1991 Volume 40 Issue 457 Pages 1290-1296
In order to examine the effect of compressive creep on crack propagation behavior, creep-fatigue tests were carried out at 823K and 1073K in air under stress waveforms with tensile and compressive holds (cc-type) and with tensile one (cp-type) using notched specimens of Type 304 stainless steel. Tests of smooth specimen were also conducted for the further discussion on fracture morphology. The results obtained are summarized as follows:
(1) There is little difference in the crack propagation rate at 923K between the cc- and cp-type tests, and the rate is correlated well with the creep J-integral range regardless of the compressive creep.
(2) At 1073K, the cp-type test shows much faster crack propagation rate than the cc-type test for the same value of creep J-integral range.
(3) While there are few small cracks inside the specimen near the macro-crack tested in the cc- and the cp-types at 923K and in the cc-type at 1073K, multiple small cracks are found along grain boundaries in the vicinity of the macro-crack in the cp-type at 1073K. The examination of smooth specimen tested reveals that small inner cracks are found only in the cp-type test at 1073K, which corresponds with the fracture morphology in the crack propagation tests.
(4) The small cracks weaken the resistance of material to the macro-crack propagation in the cp-type test at 1073K, and thus brings about the faster propagation rate.
