Role of multiple mid-temperature tempering on mechanical properties and wear behavior of carburized steel under complex service conditions

Abstract

Tempering is a necessary heat treatment process to ensure that the surface of the carburized material has adequate strength and the core has sufficient toughness. In this work, the carburized layer was tempered several times at medium temperature (400–440 °C) and the effect of tempering temperature, and number of times on microstructure, plastic toughness, and wear properties in complex environments was investigated in detail. The modified layers of the tempered samples were characterized by martensite, carbide, and a small amount of residual austenite. Primarily, the results show that the maximum ultimate tensile strength (UST, 1441 MPa) and elongation (11.4 %) were obtained with 3 times tempering at 400 °C. Simultaneously, the least erosion wear rate (0.61 mg/g) was obtained for 400 °C 3-times tempered specimens. Then, under dry friction conditions, the friction coefficients of the 3-times tempered were inferior to those of the 5-times tempered samples. In the subsurface layer, the 420 °C 3-times tempered samples had the minimum wear rate (1.73 × 10−15 m3N−1 m−1). Nevertheless, the friction coefficient under oil lubrication is dramatically lower compared to the dry friction coefficient. Finally, the medium temperature multiple tempering ensured a well-balance of wear resistance and plastic toughness.