The threshold stress intensity of stress corrosion cracking (SCC) in the NaCl solution, K_(ISCC), has been measured for five low alloy steels. The effects of yield strength, alloy elements, microstructure and grain size on K_(ISCC) were studied. The results showed that K_(ISCC) decreased exponentially with increasing yield strength, #sigma#_(ys), i.e., K_(ISCC) = 1.38 centre dot 10~6 exp(-8.26 centre dot 10~(-3) #sigma#_(ys)) for 40CrMoV steel and K_(ISCC) = 1.42 centre dot 10~6 exp(-4.66 centre dot 10~(-3) #sigma#_(ys)) for 30CrMnSiNi steel. For low-alloy high-strength steels with #sigma#_(ys) = 1400 MPa, the effect of alloy elements, microstructure and grain diameter larger than 7 #mu#m on K_(ISCC) was little. The threshold stress intensity of hydrogen-induced cracking during dynamical charging for 4OCrMoTi steel decreased linearly with the logarithm of the concentration of diffusible hydrogen, C_0, i.e., K_(IH) = 31.3-9.1 lnC_0. This equation was also applicable to SCC of a high-strength steel in aqueous solution, and in this case, Ct is constant. The critical hydrogen enrichment concentration, C_(th), necessary for SCC of high-strength steel in water decreased exponentially with the increase in yield strength. It was possible to deduce the relationship between K_(ISCC) and #sigma#_(ys) i.e., K_(ISCC) = Ak_1exp(-k_2#sigma#_(ys)), where A = 3RT (#pi##rho#)~(2/1)/2(1 + v)V-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.
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