The effect of high-pressure torsion (HPT) on hydrogen trapping in Fe-0.01 mass% C and type 310S stainless steel was studied by metallographic characterization and hydrogen measurement after hydrogen gas charging. Hardening of both materials after processing by HPT was achieved through grain refinement. Hydrogen trapping in the Fe-0.01 mass% C was significantly increased by HPT processing, because of high binding energies of hydrogen with lattice defects such as dislocations and grain boundaries in body-centred cubic iron. In the type 310S processed by HPT, the hydrogen content that trapped by dislocations was less than that dissolved within the lattice and the contribution of grain boundaries on hydrogen trapping can be neglected. In the stable austenitic stainless steel processed by HPT, decreasing the dislocation density can reduce the trapped hydrogen to the solution-treated level while the hardening by grain refinement is retained.
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