JPS63213652A - Method for carbonitriding gear - Google Patents

Abstract

PURPOSE:To prevent the chipping of a gear due to the unnecessary thickening of a layer affected, by nitriding when the surface of the gear is carbonitrided and quenched to carry out surface hardening, by carburizing the surface of the gear before the carbonitriding. CONSTITUTION:A gear 10 to be treated is put in a carburizing furnace 2, a carbon enriched gas is fed and the gear 10 is heated at about 900-930 deg.C to carburize A the surface. A door 7 is opened and the gear 10 is sent to a carbonitriding furnace 3. After the internal pressure of the furnace 2 is made higher than that of the furnace 3, a nitriding gas such as ammonia is fed into the furnace 3 and the surface of the gear 10 is carbonitrided B at about 800-870 deg.C. A door 8 is opened and the gear 10 is sent to a preparation chamber 4, put in a quenching vessel 5 and quenched C. Since high hardness is provided only to a very thin surface layer of the gear 10, the chipping of the gear 10 due to the unnecessary thickening of a hardened layer can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for carburizing and nitriding gears, particularly gears such as transmission gears used under high surface pressure.

BACKGROUND ART Conventionally, carburizing and nitriding of gears have been carried out in the same furnace chamber 2 using a heat treatment furnace 1 as shown in FIG.

That is, enrich gas and nitriding additive gas are supplied together with carrier gas, or nitriding additive gas is supplied during carburization.

Problems to be Solved by the Invention When using the above-mentioned former method, FIG. 6 shows an enlarged view of the gear tooth portion 11 of the human body 10 to be burned, FIG. 7 (A) shows the state of the hardened layer 12, As shown in (b), the nitrided affected layer becomes deeper.

This nitrided affected layer has a lower M transformation point than the carburized layer and is easier to harden, so the fact that the nitrided affected layer is deeper means that
High hardness portion of the hardened layer 12 of the gear tooth portion 11: The hardened layer 12 of the gear tooth portion 11 becomes unnecessarily thick, and there is a gap that causes chipping 13.

According to the latter method of supplying the nitriding additive gas during carburization, the nitriding influence layer can be made shallow, but it is difficult to stabilize the furnace air after the supply of the nitriding additive gas starts. However, there is a problem in that the quenching state varies greatly from heat treatment loft to loft. Therefore, in order to allow for variations in the quenched state, it remains necessary to set the nitriding-affected layer to be thick in advance.

Means for Solving the Problems Two continuous furnace chambers are provided, the two furnace chambers are shielded so that they can be opened and closed, and the material to be hardened is first carburized at a high temperature in the first furnace chamber, and then the material to be hardened is transferred to the second furnace chamber. While moving, carburizing and nitriding is performed in a shielded second furnace chamber at a temperature lower than the carburizing temperature, followed by quenching.

Operation Because carburizing and nitriding is carried out in a dedicated carburizing and nitriding furnace chamber that is openable and closably shielded from the carburizing furnace chamber, the furnace air can be stabilized easily and accurately by starting the supply of the nitriding additive gas.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a heat treatment furnace 1, in which 2 is a carburizing furnace chamber, 3 is a furnace chamber exclusively for carburizing and nitriding, and 4 is a semi-compartment equipped with a quenching tank 5. 6, 7, 8.9 are each furnace chamber 2, 3.4
It is equipped with a door that opens and closes and can be raised and lowered freely. 10
&'i It is a material to be hardened such as gears.

Next, the heat treatment of the material to be quenched 10 will be explained.
Carburizing A is carried out at a suitable temperature in the range of °C.

Thereafter, as the door 7 is opened and closed, the 10 materials to be quenched are moved from the carburizing furnace chamber 2 to the carburizing/nitriding furnace chamber 3, which is shielded from the carburizing furnace chamber 2.

After this movement, the furnace pressure in the carburizing furnace chamber 2 is made higher than the furnace pressure in the carburizing-nitriding furnace chamber 3, and then an additive gas for nitriding, such as ammonia gas, is supplied to this dedicated furnace chamber 3.

As a result, the furnace air in this dedicated furnace chamber 3 becomes a carrier gas, an enrich gas, and a nitriding additive, and the material to be quenched becomes
0 is about 8000C to 870°C lower than the carburizing temperature
Carburizing and nitriding B at a suitable temperature in the range of .

Subsequently, the material to be hardened 10 is moved to the preparation chamber 4 as n8 is opened and closed, and there, it is placed in the hardening tank 5 and hardened C is applied thereto.

The hardened material 10 treated in this way is shown in FIG. 3, which shows an enlarged view of the gear teeth 11 and its hardened layer 12, and in FIGS. 4 (a) and (b), which show the state of the hardened layer 12. As shown in Figure 2, since the nitriding-affected layer is formed shallowly, only the very surface layer has high hardness.

Effects As described above, according to the present invention, carburizing is carried out in a dedicated carburizing and nitriding furnace chamber that is shielded from the carburizing furnace chamber so that it can be opened freely.
The furnace atmosphere can be easily stabilized with high precision by starting the supply of nitriding additive gas. Therefore, only the outermost layer can be hardened to high hardness with little variation in the hardening state from heat treatment lot to lot, thereby preventing chipping of the gear teeth.

[Brief explanation of the drawing]

1 to 4 show embodiments of the present invention, and FIG. 1 is a cross-sectional plan view of a heat treatment furnace. Figure 2 is a temperature-hour diagram of heat treatment. FIG. 3 is an enlarged sectional view of the gear teeth. FIG. 4 is an explanatory diagram of the hardened state. 5 to 7 show a conventional example, and FIG. 5 is a cross-sectional plan view of a heat treatment furnace. FIG. 6 is an enlarged sectional view of the gear teeth. FIG. 7 is an explanatory diagram of the hardened state. (Explanation of symbols) 2...First furnace chamber (carburizing furnace chamber) A...
Carburizing. 3... Second furnace chamber (furnace chamber dedicated to carburizing and nitriding) B...-
...Carburizing and nitriding.

Claims (1)

[Claims] Two continuous furnace chambers 2 and 3 are provided, and the two furnace chambers are shielded so as to be openable and closable. First, high-temperature carburizing A is performed in the first furnace chamber 2, and then the material to be hardened 10 is moved to the second furnace chamber 3. A carburizing/nitriding method for gears, characterized in that carburizing/nitriding B is carried out at a temperature lower than the carburizing temperature in a shielded second furnace chamber 3, and then quenching C is carried out.