Hydrogen embrittlement in multilayer steel consisting of martensitic and twinning-induced plasticity steels

The hydrogen embrittlement behavior of multilayer steel consisting of 7 alternating layers of martensitic (MART) steel and twinning-induced plasticity (TWIP) steel was investigated through variation in the ratio of the hard layer to the soft layer, and the size of the grains according to the autenization temperature. Multilayer steels with a high fraction of MART was predicted to be vulnerable to hydrogen embrittlement, but was found to be less susceptible to hydrogen embrittlement due to the presence of a TWIP layer, which is supported in the center of the multilayer steels. In addition, when the grain size is large, twinning in the TWIP layer and subdivision in the MART layer occur, and so hydrogen embrittlement is promoted due to the trapping of hydrogen. The effect of electrochemically-charged hydrogen on the multilayer steel during deformation was analyzed using electron backscatter diffraction in terms of the microstructure-mechanical property relationships.