From the analysis of the heat treatment process, due to […]
From the analysis of the heat treatment process, due to the residual heat quenching after forging, the FAG bearing steel balls are not spheroidized and annealed, so the grains are coarse and there is a band structure; at the same time, the carbon content in the quenched martensite is very high, and the quenching after forging Higher water inlet temperature increases the quenching stress of the steel ball.
According to the analysis, the 120mm steel ball in the west is quenched by water cooling, the temperature distribution is very uneven, and a high structural stress is formed, and the surface is in a compressive stress state. The internal tensile stress is the main cause of the workpiece fracture.
In addition, the bearing steel ball has strong water quenching and cooling ability, and the layered structure in the workpiece is thick, and there is a hard structure near the core, which makes the workpiece core toughness poor, and there is a hidden danger of cracking. The workpiece is not tempered in time after quenching, and the stress after quenching is high and it has not been eliminated and released, which leads to cracking and damage of the Stainless Steel Balls. The analysis believes that quenching cracking of bearing steel balls is closely related to forging and heat treatment processes. Improper control of forging heating time or temperature causes 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 of the central part of the 120mm steel ball in the west is small, and the cooling rate is also small, so the recrystallized grains in this part are coarse, causing the steel ball to crack and break easily in the middle.
Based on the above analysis, the improvement measures of the high carbon martensite steel ball crack prevention process are as follows:
(1) Forging. Increase the forging ratio and strictly control the forging process to prevent the coarsening of the heart after forging.
(2) Lowering the water temperature of the bearing steel ball during quenching and increasing the water temperature can significantly reduce and ease the quenching stress of the workpiece.
(3) Add spheroidizing annealing before quenching to refine the structure, so that the workpiece becomes fine needle-like (fine flake) martensite after quenching, to prevent coarse structure after quenching.
(4) Temper in time after quenching, eliminate quenching stress, stabilize the structure, and further remove the hidden danger of cracking of the workpiece.
After the improvement of the above process, the failure phenomenon of FAG bearing steel ball quenching cracking is eliminated, the quality of the workpiece is excellent after heat treatment, and the production and operation are good.