Study Of 20 Steel Deformation Induced Ferrite Anti SSCC Alternative Saturated H ₂ S Solution

20steel which is commonly used in industry is considered as the research object, and hydrogen-induced cracking (HIC) and slow strain rate testing (SSRT) are used for evaluating the stress corrosion cracking (SCC) susceptibility of20steel in test solution (10-3mol/L Na2S2O3+5%NaCl+0.5%acetic acid solution) substituting for saturated hydrogen sulfide solution. The stress corrosion resistance of20steel in the condition of different strain rates(1×10-6s-1、1.45×10-6s-1、2×10-6s-1、5×10-6s-1) is also analyzed, and the highest sensitive strain rate is obtained. In addition, deformation induced ferrite transformation(DIFT) occurs in continuous cooling conditions through different deformation heat treatment of20steel specimen, and microstructure of deformation induced ferrite is obtained, after that, the microstructure and the mechanical properties are researched. Besides, the stress corrosion susceptibility of the specimen of deformation induced ferrite is researched in the test solution and the condition of most sensitive strain rate through SSRT and modern microscopic analysis method. The results are as follows:(1) Deformation induced ferrite transformation is obtained in continuous cooling conditions through different deformation heat treatment of20steel specimen, and the grain of which has a greater degree of refinement. The grain size of specimen after tempering treatment increases slightly comparing with untempered, but has a greater degree of refinement compared to the original state of the specimen.(2) The hardness value of20steel in normalizing state is approximately HRC13(Rockwell hardness standard C13), and it increases after by thermomechanical treatment and subsequent tempering treatment, but less than HRC22, which is the criterion of HIC and SSCC, while NACE (National Association of Corrosion Engineers) Association had been formulated that the value was HRC22for HIC and SSCC.(3) The strength and plasticity of20steel have been improved to some extent after thermomechanical treatment under continuous cooling conditions; then after the tempering heat treatment, the strength decreases but toughness improves to some extent comparing with untempered.(4)10"3mol/L Na2S2O3+5%NaCl+0.5%acetic acid solution substituting for saturated hydrogen sulfide solution is possible and feasible to evaluate the sulfide stress corrosion cracking (SSCC) susceptibility.(5) The sensitivity coefficient of20steel in the test solution is higher than35%, showing a high stress corrosion sensitivity while the strain rate is10-6s-1magnitude. And20steel performs a highest stress corrosion sensitivity while the strain rate is2×10-6s-1(6) The stress corrosion sensitivity of specimen decreases after by thermomechanical treatment or thermomechanical treatment and subsequent tempering heat treatment, but at the same time the stress corrosion susceptibility coefficient is higher than35%. Therefore, the formation of deformation induced ferrite slightly increases the stress corrosion resistance of the specimen after thermomechanical treatment and tempering under continuous cooling conditions, but it also performes a high stress corrosion sensitivity, that is, deformation induced ferrite also performes a high stress corrosion sensitivity.