Effect of cold deformation before heat treatment on the hydrogen embrittlement sensitivity of high-strength steel for marine risers

Herein, the effects of cold deformation before heat treatment on the hydrogen diffusion and hydrogen embrittlement sensitivity of low-alloy high-strength steel for marine risers were investigated. The influence of cold deformation on hydrogen diffusion and hydrogen embrittlement was elucidated by electrochemical hydrogen permeation test and slow strain rate tension test. A tempered martensitic structure was gradually refined by increasing the cold deformation amount. This phenomenon increased the density of hydrogen traps in the steel sample, decreasing the hydrogen effective diffusion coefficient and prolonging the hydrogen penetration time. Due to the high deformation, the hydrogen embrittlement sensitivity index of the tempered martensite decreased significantly and the brittle fracture characteristics of slow strain rate tensile fracture were insignificant. The ability of the microstructure to resist hydrogen embrittlement failure was effectively enhanced. In addition, the refinement of the martensitic structure increased the number and homogeneity of hydrogen traps in the tested steel, thereby enhancing the hydrogen solubility of the microstructure. The hydrogen content at the hydrogen traps could not attain to the critical value, inhibiting the initiation and propagation of hydrogen embrittlement cracks.