Fully restoring the damaged ductility of H-charged medium Mn steel via pulsed current

Abstract

It was found that the electric pulsed treatment (EPT) performed at 250 °C on a medium Mn steel (MMnS) can remove all the H atoms preserved in martensite and austenite by the electrochemical H-charging; as a result, the severely deteriorated ductility and strength due to hydrogen embrittlement (HE) were both fully restored. In contrast, only the H-atoms in martensite were completely removed by the conventional heat treatment (CHT) at the same temperature, but 0.3 wt ppm H remained in austenite, resulting in the damaged ductility just restored by about 50 %. The relevant mechanism on releasing H-atoms by EPT is discussed on the basis of microstructural examinations and H-desorption kinetic measurements for explaining such an unexpected phenomenon.