種々の環境下におけるSUS304鋼の応力腐食割れの力学的分類

Abstract

Stress corrosion cracking (SCC) of austenitic stainless steels does not necessarily show the same characteristics in different environments, although it has been generally attributed to so-called active path corrosion (APC). This means that the mechanism of APC is varied to some extent depending on environments, materials, etc.In this paper, for a comprehensive treatment of the SCC mechanism of austenitic stainless steels, the possibility of a systematic arrangement of various SCC characteristics was studied. As the result, the characteristics of SCC were divided into the following classes according to their stress dependency; A group (SCC in a narrow sense), transition, B group (corrosion cracking-like). The typical environment of A group is 42%MgCl2 solution (416 K). In this case, the initiation of SCC depended on yield phenomena of materials, and the SCC growth rate da⁄dt on the stress intensity factor K. In transition, the environment was represented by 20%NaCl+1%Na2Cr2O7·2H2O solution (376 K). At the initiation stage of SCC, pitting corrosion preceded SCC. It is rather difficult to put da⁄dt in order by K, because the accuracy of K was lowered with increasing secondary cracks. In B group the environment was represented by 25 kmol/m3 H2SO4+0.5 kmol/m3 NaCl solution (R.T.). The initiation of SCC did not depend on yield phenomena of materials. It is almost impossible to arrange SCC propagation processes by K because of the appearance of SCC in the form of hair cracks.