JPS6321748B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a mold. In recent years, with the spread of cold forging for automobile parts and the like, requirements for molds used for cold forging have become increasingly strict. Generally, in order to extend the life of a mold, it is necessary to have excellent wear resistance as well as high strength and toughness, but these contradictory properties can be imparted to the mold only by alloy design. is extremely difficult. Therefore, attempts have recently been made to apply various surface treatments to the molds, but each surface treatment method has its advantages and disadvantages, and it has not yet become widespread. For example, in the conventional gas carburizing method, a deep hardening depth can be obtained relatively easily, so it is thought to be quite effective in improving wear resistance. Steel has the disadvantage that a sufficient diffusion layer cannot be obtained because mesh-like carbides are formed near the surface and hinder the diffusion of C. The present invention has been made in view of such conventional circumstances, and provides a mold that has excellent wear resistance, high strength and toughness, and maintains a good balance between the wear resistance and toughness. The purpose is to provide a manufacturing method for. The method for manufacturing a mold according to the present invention, in weight%,
C: 0.50 to 0.70%, Si: 1.5% or less, Mn: 1.5% or less, Ni: 1.5% or less, Cr: more than 5.0 to 9.0%, Mo:
Contains 0.2 to 5.0%, V: 0.5 to 1.5%, and if necessary, one of W: 0.5 to 5.0%, Co: 2.0% or less
The method is characterized in that a mold of a predetermined shape is manufactured using steel containing one or two kinds of iron and the remainder is Fe and unavoidable impurities, and then the mold is subjected to vacuum carburizing. In other words, the inventors repeatedly conducted basic experiments focusing on the vacuum carburizing method, which has surface cleaning and activating effects, and found that it is possible to form a deep diffusion layer even in high-alloy steel by using the vacuum carburizing method described above. It has been found that fine and uniform spherical carbides can be formed by further applying a diffusion treatment if necessary. Thus, in the present invention, by performing vacuum carburizing treatment on a mold having a composition excellent in toughness, a mold that maintains a good balance between wear resistance and toughness is produced. From this point of view, in the present invention, regarding the chemical components of the mold, C and carbide are added in order to maintain the strength of the core necessary for the mold and to suppress the formation of coarse carbides that reduce toughness. The content of the forming elements was reduced, and the material belonged to the so-called matrix high-speed steel system. However, the Cr content was increased in order to precipitate M ₇ C ₃ type double carbide during carburizing and to improve the wear resistance of the surface layer. moreover,
In order to increase the strength of the core and at the same time make it applicable to high-load molds, we decided to add one or both of W and Co as appropriate. From the above-mentioned viewpoint, the present invention specifies that steel having the above-mentioned chemical composition range be used, and the reasons for limiting the composition range will be explained below. C (carbon): 0.50-0.70% C is at least 0.50% to obtain the hardness required for cold forming tool steel (e.g. H _R C56 or higher)
It is necessary to contain C, but if it exceeds 0.70%, toughness deteriorates, and in addition, carbide aggregates on the surface layer during carburizing, hindering the diffusion of C. Therefore, 0.50~
The range shall be 0.70%. Si (silicon): 1.5% or less, Mn (manganese): 1.5% or less Si and Mn are elements added as deoxidizing agents. Si has the effect of increasing the yield point, and Mn has the effect of increasing strength and toughness. However, if it exceeds 1.5%, workability such as forgeability will deteriorate, so each should be kept at 1.5% or less. Ni (nickel): 1.5% or less Ni is an effective element for improving hardenability, and even in the case of large molds, it is effective in increasing the toughness as a hardened structure to the center. However, 1.5%
If it exceeds 1.5%, the annealing hardness increases and machinability deteriorates, so it should be kept at 1.5% or less. Cr (Chromium): Exceeding 5.0~9.0% Cr has high hardness of Hv2000~2500 when carburized
5.0% to easily form _{M7C3 type} double carbide at carburizing temperature (e.g. 1000 to 1050℃) because it precipitates _{M7C3 type} double carbide and contributes to improving wear resistance.
Contain more than . However, if it exceeds 9.0%, eutectic carbides will crystallize during solidification and the toughness will decrease, so the upper limit is set at 9.0%. Mo (molybdenum): 0.2 to 5.0% Mo is an element that precipitates Mo ₂ C type carbide during tempering and contributes to secondary hardening.
Requires 0.2%. As the amount of addition increases, the hardness due to secondary hardening and tempering hardness increase, so it can be adjusted according to the strength required for the mold.
Adjust the amount of Mo. However, 5.0% or less is sufficient to obtain the strength required for a cold forging die, and if it exceeds 5.0%, toughness deteriorates, so this is the upper limit. V (vanadium): 0.5 to 1.5% V is an element that forms carbides and contributes to the refinement of austenite grains, and for this purpose 0.5%
% or more. However, if it exceeds 1.5%, machinability and grindability deteriorate, so 0.5 to 1.5
% range. W (tungsten): 0.5-5.0% W, like Mo, precipitates double carbides during tempering and contributes to secondary hardening, and is an effective element for improving the strength of molds. %
Approximately 1/2 the effect of Mo). Therefore, if necessary, add 0.5% or more, but if it exceeds 5.0%, the toughness will deteriorate, so this is the upper limit. Co (cobalt): 2.0% or less Co dissolves in the matrix and improves the tempering resistance of the matrix, and increases the residual amount of carbides to increase wear resistance, improving the strength of the mold, especially the core strength. Since it has an effect on improvement, it should be added as necessary. However, at present, it is expensive, and if the amount added exceeds 2.0%, the toughness deteriorates, so it is preferable to keep it at 2.0% or less. Example 1 This example was carried out using the invention steels (sample materials No. 1 to 7) and comparative steels (sample materials No. 8 and 9) shown in Table 1. In addition, sample material No. 8 is JIS SKH9
Equivalent product No. 9 is equivalent to JIS SKD11.

[Table] Therefore, for each sample material No. 1 to 7 above, the second
Vacuum carburizing was carried out under the vacuum carburizing conditions shown in the table. Sample materials No. 1, 3, and 6 were further diffused, and then tempered under the same tempering conditions shown in Table 2 to harden the core. The hardness, surface hardness and total cure depth were measured. These results are also shown in Table 2. In addition, when performing the above vacuum carburizing, the vacuum furnace main body,
The main equipment used was a gas supply device and a control panel (controlling temperature, degree of vacuum, amount of carburization, etc.). Then, the steel samples No. 1 to 7 were charged into the above-mentioned apparatus, and the atmosphere in the furnace was reduced to about 10 ^-1 mmHg.
Propane (C ₃ H ₈ ) at each temperature shown in Table 2
Gas was also supplied for the times shown in Table 2 to carburize the steel surface of each specimen material activated during vacuum heating, and depending on the specimen material, it was further diffused under the conditions shown in Table 2. I did this. After carburizing
After quenching was performed in a cooling chamber by introducing N ₂ gas, tempering was performed under each tempering condition shown in Table 2. In this Table 2, the core hardness is H _R C56 to 60 after vacuum carburizing and tempering.
It shows the carburizing performance when tempered to Hv800
A surface hardness of ~900 and a hardening depth of approximately 1.5mm have been obtained. On the other hand, sample materials No. 8 to 9 were also quenched and tempered under the conditions shown in Table 2, and the surface hardness of each was measured. These results are also shown in Table 2.

【table】

[Table] Next, the properties of carbides formed in the surface layer of the steel sample No. 5 shown in Table 2 above are shown in the microscopic structure photograph in the attached drawing. As shown in the figure, relatively spherical fine M ₇ C ₃ double carbides (Hv2000-2500) are uniformly dispersed in the surface layer.
It was also confirmed through the tests described below that this contributes significantly to improving wear resistance. Next, the wear resistance of each heat-treated sample material shown in Tables 1 and 2 above was evaluated.
For this test, an Okoshi type abrasion tester was used.
Testing was conducted using JIS SCM21 material as the mating material at a speed of 1.96 m/sec, a load of 6.5 kg, and a distance of 200 m.
The results are shown in Table 3.

[Table] As is clear from Table 3, it was confirmed that the specific wear amount of the product according to the present invention was considerably smaller than that of the conventional product, and the wear resistance was considerably superior. Next, a compression test and a Charpy impact test were conducted on each of the heat-treated test materials shown in Tables 1 and 2 above. In the compression test, a test piece with a parallel portion of 6 mmφ x 20 ml was used, and in the impact test, a 10R notched pea impact test piece was used. The results are shown in Table 4.

[Table] As is clear from Table 4, the steel of the present invention exhibits very excellent values in both strength and toughness, whereas the comparative steel has considerably poor toughness. Third
From the results in Tables and Table 4, it was confirmed that the steel of the present invention maintains an extremely good balance between wear resistance and toughness. Example 2 Here, a cutting die for an electrical steel sheet was manufactured using the steel of test material No. 4 shown in Table 1, and then vacuum carburized and tempered under the conditions shown in Table 2 to prepare it for use. provided. On the other hand, a cutting die for an electromagnetic steel sheet was manufactured in the same manner using the steel of test material No. 9 shown in Table 1, and then quenched and tempered under the conditions shown in Table 2 and used. As a result, the life of the cutting die made of steel of test material No. 9 was approximately 40,000 shots, while the life of the cutting die made of steel of test material No. 4 was approximately 10,000 shots.
It has a service life of 10,000 shots. Example 3 Here, a bolt former punch was manufactured using steel sample material No. 6 shown in Table 1, and then a second
The specimens were subjected to vacuum carburizing and tempering under the conditions shown in the table and then used. On the other hand, the sample material No. shown in Table 1.
Bolt former punches were manufactured in the same manner using No. 8 steel, and then quenched and tempered under the conditions shown in Table 2 and used. As a result, the sample material
While the punch using No. 8 steel had a lifespan of about 10,000 shots, the life of the punch using test material No. 6 steel could be extended to about 30,000 shots. As detailed above, the present invention uses chemical components of a mold that are suitable for vacuum carburizing, manufactures the mold into a predetermined shape, and then vacuum-heats the mold.
The surface of the mold activated during this vacuum heating is subjected to vacuum carburization. Therefore, a clean carburized layer can be uniformly obtained in a short carburizing time, and the surface has excellent wear resistance, as well as high strength and toughness, and a good balance between the wear resistance and toughness is maintained. We can supply the molds you want. Furthermore, it has the very excellent effect of considerably increasing the useful life of molds such as cold forging molds, cold press molds, and warm forging molds.

[Brief explanation of the drawing]

The drawing is a microscopic structure photograph of the surface layer of a sample material as a result of implementing the present invention.

Claims (1)

[Claims] 1 In weight%, C: 0.50 to 0.70%, Si: 1.5% or less, Mn: 1.5% or less, Ni: 1.5% or less, Cr: more than 5.0 to 9.0%, Mo: 0.2 to 5.0%. , V: 0.5 to 1.5%, and the remainder is Fe and unavoidable impurities.A method for manufacturing a mold is characterized in that a mold of a predetermined shape is manufactured using steel, and then the mold is vacuum carburized. 2 In weight%, C: 0.50 to 0.70%, Si: 1.5% or less, Mn: 1.5% or less, Ni: 1.5% or less, Cr: more than 5.0 to 9.0%, Mo: 0.2 to 5.0%, V: 0.5 to 1.5 %, and W: 0.5 to 5.0%, Co: 2.0% or less.
1. A method for manufacturing a mold, which comprises manufacturing a mold of a predetermined shape using steel containing one or two kinds of Fe and unavoidable impurities, and then subjecting the mold to vacuum carburizing.