Effect of cold work on hydrogen attack

A silicon killed 1020 steel was deformed to a maximum of 15 pct elongation in three point bending and exposed to hydrogen at 6.5 MPa and 450 °C for 44 to 220 h to develop hydrogen attack. In the undeformed material methane nucleated primarily on manganese sulphides and maganese silicate inclusions. With time fissures form along the entire length of the inclusions creating large fissures (>500 microns). Cold working the steel greatly enhanced the rate of fissure formation on the grain boundaries as well as the fraction of boundaries attacked. These fissures interconnect, venting methane to the surface. As a result of this venting the fissures in the deformed area swell much less and the material decarburizes at a more rapid rate than the undeformed. The degree of decarburization was independent the sign of the plastic strain. However, the direction of the fissures changed, being parallel to the free surface on the tensile side and perpendicular to the surface on the compressive side. The effect of cold work on HA was completely eliminated by an anneal at 650 °C for 1 h.