Hydrogen Delayed Fracture Properties of Copper-Added High-Mn TWIP Steels

Abstract

It is known that the addition of copper retards the twin formation due to the increase of the stacking fault energy, and results in less strain hardening owing to its reduced dynamic Hall-Petch effect and wavy dislocation glide mode. In this study, mechanical properties and hydrogen delayed fracture (HDF) properties were investigated using high-Mn twinning induced plasticity (TWIP) steel (Fe-17%Mn-0.8%C) containing various amount of copper (0, 1 and 2 wt%). Hydrogen charging was conducted by the electrochemical method, and then, the slow strain rate test (SSRT) and the thermal desorption spectrometry (TDS) were carried out to examine the HDF properties of specimens. Copper-added TWIP steels showed the comparable yield strength and the elongation to fracture, but the lower strain hardening rate as compared to those of the specimen with no copper. After hydrogen charging, the ductility was considerably reduced in all specimens. It’s due to the initiation of the surface cracks during the deformations after hydrogen charging. In case of copper-added specimens, the elongation loss was insensitive with hydrogen. It is because the surface crack initiation was delayed with the copper addition. The increase of SFE with copper changed the dislocation glide mode from planar to wavy. The stress concentrations applied on grain boundaries were reduced due to the relatively uniform deformation in the copper-added specimens