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Analysis, bearing steel forging and heat treatment and quenching cracking process are closely related. Forging heating time or temperature control properly, resulting in ball hot or burning, so coarse grains, the workpiece toughness decreases. On the other hand, the center of the West 120mm ball forging deformation is small, the cooling rate is smaller, and therefore the site recrystallized coarse grains, causing the ball first crack fracture most likely occurred in the middle.
From the analysis of the heat treatment process, as a result of heat quenched after forging, FAG ball bearings ball annealing treatment is not carried out, so the coarse grains, and there is banded; while quenched martensite in high carbon content, forged after quenching into the water temperature is high, the ball quenching stress increases. Analysts believe that the West 120mm ball using water quenching, the temperature distribution is very uneven, the formation of a high organizational stress, and its surface was compressive stress state. Internal tensile stress, the internal tensile stress is the main reason causing the workpiece fracture. In addition, water quenched steel ball bearing cooling ability, and workpiece lamellar thick, hard exist near the center portion of the organization, so that the workpiece core part toughness is poor, there is a crack crack problems. Workpiece production after quenching and tempering is not timely after quenching stress is high and has not been eliminated and released, resulting in ball cracking damage.
The foregoing analysis is proposed carbon martensite steel balls to prevent cracking process improvement measures are as follows:
(A) forging. Increasing forging ratio, strict control of the forging process, preventing heart tissue after forging thick.
(2) increased ball annealing before quenching, refine the organization, so that after quenching was fine needle (fine flakes.) Martensite after quenching produces thick to prevent tissue.
(3) reduce the bearing balls into the water quenching temperature, increase water temperature, can significantly reduce the quenching stress and relaxation. (
(4) promptly after quenching and tempering, quenching eliminate stress, stabilize the organization, and further remove the workpiece cracking risks.
After using the above process improvement, FAG ball bearings eliminate the phenomenon of quench cracking failure, the workpiece after heat treatment quality, production is running well.
| Product Model | Inside Diameter | Outside Diameter | Thickness |
| 7214ADB NSK | 70 | 125 | 24 |
| 7014CDB NSK | 70 | 110 | 20 |