Mechanism of Chloride Stress Corrosion Cracking of Austenitic Stainless Steels

Abstract

Electrochemical studies were made in aqueous LiCl, MgCl2, and MgBr2 solutions and in ZnCl2/KCl molten salt to clarify the corrosion reactions related to stress corrosion cracking (SCC) of austenitic stainless steel and to better define environmental variables critical to the occurrence of chloride SCC. Type 304 stainless steel electrodes were employed, with complementary SCC tests made with U-bend Type 304 stainless steel specimens. Several conclusions critical to an understanding of the mechanism of chloride SCC resulted from these investigations: (1) SCC was observed in concentrated MgBr2 solutions, (2) H2O must be present in the electrolyte, as SCC did not occur in dry molten ZnCl2/KCl, and (3) H2 evolution from corroding specimens may be facilitated by anodic polarization. Present studies do not support a model equating crack propagation with stress assisted anodic dissolution. Rather, evidence is presented that hydrogen evolution at the crack tip occurs and is a critical precursor to crack initiation and propagation. A model of SCC requiring hydrogen evolution at the crack tip is proposed, with emphasis being placed on the effect of anodic reactions within the crack in maintaining high acidity near the crack tip. Recent publications suggest that the role of evolved hydrogen in SCC may be related to formation of hydrogen induced martensitic platelets along paths of crack propagation.

Contribution to the knowledge of the relationship between the electrochemical and corrosion behaviour and the structure of metallic materials subjected to cold plastic deformation

“…In contrast, the conditions in which the deformation is applied with a constant rate of increase up t o the fracture of the test-piece simultaneously with the performance of the electrochemical measurements++++) (conditions under which the dislocations multiply and move during the measurements until they appear on the anode surface, with a consequent continuous increase in the state of defectiveness of the surface) are radically different, Nevertheless, it seems t o us that, taken as a whole, the results oi our electrochemical measurements and microstructural investigations can support those authors who advocate a reconsideration of the role of hydrogen evolution in stress corrosion cracking even in the case of some austenitic stainless steels (18).…”

Stress corrosion cracking for 316 stainless steel clips in a condensate stabilizer

“…The stress corrosion cracking behavior of stainless steels in chloride and other corrosive solutions has been comprehensively investigated using various methods [1][2][3][4][5][6][7]. Stress corrosion cracking is caused by either stress corrosion cracking in the narrow sense such as active path dissolution [1,2] and film rupture [3,4], or hydrogen embrittlement [5][6][7].…”

On the SCC behaviour of austenitic stainless steels in boiling saturated magnesium chloride solution

“…Stress corrosion cracking in the broad sense for austenitic stainless steels is caused by either stress corrosion cracking in the narrow sense (denoted as SCC hereafter) such as active path dissolution [1][2] and film-rupture [3][4], or hydrogen embrittlement (HE) [5][6][7]. Austenitic stainless steels such as type 304 and 316 steels, but not type 310 steel, may undergo phase transformation from γ→α' martensite due to applied stress or hydrogen charging [8][9] and α'-martensite is considered to be directly related to brittle fracture [10].…”

“…The stress corrosion cracking behaviour of austenitic stainless steels in chloride and other corrosive solutions has been extensively investigated using various methods [1][2][3][4][5][6][7]. Stress corrosion cracking in the broad sense for austenitic stainless steels is caused by either stress corrosion cracking in the narrow sense (denoted as SCC hereafter) such as active path dissolution [1][2] and film-rupture [3][4], or hydrogen embrittlement (HE) [5][6][7].…”