JPS5982154A - Production of composite casting - Google Patents

Abstract

PURPOSE:To produce a composite casting having uniformly distributed particles and an optional packing rate of particles by melting successively from an end, a molding of a mixture composed of metallic powder and hard ceramic powder, and laminating and solidifying the melt thereof from the bottom in a casting mold. CONSTITUTION:Metallic powder and ceramic powder having a high melting point are compounded at the ratio determined adequately according to the packing rate of the particles in an intended composite casting and after the two are thoroughly and intimately stirred and mixed, the mixture is made into a molding A having substantial strength in handling by press molding or the like. Such molding is attached as a consumable electrode to an electrode clamp 3 and the lower end part thereof is immersed into a molten slag S in a water-cooled moving casting mold 1 then electricity is conducted between the same and a casting ingot C from a power source 4. The molding A is then successively melten by the electric resistance heat from the end thereof thereby forming a pool B of the melt wherein the molten metal M and the ceramic particles Pc exist uniformly and mixedly in the mold 1. Such melt is cooled with the cooling water flowing between supply and drain ports 2 and 2 and is laminated and solidified from the bottom toward the upper part whereby the casting ingot C of the composite casting is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a composite casting made of a mixture of metal and ceramic particles such as tungsten carbide particles.

A mixture of metal and ceramic particles, such as hard particles such as tungsten carbide particles, is a so-called particle-reinforced composite material that has material properties that cannot be obtained with metal alone, especially high hardness and high wear resistance. have As a manufacturing method for such composite materials, the present inventors previously proposed a manufacturing method using centrifugal force or static casting (Japanese Patent Application No.
No. 1431.20, No. 57-143121, No. 57-
1.43122, 57-143128, etc.). The principle is that a molten base metal and particles with a higher specific gravity than the molten metal are mixed in a mold (a) and then each is cast separately.
The purpose is to cause particles to settle and coagulate in the molten metal due to the difference in specific gravity.
By this casting precipitation method, it is possible to obtain a casting having a dense composite structure in which the spaces between aggregated particles are filled with metal and strong metal-particle bonding.

However, the casting precipitation method has the following limitations due to its principle.

(1) If it takes a long time for the particles in the molten metal to settle, the molten metal will become viscous and coagulate as the temperature drops, and the subsequent sedimentation and
Since aggregation is prevented, a uniform and dense composite structure cannot be formed. Therefore, since it is necessary to complete sedimentation and aggregation of particles within a short period of time, the particles used are limited to coarse particles that have a high sedimentation rate. Normally, fine particles with a particle size of 50 μm or less cannot be used. Furthermore, fine, flower-like particles have poor fluidity, making it impossible to add at a uniform rate.

(11) If the particles are not compatible with the molten metal,
Even when administered into the molten metal, it is not immediately absorbed into the molten metal, but floats on the surface for a certain period of time. During this time, not only does the temperature of the molten metal progress and the base becomes more concentrated, but the floating particles tend to move on the surface of the molten metal and become locally unevenly distributed. Therefore, even though the particles are evenly distributed and administered, the formed composite structure has uneven layer thickness and uneven density of agglomeration. Furthermore, if the particles are easily oxidized, surface oxidation occurs while floating on the surface of the hot water. Therefore, in order to avoid such problems, the particles are limited to those that have good wettability with the molten metal.

(ti+) It is difficult to control the proportion of particles in the composite tissue formed (particle filling rate). This is because the casting precipitation method uses a process in which particles in the molten metal are deposited by specific gravity separation and then solidified, and the particle filling rate is usually approximately 80% (
It is extremely difficult to control the filling rate to any high or low level depending on the intended use and required performance of the casting. In reality, it is impossible to form a composite structure with a filling rate of 60% or less.

(iv) When the shape of the mold is complex, particles tend to settle and accumulate unevenly, so in practice the shape of the casting is limited to simple and thick shapes, and castings with complex shapes or hollow cylindrical shapes Manufacturing such as these is difficult.

The method for manufacturing composite castings of the present invention eliminates the above-mentioned restrictions at once, and its characteristics include using a molded body made of a mixture of metal powder and hard ceramic powder as a melting raw material, This is poured into a mold and melted sequentially from the ends, and the mixed melt of the molten metal and particles is layered and solidified in the mold from the bottom upward. The powder compact can be melted using, for example, the electroslag remelting method (hereinafter referred to as "
(hereinafter referred to as "ESR method") and vacuum arc melting method (hereinafter referred to as "vA
R-1), a vacuum plasma melting method using the molded body as a melting rod (hereinafter referred to as JPAMJ), or a similar melting method.

The present invention will be explained in detail below.

In the present invention, a molded body obtained by solidifying a mixture of metal powder and ceramic powder is used as a melting raw material.

The metal powder is obtained by crushing a ferrous or non-ferrous metal ingot, or an alloy ingot having a desired composition, into an appropriate particle size, which is selected depending on the intended use and required performance of the composite casting. In addition, ferroalloy powder may be appropriately blended to adjust the ingredients if necessary. The particle size of these metal powders may be about 10 to 150 μm.

The ceramic powder is selected from various compounds such as carbide, nitride, oxide, and ferride compounds depending on the purpose. Of course, the powder must have a high melting point so that it does not easily melt and disappear during the melting process of the compact. For example, when the base metal is a ferrous metal such as nihard cast iron and the purpose is to particularly improve wear resistance as a material property of composite castings, tungsten carbide (WC1
w2c), tungsten titanium double carbide, etc. are extremely suitable. Although there is no particular restriction on the particle size of the ceramic particles used, excessively coarse particles should be avoided in view of the performance of the resulting composite casting, and particles with a particle size of about 300 μm or less are usually preferred. It goes without saying that the specific gravity of the ceramic particles is most preferably the same as that of the molten metal in order to ensure uniform dispersion in the molten metal.
Even if the particles have a higher specific gravity than the molten metal, there is no problem in practice, and even if the particles have a slightly lower specific gravity than the molten metal, the uniformity of dispersion will not be significantly impaired.

The blending ratio of the metal powder and ceramic powder in the powder compact made of the metal powder and ceramic powder is determined as appropriate depending on the desired particle filling rate in the composite structure of the intended casting. The shape of the molded body is usually a rod-like body.

In addition, in order to obtain a composite structure in which ceramic particles are uniformly dispersed in the resulting casting, it is necessary to sufficiently stir and mix the raw material powder mixture so that the ceramic powder is evenly dispersed in the molded body.

The molded body can be manufactured by, for example, press molding, isostatic molding, rubber press, or other appropriate pressure molding methods. Of course, the molded body must not be easily damaged during handling, and must have sufficient strength (robustness) to serve as a consumable electrode in the ESR method, for example, or as a melting frame in the PAM method. If necessary for that purpose, add it to the raw material powder mixture in advance as a forming aid.
Additives that do not interfere with solubility (e.g. methylcellulose)
One method is to mix the following, or after pressure molding,
Alternatively, it is also effective to perform mild firing at the same time as pressure molding.

FIG. 1 shows an example of manufacturing a composite casting by the ESR method using the molded body manufactured as described above as a consumable electrode. (1) is a water-cooled moving mold with a cooling water droplet (2, 2), and a molded body (A) which is a consumable electrode is an electrode clamp (3).
), and its lower end is immersed in a molten slag bath (S) in the mold (1). (4) is a power source. As is well known, in the ESR method, consumable electrodes are sequentially melted from the bottom end by electrical resistance heat in a molten slag bath (S), and a pool of melted material (B) that has dripped and settled in the slag is placed in a water-cooled mold (1). It solidifies continuously. The solidification of the molten material in the mold progresses from the bottom upwards.
As the solidification progresses, the ingot (C)
is continuously drawn down the mold.

Does this device wear out? By melting the E electrode (A), as shown in FIG. ), and in this mixed state, layered solidification progresses sequentially from the bottom upwards, forming a solidified layer (C) having a composite structure.

FIG. 2 shows an example using the VAR method. (5) is the exhaust system (6
), (7) is a mold surrounded by a water cooling jacket (8), and (9) is a power source. The molded body (A), which is a melted raw material, is attached as a consumable electrode to an electrode support (1o), and its lower part is placed in the mold (7). In this melting device, the compact consumable electrode (A) is sequentially melted from the lower end by the high heat of the arc generated at the lower end, giving a mixed melt (B) of molten metal and ceramic particles in the mold (7). . The molten material in the mold is
As shown in the figure, the metal (M) and ceramic particles (
A coagulated layer (C) having a composite structure consisting of PC) is formed.

Figure 3 shows an example of the PAM method, in which the furnace body (11) has a plasma torch (1'2), a solenoid coil (13), etc., and a water-cooled mold (14) is installed at the bottom, and the powder compact is (A) is attached to a support (15) as a frame to be melted, and its tip is located above the mold (14) and is arranged so as to look into the plasma zone (pz).

(16) is a power source. The molded body (A) is melted from the end by the high heat of the plasma, and the generated melt (B) is layered and solidified in the mold (14) in the same manner as described above, and the formed solidified layer (C) is continuous. It is pulled out below the mold.

According to the method of the present invention, as described above, by melting the compact, a molten material in which ceramic particles are dispersed and mixed in a high-temperature molten metal is provided in the mold. The proportion of ceramic particles in the melt is substantially equal to the proportion of ceramic particles in the molded body. Further, the dispersion state of the particles in the melt is extremely uniform, and five solidified layers are formed in which the dispersion state is maintained due to the layered solidification.

Therefore, by adjusting the blending ratio of metal powder and ceramic powder in the molded body, it is possible to produce a uniform composite casting having a particle filling rate of any height or height. Since there is no essential limit to the blending ratio of ceramic particles in the molded body, not only can the casting precipitation method achieve a high particle filling rate of around 80%, but also a low particle filling rate that is impossible with the casting precipitation method (for example, It is also extremely easy to manufacture castings with a uniform composite structure of less than 60%.

In addition, according to the melting and casting method, the respective refining effects, such as desulfurization and deoxidation using slag in the ESR method, adsorption removal of inclusions, etc., cleaning effects such as the degassing effect under vacuum in the VAR method, etc. Quality improvement effects such as microstructural refinement can be obtained through the solidification process with a relatively fast cooling rate within the mold. However, the above-mentioned ESR method, VAR method, and P・AM method are just examples, and the basic principles of these methods may be followed, or in other words, when a powder compact, which is a raw material melting material, is sequentially melted from the end. Various melting and casting methods capable of layering and solidifying the molten material in a mold can be appropriately employed.

In the above example, a mold with a quenching structure was used to solidify the molten metal and ceramic particles while maintaining a uniformly dispersed state of the particles in the molten mixture in the mold. However, when the difference in specific gravity between the molten metal and ceramic particles is small, or when the casting shape is relatively thin and the solidification rate is fast, the separation of specific gravity of particles in the molten metal and its Under conditions in which layered solidification is achieved without causing unevenness in particle distribution density, rapid cooling means such as water cooling can be omitted.

The shape of the casting obtained by the present invention is not only a solid columnar body, but also various other shapes, such as a hollow cylindrical body (cast pipe). When the purpose is a hollow cylindrical body, for example, as shown in FIG. 4, a plurality of molded bodies (A) are arranged as consumable electrodes or frames to be melted along the opening of the mold (17), The melt may be supplied into the mold while melting each molded body. In this case, the mold (17
) is preferably rotated at an appropriate rotational speed by the rotational drive mechanism (18). Also, depending on the mold shape, the fifth
It is also effective to apply a powder compact formed into a hollow cylindrical shape as shown in the figure.

Furthermore, according to the present invention, depending on the usage conditions of the intended casting, only the parts that require wear resistance have a composite structure,
It is also possible to produce castings with the remainder having a metallic phase. For example, as shown in Fig. 6, the molded body is manufactured so that it has a part (a) in which ceramic powder (Pc) is mixed with metal powder (PM) and a part (b) in which only metal powder (PM) is mixed. If you use the molded body and melt it sequentially starting from the end, you can obtain a casting in which the metal phase part and the composite structure part where ceramic particles are mixed in the metal are alternated, so you can use expensive ceramic powder. Desired material properties can be met with savings and low cost.

Next, examples of the present invention will be described.

As the example metal powder, nihard cast iron powder (C3, 32%, Sjo, 75%, Mn0.
68%, Ni4.41%, Cr1.52%, MOo, 4
1%) and a small amount of ferroalloy (Fe-5i.

Particle size 44-7 as ceramic powder in Fe-Mn) powder
After blending 5 μm tungsten powder (w 2 C) and adding an appropriate amount of methylcellulose as a molding aid and mixing uniformly, a solid cylindrical molded body (diameter: 00+nm x length: 200mm) was formed using a press molding method. was produced.

Using the vacuum arc melting method using the above molded body as a consumable electrode,
It takes about 1 hour to melt the molded product sequentially starting from the end, and the melt is layered and solidified in a mold (water-cooled copper crucible) to create a solid cylindrical composite casting (diameter 160 mm).
x length 70 mm) was manufactured.

[A] Raw material powder blending ratio of molded body: Metal powder: Ceramic powder - 1:5.6 (weight ratio) [B
]Dissolution current: 8.5KA.

[C] Degree of vacuum in the furnace: 10” Torro [D] Solidification rate of the molten material in the mold: 1.2 mm 1 minute (in the direction of the wall).

The volume ratio of metal to tungsten carbide particles in the obtained composite casting was 0.6.9 (particle filling rate 69%), which was almost equal to the blending ratio in the molded body.

The distribution of the tungsten carbide particles in the casting is extremely uniform both in the radial and longitudinal directions. Furthermore, the bond between the carbide particles and the metal matrix is strong, and there are no microscopic casting defects. The chemical composition of the metal base is C
8.80%, Si0.76%, Mn0.69%, Cr1
．． 51%, Ni 4.38%, MO 040%.

As described in 2 below, according to the present invention, (1) By adjusting the blending ratio of metal powder and ceramic powder in the molded body, a composite casting having a particle filling ratio of arbitrary height or low, which is impossible with the casting precipitation method, can be obtained. be able to.

(11) The dispersed and mixed state of ceramic particles in the molten metal provided in the mold is uniform, and since the mixed state can be solidified in layers, the composite ffJl &
The distribution of ceramic particles is also extremely uniform.

(+i) Unlike in the casting precipitation method, sedimentation and accumulation of ceramic particles and the resulting sedimentation speed are essentially not a problem, so restrictions on ceramic particle selection, such as conditions such as specific gravity and particle size of ceramic particles, are greatly reduced. eased. For example, fine particles of 50 μm or less, which cannot be used in the casting precipitation method, may be used.

(1) By melting the compact, a mixture of metal and ceramic particles is applied to the mold at a high temperature, so even if the object is relatively small, thin, or has a complex shape, a casting with a uniform composition structure can be formed. can do.

The casting obtained by the present invention is suitable as a wear-resistant material, and depending on the selection of the base metal, it can be used for various purposes such as heat resistance and corrosion resistance.

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional explanatory diagrams showing specific examples of the melting/casting procedure of the present invention, Figure 4 N1J is a cross-sectional explanatory diagram of main parts showing another specific example, and Figure [11] is a plan view. Explanatory diagram, 5th
6 and 6 are respectively perspective views showing examples of powder compacts, and FIG. 7 is an explanatory cross-sectional view schematically showing the distribution of metal and ceramic particles in the mold. A: Powder compact, B: Melt pool, C: Solidified layer, PM
: Metal powder, PC: Ceramic powder, 1 piece 7.14: Mold, 5.11: Furnace body. Agent Patent Attorney Miyazaki Shinhachibe

Claims (4)

[Claims] (1) A molded body of a mixture of metal powder and ceramic powder is sequentially melted from its ends to provide a molten material in which molten metal and ceramic particles are evenly mixed in a mold, and the molten material is poured into the bottom of the mold. A method for manufacturing composite castings characterized by layering and solidifying from above. (2) The method according to item (1) above, characterized in that the melting is carried out by an electroslag melting method or a vacuum arc melting method using the compact as a consumable electrode, or a vacuum plasma melting method using the compact as a frame to be melted. Manufacturing method for composite castings. (3) The blending ratio of ceramic powder in the compact is 80
The method for producing a composite casting according to item (1) or item (2) above, characterized in that the amount is less than or equal to % by volume. (4) The method for producing a composite casting according to any one of items (1) to (3) above, wherein the particle size of the ceramic powder is 50 μm or less.