High carbon chromium steel can contain 8% – 20% AR (residual austenite) after normal quenching. AR in imported bearing parts has both advantages and disadvantages. In order to promote advantages and eliminate disadvantages, life of imported bearings the content of AR should be appropriate. Because the amount of AR is mainly related to the austenitizing conditions of quenching heating, and its amount will affect the carbon content of quenched martensite and the amount of undissolved carbide, it is difficult to correctly reflect the impact of AR on mechanical properties.
Therefore, the austenite heat stabilization treatment process was used to obtain different ar content under the fixed austenite condition. Here, the effect of AR content on the hardness and contact fatigue life of GCr15 steel after quenching and low temperature tempering was studied. With the increase of austenite content,life of imported bearings the hardness and contact fatigue life increase, and then decrease after reaching the peak value. However, the peak value of AR content is different. The peak value of hardness appears at about 17% AR, while the peak value of contact fatigue life appears at about 9%.
The quantity, morphology, size and distribution of undissolved carbides in quenched steel are affected not only by the chemical composition of the steel and the original structure before quenching, but also by the austenitizing conditions. There are few studies on the influence of undissolved carbides on the service life of imported bearings.
Carbide is a hard brittle phase. In addition to being beneficial to wear resistance, it will cause cracks due to stress concentration with the matrix (especially when the carbide is non spherical), which will reduce toughness and fatigue resistance. In addition to its own influence on the properties of steel, quenched undissolved carbides also affect the carbon content and AR content and distribution of quenched martensite, thus having an additional impact on the properties of steel.
Therefore, too many quenched insoluble carbides are harmful to the comprehensive mechanical properties and failure resistance of steel. Properly reducing the carbon content of imported bearing steel is one of the ways to improve the service life of parts.
In addition to the quantity of quenched undissolved carbides, the size, morphology and distribution also affect the material properties. In order to avoid the harm of undissolved carbides in imported bearing steel, it is required that undissolved carbides are small (small in quantity), small (small in size), uniform (the difference between sizes is very small, and the distribution is uniform), and round (each carbide is spherical).
It should be pointed out that it is necessary for imported bearing steel to have a small amount of undissolved carbide after quenching, which can not only maintain sufficient wear resistance, but also be a necessary condition for obtaining fine grain cryptocrystalline martensite.