Effect of grain size on the hydrogen embrittlement sensitivity of a precipitation strengthened Fe-Ni based alloy

The hydrogen embrittlement (HE) sensitivity of a precipitation strengthened Fe-Ni based alloy with various grain sizes was investigated by hot hydrogen charging experiment and tensile test. The results showed that HE sensitivity was reduced with decreasing grain size, even though the hydrogen concentration in the small-grained specimen was higher than the large-grained specimen. Fractographic features showed that intergranular fracture was less pronounced with decreasing grain size, which was related to the transport of hydrogen to the grain boundary by moving dislocations. During deformation, the number of dislocations expected in the slip bands was proportional to the grain size, leading to that a lower hydrogen concentration being accumulated at the grain boundary in the small-grained specimen.