Abstract
Carburized gear steel has a high-hardness case layer with excellent wear and fatigue resistance and a low-hardness core with high toughness. Such different microstructures imply different susceptibilities to hydrogen embrittlement (HE). However, a few or no studies have explored the HE behavior of carburized gear steel. Herein, the HE behavior of a vacuum-carburized gear steel 20Cr2Ni4A was investigated via an electrochemical hydrogen-charging and slow strain rate tensile test. For comparison, another group of specimens was prepared by a conventional quenched and tempered (QT) treatment. The volume fraction of retained austenite was significantly higher in the case layer of the carburized specimen (13.8%) than in the core and the QT specimen (4.6%). The retained austenite in the case layer showed a mainly irregular block-type morphology with wide size distribution. The room-temperature diffusible hydrogen content in the hydrogen-charged carburized specimen were almost identical to the QT specimen but the nond