JP2000054108A - Die for forging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a die high in hardness, excellent in wear resistance, impact resistance and thermal impact resistance and having a long service life, by heating the engraved face of a die to a specified temp. in an atmosphere of a gaseous mixture having a specified compsn. composed of hydrogen and ammonia, applying a specified d.c. voltage on the space between it and an anode provided in a vacuum chamber and forming a nitriding layer on the engraved face by using a bright nitrogen diffusing method. SOLUTION: The compsn. of a gaseous mixture is composed of 50 to 95% hydrogen and 5 to 50% ammonia, the heating temp. is 450 to 580 deg.C the d.c. voltage to be applied is 300 to 500 V. The nitriding layer on the outermost surface preferably has 800 to 1200 hardness by Vicker's hardness (loads: 100 gf). An upper die and a lower die are placed on a cathode in a vacuum chamber, which is exhausted, thereafter, heating is executed to a prescribed temp. in an atmosphere of a gaseous mixture, d.c. voltage is applied to the space between it and an anode to ionize the gas by glow discharge, nitrogen is diffused onto the surface of the die, and, after the treatment, natural cooling is executed. A radical nitriding layer 3C of about 30 to 300 μm is formed on the outermost surface of the engraved face 3B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forging die used for cold forging or hot forging a metal material. More specifically, by using a bright nitrogen diffusion method, a nitrocarburized layer having a higher altitude than before is formed on the engraved surface of a mold having a fine engraved pattern on the surface, abrasion resistance, impact resistance and The present invention relates to a forging die having excellent thermal shock resistance.

[0002]

2. Description of the Related Art In a forging die made of die steel or high-speed steel used for cold forging or hot forging a metal material, the engraved surface on which the metal material of the metal die is formed has a high degree. Defects such as wear and damage are liable to occur due to repeated severe forging operations. In conventional dies, quenching and tempering of the dies, nitriding and nitrocarburizing of the engraved surfaces of the dies have been performed to prevent the occurrence of these defects. However, in these treatments, the hardness of the engraved surface of the mold is insufficient, and the nitrogen compound constituting the nitrided layer is easily peeled off, so that the service life of the mold is extremely short and the productivity is poor. Was something. In addition, dies made of cemented carbide other than the above-mentioned die steel and high-speed steel are also used, but the price as a die material is high, and because it is brittle compared to die steel and high-speed steel, There are inconveniences such as inapplicability to a die for forging a product having a thin shape or a complicated shape, and improvement is required.

[0003]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention provides a sculptured surface having a higher altitude than before.
An object of the present invention is to provide a long-life forging die excellent in wear resistance, impact resistance and thermal shock resistance.

[0004]

According to a first aspect of the present invention, there is provided a forging die, wherein the engraved surface of the die is formed of 50-95% hydrogen and 5-50% hydrogen.
450-58 in a mixed gas atmosphere comprising ammonia
It is characterized by heating to 0 ° C., applying a DC voltage of 300 to 500 V between itself and an anode provided in a vacuum chamber, and forming a nitride layer on the engraved surface by using a bright nitrogen diffusion method.
In the forging die according to claim 2, the nitrided layer on the outermost surface of the engraved surface includes:
Vickers hardness (load: 100 gf) 800 to 1200
Characterized by having a hardness of

[0005]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the engraved surface of a mold (forged product and die) is produced using a bright nitrogen diffusion (hereinafter referred to as radical nitridation) method in which glow discharge is performed in a high-pressure hydrogen gas and ammonia gas atmosphere under reduced pressure. Abrasion resistance and impact resistance by forming a nitrided layer (hereinafter referred to as a radical nitrided layer) that has a higher altitude than conventional and has excellent adhesion to the steel base layer It was also found that a long life forging die excellent in thermal shock resistance was obtained.
Hereinafter, an embodiment is shown and the present invention is explained in detail.

FIGS. 1 and 2 show an example of a forging die according to the present invention. In FIG. 1, the forging die includes an upper die 2 and a lower die 3. When the upper die 2 and the lower die 3 contact the lower surface 2A of the upper die 2 and the upper surface 3A of the upper die 3, A forging space 4 surrounded by the engraving surface 2B and the engraving surface 3B of the lower mold 3 is formed.
Naturally, the shape of the forging space 4 is the same as the shape of the forged product. During the forging operation, a metal material to be formed is loaded into the forging space 4, high pressure is applied to the upper mold 2 and the lower mold 3 from above and below, and high pressure acts on the engraved surfaces 2B and 3B, so that the metal material is It is plastically worked into the shape of Thus, a high contact pressure with the metal material to be formed acts on the engraved surfaces 2B and 3B. When hot forging a metal material, a high-temperature metal material contacts the engraved surfaces 2B and 3B. For this reason, the engraved surface of the mold is subject to wear and damage due to high contact pressure, as well as cracks and fine cracks due to thermal shock and thermal fatigue.

In order to prevent the occurrence of the above-mentioned various defects, a conventional steel mold is subjected to a quenching and tempering treatment, or a nitriding treatment or a soft nitriding treatment is performed on the engraved surface of the mold. Although a hard nitrided layer was formed, it was worn in a short time due to insufficient hardness, or because the nitrided layer easily peeled off due to insufficient adhesion between the nitrided layer and the steel base layer, The service life as a forging die was extremely short.
The present invention is to obtain a long-life forging die by forming a radical nitride layer having higher altitude and toughness on the engraved surface of the die by using the bright nitrogen diffusion method.

FIG. 2 is a detailed sectional view of the lower mold 3 shown in FIG. A radical nitride layer 3C having a thickness of about 30 to 300 μm is formed on the outermost surface of the engraved surface 3B that comes into contact with the metal material to be formed. Although not shown, the upper mold 2
A radical nitride layer is also formed on the outermost surface of the engraved surface 2B.

Since the upper mold 2 and the lower mold 3 of the present invention are forging dies, it is preferable to subject the quenched and tempered die steel to a radical nitriding treatment, but the use of the die steel is not limited. Depending on the application, structural steel, case hardening steel, spring steel, high speed steel, stainless steel, etc. may be used, and in some cases, heat treatment such as quenching and tempering may not be performed before radical nitriding. .

Next, a method for forming a radical nitrided layer on the outermost surfaces of the engraved surfaces 2B and 3B of the upper mold 2 and the lower mold 3 of the present invention will be described. An upper mold 2 and a lower mold 3 made of SKD61 steel degreased and washed with an organic solvent or the like are placed on a cathode provided in a vacuum chamber, and the inside of the vacuum chamber is evacuated to about 10 ^-3 torr. In a mixed gas atmosphere consisting of
Heating is performed at 50 to 580 ° C., a DC voltage of 300 to 500 V is applied between the anode and the anode provided in the vacuum chamber, the gas is ionized by glow discharge, and nitrogen is diffused on the surface of the mold. The treatment time is about 1 to 30 hours, and then the mixture is naturally cooled in a nitrogen atmosphere or under reduced pressure. The Vickers hardness (load: 100 gf) 10
A nitrided layer having a hardness of not less than 00 and a thickness of 30 to 300 μm is obtained.

In the present invention, the temperature of the mold is set to 450 to 5
It needs to be heated to 80 ° C. If the temperature is lower than 450 ° C., the radical nitridation reaction is extremely slow. If the temperature exceeds 580 ° C., the nitride once formed is decomposed and radical nitriding does not occur. Electric heating, gas heating, or the like can be used as the heating means. The heating source can be placed inside or outside the vacuum chamber for performing the ion nitriding process, but when used in combination with an automatic control system, the programmed temperature rise and temperature maintenance can be automatically controlled.

As a gas for radical nitriding, a mixed gas of ammonia gas and hydrogen gas is used. Ammonia gas is decomposed into N and H and immediately becomes N ₂ and H ₂ , so that a radical nitridation reaction does not easily occur. However, the ammonia gas acts as an ammonia radical in a range where the plasma current density is low. The hydrogen gas acts as an auxiliary gas for stably performing the radicalization of the ammonia gas.

The NH ₃ / H ₂ volume ratio is from 1: 100 to 1: 0.
And preferably 1:10 to 2: 1. 1: 100
If it is less than 3, the radical nitriding reaction is not sufficient. If hydrogen gas is not supplied, H _{2 as an} auxiliary gas is generated by decomposition of NH ₃ , so that it does not easily act as ammonia radicals. Also,
An inert gas such as Ar gas can be added to stabilize the plasma.

The DC voltage is 300 to 500 with respect to the engraved surface.
The reason why V is applied is that glow discharge is effective for turning ammonia gas and hydrogen gas into plasma in this voltage range. If the voltage is less than 300 V, plasma cannot be sufficiently generated, and if it exceeds 500 V, a local overheating state occurs on the surface of the metal member, or effective radical nitriding treatment on the details of the engraved portion is not performed. Absent.

The vacuum chamber used for radical nitriding is
It is necessary to provide an electrode for glow discharge and a pipe for plasma gas, and an exhaust pipe connected to a vacuum pump. FIG. 3 shows a schematic diagram of a bright nitrogen diffusion method nitriding apparatus used for carrying out the present invention. The heater 20 is arranged in the outer wall of the vacuum chamber 10. A DC electrode 30 connected to a DC power supply 50 is provided inside the vacuum chamber 10.
Is arranged. An exhaust pipe 60 is connected to a lower portion of the vacuum chamber 10 and is connected to a vacuum pump 70 via a pressure adjusting valve 80. A nozzle 90 for supplying a source gas is inserted from above the vacuum chamber 10.
H ₂ gas, NH ₃ gas, and Ar gas supply sources are connected to the nozzle 90 via a mass flow controller 120, a valve 110, and an introduction pipe 100, respectively. The rectangular molds 2 and 3 made of SKD61 steel were placed on the DC electrode 30.

[0016]

EXAMPLE In one example of the present invention, heating was performed by the heating cycle shown in FIG. 4, the temperature was raised to 480 ° C. over about 1 hour, kept at a constant temperature for about 6 hours, and then kept at room temperature for about 4 hours. Cool down to As shown in FIG. 5, the gas composition in the vacuum chamber is changed in one to four periods. The first stage is a heating process, in which only gas is exhausted and no gas is supplied. The second stage is a cleaning process in which a gas composed of 100% hydrogen is supplied. The third stage is a nitrogen diffusion process in which a mixed gas consisting of 80% hydrogen and 20% ammonia is supplied.

In this third stage, 410 is provided between the upper mold 2 and the lower mold 3 which are the anode and the cathode provided in the vacuum chamber.
A direct current of V is applied, the gas is ionized by glow discharge, and nitrogen is diffused on the surface of the mold. The fourth stage is a cooling process, which is naturally cooled to room temperature in an atmosphere of 100% nitrogen or under reduced pressure.

Thus, as shown in FIG. 6, the outermost surface of the mold has a Vickers hardness (load: 100 gf) of 110.
0, and a nitrided layer from the outermost surface of the mold to a depth of 0.14 mm can be obtained. The hardness of the nitrided layer is 0.
Continuously reduced to a depth of 14mm and 0.09mm
Vickers hardness of 700 or more (load: 100
gf) is obtained. As described above, since the nitrided layer is harder and thicker than the conventional one and the hardness of the nitrided layer is continuously reduced, a nitrided layer having excellent adhesion to the steel base layer can be obtained.

[0019]

According to the present invention, the Vickers hardness (load: 100 g) is applied to the outermost surface of the engraved surface of the mold by using the bright nitrogen diffusion method.
f) A forging die on which a nitrided layer having a hardness of 800 to 1200 is formed. Since the nitrided layer is harder and thicker than in a conventional die, and the hardness of the nitrided layer is continuously reduced, steel Excellent adhesion to mother layer. Therefore, in the conventional mold, the number of times of forging was 2000 to 3000 times,
In the case of using the mold of the present invention, forging can be performed 4000 times or more, and the mold life can be obtained about twice as long as the conventional one.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a forging die according to the present invention.

FIG. 2 is a detailed sectional view of a lower die of an example of a forging die according to the present invention.

FIG. 3 is a schematic diagram of a bright nitrogen diffusion method nitriding apparatus used for carrying out the present invention.

FIG. 4 is a diagram showing an example of a heating cycle for radically nitriding a forging die according to the present invention.

FIG. 5 is a diagram showing an example of a gas composition for radical nitriding a forging die according to the present invention.

FIG. 6 is a diagram showing the relationship between the hardness of the nitrided layer and the thickness of the nitrided layer in one example of the forging die of the present invention.

[Explanation of symbols]

 2: Upper die 2A: Lower surface 2B: Engraved surface 3: Lower die 3A: Upper surface 3B: Engraved surface 3C: Radical nitride layer 4: Forging space

Claims (2)

[Claims] 1. The engraved surface of a mold is made of 50-95% hydrogen and 5%
45% in a mixed gas atmosphere consisting of ~ 50% ammonia
A forging die which is heated to 0 to 580 ° C., applies a DC voltage of 300 to 500 V between itself and an anode provided in a vacuum chamber, and forms a nitrided layer on an engraved surface using a bright nitrogen diffusion method. 2. The forging die according to claim 1, wherein the nitrided layer on the outermost surface of the engraved surface has a Vickers hardness (load: 100 gf) of 800 to 1200.