JPH0760063B2 - Gas atmosphere heat treatment furnace for metal parts - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas atmosphere heat treatment furnace for metal parts such as when quenching steel in a gas atmosphere.

[0002]

2. Description of the Related Art A furnace for heat-treating high carbon, high chrome steel, etc., using a carbon box, is conventionally known.

In the conventional carbon box furnace which has been commercially available, the heat-treating parts are mounted in the carbon box and the temperature is raised after the carbon lid is closed. The inside of the box is air. Then, due to the temperature rise, O ₂ in the air reacts with the inner surface of the carbon box and is consumed.

Therefore, in the air-encapsulation treatment method using a carbon box, it is necessary to adjust the carbon concentration of the heat-treated product. Therefore, the amounts of CO and CO ₂ must be sequentially measured and controlled.

[0005]

In the gas atmosphere heat treatment furnace of the present invention, N ₂ or Ar is used as an atmosphere instead of air. Water vapor in N ₂ or Ar (H
The amount of ₂ O) is 10 ppm when the dew point is −66 ° C., and O ₂
Since the amount is 2 ppm or less, which is a very small amount, it is not necessary to control such as an air encapsulation treatment method using air.
However, even with such a small amount of water vapor and oxygen in N ₂ ,
If it directly and continuously hits the surface of a metal component that is activated during heat treatment, it may lead to oxidation and decarburization of the steel of the metal component. The present invention solves such disadvantages and inconveniences.

[0006]

That is, the present invention relates to a muffle case made of carbon or graphite provided in a furnace through which a metal part subjected to a gas atmosphere heat treatment passes, and a means for heating the muffle case, Provided is a gas atmosphere heat treatment furnace for metal parts, which has a passage for guiding an inert gas of N ₂ or Ar into the muffle case from the outside of the furnace through a space between the muffle case and the furnace body. Is. Hereinafter, the present invention will be described in more detail by taking a steel quenching furnace using N ₂ as an example.

[0007]

EXAMPLE As shown in FIG. 1, a graphite tube 2 was used as a muffle case and installed in a heating furnace body 1.
A purge chamber 5 was provided at the inlet, a cooling chamber 8 was provided at the outlet, and doors 4, 6, 7, and 9 were attached to the respective partitions. The N ₂ gas is fed into the purge chamber 5, the inner inlet of the door 6 of the muffle case 2 and the heating furnace body through the valve 10 connected to the atmosphere gas supply source, and the respective amounts are adjusted by individual valves. I made it possible. A heating power transformer was connected to the terminal 12 provided on the muffle case. 3 is a metal part to be heat treated, and 11 is an atmospheric gas outlet.

The air in the muffle case 2 of the furnace body 1 having the above-described structure is opened to the purge chamber 5, the inner inlet portion of the door 6 and the heating furnace body by opening the N ₂ gas inlet valve.
By sending ₂ gases, the temperature was raised after the gas was replaced with N ₂ . The amount of N ₂ that was sent was 2 times 10 times the internal volume at the time of replacement.
0 minutes, thereafter squeeze the N ₂ gas feed Iriben which opens inwardly inlet portion of the purge chamber 5 and the door 6, by sending a N ₂ gas by feeding Iriben which opens into the main furnace body 1, The reactor pressure of N ₂ gas was adjusted to maintain a water column of 10 mm, and this amount was 1 on average.
m ³ / hour.

As mentioned above, water vapor (H ₂ O) in N ₂
The amount is 10 ppm when the dew point is -66 ° C, and the O ₂ amount is ₂ p.
pm or less, but nevertheless, when they directly and continuously hit the surface of the metal part activated during the heat treatment,
Induces oxidation and decarburization of steel of metal parts.

However, in the present invention, the heating furnace body 1
The N ₂ gas sent from the inflow valve opening inward hits the outer periphery of the heated muffle case 2 and is transformed before hitting the metal parts. H ₂ O and O _{2 in} this gas react with the carbon in the muffle case 2. H ₂

Therefore, N after reacting with the muffle case
Trace amounts of CO and H ₂ and ultra trace amounts of O ₂ are contained in the ₂ gases.
And H ₂ O are produced, both of which are extremely small amounts, and the oxidation and decarburization of the muffle case 2 itself are industrially negligible, and the reaction between the gas and carbon in the steel of the metal parts. Can be prevented. This is an excellent feature and effect of the present invention.

In order to quantitatively investigate these reactions,
_{CO, CO 2, H 2,} H 2 O is too small amount of accuracy can not be determined bad in normal gas measurement.

[0013] Therefore, an be determined by measuring the O ₂ partial pressure in the treatment atmosphere, it was measured O ₂ partial pressure in the atmospheric gas outlet 11 using zirconia oxygen analyzer. this is,
This is because if the O ₂ partial pressure in the atmosphere is low, it is possible to confirm that the above reaction has been performed, and the O ₂ partial pressure at this time is 10
It was ^-22 atm. Thus, since the O ₂ partial pressure was low, it could be confirmed that the above reaction was performed.

Further, in an atmosphere having an O ₂ partial pressure of 10 ⁻²¹ atm or less, the metal parts can be heat-treated without oxidation.
It is known that when the O ₂ partial pressure is 10 ⁻¹⁸ atm or less, the heat treatment can be performed without decarbonizing the carbon in the metal part, so that the N ₂ gas having an O ₂ partial pressure of 10 ⁻²² atm is non-oxidized,
It can be said that it is a non-decarburizing gas.

When SKD11 was heated at 1050 ° C. and air-quenched, the hardness was HRC61. Also SKH
6 was heated at 1240 ° C. and then air-cooled to obtain hardness HRC62. These hardnesses are the maximum hardnesses obtained when these metal materials are air-quenched, and if decarburized during heating, such hardnesses cannot be obtained. Therefore, it was confirmed that the heat treatment could be performed in the non-decarburizing atmosphere.

For further confirmation, when the material heat-treated in a gas atmosphere was cut and the structure thereof was examined under a microscope, decarburization was not observed. There was no oxide scale on the surface of the material, and it was also confirmed that the material was heat-treated in a gas atmosphere without oxidation.

[0017]

As is apparent from the above embodiments, according to the present invention, N ₂ is heated in a heated carbonaceous muffle case.
Alternatively, the metal part is subjected to a gas atmosphere heat treatment in an atmosphere of Ar gas, but the oxidizing or decarburizing impurity component brought into the atmosphere from outside the furnace by the metal part reacts with the inner wall of the muffle case and is non-oxidized, The atmosphere that is decarburized and sent into the muffle case also reacts with the outer wall of the muffle case before hitting the metal parts in the muffle case and also reacts with the outer wall of the muffle case to modify the impurities in advance. There are outstanding features.

As a result, the atmosphere is maintained under the inert atmosphere of non-oxidation / decarburization all the time, and the excellent effect that the metal parts can be heat-treated in the atmosphere without oxidation / decarburization is brought about.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view of an atmospheric heat treatment furnace according to the present invention.

[Explanation of symbols]

 1-Heating furnace body 2-Muffle case 3-Heat treatment parts 4-Inlet door 5-Purge chamber 6-Inlet partition door 7-Outlet partition door 8-Cooling chamber 9-Outlet door 10-Atmosphere gas inlet valve 11-Atmosphere gas outlet 12-Heating current terminal

Claims (1)

[Claims] 1. A carbonaceous muffle case provided in a furnace through which a metal part to be heat-treated in a gas atmosphere passes, a means for heating the muffle case, and an inert atmosphere gas in the muffle case. A gas atmosphere heat treatment furnace for metal parts, which has a passage that is guided from the outside through a space between a muffle case and a furnace body.