Phase transformation and grain refinement in hydrogenated metastable austenitic steel

The effect of hydrogen on strain-induced gamma -> alpha' transformation in type 304 steel and on the microstructure of prestrained material was studied. Hydrogenation at 543 K under a pressure of 100 MPa prevents the formation of alpha'-phase during tensile straining. Such a treatment of pre-strained steel causes alpha' -> gamma transformation and grain refinement. Ab initio calculations for the alpha- and gamma-iron demonstrate that hydrogen decreases the equilibrium temperature of both phases. The reasons for the grain refinement and decrease in temperature of martensite reversion are discussed. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.