高温ボルト材の所定応力低下後再負荷リラクセーションにおける温度依存性

概要

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In order to clarify the effect of retightening on stress relaxation behavior of high temperature bolts used in steam turbines, a series of studies on the retightening (reloading) stress relaxation were conducted previously. Examinations were made, in the present paper, for the effect of test temperature on reloading stress relaxation behavior when stress was relaxed to a specific value of residual stress for 1Cr-0.5 Mo-0.25V, 12Cr-1Mo-1W-0.25V and 19Cr-9Ni-1.4Mo-1.4W-Nb bolting steels. The relation between the testing time (t_j) and the number of loading (N) at each test temperature (T ; 4〜5 levels) was analyzed numerically for the case when the initial stress (σ_0) was relaxed to a specific value of residual stress (σ_<rj>=0.6σ_0), and an empirical equation was obtained to represent these data at various test temperature conditions. This equation was combined with our previously proposed equation^<2)3)> which concerns the data with various specific relaxed stress ratios {σ_<Rj>=(σ_0-σ_<rj>)/σ_0; 5〜9 levels) at a constant test temperature. In order to describe the retightening stress relaxation behavior of high temperature bolts at various temperatures and specific relaxed stress ratios. the following constitutive equation is proposed: t_j = KN^a σ_<Rj>^<b_0+b_1logσ_<Rj>exp((c_0+c_1logN)/T) where K, a, b_0, b_1, c_0, and c_1 are constants.
社団法人日本材料学会の論文
1983-07-15