1999 年 39 巻 4 号 p. 380-387
A new relation among the time to creep rupture, the stress and the temperature has been developed. Assuming the velocity of dislocations is controlled by a thermally activated process, the time to rupture, tr is expressed as
logtr=2.3RTQ-Vσ -C
where Q, V, σ, R, T, C are respectively the activation energy, the activation volume, the applied stress, the gas constant, the absolute temperature and the Larson-Miller constant, i.e. about 20. The new equation reads that the applied stress in a linear scale is a linear function of the Larson-Miller parameter, P=T(log tr+C).
The new relation has been applied to the long term rupture data of several heat resisting steels obtained by National Research Institute for Metals. According to the equation the rupture data for each material can be classified into 2-4 groups where the deformation mechanism differs with each other. It has been found that for each group the data are excellently fitted to the equation.
A set of the data from several hours to longer than 100000 h are roughly well fitted to another expression of a hyperbolic tangent type. The expression is the approximate equation of the above theoretical expression.
