The comparison of stress corrosion cracking behaviors of four types of commercial austenitic stainless steel in high temperature water was studied.
Tests were made at the temperature of 300° and 350°C for 300 hr in an autoclave containing the testing water with 100∼800 ppm of chloride ion added as NaCl.
The amount of dissolved oxygen in water was controlled with or without deaeration at the temperatures of 105° and 150°C, respectively.
The results were summarized as follows:
(1) Neither of the steels showed no stress corrosion cracking provided that the concentration of dissolved oxygen in the testing water did not exceed 0.2 ppm, but cracking was observed on all the types of stainless steel in the water with a concentration of dissolved oxygen higher than 0.3 ppm.
(2) Among the solution treated steels, the type SUS 32 was most resistant, and the susceptibility of other types were almost the same.
(3) Sensitizing heat treatment markedly increased the susceptibility of cracking for all the types of steels.
(4) The cracking was transgranular in the solution treated steels independently of the difference in composition, but the intergranular cracking was also observed in the sensitized type SUS 27 and 32 steels.
(5) From the observation on the pitting corrosion formed on the test pieces and also from the metallographic inspection of pits and cracks, it appears that pitting is the cause of initiation of cracking.
(6) The results of cracking tests in a boiling 42%MgCl
2 aqueous solution did not agree with those in high temperature water in regard to the process of initiation or path of cracking, and also the difference in susceptibility of cracking for the four types of steel was noticed between the two testing methods.
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