Stress corrosion cracking of high‐strength steels

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, σ ys , i.e., K ISCC = 1.38 · 10 6 exp(‐8.26 · 10 ‐3 σ ys ) for 40CrMoV steel and K ISCC = 1.42 · 10 6 exp(‐4.66 · 10 ‐3 σ ys ) for 30CrMnSiNi steel. For low‐alloy high‐strength steels with σ ys = 1400 MPa, the effect of alloy elements, microstructure and grain diameter larger than 7 μm on K ISCC was little. The threshold stress intensity of hydrogen‐induced cracking during dynamical charging for 40CrMoTi steel decreased linearly with the logarithm of the concentration of diffusible hydrogen, C 0 , i.e., K IH = 31.3‐9.1ln C 0 . This equation was also applicable to SCC of a high‐strength steel in aqueous solution, and in this case, C 0 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 σ ys , i.e., K ISCC = Ak 1 exp(‐ k 2 σ ys ), where A = 3R T √πρ /2(1 + ν)V ¯H , k 1 and k 2 are constants, which depend upon the compositions and microstructure of the steel as well as the test conditions.