Abstract
In metastable austenitic stainless steel such as Type 304 steel, strain induced martensite appears by cold working at lower temperatures than Md point. In this paper, the effect of preplastic strain and strain induced martensite by cold working on the sensitivity of stress corrosion cracking (SCC) in 42 percent Magnesium-Chloride solution (143°C) was studied. The summary of the results obtained are as follows.
In the case of material without cold working, the crack growth rate, da/dt was approximately proportional to the square of stress intensity factor, K. The SCC fracture surface was almost transgranular fracture characterized“Fan-shaped pattern”constituted with {100} plane.
In material free from strain induced martensite cold worked at a temperature near Md point, this tendency in da/dt vs. K curve was almost similar to the one without cold working, but remarkable intergranular fracture was recognized on the SCC fracture surface.
In the case of material cold worked at lower temperatures than Md point, the resistance to SCC propagation increased remarkably, but the dispersion of data broadened and the regularity of correlation between da/dt vs. K decreased as compared with the one free from martensite or cold working. This may be caused by the keying effect of martensite to SCC propagation. And in the SCC fracture surface, a peculiar“Plate-let pattern”constituted with martensite lath was recognized.
