Stress corrosion cracking of high-strength steels

The threshold stress intensity of stress corrosion cracking (SCC) in the Na Cl solution, K-ISCC, has been measured for five low alloy steels. The effec ts of yield strength, alloy elements, microstructure arid grain size on K-I SCC were studied. The results showed that K-ISCC decreased exponentially wi th increasing yield strength, sigma (ys), i.e., K-ISCC = 1.38 . 10(6)exp(-8 .26 . 10(-3)sigma (ys)) for 40CrMoV steel and K-ISCC = 1.42 . 10(6)exp(-4.6 6 . 10(-3)sigma (ys)) for 30CrMnSiNi steel. For low-alloy high-strength ste els with sigma (ys) = 1400 MPa, the effect of alloy elements, microstructur e and grain diameter larger than 7 mum on K-ISCC was little. The threshold stress intensity of hydrogen-induced cracking during dynamical charging for 40CrMoTl steel decreased linearly with the logarithm of the concentration of diffusible hydrogen, C-o, i.e., K-IH = 31.3-9.1lnC(o). This equation was also applicable to SCC of a high-strength steel in aqueous solution, and i n this case, C-o is constant. The critical hydrogen enrichment concentratio n, C-th, necessary for SCC of high-strength steel in water decreased expone ntially with the increase in yield strength. It was possible to deduce the relationship between K-ISCC and sigma (ys), i.e., K-ISCC = Ak(l)exp(-k(2)si gma (ys)), where A = 3RT root pi rho /2(1 + v) (v) over bar (H), k(1) and k (2) are constants, which depend upon the compositions and microstructure of the steel as well as the test conditions.