effect in stress τ-rupture time t curves and in plastic strain amplitude γp-cycles to rupture N curves. The relation of γpN=K was obtained under various cyclic frequencies and various temperatures, covering a wide range of N. The value of K was larger for lower frequency than for higher frequency, the effect of frequency increasing at higher temperature. The deviation was found after long time in the air, due to corrosion fatigue by high temperature oxidation.