JPH0456749A - Die for casting or apparatus to be brought into contact with molten metal excellent in erosion resistance - Google Patents

Abstract

PURPOSE:To manufacture high strength and high toughness parts free from erosion caused by the molten metal of Al alloys by manufacturing parts for a die or the like to be brought into contact with molten Al alloys of a martensitic alloy steel subjected to surface nitriding treatment. CONSTITUTION:At the time of manufacturing parts to be brought into contact with the molten metal of Al alloys such as a die used in the stage of casting Al alloys, the parts to be brought into contact with the molten metal of Al alloys are manufactured of a martensitic alloy steel contg., by weight, 0.2 to 0.8% C, 0.1 to 3% Si, 0.1 to 3% Mn and 6 to 15% Cr, or furthermore contg. total 0.5 to 5% of one or two kinds of W and Mo, or moreover contg. 0.2 to 3% V or furthermore contg. 5% of one or >= two kinds among Ni, Cu and Co, and its surface is subjected to nitriding treatment by a method such as gas nitriding and molten salt nitriding. The parts free from the generation of erosion caused by the molten metal of Al alloys can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to molds for casting molten metal, weirs, bottles, and other appliances that come into contact with molten metal (referred to as molten metal appliances in the present invention).

[Conventional technology]

Molds and molten metal equipment (casting bottles, core bottles, sprue layers, aluminum die casting sleeves, etc.) used for molding by casting molten metal (die casting, gravity casting, etc.) have conventionally been made of hot die steel, high-grade steel, etc. Steels such as speed tool steel and stainless steel and cast iron have been used.

Currently, the most commonly used metal to be formed by casting is aluminum alloy, but during casting, these metals are used in the parts of the above-mentioned steel materials used in molds and molten metal equipment that come into contact with molten aluminum alloy. The steel material is melted away by the molten aluminum alloy G, increasing the iron content in the molten aluminum alloy and deteriorating the quality of the cast parts.

Furthermore, the erosion of these molds, etc. causes various inconveniences in operation and greatly affects the length of their service life.

To solve these problems, some ceramic materials that do not react with molten aluminum alloy, W alloys, Mo alloys, etc. that do not easily cause melting damage have been used, but these materials are expensive due to their price. Of course, when used as a nest, there are various problems due to the large difference in thermal expansion coefficient with surrounding steel materials, and problems such as insufficient strength, toughness, and thermal shock resistance against bending and chipping. It is not necessarily possible to solve these problems industrially.

Furthermore, nitrides, carbides, borides, etc. (TiN, TiC, BN) are added to steel molds or molten metal equipment.

SiC+Si,N,,TtB2. It has been proposed to coat the surface with Al2O, etc. by physical vapor deposition methods such as plasma chemical vapor deposition method and sputtering method, fusion bonding method, shrink fitting method, etc. 57-131
No. 024, Japanese Patent Application No. 57-143747, Special Publication No. 1-2
No. 9133, Japanese Patent Application No. 59156337). However, in the case of chemical vapor deposition and physical vapor deposition, the film thickness is as thin as several tens of micrometers, and the surface treatment layer has fine cracks, and molten metal (for example, aluminum alloy) penetrates through these cracks. However, it reacts with the iron in the base material directly under the surface treatment layer to form an alloy, and due to this alloy formation, the area directly below the surface treatment layer expands and the treated layer peels off.After peeling off, erosion occurs rapidly. A progressive phenomenon can be seen.

On the other hand, since the surface treatment layer by carburizing or nitriding is a diffusion treatment, a deep treatment layer can be obtained and peeling is not a problem. Conventionally, efforts have been made to extend the wear life of hot die steels such as 5KD61, high speed tool steels, stainless steels, etc. by applying nitriding treatment. However, since these steels are not alloys developed to improve corrosion resistance through nitriding treatment, the inventors have found that the corrosion resistance may be insufficient depending on the application.

The present inventor has conducted various studies on corrosion damage of ferrous materials and non-ferrous alloys caused by molten metals, mainly aluminum alloys, and has found that these alloys first contain Al, Fe, and Ni at the interface with molten aluminum alloys. .

Mn, Go, etc. form an alloy layer, and the alloy components diffuse into the molten aluminum alloy through this, causing melting loss to proceed. By performing nitriding treatment, Fe, N
It was discovered that corrosion resistance increases because nitrides that do not react with aluminum are distributed on the base surface consisting of i, Mn, Go, etc., and in order to further improve corrosion resistance, the distribution density of these nitrides should be increased. I have found that increasing the amount is effective.

The present inventor previously discovered that steel materials in which a considerable amount of carbides are dispersed have significantly superior erosion resistance compared to conventional steel materials for the relevant applications, and the inventors have previously discovered that steel materials with a considerable amount of carbides dispersed in them have significantly superior corrosion resistance compared to conventional steel materials for the relevant applications, and have developed ultra-hard high-speed tool steels for low-pressure casting jigs and tools. filed a patent application for
No. 4897”).

Based on a similar idea, we proposed a new alloy that was inexpensive and had sufficient strength and toughness for practical use (Patent Application No. 1-18839).
No. 7), but it has been found that depending on the intended mold or molten metal equipment, these may lack machinability due to shape or resistance to cracking or breakage due to thermal shock, etc. .

Incidentally, as a conventional technique, there is Japanese Patent Application Laid-Open No. 1-111846, which will be discussed later.

[Problem to be solved by the invention]

It is an object of the present invention to solve these problems and provide a mold or a molten metal fixture that has improved resistance to molten metal and has practical properties such as sufficient strength and toughness.

[Means to solve the problem]

The present invention, in weight percent, C002~0.8%, SiO,1
~3%, Mn 0.1~3%, Cr 6~15%, and in some cases, one or both of W and Mo in total of 0.5~5%. Excellent corrosion resistance characterized by nitriding martensitic alloy steel containing 2 to 3% and one or more of Ni, Cu, and Co, with the remainder being Fe and unavoidable dull materials. It is a mold for casting or a tool for welding molten metal.

[Effect]

The present invention focuses on the effectiveness of the nitrided layer against melting loss, and aims to obtain a more effective nitrided layer and further improve the nitridability, as well as improve practical aspects such as thermal shock resistance, toughness, and workability. It was selected taking into consideration the problems, and as a result, it has a component range of medium C, high Cr martensitic system, which satisfies these required characteristics at a high level and harmonizes them.

As mentioned above, Japanese Patent Laid-Open Nos. 1 to 111486 are known as materials having similar chemical compositions to those used in the mold or molten metal device of the present invention.

JP-A-1-111846 lists A1 as an element that imparts nitriding properties, and uses this as a constituent element of 0.1-1.
5 wt% is added. On the other hand, the present invention is based on the discovery that the effect of adding Cr is extremely significant compared to AI, and the amount of Cr is increased without adding AI. That is, the Cr content of all of the proposed examples is less than 6%, whereas the Cr content of the present invention is 6% or more. In other words, the proposed steel for the same purpose is Cr.
In contrast to hot work tool steel with a Cr content of less than 6%, the present invention is a steel containing 6% or more of Cr, and when this steel is nitrided, a nitrided layer has a great effect on improving corrosion resistance. This is due to the discovery that the formation of

The alloy material having the composition of the present invention can be produced by ordinary casting or forging, and by performing martensitic quenching or similar quenching and tempering, excellent strength and toughness can be obtained, and coarse carbide particles can be obtained. Since this does not occur, machinability is not a practical problem. After processing this material into a predetermined mold or molten metal device, it is subjected to a nitriding treatment to produce a mold or molten metal device with excellent corrosion resistance.

Next, the reason for limiting the composition range of the steel of the present invention will be described.

C is added in order to obtain excellent hardenability, tempering hardness, and toughness of the steel of the present invention, and makes the structure martensite during hardening. In addition, C combines with carbide-forming elements such as W, Mo, V, and Cr to form carbides, resulting in refinement of crystal grains and
It is added to provide wear resistance, temper softening resistance, and high temperature hardness. If it is too high, excessive carbides will be produced, which will significantly reduce forgeability and workability, resulting in practical problems, so it should be 0.8% or less, and if it is too low, the above effects of addition cannot be obtained, so 0.2%. % or more.

Si is added in an amount of 0.1% or more for the deoxidizing effect during steel manufacturing. If it is too large, the thermal conductivity will decrease, so it should be 3% or less.

Mn improves hardenability, but if it is too large, it excessively lowers the A1 transformation point, increases annealing hardness excessively, and reduces machinability, so it should be 0.1% or more and 3% or less. shall be.

By setting the appropriate amount of addition, Cr improves temper softening resistance and high-temperature strength, combines with C to form carbides, improves wear resistance, improves hardenability, and provides rapid nitriding. It is something that you have. Further, during nitriding treatment, Cr combines with N to form nitrides, thereby imparting corrosion resistance, which is the most important feature of the steel of the present invention. Melting loss of steel materials due to molten metal is a phenomenon in which the molten metal and the parent phase Fe and N1 form a compound, and the steel material diffuses to the molten metal side through this compound, and progresses. By distributing nitrides in a high density in the matrix, the reaction interface between the matrix and the molten metal is made small, making it difficult for melt damage to proceed. However, excessive addition of Cr produces excessive carbides and significantly reduces toughness and workability, causing practical problems, so the content is set at 6% or more and 15% or less.

W and Mo form carbides that are difficult to dissolve in the matrix during quenching and heating, and are effective in improving wear resistance.They also precipitate fine carbides during tempering, improving softening resistance and high-temperature strength. This has the effect of increasing the

Furthermore, W and Mo combine with N to form nitrides during nitriding treatment, and similarly to the above-mentioned Cr, they reduce the reaction interface between the matrix and the molten metal, thereby making it difficult for melting loss to progress. W
, Mo needs to be added in a large amount in order to obtain the above effects when compared with Cr, and if it is too large, it tends to have the effect of reducing toughness, so the total amount of one or two types is 5% or less,
If it is too low, the effect of the above addition cannot be obtained, so the content should be 0.5% or more.

■ is effective in improving wear resistance and seizure resistance by forming carbides that are difficult to dissolve in solid solution.They dissolve in solid solution in the matrix during quenching heating and precipitate fine carbides that do not easily aggregate during tempering. , is an effective element for increasing softening resistance in high temperature ranges and providing large high-temperature proof strength. Particularly in the case of die-casting molds or molten metal equipment, the flow rate of the molten metal is extremely high, and as a result, the surface of the mold or molten metal equipment heats up to a high temperature or is subject to frictional effects due to the collision or passage of the molten metal. box office. In this sense, softening resistance in a high temperature range and high high temperature proof strength are required.

If the amount is too high, the toughness is reduced, such as the formation of giant carbides, so the content should be set at 3% or less. If the content is too low, the above-mentioned effects of addition may not be achieved, such as premature softening of the mold surface, so the content should be set at 0.2% or more.

Ni and Cu are shown in the phase diagram of each element and A1, and the F
As can be seen from the comparison of the phase diagrams of e and MO and A1, MO has a solid solubility in molten metal A1 equal to or higher than that of Fe, and is widely known to be resistant to erosion.
Compounds (FeA1., NiAl, etc.) that have a higher solid solubility than Al and that form a compound layer with Al are also easily formed at low temperatures, so they are not actively added, but 5% of each is added.
The following may be included to improve toughness and oxidation resistance, since they do not cause a significant decrease in erosion resistance that would pose a practical problem.

From its phase diagram with respect to Al, it can be seen that Go exhibits almost the same melting behavior as Fe, and on the other hand, it improves oxidation resistance, so it can be added as necessary.

Note that it is possible to improve these characteristics by adding various known free-cutting elements to the mold, etc. and material of the present invention.

〔Example〕

Next, the present invention will be explained in detail based on examples.

Example 1 First, materials with the composition shown in Table 1 were prepared, and from this
The test pieces shown in the figure were prepared and used as an aluminum erosion resistance test piece and a zinc erosion resistance test piece.

The products of the present invention and Comparative Example U (SKD61) were 920~. 11
After quenching at 50°C, tempering was performed at 580 to 620°C to give a hardness of approximately HRC40. Comparative Example V (carbide high-speed tool #l) and Comparative Example X (4I Application Hei 1-188397
The steel described in No. 1) was left as annealed, and Comparative Example W (powdered high-speed tool steel) was subjected to a prescribed heat treatment to have a hardness of approximately HR.
It was set as C50.

Some of the erosion resistance test pieces were surface treated. All steels of the present invention were subjected to nitriding treatment. Table 2 shows the treatment conditions for each of these surface treatments and the thickness of the treated layer (the molten salt method for the product of the present invention is the so-called tuftride method).

The aluminum corrosion resistance test was conducted using aluminum alloy ADC12 700.
The specimens were immersed in a molten metal of 740°C and a B590 alloy (Al-17%Si) for 2 hours each, and the melting loss resistance was compared based on the weight ratio of the test pieces before and after the test. The 8390 alloy is a wear-resistant aluminum alloy, but in order to provide wear resistance, the Si content is higher than that of ADC12 (ADC12 is about 11%). Therefore, since the melting point is high and it is cast at a high temperature, the test temperature was also set at 740°C.

The same was true for the zinc corrosion resistance test, in which the test piece was immersed in a molten zinc alloy ZAC2 at 600°C for 10 hours.

Table 3 shows the results of the erosion resistance test.

Table 2 Comparative Example W (powder high-speed IRT i C processed product) is applied to core pins of practical aluminum die-casting, and has a good track record of long lifespan against seizure of aluminum alloy or erosion by aluminum alloy. It is something.

As can be seen from Table 3, the corrosion resistance of the inventive product is 700°C for ADC12, which has a large weight loss rate, and 7i0°C for No. 8390 gold. (SKD61 sulfur-nitrided) and Comparative Example (3) (superhard high-speed steel 9 without surface treatment). In addition, in the product of the present invention, the most effective nitriding method is the sulfur-nitriding method, which has an ADC12 of 700
Regarding the weight loss rate in °C, except for Comparative Example Y (ceramics),
The particle size is almost the same as Comparative Example W and Comparative Example X, which is a Yahari sulphonitriding treatment, and the grain size is slightly inferior to Comparative Example X in terms of the weight loss rate of B590 alloy at 740°C.

In addition, Comparative Example W (powdered high-speed tool steel TiC treated product) is
At 700°C for ADC12, the loss loss rate due to melting was small as described above, but at 740°C for 8390 alloy, melting loss progressed rapidly. When we observed the sample after this test, we found that
The TiC coating had peeled off, and a reaction between the exposed base material and the aluminum alloy had occurred, leading to progressing erosion. This behavior is similar to other carbide-, nitride-, and boride-based (VC
, NbC, TiN, BN, etc.), the phenomenon was similar to that which normally occurs.

The erosion resistance of the products of the present invention due to sulfonitriding was determined by Comparative Examples Y (ceramics) and X (Japanese Patent Application No. 118839), as described above.
Although it was inferior to No. 7), it was extremely superior in terms of thermal shock resistance and machinability, which are important issues when these are put into practical use, as will be described later.

Next, the results of the thermal shock resistance test will be described. The test is 3
A 0 mm square x 20 mm* sample was prepared by applying the same heat treatment and surface treatment as above, and heated to 700°C with a gas burner.
After heating, the specimens were immediately immersed in a water bath at 20° C., and the number of times until the surface cracks reached a predetermined level was determined. The target products are the products of the present invention (A, C, and E each subjected to sulfur-nitriding), Comparative Example X, and Comparative Example Y. As a result, in Comparative Example Y (ceramics), the cracks were scattered after one application, and in Comparative Example X, it was performed 50 times. A sketch of Comparative Example X is shown in FIG. No change was observed in any of the products of the present invention after testing up to 100 times, and the tests were discontinued thereafter.

In contrast, A and C according to the present invention each have a value of 0.
15w (after cutting 1m), 0.28mm (after cutting 2m), 0.22mm (after cutting 1m), 0.41mm (after cutting 2m)
After cutting) and compared to Comparative Example X, it showed significantly higher machinability.

Table 4 Table 5 Table 4 shows the stiffness test results, and Table 5 shows the cutting conditions. In the test, the wear amount of the end mill cutting edge was measured when each sample base material in an annealed state was cut with an end mill. Ceramics cannot be processed at all, and Comparative Example
The wear on the cutting edge after cutting was as large as 0.85 mm, and further processing could not be carried out. The thermal shock resistance and stiffness test results have been described above, and it can be seen that the product of the present invention is superior to each of the comparative examples in these, and has high overall performance.

In addition, the present invention G contains Ni and Co, and is slightly inferior in erosion resistance compared to the present inventions A to F. However, it is still significantly better than Comparative Example U, and in the case of sulfonitriding, it is much better than Comparative Example (■). In addition, since Ni was included, the impact properties were increased. This indicates that it is effective to contain this amount of Ni and other elements when cracking resistance or breakage resistance is important depending on the application.

In this example, the results of the melting test for aluminum alloys and zinc alloys were shown, but melting damage of molds, etc. caused by molten metal is generally caused by contact between the molten metal and the parent metal of the mold, etc. Therefore, the molds, etc. and materials of the present invention have excellent corrosion resistance against other molten metals, such as iron-based and copper-based alloys, as well as against aluminum-based and zinc-based alloys. is inferred.

Example 2 Next, a mold was manufactured from the above-mentioned material and a practical test was conducted.The results will be shown below.

The heat treatment and surface treatment were the same as in Example 1 (this product was sulfur-nitrided), and a part of the aluminum die-casting mold was manufactured as a nest. The insert was built into the front part of the gate, where the molten aluminum alloy directly collides with the gate. The temperature of the molten aluminum alloy is 750°C.

Further, although the child itself is a nest, its dimensions are large (approximate dimensions: 150 x 200 x 100), and its shape is complicated, with a portion of corners. In addition, the surface of the insert is water-cooled after the aluminum alloy solidifies and is removed from the mold, and at this time, large thermal stress acts on the surface, and excessive thermal stress acts on some corners due to stress concentration. It is something.

Table 6 Table 6 shows the mold life of each mold insert.

In Reference Example Z, after 500 shots were used, the surface of the mold became rough due to melting damage, and its use was discontinued.

Comparative example U (SKD61 sulfonitriding) is l, 500
The shot caused skin irritation. Further, in Comparative Example X, no melt damage occurred, but a crack deeper than the corner R portion occurred after 1,800 shots, and the use was discontinued.

This supports the results shown in FIG.

On the other hand, product A of the present invention caused skin roughness after 5,000 shots, and product E showed slight skin roughness after 5,000 shots, but the test was discontinued. This means that E is W, MO,
This is because it has strong high-temperature strength because it contains V, and has a strong backup effect on the nitrided layer.

When high-temperature molten metal collides with the surface of a jig and tool at high speed as in this application, the surface of the jig and tool is mechanically eroded by the rise in temperature and the kinetic energy of the molten metal. In such cases, addition of W, Mo, and V is effective.

Example 3 Next, core bottles used in aluminum die-casting were manufactured from the materials shown in Table 7 (heat treatment and surface treatment were the same as in Example 1). The durability life of these is shown in the same table.

From the wooden table, all of the products of the present invention and Comparative Example X are 1 of Comparative Example U.
It can be seen that it has more than 0 times the durability. However, although Comparative Example X was not damaged, some of the pins were cracked, indicating that the pin had only a short life remaining. In contrast, these cracks did not occur in products B, D, and F of the present invention. Furthermore, in the case of aluminum die casting, the mold, core bottle, etc. are water-cooled and rapidly cooled after casting, so the ceramic core bottle, which has low thermal shock resistance, was damaged during the first casting.

Table 7 Example 4 Next, cast bottles used for forming aluminum products by low-pressure casting were manufactured using the materials shown in Table 8. The heat treatment conditions and surface treatment are the same as in Example 1. However, V' is made of the same material as V. Its shape is shown in FIG. The dimensions are d in Figure 3.
=5mmφ, length is 200mm. The table shows a comparison of the durability of cast bottles made from each material. In Reference Example Z, after 200 castings, the diameter of the bottle became thinner due to melting damage, and the bottle became unusable due to dimensional defects. Comparative Example (3) suffered from seizure breakage after 150 castings, and in the case of Comparative Example V', which was subjected to sulfur-nitriding to improve corrosion resistance, breakage (50 pieces) occurred even earlier. On the other hand,
Products A to G of the present invention (bottles subjected to tuff-riding treatment, which is a type of nitriding treatment using the molten salt method) do not break, and
All of them could be used up to approximately 1,200 times, and eventually aluminum alloy adhered to the bottles.

Table 8 [Effects of the Invention] As described above, the present invention performs nitriding in a mold or welding device for casting molten metal such as aluminum alloy. It is not a product that has been nitrided on existing materials such as hot die steel and powder high-speed tool steel. In consideration of overall performance such as thermal shock resistance, toughness, and machinability, we selected a new base material component of medium C and high Cr martensitic materials, so compared to conventional materials,
Since it has excellent overall performance as well as corrosion resistance, it has the effect of significantly improving the durability life of these products.

Therefore, whereas ultrahard high-speed tool steel and ceramics, which have excellent corrosion resistance, have not been sufficiently applied in industrial practice due to problems of breakage and breakage, the molds and materials of the present invention have the above-mentioned advantages. It has excellent toughness, flexural strength, and thermal shock resistance, making it highly practical. Furthermore, it can be manufactured at a lower cost than W or Mo alloys.

In addition, the corrosion-resistant steel proposed by the present inventor (Japanese Patent Application No. 1999-188
No. 397), but the product of the present invention is highly practical for applications where thermal shock resistance and machinability are problematic.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the erosion test piece used for molten aluminum and zinc in Example 1, and Figure 2 is a sketch of the appearance of the test piece after the thermal shock test was conducted in Example 1 for comparison. Example X
Figure 3 shows the situation after 50 tests and Figure 3 shows the cast bottle used in Example 4.

Claims (1)

[Claims] 1% by weight, C0.2-0.8%, Si0.1-3%
, Mn0.1~3%, Cr6~15%, balance Fe
Also, a casting mold or a molten metal tool with excellent erosion resistance, which is characterized by subjecting martensitic alloy steel containing unavoidable impurities to nitriding treatment. 2% by weight, C0.2-0.8%, Si0.1-3%
, Mn0.1-3%, Cr6-15%, and W, Mo
Casting with excellent erosion resistance characterized by being nitrided on martensitic alloy steel containing a total of 0.5 to 5% of one or two of the above, with the remainder being Fe and unavoidable impurities. molds or welding equipment. 3% by weight, C0.2-0.8%, Si0.1-3%
, Mn0.1-3%, Cr6-15%, and W, Mo
0.5 to 5% in total of one or two kinds of V0.
1. A casting mold or a molten metal tool, characterized in that a martensitic alloy steel containing 2 to 3% Fe and unavoidable impurities is subjected to a nitriding treatment. 4% by weight, C0.2-0.8%, Si0.1-3%
, Mn0.1-3%, Cr6-15%, a total of 0.5-5% of one or two of W and Mo, V0.2-3%, and one or two of Ni, Cu, and Co. A casting mold or a molten metal tool, characterized in that a martensitic alloy steel comprising 5% or less of each of the above, and the balance Fe and unavoidable impurities is subjected to a nitriding treatment.