JPH10286647A - Forming tool having hardness difference - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forming die long in service life by reducing sensibility to the cracks of the forming tools such as a die, a liner, a cylinder, to be used for cold forging press, high pressure forming, etc. SOLUTION: It is preferable that the hardness of the surface in contact with a work is lower than that of the opposite surface part by 1HRC or above and the hardness difference thereof is 3HRC or above. The hardness level of the surface in contact with the work is defined as 50 to 60 HRC, and those of the opposite surfaces are defined as 55 to 65HRC. As for the composition of the tool, normal high speed tool steel, cold tool steel and the improved steels thereof are applicable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cold forging press,
The present invention relates to various forming tools, such as dies, liners, cylinders, and the like, which are used for high-pressure forming and in which high pressure acts on the inner diameter surface during forming.

[0002]

2. Description of the Related Art Dies, liners, cylinders and other tools conventionally used in cold forging presses, high pressure forming and the like, which are the above-mentioned applications, are medium to high C-5 to 1 represented by SKD11.
A high-speed tool steel represented by 3% Cr-based die steel or SKH51 or an improved steel of these die steel or high-speed tool steel is subjected to a quenching and tempering heat treatment to obtain a total of 55 to 65H.
The so-called outer hard and inner soft type tools that have been adjusted to almost uniform hardness of RC, and furthermore, these heat-treated products are subjected to surface treatment such as nitriding, sulfurizing, carburizing, etc., and the surface layer is extremely hardened. Used in

[0003] Tools such as the above-mentioned cold forging press and high-pressure forming are used to cope with wear due to sliding between the tool and the workpiece, fatigue fracture due to repeated stress, or deformation and deformation due to processing pressure. It is heat-treated to a high hardness of 55 to 65 HRC or further subjected to a surface treatment to be used in an outer hard / inner soft structure. On the other hand, hardness (strength) and toughness are generally inversely related, and it is known that increasing hardness decreases toughness, and the life of tools and machine parts is a combination of hardness and toughness. Depends on
Depending on the purpose, the material is selected and optimal hardness and toughness are given.

[0004] In recent years, there has been a movement to increase the life of a die-casting die by increasing the hardness, but increasing the hardness increases the toughness, thereby increasing the susceptibility to cracking. In the die-casting mold, cracks originating from the water-cooled holes may expand and develop into large cracks, so only the vicinity of the water-cooled holes may be tempered at a higher temperature or a difference in the hardness of the entire mold may be provided. Attempts have been made to reduce the susceptibility of cracks by processing water-cooled holes in low hardness parts. Based on such a concept,
No. 360, Japanese Unexamined Patent Publication No. 6-315753, etc.
There is disclosed a die casting mold having a lower hardness mainly in the vicinity of the water cooling hole than the engraved portion.

[0005]

A difference in hardness between the engraved portion and the vicinity of the water-cooled hole as described above is provided, and the die-engraved portion of the die-cast portion having a high toughness in the vicinity of the water-cooled hole also has a high hardness. Therefore, there is a danger that, depending on the use conditions, micro cracks may develop due to insufficient toughness and break. Further, the tools used in the cold forging press and the high pressure forming as described above are heat-treated to a hardness of 55 to 65 HRC, and the hardness is determined by the sliding between the tool and the workpiece. Hardness is often set to a high level in order to cope with wear caused by motion, fatigue fracture due to repeated stress, or pressure drop due to inner diameter expansion due to internal pressure. For this reason, there is a problem that, since the susceptibility to cracking is very high, cracking may occur early in some cases.

The present invention solves the above-mentioned problems and reduces the susceptibility of a forming tool such as a die, a liner, and a cylinder used for cold forging press or high pressure forming to cracks, and provides a tool having a long life. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION The present invention provides various tools used for cold forging presses and high-pressure forming, in order to solve the above-mentioned problems, and to study the conditions for setting the hardness. Thus, the present invention has been reached based on an idea which has not been seen at all. More specifically, the present invention
The hardness of the side in contact with the workpiece is 1H higher than that of the opposite side.
It is a forming tool having a hardness difference characterized by being lower than RC, and desirably has a hardness difference of 3 HRC or more.

Further, the hardness of the present invention is such that the hardness on the side in contact with the workpiece is 50 to 60 HRC, and the hardness on the opposite side is 55 to 65 HRC.
5-2.5%, Si ≦ 1.5%, Mn ≦ 1.5%, C
r: 3 to 15%, further contains 30% or less of Ni, W, Mo, V, and Co alone or in combination, and the balance is composed of Fe and unavoidable impurities. And systematically, the present invention provides that the amount of primary carbide is 2% in area ratio.
１５15%, and is characterized in that it is a forming tool used for closed mold forming for use.

The most characteristic feature of the present invention is that the hardness of the side of the tool, which has not been considered conventionally, in contact with the workpiece is lower than that of the other side. As described above, the tool to which the present invention is directed is to apply a surface treatment to increase the hardness of the surface in contact with the work material, thereby mainly providing wear resistance and extending the life. Was the general idea. However, increasing the hardness is disadvantageous in terms of toughness. Therefore, in a forming tool used under severe conditions that need to have both strength (hardness) and toughness, fine cracks may develop at an early stage. May be destroyed.

Therefore, in the present invention, in the various tools represented by the conventional forming tools, not only the idea but also the work material, which is said to be rather evil in terms of wear resistance, is considered. By positively lowering the contacting side, the toughness of this portion is to be increased and the life is to be prolonged, and the invention has been completed based on an idea completely opposite to the conventional one. Even in the die casting mold as described above,
The part in contact with the workpiece is maintained at a higher hardness.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, a fracture mechanism of a metal member subjected to repeated stress is said to be a stack of shear stress as well as tensile stress, and a slip band is generated by the shear stress. It is said to have developed and cracked, and this has developed and led to destruction. When considering the fatigue fracture life of an actual forming tool, it is necessary to determine how crack initiation and propagation are related to the strength and toughness of the tool. In other words, in a tool with relatively high stress and high rigidity, that is, a tool with low toughness, once a fatigue crack occurs, it will break in a short time, so the occurrence of cracks will be the limit of life, but in a general mold, In addition, even if a fine crack is generated, the life is improved by considering the growth rate of the crack without immediately breaking it.

In the present invention, which mainly relates to the latter case, as is well known, the progress of fatigue cracks in tool materials is highly dependent on hardness and low in hardness (high toughness).
The crack growth is slower. However, if the hardness is reduced in a closed mold having a particularly high stress, buckling may occur due to the high stress and the crack may be accelerated, resulting in early damage. Therefore,
In the present invention, the overall hardness of the forming tool is such that the side on which normal high hardness is maintained and which comes into contact with and slides with the workpiece (usually the inner diameter surface)
By only slightly lowering the hardness of
It is intended to greatly improve the service life.

As for the difference in hardness, if the hardness is 1 HRC or less, the above-mentioned effect cannot be sufficiently exerted. Therefore, a difference in hardness is required to be greater, more preferably 3 or more. As for the level, if it is too low on the side that is in contact with the workpiece (usually the inner diameter surface), the wear resistance is reduced, causing early wear and seizure. The above effect is not exerted even if there is a hardness difference of 50 to 60 HRC. In addition, the hardness of the portion on the outer diameter side that does not come into contact with the workpiece is 55 to 65 HRC in order to maintain the compression resistance and the effect of preventing deformation as described above.

As described above, the material of the forming tool to be applied remains after the heat treatment because of maintaining the wear resistance even when the hardness is reduced and the necessity of being present as an obstacle to prevent the crack from growing. It is important that the primary carbides to be dispersed are dispersed. The chemical component for that is to form a primary carbide mainly composed of Cr-based carbide in tool steel,
It was determined as follows. C forms a hard carbide by forming a solid carbide by combining with Cr, Mo, W, V, etc. in order to increase the hardness by forming a solid solution in the matrix, and to form an obstacle which keeps wear resistance and prevents the growth of fatigue cracks. It is an indispensable element for its function. For that purpose, 0.45% or more is necessary. However, if it is too much, its effect is saturated and the toughness is reduced, so the upper limit is 2.5%. And

Although Si is usually added as a deoxidizing agent on steel making and has the effect of increasing the secondary hardening hardness, even if it is added in a large amount, its effect is not so expected, and conversely, it is brittle. Is increased, so the upper limit is 1.5%. Similarly, Mn is used as a deoxidizing agent and has an effect of enhancing hardenability. However, when added in a large amount, retained austenite increases during quenching, hardening hardness decreases, and hot workability is impaired. The upper limit is 5%. Cr is an element that enhances the hardenability and combines with C to form carbides and exhibit the above-described effects. The content is determined by the balance with C. However, if the content is less than 3%, the effect is generally not expected. If the content is too large, the quenching hardness is reduced, and the amount of carbide is excessively large, and the toughness is deteriorated. 15% is the upper limit.

Mo, W, and V are strong carbide-forming elements like Cr, and are elements that exhibit the same effect as Cr and have a large hardening effect due to precipitation of secondary carbides. Ni has an effect of mainly improving hardenability and toughness of the matrix, and Co is an element having a secondary hardening effect. These elements may be added alone or in combination, if necessary. However, if the amount is too large, the above-mentioned effect may not be obtained. Therefore, it is appropriate to limit the addition to at most 30%. With such a chemical component, the amount of the remaining primary carbide can be 2% or more and 15% or less. For the above purpose, at least 2% or more is required. Since it easily becomes a starting point of generation, the content is limited to 15% or less.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. First, steel materials having the chemical components shown in Table 1 were prepared. In Table 1, the symbols A to F correspond to the range of chemical components to which the “forming tool having a difference in hardness” of the present invention can be applied, and the symbols G to I have chemical components protruding from this range. doing.

[0018]

[Table 1]

From this steel material, an outer diameter of 90 mφ and an inner diameter of 15 mm
After processing into a generally donut-shaped forming tool (die) having a diameter of 60 mm and a height of 60 mm, the hardness was adjusted to a predetermined value by a quenching and tempering process optimal for each material.
, Except that only the inner surface was re-tempered by high-frequency heating at a temperature higher than the tempering temperature after the first quenching, thereby lowering the hardness. Here, for the sample 11 (comparative example), the outer peripheral portion was immersed in a salt bath set at a temperature higher than the entire tempering temperature in order to increase the hardness of the inner diameter surface in contact with the workpiece, and the donut shape was obtained. While rotating around the center axis of, only the outer periphery was tempered at a higher temperature.

As shown in FIG. 2, the hardness was measured on the inner diameter side at a depth of 3 mm from the inner surface, and on the outer diameter portion at the end surface at a position 20 mm from the outer circumference. Table 2 shows the hardness measurement results.
Shown in Table 2 also shows the results of measuring the primary carbide content of the steel materials shown in Table 1 by area ratio. When the result of the hardness measurement is represented by a cross section of the die, the situation is as shown in FIG. The hatched part shown in FIG. 1 is a part according to the present invention with reduced hardness.

On the other hand, an outer diameter of 15 mm
× A punch having a length of 120 mmL was prepared and heat-treated with the aim of HRC63. When the hardness was measured, HRC6
3.6. The die and the punch described above are combined as shown in FIG. 3, and a work piece of 14 mmφ × 20 mmL of an aluminum alloy (alloy No. 1100) shown in JIS H4000 is applied for 15 m under a static load of an internal pressure of 3000 MPa.
It was molded to mφ and the number of life until the die was broken was measured. As a result, when compared within the same steel type, it can be seen that the lower the hardness of the inner diameter surface with respect to the outer diameter surface, the greater the life number.

[0022]

[Table 2]

[0023]

As described above, the forming tool having a difference in hardness according to the present invention is such that it has never been considered before.
By improving the toughness by lowering the hardness of the inner diameter surface mainly in contact with the work material compared to other parts, the sensitivity to cracking is reduced, and the cracking of the tool due to insufficient toughness against the operating conditions is greatly reduced. Since it can be reduced, the reliability of the forming tool can be improved. Also,
In the present invention, as means for lowering the hardness of the inner diameter surface, re-tempering can be performed by high-frequency heating, so that the desired forming tool (die) can be obtained simply and inexpensively, and the steel is well known. Since high-speed tool steel, cold tool steel, or improved steels thereof can also be applied, in such a case, it is not necessary to use a steel material having a special chemical composition. The effect is very large.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which the hardness on the inner diameter side of a die relating to a forming tool having a hardness difference according to the present invention is reduced.

FIG. 2 is a conceptual diagram showing a state of measuring the hardness of a die relating to a forming tool having a hardness difference according to the present invention.

FIG. 3 is a conceptual diagram showing a situation in which molding is performed at a high pressure using a molding tool having a difference in hardness according to the present invention.

[Explanation of symbols]

 1 die, 2 punches, 3 materials

Claims (6)

[Claims] 1. A forming tool having a difference in hardness, wherein the hardness on the side in contact with the workpiece is lower than the opposite side by at least 1 HRC. 2. The forming tool having a difference in hardness according to claim 1, wherein the difference in hardness is 3 HRC or more. 3. The hardness of the side in contact with the workpiece is 50 to 6
The forming tool having a hardness difference according to claim 1 or 2, wherein the hardness of the opposite part is 0 to 55 HRC. 4. The chemical composition of the forming tool is C: 0.45 to 0.45.
2.5%, Si ≦ 1.5%, Mn ≦ 1.5%, Cr: 3
The composition according to any one of claims 1 to 3, further comprising 30% or less of Ni, W, Mo, V, and Co, alone or in combination, and the balance of Fe and inevitable impurities. Molding tools. 5. The amount of primary carbide is 2 to 15% in area ratio.
The forming tool having a difference in hardness according to any one of claims 1 to 4, wherein 6. A forming tool having a difference in hardness according to claim 1, which is a forming tool used for closed mold forming.