JP2002363690A - Steel for plastic molding die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce steel for a plastic molding die which has general properties required for the die equally to the conventional steel for a plastic molding die, has little pinholes, fine pits and ruggedness compared with the conventional one, and has excellent mirror finishing properties. SOLUTION: In the steel for a plastic molding die, Al based inclusions essentially consist of CaO-AlO3 , and the length in the longitudinal direction of clustery inclusions in which the inclusions are flocculated is <=150 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel for a plastic molding die, and more particularly to a steel for a plastic molding die having excellent mirror finish.

[0002]

2. Description of the Related Art Molds used for molding plastics are usually manufactured by machining or electrical discharge machining of steel. Therefore, steels for plastic molding dies have excellent machinability in machining, Excellent surface smoothness after electrical discharge machining is required. Further, since welding may be performed in repair, design change, assembly, and the like, excellent weldability is required. In addition, since the shape of the mold surface appears on the surface of the molded plastic product, it has excellent general properties required for the mold such as hardness, proof stress, toughness, etc.
It is required that there are few fine pits and unevenness.

Conventionally, as steel for plastic molds, C:
0.10 to 0.25%, Si: 0.05 to 0.80%,
Mn: 0.50 to 2.00%, P: 0.030% or less,
Cr: 0.50 to 2.50%, Mo: 0.05 to 1.0
0%, V: 0.01 to 0.10%, Al: 0.005 to
0.080%, Ti: 0.005 to 0.10%, B:
0.0005-0.0030%, N: 0.0060% or less, O: 0.0050% or less, and S:
0.04 to 0.07%, Zr: 0.05 to 0.15%,
Ca: 0.001 to 0.05%, and Pb: 0.10
A pre-hardened steel for plastic molds containing at least one kind of machinability improving element selected from the group consisting of 0.30% is known (Japanese Patent Application Laid-Open No. Sho 62-149811).

[0004] Further, C: 0.05-
0.25%, Si: 0.20 to 0.40%, Mn: 0.
25-2.0%, s-Al: 0.010-0.030
%, O: 0.0020% or less, Cr: 0.1 to 3.0%, Mo: 0.5 to 1.0
%, V: one or more of 0.05 to 0.6%, and if necessary, S: 0.001 to 0.10%,
Pb: 0.03-0.2%, Ca: 0.0005-0.5%.
010%, Zr: 0.003-0.2% and Bi: 0.
There is known a plastic mold steel containing 0.1 to 0.20% of one or more kinds, the balance being Fe and unavoidable impurities (Japanese Patent Application Laid-Open No. H11-111).
158579).

[0005] However, the plastic molding prehard mold steel disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 62-149811 contains a large amount of Al, so that the amount of Al ₂ O ₃ -based inclusions is large. However, when they are polished, they fall off to cause pinholes and fine pits, and because the clusters are hard, they cause irregularities, and there is a problem that the mirror finish is not so good. In addition, Japanese Patent Application Laid-Open No.
No. 158579 also has a smaller number of clusters in which inclusions are agglomerated than in the above-mentioned publication, but the steels for plastic molding dies described in JP-A-158579 are large and fall off during polishing to cause pinholes and fine particles. Cause a serious pit,
In addition, since the clusters are hard, they cause irregularities, and there is a problem that the specularity is not so good.

[0006]

SUMMARY OF THE INVENTION The present invention has the general properties required for a mold equivalent to the conventional steel for plastic molding dies, and has more pinholes, fine pits and irregularities than the conventional ones. It is an object of the present invention to provide a steel for plastic molding dies having a low mirror finish.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on the shape, shape, etc. of inclusions that reduce the mirror surface of steel for plastic molding dies. The inclusions in the plastic mold metal steel used in (1) are clusters in which Al ₂ O ₃ -MgO (spinel) inclusions are aggregated in a rosary, and the length of the cluster inclusions is 150 μm or more. There is also a thing that such a long thing falls during polishing, generating pinholes and fine pits, Al ₂ O ₃ -MgO-based inclusions are hard,
Since it is not polished from the periphery during polishing, it is easy to generate irregularities on the polished surface, and inclusion of Ca causes CaO-A
becomes l ₂ O ₃ based inclusions, for the inclusions not be aggregated in large clusters, it hardly falls when polishing, CaO-Al ₂ O ₃ based inclusions of, Al ₂ O ₃
-Obtained the knowledge that unevenness is hardly generated on the polished surface because it is softer than the MgO-based inclusions and easily polished at the same time as the surroundings during polishing. The present invention has been made based on these findings.

That is, in the steel for a plastic molding die of the present invention, Al-based inclusions are mainly composed of CaO-Al
₂ O ₃ , and the length in the longitudinal direction of the cluster-like inclusions in which the inclusions were aggregated was set to 150 μm or less.

Further, in the steel for a plastic molding die of the present invention, C: 0.10 to 0.30%, Si: 0.0
5 to 1.50%, Mn: 0.90 to 2.00%, P:
0.030% or less, S: 0.010% or less, Cu: 0.
25% or less, Ni: 0.25% or less, Cr: 1.00
2.50%, Mo: 0.20 to 0.60%, V: 0.0
5 to 0.20%, B: 0.0020% or less, S-Al:
0.035% or less, O: 0.0030% or less, N: 0.
0200% or less and Ca: 0.0005 to 0.0050
%, The balance being substantially composed of Fe, the Al-based inclusions mainly consisting of CaO—AlO ₃ , and the length of the cluster in which the inclusions are aggregated in the longitudinal direction is 150 μm. What we did below.

[0010]

Next, the steel for a plastic molding die of the present invention will be described in detail. In the present invention, A
The reason that the l-based inclusions are mainly CaO-Al ₂ O ₃ -based inclusions is that CaO-Al ₂ O ₃ -based inclusions are easily dispersed,
This is because they do not agglomerate into large clusters, so that they do not easily fall during polishing, so that it is difficult to generate pinholes or fine pits that deteriorate the mirror surface, and CaO-A
Since l ₂ O ₃ inclusions are soft, because they are polished similarly to the surrounding during polishing, because it becomes difficult to generate the unevenness to lower the specularity to the polished surface. Further, in the present invention, Ca
The reason why the longitudinal length of the cluster-shaped inclusions in which the O-Al ₂ O ₃ -based inclusions are aggregated is set to 150 μm or less is that, when the inclusions become long, they fall during polishing and reduce the specularity. Creates pits whose length is 150 μm
This is because if the thickness is 110 μm or less, pinholes and fine pits are unlikely to occur.

Next, the component composition of the steel for a plastic molding die of the present invention will be described. Specularity excellent plastic molding die steel of the present invention, those with predominantly CaO-Al ₂ O ₃ and Al-based inclusions, and the longitudinal length of the cluster that the inclusions are aggregated to 150μm or less In this case, the mirror surface is excellent, so that it is sufficient if the steel is used for plastic molding dies.
Although the component composition is not specified, since it is specified in claim 2 as a preferable component composition, the reason for specifying there is explained.

C: 0.10% to 0.30% C is an element contained for increasing the hardness. In order to obtain the required hardness (about 285 HB), it is necessary to contain 0.10% or more, preferably 0.13% or more. However, if the amount is too large, welding becomes difficult and hardness becomes high. And reduce the machinability,
0.30% or less, preferably 0.24% or less.

Si: 0.05-1.50% Si is a deoxidizing agent at the time of smelting and enhances hardenability, and is an element to be contained therein. In order to obtain these effects, 0.05% or more, preferably 0.1% or more.
The content must be 25% or more, but if it is increased, the toughness is reduced. Therefore, the content is 1.50% or less, preferably 1.35%.
% Or less.

Mn: 0.90 to 2.0% Mn is a deoxidizing agent at the time of melting and enhances hardenability, and is an element to be contained for them. 0.90% or more, preferably 1.
It is necessary to make the content 0.5% or more. However, if the content is too large, the toughness is reduced, so the content is made 2.0% or less, preferably 1.6% or less.

P: 0.030% or less P is an impurity, and reduces the weldability and the toughness and fatigue strength. Therefore, the content of P is 0.030% or less, preferably 0.0015% or less.

S: 0.0100% or less S is an impurity and becomes MnS, which causes pinholes at the time of polishing and lowers the specularity.
0100% or less, preferably 0.0050% or less.

Cu: 0.25% or less, Ni: 0.25%
Hereafter, Cu and Ni are not necessary elements for the plastic molding die steel of the present invention, but are impurities mixed from the raw material for melting, and when they are increased, they harden and become too hard to lower the machinability. Therefore, the content is set to 0.25% or less of the ordinary impurity.

Cr: 1.0 to 2.50% Cr is an element to be contained for increasing the hardenability and the tempering softening resistance at 600 ° C. or higher. 1.0% to obtain these effects
As described above, the content should preferably be 1.1% or more. However, if the content is too high, the hardness becomes too high and the machinability is reduced. Therefore, the content is made 2.50% or less, preferably 2.40% or less.

Mo: 0.20 to 0.60% Mo is an element to be contained for increasing the hardenability and the tempering softening resistance at 600 ° C. or higher. To obtain these effects, 0.20
% Or more, preferably 0.26% or more. However, if it is too high, it becomes too hard and reduces machinability. Therefore, the content is made 0.60% or less, preferably 0.55% or less.

V: 0.05 to 0.20% V is an element to be contained for the purpose of refining crystal grains to improve toughness and tempering softening resistance. 0.05% to obtain these effects
As described above, it is necessary to make the content preferably 0.07% or more. However, as the content increases, the machinability is reduced and the toughness is reduced, so the content is made 0.20% or less, preferably 0.18% or less.

B: 0.0020% or less B is preferably used in a small amount because B enhances the welding sensitivity, but is preferably 0.0020% or less, preferably 0.0010%.
Since the effect is small if it is less than 0.0020% or less,
Preferably it is 0.0010% or less.

S-Al: 0.035% or less Al is an element to be contained as a deoxidizing agent during melting.
But, as an oxide, Al_TwoO _Three-MgO-based inclusions are generated and
Aggregate to form large clusters and fall during polishing
To generate pinholes and fine pits,_TwoO
_Three-MgO-based inclusions are hard and are polished from the periphery during polishing.
Since there is no unevenness on the polished surface, 0.003
5% or less, preferably 0.0025% or less.

O: 0.0030% or less O is an impurity and combines with Al or the like to form Al ₂ O ₃ -MgO-based inclusions, which are aggregated to form large clusters and are formed during polishing. It falls to form pinholes and fine pits, and since the Al ₂ O ₃ -MgO-based inclusions are hard, they are not polished from the surroundings during polishing, so that irregularities are generated on the polished surface. , Preferably 0.0015
% Or less.

N: 0.0200% or less N combines with C, Cr, Mo, V, etc. to form nitrides to make crystal grains fine, but the nitrides cause pinholes and cause thermal problems. 0.0200
% Or less.

Ca: 0.0005% to 0.0050% Ca becomes an oxide and combines with Al-based inclusions to form CaO.
-Al ₂ O ₃ -based inclusions are formed, but these inclusions are unlikely to aggregate and form large clusters, so they are difficult to fall during polishing, and CaO-Al ₂ O ₃ -based inclusions are soft and polished. In this case, since it is polished in the same manner as the surroundings, it is difficult to form irregularities on the polished surface. In order to obtain these effects, it is necessary to contain 0.0005% or more, preferably 0.0010% or more. However, if the content increases, the inclusions themselves become coarse, so the content is 0.0050% or less. Preferably 0.004
Reduce to 5% or less.

Next, a method for producing the steel for a plastic molding die of the present invention will be described. In the steel for a plastic molding die of the present invention, Al-based inclusions are mainly CaO-AlO.
₃ , and the length in the longitudinal direction of the cluster-like inclusions in which the inclusions are aggregated is set to 150 μm or less. For example, the inclusions can be manufactured by the following method. The plastic molding die steel of the present invention is prepared by first melting a molten raw material by a normal arc furnace melting method, adding an Al alloy to deoxidize the molten steel, transferring only the molten steel to a ladle refining furnace, and then heating the molten steel. It can be manufactured by charging CaO and CaF ₂ to form a slag, adjusting the component composition of the alloy, and then charging CaSi to melt the inclusions as CaO-AlO ₃ , casting and the like.

Hereinafter, embodiments of the present invention will be described.

EXAMPLES The steels for plastic molding dies of Examples and Comparative Examples of the present invention shown in Table 1 below were melted by a usual arc furnace melting method, an Al alloy was added and deoxidized, and only molten steel was ladle refining. After being transferred to the furnace, the molten steel is heated and CaO and CaF ₂ are charged to form a slag, and the composition of the alloy is adjusted.
i was charged to complete the smelting and cast to form an ingot. Then, after forging, a quenching and tempering treatment was performed to obtain a test material. A test piece was cut out from this test material, and the maximum length in the longitudinal direction of the inclusion was measured by the following method.
The form of the Al-based compound was analyzed by EPMA. Maximum length in the longitudinal direction of the inclusion: 15 mm ×
The maximum length in the longitudinal direction of the inclusion was measured in a visual field of 20 mm, and determined as an average value in 40 visual fields.

[0028]

[Table 1]

A test piece was cut out from the above-mentioned test material, mirror-finished, and the hardness was measured with a Brinell hardness tester. The number and size of pinholes on the mirror-finished surface were measured by the following method. The results are shown in Table 2 below. Number and size of pinholes: 15 mm by microscopic observation of the mirror-finished surface of the test piece
The number and size (diameter in the longitudinal direction) of the pinholes were measured in a field of view of × 20 mm, and the average value was obtained in 40 fields of view.

[0030]

[Table 2]

According to the results in Table 2, the embodiment of the present invention is as follows.
The hardness was similar to that of the comparative example, but the average number of pinholes on the mirror-finished surface was 4 and 3, and the average size was 130 μm and 100 μm. On the other hand, in the comparative example in which the form of the Al-based inclusion was different from that of the present invention and the maximum length of the cluster was out of the range of the present invention, the hardness was almost the same as that of the example, The average number of pinholes on the surface was 10 to 18, and the average size was 240 to 280 μm.

[0032]

The steel for plastic molding dies of the present invention is
By having the above configuration, while having the general properties required for a mold equivalent to conventional plastic molding die steel, there are fewer pinholes and fine pits, and the unevenness of the polished surface is reduced, There is an effect that the specularity becomes particularly excellent.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Norio Honjo 500 Ishihara, Shibukawa-shi, Gunma Daido Special Steel Co., Ltd.Shibukawa Plant (72) Inventor Hiroshi Yamashita 500 Ishihara, Shibukawa-shi, Gunma Daido Special Steel Co., Ltd. Shibukawa factory

Claims (2)

[Claims] 1. An Al-based inclusion mainly comprising CaO—Al ₂
A steel for plastic molding dies, characterized by being O ₃ , and wherein the length of the cluster-like inclusions in which the inclusions are aggregated is 150 μm or less in the longitudinal direction. 2. In% by weight (the same applies hereinafter), C: 0.10
0.30%, Si: 0.05 to 1.50%, Mn: 0.
90 to 2.00%, P: 0.030% or less, S: 0.0
10% or less, Cu: 0.25% or less, Ni: 0.25%
Hereinafter, Cr: 1.00 to 2.50%, Mo: 0.20 to
0.60%, V: 0.05 to 0.20%, B: 0.00
20% or less, S-Al: 0.035% or less, O: 0.00
30% or less, N: 0.0200% or less and Ca: 0.0
005-0.0050%, the balance being substantially Fe
And the Al-based inclusions are mainly Ca
Consists O-Al ₂ O _3, and a plastic molding die steel in the longitudinal direction of the length of the inclusions cluster-like inclusions agglomerate is equal to or is 150μm or less.