JP6875886B2 - Vanadium nitride film coating member and its manufacturing method - Google Patents

Description

The present invention relates to a coating member coated with a hard film, a vanadium nitride film, and a method for producing the same.

Conventionally, vanadium nitride film (VN film) and vanadium carbide have high film hardness and excellent lubricity as a hard film on the surface of press molding dies, cutting tools, gear cutting tools, forging tools, automobile parts, etc. Vanadium-based films such as a film (VC film) and a vanadium nitride film (VCN film) have been formed.

As a conventional method for forming a vanadium-based film, Patent Document 1 describes a method for forming a vanadium nitride film, a vanadium carbide film, and a vanadium nitride film by an ion plating method. Further, Patent Document 2 also describes a method for forming a vanadium nitride film by an ion plating method. Further, Non-Patent Document 1 discloses that a vanadium-based film contains silicon to form a vanadium nitride film (VSiN film).

JP-A-2002-371352 Japanese Unexamined Patent Publication No. 2005-46975

Hongjian Zhao, 3 others, "Structure and properties of Si-implanted VN coatings prepared by RF magnetron sputtering", Materials TEXT, ELSEVIER, April 27, 2016, Volume 117 (2016), p.65-75

The hard film is formed on various substrates according to the characteristics required for the product, but the applicant applied a vanadium nitride film on the surface of so-called cold tool steel such as SKD11 and DC53 and cold mold steel. When formed, it was found that the adhesion between the steel material and the vanadium nitride film in the Rockwell indentation test was low. Therefore, it is desired to improve the adhesion between the steel material and the vanadium nitride film in order to improve the performance as the vanadium nitride film coating member.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the adhesion between a steel material and a vanadium nitride film in a vanadium nitride film-coated member.

The present invention, which solves the above problems, is a vanadium nitride film coating member, which is a steel material containing 3 to 16% Cr in mass% and a surface modification containing a chromium nitride compound formed on the surface of the steel material. It is characterized by having a layer, a vanadium nitride film formed on the surface-modified layer, and a vanadium nitride film formed on the vanadium nitride film.

The present invention from another viewpoint is a method for producing a vanadium nitride film coating member, which is a nitriding treatment for forming a surface modified layer containing a chromium nitride compound on the surface of a steel material containing 3 to 16% Cr in mass%. It has a nitriding step of forming a vanadium nitride film on the surface of the steel material after the nitriding step, a vanadium nitride film forming step of forming a vanadium nitride film on the vanadium nitride film, and a vanadium nitride film forming step of forming the vanadium nitride film on the vanadium nitride film. It is characterized by that.

According to the present invention, in the vanadium nitride film coating member, the adhesion between the steel material and the vanadium nitride film can be improved.

It is a figure which shows the schematic structure of the vanadium nitride film coating member which concerns on embodiment of this invention. It is a figure for demonstrating the surface modification layer which concerns on embodiment of this invention. It is a figure for demonstrating the surface modification layer which concerns on embodiment of this invention. It is a figure for demonstrating the surface modification layer which concerns on embodiment of this invention. It is a figure which shows the schematic structure of the film forming apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the definition of a duty ratio. It is a cross-sectional image of the test piece of Example 1. It is a cross-sectional image of the test piece of Example 2. It is a cross-sectional image of the test piece of Example 3. It is a cross-sectional image of the test piece of Comparative Example 1. It is a cross-sectional image of the test piece of Example 4. It is a cross-sectional image of the test piece of Example 5. It is a cross-sectional image of the test piece of Example 6. It is a cross-sectional image of the test piece of Comparative Example 2. It is a figure which shows the rockwell indentation test result of an Example and a comparative example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

In the present embodiment, the steel material is first subjected to plasma nitriding treatment, and then vanadium nitride film forming treatment and vanadium nitride film forming treatment are performed to manufacture a vanadium nitride film coating member. As shown in FIG. 1, the vanadium nitride film coating member 1 of the present embodiment has the steel material 2, the surface modified layer 2a formed on the surface of the steel material 2, and the nitride formed on the surface modified layer 2a. It is composed of a vanadium film 3 and a vanadium nitride film 4 formed on the vanadium nitride film 3.

The steel material 2 contains Cr in which a chromium nitriding compound is formed by the nitriding treatment. Although the content of Cr depends on the steel material, it is preferably one containing 3 to 16% of Cr, and for example, so-called cold tool steels such as SKD11 and DC53 and cold mold steels are used.

The surface modified layer 2a refers to a region containing a chromium nitriding compound formed immediately below the surface of the steel material 2 by the nitriding treatment. Hereinafter, the surface modification layer 2a will be described. FIG. 2 is a diagram schematically showing the structure near the surface of the steel material 2 before the plasma nitriding treatment, but the steel material 2 before the plasma nitriding treatment has various sizes of precipitates P1 including coarse carbides and minute carbides. ~ P7 is formed. When such a steel material 2 is subjected to plasma nitriding treatment, nitrogen gradually diffuses from the surface of the steel material toward the inside of the steel material. At this time, carbon in the precipitate is replaced with nitrogen, and the precipitate existing as a carbide changes to a nitride.

In the example shown in FIG. 3, the carbides of the precipitates P1 and P2 are changed to nitrides. On the other hand, since the precipitate P3 has a large size of the precipitate itself, only a part of the carbides are nitrides at the end of the plasma nitriding treatment. That is, the boundary between the nitride and the carbide exists inside the precipitate P3. Since the change from the carbide to the nitride proceeds from the surface where the nitrogen diffused from the surface of the steel material 2 and the precipitate P3 come into contact with each other, not only from the upper surface of the precipitate P3 but also from the lateral side surface of FIG. 3 of the precipitate P3. Change goes on. Therefore, the boundary between the nitride and the carbide has a shape having a portion parallel (including substantially parallel) to the surface of the steel material 2 as shown in FIG. 3 (hereinafter, “parallel portion”) and a portion extending in the depth direction. It becomes. The precipitate P4 is located at the same depth as the position where the nitride and the carbide of the precipitate P3 coexist, but due to the small size of the precipitate itself, the time until the carbide changes to the nitride. Is shorter than the precipitate P3. Therefore, the precipitate P4 is a nitride. On the other hand, since the precipitate P5 located at the same depth as the precipitate P4 is larger in size than the precipitate P4, only a part of the precipitate P5 is a nitride like the precipitate P3. Regarding the precipitates P6 and P7, the change from the carbide to the nitride was not started at the end of the plasma nitriding treatment in the example of FIG. 3, and the precipitates remained as the carbides as before the plasma nitriding treatment.

In this way, carbides and nitrides are mixed in a state immediately below the surface of the steel material 2 after the plasma nitriding treatment, depending on the size and shape of the precipitates, and precipitates such as precipitates P3 and precipitates P5. There are some that have a boundary between nitride and carbide inside. In the present specification, among the boundaries between nitrides and carbides that appear when a part of such precipitates becomes nitrides, the region from the boundary located on the surface side of the steel material 2 to the surface of the steel material 2 is the region. Is called a surface modification layer. In the example shown in FIG. 3, among the boundaries between the nitride and the carbide generated in the precipitate P3 and the precipitate P5, the boundary of the precipitate P3 is closer to the surface side of the steel material 2. Further, among the boundaries of the precipitate P3, the portion closest to the surface side of the steel material 2 is a parallel portion of the boundary. That is, in the example shown in FIG. 3, the region from the surface of the steel material 2 to the parallel portion of the boundary between the nitride and the carbide of the precipitate P3 is the surface modification layer 2a.

By forming the surface modification layer 2a as in the present embodiment on the surface of the steel material 2, the adhesion between the surface modification layer 2a and the vanadium nitride film 4 is improved, although the reason is not clear. .. Since the adhesion between the surface modified layer 2a and the vanadium nitride film 3 is improved and the adhesion between the vanadium nitride film 3 and the vanadium nitride film 4 is high, the vanadium nitride formed on the surface modified layer 2a The adhesion between the film 3 and the vanadium nitride film 4 formed on the vanadium nitride film 3 is also improved. The morphology of the nitride in the surface modified layer 2a is not clear, but it is considered that various morphologies contribute to the adhesion.

The thickness of the surface modification layer 2a is preferably 0.5 to 50 μm. When the thickness of the surface modified layer 2a is less than 0.5 μm, the surface modified layer 2a is close to the absence of the surface modified layer 2a, and a film containing the surface modified layer 2a and vanadium nitride immediately above the surface modified layer 2a (in the present embodiment). The effect of improving the adhesion with the vanadium nitride film 3) may be reduced. On the other hand, if the thickness of the surface modification layer 2a exceeds 50 μm, the time required for the plasma nitriding treatment becomes long, which may increase the treatment cost and reduce the effect of the vanadium nitride film as a hard film. The preferable lower limit of the thickness of the surface modification layer 2a is 0.7 μm, and the more preferable lower limit is 1.0 μm. Further, the preferable upper limit value of the thickness of the surface modification layer 2a is 40 μm, and the more preferable upper limit value is 35 μm.

The vanadium nitride film 3 functions as a buffer film that suppresses a sudden change in composition from the surface modification layer 2a formed on the surface of the steel material 2 to the vanadium nitride film 4. As a result, the adhesion between the steel material 2 and the vanadium nitride film 4 can be improved as compared with the case where the vanadium nitride film 4 is directly formed on the surface modification layer 2a formed on the surface of the steel material 2. .. However, it is possible to improve the adhesion between the steel material 2 and the vanadium nitride film 4 without forming the vanadium nitride film 3. The vanadium nitride film 3 is a film in which the total of the vanadium element concentration and the nitrogen element concentration is 90 at% or more. The composition ratio and the film thickness of the vanadium element concentration and the nitrogen element concentration are appropriately changed according to the characteristics required for the vanadium nitride film coating member 1, but the film thickness of the vanadium nitride film 3 is more than 0. It is preferably ~ 4 μm.

The vanadium nitride film 4 is a film in which the total of the vanadium element concentration, the silicon element concentration and the nitrogen element concentration is 90 at% or more. The composition ratios and film thicknesses of the vanadium element concentration, the silicon element concentration, and the nitrogen element concentration are appropriately changed according to the characteristics required for the vanadium silicate film coating member 1, but the composition ratio is a = vanadium. Element concentration [at%] / (vanadium element concentration [at%] + silicon element concentration [at%] + nitrogen element concentration [at%]), b = silicon element concentration [at%] / (vanadium element concentration [at%]) ] + Silicon element concentration [at%] + Nitrogen element concentration [at%]), it is preferable that 0.30 ≦ a / b ≦ 1.7 and 0.24 ≦ b ≦ 0.36 are satisfied. .. When 0.30 ≦ a / b ≦ 1.7 is satisfied, the hardness of the vanadium nitride film 4 can be further improved. The preferable lower limit value of a / b is 0.4, and the more preferable lower limit value is 0.8. The preferable upper limit value of a / b is 1.5, and the more preferable upper limit value is 1.3. When 0.24 ≦ b ≦ 0.36 is satisfied, the oxidation resistance can be further improved. The film thickness of the vanadium nitride film 4 is preferably 0.5 to 4 μm.

Next, a method for manufacturing the vanadium nitride film covering member 1 will be described.

In the present embodiment, the vanadium nitride coated member 1 is manufactured by using a plasma chemical vapor deposition method (so-called plasma CVD method). As the manufacturing apparatus for that purpose, the plasma processing apparatus 10 as shown in FIG. 5 is used. The plasma processing apparatus 10 includes a chamber 11 into which the steel material 2 is carried, an anode 12, a cathode 13, and a pulse power supply 14. A gas supply pipe 15 for supplying raw material gas is connected to the upper part of the chamber 11, and a gas exhaust pipe 16 for exhausting the gas in the chamber is connected to the lower part of the chamber 11. A vacuum pump (not shown) is provided in the gas exhaust pipe 16. The cathode 13 also has a role as a support base for supporting the steel material 2, and the steel material 2 carried into the chamber is placed on the cathode. Further, a heater (not shown) is provided inside the chamber 11, and the temperature of the steel material 2 is adjusted by adjusting the ambient temperature in the chamber by the heater.

The configuration of the plasma processing apparatus 10 is not limited to that described in this embodiment. For example, a high-frequency power supply may be used instead of the pulse power supply 14, or a shower head for supplying the raw material gas may be provided and used as the anode 12. Further, the steel material 2 may be heated only by the glow current without providing the heater. That is, the plasma processing apparatus 10 has a structure capable of converting the raw material gas supplied into the chamber into plasma and forming the vanadium nitride film 4 on the steel material 2 to manufacture the vanadium nitride film covering member 1. It should be.

<Preparation for film formation>
First, the steel material 2 is carried into the chamber 11 and the steel material 2 is set at a predetermined position. After that, vacuum exhaust is performed so that the pressure in the chamber becomes, for example, 10 Pa or less. At this time, the temperature inside the chamber is about room temperature. Subsequently, the heater is operated to perform the baking process of the steel material 2. After that, the power of the heater is turned off once, and the plasma processing device 10 is left for a predetermined time.

<Heating process>
Next, a small amount of hydrogen gas is supplied into the chamber, and the heater is operated again. In this heating step, the temperature of the steel material 2 is raised to near the plasma processing temperature. The pressure in the chamber is maintained at, for example, about 100 Pa.

<Plasma processing process>
(Hydrogen plasma process)
In the present embodiment, hydrogen gas is turned into plasma prior to the plasma nitriding treatment of the steel material 2. Specifically, the pulse power supply 14 is operated in a state where the hydrogen gas supplied in the heating step is continuously supplied. As a result, hydrogen gas is turned into plasma between the electrodes. The hydrogen radicals thus generated reduce the oxide film on the surface of the steel material, and the surface of the steel material is cleaned before film formation. The voltage, frequency, duty ratio, etc. of the pulse power supply 14 are appropriately set so that the gas supplied into the chamber becomes plasma.

(Plasma nitriding process)
After the hydrogen gas is turned into plasma, nitrogen gas and argon gas are further supplied into the chamber to which the hydrogen gas is supplied. As a result, plasma of hydrogen gas, nitrogen gas and argon gas is generated, and plasma nitriding treatment of the steel material 2 is performed. Along with this, the carbides deposited near the surface of the steel material 2 are changed to nitrides, and the surface modification layer 2a is formed. In this plasma nitriding step, it is necessary to form the surface modification layer 2a so that the thickness of the surface modification layer 2a is 0.5 to 50 μm. The thickness of the surface modified layer 2a increases in proportion to the nitriding treatment time, but the formation rate of the surface modified layer 2a with respect to the nitriding treatment time differs depending on the shape and size of the precipitates inside the steel material 2. Therefore, the nitriding treatment time is appropriately changed, but is preferably 30 to 240 minutes, for example. More preferably, it is 60 to 240 minutes. Incidentally, the partial pressure ratio of hydrogen gas and nitrogen gas in the plasma nitriding _{step, H 2: N 2 = 1} : 6~6: a is preferably _{1, H 2: N 2 =} 1: 2~4: 1 More preferably. Further, in the plasma nitriding step, the atmospheric temperature in the chamber is preferably maintained at 350 to 650 ° C, more preferably 450 to 550 ° C. The ambient temperature in this chamber is achieved by adjusting the heater set temperature according to the plasma conditions. Further, in the plasma nitriding step, the voltage of the pulse power supply is preferably 500 to 1500 V, more preferably 900 to 1300 V.

(Vanadium nitride film forming process)
After forming the surface modification layer 2a of the steel material 2, vanadium chloride gas is further supplied into the chamber as a vanadium source gas. As a result, nitrogen gas, vanadium chloride gas, hydrogen gas, and argon gas are supplied into the chamber as raw material gases for forming the vanadium nitride film 3. The partial pressure ratios of nitrogen gas, vanadium chloride gas, hydrogen gas, and argon gas are set to, for example, (9 to 10) :( 0.9 to 1.2) :( 35 to 50) :( 0.5 to 5). Will be done. The pressure in the chamber is set to, for example, 50 Pa or more and 200 Pa or less.

As the vanadium chloride gas, for example, vanadium tetrachloride (VCl ₄ ) gas and vanadium trichloride (VOCl ₃ ) gas are used. It is preferable to use vanadium tetrachloride gas from the viewpoint that the number of elements constituting the gas is small and impurities in the vanadium nitride film can be easily removed. Vanadium tetrachloride gas is also preferable because it is easily available, is liquid at room temperature, and is easily supplied as a gas. Further, the nitrogen source gas is not limited to nitrogen gas, and may be, for example, ammonia gas. Further, nitrogen gas and ammonia gas may be mixed and supplied as the nitrogen source gas.

When the vanadium chloride gas is supplied into the chamber, the vanadium chloride gas is turned into plasma between the electrodes. Since the vanadium gas and nitrogen gas that are plasmatized between the electrodes are adsorbed on the steel material 2, the vanadium nitride film 3 is formed on the surface modification layer 2a of the steel material 2. The ambient temperature in the chamber during the film formation treatment of the vanadium nitride film 3 is preferably 450 ° C. or higher and 550 ° C. or lower. Further, the voltage during the film forming process is preferably 700 V or more and 1500 V or less.

(Vanadium nitride film forming process)
After forming the vanadium nitride film 3 on the surface modification layer 2a of the steel material 2, a silane source gas is further supplied into the chamber. At this time, the partial pressure ratios of nitrogen gas, vanadium chloride gas, silane source gas, hydrogen gas, and argon gas are, for example, {(61.25-0) when the duty ratio is x (however, 10 ≦ x ≦ 65). .875 × x) to (86.25-0.875 × x)}: {(0.25 + 0.025 × x) to (3.25 + 0.025 × x)}: {(3.5-0.04) × x) to (6.2-0.04 × x)}: {100}: {(0.5 to 5)} is set. The pressure in the chamber is set to, for example, 50 Pa or more and 200 Pa or less. The duty ratio is defined by the voltage application time per cycle as shown in FIG. 6, and the duty ratio = 100 × application time (ON time) / {application time (ON time) + application stop time (OFF time). } Is calculated.

As the silane source gas, for example, a silane gas such as silicon tetrachloride gas, silane trichloride gas, silane dichloride gas, silane chloride gas, silane, and silicon tetrafluoride is used. The gas exemplified here may be supplied alone or may be supplied by mixing one or more kinds of gases. Further, among these gases, it is preferable to use _{silicon tetrachloride (SiCl 4} ) gas, which can easily remove chlorine atoms by hydrogen plasma, is thermally stable and decomposes only in plasma.

Further, since the partial pressure of the silane source gas affects the increase / decrease in the amount of silicon in the vanadium nitride film, if the amount of silicon in the vanadium nitride film is desired to be changed, the partial pressure of the silane source gas is adjusted. You may do so. Since the partial pressure of vanadium chloride gas and the partial pressure of hydrogen gas affect the increase and decrease of the amount of vanadium in the vanadium nitride film, if you want to change the amount of vanadium in the vanadium nitride film, vanadium chloride gas At least one of the partial pressure of the hydrogen gas and the partial pressure of the hydrogen gas may be adjusted. Since the partial pressure of the nitrogen source gas affects the increase or decrease in the amount of nitrogen in the vanadium nitride film, if you want to change the amount of nitrogen in the vanadium nitride film, adjust the partial pressure of the nitrogen source gas. You may.

The voltage of the vanadium nitride film 4 during the film formation process is preferably 700 V or more and 1800 V or less. In addition, the glow current value during plasma treatment affects the increase / decrease in the amount of silicon and nitrogen in the vanadium nitride film, so if you want to change the amount of silicon and nitrogen in the vanadium nitride film, the glow current value May be adjusted. Further, the ambient temperature in the chamber during the film formation treatment of the vanadium nitride film 4 is preferably 450 ° C. or higher and 550 ° C. or lower. Since the ambient temperature can contribute to the amount of vanadium in the vanadium nitride film, even if the ambient temperature is adjusted as one method for adjusting the amount of vanadium in the vanadium nitride film. good. By increasing the ambient temperature in the chamber, the amount of vanadium in the vanadium nitride film can be increased.

By supplying the silane source gas into the chamber, the silane source gas is turned into plasma between the electrodes, and silicon is adsorbed on the surface of the vanadium nitride film 3 together with vanadium and nitrogen that have already been turned into plasma. As a result, the vanadium nitride film 4 is formed on the surface of the vanadium nitride film 3, and the vanadium nitride film covering member 1 can be obtained.

In the film forming method of the present embodiment, vanadium chloride gas is used as the vanadium source gas when the vanadium nitride film 3 is formed and when the vanadium nitride film 4 is formed. Therefore, the film of the vanadium nitride film 3 inevitably contains chlorine as an impurity as a balance excluding vanadium and nitrogen. Further, the film of the vanadium nitride film 4 inevitably contains chlorine as an impurity as a balance excluding vanadium, silicon and nitrogen. On the other hand, since hydrogen gas contained in the raw material gas is easily combined with chlorine, when hydrogen gas is contained as the raw material gas as in the present embodiment, chlorine generated from the vanadium chloride gas is combined with hydrogen to form a system. It becomes easy to be discharged to the outside, and it is possible to suppress the mixing of chlorine into the films of the vanadium nitride film 3 and the vanadium nitride film 4. The remaining portion of the vanadium nitride film 3 and the vanadium nitride film 4 may contain unavoidable impurities other than chlorine as in the present embodiment.

Further, the flow rate of hydrogen gas during the plasma treatment is preferably 25 times or more the flow rate of vanadium chloride gas. Further, in the present embodiment, the raw material gas contains argon gas, but the supply of argon gas is not essential. Argon gas is preferably supplied as needed because argon ions contribute to stabilizing the plasma and improving the ion density by ionizing other molecules.

Further, in the present embodiment, the surface modified layer 2a is formed by plasma nitriding the steel material 2, but the surface modified layer 2a can be formed even by other nitriding treatments such as gas nitriding. It can be done and the adhesion can be improved. However, a step of replacing the steel material 2 from the plasma processing apparatus 10 with another nitriding processing apparatus is required, which increases the manufacturing process of the vanadium nitride film coating member 1. Further, when the steel material 2 is taken out of the vacuum chamber 11, the surface of the steel material 2 may be contaminated. Therefore, it is preferable to perform plasma nitriding in the nitriding step so that the nitriding treatment of the steel material 2 and the formation treatment of the vanadium nitride film 4 can be performed in the same container.

Although the embodiments of the present invention have been described above, the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical idea described in the claims, and of course, the technical scope of the present invention also includes them. It is understood that it belongs to.

A surface-modified layer was formed on the steel material, and a test piece having a vanadium nitride film formed on the surface-modified layer was prepared and various evaluations were carried out. For the steel material for the test piece, after quenching and tempering a φ22 round bar made of the steel types shown in Table 1 below, the round bar is cut at intervals of 6 to 7 mm, and the surface of each cut member is mirror-polished. I used the one that I did. Each hard film is formed on the mirror-polished side surface of the steel material. The film forming apparatus had a structure as shown in FIG. 6, and a pulse power source was used as the power source.

<< Example 1 >>
Next, a method for producing the test piece of Example 1 will be described. The processing conditions in each step of Example 1 are as shown in Table 2 below. The flow rates of hydrogen gas, nitrogen gas, argon gas, vanadium tetrachloride gas, and silicon tetrachloride gas in the following description are volumetric flow rates at 0 ° C. and 1 atm.

<Preparation for film formation>
First, a steel material for a test piece is set in the chamber of the film forming apparatus, and the inside of the chamber is evacuated for 30 minutes to reduce the pressure in the chamber to 10 Pa or less. At this time, the heater is not operated. The heater is provided inside the chamber, and the ambient temperature inside the chamber is measured by a sheath thermocouple. Subsequently, the set temperature of the heater is set to 200 ° C., and the steel material is baked for 10 minutes. After that, the power of the heater is turned off, and the film forming apparatus is left for 30 minutes to cool the inside of the chamber.

<Heating process>
Next, hydrogen gas is supplied into the chamber at a flow rate of 100 ml / min, and the displacement is adjusted so that the pressure in the chamber is 100 Pa. Then, the set temperature of the heater is set to 485 ° C., and the steel material is heated for 30 minutes. This heating step raises the temperature of the steel material to near the plasma treatment temperature.

<Plasma processing process>
(Hydrogen plasma process)
Next, the pulse power supply is operated in a voltage: 800 V, a frequency: 25 kHz, a duty ratio: 30%, and a unipolar output format. As a result, hydrogen gas is turned into plasma between the electrodes in the chamber, and the surface of the steel material is cleaned by hydrogen radicals.

(Plasma nitriding process)
After that, the flow rate of hydrogen gas is increased to 200 ml / min, and nitrogen gas and argon gas are supplied into the chamber. Then, the voltage of the pulse power supply is raised to 1100V. As a result, hydrogen gas, nitrogen gas, and argon gas are turned into plasma between the electrodes. The flow rate of nitrogen gas at this time is 100 ml / min, and the flow rate of argon gas is 5 ml / min. The voltage division ratio of hydrogen gas and nitrogen gas is 2: 1. Further, the displacement is adjusted so that the pressure in the chamber is 58 Pa. The nitriding treatment time is 60 minutes. The processing conditions for the plasma nitriding step of Example 1 are those of "Condition A" in Table 3 below.

(Vanadium nitride film forming process)
Subsequently, vanadium tetrachloride gas is supplied into the chamber at a flow rate of 4.5 sccm to raise the voltage of the pulse power supply to 1500 V. As a result, vanadium tetrachloride gas is decomposed into vanadium and chlorine. Then, the plasma-generated vanadium and nitrogen are adsorbed on the steel material, so that a vanadium nitride film that contributes to improving the adhesion between the steel material and the vanadium nitride film is formed on the surface of the steel material. This state is maintained for 30 minutes to form vanadium nitride on the surface of the steel material.

(Vanadium nitride film forming step)
Subsequently, silicon tetrachloride gas is supplied into the chamber at a flow rate of 5.0 sccm. As a result, silicon tetrachloride gas is decomposed into silicon and chlorine. Further, the flow rate of nitrogen gas is set to 75 ml / min. Then, the plasma-ized silicon, the vanadium continuously supplied from the previous process, and the nitrogen whose supply amount has increased as compared with the previous process are adsorbed on the steel material, so that the vanadium nitride film is formed on the surface of the vanadium nitride film. To go. This state is maintained for 120 minutes.

Through the above steps, a test piece of Example 1 coated with a vanadium nitride film was prepared. The following evaluation was carried out using this test piece.

<Surface modified layer cross-section observation>
The test piece was cut perpendicular to the surface with a cutting machine, the cross section was polished with emery paper, and the polished surface was mirror-finished with a buff. Then, based on the nitric acid alcohol method (Nital method) specified in JIS G 0553, nitric acid (equivalent to 62% of JIS K 1308) and ethanol are mixed and tested on the obtained corrosive solution of 3% nitric acid. The pieces were soaked for 5 minutes. Then, the cross section of the test piece was observed at a magnification of 1000 times using a metal (optical) microscope, and a cross section image was obtained. Then, the thickness of the surface modified layer was measured from the obtained cross-sectional image.

<Film thickness measurement>
The cut surface of the test piece used for observing the cross section of the surface modified layer was observed at a magnification of 1000 times with a metallurgical microscope, and a cross section image was obtained. Then, the film thicknesses of the vanadium nitride film and the vanadium nitride film were measured from the acquired cross-sectional image.

<Composition analysis of hard film>
The composition of the hard film formed on the test piece was analyzed. The analysis conditions are as follows.
EPMA: JXA-8530F manufactured by JEOL Ltd.
Measurement mode: Semi-quantitative analysis Acceleration voltage: 15 kV
Irradiation current: 1.0 × ^10-7 A
Beam shape: Spot Beam diameter set value: 0
Spectral crystals: LDE6H, TAP, LDE5H, PETH, LIFH,
LDE1H

<Rockwell indentation test>
The Rockwell hardness tester is set to C scale to give indentations to the surface of the vanadium nitride film of the test piece. Then, the circumference of the indentation was observed using a metallurgical microscope. Then, the degree of film peeling of the test piece was determined based on the well-known indentation peeling criteria in the Rockwell indentation test, and the adhesion of the vanadium nitride film was evaluated.

A summary of the above results is shown in Table 4 below. Further, a cross-sectional image of the test piece of Example 1 is shown in FIG. 7, and an image of the indented portion of the test piece after the Rockwell indentation test is shown in FIG.

In addition, test pieces of Examples 2 to 6 and Comparative Examples 1 and 2 were prepared under the following conditions and evaluated in the same manner.

<< Example 2 >>
In the plasma nitriding step, except that the set temperature of the heater was set to 400 ° C., the flow rate of hydrogen gas was set to 100 ml / min, the flow rate of nitrogen gas was set to 200 ml / min, and the nitriding treatment time was set to 180 minutes. A test piece was prepared under the same conditions. The processing conditions for the plasma nitriding step of Example 2 are those of "Condition B" in Table 3 above. Table 4 below shows the thickness of the surface modified layer, the film thickness measurement and composition analysis of the vanadium nitride film and the vanadium nitride film, and the results of the Rockwell indentation test examined by the same method as in Example 1. Further, a cross-sectional image of the test piece of Example 2 is shown in FIG. 8, and an image of the indented portion of the test piece after the Rockwell indentation test is shown in FIG.

<< Example 3 >>
A test piece was prepared under the same conditions as in Example 1 except that the vanadium nitride film forming step was not carried out. Table 4 below shows the thickness of the surface modified layer, the film thickness measurement and composition analysis of the vanadium nitride film and the vanadium nitride film, and the results of the Rockwell indentation test examined by the same method as in Example 1. Further, a cross-sectional image of the test piece of Example 3 is shown in FIG. 9, and an image of the indented portion of the test piece after the Rockwell indentation test is shown in FIG.

<< Comparative Example 1 >>
A test piece was prepared under the same conditions as in Example 1 except that the plasma nitriding step was not performed. Table 4 below shows the thickness of the surface modified layer, the film thickness measurement and composition analysis of the vanadium nitride film and the vanadium nitride film, and the results of the Rockwell indentation test examined by the same method as in Example 1. Further, a cross-sectional image of the test piece of Comparative Example 1 is shown in FIG. 10, and an image of the indented portion of the test piece after the Rockwell indentation test is shown in FIG.

<< Example 4 >>
A test piece was prepared under the same conditions as in Example 1 except that the steel type of the steel material for the test piece was DC53 in Table 1 above. Table 4 below shows the thickness of the surface modified layer, the film thickness measurement and composition analysis of the vanadium nitride film and the vanadium nitride film, and the results of the Rockwell indentation test examined by the same method as in Example 1. Further, a cross-sectional image of the test piece of Example 4 is shown in FIG. 11, and an image of the indented portion of the test piece after the Rockwell indentation test is shown in FIG.

<< Example 5 >>
A test piece was prepared under the same conditions as in Example 2 except that the steel type of the steel material for the test piece was DC53 in Table 1 above. Table 4 below shows the thickness of the surface modified layer, the film thickness measurement and composition analysis of the vanadium nitride film and the vanadium nitride film, and the results of the Rockwell indentation test examined by the same method as in Example 1. Further, a cross-sectional image of the test piece of Example 5 is shown in FIG. 12, and an image of the indented portion of the test piece after the Rockwell indentation test is shown in FIG.

<< Example 6 >>
A test piece was prepared under the same conditions as in Example 3 except that the steel type of the steel material for the test piece was DC53 in Table 1 above. Table 4 below shows the thickness of the surface modified layer, the film thickness measurement and composition analysis of the vanadium nitride film and the vanadium nitride film, and the results of the Rockwell indentation test examined by the same method as in Example 1. Further, a cross-sectional image of the test piece of Example 6 is shown in FIG. 13, and an image of the indented portion of the test piece after the Rockwell indentation test is shown in FIG.

<< Comparative Example 2 >>
A test piece was prepared under the same conditions as in Comparative Example 1 except that the steel type of the steel material for the test piece was DC53 in Table 1 above. Table 4 below shows the thickness of the surface modified layer, the film thickness measurement and composition analysis of the vanadium nitride film and the vanadium nitride film, and the results of the Rockwell indentation test examined by the same method as in Example 1. Further, a cross-sectional image of the test piece of Comparative Example 2 is shown in FIG. 14, and an image of the indented portion of the test piece after the Rockwell indentation test is shown in FIG.

In this example, it was difficult to analyze the composition of the vanadium nitride film because the film thickness of the vanadium nitride film was thin. Therefore, the composition of the vanadium nitride film in Table 4 is estimated based on the comparison with the processing conditions of another film formation test in which the vanadium nitride film having a sufficient thickness is formed.

The portion of the cross-sectional image shown in FIGS. 7 to 14 that looks like a white mass is a precipitate. Of the plurality of precipitates, the portion that appears relatively white is a carbide, and the portion that appears relatively gray is a chromium nitride compound. It was confirmed that the white part is a carbide and the gray part is a chromium nitride compound by comparing the carbon presence position, the nitrogen presence position and the chromium presence position by element mapping by EPMA. .. The numerical values in FIGS. 7 to 9 and 11 to 13 are the thickness of the surface modified layer. Further, the reason why the inside of the steel material is white as a whole in FIGS. 10 and 14 is that nitrogen is not diffused inside the steel material because the plasma nitriding treatment of the steel material is not performed.

As shown in Tables 4 and 15, in Comparative Examples 1 and 2 in which plasma nitriding of the steel material was not performed, the hard film was peeled off at the time of indentation. On the other hand, in Examples 1 to 6, the steel material and the hard film had sufficient adhesion. Further, comparing Examples 1 and 2 with Example 3, it can be seen that the adhesion is improved by forming the vanadium nitride film between the steel material and the vanadium nitride film. Similarly, when Examples 4 and 5 are compared with Example 6, it can be seen that the adhesion is improved by forming the vanadium nitride film between the steel material and the vanadium nitride film.

Next, a test piece different from the test piece prepared for the above-mentioned adhesion evaluation was prepared, and the oxidation resistance of the vanadium nitride film was evaluated.

The oxidation resistance is evaluated by soaking the test piece in an air atmosphere and comparing the hardness of the test piece before and after the soaking heat treatment. Hardness measurement is performed by the nanoindentation method using FISCHER SCOPE® HM2000 manufactured by Fischer Instruments. Specifically, the Vickers indenter is pushed into the test piece with the maximum pushing load of 10 mN, and the pushing depth is measured. Based on the result, the measuring device calculates the Martens hardness and the Vickers hardness converted from the Martens hardness. The calculated Vickers hardness is displayed on the screen of the measuring device, and this value is treated as the hardness of the film at the measuring point. In this example, the Vickers hardness of any 20 points on the surface of each test piece is obtained, and the average value of the obtained hardness is recorded as the hardness of the film. When pushing the indenter into the test piece, the pushing load may propagate up to about 10 times the maximum pushing depth of the indenter. Therefore, if the propagation of the pushing load reaches the steel material of the test piece, the effect of the steel material may be included in the hardness measurement result. Therefore, in order to measure the hardness of a pure hard film, it is necessary to satisfy "the film thickness of the hard film> the maximum indentation depth of the indenter x 10".

The results of the oxidation resistance evaluation of each test piece are shown in Table 5 below. All the test pieces used for this oxidation resistance evaluation have not been subjected to plasma nitriding treatment of steel materials. Further, the plasma CVD method is used for the film formation process of the hard film. The film thickness measurement method and composition analysis method of the hard film are the same as the methods carried out in the above-mentioned adhesion evaluation.

As shown in Table 5, the hardness of the test piece of Example 7 before the soaking heat treatment was 3022 HV, and the hardness of the test piece of Comparative Example 3 was 2989 HV. On the other hand, after the soaking heat treatment, the hardness of the test piece of Example 7 was 2700 HV, but the hardness of the test piece of Comparative Example 3 was 200 HV, and the hardness decreased. Therefore, it can be seen that the vanadium nitride film of Example 7 is a film having excellent oxidation resistance to the vanadium nitride film.

The hardness of the test piece of Comparative Example 4 before the leveling heat treatment was 2977 HV, but the hardness of the test piece after the leveling heat treatment of Comparative Example 4 was 40 HV. Therefore, it can be seen that the vanadium nitride film of Example 7 has improved oxidation resistance as compared with the vanadium nitride film of Comparative Example 4. When the test pieces of Example 7 and Comparative Example 4 were cut vertically and elemental mapping was performed on the cut surface, a film composed of vanadium, silicon and nitrogen was confirmed for the test piece of Example 7. On the other hand, in the test piece of Comparative Example 4, a film containing vanadium and silicon was not confirmed, and it was confirmed that an oxide film of iron or chromium was growing. As shown in Table 5, there is a difference in the silicon element concentration between the vanadium nitride film of Example 7 and the vanadium nitride film of Comparative Example 4, and this difference in the silicon element concentration is the film quality after soaking. It is thought that it is affecting. Considering the results of this example, b indicating the silicon element concentration [at%] with respect to the sum of the vanadium element concentration [at%], the silicon element concentration [at%] and the nitrogen element concentration [at%] is 0.24 or more. If so, the oxidation resistance of the vanadium nitride film can be improved.

Since the oxidation resistance of the hard film is an index showing the resistance to the oxidation reaction of the film surface, it is not particularly affected by the steel material coated with the hard film. Therefore, the vanadium nitride film of the test piece used for the above-mentioned adhesion evaluation also has the same oxidation resistance as the vanadium nitride film of Example 7. That is, the test pieces of Examples 1 to 6 are hard film covering members having excellent adhesion and oxidation resistance.

The present invention can be applied to hard coating treatment of molds and tools, for example, automobile parts such as gears. That is, the vanadium nitride film coating member according to the present invention is used, for example, as a mold, a tool, or an automobile part.

1 Vanadium nitride film coating member 2 Steel material 2a Surface modification layer 3 Vanadium nitride film 4 Vanadium nitride film 10 Plasma processing device 11 Chamber 12 Anode 13 Cathode 14 Pulse power supply 15 Gas supply pipe 16 Gas exhaust pipe

Claims (7)

With a steel material containing 3 to 16% Cr in mass%,
A surface modification layer containing a chromium nitride compound formed on the surface of the steel material and
The vanadium nitride film formed on the surface modification layer and
A vanadium nitride film coating member having a vanadium nitride film formed on the vanadium nitride film. The vanadium nitride film coating member according to claim 1, wherein the surface modification layer has a thickness of 0.5 to 50 μm. The vanadium nitride film coating member according to claim 1 or 2 , which is used as a mold. The vanadium nitride film coating member according to claim 1 or 2 , which is used as a tool. The vanadium nitride film coating member according to claim 1 or 2 , which is used as an automobile part. A nitriding step of forming a surface modified layer containing a chromium nitride compound on the surface of a steel material containing 3 to 16% of Cr in mass%, and a nitriding process.
A vanadium nitride film forming step of forming a vanadium nitride film on the surface of the steel material after the nitriding step,
A method for producing a vanadium nitride film coating member, which comprises a vanadium nitride film forming step of forming a vanadium nitride film on the vanadium nitride film. The vanadium nitride film coating according to claim 6 , wherein the nitriding step is a plasma nitriding step, and the plasma nitriding step is carried out in the same processing container as the processing container used in the vanadium nitride film forming step. Manufacturing method of parts.

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