After several introductions of ball bearings steel, you all have a certain understanding of it. Today, the editor will talk about the knowledge of the heat treatment process of ball bearing steel balls. Everyone, please pay close attention!
Through thermal treatment process analysis, due to the post-forging residual heat quenching, FAG bearing steel balls were not subjected to spheroidizing annealing treatment, resulting in coarse grain structure and the presence of lamellar tissue; simultaneously, the carbon content in the quenched martensite is high, and the water immersion temperature during post-forging quenching is too high, which increases the quenching stress of the steel balls.
The analysis indicates that the 120mm steel ball, using water quenching, exhibits uneven temperature distribution, leading to high organizational stress. Its surface is in a compressive stress state, while internally it is in tensile stress, which is the primary cause of the workpiece's fracture.
Additionally, the bearing steel ball has strong water quenching cooling ability, and the inner layer-like structure of the workpiece is coarse, with a harder tissue near the core, resulting in poor toughness at the core and potential cracks and cracking hazards. During the production process, the workpiece was not annealed promptly after quenching, leading to high residual stress post-quenching that was not eliminated or released, thereby causing the steel ball to crack and damage. Analysis indicates that the quenching cracks in the bearing steel balls are closely related to the forging and heat treatment processes. Improper control of forging heating time or temperature can lead to overheating or overburning of the steel ball, resulting in coarse grain size and decreased toughness. On the other hand, the central part of the 120mm steel ball has minimal forging deformation and a slower cooling rate, which causes the recrystallization grain size to be coarse in this area, making the steel ball prone to cracking and fracturing first at the middle section.
In summary, the following process improvement measures for preventing cracking in high-carbon martensitic steel balls are proposed:
Forge: Increase forging ratio, strictly control forging process, and prevent coarse core structure after forging.
Lowering the quenching temperature of bearing steel ball in water and increasing the exit temperature can significantly reduce and mitigate the quenching stress of the workpiece.
Pre-treatment with spheroidizing annealing before quenching refines the structure, resulting in a fine needle-like (sheet-like) martensite after quenching, preventing the formation of coarse structures.
Post-quenching, timely tempering is performed to relieve quenching stresses, stabilize the structure, and further eliminate the potential for cracking in the workpiece.
Following the process improvements, the cracking failure of FAG bearing steel balls during quenching has been eliminated, resulting in excellent quality after heat treatment and smooth production operation.
Here's the brief introduction to the heat treatment technology of ball bearing steel we've provided for you. Although the explanation is somewhat superficial, it's still quite helpful to many.
