Effect of microstructure and inclusions on hydrogen induced cracking susceptibility and hydrogen trapping efficiency of X120 pipeline steel

The susceptibility to hydrogen induced cracking (HIC) was evaluated for X120 steels containing different amounts of Mn and Al in a H2S environment. The hydrogen trapping efficiency was investigated by measuring the permeability (J∞L) and the apparent diffusivity (Dapp). The results demonstrated that larger amount of the inclusions, and larger area and volume fraction of the inclusions make steels more susceptible to HIC. The steel with a microstructure consisting of granular bainite and M/A (martensite/austenite) microconstituents is more susceptible to HIC. The ability of the microstructure and the inclusions to trap hydrogen was explained in terms of the apparent diffusivity (Dapp), permeability (J∞L), and solubility of hydrogen in steels (capp). The lower the values of Dapp and J∞L and the higher the value of capp are, the more the hydrogen trapping occurs in the steel, and the more the steel is susceptible to HIC.