JPH1030154A - Metal mold for plastic molding, excellent in finishing precision, and steel for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal mold for plastic molding, capable of providing sufficient dimensional accuracy required of a metal mold for high precision plastic molding by means of a single machining before age hardening treatment, and also to produce a steel for the metal mold for plastic molding. SOLUTION: This steel has a composition containing, as alloying elements, <=0.03%, by mass, C, <=0.10% Si, <=0.10% Mn, 6.0-8.0% Ni, 8.1-9.0% Cr, 5.0-9.0% Mo, 5.0-9.0% Co, 0.10-1.0% Ti, 0.05-0.15% Al, and <=0.0080% N and having the balance Fe with inevitable impurity elements. Because the ratio of dimensional change before age hardening treatment is low, satisfactory dimensional accuracy required of a metal mold for high precision plastic molding can be obtained. At this time, age hardening treatment can be replaced by a surface treatment at 400-550 deg.C, such as PVD treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a maraging steel suitable as a plastic mold requiring high precision.

[0002]

2. Description of the Related Art In recent years, plastics have been used for mechanical element parts such as gears, bearings, cams, screws, and springs, or lens systems.
Due to their use as parts for precision instruments such as diaphragms and terminal board covers, and their shapes have become more complex, the demands for improved dimensional accuracy and surface finish accuracy of plastic molding dies are extremely severe. It has become. In addition, there is a strong demand for increasing the hardness of the mold in order to extend the life of the mold.

In order to satisfy the above requirements, conventionally, a die is machined in a hardened state using high carbon steel such as tool steel, and then quenched and tempered to obtain a required hardness. Had been used. When quenching and tempering such a high-carbon steel, a large heat treatment distortion is generated. Therefore, in a mold requiring high finishing accuracy, it is necessary to perform finishing after the heat treatment, and two machining operations are required. There is a problem that it takes a long time to manufacture the mold and the manufacturing cost increases.

[0004] Maraging steel has a very low C and a large amount of N.
A steel containing elements such as i, Co, Mo, etc., which is formed into a martensite structure by solution heat treatment and then hardened by subjecting it to age hardening treatment to precipitate an intermetallic compound on the martensite ground. . Martensite of maraging steel has a relatively low hardness and can be machined relatively easily. Further, the heating temperature in the age hardening treatment of the maraging steel is as low as about 500 ° C., and the strain generated during the age hardening treatment is small, so that the heat treatment deformation is much less than that during quenching and tempering of the high carbon steel. .

[0005] Therefore, if machining is performed to finish dimensions by using a maraging steel in a solution heat treatment state and the hardness is increased by performing age hardening treatment, then one machining operation is performed without performing finishing processing again. Thus, required dimensional accuracy can be obtained. For example, JP-A-7-243003
(Japanese Patent Application No. 6-54923) discloses that as a steel capable of producing a mold by one machining before the age hardening treatment as described above, a heat-resistant steel which can be suitably used for a die-casting mold. A maraging steel excellent in checkability is disclosed.

The above-mentioned Japanese Patent Application Laid-Open No. 7-243003 (Japanese Patent Application No.
The steel disclosed in Japanese Patent No. 54923) can obtain a required dimensional accuracy as a die-casting die by one machining, but, for example, a steel manufactured by a plastic such as an electronic component has a problem. Dimensional accuracy and surface finish requirements of parts themselves are stricter than die cast products,
As a result, demands on plastic molds are strict,
The publication does not suggest whether the dimensional accuracy required for the plastic mold is satisfied, nor does it suggest whether the mirror finish required for the plastic mold can be obtained.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and an object of the present invention is to reduce the heat treatment distortion during the age hardening treatment so as to reduce the distortion before the age hardening treatment. An object of the present invention is to provide a plastic mold and a plastic mold steel capable of obtaining sufficient dimensional accuracy as a high-precision plastic mold by multiple machining operations.

[0008]

In order to achieve the above object, the plastic mold steel according to the present invention has a content of alloying elements in mass%, C: 0.03% or less, and Si: 0.10.
%, Mn: 0.10% or less, Ni: 6.0 to 8.0
%, Cr: 8.1 to 9.0%, Mo: 5.0 to 9.0
%, Co: 5.0 to 9.0%, Ti: 0.10 to 1.0
%, Al: 0.05 to 0.15%, N: 0.0080
% Or less, and is composed of residual Fe and unavoidable impurity elements.

Further, the plastic mold of the present invention having excellent finishing accuracy has a content of alloying elements in mass% and C: 0.
03% or less, Si: 0.10% or less, Mn: 0.10%
Hereinafter, Ni: 6.0 to 8.0%, Cr: 8.1 to 9.0
%, Mo: 5.0 to 9.0%, Co: 5.0 to 9.0
%, Ti: 0.10-1.0%, Al: 0.05-0.
15%, N: 0.0080% or less, steel comprising residual Fe and unavoidable impurity elements is processed into a required shape in a solution heat treatment state, and then subjected to a surface hardening treatment at a temperature of 400 to 550 ° C. It is characterized by becoming.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The plastic mold steel of the present invention having excellent finishing accuracy is different from the conventional maraging steel.
In order to reduce the dimensional change rate during the age hardening treatment, after adding an appropriate amount of Cr and optimizing the Ni and Co contents,
The essence is to limit the N content in order to optimize the balance of the content of each alloy element and to improve the surface finish required for the plastic mold. Hereinafter, the reasons for limiting the alloy composition in the plastic mold steel having excellent finishing accuracy of the present invention will be described.

C: not more than 0.03% If C exceeds 0.03%, the toughness of the steel is deteriorated, and the age hardening at the time of the age hardening treatment is inhibited, so that the upper limit of the content is 0.03%. And Si: 0.10% or less If the Si content exceeds 0.10%, the toughness of the steel deteriorates, so the upper limit of the content is set to 0.10%.

Mn: 0.10% or less If the Mn content exceeds 0.10%, the toughness of the steel deteriorates. Therefore, the upper limit of the content is set to 0.10%. Ni: 6.0 to 8.0% Ni is an essential element for lowering the martensitic transformation point of steel to form a tough low-carbon martensite and for forming an age hardening element. If the Ni content is less than 6.0%, tough martensite cannot be obtained and the age hardening property is not sufficient, so the lower limit of the Ni content is set to 6.0%. However, when Ni is excessively contained, the martensitic transformation point decreases, and sufficient hardness cannot be obtained after the age hardening treatment, and the dimensional change rate during the age hardening treatment increases. Therefore, the upper limit of the Ni content is set to 8.0. %.

Cr: 8.1-9.0% In the steel of the present invention, Cr is an essential element for reducing the dimensional change rate during age hardening. Further, since it is an element that lowers the martensitic transformation point of steel, the content of Cr is set to 8.1% or more in balance with other elements. However, if it is contained excessively, the age hardening property due to the decrease of the martensitic transformation point is reduced and the toughness is deteriorated.
The upper limit of the r content is set to 9.0%. Thereby, the dimensional change rate during the age hardening treatment is smaller than that of a conventional general maraging steel.

Mo: 5.0-9.0% Mo is an element essential for forming age hardening elements and is an element which raises the martensitic transformation point of steel. However, if it is contained excessively, the hardness of the solution heat treatment is increased to impair the machinability, and the age hardening treatment causes the Ni3 Mo, Fe
A large amount of intermetallic compounds such as 2Mo are formed to deteriorate the toughness of steel. Therefore, in the steel of the present invention, the lower limit of the Mo content is set to 5.0%, and the upper limit is set to 9.0%.

Co: 5.0 to 9.0% Co is an element that promotes age hardening of steel and increases the martensitic transformation point. In order to exhibit the effect, the lower limit of the content needs to be 5.0%. However, if the content is excessive, the dimensional change rate during the age hardening treatment increases, and the toughness of the steel deteriorates and the cost increases, so the upper limit of the content is set to 9.0%. Preferably, the upper limit of the content is less than 7.0%. Ti: 0.10 to 1.0% If the content of Ti is less than 0.1%, the age hardening property of the steel is insufficient, and the crystal grains of the steel are coarsened. On the other hand, when the content is 1.
If it exceeds 0%, the amount of inclusions increases and the surface finish of the mold is impaired. Therefore, in the steel of the present invention, the lower limit of the Ti content is 0.10.
%, And the upper limit is 1.0%.

Al: 0.05 to 0.15% Al has a deoxidizing effect on molten steel during smelting and contributes to age hardening of steel. Therefore, the lower limit of the content is 0.05
%. However, if contained excessively, the intermetallic compound Ti3
Since the formation of Al deteriorates the toughness of the steel, the upper limit of the content is set to 0.15%.

N: 0.0080% or less N combines with alloying elements in steel, particularly Ti and V, to form hard TiN and VN, and is dispersed in the steel as inclusions.
Since such inclusions impair the mirror finish of the plastic mold, the N content is desirably as small as possible, but the upper limit of the N content is 0.0080 from the viewpoint of raw material and steelmaking costs.
%.

The plastic mold steel of the present invention is adjusted to the required dimensional accuracy and surface condition by a machining process and a finishing process such as lapping, paper, electrolytic polishing, etc. in a solution heat treatment state. By doing so, it is used as the required hardness. The heating temperature for the age hardening treatment is preferably from 400 to 550 ° C. If the heating temperature is too low, it takes a long time for age hardening, and if the heating temperature is too high, it is difficult to obtain high aging hardness.

400 to 550 instead of the age hardening treatment
The surface hardening treatment can be performed at ℃. Preferred surface hardening treatments include gas nitriding, gas nitrocarburizing, PVD
Processing.

[0020]

Embodiments of the present invention will be described below. Steel having the chemical composition shown in Table 1 was produced using a vacuum melting furnace. Each steel is 70mm wide x 30mm thick by hot forging
And then subjected to a solution heat treatment at 830 ° C. × 1 hr air cooling to obtain a test material. 60mm width from the test material
A test piece having a thickness of 20 mm and a length of 100 mm was cut out, finished to a surface roughness of 0.8 S, and mirror-finished by electrolytic polishing to obtain a test piece.

[0021]

[Table 1]

Next, an age hardening treatment was performed under the age hardening conditions shown in Table 2. In each of Examples except for Example 6, the test piece was subjected to age hardening treatment in an argon atmosphere. In Example 6, a PVD treatment was performed in a nitrogen atmosphere also as an age hardening treatment. The dimensions of the test piece in the L direction (length direction) and the T direction (width direction) before and after the age hardening treatment were measured. The measurement was performed at a measurement accuracy of 1 μm, with five points in the L direction and six points in the T direction, and the average value was determined. The value of (dimension after age-hardening treatment-dimension before age-hardening treatment) / dimension before age-hardening treatment was determined and defined as the dimensional change rate. Further, the test material and the hardness after the age hardening treatment were measured, and the results are shown in Table 2 as solid solution hardness and aging hardness, respectively.

[0023]

[Table 2]

According to Table 2, the solid solution hardness of each of the examples of the present invention is an appropriate hardness that can be easily machined, and a high aging hardness can be obtained by the age hardening treatment. Further, it is clear that the dimensional change rate of each example of the present invention in both the L direction and the T direction is extremely smaller than that of the comparative example. In addition, it was found that Comparative Example 3 containing V and having a high N not only had a large rate of change in technique after aging but also had poor mirror surface finish. It was also found that Comparative Example 4 containing 11.2% of Co also had a large dimensional change rate.

When the surface hardness of Example 6 was measured by a microhardness tester, a surface hardness of 935 HV was obtained. In each of the examples of the present invention, no beautiful pits or uneven polishing was caused by the electrolytic polishing, and a beautiful mirror-finished surface was obtained, indicating that the steel of the present invention is suitable as a plastic mold steel. Was.

[0026]

As described above, according to the plastic mold steel of the present invention, machining can be easily performed in a solution heat treatment state, and the dimensional change rate when hardened by age hardening is small. There is no need to perform a finishing process after the age hardening treatment, and a high-precision plastic mold having excellent dimensional accuracy can be obtained by only one machining before the age hardening process. 400-55 instead of the age hardening treatment
By performing the surface hardening treatment at a temperature of 0 ° C., a high-precision plastic mold having a higher surface hardness can be obtained in addition to the above effects.

Claims (2)

[Claims] 1. The content of alloying elements is% by mass, C: 0.03% or less, Si: 0.10% or less, Mn: 0.10% or less, Ni: 6.0 to 8.0%, Cr: 8.1 to 9.0%, Mo: 5.0 to 9.0%, Co: 5.0 to 9.0%, Ti: 0.10 to 1.0%, Al: 0.05 to 0.15%, N: 0.0080% or less, characterized by being composed of residual Fe and unavoidable impurity elements. 2. The alloy element content in mass%, C: 0.03% or less, Si: 0.10% or less, Mn: 0.10% or less, Ni: 6.0 to 8.0%, Cr: 8.1 to 9.0%, Mo: 5.0 to 9.0%, Co: 5.0 to 9.0%, Ti: 0.10 to 1.0%, Al: 0.05 to 0.15%, N: not more than 0.0080%, and a steel comprising residual Fe and unavoidable impurity elements is processed into a required shape in a solution heat treatment state.
A plastic mold having excellent finishing accuracy, which is obtained by performing a surface hardening treatment at a temperature of 0 to 550 ° C.