The effect of nanosized (Ti,Mo)C precipitates on hydrogen embrittlement of tempered lath martensitic steel

Nanosized (Ti,Mo)C precipitates in a high-strength tempered lath martensitic steel are shown to increase resistance to hydrogen embrittlement. The hydrogen-induced failure mode transitions from failure along lath and prior austenite boundaries in the absence of the (Ti,Mo)C precipitates to a mixed failure mode of microvoid coalescence and lath boundary failure in their presence. In the absence of hydrogen and regardless of the presence or absence of the (Ti,Mo)C precipitates, failure occurs via ductile microvoid coalescence. By correlating the macroscale mechanical properties, the fractography of the resulting failure surfaces and observation of the evolved deformation structure immediately beneath the fracture surfaces, a hydrogen-enhanced and plasticity-mediated failure mechanism is proposed in which the role of the nanosized (Ti,Mo)C precipitates is to serve as effective traps for hydrogen.