From the heat treatment process analysis, because of the heat treatment after the forging, the hardened ball bearing steel ball has not been annealed, so the grains are coarse, and there are banded tissues; Meanwhile, the quenching martensite has high carbon content and high water temperature in the quenching process makes the quenching stress of the steel ball increase.
The analysis shows that the 120mm steel ball is water-cooled quenching, the temperature distribution is very uneven, and the surface is compressive stress state. Internal tensile stress is the main cause of fracture of workpiece.
In addition, the bearing steel ball water quenching ability is strong, and the workpiece inner layer is coarse, close to the heart of the hard tissue, so that the core of the workpiece toughness is poor, there are cracks crack potential. When the workpiece is quenched and tempered after quenching, the stress after quenching is very high without being eliminated and released, which causes the cracking of the steel ball to be damaged. It is concluded that the quenching cracking of bearing steel ball is closely related to forging and heat treatment process. The forging heating time or the temperature control is improper, causes the steel ball to overheat or excessively burns, therefore the grain coarse, the workpiece toughness drops. On the other hand, the central part of the West 120mm steel ball is small in forging deformation, and the cooling speed is smaller, so the site recrystallization is coarse, which causes the crack fracture of steel ball to occur first in the middle.