Influence of vacuum heat treatment on tooth surface structure

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Advantages of vacuum heat treatment

Automobile transmission manufacturers have clear regulations on decarburization of gear teeth. Decarburization may cause problems such as low tooth surface hardness and non-martensitic structure on the tooth surface, which seriously affects the normal use of gears. Therefore, it is necessary to control the degree of gear decarburization during vacuum heat treatment of gears (vacuum carburizing-vacuum quenching, vacuum tempering). Different from conventional controllable atmosphere carburizing and quenching heat treatment (different, this part is vacuum heat treatment, adopts low-pressure vacuum carburizing, high-pressure N₂ quenching process, the part is always in a vacuum state, no internal oxidation occurs, and avoids oxidation due to oxidation during carburizing. Non-martensite and other undesirable structures caused by the atmosphere. In addition, the vacuum heat treatment carburizing temperature is high, and the parts have high surface activity, thereby reducing the carburizing time, and high-pressure N₂ vacuum quenching; at the same time, the content of retained austenite can be reasonably controlled to obtain good Tooth surface structure; no exhaust gas, environmental protection and energy saving.

Influence of Vacuum Heat Treatment on Tooth Surface Structure

The forging blank of parts adopts hot forging + cold finishing process. After forging, the combined teeth are no longer machined. After the gear teeth and end faces are processed, low-pressure vacuum carburizing + high-pressure N₂ vacuum quenching is carried out as a whole. Therefore, the decarburization problem caused by the combined teeth during the forging process will directly affect the vacuum carburizing. Microstructure and performance of gear teeth after quenching.

The decarburization of the tooth surface has a direct impact on the generation of non-martensitic structure on the tooth surface after heating, and has no obvious effect on the effective hardened layer depth of the tooth surface and the hardness value at 0.05 mm on the subsurface. Comparing the tooth surface structures before and after heating, it can be seen that the depth of the decarburization layer directly affects the depth of the non-martensitic structure of the tooth surface after heating; it also affects the depth of the effective hardened layer on the tooth surface and the hardness value at 0.05 mm on the subsurface. But it is not obvious; the generation of non-martensitic structure is mainly due to the decrease of surface hardenability, except for the effect of carbon element, it is mainly the effect of alloying elements.

The conclusion of the effect of vacuum heat treatment on tooth surface structure

(1) The non-martensitic structure will not be produced after vacuum carburizing heat treatment on the gear tooth surface without decarburization;

(2) The decarburization depth of the tooth surface is directly related to the generation of non-martensitic structure on the tooth surface after vacuum heat treatment, and has no obvious effect on the hardness value at the subsurface (0.05 mm) of the tooth surface and the effective hardened layer depth of the tooth surface;

(3) The formation of non-martensitic microstructure after heating in the decarburized layer area is mainly due to the loss of alloying element Mn.

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