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Core Hardness Control of Carburized Gears

In the process of automobile manufacturing, the requirements for each component must meet high standards. In the actual implementation process, the results obtained will be different due to the influence of materials, conditions, equipment, etc., and for the gears that are constantly running, In order to transmit power, it needs to withstand the impact and compression of various forces during meshing, which has a strong requirement for the hardness of the heart of carburized gears.

There are many factors affecting the quality of gears, because they need to bear pulsating impact force and bending stress during operation, so there are strict requirements on their manufacturing process, so as to control the hardness of the core and still provide sufficient strength for carburized gears during work. Support and strength. When manufacturing gears, different materials will be provided according to different requirements to ensure the quality, and the quality after carburizing will be tested by hardness and metallography to ensure that the hardness of the core reaches the standard that can withstand impact.

Influence of new technology and manufacturing process on gear core hardness

Effect of Carbide on Carburized Gear

With the promotion of high technology to the technical level, relevant experimenters have embarked on a new journey in the research of carburized gears. There are many studies on carbides with a hardness of more than Hv1000. The reason why carburized gears are used in car gears is that, The carbides in the carburized layer are in the shape of blocks and corners to facilitate the concentration of micro-area stress, and the formed network will increase the brittleness and reduce the fatigue life of the gear.

Vacuum quenching

The vacuum carburizing step is generally to improve the wear resistance of the gear surface, the carbon concentration is proportional to the wear resistance, and the increase of the carbon concentration will improve the wear resistance. The normalized structure of high-carbon steel obtained without quenching after carburizing can obtain network carbides to reduce fatigue life when the carbon concentration is sufficient and the cooling rate is slow enough, and it is difficult to produce a wear-resistant structure for parts without heat treatment. Then the purpose of vacuum quenching is to increase the hardness and obtain more martensite structure, so as to facilitate the secondary decomposition into sorbite to obtain better mechanical properties. What professional manufacturers know is that the hardness of the core of the gear happens to be mainly dependent on the hardenability of the raw material, because the core of the carburized gear has almost no carburization and can maintain the original chemical material. The vacuum quenching process is widely used, and it is required in the manufacturing industries such as tools, abrasives, and components. In the process of vacuum quenching, the parameter requirements of all aspects need to be strictly implemented, especially the different control of the temperature during quenching will have different effects. The adjustment of vacuum heat treatment process parameters, especially the adjustment of quenching temperature, can also have a certain impact. As a vacuum heat treatment process used to improve hardness, strength and wear resistance, vacuum quenching requires rapid cooling after heating to a certain temperature, so the choice of cooling medium is worth discussing. The ideal state of the quenching cooling medium should have the condition that the parts can be quenched into martensite, but it will not cause too much stress, so the stirring speed should be controlled to achieve the ideal effect. On this basis, some methods to improve efficiency are sorted out, such as: increasing the quenching temperature, increasing the stirring speed and other process parameters to increase the cooling rate, or starting from other angles, such as increasing the hardenability zone position of the material and directly using the cooling rate Fast medium. Faced with the fact that the hardness of the center of the carburized gear is still low after vacuum quenching, if the shape of the part is allowed to be deformed within a certain range, methods such as increasing the quenching temperature and strengthening cooling can be used to reheat the quenching, or use an appropriate increase The method of carburized layer thickness to meet the standard requirements.

Core Hardness Control of Carburized Gears

Adjustment of Process Parameters for Vacuum Heat Treatment

The vacuum quenching and vacuum tempering of materials is the most important process in the heat treatment process, and it is also an extremely widely used process in many manufacturing industries. After understanding some basic knowledge of vacuum heat treatment, you will have a more comprehensive understanding of the role of vacuum quenching, coupled with vacuum tempering at different temperatures, can reduce the internal stress generated, and at the same time achieve the purpose of increasing strength. On the basis of the above vacuum carburizing process, the quenching temperature was strictly controlled to (890±10) °C, and the furnace load was reduced to 140 pieces per furnace, and then other parameters were kept unchanged. The adjusted vacuum heat treatment process After the smooth progress, the hardness of the core was tested. The specific test data shows that the adjustment of the vacuum heat treatment process parameters will indeed have a certain impact on the strength of the core. Especially after increasing the quenching temperature and reducing the furnace load, the hardness of the core has indeed increased, but there will still be insufficient hardness after heat treatment as analyzed above, and even deformation will occur. Due to the strength of the core of automotive gear parts It is difficult to achieve stable controllability, and it will cost a lot of money to manufacture again, which is a burden to the manufacturing industry itself. Therefore, control the parameters of the vacuum heat treatment process, strictly implement the requirements and standards for testing, and the expected test results will be obtained. The specific examples of adjusting the parameters of the heat treatment process include: the purpose of increasing the quenching temperature is to increase the transformation amount of supercooled austenite into martensite, thereby increasing the hardness of the core. And reducing the amount of furnace can increase the quenching intensity to some extent to increase the hardness of the core.

Adjustment of vacuum quenching cooling medium

Whether it is vacuum carburizing quenching, induction heating quenching or others, the heat treatment quality problems that may occur during the cooling process mainly include: insufficient hardness, unevenness, and insufficient depth after quenching; excessive hardness of the core after quenching, etc. Such quality problems in the manufacture of automotive gears are related to heat treatment and quenching cooling. It is also a good experimental method to adjust the appropriate cooling medium. For small and medium gears, insufficient quenching hardness is caused by insufficient cooling rate, which requires adjusting the cooling rate. The low quenching cooling rate will cause the gears to have quality problems such as insufficient hardness, unevenness or insufficient hardening depth. However, according to the actual quenching gear material, shape and other conditions and heat treatment process requirements, it will be automatically divided into several different temperatures and speeds. Case. Whether it is quenching oil or water-soluble quenching medium, it will be affected by many effects after being exposed to high temperature, which will cause changes in the medium to varying degrees. The water-soluble quenching agent can greatly promote the reduction of the low-temperature cooling rate of water. On the contrary, the water-soluble quenching liquid will gradually increase the low-temperature cooling rate. The deterioration of the cooling medium is an inevitable phenomenon. It may be due to the small amount of work that has just been added, and the degree of deterioration is not enough to cause a huge impact, and it cannot reflect the deterioration of the gear. However, in order to avoid the increase of the quenching amount, The degree of deterioration may reach more, which will have an inferior impact on the quality of the parts. It can be considered to directly use a cooling medium with a faster cooling rate, or to increase the stirring speed to control the progress of the entire system.

Optimization of material hardenability

Because the test results of the core hardness depend on parameters such as steel composition and material hardenability, and the core strength obtained from gears of different materials is also different. The hardenability of the material is often expressed by the depth of the hardened layer. The greater the depth, the better the hardenability, and the hardenability of the material is its own property, which only depends on its own internal factors. , regardless of external factors. The hardenability of steel for manufacturing automotive gears mainly depends on its chemical composition. Heating temperature and holding time are all factors that will affect it. In order to achieve stable control requirements for the hardness of the core of carburized gears, it is used to optimize the manufacturing process. The hardenability of the material is also improved. For example, try to expand the hardenability zone of the part from the original J9: 30 ~ 36HRC to J9: 33 ~ 38HRC.

Epilogue

In order to adapt to the competition mode of the times, considering the current market economic situation, stable product performance requires high technical indicators. After many tests and analysis of data, we know that it is necessary to adjust the vacuum heat treatment process parameters and adjust the vacuum quenching needs. Medium, improve the technical requirements in all aspects, but this can not achieve the control of the production process, you can choose to use the method of adjusting the hardenability zone of steel to stabilize the core hardness of the product. For the parameters used in automotive carburized gears, the requirements are very high, not only need to achieve a certain bending strength, but also need to have sufficient impact resistance. Under such a high standard requirement, it is beneficial to control and reduce the deformation during heat treatment, and to obtain high-quality gears in the continuous progress of the process.