From the analysis of the heat treatment process, due to the waste heat quenching after forging, the FAG bearing steel ball has not been spheroidized and annealed, so the grains are coarse and there is a band-like structure; at the same time, the carbon content in the quenched martensite is very high. The high water inlet temperature increases the quenching stress of the steel ball.
According to analysis, the west 120mm steel ball adopts water-cooling quenching, the temperature distribution is very uneven, forming a high structural stress, and its surface is in a state of compressive stress. The internal tensile stress is the main reason for the fracture of the workpiece.
In addition, the bearing steel ball has strong water quenching cooling ability, and the internal layered structure of the workpiece is coarse, and there is a harder structure near the core, which makes the core of the workpiece poorly tough, and there is a hidden danger of cracking. The workpiece is not tempered in time after quenching during the production of the workpiece, and the stress after quenching is so high that it has not been eliminated and released, resulting in cracking and damage of the steel ball. Analysis believes that quenching cracking of bearing steel balls is closely related to forging and heat treatment processes. Improper forging heating time or temperature control will cause the steel ball to overheat or burn, so the grains are coarse and the toughness of the workpiece decreases. On the other hand, the forging deformation in the center of the 120mm steel ball in the west is small, and the cooling rate is also small. Therefore, the recrystallized grains in this part are coarse, causing the middle of the steel ball to be the first to crack.