The Effect of Retained Austenite and Nickel on the Rolling-Sliding Contact Fatigue of Carburized Steels

The influences of nickel content and retained austenite on rolling-sliding contact fatigue (RSCF) life in carburized steel is not well understood. In order to evaluate nickel and retained austenite effects, this study utilizes carburized steel specimens of 4120 (0.13 wt pct Ni), 4820 (3.38 wt pct Ni), and EN-30B (4.15 wt pct Ni), which were subjected to RSCF testing. The specimens were gas carburized with a resulting case depth of approximately 1.3 mm, based on a hardness of 500 HV. Specimens were surface ground to a surface roughness of 0.2 µm to decrease the effect of as-carburized surface roughness on the fatigue life. The specimens underwent RSCF testing, with a load of 10.3 kN and a slide to roll ratio of -20%, until a pit formed, as detected by an accelerometer. The fatigue life of the 4820 specimens is higher than the fatigue life of the 4120 specimens, establishing that more nickel is beneficial to the fatigue life. The results of the EN-30B will be compared to the 4820 and 4120 fatigue life results. Carburized specimens have also undergone cryotreatment and tempering to decrease the retained austenite within the specimens while keeping the nickel content constant. Comparing the fatigue life of the carburized specimens and the carburized and cryotreated specimens will illuminate the relationship between nickel content and retained austenite.