JPH0317891B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The disclosed technology belongs to the field of mold materials used in cold working such as cold casting and processing technology thereof. <Summary of the gist> The invention of this application forms the mold body from high-grade tool steel having excellent strength and compressive deformation resistance similar to SKH9, etc., and furthermore, the mold body is made of high-grade tool steel that has excellent strength and compressive deformation resistance similar to SKH9, etc. The present invention relates to a mold for cold working such as cold forging, which is provided with a nitrided coating layer that has high corrosion resistance and seizure resistance.
0.35-0.7%, Si less than 1.0%, Mn less than 1.0%,
Cr 1.0~5.0%, Mo 0.1~7.0%, V 0.1~4.0
%, W is 4 to 20%, and the balance is Fe. It is hardened and tempered using standard heat treatment, and then nitrided at a temperature lower than the tempering temperature to form a nitrided coating layer. By forming a mold, there is less heat treatment distortion and post-processing is minimized, or in addition, it is possible to form a cold working mold with a hardened surface layer such as TiN formed by low-temperature physical vapor deposition such as ion plating. This is such an invention. <Prior art> As is well known, in cold forging, sintering forming, press forming, etc. used in automobile production factories,
Cold working is widely used, and forming dies are selected and used depending on the application and processing conditions, and the material for the punch etc. also varies depending on the load during use, for example, from SKD11 (cold die steel) according to the JIS standard.
There is a wide variety of products such as SKH9, SKH57 (high speed steel), and even cemented carbide. By the way, the mold material used is selected as described above in order to ensure the long life of the mold from the relationship between the load conditions during use and durability, but the wear and tear condition of the mold that affects the lifespan is determined by the strength, So-called partial chipping, such as large mold cracks and chips due to lack of toughness,
In addition, mold surface wear, galling, and seizure occur due to insufficient wear resistance, galling resistance, and seizure resistance, and mold deformation occurs mainly due to insufficient strength (compressive yield strength). It has been found that there is a deep correlation between the mold material properties related to mold wear and the composition of the mold material. That is, the mold material changes from SKD11 to SKH9, SKH9
It is known that the toughness properties steadily decrease as the composition moves from SKH57 to higher grade compositions. On the other hand, when considering the lifespan of molds, as the required level of mold deformability, wear resistance, galling resistance, and seizure resistance of mold materials increases, from SKD11 to SKH9, and further from SKH9 to SKH57.
There is a tendency to upgrade from SKH57 to cemented carbide. <Problems to be Solved by the Invention> In some cases, a hard carbide or hard nitride film is formed as a measure against surface hardening of the mold material. However, as mentioned above, as mold materials become more sophisticated, the toughness decreases and chipping, etc., cannot be avoided. To deal with this, several materials have recently been developed to improve toughness, but these techniques only improve the material itself, so although toughness can be improved, in return, hardness has improved. This resulted in problems such as a decrease in wear resistance and wear resistance. Therefore, as a completely different method, materials such as ICS6 and ICS22, which are special low carbon steels that are quenched and then carburized, have been devised as toughness improving materials, but they are used for mold materials with relatively low loads compared to cold forging etc. Therefore, when subjected to high-stress compression as in cold forging, the shape deforms into a so-called cylindrical shape, making it difficult to put it to practical use. Furthermore, since the carburizing temperature is higher than the tempering temperature, there is an inconvenience that heat treatment distortion such as deformation and dimensional change is unavoidable, and post-processing such as mold finishing is required after the carburizing process, which increases the number of man-hours. The disadvantage is that it takes a lot of time, the work is complicated, and it results in high costs. The purpose of the invention of this application is to solve the problems of mold materials and processing of cold working molds based on the above-mentioned prior art, and to solve the problems of mold materials and processing for cold working molds based on the above-mentioned prior art.
By selecting a high-alloy steel shape that contains Cr, Mo, V, and W in a predetermined proportion, it has excellent strength and compressive deformation resistance comparable to high-grade tool steels such as SKH9 and SKH57. In addition, the mold surface is nitrided at a temperature lower than the tempering temperature to provide good wear resistance, galling resistance, and seizure resistance. At the same time, it is an object of the present invention to provide an excellent mold for cold working which is useful in the field of processing technology used in metal product manufacturing work by minimizing post-processing as much as possible. <Means for Solving the Problem> In order to solve the above-mentioned problem, the invention of this application, which is based on the above-mentioned claims, has a mold body made of high-grade tool steel and the mold. A cold working mold having a nitriding coating layer on the main body surface, containing 0.35 to 0.7% C, less than 1.0% Si, and Mn.
is less than 1.0%, Cr is 1.0-5.0%, Mo is 0.1-7.0%,
A nitriding coating layer formed at a treatment temperature lower than the tempering temperature is provided on the surface of the mold body made of high alloy steel with a composition of 0.1 to 4.0% V, 4 to 20% W, and the balance Fe. The cold working mold is based on a cold working mold, and further has a mold body made of high-grade tool steel and a nitriding coating layer on the surface of the mold body, and has a carbon content of 0.35 to 0.7%. Si less than 1.0%, Mn
Less than 1.0%, Cr 1.0-5.0%, Mo 0.1-7.0%, V
A nitriding coating layer formed at a treatment temperature lower than the tempering temperature is provided on the surface of the mold body of a high alloy steel having a composition of 0.1 to 4.0% W, 4 to 20% W, and the balance Fe, and further, This is a mold for cold working, which is coated with a hardened layer formed by physical vapor deposition. <Function> Therefore, as the mold material forming the mold body, C is 0.35~
0.7%, Si less than 1.0%, Mn less than 1.0%, Cr 1.0
~5.0%, Mo 0.1~7.0%, V 0.1~4.0%, W 4~20%, and the balance Fe. It has quenching properties that give a uniform hardness of H _R C58 to 60, and has strength and compressive deformation resistance equivalent to conventional high-grade tool steel, as well as excellent heat treatment properties and toughness properties, and has a temperature of 550℃ or higher. Nitriding is performed at a temperature lower than the tempering temperature of A technical measure has been taken to cover it with a hardened layer such as TiN. The reason for limiting the range of the above-mentioned distribution composition is as follows. That is, C is effective in improving the strength and compression resistance of the mold body 2, but if it is less than 0.35%, the improvement effect is not sufficient, and if it exceeds 0.7%, it will cause the formation of carbides and nitrides. The amount of formation increases and the toughness decreases. As for Si, if it exceeds 1.0%, it is not preferable because the toughness deteriorates. Furthermore, Mn is effective in improving the hardenability of the mold material, but if it exceeds 1.0%, inclusions increase and the toughness is impaired. As for Cr, we also improved the hardenability,
Furthermore, it effectively works to increase the depth of the hardened layer during nitriding, but if it exceeds 1.0%, this effect becomes noticeable, and if it exceeds 5.0%, it promotes the formation of carbides and nitrides, reducing toughness. This is undesirable because it inhibits Furthermore, like Cr, Mo contributes to hardenability and hardened layer growth, but if it is less than 0.1%, it does not work effectively, and if it exceeds 7.0%, it increases carbides and nitrides and deteriorates toughness. It turns out. Furthermore, V increases the surface hardness and hardening depth associated with nitriding, but if it is less than 0.1%, it has no effect, and if it exceeds 4.0%, it will also cause carbides,
It helps the formation of nitrides, inhibits toughness and does not impress. Therefore, W works effectively by increasing the heat resistance and resistance to temper softening of the mold material, but if it is less than 4% it has no effect, and if it exceeds 20%, it also increases carbides and nitrides and deteriorates toughness. let After forming the mold body 2 using the above-mentioned high alloy steel in a prescribed manner, the entire body is made uniform in hardness by standard heat treatment, and then subjected to ion nitriding, gas nitriding, salt bath nitriding, and solid state at a temperature below 550°C, which is lower than the tempering temperature. A nitriding treatment is performed using an appropriate means such as nitriding, and a nitriding coating layer 3 is formed on the surface of the mold body 2 to a sufficient depth to improve the wear resistance, galling resistance, and seizure resistance of the surface. . Therefore, there is no distortion due to high temperatures such as carburizing treatment, and post-finishing is not required. Then, depending on the design, a physical vapor deposition treatment at a low temperature is further performed by means such as ion plating to coat a hardened layer 4 of nitride or carbide such as TiN having a hardness of about Hv1200 or more. Of course, the strength and compression resistance of the mold body are not impaired in any way by the above-mentioned nitriding treatment and physical vapor deposition, and in this way, the mold body's high toughness and surface wear resistance, galling resistance, and Seizure resistance can be divided into different parts. <Example> Next, an example of the invention of this application will be described below with reference to the drawings. 1 is a punch for a cold forging die which constitutes the gist of the invention of this application, and the die body 2 is made of high alloy steel with 0.55% C, 0.3% Si, 0.4% Mn, and Cr.
The high alloy steel was quenched in salt at 1200°C and tempered at 560°C. In addition, as a comparative example, a conventional material of JIS standard
Each of SKD11, SKD9, and SKD57 was heat treated under its standard conditions. The hardness _HRC , Shapey impact value (10R notch), and bending strength were determined for the above-mentioned high alloy steel of the invention of this application and three conventional materials as comparative examples, and the results shown in the table below were obtained.

[Table] As is clear from the above table, the high alloy steel of the invention of this application has a level comparable to conventional materials in terms of hardness and bending strength, and also has a Shear Pey impact value (toughness). It can be seen that this material has excellent properties that far exceed those of conventional materials. Thereafter, gas nitriding treatment was performed on the mold body 2 at 550°C for 20 hours, resulting in a nitrided coating layer 3 with a surface hardness of Hv1200 or more and a hardened layer depth of 0.3.
It was found that the mold body had a deep depth of more than mm, and the wear resistance, galling resistance, and seizure resistance were significantly improved compared to mold body 2. Finally, by ion plating
A hardened surface layer 4 of TiN was obtained, the thickness of which was 0.5-20μ. It goes without saying that the embodiments of the invention of this application are not limited to the above-mentioned embodiments, and can be applied to various types of molds, such as press molding and sintering molds, in addition to cold forging. <Effects of the Invention> As described above, according to the invention of this application, the physical and mechanical functions are basically divided between the mold body and the hardened surface layer, and therefore the mold body is different from the hardened layer. There is no need to take into account the wear resistance, galling resistance, and seizure resistance required for this product, and therefore, the hardenability that can be obtained uniformly through standard heat treatment can be maintained even after nitriding treatment and physical vapor deposition treatment. The hardened layer has the excellent effect of improving wear resistance, galling resistance, and seizure resistance. Therefore, instead of having to make contradictory choices between wear resistance, galling resistance, seizure resistance, and toughness as in the past, it is possible to obtain an excellent mold that can satisfy the required characteristics of both properties. There is. Therefore, after the heat treatment of the mold body, nitriding can be performed at a temperature lower than the tempering temperature, and a hardened layer of the nitrided coating layer can be obtained. Since it is as follows, there is no heat treatment distortion or size change, and therefore no heat treatment finishing is required, which has the advantage of reducing man-hours and cost. In addition, by performing physical vapor deposition such as ion plating on the nitrided coating layer to obtain a final surface hardening layer, the carbides and nitrides are as strong as or better than conventional CVD and TD treatments. It has the effect of imparting wear resistance, galling resistance, and seizure resistance, providing excellent surface properties, and further improving the double hardened layer. As for the toughness of the mold body, by using the above-mentioned high-alloy steel composition, it is possible to ensure that the mold body itself is effective while acting as a mutual tension and sharing the function of the hardened layer. There is a possible effect.

[Brief explanation of the drawing]

The drawings show one embodiment of the invention of this application, and are a model of a cold forging punch, of which FIG. 1 is a schematic bottom view and FIG. 2 is a partially longitudinal sectional side view. 1...Mold, 2...Mold body, 3...Nitrided coating layer, 4...Hardened layer.

Claims (1)

[Claims] 1. A cold working mold having a mold body made of high-grade tool steel and a nitriding coating layer on the surface of the mold body, containing 0.35 to 0.7% of C, less than 1.0% of Si, and Mn. but
Less than 1.0%, Cr 1.0-5.0%, Mo 0.1-7.0%, V
A nitriding coating layer formed at a treatment temperature lower than the tempering temperature is provided on the surface of the mold body of high alloy steel with a composition of 0.1 to 4.0% W, 4 to 20% W, and the balance Fe. A cold working mold featuring: 2. In a cold working mold having a mold body made of high-grade tool steel and a nitriding coating layer on the surface of the mold body, C is 0.35 to 0.7%, Si is less than 1.0%, and Mn is
Less than 1.0%, Cr 1.0-5.0%, Mo 0.1-7.0%, V
A nitriding coating layer formed at a treatment temperature lower than the tempering temperature is provided on the surface of the mold body of high alloy steel with a composition of 0.1 to 4.0% W and 4 to 20% W with the balance being Fe. A mold for cold working, characterized in that the top thereof is coated with a hardened layer formed by physical vapor deposition.