JP2833051B2 - Vacuum heat treatment method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heat-treating an article to be treated by heating it in a vacuum, and more particularly to a vacuum heat-treatment method for obtaining a heat-treated article having brilliancy.

[Prior art] Normally, heat-treated products quenched in an atmospheric furnace or an atmosphere furnace are:
Generally, annealing or tempering is performed in a similar atmosphere furnace or atmosphere furnace as it is, and an oxide scale adheres to the obtained heat-treated product, and the surface has no glitter. Similarly, a heat-treated product annealed in an air furnace or an atmosphere furnace is generally tempered in an air furnace or an atmosphere furnace, and the surface of the obtained heat-treated product has no glitter.

By the way, recently, there is an increasing demand for bright heat treatment to heat-treat stainless steel and other steel products to produce a bright heat-treated product. For this purpose, the entire heat treatment process must be performed, especially with a low dew point or strong reducing atmosphere. It has to be carried out in a furnace having a reduced atmosphere, and there is a problem that time and cost are increased, for example, seasoning of the furnace body for a long time to lower the dew point and use of a large amount of atmosphere gas for a long time.
It is also conceivable that all the steps of the heat treatment are performed in a vacuum furnace. However, maintaining the vacuum for a long time increases the operating cost, and occupying the vacuum furnace for a long time lowers the equipment rotation rate, which is not preferable.

Therefore, a heat treatment product with a scale that has been subjected to general quenching or annealing in the above-mentioned atmospheric furnace or atmosphere furnace is heated to about 900 ° C. in a vacuum furnace under vacuum, and tempering and annealing are performed in the latter half of the heat treatment. Although it is conceivable that in this case, the large scale can be removed by the vacuum heat treatment, but the surface does not reach the brilliancy.

[Problems to be solved by the invention]

An object of the present invention is to solve the above-mentioned conventional problems and to provide a vacuum heat treatment method capable of performing a bright heat treatment in a short time and economically.

[Means for solving the problem]

Thus, the vacuum heat treatment method of the present invention heats an article to be treated having an oxide scale adhered to a surface thereof in a vacuum-evacuated furnace according to a heating curve corresponding to a predetermined heat treatment, and the article to be treated is heated by the heating curve. At an appropriate time while being maintained at the above predetermined high temperature, argon gas and hydrogen gas are supplied into the furnace, a DC glow discharge is generated using the object to be treated as a cathode, and argon ions and hydrogen ions are generated. It is characterized in that the surface of the article to be treated is made bright by sputtering.

In the present invention, as the article to be treated having the oxide scale adhered to the surface, a product or material that has been subjected to a treatment such as quenching, annealing, carburizing, or nitriding in an atmospheric furnace or an atmospheric furnace can be used.

In the present invention, the heating of the article to be processed in the vacuumed furnace may be performed according to a heating curve according to a predetermined heat treatment such as annealing, tempering, normalizing, and quenching. The direct current glow discharge using the article to be treated as a cathode may be performed at an appropriate time during the heating curve after the article has been heated and maintained at a predetermined high temperature.

[Action]

In the vacuum heat treatment method of the present invention, the large oxide scale attached to the workpiece is released by the vacuum heating in the furnace, and the ionized hydrogen ions and argon ions are reduced by DC glow discharge in the presence of argon gas and hydrogen gas. Since it collides with the surface of the article to be processed and spatters the iron oxide on the surface of the article to be scattered, a heat-treated article having a bright surface can be obtained. The DC glow discharge is performed while the article to be processed is maintained at a predetermined high temperature on a heating curve corresponding to the heat treatment, so that a stable glow discharge can be performed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

1 and 2 show an example of the apparatus used in the present invention. In the figures, 1 is a steel furnace shell, 2 is an anode also serving as a graphite heat insulating material, and 3 is formed in the anode. The heating chamber 4 is a stainless steel cathode, the base of which is fixed to the furnace shell 1 via an insulator 5. Reference numeral 6 denotes an article to be processed attached to a mounting jig, and reference numeral 7 denotes a graphite hearth on which the article 6 to be processed is mounted, which is fitted to the upper end of the cathode 3. Reference numeral 8 denotes a graphite rod heater, which is connected to an AC power supply 9 and generates heat by resistance heating to heat the workpiece 6 mainly by radiant heat. Reference numeral 10 denotes a graphite processing gas supply. A plurality of gas manifolds are provided in parallel above the article to be processed 6, and have a plurality of outlets for blowing out the processing gas toward the article to be processed 6, and are connected to the processing gas supply source 11. ing. A vacuum pump 13 is provided in an exhaust port 12 provided in the furnace shell 1.
Is connected, and a DC power supply 14 is connected between the anode 2 and the cathode 4. Reference numeral 15 denotes a gate valve-type entrance door, and reference numeral 16 denotes a pneumatic cylinder for driving the door up and down. A quenching chamber 20 is provided adjacent to the ion carburizing (plasma carburizing) furnace 17 having the above configuration, and forms an ion carburizing (plasma carburizing) apparatus 30 as a whole. Reference numeral 21 denotes an oil tank for quenching, reference numeral 22 denotes an elevating frame driven by an elevating cylinder 23, and reference numeral 24 denotes a conveying fork for conveying an article to be processed, which moves transversely to the elevating frame 22.

Example 1 In an atmosphere furnace not shown, 65
The workpiece 6 consisting of a bearing part made of SNCM815 having an oxidation scale layer having a thickness of about 0.1 mm adhered to the surface of the workpiece 6 by annealing at 0 ° C. × 2 hours by a transport fork 24 in the ion carburizing apparatus 30 shown in FIG. It is placed on the hearth 7 of the ion carburizing furnace 17, the door 15 is closed and the inside of the furnace is evacuated to about 0.5 to 10 Torr,
Electric current was supplied to the heater 8 to heat the workpiece 6 to 800 ° C. in vacuum. During this holding time at 800 ° C. (1.5 hours), a mixed gas of argon and hydrogen is supplied from the processing gas supply source 11 to the gas manifold 10 and blown out from the outlet thereof into the heating chamber 3 so that the anode 2 and the processing target are processed. Glow discharge was generated between the articles 6 for about 10 minutes to perform sputtering by low-temperature plasma, thereby removing iron oxide on the surface of the article 6 to be treated. After the elapse of the heating and holding time, the article to be treated 6 is transferred to the transport fork 24
And quenched at a predetermined cooling rate by immersion in an oil tank 21 for quenching and oxidation. As a result, an oil-quenched product (heat-treated product) having a bright surface was obtained.

Example 2 In an atmosphere furnace (not shown), a gas carburizing treatment was performed at 870 ° C. for 5 hours, and an object to be treated 6 consisting of gears made of SCM420 having an oxide scale layer having a thickness of about 0.1 mm adhered to the surface thereof was vacuumed. Except that the heating temperature was 850 ° C. and the heating holding time was 1 hour, vacuum heat treatment and spattering were performed under the same conditions as in the first embodiment, and then oil quenching was performed as in the first embodiment. A carburized and quenched product (heat-treated product) having a bright surface was obtained.

Example 3 In an atmosphere furnace (not shown), a gas carburizing treatment was performed at 920 ° C. for 30 hours, and an object to be treated 6 consisting of a bearing part made of SNCM815 having an oxide scale layer having a thickness of about 0.15 mm adhered to the surface was treated. Except that the vacuum heating temperature was 650 ° C. and the heating holding time was 1 hour, vacuum heating treatment and sputtering were performed under the same conditions as in the first embodiment, and then annealing was performed by gradually cooling in the ion carburizing furnace 17. Where I learned
A carburized and quenched product (heat-treated product) having a bright surface was obtained.

The present invention is not limited to the above embodiments,
For example, as the article 6 to be processed before the vacuum heating, a product or material subjected to a process other than the above may be used, and the vacuum heating and the subsequent process may be a heat treatment method other than the above. The apparatus used in the present invention is also a quenching chamber.
It is also possible to use an apparatus not provided with 20, an ion nitriding furnace (plasma nitriding furnace), an ion carbonitriding furnace that performs ion carburizing and ion nitriding alone or simultaneously.

〔The invention's effect〕

As described above, according to the present invention, a heat treatment curve corresponding to a predetermined heat treatment is applied to an article to be treated with an oxide scale in which a part of the heat treatment or a pretreatment is performed in an atmospheric furnace or an atmospheric furnace. Since it is sufficient to perform a DC glow discharge at an appropriate time during the maintenance of the vacuum heating and the predetermined high temperature on the heating curve, the processing time in the vacuum furnace may be short, and may be shorter. The amount of gas used during the glow discharge is small, and the vacuum heating for removing the large oxide scale adhering to the workpiece and the high-temperature heating for stabilizing the glow discharge (and thus spattering) are all performed at the predetermined temperature. Since the heating for the heat treatment is used, the surface of the article to be treated can be made bright during this heat treatment step, and the bright heat treatment can be performed economically in a short time.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of an ion carburizing apparatus used in the present invention, and FIG. 2 is a sectional view taken along line AA of FIG. 1 ... furnace shell, 2 ... anode, 3 ... heating chamber, 4 ... cathode,
6 ... processed object, 8 ... heater, 9 ... AC power supply, 10 ...
... gas manifold, 11 ... processing gas supply source, 13 ... vacuum pump, 14 ... DC power supply, 17 ... ion carburizing furnace, 20 ...
… Quenching room, 30… Ion carburizing equipment.

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Claims (1)

(57) [Claims] An object to be treated having an oxide scale adhered to a surface thereof is heated in a vacuum-evacuated furnace according to a heating curve according to a predetermined heat treatment, and the object to be processed is heated to a predetermined height on the heating curve. At an appropriate point in time while the temperature is maintained, argon gas and hydrogen gas are supplied into the furnace, a DC glow discharge is generated using the workpiece as a cathode, and the workpiece is sputtered with argon ions and hydrogen ions. A vacuum heat treatment method, characterized in that the surface of the product is made bright.