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Advanced vacuum high pressure gas quenching technology

1.High pressure gas quenching and its advantages

After the workpiece is heated to the austenitizing temperature, 0.5 to 2MPa (5 to 20bar) high-pressure gas quenching is applied, which can achieve the quenching effect of static oil or high-speed circulating oil or even water. The gas quenching mechanism of the workpiece is different from that of liquid medium quenching. The cooling in the gas is more uniform than the cooling in the liquid, and uniform cooling from the surface to the inner layer can be achieved. Therefore, the gas quenching distortion is very small and less (no) grinding can be achieved. . High-pressure gas quenching uses neutral gas N₂, reducing gas H₂ and inert gases Ar, He, etc. These gases are discharged into the atmosphere and are pollution-free, avoiding the smoke pollution caused by oil quenching, and can eliminate the alkali cleaning process and Discharge of oily liquids. The surface cleanliness of the treated parts is high, there is no need for subsequent cleaning and shot blasting processes, and there are no SO₂ and CO emission issues, so it is a clean heat treatment technology.

During high-pressure gas quenching, the high-pressure gas flow can control the pressure and flow rate of the gas through the computer, change the cooling characteristics of the gas, and combine with the supercooled austenite transformation phase diagram of the steel to achieve the most ideal quenching cooling and obtain the ideal metallographic structure. , effective hardened layer depth and heat treatment distortion.

To achieve the cooling rate of oil quenching when batches of alloy steel carburized parts are cooled in gas, the gas must be maintained at a pressure above 1MPa, and good heat exchange and flow circulation conditions of the gas itself must be provided.

2.Application

1) After gas carburizing in a sealed multi-purpose furnace, gas quenching is performed in an inert gas at a high pressure of 1 to 2 MPa (10 to 20 bar) to replace oil quenching.

2) The gas carburizing furnace produced by SIMUWU is equipped with a gas quenching chamber to give full play to the advantages of gas quenching technology, making the gas carburizing production line have high production capacity and reasonable heat treatment costs.

3) Vacuum low-pressure carburizing + high-pressure gas quenching application

① In the automobile industry, high-pressure gas quenching can use single-chamber, double-chamber, or three-chamber low-pressure carburizing high-pressure gas quenching vacuum cycle furnaces and multi-chamber production lines composed of low-pressure carburizing and high-pressure gas quenching. After the synchronizer gear sleeve of the automobile transmission, the main reduction sun gear shaft of the automatic transmission, etc. are processed by this process, the thermal distortion of the parts is controlled within a very narrow range, the pass rate is greatly improved, and the dimensional accuracy of the parts is significantly improved.

② Low-pressure ion carburizing can be performed by applying an electric field in double-chamber and three-chamber furnaces.

③Vacuum carburizing + high-pressure gas quenching has also been applied to motorcycle small module gears.

3.High pressure gas quenching gas

After the workpiece is heated in a vacuum furnace or low-pressure carburizing (carbonitriding), it is gas quenched using high-pressure N₂, He, and H₂. By recycling the air cooling system of N2, He and H₂, the cooling capacity is greatly improved. High-pressure gas quenching can easily control the gas flow rate, pressure and flow direction through computer programs, change the cooling characteristics of the gas, and make the workpiece cool evenly. Small air volume is used in the martensitic transformation zone, thereby reducing the quenching distortion of the workpiece.

After carburization, the steel parts are cooled more uniformly in gas than in liquid, so the quenching distortion is also small. To achieve the cooling rate of oil quenching when batches of alloy steel carburized parts are cooled in gas, the gas must be kept at a pressure above 1MPa, and good heat exchange (cooling) and flow circulation conditions of the gas itself are required. The heat transfer properties of various gases are very different. Hydrogen (H₂) has the best heat transfer performance, followed by helium (He) and nitrogen (N₂). Although N2 has poor cooling performance, it is the lowest price, so N₂ is currently used for high-pressure gas quenching.

φ60mm high-speed steel can obtain a hardness of 64~65HRC and good hot hardness when cooled with 0.5~0.6MPa high-purity N₂ under industrial furnace loading. The use of gas N2 and H₂ recovery technology can greatly reduce costs and promote the popularization of mixed gas quenching technology.