Effect of Cold Work on the Susceptibility of F. C. C. Alloys to Stress-Corrosion Cracking

Abstract

A study was made of the effect of cold work on the stress-corrosion cracking susceptibility of some commercial F. C. C. alloys, i.e. two different heats of Type 301 steel, one heat of Type 310 steel, and one heat of 70/30 brass. The specimens, prepared from annealed and cold worked sheets, were stressed by cantilever method and exposed to boiling 35% aqueous MgCl₂ solution (in the case of stainless steel) or to 0.94M aqueous ammonia solution containing small amounts of Na₂CrO₄ and NaCl (in the case of brass). The susceptibility was determined by recording the time to failure in the test solutions.
The effect of cold work on the stress-corrosion cracking must be explained on the basis of the physical and metallurgical changes produced by cold working, such as work-hardening, heterogeneous distribution of tensile stress, and martensitic transformation. It is therefore different according to the stress level applied. It can be said that, when the cold worked specimen is loaded at the stress around its yield strength, the susceptibility depends on its deformability. This fact suggests that the stress-corrosion cracking process involves a brittle fracture step. If the stress applied is far below the yield strength of the specimen in question, the susceptibility would be determined by a competitive action between strengthening of material and heterogenizing of stress distribution. Whether the phase formed by martensitic transformation hinders stresscorrosion cracking or not depends both on the stress level applied and on the degree of prior cold working. In general quasi-martensite lowers the susceptibility to stress-corrosion cracking. Potential measurements under tensile stress were also made.