Evaluation of susceptibility of AISI 304 to stress-corrosion cracking in terms of crack nucleation and crack propagation

Abstract

This thesis presents the work performed to evaluate the susceptibility of AISI 304 to stress-corrosion cracking in terms of time to crack nucleation and rate of crack propagation. U-bend specimens were exposed to magnesium chloride solutions boiling at atmospheric pressure for some predetermined time. The concentrations of magnesium chloride employed were 40, 42, and 44 per cent by weight. After exposure, specimens were microscopically examined and crack depths were measured and recorded.

It was found that a straight-line relationship existed between maximum crack depth and exposure time which may be expressed by the empirical equation Log t = D/M+ Log C. The constants M and C are characteristic of the conditions of exposure and increase with a decrease in chloride ion concentration. The rate of crack propagation was found to be inversely proportional to time.

Microscopic examination revealed that cracking was both transgranular and intergranular. There are indications that intergranular cracking was more pronounced at the low concentrations of the chloride ion.

The results obtained justify the continuation of the work to determine factors affecting susceptibility in terms of constants M and C.