1988 年 37 巻 423 号 p. 1442-1448
By using 0.1%, 0.3% and 0.6% carbon steels, the effect of microstructure on the formation of hydrogen-induced microcracks and the relation between the formation of microcracks and the acoustic emission (AE) caused by hydrogen charging have been studied.
The results obtained are as follows:
(1) Many microcracks were generated in ferrite grains in carbon steels with spheroidized structure, and at pearlite-ferrite interfaces and/or in pearlite in carbon steels with ferrite-pearlite structure. (2) The formation of microcracks was more remarkable in carbon steels with ferrite-pearlite structure than those with spheroidized structure. (3) The formation of microcracks could be detected as the signals of AE, and the total count of AE was proportional to the number of microcracks. (4) The addition of external stress to the specimen had no influence on the nucleation site of the microcracks nor on the number of microcracks generated by hydrogen charging. Therefore, the generation of microcracks is mainly governed by the internal stress due to dissolved and precipitated hydrogen atoms. (5) The addition of pre-strain to the specimen enhanced the formation of microcracks. (6) The microcracks are assumed to be formed by the following processes; (i) the appearance of large internal stress by hydrogen trapped at the interface, (ii) the generation of dislocations from the interface and the formation of dislocation walls, (iii) the nucleation of cracks along the dislocation walls by the large internal stress due to hydrogen trapped there.