JPH1081949A - Formation of film on base material surface and metallic mold for press working - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve adhesion between a base material and a super hard film by forming an intermediate layer having a specific composition on a surface of a metallic mold in advance, forming the super hard film thereon and subjecting them to heat treatment under a specific condition at the time of forming the super hard film on the surface of the metallic mold for press working by a vacuum thermal spraying method. SOLUTION: A thermal-sprayed film 105 is formed on a metallic mold base material surface 104 by discharging electricity between an anode nozzle 101 of a plasma thermal- spraying gun and a cathode 102 made of W (tungusten) in an evacuated chamber in a vacuum state to generate a plasma jet on a punch part surface 104 of the metallic mold for press working and supplying thermal spraying material powder therein. In this case, an intermediate thermal spraying layer made of alloys such as Ni-Cr and Ni-Al is formed on the base material surface and a film made of W-12% Co as the super hard layer is formed thereon by thermal spraying. Then, heat treatment in which these two layers are held at 1000 deg.C for 1.5 hours under reduced pressure, are cooled by gaseous nitrogen, are held at 500 deg.C for 1 hour and then are cooled by gaseous nitrogen, is executed. Thus, the super hard film 105 excellent in close adhesion can be formed on the metallic mold base material surface 104.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for improving the adhesion between a coating formed by a thermal spraying technique and a base material by a heat treatment so that a high adhesion between the treated coating and the base material is required. The present invention relates to a surface modification technology that can be applied to surface modification of deep drawing dies and the like.

[0002]

2. Description of the Related Art Recent advances in thermal spraying technology have been remarkable, and new thermal spraying technologies such as low-pressure plasma spraying, Jet-Kote method or D-Gun method have been developed one after another, and the characteristics of sprayed coatings have been dramatically improved. As a result, the application range of thermal spraying technology for surface modification of materials has been significantly expanded.

[0003] The thermal spraying technique has features that are not present in other film forming methods, such as being capable of forming a thick film of several hundred µm in a very short time and being capable of thermal spraying a large-area material surface. Therefore, the demand for applying such a thermal spraying technique to the surface modification of a press die or the like has been remarkably increased in recent years.

[0004]

However, the biggest disadvantage of the thermal spraying technique is that it is improved as compared with the conventional technique, but it is harder than the conventional techniques such as hard chromium plating, diffusion infiltration treatment, PVD and CVD. Poor adhesion, which is the biggest reason preventing its application in this field.

[0005] For example, in the case of a press die, a die exchanging operation by a press machine is not easy, and requires considerable labor and time. Therefore, the shorter the life of the mold, the more frequently the mold needs to be replaced, and the shorter the operation time of the press machine, and the higher the production cost.

There is also a hard film treatment method by thermal CVD, but the heat treatment temperature is about 1200 ° C.
The materials used are also limited. That is, a hard film processing method by thermal CVD cannot be used for SKD11 generally used as a mold material.

[0007] The present invention focuses on such a problem, and it is easy and simple to apply the reduced pressure plasma spraying technique, which is one of new spraying techniques, to the surface modification of a base material such as a press die. It is an object of the present invention to obtain a low-cost, ultra-hard and highly wear-resistant film or a press die on which the film is formed.

[0008]

According to the first aspect of the present invention, an ultra-hard coating is formed on a surface of a base material requiring ultra-hardness by vacuum plasma spraying under predetermined conditions. This is a method of forming a base material surface film. The condition referred to here is that the pressure value in the decompression chamber is 6.7 × 10
³ Pa, spray current value is 500 A, spray distance is 400 mm
It is. Plasma spraying has various advantages because it is performed in a vacuum chamber that is isolated from the atmosphere. That is,
Oxidation and nitridation of the sprayed material are prevented, a clean film can be formed, non-oxidizing thermal spraying of active metals and carbides can be performed, a low-porosity, high-density film can be formed, base material surface Can be sufficiently preheated without being oxidized, so that a film having good adhesion can be formed.

FIG. 10 shows the effect of the combination of the chamber pressure and the spray current on the hardness of the hard coating. The vertical axis indicates Vickers hardness, and the horizontal axis indicates the chamber pressure value. The vertical axis indicates the changing state when the spray current is changed from 400 A to 700 A. As is apparent from this figure, in order to form the hardest film, the combination of the pressure value in the decompression chamber and the spray current value is optimal.

FIG. 11 shows that the chamber pressure is 6.7 × 10
^It shows the effect of the spray distance on the hardness of the hard coating when the spraying current is ³ Pa and the spray current is 500 A. The vertical axis indicates Vickers hardness and the horizontal axis indicates the spray distance. As is clear from this figure, to form the hardest film, the spraying distance is optimally 400 mm.

As a method of forming a superhard coating, there is a high-speed frame spraying in addition to the plasma spraying, but in the latter case, the above condition is different.

[0012] According to the second aspect of the present invention, the surface of the base material for which wear resistance is required is subjected to WC-C
o A method of forming a base material surface film, which comprises performing a heat treatment of a predetermined content for enhancing the adhesion between the base material and the super hard film after forming the superhard film.

The content of the heat treatment here is a vacuum heat treatment, and the degree of vacuum is 1.06 × 10 ⁻² Pa. By performing the vacuum heat treatment in this manner, oxidation of the hard coating is prevented.

The heat treatment is performed under the above-described vacuum for 100 hours.
After 1.5 hours at 0 ° C., the mixture was cooled with N ₂ gas.
After 1 hour at 500 ° C., it is cooled with N ₂ gas. By this heat treatment, a diffusion layer is formed at the interface with the hard coating,
The bonding strength with the hard coating is improved. This heat treatment also has the meaning of quenching and tempering.

According to the third aspect of the present invention, a composite coating is formed on the surface of the punch portion of the press die, and the composite coating is formed by low-pressure plasma spraying under predetermined conditions. And a heat treatment having a predetermined content. The ultra-hard coating is a WC-Co super-hard coating. It is. The specific conditions and contents are as follows.

As the thermal spray powder of the intermediate layer, Ni (80
%)-Cr (20%) is used. Ni (95%)
This is because hardness and wear resistance are superior to the case where -Al (5%) is used. By forming the intermediate layer on the surface of the punch portion, thermal stress between the surface of the punch portion and the hard coating can be reduced.

The punch is preheated at 300 ° C.
Chamber pressure is 10.0 × 10 ³ Pa, spraying current is 7
An intermediate layer is formed under the conditions of 00A and a spray distance of 400 mm. As the main gas in the plasma spray gun at that time,
Ar gas is introduced at a flow rate of 50 l / min, and H ₂ gas is introduced at a flow rate of 10 l / min as an auxiliary gas. This is the optimum condition for the intermediate layer.

A hard coating is formed on the intermediate layer. The thermal spray powder of the hard coating is WC-Co, and the ratio of Co is not limited, but may be, for example, 12%. At the time of thermal spraying of the hard coating, the chamber pressure is 6.7 × 10 ³ Pa and the thermal spraying current is 500, similar to the condition of claim 1.
A, The spray distance is 400 mm. The main gas and the auxiliary gas in the plasma spray gun are A
The flow rate of the r gas is 50 l / min, and the flow rate of the H ₂ gas is 10 l / min. By such processing,
A film hardness of about Hv1200 which is generally called a super hard film
A WC-Co film is formed.

The content of the heat treatment is a degree of vacuum 1.06 ×
This is a vacuum heat treatment of 10 ⁻² Pa, in which heat treatment is performed at 1000 ° C. for 1.5 hours, cooled with N ₂ gas, and then heat treated at 500 ° C. for 1 hour and cooled with N ₂ gas. The present invention
The reduced pressure plasma spraying method in the new spraying technique described above forms a Ni-Cr alloy layer on the base material as an undercoat layer to reduce thermal stress, and WC
After forming a composite film by laminating a top coat layer of -Co, the adhesion between the base material and the film is strengthened by vacuum heat treatment to form a surface modified layer with a hardness of approximately Hv1200. is there. A feature of the present invention is that a diffusion layer is formed at each interface of the base material / undercoat layer / topcoat layer by heat treatment after thermal spraying, so that the adhesion between the base material and the composite coating is significantly enhanced, and the conventional application is not possible. It is possible to apply it to the surface modification of the abrasion resistance of materials in deep drawing dies for presses and other broad fields that were possible.

That is, the present invention can be carried out as long as the die material for pressing is a high temperature having a quenching temperature of about 1000 ° C. and can be air quenched.
Therefore, it is possible to use the SKD11 material most frequently used as a die material for pressing. In addition, by performing a combined treatment of the thermal spraying technique and the heat treatment technique as in the present invention, it is possible to modify the surface of a mold in a severe ironing process such as deep drawing of a press.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic view of a plasma spray gun. This water-cooled copper anode nozzle 101, a spray gun in which the tungsten cathode 102, Ar gas as a main gas during the thermal spray gun, the H ₂ gas is introduced as the auxiliary gas, A between both - click Discharge is generated to generate plasma. Since the nozzle is water-cooled by the water-cooled water 103, the plasma undergoes rapid volume expansion due to the thermal pinch effect and is jetted as a jet stream. When the thermal spray material powder is supplied into the high-temperature plasma, the powder flies in a molten or semi-molten state by a jet stream, and is sprayed on the base material surface 104 to be solidified and laminated to form a film 105. Thus, plasma spraying is performed. The reduced pressure plasma spraying is performed under reduced pressure in which the plasma spraying is cut off from the atmosphere in a reduced pressure chamber.

First, an undercoat layer (intermediate layer) is formed on the base material surface 104 using a plasma spray gun. Here, the undercoat layer (intermediate layer) is formed when the hard coating is directly sprayed on the base material, and thermal stress is generated due to a difference in thermal expansion coefficient between the two, so that the thermal stress is generated. This is because an excellent hard film is not formed.

As the thermal spray powder of the intermediate layer, Ni (80%) −
Cr (20%), Ni (95%)-Al (5%) are used, and WC-12% Co is used as the thermal spray powder for the super hard coating. Thus, a composite film is constituted by the intermediate layer and the hard film. In order to form a super hard film with good properties, it is necessary to melt the raw material powder and apply enough heat to form a dense film, but WC is thermally decomposed to W-Co carbide. Do not give enough heat to alter. The following results are the conditions that have been carefully considered and narrowed down.

That is, the preheating of the substrate is performed by Ni (80%)-Cr
(20%) is 300 ° C., Ni (95%)-Al (5%) is 500 ° C., Ar gas is used as a main gas in the spray gun at a flow rate of 50 l / min, and H ₂ gas is used as an auxiliary gas. The gas is introduced into the spray gun at a flow rate of 10 liter / min.

An intermediate layer is formed under this condition. Plasma spraying is performed in a decompression chamber of 10.0 × 10 ³ Pa under reduced pressure cut off from the atmosphere. The spray current is 70
0 A and the spraying distance are 400 mm.

The hard coating is made of a sprayed powder of WC-12% Co and has a chamber pressure of 6.7 × 10 ³ Pa.
Thus, the spraying current is 500 A and the spraying distance is 400 mm. When a composite coating composed of an intermediate layer and a hard coating is formed under these conditions, a WC-Co hard coating having a coating hardness of about Hv1200 is formed.

When abrasion resistance is required, a heat treatment having the following contents is further performed. That is, the degree of vacuum is 1.06 × 1
If the heat treatment is performed at 0 ^-2 Pa at a temperature of 1000 ° C. × 1.5 hours with N ₂ gas and then at a temperature of 500 ° C. × 1 hour with N ₂ gas, the wear resistance is improved.

Here, SKD11 (25.times.25.times.3) is applied to the plasma spray gun shown in FIG.
mm) of the thermal spray coating formed on the base material
(N ₂ cooling) vacuum heat treatment was performed, and EPMA confirmed that a diffusion layer was formed at each interface of the base material / intermediate layer / ultra-hard coating. The results are shown in FIGS. 2 to 4. Figure 2 shows the thermal spray coating C
FIG. 3 shows the results obtained by examining r-Kα, and FIG.
FIG. 4 shows the case of Ni-Lα.

From these results, it was found that Cr and Ni diffused from the undercoat layer (intermediate layer) to the top coat layer (ultra-hard coating) and the base material side, and Fe diffused from the base material to the undercoat layer side. It is presumed that the respective diffusion layers were formed to enhance the adhesion between the base material and the composite film.

In order to prove this, the heat-treated test piece and the as-spray test piece subjected to the heat treatment described above were subjected to severe wear conditions by an Ogoshi-type abrasion tester, with the mating material being SCM415, Friction speed at which cohesive wear begins 4.39
FIG. 5 shows the results of a friction and wear test performed under wear conditions of m / s and a final load of 184 N. The heat-treated film tended to have a smaller specific wear amount than the as-spray film at all the friction distances tested, demonstrating that the wear resistance was improved by the heat treatment. 900-
At the heat treatment temperature of 1100 ° C., the WC carbide in the film is finer than in the as-spray film, which is considered to be the reason for improving the wear resistance.

Next, a second embodiment of the present invention will be described. In this embodiment, a punch of a deep drawing die for press is used, and the shape of a substantially cylindrical punch is shown in FIG. The material of the punch is S which is generally used as a mold.
KD11 (non-heat-treated material), and the periphery of the tip 601 is cut deeper by 0.15 mm than other portions. At the tip 601, a composite film having a thickness of 0.25 mm is formed under the conditions of the first embodiment described above, but is polished 0.1 mm after the heat treatment as described later.

Thereafter, a predetermined heat treatment is performed. That is,
Degree of vacuum 1.06 × 10 ^-2 Pa, 1000 ° C. × 1.5 h (N ₂
After performing a vacuum heat treatment at 500 ° C. × 1 h (cooling with N ₂ ), grinding to a predetermined size, mirror finishing with a diamond wrap (# 400, 800, 1200) was performed for actual machine test. The material to be pressed is a hot-rolled material having a thickness of 2 mm, and is formed by drawing as shown in FIG. The press working is performed by the transfer press shown in the schematic diagram of FIG. 8 and the drawing load is 23.7 GPa, the number of shots is 25 to 28 / mi.
n Actual production conditions. 801 is a die, 802
Is a punch, 803 is a punch holder for holding the punch, 8
Reference numeral 04 denotes a material to be pressed shown in FIG.

As shown in FIG. 9, although the life of the as-spray punch was only about 50 shots, the heat-treated punch did not show any abnormality even after processing 300,000 shots. It showed an order of magnitude more durability than the spray punch.
In addition, the life of the hard chrome plating punch is 8000 to 90.
The durability was nearly 6 times that of the 00 shot, demonstrating the effectiveness of the composite surface modification technique using both thermal spraying and heat treatment.

[0034]

According to the first aspect of the present invention, the surface modification treatment for making the surface of the base material super-hard can be achieved at low cost.

According to the second aspect of the present invention, the range of materials which can be used for the surface modification treatment for improving the wear resistance of the base material surface is widened, and for example, it can be used for SKD11. Further, this surface modification treatment is achieved at low cost.

According to the third aspect of the present invention, the hardness of the press mold is improved, and the wear resistance of the press mold is significantly improved by easy heat treatment. The frequency of mold replacement work can be reduced, and the manufacturing cost by a press machine can be reduced. In addition, since the heat treatment of this content can be performed on the SKD 11 generally used as a pressing die, the manufacturing cost of the die itself can be reduced.

[Brief description of the drawings]

FIG. 1 is a principle view of a plasma spray gun used in the present invention.

FIG. 2 is a concentration mapping of Cr-Kα ray by EPMA.

FIG. 3 is a concentration mapping of Ni-Lα ray by EPMA.

FIG. 4 is a concentration mapping of Fe-Kα ray by EPMA.

FIG. 5 is a view showing a wear test result of an as-spray film and a heat-treated film.

FIG. 6 is a schematic diagram of a punch of a deep drawing die for press applied to an actual machine test.

FIG. 7 is a schematic view of a press-formed product.

FIG. 8 is a schematic diagram of press working.

FIG. 9 is a shot number showing the durability of each punch.

FIG. 10 is an explanatory diagram showing the influence of chamber pressure on the hardness of a hard coating.

FIG. 11 is an explanatory diagram showing the effect of the spraying distance on the hardness of the hard coating.

[Description of Signs] 101 anode 102 cathode 103 cooling water 104 base material surface 105 coating

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Shozo Murata 1-30-45 Kitamaruko, Shizuoka City, Shizuoka Prefecture Inside Murata Boring Giken Co., Ltd.

Claims (3)

[Claims] 1. A method for forming a surface coating of a base material, comprising forming a superhard coating on a surface of a base material required to have superhardness under reduced pressure plasma spraying under predetermined conditions. 2. After forming a WC-Co ultra-hard coating on the surface of a base material for which wear resistance is required by reduced pressure plasma spraying, a predetermined method for enhancing the adhesion between the base material and the super-hard coating is used. A method for forming a base material surface film, wherein a heat treatment of the specified contents is performed. 3. A composite film is formed on the surface of the punch portion of the pressing die, and the composite film is an intermediate layer and a super hard film formed by low pressure plasma spraying under predetermined conditions. A press die, which is configured and heat-treated with predetermined contents, and wherein the superhard coating is a WC-Co superhard coating.