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 simulated service condition of turbine blades, i.e. combined stresses of static tension and alternating bending at elevated temperature of 450°C. The frequency of alternating bending stress was 780 cpm and the test period was 0.2 to 200 hrs. 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 a1ways increases creep strain. In the range of small stress ratio (alternating bending stress divided by static stress) alternating bending stress clogs the increases in creep strain. 3. The hindrance of increase in creep strain by the alternating bending stress is interpreted by the hardening effect of material by stress alternation. 4. An analysis was made which led to the estimation of dynamic creep strain under combined alternating bending stress and static tensile stress by using static tensile creep data.