Internal spline gear heat treatment deformation control

Our company is a professional manufacturer engaged in the processing of automobile transmissions and front and rear axle gears. Among them, there are more than ten varieties of gears with internal splines, including the middle five-speed gear of 255 transmission, two gears exported to Italy and most recently. Developed more than ten kinds of gears exported by Aike. During the processing of these products, there is often a problem of excessive deformation of the workpiece after heat treatment carburizing and quenching. When the gear cross-bar distance is measured in the subsequent cutting process, the span distance exceeds the required range, or when the integrated plug gauge is used, the plug gauge cannot pass. When the spline diameter is measured by the large-diameter spindle, the taper mandrel passes. However, or the quality problem of wearing it completely. Faced with this situation, while increasing the control of raw materials and optimizing the hot and cold processing technology, the company focused on systematic analysis and discussion of the production process of such gear heat treatment , and found measures to reduce gear heat treatment deformation. Has achieved good results.

The influence and control of raw materials on deformation

The metallurgical quality of gear steel not only affects the mechanical properties of the gear, but also has a great influence on its fatigue performance, and also plays a key role in the cold and hot processing performance of the gear manufacturing process.

Chemical composition

The carbon content of the gear steel and the chemical composition of the alloying elements shall comply with the national regulations for automotive gear steel. The oxygen content of the steel is wO<0.002%. The allowable deviation of the chemical composition of the steel should comply with the relevant provisions of the national standard. The allowable deviation of the aluminum element is ±0.005%, and the allowable deviation of the sulfur element is ±0.005%.

2. Steel smelting method and delivery status

The metallurgical quality of gear steel is particularly important for the purity, hardenability and original structure of the steel. The main factor affecting the purity of steel is the oxygen content. Vacuum degassing and smelting has obvious effects on purifying steel. The smelting method of our company's steel is smelted by electric furnace or converter, and is vacuum degassed. The steel is delivered in hot-rolled slow-cooling state, and the delivery hardness is not more than 200-220HBW.

3. Low-magnification of steel

In the low-magnification structure of the gear steel, after the acid cross-section of the cross-section, the low-density test piece cannot have visually visible shrinkage cavities, bubbles, cracks, inclusions, peeling, white spots and residual dendrites. The specific acid leaching low-magnification organization is based on the national standard: the three types of center loose, general loose and ingot segregation should not be greater than level 2.

4. Inclusions

In the high-strength state, the fatigue strength of steel for gears decreases rapidly with the increase of the content of non-metallic inclusions, and also decreases with the increase of the size of inclusions (mainly oxides), and with steel The strength is increased, and the inclusions increase the extent of the fatigue strength of the steel. Non-metallic inclusions in steel are classified into sulfides (class A), aluminas (class B), silicates (class C), spheroidal oxides (class D), and single-particle spheroids (Ds). In the five categories, the grades selected for our company's steel meet the requirements shown in Table 1.

Table 1 Steel non-metallic inclusion selection level

5. Grain size

The austenite grain size of steel is an important structural parameter in metal materials, which has a great influence on the quenching cracking and distortion tendency of steel. The fine and uniform austenite grains can effectively stabilize the hardenability of the gear steel, and reduce the heat treatment deformation, especially the anti-brittle breaking ability of the carburized steel. The grade of grain size is divided into 15 grades, of which grades 1 to 5 are coarse grains and grades 6 to 15 are fine grains. The greater the grain size, the greater the tendency of steel to quench cracking and distortion. Our company has a grade of 6 to 10 grades for the austenite grain size of steel (carburizing method). In particular, if the phenomenon of mixed crystals occurs in steel, the structural strength of the steel will be drastically reduced and the stress concentration zone will become brittle. Therefore, when using steel, it is necessary to prevent the occurrence of mixed crystals.

6. Banded tissue

The band structure is that the ingot forms dendritic segregation during solidification and then is formed during the rolling process. Such a banded structure is particularly prone to form severe mixed crystals, and at the same time, segregation of the steel component causes uneven quenched martensite, retained austenite, and different effective hardened layers and hardness. When the band structure is severe, the machinability of the steel is poor, and the thermal deformation fluctuates greatly. The strip structure of our company's steel samples after normalizing is ≤2.

7. End hardenability

The end hardenability of steel is mainly determined by its chemical composition. The hardenability of steel mainly includes two aspects: First, the hardenability of steel. It mainly guarantees the hardness of the core of different gears to meet the requirements of gear contact fatigue strength and bending fatigue strength; on the other hand, the width of the hardened belt. The width of the hardened strip as small as possible is very beneficial to the control of the heat treatment deformation of the gear, especially for mass-produced gears. In the newly revised GB/T 5216 standard, the hardenability bandwidth has been reduced from the original 12HRC to 8HRC. After testing and verification, the heat treatment specification and end hardenability of a steel SAE8620H commonly used by our company meet the requirements shown in Table 2.

Table 2 End hardenability of steel

The catalyst is a deoxygenation catalyst supported by precious metal (palladium) on active alumina. It is mainly used for deoxygenation in hydrogen and hydrogenation and deoxygenation of inert gases such as nitrogen, nitric oxide, nitrogen dioxide and argon.

Project parameters

High diameter ratio of catalytic reaction                               â‰¥3

The use of temperature                                                     80-280 degrees

Use the space velocity                                                     (5000~10000)hr-1  

Oxygen content of air source                                              â‰¤2% 

The residual oxygen content of the gas after purification       â‰¤1ppm

Particle size (mm)                                                              2 ~ 3 or 3 ~ 4 Φ

Bulk density (g/L)                                                              ≥680

Mechanical strength                                                           â‰¥95N

The service life of the                                                         â‰¥3year

Product features:

1. Precious metal (palladium) - semiconductor system, high catalytic performance;
2. No activation regeneration, no pretreatment for first use;
3. Deep purification, with residual oxygen less than 1ppm;
4. Strong anti-poisoning ability, especially excellent anti-virus ability for H2S, SO2, CI2, NH3, etc.;
5. High temperature, 650 ℃ not ablation (similar products up to 450 ℃);

6. High strength, no pulverization, continuous use activity for many years;

Usage method and matters needing attention

1. The catalyst is evenly loaded into the reactor and the air in the system is drained with nitrogen.
2. Enter the gas to be purified, and it can be put into use;
3. Use after a certain period of time, once the catalytic deoxidization effect decline or soaked by water fails, can be heated to 200 ℃ or so regeneration;
4. Using temperature is 450 ℃;
5. The catalyst should avoid contact with chlorides, sulfides, etc., in case of poisoning failure.

Palladium Catalyst

Palladium Catalyst,Palladium Chloride Catalyst,High Palladium Catalyst,Palladium Catalyst Capacity

Zhejiang Changxing Haihua Chemical Co.,Ltd. ,