JP3983502B2 - Mold with excellent resistance to aluminum erosion and its processing method - Google Patents

Description

【００１４】
【表２】

【００１５】
表１および表２に示すように、供試材Ａは本発明例であり、供試材Ｂ〜Ｅは比較例である。表１に示す溶損試験結果によれば、本発明例Ａは比較例Ｂ〜Ｅに比較して、溶損減量率が低く、特に比較例Ｂ、Ｃは溶損減量率が高い。また、本発明例Ａの被削性指数１００に対し、比較例は、いずれも切削長が長く、特に比較例Ｄ、Ｅは被削性の悪いことが分かる。さらに、表２には実機試験の結果を示すように、本発明供試材Ａは、比較例である供試材Ｅと比べて型寿命は同等であるが、しかし、型作製コストは大幅に低いものである。
【００１６】
【発明の効果】
以上述べたように、本発明による焼入れ、焼戻しを省略して焼鈍と窒化処理によるダイカスト金型を作製することが出来、得られた金型の耐熱疲労クラック性は良好で、しかも金型作製コストを大幅に低減することが可能となり、生産コストを大幅に削減できる耐アルミ溶損性に優れた金型を提供するもので工業的に極めて優れた効果を奏するものである。
【図面の簡単な説明】
【図１】アルミ溶損試験機の概略図である。
【符号の説明】
１ 溶解槽
２ アルミ合金
３ ヒーター３
４ 試験片
５ ホルダー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mold having excellent resistance to aluminum erosion used for manufacturing an aluminum die-cast product formed by a low-pressure casting method, and a processing method thereof .
[0002]
[Prior art]
In general, molds for aluminum die casting are repeatedly exposed to high temperatures and high pressures, so the surface of the mold is subjected to compressive and tensile thermal stress, and this thermal stress is repeatedly applied. Cracks and mold cracks occur and are transferred to the workpiece. The thermal fatigue cracks and mold cracks become severe and the mold cannot be used. Therefore, the mold is required to have resistance to thermal fatigue cracks and mold cracks.
[0003]
In the above-described mold, it is effective to improve hardness in order to provide resistance to thermal fatigue cracks. In order to provide resistance to mold cracking, it is effective to improve toughness. Therefore, it is usually produced by quenching and tempering to an appropriate hardness, and finally finishing, like the commercially available JIS standard SKD61. Thus, since SKD61 has excellent hardenability, the mold can be sufficiently hardened by the quenching and tempering steps and the toughness can be improved. Therefore, the obtained mold is less likely to generate thermal fatigue cracks and mold cracks.
[0004]
On the other hand, as disclosed in Japanese Patent Laid-Open No. 5-140695, after being tempered to a hardness of HRC50 or higher as steel for an aluminum extrusion die, it is used after nitriding, or as disclosed in Japanese Patent Laid-Open No. 7-207414. A die steel for forging aluminum that has a hardness of HRC 46 or higher is disclosed. Both are known as aluminum molds that have high toughness, excellent temper softening resistance when processed into dies, and are less susceptible to deflection, thermal fatigue cracks, and mold cracks throughout the dies.
[0005]
[Problems to be solved by the invention]
As described above, all of the conventional aluminum molds are quenched, tempered, or quenched, tempered, and then used for nitriding treatment. Quenching, tempering processes, and finishing processes are required, and there is the biggest problem of cost increase.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors have made extensive developments, and as a result, the quenching, tempering process, or finishing process is omitted, and the total cost is reduced by annealing and repeated nitriding. Is to provide an excellent mold and a processing method thereof.
The gist of the invention is that
(1) By mass%, C: 0.3 to 0.5%, Si: ≦ 2.0%, Cr: 3.0 to 6.0%, Mo: 1.0 to 3.0%, V: In hot tool steel comprising 0.2 to 1.5% and the balance Fe and unavoidable impurities, the base material hardness is 80 to 102HRB , and the nitrided layer when nitrided without quenching and tempering . Mold having excellent resistance to aluminum erosion used for the manufacture of aluminum die-cast products formed by low-pressure casting, characterized in that the internal hardness of 30 μm is 600 HV or more and the nitridation depth is 50 to 250 μm .
(2) the A mold according to (1), excellent resistance to aluminum corrosion resistance for use in the production of aluminum die cast product molded by low-pressure casting method characterized by applying Repetitive returns nitriding Mold.
(3) the A mold according to (1), excellent resistance to aluminum corrosion resistance for use in the production of aluminum die cast product molded by low-pressure casting method characterized by applying Repetitive returns nitriding In the processing method of the mold.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
Although it does not specifically limit as hot tool steel which concerns on this invention, Cr-Mo-V type hot tool steel is desirable, for example, as shown in an Example below, C: 0.3-0.5% Si: ≦ 2.0%, Cr: 3.0-6.0%, Mo: 1.0-3.0%, V: 0.2-1.5%, the balance Fe and inevitable impurities Hot tool steel consisting of If necessary, it is also possible to use hot tool steel containing free cutting elements such as Nb, Ni, W, Co and S. C is an element added to maintain high-temperature hardness and to form carbides such as Mo, V, and Cr, and to provide a crystal grain refining effect, wear resistance, and high-temperature hardness. Si is a deoxidizer and is an element necessary for maintaining the hardness of 80 to 102HRB of the present invention and obtaining the strength necessary for steel for dies.
[0008]
Cr is improved in high-temperature strength by setting an appropriate addition amount, and improved in wear resistance by forming carbide by combining with C. Further, during nitriding, it combines with N to form nitride. The melt resistance, which is the greatest feature of the present invention, is imparted. This is because when the nitride is distributed at a high density in the base material, the reaction interface between the base material and the molten metal is made small, so that the melting damage is difficult to proceed. This is because Mo and V combine with N during nitriding to form nitrides and reduce the reaction interface between the base material and the molten metal in the same manner as Cr, so that the melting damage is less likely to proceed. Moreover, it is a component which improves heat-resistant fatigue crack property.
[0009]
Next, the reason why the base material hardness is 80 to 102 HRB is that the base material hardness is necessary as the mold strength, and if it is less than 80 HRB, the optimum mold strength cannot be obtained. Since the machinability deteriorates, the range is set to 80 to 102HRB. The reason why the hardness inside the 30 μm nitride layer is set to 600 HV or more is necessary for resistance to aluminum erosion, and since the effect is insufficient when it is less than 600 HV, the lower limit is set. The reason why the nitriding depth is 50 to 250 μm is necessary for resistance to aluminum erosion, and if it is less than 50 μm, the effect cannot be obtained, and if it exceeds 250 μm, the risk of large cracks increases. The range was 50 to 250 μm.
[0010]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
As test materials, C: 0.3 to 0.5%, Si: ≦ 2.0%, Cr: 3.0 to 6.0%, Mo: 1.0 to 3.0%, V: 0.00. Using 2 to 1.5% steel, 300 kg was melted in a vacuum induction melting furnace, cast into an ingot, heated to 1100 ° C., forged to φ30 mm, and annealed to 870 ° C. (sample D is omitted). Thus, an aluminum erosion test piece was produced. On the other hand, it was forged to 30 × 100 × 100 mm and annealed at 870 ° C. to produce a machinability test piece. Further, it was forged to 65 mm, a mold was fabricated after annealing at 870 ° C., and the actual machine was evaluated. The results are shown in Tables 1 and 2.
[0011]
The nitriding treatment conditions of the test piece are as follows: nitriding method: ion (plasma) nitriding, N / H ratio: 25/75, gas pressure: 6 Torr, processing temperature: 500 to 600 ° C., processing time: 2 to 15 hours I did it. The nitriding depth was measured by measuring the hardness from the outermost surface of the nitrided layer using a micro Vickers hardness tester, and was taken as the distance until it matched with the base material hardness. The base material hardness was measured using a Rockwell hardness meter B scale. As the aluminum melt damage test conditions at that time, aluminum alloy: ADC12 (Al-12Si-2Cu), molten metal temperature: 720 ° C., rotation speed: 25 rpm (rotation radius 10 cm), immersion time: 60 minutes, immersion depth: 50 mm, n number: It carried out on condition of 2. A schematic diagram of the aluminum erosion tester in that case is shown in FIG.
[0012]
As shown in FIG. 1, the aluminum alloy 2 is heated in the melting tank 1 by the heater 3 to melt the aluminum alloy 2, and the test piece 4 is rotated to a depth of 50 mm on the surface of the aluminum alloy 2 by the holder 5. An aluminum melting test was conducted. The machinability evaluation was performed using a φ12 high-speed end mill under the conditions of a rotation speed of 900 rpm, a cutting speed of 50 m / min, a 1-blade cutting of 0.1 mm / blade, and no cutting oil. Further, the cutting length when the tool wear amount is 0.2 mm is indexed as the machinability index. The actual machine test was performed under the conditions of Al alloy: ADC12, in-mold pressure: 1.2 atm, and molding time for one product: 2 minutes / shot.
[0013]
[Table 1]

[0014]
[Table 2]

[0015]
As shown in Table 1 and Table 2, sample material A is an example of the present invention, and sample materials B to E are comparative examples. According to the results of the erosion test shown in Table 1, Invention Example A has a lower erosion loss rate than Comparative Examples B to E, and Comparative Examples B and C in particular have a higher erosion loss rate. Further, it can be seen that the comparative example has a long cutting length with respect to the machinability index 100 of Example A of the present invention, and in particular, Comparative Examples D and E have poor machinability. Furthermore, as shown in Table 2, the test results A of the present invention have the same mold life as that of the test sample E, which is a comparative example, but the mold production cost is greatly increased. It is low.
[0016]
【The invention's effect】
As described above, it is possible to produce a die-casting die by annealing and nitriding treatment by omitting quenching and tempering according to the present invention, and the obtained die has good heat fatigue crack resistance, and the die production cost Therefore, it is possible to significantly reduce the production cost, and it is possible to provide a mold having excellent resistance to aluminum erosion that can greatly reduce the production cost.
[Brief description of the drawings]
FIG. 1 is a schematic view of an aluminum erosion tester.
[Explanation of symbols]
1 Melting tank 2 Aluminum alloy 3 Heater 3
4 Test piece 5 Holder

Claims (3)

% By mass
C: 0.3-0.5%
Si: ≦ 2.0%,
Cr: 3.0-6.0%,
Mo: 1.0-3.0%,
V: 0.2-1.5%
In the hot tool steel consisting of the balance Fe and inevitable impurities, the base material has a hardness of 80 to 102 HRB , and the hardness inside the 30 μm nitride layer when nitriding without quenching and tempering is 600 HV or more A die having excellent aluminum erosion resistance used for manufacturing an aluminum die cast product formed by a low pressure casting method, characterized in that the nitriding depth is 50 to 250 μm. A mold according to claim 1, Repetitive returns superior mold resistance aluminum corrosion resistance for use in the production of aluminum die cast product molded by low-pressure casting method characterized by applying the nitriding treatment. A mold according to claim 1, Repetitive returns of aluminum die cast product molded by low-pressure casting method characterized by performing a nitriding treatment of superior mold resistance aluminum corrosion resistance for use in the production Processing method.

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