Influence of hydrogen pressure and the concentration of hydrogen on the variations of the mechanical characteristics of pipe steel of K52 strength class

We present the results of quantitative evaluation of the resistance to hydrogen embrittlement of a domestic K52 low-alloy pipe steel with dispersed ferrite–bainite structure. As a result of tensile tests carried out at a low strain rate (slow strain-rate tests (SSRT)) in hydrogen-containing media with the use of smooth cylindrical samples (in a high-pressure chamber), we determine the coefficients of hydrogen embrittlement for the relative elongation and contraction (δ and ψ). Plasticity indices exhibit a trend to decrease as the concentration of hydrogen in the gas mixture increases (from 15 up to 100%) under a total pressure of 10 MPa but the relative lowering of the values of properties does not exceed 6%. The variations of the ductility of steel in terms of the relative contraction, which differs from the level of statistical error, were recorded in an atmosphere of pure gaseous hydrogen as the pressure increased up to 14 MPa and their level remained as high as 10%. The coefficient of hydrogen embrittlement of the studied steel obeys the regularity established in analyzing the literature data accumulated for pipe steels (of K52 strength level). The results of investigations enable us to conclude that K52 steel with dispersed ferrite-bainite structure is characterized by a high resistance to hydrogen embrittlement in pure hydrogen under a pressure of up to 14 MPa.