Hydrogen Absorption Behavior and Absorbed Hydrogen Trapping Sites in Rolling Contact Fatigue

Hydrogen absorption behavior and microstructural change of carburized JIS SCr420 steels containing different amounts of retained austenite in rolling contact fatigue were investigated. The thermal desorption analysis confirmed hydrogen desorption at the second-peak between 423 and 623 K after rolling contact fatigue. The hydrogen concentration at the second-peak increased with number of cycles in the rolling contact. This increment was larger when using the steel with higher amount of retained austenite before the fatigue test. It was still large even when the amount of martensitic transformation from retained austenite under cyclic stress to introduce dislocation with trapping capacity was small. The activation energies of desorption for the second-peak hydrogen were calculated to be 50.6 kJ·mol−1 for the steel with 10.4% retained austenite and 55.8 kJ·mol−1 for the steel with 4.9% retained austenite. The activation energies of cathodically charged 0.8%C steels with 10.9% and 6.0% retained austenite, simulating carburized layer before the test, were 36.2 and 42.2 kJ·mol−1, respectively. This means that the activation energy of hydrogen desorption increased during rolling contact. The absorbed hydrogen during the rolling contact fatigue was likely trapped in more stable trapping sites related to the retained austenite which were formed under cyclic stress.