Effects of Ni/Cu replacement on improvement of tensile and hydrogen-embrittlement properties in austenitic stainless steels

Effects of Ni/Cu replacement and subsequent aging treatment on tensile and hydrogen embrittlement (HE) properties were investigated in Fe-Cr-Ni austenitic stainless steels. With the Ni/Cu replacement, tensile strength and ductility were reduced in the as-annealed state by the increased stacking fault energy (SFE), whereas they were enhanced in the aged state due to the consumption of Cu in the matrix by the precipitation and resultantly lowed SFE. After the electrochemical H-charging, the H permeation depth decreased in the aged Cu-containing steels, indicating that Cu-rich precipitates effectively interfered the diffusion of H to increase the HE resistance. However, the excessive formation of Cu-rich precipitates destabilized the austenite phase, and induced the martensitic transformation. This alpha'-martensite preferably formed inside or at intersections of deformation twins, along with austenite grain boundaries, thereby providing H-induced crack propagation paths. These cracks caused the earlier brittle fracture and severe HE as a consequence. This result would suggest that the formation of Cu-rich precipitates by replacing expensive Ni could enhance both tensile properties and HE resistance, but a delicate control of SFE should be required to overcome the trade-off relationship of strength and HE resistance. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The effects of Ni/Cu replacement and subsequent aging treatment on the tensile and hydrogen embrittlement properties of Fe-Cr-Ni austenitic stainless steels were investigated. The results showed that the replacement enhanced tensile strength and ductility in the aged state, but reduced these properties in the as-annealed state. The formation of Cu-rich precipitates effectively interfered with hydrogen diffusion and increased the resistance to hydrogen embrittlement. However, excessive formation of Cu-rich precipitates destabilized the austenite phase and induced martensitic transformation, leading to earlier brittle fracture and severe hydrogen embrittlement.