JP2008126310A - Member for forming - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a member for forming in which a thickened layer is uniformly formed in the vicinity of the surface of a cooling hole, and to provide the member for forming in which the crack of the water cooled hole can be suppressed. <P>SOLUTION: A die 1 is composed of a steel member comprising, by mass, 0.21 to 0.80% C, 0.01 to 2.0% Cu and 0.02 to 5.0% Ni. The die 1 is provided with a cooling hole 2 to be the flow passage of a coolant, a concentrated layer Q on which Cu and Ni are thickened is formed in the vicinity of the surface of the cooling hole 2, and the thickened layer Q has a thickness δsatisfying 1 μm≤δ≤15 μm. Further, the concentration β of the elements X (Cu and Ni) contained in the thickened layer Q is ≥1.2 times of the concentration α of the elements X contained in the steel member or above. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a molding member suitable for use in die casting, forging, injection molding of plastics and rubber, and more specifically, a molding member in which penetration of a water-cooled hole crack to a design surface hardly occurs even when a high cycle is performed. About.

  Die casting refers to casting a molten metal, for example, a molten aluminum alloy, into a gap between molds and solidifying the mold, and at the same time transferring the shape of the mold to produce a casting. A die-cast product refers to a product produced by die casting, and the number of die-cast products that can be produced per unit time is called a die-cast product production cycle (also called a casting cycle). In recent years, there has been a growing demand to increase the production cycle of die-cast products, that is, to increase the number of die-cast products that can be produced per unit time. This is called high cycle.

  However, the die used in die casting takes heat from the molten aluminum alloy and hardens the molten aluminum alloy. Therefore, when the high cycle is performed, the cooling time of the mold that has been deprived of heat and brought to a high temperature becomes insufficient. Then, the next die casting is performed while the temperature of the mold is high. Cooling of a molten aluminum alloy using a high-temperature mold that is not sufficiently cooled roughens the structure when the molten aluminum alloy is solidified and impairs the quality characteristics (strength, impact value) of the die-cast product. That is, when the high cycle is performed, there is a problem that the temperature of the mold cannot be sufficiently lowered from the end of the die casting to the next die casting.

  Therefore, as shown in FIG. 8, in order to enhance the internal cooling of the mold, a water cooling hole 2 is formed in the mold 1 and the cooling water is circulated therein to cool the mold. It has been broken. Incidentally, the temperature of the cooling water is 10 to 80 ° C. (varies depending on the circulation part and season), and the temperature of the molten aluminum alloy is about 620 to 720 ° C.

  Now, regarding the relationship between the water cooling holes 2 and the high cycle, when the high cycle is performed, the water cooling holes 2 are formed on the design surface 3 (the design surface is the gold on the material to be molded) in order to quickly lower the temperature of the mold. The internal cooling is strengthened by approaching the mold shape (refer to the arrow A in FIG. 8). This is because if the water cooling hole 2 is close to the design surface 3, the temperature of the high temperature design surface 3 in contact with the molten aluminum alloy can be quickly cooled. If it can be cooled quickly, the quality characteristics of the die-cast product will not be impaired.

  However, when the water-cooled hole 2 and the design surface 3 are brought close to each other, the problem of water-cooled hole cracking indicated by reference numeral 4 in FIG. The water-cooled hole crack 4 is a crack from the inner wall surface of the water-cooled hole 2 toward the design surface 3 as shown by arrow B in FIG. Therefore, the penetration of the water-cooled hole crack 4 into the design surface 3 is fatal for the die casting company. Further, penetration of the water-cooled hole crack 4 to the design surface 3 cannot be visually confirmed until a crack from the inner wall surface of the water-cooled hole 2 to the design surface 3 penetrates. Therefore, there has been a problem that the water-cooled hole crack 4 cannot be periodically repaired.

  As for the cause of the water-cooled hole crack 4, in die casting, a molten aluminum alloy is poured on the design surface 3 (mold heating) in a predetermined production cycle, and cooling water is fed to the water-cooled hole 2 (mold cooling). Cooling is performed repeatedly. Then, a tensile force acts on the inner wall surface of the water cooling hole 2. Further, the water cooling holes 2 are usually rusted because the cooling water of 10 to 80 ° C. circulates for 24 hours. Then, cracks are generated starting from the rust corrosion pits (see FIG. 9B). And the tensile force accompanying heating and cooling acts on the crack. Further, when hydrogen ions enter the crack (see FIG. 9C), this promotes the progress of the crack. These are considered to cause the water-cooled hole crack 4 shown in FIG. 9A to penetrate the design surface 3.

In order to prevent water-cooled hole cracking, first, a material having high corrosion resistance such as stainless steel is used. This is because if the rust is prevented, the water-cooled hole corrosion can be prevented, and it is considered that the starting point of the crack does not occur.
Second, alkaline water is used as cooling water. If alkaline water is used, it is difficult to generate hydrogen ions, so corrosion can be suppressed, and even if corrosion pits are formed as the starting point of cracks, it is difficult to generate hydrogen ions, so the development of cracks can be suppressed. Because it is considered.

  Third, rust-proof plating is performed on the inner wall surface of the cooling hole in order to prevent the entry of hydrogen ions. This is because it is considered that the rust-proof plating serves as a barrier for preventing hydrogen ions from entering and hydrogen ions do not enter the mold.

Fourth, in order to improve the corrosion resistance of the steel material itself, a concentrated layer such as Ni is formed near the surface. This is also considered to be a barrier against entry of hydrogen ions. For example, in Patent Document 1, for the purpose of providing an inexpensive high corrosion resistant steel that can further improve the corrosion resistance of the weather resistant steel and suppress the occurrence of flow rust, C: 0.01 to 0.20 mass%, Ni: 0.04-4.0% by mass, Cu: 0.1-1.0% by mass, etc., with a balance of 3 μm or more in the vicinity of the surface of the base iron having a composition consisting of Fe and inevitable impurities. A highly corrosion resistant steel having a Ni enriched layer is disclosed.
Further, in Patent Document 2, Cu: For the purpose of providing a high corrosion resistance steel material that can have excellent corrosion resistance without causing deterioration of mechanical properties and weldability due to excessive addition of an element for improving corrosion resistance. 0.05 to 3.0% by mass, Ni: 0.05 to 6.0% by mass, C: 0.02 to 0.20% by mass, etc., in the region from the steel material outermost surface to a depth of 500 μm, It has a Cu + Ni concentrated layer whose Cu amount + Ni amount is “1.2 times or more of the Cu amount + Ni amount of steel and 1.0% by mass or more”, and the thickness of the concentrated layer is 1 μm or more. A high corrosion resistance steel material is disclosed.

JP-A-2005-281840 JP 2006-169626 A

  However, the use of the above-described stainless steel and the use of alkaline cooling water have a problem of high costs. Further, the rust-proof plating has a problem that the plating thickness varies depending on the position of the water cooling hole of the mold. This is because the inside of the mold has a very complicated shape, and it is very difficult to make the pressure of the plating solution uniform in all the water cooling holes. When the plating thickness varies depending on the position of the cooling hole, naturally, hydrogen ions easily enter the portion where the plating is thin. Therefore, once corrosion pits are formed in the thin plating portion, cracks develop from there and lead to water-cooled hole cracks.

  Further, in the high corrosion resistance steel of Patent Document 1, the C content is 0.01 to 0.20 mass%, and in the high corrosion resistance steel material of Patent Document 2, the C content is 0.02 to 0.20 mass. Therefore, when steel disclosed in Patent Documents 1 and 2 is used for a mold used in an environment where heating and cooling are repeatedly performed, there is a problem that strength is low.

  Furthermore, no example is disclosed in which the cooling hole depth L (see FIG. 4) from the design surface to the inner wall surface of the water cooling hole is optimized in order to adapt to the high cycle of die casting.

The present invention has been made in view of the above circumstances, and the first object thereof is that the concentrated layer of Cu and Ni is uniformly formed in the vicinity of the surface of the cooling hole and has excellent quality characteristics. The object is to provide a molding member.
The second object of the present invention is to provide a molding member capable of suppressing penetration of a water-cooled hole crack into a design surface.
A third object of the present invention is to provide a molding member capable of high cycle die casting at a low cost.

In order to solve the above problems, the molding member according to the present invention is, in mass%, C: 0.21 to 0.80%, Cu: 0.01 to 2.0%, Ni: 0.02 to 5. It consists of a steel material containing 0%,
With cooling holes that serve as coolant flow paths,
In the vicinity of the surface of the cooling hole, a concentrated layer in which Cu and Ni of the steel material are concentrated is formed,
The thickening layer is characterized in that the thickness δ is 1 μm ≦ δ ≦ 15 μm.

In this case, the amount of Cu and the amount of Ni contained in the concentrated layer may be 1.2 times or more the amount of Cu and the amount of Ni contained in the steel material, respectively.
In this case, the concentrated layer preferably contains Cu: 0.025 to 5.0% and Ni: 0.05 to 15.0% by mass.
In this case, it is preferable that at least one of the cooling holes has a cooling hole depth L from the design surface that contacts the material to be molded to the inner wall surface of the cooling hole, L <25 mm.
In this case, the steel material may contain C: 0.07 to 0.80% in mass%.

  The forming member according to the present invention is a steel material containing, in mass%, C: 0.21 to 0.80%, Cu: 0.01 to 2.0%, Ni: 0.02 to 5.0%. Thus, since a concentrated layer in which Cu and Ni of the steel material are concentrated is formed, the concentrated layer of Cu and Ni is uniformly formed in the vicinity of the surface of the cooling hole without unevenness. Further, the molding member according to the present invention contains, in mass%, C: 0.21 to 0.80%, Cu: 0.01 to 2.0%, Ni: 0.02 to 5.0%. Since it is made of steel, it has moderate strength and impact value as a molding member.

  The molding member according to the present invention according to the present invention is, in mass%, C: 0.21 to 0.80%, Cu: 0.01 to 2.0%, Ni: 0.02 to 5.0%. Since the thickness δ of the concentrated layer made of the steel material containing the concentrated Cu and Ni of the steel material is 1 μm ≦ δ ≦ 15 μm, it has an appropriate strength and impact value as a molding member, and has water cooling holes. Cracking can be suppressed.

  In the molding member according to the present invention, the Cu amount and Ni amount contained in the concentrated layer are 1.2% or more of the Cu amount and Ni amount contained in the steel material in mass%, respectively. It is possible to block the penetration of hydrogen ions that promote the development of the cracks that are caused. Moreover, since the thickening layer contains Cu: 0.025-5.0% and Ni: 0.05-15.0% by mass%, the member for shaping | molding which concerns on this invention causes water-cooled hole cracking. Intrusion of hydrogen ions that promote the development of cracks can be blocked.

In the molding member according to the present invention, the cooling hole depth L from the design surface contacting the material to be molded to the inner wall surface of at least one cooling hole is L <25 mm. Also, the temperature of the molding member can be quickly cooled to an appropriate temperature. Therefore, according to the molding member according to the present invention, a die-cast product having excellent quality characteristics can be obtained.
Moreover, since the molding member according to the present invention does not use a high-cost steel material, it can be produced at a low cost.

Hereinafter, a mold as an example of a molding member according to an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 schematically shows a side surface of a mold 1 according to an embodiment of the present invention, and FIG. 2 shows an inside enlarged from the surface layer of a water cooling hole 2. The mold 1 shown in FIG. 1 contains, by mass%, C: 0.21 to 0.80%, Cu: 0.01 to 2.0%, Ni: 0.02 to 5.0%, and the like. The mold is made of a steel material with the balance being Fe and inevitable impurities. The mold 1 includes a water cooling hole 2 as a cooling hole serving as a coolant flow path. The water cooling holes 2 are uniformly formed with a concentrated layer in which Cu and Ni are concentrated in the vicinity of the surface thereof. The thickness δ of the concentrated layer is 1 μm ≦ δ ≦ 15 μm.

The “cooling liquid” is water of about 60 ° C., but is not limited thereto. As the cooling liquid, alkaline water quality is preferable. This is to suppress the generation of hydrogen ions that promote the development of cracks that cause water-cooled hole cracking.
The water cooling hole 2 is a flow path for the coolant, and is about φ8 to φ30. The water cooling hole 2 has an oxide scale P formed on its outermost surface (surface in contact with the cooling liquid), and a concentrated layer Q is formed on the inner layer side thereof. In the concentrated layer Q, Cu, Ni, and the like are concentrated, but the inside of the mold on the inner layer side has the composition of the steel material itself.

  As shown in FIG. 2, “near the surface” means an interface between the oxide scale P and the concentrated layer Q, that is, a portion from the surface of the ground iron to a depth of about 200 μm on the inner layer side. In addition, the oxide scale P of the water cooling hole 2 is formed when the mold 1 is quenched, and is used without being cut. The reason is that the water cooling holes 2 are used for cooling the mold 1 and that the presence or absence of the oxide scale P does not particularly adversely affect the die cast product. In addition, the design surface 3 is cut and polished to remove the oxide scale and the concentrated layer.

  The concentrated layer Q is a layer formed on the inner layer side of the oxide scale P formed on the inner surface of the cooling hole 2 as shown in FIGS. Specifically, as shown in FIG. 1B, the concentrated layer Q has a “Cu and Ni (element X) concentration β” of 1.2, which is a “steel Cu and Ni concentration α”. It is a layer that is twice or more, and its thickness δ is 1 μm ≦ δ ≦ 15 μm, but is not particularly limited. A particularly preferable thickness δ is 2 μm ≦ δ ≦ 12 μm. The enriched layer Q is formed by enriching elements other than Fe, such as Cu and Ni, because Fe in the steel material is consumed when an oxide scale is formed in quenching.

The reasons for limiting the composition of the steel material and the composition of the concentrated layer are as follows.
C: 0.07 to 0.80 mass%
C is an element that dominates the hardness when steel becomes a forming member (for example, a mold or a tool). If the C content of the steel material is too small, the strength (hardness) is insufficient. On the other hand, if the C content of the steel material is excessive, coarse carbides increase, and the impact value and fatigue strength of the molding member (for example, a mold or a tool) are reduced. Therefore, the content of C in the steel material is preferably 0.07 to 0.80 mass%, and more preferably 0.1 to 0.80 mass%. In the case of a mold or a tool (for example, a plastic injection mold) as a molding member that does not require much strength, the C content may be 0.07 to 0.20 mass%. . The more preferable content of C is 0.21 to 0.80%, and still more preferably 0.21 to 0.50% by mass that provides HRC36 to HRC52 after tempering. The more preferable content of C is 0.30 to 0.45%.

Cu: 0.01-2.0 mass%
Cu is an element that concentrates in the vicinity of the surface when a molding member (for example, a mold or a tool) is quenched. The concentrated layer serves as a barrier that prevents intrusion of hydrogen ions. For example, in a die casting mold, water-cooled hole cracking is prevented. In order to form a Cu enriched layer during quenching, the Cu content in the steel material is preferably 0.01% by mass or more. On the other hand, Cu is an element that degrades the hot workability of steel, and when the Cu content of the steel material is excessive, the yield of the mold material is significantly reduced. Therefore, the content of Cu in the steel material is preferably 0.01 to 2.0% by mass. The more preferable Cu content of the steel material is 0.4 to 1.5% by mass with which a thickened layer having a sufficient thickness is formed and the adverse effect on hot workability is small.

In the concentrated layer, the relationship of [Cu amount of concentrated layer] ≧ [Cu amount of steel] × 1.2 may be satisfied. Specifically, the content of Cu in the concentrated layer may be 0.025 to 5.0% by mass. This is because if the Cu content is such a level, the concentrated layer thickness δ sufficient as a barrier against the entry of hydrogen ions can be obtained. The Cu concentrated layer near the surface is more excellent as a barrier for hydrogen penetration as the Cu concentration is higher, but satisfies the relationship of [Cu content of concentrated layer] ≧ [Cu content of steel] × 1.2. For this purpose, it is necessary to consume a relatively large amount of Fe in the vicinity of the surface in order to form an oxide scale during quenching (formed simultaneously with the formation of the concentrated layer). As a result, the thickened layer itself becomes thick, and a sufficient thickened layer thickness δ is obtained.
In addition, especially the amount of Cu of a concentrated layer is 0.60-3.0 mass%. The reason is that a very excellent barrier effect is exhibited at 0.60% by mass or more. Moreover, although it was set as 3.0 mass% or less, it is excellent in the barrier effect of hydrogen ion penetration, so that there are many Cu in a concentrated layer, but when Cu exceeds 3.0 mass%, the effect shows a saturation tendency, This is because material costs and heat treatment costs are increased.

Ni: 0.02-5.0 mass%
Ni is an element that is concentrated near the surface when a molding member (for example, a mold or a tool) is quenched. The concentrated layer serves as a barrier that prevents intrusion of hydrogen ions, and in the die casting mold, prevents water-cooled hole cracking. In order to form a concentrated Ni layer during quenching, the Ni content of the steel material is preferably 0.02% by mass or more. On the other hand, Ni is an element that degrades the annealability of steel, and if the Ni content of the steel material is excessive, the material is softened, resulting in a significant increase in cost. Moreover, the addition of Ni in the steel material itself greatly increases the material cost. Therefore, the content of Ni in the steel material is preferably 0.02 to 5.0 mass%. The Ni content of the steel material is more preferably 0.4 to 3.5 mass% in which a thickened layer having a sufficient thickness is formed and the adverse effect on annealing and cost is small.

In the concentrated layer, the relationship of [Ni content of concentrated layer] ≧ [Ni content of steel] × 1.2 may be satisfied. Specifically, the Ni content of the concentrated layer may be 0.05 to 15.0% by mass. This is because if the Ni content is such a level, the concentrated layer thickness δ sufficient as a barrier against the penetration of hydrogen ions can be obtained. The Ni concentrated layer in the vicinity of the surface is more excellent in the function as a barrier for hydrogen penetration as the Ni concentration is higher, but satisfies the relationship of [Ni content of concentrated layer] ≧ [Ni content of steel] × 1.2. For this purpose, it is necessary to consume a relatively large amount of Fe in the vicinity of the surface in order to form an oxide scale during quenching (formed simultaneously with the formation of the concentrated layer). As a result, the thickened layer itself becomes thick, and a sufficient thickened layer thickness δ is obtained.
The particularly preferred amount of Ni in the concentrated layer is 0.60 to 8.0% by mass. The reason is that a very excellent barrier effect is exhibited at 0.6% by mass or more. Moreover, although it was set as 8.0 mass% or less, it is excellent in the barrier effect of hydrogen ion penetration, so that there are many Ni in a concentrated layer, but when Ni exceeds 8.0 mass%, the effect will show a saturation tendency, This is because it only causes an increase in material costs and heat treatment costs.

The reason for limiting the thickness δ of the concentrated layer is as follows.
δ: 1μm ≦ δ ≦ 15μm
The Cu and Ni concentrated layer serving as a barrier for preventing the entry of hydrogen ions has no effect of preventing the entry of hydrogen ions if the thickness is too thin, and the effect is saturated if the thickness is too thick.
This will be described with reference to FIG. FIG. 4 is a graph showing the correlation between the die-cast life and the concentrated layer thickness δ. This graph is a result of investigation by adjusting the thickness δ of the Ni-concentrated layer on the surface of the water-cooled hole, targeting a die casting die of an aluminum wheel for passenger cars. In this investigation, the water cooling hole depth L (see FIG. 4) from the design surface in contact with the molding material to the inner wall surface of the cooling hole was set to 25 mm. The mold life was expressed by the number of shots in which water-cooled hole cracks penetrated the design surface. As shown in FIG. 3, when the thickness δ of the concentrated layer was less than 1 μm, there was almost no effect of preventing water-cooled hole cracking by the concentrated layer. On the other hand, when the thickness δ of the concentrated layer exceeded 15 μm, the effect of preventing water-cooled hole cracking by the concentrated layer was saturated. Therefore, the thickness δ of the concentrated layer is set in the range of 1 μm ≦ δ ≦ 15 μm. Although there is no problem with the thickened layer thickness δ, the formation of a thickness δ exceeding 15 μm requires a large amount of Cu and Ni to be added and changes in the tempering conditions, resulting in enormous costs. There is no real profit because it is high.

The reason for limiting the water cooling hole depth L is as follows.
L: L <25mm
FIG. 4 schematically shows the water cooling hole depth L. FIG. As shown in the figure, the water cooling hole depth L refers to the shortest distance from the design surface 3 that contacts the material to be molded to the inner wall surface of the cooling hole. The shape of the design surface 3 and the shape of the cooling hole 2 are not limited. In order to increase the cycle of die casting, it is necessary to efficiently lower the temperature of the design surface of the die casting mold. Therefore, the water cooling hole depth L is preferably shorter. In the present embodiment, the water cooling hole depth L may be L <25 mm.

  This will be described with reference to FIGS. FIG. 5 shows the correlation between the temperature of the design surface and the depth L of the water-cooled hole for a die casting die in which no Ni concentrated layer is formed. FIG. 6 shows the correlation between the mold life and the water-cooled hole depth L for the die-casting mold in which the Ni-concentrated layer is not formed. Expressed as the number of shots penetrating. These are the results of investigation by adjusting the position of the water cooling hole closest to the design surface for the die cast type of aluminum wheels for passenger cars (there is no Ni concentrated layer on the surface of the water cooling hole). The shorter the water-cooled hole depth L is, the more efficiently the design surface temperature can be cooled (see FIG. 5). On the other hand, water-cooled hole cracks penetrate the design surface with a small number of shots. (See FIG. 6). Therefore, in order to lower the design surface temperature, it is an effective means to shorten the water cooling hole depth L, but it is necessary to consider the problem of water cooling hole cracking. Therefore, in the die casting mold in which the concentrated layer is not formed, the lower limit value of the water cooling hole depth L is generally set to 25 mm. The value of the water cooling hole depth L of 25 mm is also an industrial experience value that optimizes the balance of die casting quality, productivity, and mold cost.

  Therefore, even if the concentrated layer is not formed, the lower limit value of the water cooling hole depth L is 25 mm. Therefore, if the concentrated layer is formed, the water cooling hole depth L can achieve L <25 mm. For example, in the case of a die casting die that takes the above-described values according to the present embodiment as the concentration of Cu and Ni and the thickness δ of the concentrated layer, the water cooling hole depth L is, in particular, 2 mm ≦ L ≦ 20 mm. More preferably, it is 2 mm <= L <= 15mm. This is because as the depth L of the water-cooled hole is shortened, the effect of lowering the design surface temperature becomes more prominent, and a great contribution to high cycle can be expected.

(Production method)
Next, the manufacturing method of the metal mold | die which concerns on this embodiment is demonstrated with reference to FIG. As shown in the figure, the mold according to the present embodiment is manufactured through steps of material block production → cutting (rough machining) → quenching → tempering → cutting (fine machining).

The material block production is performed as follows. That is, a raw material block (steel material) is manufactured by a process in which a molten metal adjusted to a predetermined component is solidified to form an ingot, which is formed by means such as rolling or forging. The material block (the steel material is not particularly limited as long as the steel material contains a predetermined amount of C, Cu and Ni. For example, the material block (steel material) has Mo, V, Co for the purpose of impact value and high-temperature strengthening. Etc. may be contained.

  In cutting (rough machining), a material block (steel material) is cut into an approximate shape of a mold.

The quenching, the material block (steel) is _{A c1} transformation point or above (in many die casting steel from 1010 to 1,050 ° C. is preferred) it is heated in order to keep its quenching temperature for a predetermined time (1-600 minutes), heated After that, it is cooled rapidly. The enriched layer of Cu and Ni is formed at the same time as the oxide scale is formed during this quenching. Therefore, in order to obtain a concentrated layer of Cu and Ni, quenching may be performed in an atmosphere in which an oxide scale is formed.
The heating time for keeping the material block (steel material) reaching the quenching temperature at that temperature may be 1 to 600 minutes. When the heating time is shorter than 1 minute, the oxide scale is not sufficiently formed, the thickness δ of the concentrated layer does not reach 1 μm, and when the heating time is longer than 600 minutes, the productivity is lowered and the effect of preventing water-cooled hole cracking is further improved. It is because it cannot reach. If it is 1 to 600 minutes, 1 μm ≦ δ ≦ 15 μm suitable as the thickness δ of the concentrated layer of Cu and Ni can be obtained. A preferable heating time is 30 to 240 minutes. This is because the carbide is sufficiently dissolved in the austenite phase to obtain strength and impact value after tempering. The thickness δ of the concentrated layer is thin when the heating time at the time of quenching is short, and becomes thick when the heating time is long, and has a positive correlation with the thickness of the oxide scale. The heating time may be adjusted so that it can be obtained.

In tempering, the martensite structure produced by quenching is heated to a temperature of A ₁ point or less and then cooled. A preferable tempering temperature is 550 to 650 ° C. This is because toughness does not appear when the temperature is lower than 550 ° C., and strength does not appear when the temperature exceeds 650 ° C. Tempering is performed because the mold after heating to a temperature _{equal to} or higher than the _Ac1 transformation point is quenched by cooling, but cannot be used because it is too hard and has low toughness. That is, in tempering, the hardness is slightly reduced and at the same time the toughness is increased.

In cutting (fine machining), the design surface is cut into a shape of a mold product and polished for use in actual production. However, the cooling holes are not cut or polished, and are kept in the quenching and tempering state (the state where there is an oxide scale and a concentrated layer). This is because if the surface of the cooling hole is cut or polished, the concentrated layer of Cu and Ni is removed.
Through the above steps, the mold according to the present embodiment is obtained.

(Function)
Next, the operation of the mold according to this embodiment will be described. The metal mold | die which concerns on this embodiment is the mass%, From the steel materials containing C: 0.21-0.80%, Cu: 0.01-2.0%, Ni: 0.02-5.0%. Therefore, it has an appropriate strength and impact value as quality characteristics required for a die casting die.
Further, the concentrated layer of Cu and Ni formed in the vicinity of the surface of the cooling hole of the mold according to the present embodiment is uniform without unevenness because Cu and Ni of the steel material are concentrated. And the concentrated layer contains Cu and Ni at least 1.2 times the amount of Cu and Ni in the steel material, or Cu is 0.025 to 5.0% by mass and Ni is mass%. 0.05 to 15.0%. The thickness δ of the concentrated layer is 1 μm ≦ δ ≦ 15 μm. Therefore, the presence of the concentrated layer suppresses rust itself, which is the starting point of water-cooled hole cracking, and the Ni-concentrated layer blocks hydrogen ions that promote the progress of water-cooled hole cracking, leading to cracks penetrating to the design surface. Progress is suppressed.
In the mold according to the present embodiment, the water cooling hole depth L from the design surface in contact with the material to be molded to the inner wall surface of the cooling hole is L <25 mm, so even if a high cycle of about 15% is achieved. Since the mold is sufficiently cooled by the cooling liquid every casting cycle, the die-cast product has the conventional quality characteristics. Further, when the production is performed in the production cycle of the conventional die casting, the mold is cooled to a temperature lower than that of the conventional one, so that the quality characteristics of the die cast product are improved.

  Next, since a test die according to an embodiment of the present invention was manufactured and evaluated, it will be described. In addition, this Example is only a mere illustration and does not limit this invention.

(Evaluation Test and Results-Part 1)
(Production of test mold)
About Examples 1-9 shown in Table 1 and Comparative Examples 1-6, the manufacturing conditions shown in Table 2 using steel materials having the composition shown in the same table (unit: mass%, balance: Fe and inevitable impurities) A die mold for die casting having a weight of about 500 kg was prepared under (heat treatment conditions, etc.). The test mold was manufactured according to the following procedure (see Table 2 and FIG. 7). The steel materials of Examples 1 to 9 and Comparative Examples 1 to 6 in the annealed state are roughly processed into test molds, and then these test molds are quenched in an air atmosphere (Comparative Example 6 is under vacuum). It was. In the quenching, each test mold was heated to 1030 ° C. and kept at a quenching temperature for 120 minutes (700 minutes in Comparative Example 4), and then each test mold was cooled. In the next tempering, each test mold was held at 595 ° C. for 3 hours and then held at 585 ° C. for 3 hours. Thereby, each test die was adjusted to an appropriate hardness according to the amount of C (in addition, when this tempering was finished, the strength and impact values shown in Table 3, the Cu and Ni in the concentrated layer) The concentration and the thickness of the concentrated layer were measured). In the final precision processing, each test mold was subjected to final finishing of the die casting mold.

(Measurement and evaluation of strength and impact value)
The strength and impact value of each test mold of Examples 1 to 9 and Comparative Examples 1 to 6 before fine processing after quenching and tempering were measured. The test piece is a JIS No. 3 type (U notch), and the impact value [J / cm ² ] is obtained by dividing the absorbed energy [J] by the cross-sectional area of the test piece. The results are shown in Table 3. It turned out that Examples 1-9 were equipped with the intensity | strength and impact value required as a die-casting die or a tool. The strength required for a die casting tool or tool is an allowable limit for HRC37. Since the strength of Example 8 with the smallest amount of C was the lowest HRC37.2 in all Examples, the amount of C is preferably 0.1% by mass or more, more preferably 0.21. It was found that it was necessary to contain at least mass%.

(Measurement of Cu and Ni concentration in the concentrated layer)
The concentrations of Cu and Ni in the concentrated layers of the steel materials of Examples 1 to 9 and Comparative Examples 1 to 6 before the fine processing after quenching and tempering were measured. The concentrated layer was a portion where Ni and Cu were 1.2 times or more the Ni and Cu concentrations of the steel material (the portion that was not the concentrated layer) (see FIG. 1). EPMA was used to identify the concentrated layer. The concentrations of Cu and Ni in the concentrated layer were judged from the values of line analysis by EPMA. As a result, the concentrated layer was uniformly formed without unevenness. Table 3 shows the results.

(Measurement of thickened layer thickness δ)
Next, the thickness δ of the concentrated layer identified by the above EPMA (the portion where Ni and Cu are 1.2 times or more the Ni and Cu concentrations of the steel material (the portion that is not the concentrated layer)) is measured. did. Table 3 shows the results. In Examples 1 to 9, a concentrated layer having a thickness of 7 to 14 μm was uniformly formed under the oxide scale. On the other hand, in Comparative Examples 1 and 2, the thickness of the concentrated layer was as thin as 0.3 μm, and in Comparative Examples 3 and 6, the concentrated layer was not formed. In Comparative Examples 4 and 5, a thick concentrated layer was formed.

(Measurement and evaluation of crack depth D of water-cooled hole)
Next, in order to evaluate the resistance to water-cooled hole cracking when the test molds of Examples 1 to 9 and Comparative Examples 1 to 6 which have been subjected to precision processing are applied to die casting, the crack depth D of the water-cooled hole Was measured. This measurement was performed according to the following procedure. Each die was assembled in a die casting machine having a clamping force of 2000 tons, and die casting products (cylinder blocks for automobiles) were cast. The hot water material used for casting was aluminum die casting ALC12, and the hot water temperature (in the melting and holding furnace) was 670 ° C. The die-cast product was a cylinder block for automobiles. Casting was carried out for 65 seconds per cycle, and the mold was cut when 50,000 shots (cumulative about one month) were completed, and the crack depth D of the water-cooled hole at a position 15 mm from the design surface was measured. The results are shown in Table 3.

  In Examples 1 to 9, good results were obtained in which the crack depth D was D ≦ 200 μm. The reason why 200 μm is used as a quality criterion is that cracks are generated even in water-cooled holes located far from the design surface (water-cooled hole depth L is 40 mm or more), but the crack depth does not greatly exceed 200 μm. Because. In Examples 1 to 9, although the water-cooled hole depth L was 15 mm, the crack depth D was less than 200 μm, and therefore, it is considered to have extremely excellent resistance to water-cooled hole cracks. Therefore, in the case of Examples 1 to 9, it is considered that the possibility of cracks reaching the design surface is low even if the number of shot shots is further increased.

  On the other hand, Comparative Examples 1, 3, and 6 in which almost no thickened layer was formed had a crack depth D> 10 mm. Therefore, in these comparative examples, it is considered that if the number of shots is increased a little, the crack reaches the design surface and the cooling water may be ejected from the crack. In Comparative Examples 2, 4, and 5, the crack depth D is short. However, since Comparative Example 2 is made of stainless steel, the cost is high, and stress corrosion cracking due to local corrosion is a concern. In Comparative Example 4, the heating time is too long and productivity is deteriorated. In Comparative Example 5, Ni is high. It is not suitable for mass production because the material cost is too high. In addition, although concentration of Si, Mn, Cr, Mo, V, etc. was recognized, these have no effect of preventing water-cooled hole cracking. Moreover, in the Example and the comparative example, since these steel material components are the same, it excluded from the evaluation object.

  From the above, it has been found that the formation of a concentrated layer having an appropriate thickness and enriched in Cu and Ni is effective in preventing water-cooled hole cracking and suppressing its progress.

(Evaluation test and results-2)
From the results of Examples 1 to 9, it was found that the formation of the concentrated layer was effective in preventing water-cooled hole cracking, and therefore, the effectiveness of high cycle formation was verified for one of the steel types.
(Production of test mold)
For Examples 10 and 11, Reference Examples 1 and 2 and Comparative Examples 7 to 10 shown in Table 4, using steel materials having the composition shown in the same table (unit: mass%, balance: Fe and inevitable impurities) A die mold for die casting having a weight of about 500 kg was manufactured. That is, the test molds of Examples 10 and 11 were obtained through the same heat treatment as Example 2 using the same material as Example 2 shown in Table 1. In addition, the test molds of Reference Examples 1 and 2 and Comparative Examples 7 to 10 were respectively obtained through the same heat treatment as in Example 2 using the same material as in Example 2. In addition, although Reference Examples 1 and 2 are based on Examples 10 and 11, since the conventional standard position was adopted as the water cooling hole depth L shown in Table 5 to be described later, it is not considered as an example. .

(High cycle test and evaluation)
Examples 10 and 11, water cooling hole depth L of water cooling holes provided in the test molds of Reference Examples 1 and 2 and Comparative Examples 7 to 10, presence / absence of fine processing to water cooling holes, concentration layer of water cooling holes The presence or absence was as shown in Table 5.
Then, the test dies of Examples 10 and 11, Reference Examples 1 and 2 and Comparative Examples 7 to 10 were assembled in a die casting machine having a clamping force of 2000 tons, and die casting products (cylinder blocks for automobiles) were cast. The hot water used for casting was aluminum die casting ALC12, and the hot water temperature (in the melting and holding furnace) was 670 ° C. The casting cycles (1 cycle) and design surface temperatures of Examples 10 and 11, Reference Examples 1 and 2 and Comparative Examples 7 to 10 were as shown in Table 5. Note that the design surface temperature is the one immediately after the mold is opened to cool the design surface by spraying in order to take out the die-cast product, and after the mold release agent is applied, immediately before the mold is closed, and measured by a thermoviewer. . Then, the presence or absence of water-cooled hole cracking on the design surface was observed (in the case where water-cooled hole cracking did not occur, casting was stopped when 50000 shots (cumulative about one month) were completed). The results are also shown in Table 5.

  In Examples 10 and 11, the water-cooled hole crack was provided on the design surface even though the water-cooled hole was provided at a position where the distance (water-cooled hole depth L) from the design surface to the inner wall surface of the water-cooled hole was 10 mm. Did not penetrate. Among them, in Example 10, since the casting cycle was standard (65 seconds), the design surface temperature could be sufficiently cooled, and the cooling efficiency was good. Example 11 is a high cycle (55 seconds) using the test mold of Example 10, and a design surface temperature of a conventional level could be realized even if the cycle was shortened by 15%. . In Examples 10 and 11, when the crack depth D on the inner surface of the water-cooled hole was further confirmed, the crack depth was less than 200 μm. This value is about the same as the crack depth generated in the water-cooled hole, where the distance from the design surface is far and water-cooled hole cracking does not cause any problem. Therefore, in Examples 10 and 11, it was found that even if the water cooling holes are arranged close to the design surface, there is very little risk that the water cooling hole cracks penetrate the design surface. From the above, it was found that the high cycle as in Example 10 → Example 11 can be achieved.

  On the other hand, in Reference Example 1, water cooling holes are provided at a conventional standard position where the distance from the design surface to the inner wall surface of the water cooling holes (water cooling hole depth L) is 40 mm, and the casting cycle is also standard. As a result, water-cooled hole cracks did not penetrate the design surface. Reference Example 2 was an example in which the test mold of Reference Example 1 was used to perform high cycle, and the design surface temperature significantly increased. As in Reference Example 2, when the design surface temperature is remarkably increased, the casting quality is deteriorated due to a decrease in the solidification rate, so that it cannot be put into practical use. From this, it was found that if the water-cooled holes were provided at the conventional positions as in Reference Example 1, high cycle could not be achieved.

  Comparative Example 7 is a conventional standard example in which the water-cooled holes are brought close to the design surface in the absence of the concentrated layer, and the water-cooled hole cracks penetrate the design surface in about 30000 shots, became. In Comparative Example 7, the effect of lowering the design surface temperature is large, but it cannot be put into practical use from the viewpoint of mold life. The same applies to Comparative Example 8. In Comparative Example 9, the casting cycle and the water-cooled hole depth were standard conditions in the past, and water-cooled hole cracks penetrating the design surface did not occur despite the absence of the concentrated layer, Compared to Reference Example 1, the crack depth on the inner surface of the water-cooled hole is longer. Comparative Example 10 is an example in which the high cycle was performed in Comparative Example 9, and the design surface temperature significantly increased. Therefore, Comparative Example 10 cannot be put to practical use because the casting quality deteriorates due to the decrease in the solidification rate. Further, as in Comparative Example 9, the crack depth on the inner surface of the water-cooled hole was longer than in Reference Example 1 in which the concentrated layer was present. Therefore, Comparative Example 10 has a risk of progressing to water-cooled hole cracking and cannot be put into practical use.

From the above, if a thick layer of Cu and Ni having an appropriate thickness is formed, penetration of the water-cooled hole crack into the design surface is suppressed even if the water-cooled hole is brought close to the design surface, and a high cycle can be achieved. all right. Further, it has been found that the high cycle can be realized at low cost without using high cost materials.
The mold according to the present embodiment can reduce the design surface temperature to the conventional level even if it is subjected to high cycle, and further, it has been found that water-cooled hole cracks do not penetrate, and thus has excellent thermal fatigue characteristics. It was.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. The present invention can be variously modified and applied without departing from the spirit of the present invention. For example, in the above-described embodiment, the example of using the die casting die as an example of a molding member has been shown in the above embodiment, but the present invention is also applied to tools such as plastic molding such as injection molding of resin and glass, and forging and rolling. However, the present invention is not limited to the applications shown in the embodiments. In addition, the present invention is not limited to the molding member (for example, a mold or a tool) obtained by the quenching and tempering conditions shown in the examples, and quenching and tempering according to the chemical composition of the steel material. A molding member (for example, a mold or a tool) obtained according to conditions is also included in the scope of the present invention.

  Since the molding member according to the present invention is excellent in thermal fatigue properties, many demands are expected, and die casting, forging, molds and tools for injection molding of plastics and rubber, and manufacturers of the present invention, It has high utility value for manufacturers that manufacture die-cast products using molding members.

It is a figure for demonstrating a concentrated layer, (a) shows typically the side surface of the metal mold | die 1, (b) is a figure which shows the correlation with the density | concentration of the element X, and the distance from a cooling hole surface. . It is a figure for demonstrating the water cooling hole depth L, and is a figure which expands and shows an inside from the surface layer of a water cooling hole. 6 is a graph showing a correlation between a thickened layer thickness δ and a die life of a die casting die. It is a figure for demonstrating the surface vicinity of a cooling hole. It is a graph which shows the correlation with the water cooling hole depth L and the design surface temperature. It is a graph which shows the correlation of the water cooling hole depth L and a metal mold | die lifetime. It is a figure which shows the manufacturing process of the metal mold | die which concerns on one Embodiment of this invention. It is the figure which showed the side surface of the common metal mold | die with a water cooling hole. It is a figure for demonstrating the phenomenon of a water cooling hole crack.

Claims (5)

A molding member made of a steel material containing, by mass%, C: 0.21 to 0.80%, Cu: 0.01 to 2.0%, Ni: 0.02 to 5.0%,
With cooling holes that serve as coolant flow paths,
In the vicinity of the surface of the cooling hole, a concentrated layer in which Cu and Ni of the steel material are concentrated is formed,
The thickening layer has a thickness δ of 1 μm ≦ δ ≦ 15 μm.   2. The forming member according to claim 1, wherein the amount of Cu and the amount of Ni contained in the concentrated layer are 1.2 times or more the amount of Cu and the amount of Ni contained in the steel material, respectively.   3. The molding member according to claim 1, wherein the concentrated layer contains, by mass%, Cu: 0.025 to 5.0% and Ni: 0.05 to 15.0%. .   The at least one cooling hole among the cooling holes has a cooling hole depth L from a design surface in contact with the molding material to an inner wall surface of the cooling hole of L <25 mm. 4. The molding member according to any one of 3.   The forming member according to claim 4, wherein the steel material contains C: 0.07 to 0.80% in mass%.

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