JP3978116B2 - Die casting machine member and manufacturing method thereof - Google Patents

Description

【００３０】
表１から分かるように、本発明に基づく鋳抜きピン（供試体１）の寿命は、従来品（供試体２）の約５倍であった。
【００３１】
また、ＳＵＳ６３０からなる基材にガス窒化処理を施したもの（供試体３）は、従来品と比べて寿命が余り変わらなかった。その理由として、基材のＳＵＳ６３０中に含まれているＣｒ量のみでは、表層部に形成されるクロム窒化物の量が十分ではなく、耐溶損性に及ぼす効果が少ないことが考えられる。
【００３２】
【発明の効果】
本発明に基づくダイカストマシン用部材によれば、金属溶湯と接触する部材の耐溶損性が改善されるので、それらの部材の寿命を増大させることができる。更に、それらの部材の寿命が増大する結果、ダイカストマシンの稼働率が上がるとともに、ダイカスト製品の品質が安定して良品率が向上する。
【図面の簡単な説明】
【図１】本発明に基づくダイカストマシン用部材の断面組織の一例を示す図。
【図２】図１に示したダイカストマシン用部材の製造方法について説明する図。
【図３】本発明に基づくダイカストマシン用部材の断面組織の他の例を示す図。
【図４】図３に示したダイカストマシン用部材の製造方法について説明する図。
【図５】本発明に基づく供試体（Ｃｒ拡散後ガス窒化処理）の断面の顕微鏡組織写真。
【図６】本発明に基づく供試体の表層部分のＸ線回折結果を示す図。
【図７】本発明に基づく供試体の中間層部分のＸ線回折結果を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a die-casting machine for aluminum or magnesium, etc., in a part in contact with a molten metal, that is, a mold member including an insert, a core, an extrusion pin, a cast pin, etc., an injection sleeve, a plunger tip, etc. The present invention relates to a die casting machine member to be used.
[0002]
[Prior art]
Conventionally, alloy tool steel such as SKD61 (JIS) has been widely used for the die of a die casting machine. Since the molten Al has a very high activity, the member in contact with it is easily melted by reaction with Al. Moreover, since Al is also contained in the Mg alloy used as the material for die casting, the member in contact with the molten metal is similarly melted.
[0003]
In general, surface treatment such as nitriding treatment is performed on the surface of a die casting machine member for the purpose of preventing melting damage due to contact with molten metal.
[0004]
When nitriding is applied to the surface of the steel member, an Fe—N compound is formed in the Fe substrate at the surface layer portion. Since this Fe—N compound does not easily react with molten Al, the resistance to erosion of the member is improved. However, since the decomposition temperature of the Fe—N compound is relatively low, the decomposition gradually proceeds during use, and a reaction occurs between Fe and Al. For this reason, it is difficult to realize sufficient melt resistance by only the conventional nitriding treatment.
[0005]
A compound having a high decomposition temperature is chromium nitride (CrN). Japanese Patent Application Laid-Open No. 9-108807 (Patent Document 1) describes a method of nitriding an alloy steel containing 10 wt% or more of Cr in order to use CrN. However, most of the members for die casting are required to have high mechanical properties as well as resistance to melting. The Cr concentration of high Cr alloy steel suitable as a member for die casting is almost 13 to 18%, and even if CrN is formed by nitriding, great improvement in resistance to melting cannot be expected. Although there is an alloy steel having a Cr concentration of nearly 30%, it is not suitable as a die casting member because of its low strength.
[0006]
Further, for example, Japanese Patent Laid-Open No. 2001-25856 (Patent Document 2) describes a method of forming CrN by diffusing chromium after nitriding the steel. In this case, the CrN existing area is 5 to 25 μm, and it is industrially difficult to make it thicker than this. However, since the metal mold member is used while polishing off the adhered molten metal, a significant improvement in the life cannot be expected with a CrN layer of about 5 to 25 μm. In addition, cracks occur on the surface due to thermal shock, but the cracks pass through the CrN layer at an early stage and reach a region having a low resistance to melt damage, so that the melt damage starts from the cracks.
[0007]
Further, for example, Japanese Patent Laid-Open No. 10-237624 (Patent Document 3) describes a method of forming a CrN film by PVD treatment such as arc ion plating or sputtering. In the case of this method, since a CrN thin film is coated, cracking and peeling easily occur when the CrN layer is thickened. In practice, the thickness of the CrN layer is 10 μm or less. Therefore, as in the above method, since the CrN layer is thin, a significant improvement in life cannot be expected.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-108807
[Patent Document 2]
Japanese Patent Laid-Open No. 2001-25856
[Patent Document 3]
Japanese Patent Laid-Open No. 10-237624
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems with conventional die casting machine members, and an object of the present invention is to provide a die casting machine member having excellent resistance to melting damage. In addition, the object of the present invention is to form the above-mentioned member for die casting by machining after forming the surface layer portion, without causing problems such as peeling, while allowing the surface layer portion with excellent resistance to melting damage to be formed thicker. It is in providing the manufacturing method of the member.
[0012]
[Means for Solving the Problems]
The die casting machine member of the present invention is
A steel substrate;
A surface layer formed on the surface of the base material, in which iron nitride and chromium nitride are mixed and dispersed,
An intermediate layer formed between the surface layer and the base material, in which chromium nitride is dispersed in steel,
The chromium concentration in the intermediate layer is 20 wt% or more and 45 wt% or less.
[0013]
When chromium is first diffused from the surface of the steel substrate and then nitrogen is diffused, a layer (surface layer) made of iron nitride and chromium nitride is formed on the surface layer, and inside the matrix made of steel A layer (intermediate layer) in which chromium nitride is dispersed is formed. According to this method, it is possible to form the surface layer and the intermediate layer with a sufficient thickness of 100 μm or more. Therefore, the die-casting machine member of the present invention is excellent in wear resistance, and as a result, maintains the damage resistance caused by the diffusion layer of nitrogen and chromium formed on the surface of the substrate over a long period of time. Can do.
[0014]
Here, the reason why the chromium concentration of the intermediate layer is defined as described above is that when the chromium concentration is 20 wt% or less, since the formed CrN is small, a large improvement in resistance to melting damage cannot be expected, while the chromium concentration is 45 wt%. If it is at least%, brittle iron-chromium intermetallic compounds may be formed, and toughness may be reduced.
[0015]
Preferably, the thickness of the intermediate layer is 30 μm or more and 300 μm or less. The reason for this is that if the thickness of the intermediate layer is 30 μm or less, the effect of improving the life is reduced due to wear during use, polishing during maintenance, melting damage from the crack portion, etc. If the thickness is 300 μm or more, heating for a long time is required at a high temperature in order to diffuse Cr, and the mechanical properties of the substrate deteriorate.
[0016]
Preferably, the carbon content of the steel constituting the substrate is 0.2 wt% or less. The reason is that when the amount of carbon in the substrate is 0.2 wt% or more, a dense carbide layer is formed on the surface by the reaction of carbon and chromium in the substrate, which prevents diffusion of chromium. .
[0017]
In addition, when diffusing nitrogen after diffusing chromium in the base material, it is desirable to make the nitrogen diffusion region shallower than the chromium diffusion region. This is because if the diffusion region of nitrogen is deeper than the diffusion region of chromium, the diffusion region of chromium becomes easy to peel off. In this case, a second intermediate layer in which chromium is diffused in the steel is further formed between the intermediate layer (first intermediate layer) and the base material.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of a cross-sectional structure of a die casting machine member according to the present invention. In FIG. 1, a surface layer 3 is formed on the surface of a base material 1 made of steel with an intermediate layer 2 interposed therebetween. The surface layer 3 is a layer in which iron nitride Fe ₄ N and chromium nitride CrN are mixed and dispersed. The intermediate layer is a layer in which chromium nitride CrN is dispersed in steel.
[0019]
As shown in FIG. 2, the cross-sectional structure as described above is formed by first diffusing chromium from the surface and then diffusing nitrogen in the steel substrate 1. Nitrogen diffused inside the substrate 1 reacts with chromium in the surface layer 3 and the intermediate layer 2 therebelow to form chromium nitride CrN.
[0020]
FIG. 3 shows another example of the cross-sectional structure of the die casting machine member according to the present invention. In FIG. 3, the surface layer 3 is formed on the surface of the base material 1 made of steel, with the second intermediate layer 22 (inner side) and the first intermediate layer 21 (front side) sandwiched therebetween. The surface layer 3 is a layer in which iron nitride Fe ₄ N and chromium nitride CrN are mixed and dispersed. The first intermediate layer 21 is a layer in which chromium nitride CrN is dispersed in steel. The second intermediate layer 22 is a layer in which chromium Cr is dispersed in steel.
[0021]
As shown in FIG. 4, the cross-sectional structure as described above is formed by first diffusing chromium from the surface into the steel substrate 1, and then diffusing nitrogen more shallowly than the diffusion region of chromium. Nitrogen diffused inside the substrate 1 reacts with chromium in the surface layer 1 and the lower side thereof to form chromium nitride CrN (first intermediate layer 21). In the portion where the nitrogen below the first intermediate layer 21 has not reached, a layer in which chromium Cr is diffused in the steel remains (second intermediate layer 22).
[0022]
Next, the result of the performance evaluation test of the member for die casting machines based on this invention is demonstrated.
[0023]
A cast pin (φ20 × 150) for a die casting machine was produced by the following procedure:
(A) A SUS630 (JIS) material is roughly processed to produce a substrate;
(B) In a state where the Cr alloy powder is in contact with the base material, the base material is heated at 1040 ° C. for 10 hours to diffuse Cr in the surface layer portion of the base material;
(C) Finishing the surface;
(D) performing gas nitriding treatment;
(E) The surface is polished.
[0024]
FIG. 5 shows a micrograph of a cross section of a specimen (sample 1) subjected to gas nitriding after Cr diffusion. Cr diffuses to a depth of about 75 μm from the surface, and N diffuses to a depth of about 50 μm from the surface.
[0025]
In FIG. 6, the X-ray-diffraction result of the surface layer part (surface layer 3) of said test body is shown. The detected peaks are indicative of CrN, Fe ₄ N and Fe.
[0026]
FIG. 7 shows an X-ray diffraction result of the surface layer portion (intermediate layer 2) obtained by grinding the surface of the above-described specimen 30 μm. The detected peaks are indicative of CrN and Fe.
[0027]
The core pin (specimen 1) produced by the above procedure was incorporated into a die casting machine, and its life was investigated. As comparative materials, a base material made of a conventional alloy tool steel SKD61 was subjected to nitriding treatment (Specimen 2), and a base material made of precipitation hardening stainless steel SUS630 having a high Cr content was subjected to nitriding treatment. The life of the test piece (Specimen 3) was also investigated by the same method.
[0028]
The results are shown in Table 1.
[0029]
[Table 1]

[0030]
As can be seen from Table 1, the life of the cast pin (specimen 1) according to the present invention was about five times that of the conventional product (specimen 2).
[0031]
Moreover, the thing (specimen 3) which performed the gas nitriding process to the base material which consists of SUS630 did not change the lifetime so much compared with the conventional product. The reason is considered that the amount of chromium nitride formed in the surface layer portion is not sufficient only by the amount of Cr contained in the SUS630 of the base material, and the effect on the melt resistance is small.
[0032]
【The invention's effect】
According to the member for die-casting machines based on this invention, since the erosion resistance of the member which contacts a molten metal is improved, the lifetime of these members can be increased. Furthermore, as a result of increasing the lifetime of these members, the operating rate of the die casting machine is increased, the quality of the die casting product is stabilized, and the yield rate is improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a cross-sectional structure of a member for a die casting machine according to the present invention.
FIG. 2 is a view for explaining a method of manufacturing the member for die casting machine shown in FIG.
FIG. 3 is a view showing another example of a cross-sectional structure of a member for a die casting machine according to the present invention.
4 is a view for explaining a method of manufacturing the member for die casting machine shown in FIG. 3. FIG.
FIG. 5 is a micrograph of a cross-sectional structure of a specimen (gas nitriding after Cr diffusion) according to the present invention.
FIG. 6 is a view showing an X-ray diffraction result of a surface layer portion of a specimen according to the present invention.
FIG. 7 is a view showing an X-ray diffraction result of an intermediate layer portion of a specimen according to the present invention.

Claims (3)

A steel substrate;
A surface layer formed on the surface of the base material, in which iron nitride and chromium nitride are mixed and dispersed,
A first intermediate layer formed under the surface layer, in which chromium nitride is dispersed in steel;
A second intermediate layer formed between the first intermediate layer and the substrate and having chromium diffused in the steel;
A die casting machine member, wherein a chromium concentration in the first intermediate layer is 20 wt% or more and 45 wt% or less. 2. The member for a die casting machine according to claim 1 , wherein the thickness of the first intermediate layer is not less than 30 μm and not more than 300 μm. First, chromium is diffused from the surface to a steel substrate having a carbon content of 0.2 wt% or less,
Next, nitrogen is diffused shallower than the diffusion region of chromium to react chromium and nitrogen inside the substrate,
Thus, a surface layer in which iron nitride and chromium nitride are mixed and dispersed is formed below the surface layer, chromium nitride is dispersed in the steel, and the chromium concentration is 20 wt% or more and 45 wt% or less. Forming an intermediate layer, and a second intermediate layer formed between the first intermediate layer and the substrate and having chromium diffused in the steel;
A method for producing a member for a die-casting machine characterized by the above.

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