Formation of iron hydride in α-Fe under dislocation strain field and its effect on dislocation interaction

Atomistic simulation of hydride formation under dislocation strain field piled up at inclusions in α-Fe was performed using a new Finnis–Sinclair-type embedded atom method potential. Two 1/2 [1 1 1] (101¯) edge dislocations were introduced in BCC α-Fe to study the effects of dislocation interaction on the formation of hydride. Our simulation demonstrated that the interaction of dislocation-inclusion could produce ultrahigh stress that resulted in the formation of iron hydride. In addition, the dissociation of one of the two 1/2 [1 1 1] edge dislocations into [0 0 1] + 1/2 [111¯] two perfect dislocations can occur under a large applied shear (5%) or smaller shear (0.5%) when a hydride plate forms, despite the dissociation not satisfying the energy condition of dislocation reaction. The [0 0 1] perfect dislocation is usually considered the origin of cleavage on {1 0 0} planes, which is not stable without large applied load or hydrogen. In our model, the densities of both dislocation and inclusion on the glide plane could be changed to correspond to the dislocation density and inclusion (carbide) density in real martensitic steels. The results indicated that low dislocation density and small size of inclusions could prevent the formation of hydride. From these findings, tempering was suggested as a measure of preventing hydrogen embrittlement because proper tempering can effectively reduce the residual stress caused by quenching, precipitate dispersive and fine carbides (inclusion) and, in addition, decrease dislocation density in quenching and tempering martensitic steels.