Effect of Heat Treatment on Rolling Contact Fatigue Performance of Pyrowear 675 with Type II Ester Oil

Abstract This research presents the effects of heat treatment on rolling contact fatigue (RCF) life and corrosion performance of stainless-steel Pyrowear 675 (P675). P675 was heat treated using two heat treatment (HT) processes with an order of magnitude difference in total cycle time. They are identified at a short heat-treated (SHT) cycle and long heat-treated (LHT) cycle. The carburized specimens from both HT were tempered at 316°C (low temperature tempered [LTT]) and 496°C (high temperature tempered [HTT]). The HT and tempered P675 samples were evaluated for RCF life using a ball-on-rod tester at a maximum Hertzian stress of 5.5 GPa in a hybrid configuration (with silicon nitride rolling elements) and at a temperature of 218°C, using gas turbine engine type II ester oil conforming to MIL-PRF-23699 G, Performance Specification: Lubricating Oil, Aircraft Turbine Engine, Synthetic Base, Nato Code Numbers: O-152, O-154, O-156, and O-167. The corrosion resistance was evaluated using electrochemical impedance spectroscopy (EIS) in simulated synthetic seawater. The heat treatment cycle has a significant effect on microstructure, corrosion resistance, RCF life, and wear performance. The SHT cycle with both tempers resulted in carbide necklacing at grain boundaries and lower carburized case depth. The longer heat treatment cycle showed superior RCF life and lower wear rate compared to the shorter heat treatment cycle. However, the shorter heat treatment cycle showed improved corrosion resistance. Post test analysis showed significant differences in microstructural changes between HTs.