Cr-Mo-V鋼の疲労寿命に及ぼすクリープ損傷の影響

概要

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The effect of creep damage on low-cycle fatigue life at high temperatures has been studied with the object of making clear the mechanism of interaction between creep and fatigue of Cr-Mo-V turbine rotor steel. Prior creep tests for introducing the damage were carried out under two conditions suitable to case transgranular and intergranular creep fractures; at 500℃ and 32 kgf/mm^2, and at 575℃ and 18kgf/mm^2, respectively. In addition to the prior creep test, isothermal aging tests were conducted at 500 and 575℃. Both the prior creep at 500℃ and 32 kgf/mm^2 and the isothermal aging considerably increased the fatigue life. This increase was explained by the reduction in stress range at half strain cycles to fatigue failure, which is cased mainly by softening during creep or aging. On the other hand, the prolonged prior creep at 575℃ and 18 kgf/mm^2 produced the extensive growth of grain boundary cavities in addition to the softening, and decreased the fatigue life remarkably. Metallographic observation showed that this growth of grain boundary cavities changed the fatigue fracture mode from transgranular fracture with striations to intergranular fracture with grain boundary cracks. It is suggested that grain boundary cavities reduce the fatigue life by their acceleration effects on initiation and propagation of fatigue cracks.
社団法人日本材料学会の論文
1985-04-15