Role of microstructure in susceptibility to hydrogen embrittlement of X70 microalloyed steel

The effect of phases and steel processing on hydrogen uptake (diffusible and residual), surface and internal damage were evaluated using optical and scanning electron microscopy. The results have shown the fastest formation of blisters in ferrite-pearlite microstructure of strip, followed by equaixed ferrite-pearlite microstructure in normalised condition, then by ferrite-bainite microstructure. No blistering was observed in heat affected zone samples for up to 24 hrs charging. Analysis of hydrogen-induced cracking using electron back scattering diffraction has revealed that crack propagation has predominantly intragranular character without a clear preference on {001}, {110}, {112} and {123} planes and is independent of the steel microstructure and prior processing.