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Vacuum Heat Treatment Applications for Metal Machine Tools and Gear Parts

Application 1 Vacuum Quenching of Cr12MoV Steel Triangular Parts

Material: Cr12MoV steel

Technical requirements: overall 62～65HRC, deformation less than 0.10 mm

The parts are: the lower plate press needle, the needle lifter and the thimble on the textile machine.

Dimensions of various triangular parts used in the knitting machine, the material is Cr12MoV steel, and the original structure is forged and annealed. The profiles are formed by wire cutting, and are directly installed and used after vacuum heat treatment without further processing. The hardness requirement is 62-65HRC.

According to the vacuum heating calculation heating time and the conventional heat treatment and quenching process of Cr12MoV steel, the vacuum quenching process curve of the parts is formulated.

According to the process of vacuum heat treatment, the production cycle of each furnace needs 3h. In order to improve production efficiency and reduce the cost of heat treatment, a new vacuum heat treatment process has been formulated. Compared with the original process, the preheating temperature of the first and second stages is increased, and the through-fire time at high temperature is shorter than that at low temperature. It is shortened by 1/3. Taking into account the increase of preheating temperature, the vacuum quenching heating and holding time can be shortened. After the process is implemented, the deformation and cracking caused by thermal stress are completely prevented, and the production cycle can be shortened at the same time. The workpiece only needs about 2 hours when the furnace load reaches 20kg, and the quenching hardness is 63~64HRC. After being out of the furnace, it is vacuum tempered at 160~180℃×2h in the oil tank, and the final hardness is still 63~64HRC. It can be directly installed and used after being serialized by the serial light machine.

Application 2 Vacuum Quenching of GCr15 Steel Parts

Material: GCr15 steel

Technical requirements: Overall 63~64HRC, deformation 0.10mm. The parts are: the upper plate of the textile machine.

0911A profile GCr15 steel for upper plate of knitting machine parts, technical requirements 62-64HRC

Upper plate of knitting machine parts 0019AGCr15 steel, technical requirements 62-64HRC

The representative of GCr15 steel parts used in large quantities on knitting machines, its original structure is cast, the vacuum quenching temperature of GCr15 steel is about 840°C, and the fatigue strength, hardness and impact toughness are the highest after vacuum quenching and tempering, at 840°C When left and right vacuum quenching, the mass fraction of dissolved carbides in austenite is 0.5% to 0.6%, the mass fraction of chromium is 0.8%, and there are still some undissolved carbides. The dissolved carbon and alloy elements ensure its hardenability and hardenability, while the undissolved carbide prevents the grain from growing. If the vacuum quenching temperature is low, the amount of carbide dissolved in austenite is small, and the carbon and chromium content in austenite is low, which will inevitably affect the hardness after vacuum quenching. If the vacuum quenching temperature is too high, it will cause overheating, which will make the quenched martensitic needles thicker, and the deformation will increase, which will affect the mechanical properties. The heating time is closely related to the heating temperature, the heat transfer medium, the effective thickness of the parts and the amount of the furnace. Under the same temperature conditions, if the heating time is too short, the austenitization will not be sufficient, the carbides will not be completely dissolved, and the degree of alloying of the solid solution will be low, which will make the quenching temperature lower. If the heating time is too long, the grains will be coarse. And the cost increases.

After a lot of experiments, the vacuum quenching process curve is determined. The quenching temperature is 855°C. At the same time, the cooling time is properly controlled. It can be completely hardened, the hardness reaches 63-64HRC, and the deformation meets the process requirements.