Accelerating Cementite Precipitation during the Non-Isothermal Process by Applying Tensile Stress in GCr15 Bearing Steel

Abstract

In this work, the non-isothermal process of GCr15 bearing steel after quenching and tempering (QT) under different tensile stress (0, 20, 40 MPa) was investigated by kinetic analysis and microstructural observation. The Kissinger method and differential isoconversional method were employed to assess the kinetic parameters of the microstructural evolution during the non-isothermal process with and without applied stress. It is found that the activation energy of retained austenite decomposition slightly increases from 109.4 kJ/mol to 121.5 kJ/mol with the increase of tensile stress. However, the activation energy of cementite precipitation decreases from 179.4 kJ/mol to 94.7 kJ/mol, proving that tensile stress could reduce the energy barrier of cementite precipitation. In addition, the microstructural observation based on scanning and transmission electron microscopy (SEM and TEM) shows that more cementite has formed for the specimens with the applied tensile stress, whereas there is still a large number of ε carbides existing in the specimens without stress. The results of X-ray diffraction (XRD) also verify that carbon in martensite diffuses more and participates in the formation of cementite under the applied tensile stress, which thus are in good agreement with the kinetic analysis. The mechanisms for the differences in cementite precipitation behaviors may lie in the acceleration of carbon atoms migration and the reduction of the nucleation barrier by applying tensile stress.

Thermal Behavior of Sweet Potato Starch by Non-Isothermal Thermogravimetric Analysis

“…Non-isothermal tests are mostly preferred for the dynamic analysis. To this end, many models, such as Kissinger, Flynn–Wall–Ozawa, Šatava–Šesták, and Friedman, were established to study the dynamic parameters of various materials based on the Arrhenius equation [ 5 , 6 , 7 , 8 , 9 ].…”

High Temperature Dry Tribological Behavior of Nb-Microalloyed Bearing Steel 100Cr6

“…The traditional bearing steel 100Cr6 has high hardness and good wear resistance, but it has defects in toughness and temperature bearing capacity. In recent years, many scholars have done a lot of research on the microstructure evolution and manufacturing process optimization of 100Cr6 steel [6,7]. Yusuke et al [8] found that the quenched structure with almost no grain boundary carbides can be obtained by grain boundary amelioration (GBA) treatment, and the toughness can be increased to more than 5 times of the conventional one.…”

Effects of niobium on network carbide in high-carbon chromium bearing steel by in situ observation analysis

“…High-carbon chromium bearing steel probably is the most important material used for mechanical rolling components, which should have excellent surface hardness for wear and fatigue resistance as well as microstructural stability at extreme temperatures [6,7]. However, since high-carbon chromium bearing steel is a hypereutectoid steel, excessive secondary cementite will precipitate along the grain boundary to form network carbide during the process of cooling after rolling, thus increasing the brittleness of steel and reducing its fatigue life [8]. Generally speaking, to reduce the amount of network carbide including two ways: one is to control the precipitation of carbide in the cooling process and the other is to relieve the formed network carbide.…”