1%Cr-1%Mo-0.25%V鋼の切欠クリープ破断強度について
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概要
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To establish the influence of heat treatments and notch sharpness of specimens upon the notched-bar creep rupture strength of a Cr-Mo-V steel for steam turbine rotor forgings, creep rupture tests were conducted with variously heat treated at 950℃ for 20hr (Sample A), heating at 1 000℃ for 20hr (Sample B), and heating at 1 000℃ for 20hr, followed by cooling to 950℃ and holding at the temperature for 1hr (Sample C). All the specimens were tempered at 675℃ for 24hr. Two kinds of notch sharpness were used, one had a notch with elastic stress concentration factor k_t of 6.5 and another of 2.5. The creep rupture tests were conducted with these specimens for about 4 000 hr at 550℃. The results obtained were as follows. (1) The sample B showed the highest plain bar creep rupture strength of these three samples, the sample C was second to the sample B, and the sample A was the poorest. (2) Both the sample A and sample C were notch strengthened within the range of this investigation. However the sample B austenitized at 1 000℃ was notch weakened at about 1 300 hr for k_t of 2.5 and about 500hr k_t of 6.5. (3) The plain bar creep rupture properties of the sample C were similar to those obtained with the sample B, while for the notched bar specimen the sample C showed a similar behavior to the sample A. From these results it was found that austenitizing at 1 000℃ was effective for the plain bar creep rupture strength, and cooling form 950℃ was effective for the notched bar creep rupture strength. (4) The rupture time ratios of notched bar specimens for k_t of 2.5 were higher than those for k_t of 6.5 in all the three sample. (5) From the results of observation of cracks at the notch root, it was found that in specimens for k_t of 6.5 cracks were formed in comparatively earlier stage of test, i.e., within 30% of rupture life, while in the specimens for k_t of 2.5 no crack could be observed within 90% of rupture life. Consequently, it was supposed that in the specimens for k_t of 6.5 almost all of rupture lives were consumed by the propagation of cracks, while rupture lives of the specimens for k_t of 2.5 were decided by initiation of cracks.
- 社団法人日本材料学会の論文
- 1965-02-15
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