JPS593552B2 - Alloy steel surface treatment method - Google Patents

Description

Detailed Description of the Invention 10 The present invention relates to a method for surface treatment of alloy steel, particularly for preventing galling of tools used in sliding members or molds for plastic working. This invention relates to a surface treatment method.

Various materials are used as mold materials for plastic working15, among which high-alloy tool steel is often used as mold material for forming workpieces under high loads such as extrusion and cold forging. There is.

In general, these alloys are used by subjecting the workpiece to a solid lubrication treatment and not subjecting the mold to a paving treatment20, so galling or seizure may occur during plastic working.

Therefore, a liquid lubricant such as wax or mineral oil may be applied to the mold for plastic working. However, liquid lubricants are not sufficient for molding under high loads, and application of solid lubricants to molds has been desired. As a solid lubrication treatment for the workpiece, a phosphoric acid or peroxylic acid coating treatment is generally used in cold molding.

By the way, the general effects of lubricants are as follows.

When two solid bodies are kept in contact and one slides against the other, a frictional force is generated on the contact surfaces in the opposite direction to the sliding direction.

At this time, if a liquid or solid is inserted between the two surfaces,
It is possible to reduce the magnitude of the frictional force from a fraction to a few hundred times. The frictional force in this case is due to the internal friction of the lubricant itself and is very small, so the friction coefficient has an extremely small value. However, this lubrication state is only possible if the thickness of the liquid layer is 1←3.
mm or more, and when the V1 contact pressure becomes high and the liquid layer thickness ▲ becomes less than the depth of microscopic irregularities existing on the solid surface, the direct contact between the solids or the thin film of several molecular layers of the liquid will be removed. A contact area will be created between the two.

Under such conditions, foreign molecules that are mechanically sandwiched between the solid surfaces will protrude from the contact point due to the relative movement of the solids, making it difficult to achieve good lubrication. Therefore, in order to intervene at the point of contact and influence the friction, it is desirable that the lubricant be adsorbed onto the surface of the material and form a film that is fairly strongly bonded to the material. A typical method that produces a strong lubricating film through a chemical reaction with the metal surface and is most effective against the high working pressure during cold forging is, for example, applying a phosphate film or oxalic acid to the metal surface. After forming a salt film, a chemical conversion coating treatment is known in which a fatty acid soda soap is applied and a metal soap is formed between the two.

However, although these coating treatments have a relatively strong bonding force and are effective on general low-alloy steel, they tend to peel off on high-alloy tool steel used as mold material, and are hardly effective. do not have.

In particular, alloy steel containing 3% by weight or more of Cr has almost no adhesion, making it difficult to create a lubricated surface. In other words, for molds or sliding members that are subjected to friction under high loads, the material itself needs to have rigidity or hardness, so high alloy tool steel containing a large amount of carbide-forming elements, especially Cr, is generally used. . However, when the amount of Cr added increases, strong and dense oxides are formed on the surface. However, there is a problem in that these oxides reduce the adhesion of the coating during chemical conversion coating treatment. On the other hand, conventionally, a method has been used in which a film of solid lubricant is applied to the workpiece side, but this method does not apply to the entire workpiece, for example, when applying plastic stress to a part of a large workpiece. It is necessary to carry out coating treatment, and the equipment becomes large, which is disadvantageous in terms of handling and economy.

Furthermore, even if we comprehensively consider issues such as post-processing of processed products, resource saving, energy saving, or man-hours, it is not a good idea to apply a film treatment to the processed materials when processing large items.
It is generally advantageous to lubricate the mold or tool.
Next, regarding wear, when two solid bodies are kept in contact and one slides against the other, friction occurs and the surfaces of the two solids are completely damaged, resulting in surface damage.

Is this phenomenon due to wear? Is it possible to contact two solids with different hardness? When sliding, the amount of wear on the side with higher hardness ▲ is much smaller than on the side with lower hardness. That is, the harder the material, the less wear it will cause, and tool steel, which is a hard material, is used for products that are used under high loads, such as molds for plastic working. However, even tool steel is not sufficient,
These are often subjected to surface hardening treatments such as carburizing and nitriding. However, in all conventional methods, the surface treatment for applying lubricant to the mold and the like and the surface hardening treatment are not performed in a single step, and are not economical. The present invention aims to eliminate the drawbacks of the above-mentioned conventional methods. With what I received,
The purpose of the present invention is to provide a surface treatment method for alloy steels such as tool steels containing a relatively large amount of chromium (3 to 25% by weight), which can improve wear resistance and at the same time provide a lubricating effect. shall be.

In the present invention, an alloy steel having a chromium content of 3 to 25% by weight is inserted into a vacuum container, the alloy steel is used as a cathode, and a gas containing at least one of nitrogen and carbon is introduced into the container. At the same time, a nitrided layer, a carburized layer or a carbonitrided layer is formed on the surface of the alloy steel by glow discharge by applying a DC voltage of 300 to 2000 V, and then a solid lubricating effect is exerted on the surface of the treated steel. The above object is achieved by forming a chemical conversion film.

Alloy steels used for plastic working molds, cutting tools, sliding surfaces, etc. are added with Cr, W, CO, MO, etc. to improve strength, hard nail oxidation resistance, or corrosion resistance. Particularly for parts that require hard claw strength, chromium is 3 to 5% by weight.
Added alloy tool steel is used. This added chromium forms a strong oxide on the surface of the steel material and improves corrosion resistance, but on the other hand, this oxide film is not stable even after chemical conversion treatments such as phosphate or oxalate. As a result, as mentioned above, the adhesion density of the lubricant decreases or chemical bonding is inhibited, causing the oil lubricant to run out when used under high loads. The present inventors conducted detailed research on methods for preventing lubricant loss on surfaces that slide (relative motion) under high loads, and found that in order to prevent rudder D caused by lubricant loss, it is necessary to use lubricant. It was found that treatment of the base material surface before coating is extremely important. In order to prevent this galling, it is effective to roughen the surface of the base material to prevent the lubricant from peeling off.It is also important to roughen the surface as finely as possible. I discovered that. Although the surface can be roughened by a method of mechanically roughening the surface, such as by shot blasting, the unevenness of the surface is large and not fine, so it does not have a soft effect. Based on the above findings, the present invention proposes a method for destabilizing or removing oxides adhering to the surface of alloy steel and at the same time extremely hardening the surface layer by applying ion nitriding or ion carbonitriding treatment. The surface is chemically and physically activated to improve the adhesion of the subsequent chemical lubricant coating, so that it can be used as a mold for plastic working or as a sliding member.

In the process of the present invention, parts such as molds, tools, and sliding members whose surfaces are coated with lubricant are first placed in an airtight container.
After reducing the pressure to 0-2T0rr or less, fill it with nitrogen-containing gas or nitrogen and carbon-containing gas to 10-1
-10T0rr pressure, then the container itself as an anode,
A glow discharge is generated by applying a DC voltage of 300 to 2000 V using the object to be treated as a cathode.

When the pressure is reduced to -1022T0rr or less, oxygen remaining in the reduced pressure container becomes difficult to be adsorbed on the surface of the material to be treated, and formation of oxides on the surface of the material to be treated can be prevented. Regarding the conditions of the applied voltage, if the applied voltage is lower than 300V, the sputtering effect on the surface due to glow discharge will not be sufficient, while if the applied voltage is higher than 200V, the gas pressure sealed in the vacuum container will decrease and the speed of sputtering will decrease. It's late v
The spatter cleaning effect decreases.

Ionization of alloy steel with a chromium content of 3 to 25% by weight through ion treatment using glow discharge? Nitrogen or nitrogen and carbon collide with the surface of the product to be treated, destroy oxides formed on the surface, and cause diffusion and penetration? It will be done.

Therefore, when the applied voltage is outside the range of 300 to 2000,
Although chemical conversion coating treatment after ion treatment is virtually impossible, under the applied voltage conditions according to the present invention, the chromium content is 3.
Chemical conversion coating treatment is also possible for alloy steels containing up to 25% by weight. In general treatment, the temperature is 400 to 600°C, but in the present invention, the temperature is preferably 300 to 500°C. In other words, since the nitrided layer or carbonitrided layer is hard and brittle,
The thickness ▲ has an appropriate value. According to the inventors' experiments,
For tool steel molds, the diameter is 0.1 to 20 μm, preferably 0.5
~5 μm is preferable. Is the surface obtained in this way formed by nitrogen or a compound of nitrogen and carbon? Is it hard to get wet? In addition, an atomically uneven surface is formed by spatter cleaning, which is most effective against dirt and lubricant film adsorption. After the above-mentioned sputter link treatment, a chemical conversion coating treatment is performed, which first forms a film of phosphate or oxalate (for example, zinc phosphate or iron oxalate). After that, a coating of soda-based soap such as sodium stearate or oil or fat is further formed thereon.

The above-mentioned phosphates or oxalates,} and soda-based soaps or oils are generally applied in the form of aqueous solutions or suspensions, typically in the form of so-called Bonderite to Bonderite (American Parker Rust Pr'00fC).
A combination of lubricants called 0 (trade name) is preferably used. The film formed by this treatment method shows that although the metal itself has poor lubricating ability, the film produced by the chemical reaction between the metal surface and fatty acids has a very effective lubricating effect. It has the advantage of not peeling off even under great pressure. As mentioned above, when the alloy steel surface is pretreated by ion nitriding or ion carbonitriding and then chemical conversion coating is applied, a lubricating film is formed on the uneven surface due to spatter cleaning, and the relative movement of the solid Since the plate has a lubricating effect and a chemically bonded lubricating film is formed, the lubricant does not protrude from the contact surface, and the metal is used for plastic processing that involves sliding under high loads. A highly effective lubricating surface can be provided for molds, cutting tools, or sliding members.

Furthermore, since nitrogen or a compound of nitrogen and carbon is formed on the surface, wear resistance is also good. The present invention will be explained in more detail with reference to Examples. Example 1 A mold for plastic working as shown in FIG. 1 was made of alloy tool steel having a chemical composition as shown in Table 1.

These molds are treated according to their materials and refined to a hardness (HRC) of 57 or higher as shown in Table 1.The numbers in the table indicate the number of times the molding test occurred for each mold. . Second
As is clear from the table, for the heat-treated products, several times
In the case of chemical conversion coating treatment after shot blasting treatment, rudder v occurs after several hundred times, and since the Cr weight percent of sample waterfall 1 is relatively small, chemical conversion coating treatment is possible without pretreatment. Even when I tried it a few thousand times, a crack occurred.

I made these. After heat treating these alloy steels, finishing processing and polishing are performed. Furthermore, it has a wrap finish. Regarding the molds of each composition above, (1) as-heat treated, (2) shot blasted and then phosphate coated, and (3) ion nitrided and then phosphate coated. , and (4) ion carbonitriding followed by phosphate coating treatment. Four types of molds were produced. The ion nitriding treatment or the ion carbonitriding treatment includes 1
After charging into a vacuum container whose pressure is reduced to 0-2T0rr or less,
Using the reduced pressure container itself as an anode and the mold as a cathode, nitrogen gas or a mixed gas of a nitrogen chamber and hydrocarbons is introduced to a pressure of 1T0rr, and glow discharge is performed for about 30 minutes with the temperature of the processed product reaching 500℃. It is something that has become familiar.

Further, shot blasting was carried out using #120 steel pieces at a pressure of 7 kg/cm2. The chemical conversion coating treatment after these pretreatments was carried out by coating the mold with phosphate and then forming a fatty acid coating thereon. To give an example of this process, after going through preliminary treatments such as degreasing the mold, washing it with water, and washing the chains, it goes through the steps of applying a phosphate solution, washing it with water, neutralizing it, applying a fatty acid solution, and drying it. It will be done. As shown in Fig. 1, the mold treated as described above is press-formed by putting the workpiece (SUS3O4) 2 into the mold 1 and applying lubricating oil such as wax with the punch 3. There was one.

The experimental results at this time are shown in Table 2. A sliding wear test was conducted using 13Cr steel as a mating material with a load of 100 kg and a sliding distance of 55 mTIL.

The results are shown in Table 3 below. The numbers in the table indicate the number of sliding movements until a certain level of wear is reached.

As is clear from Table 3, it is recognized that the wear life of V1 sliding members is extended by applying the surface treatment of the present invention.

Having explained the above, the present invention is a surface treatment method for alloy steel, in which substances other than iron are diffused and penetrated into the surface of alloy steel. This method forms a hardened layer with a rough surface, and then forms a chemical conversion film having a solid lubricating effect on the surface of the treated steel. It has the excellent effect of providing a surface with good wear resistance and excellent lubrication even for alloy steels with a high content of 3 to 25% by weight.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a mold when a processing test is performed using molds for plastic working according to examples and comparative examples of the present invention. 1...Mold, 2...Work material, 3...
...Ponchi.

Claims (1)

[Scope of Claims] 1. An alloy steel having a chromium content of 3 to 25% by weight is inserted into a reduced pressure container, the alloy steel is used as a cathode, and a gas containing at least one of nitrogen and carbon is placed in the container. while applying a DC voltage of 300 to 2000 V to form a nitrided layer, carburized layer, or carbonitrided layer on the surface of the alloy steel by glow discharge, and then solid lubrication on the surface of the treated alloy steel. A method for surface treatment of alloy steel, characterized by forming a chemical conversion film having an action. 2. In claim 1, the chemical conversion coating is:
1. A method for surface treatment of alloy steel, which is obtained by forming a phosphate or oxalate film and then further forming a soda soap or oil film thereon.