Fatigue and Dynamic Creep Properties of 13 Cr Steel at Elevated Temperature under Combined Stresses of Static Tension and Alternating Bending

Abstract

The fatigue and dynamic creep tests were made under the simulated service condition of turbine blades, i.e. combined stresses of static tension and alternating bending at an elevated temperature of 450°C. The frequency of alternating bending stress was 780 c.p.m. and the test period was 0.2 to 200 hours. The results are summarized as follows : 1. Alternating bending stress superimposed on static tensile stress reduces the fatigue life. 2. Alternating bending stress which is combined with static tensile stress does not always increases creep strain. In the range of small stress ratio (alternating bending stress divided by static stress) alternating bending stress blocks the increase in creep strain. 3. The hindrance of increase in creep strain by alternating bending stress is explained by the hardening effect of materials by stress alternation.