The surface strengthening of steel ball (also called pressure) is that the surface of steel ball is strengthened by the collision of steel ball, which causes the macroscopic elastic deformation and microscopic plastic deformation of the steel ball surface, and the hardness of the steel ball surface layer is increased and uniform, and the surface is strengthened by the distribution of compressive stress.
During operation, fatigue cracks in ball bearings primarily develop at the maximum shear stress depth beneath the surface. Under alternating stress conditions, these micro-cracks propagate toward the surface, ultimately causing fatigue spalling. Surface strengthening treatment for steel balls generates residual compressive stress at the maximum shear stress depth, eliminating tensile stress that promotes crack initiation and propagation. This transformation converts tensile stress into compressive stress, thereby enhancing the fatigue strength and wear resistance of steel balls. Bearings equipped with strengthened steel balls can achieve a lifespan improvement of over two times.
The surface strengthening of steel balls induces compressive stress, a phenomenon associated with cold-state plastic deformation. During this process, the metal’s lattice undergoes distortion, elongation, and fragmentation, displacing atoms from their densest arrangement. This results in reduced density and volume expansion of the metal. Meanwhile, the sub-surface layer retains its elastic properties without undergoing plastic deformation, effectively resisting the surface metal’s expansion. Consequently, the sub-surface layer exerts compressive stress on the surface metal.
Surface strengthening of steel balls is commonly achieved through mechanical impact. A horizontal metal cylinder wall is equipped with a copper plate along its circumference, evenly spaced with lifting buckets for steel balls. A small amount of diesel oil is added inside the cylinder, which rotates at low speed to cause mutual collisions between steel ball surfaces, thereby enhancing their surface hardness. For small steel balls (with a diameter of 10mm), a high-speed rotating inner cylinder is additionally installed within the main cylinder to intensify the collision force. This strengthening process is typically scheduled after hard grinding and before precision grinding.
