At present, with the official establishment of the company's aircraft landing gear specialized manufacturing plant, our vacuum heat treatment production is more mature and perfect. After the original isothermal annealing treatment, when the metallographic structure of the forged piece was detected, it was found that the metallographic structure was uneven, some forgings had fine grain size, the grain size was 56 (a), and other forgings were coarse, up to 23 (b) At the same time, banded tissue (c) appears. After testing the hardness after isothermal annealing treatment, some forgings have higher hardness, reaching 200240HB, and some hardness is lower, reaching 145160HB, and the hardness difference is large. Therefore, the workpiece quality is unqualified after isothermal annealing using this process. The original isothermal annealing process gear forgings (referred to as forgings) isothermal annealing is carried out in two 150kW trolley furnaces. The process route is: forgings are heated at high temperature in No. 1 trolley furnace and air-cooled to the outer surface of forgings is dark red No. 2 trolley furnace Isothermal treatment of the furnace. The high temperature heat treatment process of the No. 1 trolley furnace (high temperature furnace) is: (940950) (45) h, and the fan is cooled by a long distance after the forging is released. The isothermal treatment process of the No. 2 trolley furnace (isothermal furnace) is (650670) (56) h, and the air is cooled. The forgings produced by the original isothermal annealing process have uneven microstructure and hardness, resulting in unqualified quality. The isothermal annealing process refers to the fact that the completely austenitized part is rapidly cooled to a suitable temperature in the pearlite transformation zone in a short period of time, and is sufficiently insulated at this temperature to ensure that the structural transformation is completed, and a uniform ferrite sheet is obtained. Pearlite and uniform hardness.
22CrMoH steel belongs to alloy steel with high hardenability. When cooling is too fast, granular bainite structure will appear in some forgings. The hardness is too high, which affects the cutting performance. If the cooling speed is too slow, the temperature of the forging in the middle position is much higher. At isothermal temperature, the microstructure is coarse and the hardness is low, which affects the mechanical properties. From this point of view, the control of isothermal annealing cooling is the key to the quality of forging heat treatment.
Improvement measures The improvement process of the isothermal annealing process of 31 car furnaces After the high temperature of the forgings is released, the axial fan blows away for a long time and then enters the isothermal furnace for heat preservation, and then the air is cooled, resulting in uneven heat and cold for the forgings, which makes the tissue change different. Therefore, the forging is not uniform in hardness. To this end, the forgings are heated and insulated in the (940950) high-temperature trolley furnace. After the furnace is discharged, the axial fan is cooled by a long-distance blower for about 10 minutes. After the surface of the forging is dark red, return to the high-temperature furnace that has been powered off for a short-term average temperature. Then it is cooled out. This was repeated (23) times, and then heated in an (650670) isothermal furnace and kept warm for (56) h, and then air-cooled. At the same time, the forgings are assembled into vertical cross stacks and placed in special baskets to facilitate uniform heat dissipation, so that the forgings obtain uniform metallographic structure and hardness.
It is more suitable to use a continuous isothermal annealing furnace to improve the quality. It is more suitable for the small batch forgings to be isothermally annealed by two trolley furnaces, but the cooling control after high temperature heating is not stable enough, which is a gear that requires less distortion and isotherm. Annealing quality is difficult to guarantee, especially for direct quenching parts. In order to ensure the quality of forgings and reduce distortion, it is necessary to use a continuous isothermal annealing furnace for large quantities of forgings. The parts processed by the continuous isothermal annealing automatic line have good cutting performance, the distortion is small after carburizing and quenching, the loading is stable, and the vibration and noise are reduced [3]. The process route is as follows: 940 (heating zone 1) 940 (heating zone 2) 940 (heating zone 3) 650 (isothermal zone 1, air-cooling zone) 650 (isothermal zone 2) 650 (isothermal zone 3) air-cooling. The key to obtain a good uniform structure and hardness by continuous isothermal annealing furnace is: in the initial stage of cooling, the forgings in the isothermal 1 zone air-cooling chamber are rapidly cooled by air with a flow rate of 10000 m3/h, and when the temperature difference between different parts is large, gradually Increase the circulating hot air to reduce the temperature difference of the forgings; the use of cross-stacking forgings is conducive to ventilation and heat dissipation, ensuring that the forgings can be quickly and evenly cooled, thereby obtaining uniform structure and hardness. The supporting processing route is a rough grinding and tempering drilling and grinding assembly.
Fig. 1Schemeofcrossrollerslewingbearing1: The delivery state of the blank is normalized. When the blank is rough, almost half of its own mass is cut, so the cutting stress is very large. Therefore, the 5m well tempering furnace is first used for stress relief annealing. The process is (55010) 6h, and the car is refined after annealing to make the raceway concentric with the outer circle. In order to solve this problem, the following improvements are made: the double-twisted inductor is used for quenching, and the inductor is welded and bent with a rectangular copper tube of 12 mm 6 mm 2 mm; in order to prevent the sharp corner effect at the chamfer of the outer raceway, the ends of the inductor are slightly tilted. The front end of the sensor is made 86 to ensure that the coupling gap between the sensor and the raceway is small to large. To increase the heating efficiency, a magnetizer is attached to the inductor as shown. Now it is inclined to face 30 degrees downward with the horizontal direction, and the water spray hole is changed from 10mm to 12mm. This slightly relieves the large pressure caused by the direct spray of water onto the raceway to reduce the possibility of cracking.
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