Rolling Contact Fatigue Performances of Carburized and High-C Nanostructured Bainitic Steels

Abstract

In the present work, the nanostructured bainitic microstructures were obtained at the surfaces of a carburized steel and a high-C steel. The rolling contact fatigue (RCF) performances of the two alloy steels with the same volume fraction of undissolved carbide were studied under lubrication. Results show that the RCF life of the carburized nanostructured bainitic steel is superior to that of the high-C nanostructured bainitic steel in spite of the chemical composition, phase constituent, plate thickness of bainitic ferrite, hardness, and residual compressive stress value of the contact surfaces of the two steels under roughly similar conditions. The excellent RCF performance of the carburized nanostructured bainitic steel is mainly attributed to the following reasons: finer carbide dispersion distribution in the top surface, the higher residual compressive stress values in the carburized layer, the deeper residual compressive stress layer, the higher work hardening ability, the larger amount of retained austenite transforming into martensite at the surface and the more stable untransformed retained austenite left in the top surface of the steel.

Effect of Two-Step Austempering Process on Transformation Kinetics of Nanostructured Bainitic Steel

“…Nanostructured bainitic microstructure not only possesses excellent strength and toughness [1,2,3,4,5], but exhibits a high wear resistance and has a better rolling contact fatigue performance compared to the martensitic microstructure [6,7,8,9,10,11]. This material is therefore suitable for the bearing application [12,13,14].…”

Research and Application Progress of Nanostructured Bainitic Steel in Bearings

“…The high-C-Cr nanostructured bainitic bearing steel GCr15Si1Mo, whose microstructure is shown in Figure 4b, has been adopted in the manufacture of rolling element of 5 MW wind power yaw bearings, pitch bearings and spindle bearings. The rolling contact fatigue lives of the nanostructured bainitic bearing steel GCr15Si1Mo were approximately 106%-112% greater than those of the bainitic bearing steel GCr15SiMo [23,25], (Table 3 & Figure 5b). …”

“…The nanostructured bainite was first studied by Bhadeshia and his coworkers. [20,23] Novel high-C-Cr nanostructured bainitic bearing steels GCr15SiAl by Si-Al alloying and GCr15Si1Mo by Si-Mo alloying were developed at 2015 [19][20][21]. Research results showed that the fully nanostructured bainitic microstructure not only had excellent strength and toughness, but also had the optimal wear resistance compared with the mix microstructure of nanostructured bainite, martensite and retained austenite (Table 2 & Figure 3).…”

“…After carburizing plus high-temperature tempering and low-temperature austempering, nanostructured bainite with the plate thickness of 68 nm and dispersed carbide particles with the average equivalent diameter of 0.25μm were obtained in the surface, which were shown in Figure 4a. The rolling contact fatigue lives of the carburizing G23Cr2Ni2Si1Mo nanostructured bainitic steel were approximately 210%-254% greater than those of the traditional carburizing G20Cr2Ni4 martensitic steel [23,24] (Table 3 & Figure 5a). Moreover, the impact toughness of the center with low-carbon martensite after isothermal treatment is improved 33% as compared with that of the oil-quenched treatment.…”

“…Supported by the national high technology research and development program of China, the novel nanostructured bainitic steels G23Cr2Ni2Si1Mo and GCr15Si1Mo used for high-power wind power bearing were developed [22,23]. The carburizing G23Cr2Ni2Si1Mo bainitic steel is suitable for manufacturing high-power wind power spindle bearing ring.…”