高温ボルト材の所定時間後再負荷リラクセーションに於ける温度依存性

抄録

In the previous studies a series of reloading stress relaxation tests⁸⁾¹⁰⁾ were conducted to clarify the effect of retightening on stress relaxation behavior of high temperature bolts used in steam turbines.
In the present paper, the effect of test temperature on reloading stress relaxation data with a specific reloading time interval was examined on several types of bolting steels; 1Cr-0.5Mo-0.25V, 12Cr-1Mo-1W-0.25V and 19Cr-9Ni-1.4Mo-1.4W-Nb steels. Discussions were made for the relation between the relaxed stress ratio {σ_Ri=(σ₀-σ_ri)/σ₀} and the number of loadings (N) at each temperature (T; 4∼5 levels), where σ₀ is the initial stress, σ_ri is the residual stress, and t_i is the specific reloading time, say 240h. Numerical analyses were made on the present data as well as on the previously obtained ones which concern the effect of time interval (t_i; 4 levels) on the reloading stress relaxation data at a constant test temperature.
These reloading stress relaxation data with various time interval and temperature conditions can be successfully incorporated into the following empirical equation.
σ_Ri=KN^at_i^{b₀+b₁logt_i}exp(c₀+c₁logN/T+c₂/T₂)
where k, a, b₀, b₁, c₀, c₁ and c₂ are constants.