JP2024061966A - Metal plastic processing die and manufacturing method thereof - Google Patents

Abstract

[Problem] The durability of the coating is improved by evaluating and controlling the composite hardness. [Solution] A metal plastic processing die having excellent durability of a coating, the surface of which is coated with a hard coating containing either a nitride or a carbonitride containing at least one of Ti, Al, and Cr, the hard coating having a thickness of 1 μm or more, and the composite hardness being defined as the Vickers hardness when a hardness test is carried out on the hard coating formed on the surface of the die base material under loading conditions according to the hardness symbol HV0.1 specified in JIS Z 2244-1, the composite hardness being 800 HV0.1 or more. [Selected Figure] Figure 1

Description

This relates to dies for plastic processing, which are used in press processing, forging processing, etc. and require wear resistance.

Dies made of metals or steels such as cold die steel, hot die steel, high-speed tool steel, and cemented carbide have been used for plastic processing such as forging and pressing. The above processing methods are classified into cold processing, in which processing is performed at around room temperature, and warm processing or hot processing, in which the workpiece is heated to 400°C or higher. With any type of die, adhesive wear with the workpiece can be an issue, and wear resistance is required for the working surface.

In recent years, with the increasing strength of workpiece materials and improvements in surface modification technology, various dies have been proposed that have hard coatings formed on the die surface to improve wear resistance. Methods for applying hard coatings include CVD (chemical vapor deposition), PVD (physical vapor deposition), TRD (thermal reactive deposition diffusion), and PCVD (plasma chemical vapor deposition). In particular, the PVD and PCVD methods are widely used because the application temperature is kept relatively low at 500°C or less, which results in little dimensional change in the die and does not require heat treatment after coating.

In dies that have been subjected to such coating processing, the die life is mainly due to peeling of the coating. Coating peeling occurs because the coating cannot follow the deformation of the die base material, leading to the occurrence of cracks and peeling. For example, Patent Document 1 discloses a durable hard material coated die for plastic processing in which the film composition, film structure, film thickness, and hardness difference from the base material are controlled. Patent Document 2 discloses a die that combines good adhesion resistance and smoothness by controlling the surface roughness and film type of the working surface of the die.

Patent No. 4771223 Patent No. 7029646

As mentioned above, the stress applied to the surface in the environment in which the mold is used causes the coating to be unable to follow the deformation of the substrate, leading to the generation of cracks and peeling of the coating, which then brings about the end of the mold's life. Therefore, it is important to make the mold surface as resistant to dents as possible. However, in the past, there was no clear guideline for the dent resistance of the mold surface, nor any consideration of the factors that control it, leaving room for improvement. Furthermore, even if the mold surface is resistant to dents, if the adhesion between the hard coating and the mold substrate is poor, the hard coating will peel off early, bringing about the end of the mold's life.

The present invention improves the durability of the coating by evaluating and controlling the combined hardness of the mold substrate and the hard coating, and the adhesion between the mold substrate and the hard coating.

In order to solve the above problems, the metal plastic processing die of the present invention is (1) a metal plastic processing die having a surface of a die base material coated with a hard coating of either a nitride or a carbonitride containing at least one of Ti, Al and Cr, the hard coating having a thickness of 1 μm or more, and a composite hardness of 800 HV 0.1 or more, when the composite hardness is defined as the Vickers hardness measured when a hardness test is carried out on the hard coating formed on the surface of the die base material under loading conditions in accordance with the hardness symbol HV _0.1 specified in JIS Z 2244-1.

(2) A metal plastic processing die having excellent durability of the coating described in (1) above, characterized in that the surface roughness of the die base material is Ra<0.1 μm, Rz<0.5 μm.

(3) A metal plastic processing die having excellent durability of the coating described in (1) or (2) above, characterized in that the die base material is composed of cold die steel containing 0.9 mass% or less of C, 9 mass% or less of Cr, and the balance being mainly Fe.

(4) A metal plastic processing die having excellent durability of the coating described in (1) or (2) above, in which the die base material is made of powdered high-speed tool steel containing 1.0 to 1.3 mass% C, 9 mass% or less Cr, and the remainder being mainly Fe.

(5) A metal plastic processing die in which the surface of the die base material is nitrided and the coating described in (3) above has excellent durability.

(6) A metal plastic processing die in which the surface of the die base material is nitrided and the coating described in (4) above has excellent durability.

(7) The manufacturing method of a die for plastic processing according to the present invention is a manufacturing method of a die for plastic processing in which a surface of a die base material is coated with a hard coating of either a nitride or a carbonitride containing at least one of Ti, Al, and Cr, and is characterized in that, when the Vickers hardness obtained when a hardness test is performed on the hard coating formed on the surface of the die base material under loading conditions in accordance with the hardness symbol HV0.1 specified in JIS Z 2244-1, the composite hardness is defined as the composite hardness, and the manufacturing conditions for the die base material and the hard coating are determined in advance so that the composite hardness is 800 _HV0.1 or more under conditions in which the film thickness of the hard coating is 1 μm or more, and the die for plastic processing is manufactured based on the determined manufacturing conditions.

(8) The method for manufacturing a die for plastic processing described in (7) above, characterized in that in the manufacturing condition determination step, the surface roughness of the die base material is set to Ra<0.1 μm and Rz<0.5 μm.

(9) The method for manufacturing a die for plastic working described in (7) or (8) above, characterized in that in the manufacturing condition determination step, a cold die steel containing 0.9 mass% or less C, 9 mass% or less Cr, and the remainder mainly composed of Fe is determined as the material for the die base material.

(10) The method for manufacturing a die for plastic processing described in (7) or (8) above, characterized in that in the manufacturing condition determination step, a powder high-speed tool steel containing 1.0 to 1.3 mass% C, 9 mass% or less Cr, and the remainder mainly Fe is determined as the material for the die base material.

(11) The method for manufacturing a die for plastic processing described in (9) above, in which, in the manufacturing condition determination step, it is determined that the surface of the die base material is to be nitrided.

(12) The method for manufacturing a die for plastic processing described in (10) above, in which, in the manufacturing condition determination step, it is determined that the surface of the die base material is to be nitrided.

According to the present invention, by increasing the combined hardness and adhesion of the mold substrate and hard coating, it is possible to obtain a mold in which the mold surface is less likely to be dented, coating peeling is suppressed, and the coating has high durability.

FIG. 1 is a schematic diagram of a composite hardness testing device.

An embodiment of the present invention will be described. The die of this embodiment is a die for plastic processing (hereinafter sometimes abbreviated as die) that is used for press processing, forging processing, etc. and requires wear resistance. The die is composed of a die base material and a hard coating.

(About mold base material)
The die substrate is preferably a high-strength tool steel, more preferably a cold die steel, a hot die steel, a high-speed tool steel, or a powdered high-speed tool steel. By using cold die steel, hot die steel, high-speed tool steel, or powdered high-speed tool steel that undergoes secondary hardening during tempering, softening during coating can be suppressed.

Here, die steel is a material that contains chromium, manganese, molybdenum, vanadium, etc., and is quenched and tempered when used in dies, etc., and has good hardness and wear resistance, little quenching distortion, and excellent toughness. Cold die steel contains more carbon than hot die steel, and is more likely to lose hardness when heated than hot die steel.

High-speed tool steel is used in cutting tools and general-purpose tools, and is also called high-speed steel. High-speed steel may be powdered high-speed steel (powdered high-speed tool steel) or molten high-speed steel. Powdered high-speed steel is made by sintering powdered material under pressure and molding it, and has excellent toughness and wear resistance. Molten high-speed steel is made by rolling material melted in an electric furnace and molding it, and has excellent wear resistance and cost.

Among these tool steels, the use of tool steels with high toughness can suppress cracking and chipping of the die. From this viewpoint, it is desirable to use cold die steels mainly made of Fe containing 0.9 mass% or less C and 9 mass% or less Cr, or powder high-speed tool steels mainly made of Fe containing 1.0 to 1.3 mass% C and 9 mass% or less Cr. The cold die steels have excellent toughness because they contain few primary carbides. It is more desirable to set the C content to 0.6 mass% or more in the cold die steels and the Cr content to 5 mass% or more. The powder high-speed tool steels have excellent toughness because the size of the primary carbides is small, at 1 to 2 μm. It is more desirable to set the Cr content to 3.5 mass% or more in the powder high-speed tool steels.

(Surface roughness)
It is desirable to give a predetermined surface roughness to the mold substrate by performing a shape processing process. The surface roughness is preferably Ra<0.1 μm, Rz<0.5 μm, and more preferably Ra<0.05 μm, Rz<0.3 μm. By adjusting the surface roughness to this range, the adhesion between the coating and the mold substrate can be improved.

The surface roughness can be adjusted by subjecting the surface of the mold substrate to grinding, polishing, cutting, electrical discharge machining, etc. Here, the shape processing step may be a combination of multiple steps, and the surface roughness may be adjusted, for example, by rough processing by grinding followed by finishing by polishing. Buffing using diamond paste may be performed to ensure that the desired surface roughness is obtained.

(Regarding nitriding)
After adjusting the surface roughness, it is desirable to perform a nitriding treatment on the surface of the mold base material. By performing the nitriding treatment, the composite hardness can be improved. The nitriding treatment is preferably an ion nitriding treatment or a radical nitriding treatment. Since the ion nitriding treatment and the radical nitriding treatment are unlikely to form a compound layer during the treatment, it is possible to prevent a decrease in adhesion due to an increase in surface roughness caused by the formation of a compound layer.

Ion nitriding (plasma nitriding) is a method in which nitrogen and hydrogen are used as nitriding gases, a DC voltage is applied between the mold substrate and the wall of the nitriding furnace in a vacuum atmosphere to generate a glow discharge, and the nitrogen ions and hydrogen ions obtained by this glow discharge collide with the substrate surface to perform the nitriding process. The pressure in the vacuum atmosphere is preferably 13 Pa or more and 1.3 kPa or less. The DC voltage is preferably about several hundred volts.

Radical nitriding is a method of nitriding that efficiently uses radicals with high nitriding properties obtained by controlling gas flow rate, processing pressure, plasma output, etc. with high precision, and can suppress the formation of a compound layer by adjusting the amount of ions and radicals generated during the nitriding process.

However, nitriding processes other than ion nitriding and radical nitriding (for example, gas nitriding) may be used. In this case, it is desirable to remove the chemical layer after the nitriding process. This allows the desired surface roughness to be obtained.

(About hard coating)
The hard coating is composed of a nitride or carbonitride containing at least one of Ti, Al, and Cr. In the case of a hard coating mainly composed of Al or Cr, the oxidation resistance of the coating is high, and the decrease in hardness and peeling of the coating due to oxidation are suppressed, so that it is particularly preferable when the temperature of the mold surface increases. In addition, Si may be contained in the hard coating within a range that does not impair the effects of the present invention. By adding Si, the oxidation resistance of the hard coating can be improved. Here, the nitride is preferably TiN, and more preferably CrN or AlCrN. In addition, the carbonitride is preferably TiCN. The nitride may be composed of one type of nitride, or may be composed of two or more types of nitrides. For example, the hard coating may be composed of only one type of CrN, TiN, AlCrN, and TiCN, or may be composed of multiple types of hard coatings.

The hard coating is preferably formed by CVD (chemical vapor deposition), PVD (physical vapor deposition), TRD (thermal reactive deposition diffusion), or PCVD (plasma chemical vapor deposition), more preferably PVD or PCVD. The PVD and PCVD methods are preferably used because the application temperature is 500°C or less, there is little dimensional change in the mold during application, and no heat treatment is required after application of the coating.

PVD methods include vacuum deposition, sputtering, and ion plating. Ion plating is preferred from the standpoint of the range of applicable parts and the dimensional accuracy of the mold. From the standpoint of dimensional accuracy and hardness, the processing temperature is preferably 500°C or less.

The thickness of the hard coating is 1 μm or more, and preferably 2 μm or more. By setting the thickness to 1 μm or more, the desired wear resistance effect and composite hardness can be obtained. Composite hardness is an evaluation index that quantitatively expresses the resistance of the mold surface to dents, and the higher the composite hardness, the less likely the mold is to be dented.

Here, composite hardness refers to the hardness of the composite consisting of the hard coating and the mold base material, and is the Vickers hardness when a hardness test is carried out on the hard coating formed on the surface of the mold base material under loading conditions in accordance with the hardness symbol HV0.1 specified in JIS Z 2244-1.

The composite hardness is 800HV _0.1 or more, preferably 850HV _0.1 or more, and more preferably 900HV _0.1 or more. The subscript 0.1 to the right of HV indicates the load (0.98N) during the hardness test.

Example 1
The present invention will now be described in detail with reference to examples.

For the samples shown in Table 1, surface roughness measurement, composite hardness measurement, film thickness measurement, and scratch test (adhesion evaluation) were performed. Plate-shaped test pieces made of cold die and powdered high-speed tool steel were used as the samples. The cold die steel was air-cooled and quenched at a temperature of 1030 to 1050 ° C. in the atmosphere, tempered at a temperature of 500 to 600 ° C., processed into a plate (one side 40 mm, the other side 50 mm, and the thickness 7 mm), and the test surface was ground. The powdered high-speed tool steel was oil-cooled and quenched at a temperature of 1130 to 1150 ° C., tempered at a temperature of 560 to 600 ° C., processed into a plate (one side 40 mm, the other side 50 mm, and the thickness 7 mm), and the test surface was ground. The Rockwell hardness (HRC) of each plate-shaped test piece was also measured based on JIS Z2245.
The components of the substrate are as shown in Table 1, which lists the components other than Fe contained in the substrate.

The surface roughness (Ra, Rz) of the test surface after grinding (i.e., before the formation of the hard coating) was measured using a Surfcom 1400D-3DF (Tokyo Seimitsu). The measurement length was 5 mm, the cutoff value was 0.8 mm, the filter type was Gaussian, and the measurement speed was 0.3 mm/s.

For some of the samples to be nitrided (sample No. 6), the surface roughness (Ra, Rz) was measured, and then ion nitriding was carried out at 500°C for 2 hours. When the properties after nitriding were checked, there was no compound layer, and the diffusion layer was about 30 μm.

A hard coating consisting of one of AlCrN (commercial product), TiN (commercial product), TiCN (commercial product) and CrN (commercial product) was formed on the test surface of each plate-shaped test piece by the PVD method. A hard coating was formed on some of the nitrided samples after nitriding. The thickness of the hard coating was evaluated by the Calotest method. Specifically, using an Autocrater (Nanotech Co., Ltd.), the sample surface was polished with a rotating steel ball while dropping diamond slurry under the conditions of ball diameter 30 mm, motor speed 400 rpm, test time 30 seconds and diamond slurry 1 μm, and then the thickness was calculated based on the polishing marks and the radius of the steel ball.

As shown in the schematic diagram of Figure 1, a micro Vickers hardness tester (Future Tech FM-700) was used to press an indenter into the surface of the hard coating to determine the Vickers hardness _HV0.1 (test load: 0.98 N). The same Vickers hardness test was carried out five times for each plate-shaped test piece, and the average values are shown in Table 1.

The adhesion of the hard coating was evaluated by a scratch test. In the scratch test, a diamond indenter is pressed against a sample fixed on a table, and a load is gradually applied while the table is moved at a constant speed to measure the adhesion of the film. The test was carried out using a CSR1000 (manufactured by Rhesca) with an indenter radius of 200 μm, an initial load of 1 N, a final load of 121 N, and an indenter scanning speed of 10 mm/min. The critical load was set to the load at which the frictional force rises sharply.

In sample No. 9, the thickness of the hard coating was 1 μm or less, so the composite hardness was less than 800 HV _0.1 . In sample No. 10, the carbon and chromium were excessive, so the composite hardness was less than 800 HV _0.1 . In sample No. 11, the surface roughnesses Ra and Rz were excessively large, so the composite hardness was 800 HV _0.1 or more, but the critical load was low and the adhesion was poor. Comparing samples No. 1 and 6, it was found that the composite hardness and critical load were increased by applying the nitriding treatment.

Example 2
Using plate-shaped test pieces of samples No. 2 and No. 10 in Table 1, cup-molding dies with a diameter of 30 mm and a height of 250 mm were fabricated, and the life of the actual dies was evaluated. The hard coating was formed after each plate-shaped test piece was molded into a cup shape. Then, S55C was used as the workpiece, and cold forging was performed. The life of the die was determined as the number of molded pieces (the number of cup-shaped molded products) when coating peeling occurred visually. The results are shown in Table 2.

Claims (12)

A die for plastic working, comprising a die base material having a surface coated with a hard coating of either a nitride or a carbonitride containing at least one of Ti, Al, and Cr,
A metal plastic processing die having excellent durability of a coating, characterized in that the hard coating has a thickness of ₁ μm or more, and when the Vickers hardness measured when a hardness test is carried out on the hard coating formed on the surface of the die base material under loading conditions in accordance with the hardness symbol HV0.1 specified in JIS Z 2244-1 is defined as the composite hardness, the composite hardness is 800 HV0.1 or more. A metal plastic processing die having excellent durability of the coating according to claim 1, characterized in that the surface roughness of the die base material is Ra<0.1 μm, Rz<0.5 μm. The metal plastic processing die having excellent durability of the coating according to claim 1 or 2, characterized in that the die base material is made of cold die steel containing 0.9 mass% or less of C, 9 mass% or less of Cr, and the balance being mainly Fe. The metal plastic processing die according to claim 1 or 2, in which the die base material is made of powdered high-speed tool steel containing 1.0 to 1.3 mass% C, 9 mass% or less Cr, and the remainder being mainly Fe, has excellent durability as a coating. A metal plastic processing die having excellent durability of the coating according to claim 3, in which the surface of the die base material is nitrided. A metal plastic processing die having excellent durability of the coating according to claim 4, in which the surface of the die base material is nitrided. A method for manufacturing a die for plastic working, comprising: coating a surface of a die base material with a hard coating of either a nitride or a carbonitride containing at least one of Ti, Al, and Cr, comprising:
When a hardness test is performed on a hard coating formed on the surface of a mold base material under a load condition in accordance with the hardness symbol HV0.1 specified in JIS Z 2244-1, the Vickers hardness is defined as the composite hardness.
A manufacturing condition determination step of determining manufacturing conditions for a mold base material and the hard coating in advance so that the hard coating has a thickness of 1 μm or more and a composite hardness of 800 HV _0.1 or more;
A method for manufacturing a die for plastic working, comprising manufacturing the die for plastic working based on the determined manufacturing conditions. The method for manufacturing a die for plastic processing according to claim 7, characterized in that in the manufacturing condition determination step, the surface roughness of the die base material is set to Ra < 0.1 μm and Rz < 0.5 μm. The method for manufacturing a die for plastic working according to claim 7 or 8, characterized in that in the manufacturing condition determination step, a cold die steel containing 0.9 mass% or less C, 9 mass% or less Cr, and the remainder mainly Fe is determined as the material for the die base material. The method for manufacturing a die for plastic processing according to claim 7 or 8, characterized in that in the manufacturing condition determination step, a powder high-speed tool steel containing 1.0 to 1.3 mass% C, 9 mass% or less Cr, and the remainder mainly Fe is determined as the material for the die base material. The method for manufacturing a die for plastic processing according to claim 9, wherein in the manufacturing condition determination step, it is determined that the surface of the die base material is to be nitrided. The method for manufacturing a die for plastic working according to claim 10, wherein in the manufacturing condition determination step, it is determined that a nitriding treatment is to be performed on a surface of the die base material.