JPS6046857A - Production of composite casting - Google Patents

Abstract

PURPOSE:To prevent nonuniformity in structure owing to collapse of carbide particles and to improve the yield of a composite casting by decreasing continuously or intermittently casting temp. from the beginning to end period of casting in the stage of casting a molten metal and the carbide particles having the specific gravity larger than the specific gravity of the molten metal. CONSTITUTION:The casting temp. of particles P is increased to prevent abrupt temp. drop of the molten metal and an increase in the viscosity thereof owing to absorption of heat by the particles P in the stage of an initial period when the temp. of the molten metal in a casting mold 1 is relatively low and the amt. of the molten metal is small. The casting temp. of the particles P is decreased to relieve the excessive thermal influence from high-temp. molten metal on the particles P and to prevent the collapse thereof in the late period of casting.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a composite casting having a composite structure in which carbide particles and metal are uniformly mixed and strongly bonded.

By casting a molten metal and carbide particles with a higher specific gravity, for example, molten iron metal and tungsten carbide particles in a mold, and depositing the particles downward due to the difference in specific gravity, the seventh
As shown in the figure, in the mold (1), carbide particles are separated by specific gravity and the metal phase part (Bl) consists essentially only of molten metal, and the aggregated carbide particles (P) group fills the gaps between the particles. A composite phase portion cA) consisting of metal (goods) is formed. After solidification, the cast body is taken out of the mold and the metal phase portion (Bl) is cut and removed to obtain a composite phase portion (A) as a composite casting (product).The present invention relates to a method for manufacturing this composite casting. have already made several proposals (Japanese Patent Application No. 57-143120, No. 57-143)
No. 122, No. 58-1957, etc.).

The composite casting thus obtained has the characteristics of both carbide particles and metal, and is particularly excellent in wear resistance and toughness, due to the strong bond between the densely aggregated carbide particles and the metal.

However, when observing the composite structure in detail, there are differences in particle morphology depending on the part of the product, as shown below. That is,
In Fig. 7, near the bottom (m+) of the composite phase part (5), as shown in Fig. 9, each particle [Pl has a healthy grain morphology, whereas the particle fPl in the upper part (η) As shown in Figure 8, the grain size is non-uniform and it appears that they have partially collapsed.The collapse rate of these particles (the proportion of collapsed particles) is approximately 40%, although it depends on the casting conditions. ~50%
It extends to. Therefore, in order to guarantee the soundness and homogeneity of the composite casting (product), it is necessary to cut off and remove the upper part, which lacks structural uniformity due to partial collapse of the carbide particles. However, this results in a decrease in product yield and an increase in costs.

The present invention aims to maintain the soundness of the particle morphology of carbide particles and form a homogeneous composite structure throughout the composite phase portion.

Examining various causes of the collapse of the carbide particles, it is thought that the carbide particles added to the molten metal receive excessive thermal energy from the molten metal, exceeding the amount necessary to form a bond with the molten metal. It will be done. Considering this in the actual casting process, in Fig. 7 above, the molten metal is
Assuming that the casting of coal particles starts from the time when the particles are poured up to the surface, the first particles cast will move through the molten metal (
The particles that are finally cast will settle from the (/X) plane to the (b) plane in the molten metal. At this time, the temperature of the molten metal in the mold is lower as it goes downward, and higher as it goes upward. This is because the molten metal that is initially cast comes into contact with the hopper, casting trough, or inner wall of the mold, which is the casting path, and a considerable amount of heat is lost.
This is because when the subsequent molten metal is poured, the casting path and mold are heated by the previous molten metal, and the amount of heat taken away is small. In order to compensate for the initial drop in temperature of the molten metal in actual casting, the casting temperature of the molten metal must be set high, so the molten metal in the upper part, where less heat is taken away, becomes slightly overheated.

For this reason, the carbide particles in the molten metal that are poured in the early stages settle and agglomerate while maintaining a healthy grain shape without causing any particular abnormalities, whereas the particles that are poured in later are deposited and aggregated in the molten metal at a relatively high temperature. The particles that are deposited at the end are
It is thought that the decomposition described above occurs as a result of excessive thermal energy being applied while passing through the high-temperature molten metal from (c) to (b) (this distance is usually longer than 4 to 3 mm). .

Therefore, as a measure to prevent the decomposition of carbide particles, the distance between the molten metal (holes 1-r) 1 in FIG. Or, the preheating temperature of the mold is higher at the bottom.
It is possible to think of a method such as making it lower in some parts, but (mouth 1-
(Reducing the distance between /11 has limitations in terms of securing the amount of feeder and the amount of heat for the entire molten metal in the mold, and it is actually difficult to adjust the molten metal temperature, and there is a difference in preheating temperature at the top and bottom of the mold.) However, it is not easy to provide a temperature difference large enough to produce a substantial effect.The present invention substantially eliminates the formation of carbide particles in the molten metal by adjusting the casting temperature (preheating temperature) of the carbide particles. This makes it possible to completely prevent this.

The casting method of the present invention is characterized in that carbide particles are cast with a temperature gradient such that the casting temperature is high at the initial stage of casting and becomes low as described later.

In other words, in the early stage of casting when the temperature of the molten metal in the mold is relatively low and the amount of molten metal is small (therefore, the amount of heat retained is also relatively small), by increasing the casting temperature of the particles, the heat absorption of the particles can be reduced. While preventing the rapid temperature drop and viscosity of the molten metal, it is also possible to reduce the pouring temperature of the particles in the later stages of casting to alleviate the excessive thermal influence from the high temperature molten metal on the particles and prevent their collapse. It is to prevent it.

The change in casting temperature over time from the start to the end of casting of carbide particles in the present invention may be continuous or may be intermittent. Examples are shown in FIGS. 1 and 2. FIG. 1 shows an example in which the casting temperature was continuously lowered, and FIG. 2 shows an example in which the casting temperature was lowered intermittently.

The appropriate casting temperature for carbide particles depends on casting conditions such as the specific heat of the molten metal, the solidification temperature, the specific heat of the particles, the ratio of the casting amount of the molten metal to the particles, and the ratio of the casting amount per unit time (casting speed) of the particles to the molten metal. For example, the molten metal is an iron-based alloy such as cast iron, the carbide particles are tungsten carbide particles, and the volume ratio of the particles to the metal in the composite phase is 65:35 to 65:35.
In the casting of composite castings with a ratio of 75:25 (particles: metal), the casting temperature of the molten metal is approximately 1 from the start to the end of casting.
If the temperature is approximately constant within 550 to 1650°C, the casting temperature at the beginning of particle casting should be approximately 400 to 500°C, and at the final stage of casting, approximately 250 to 350°C, so that the temperature difference between the initial and final stages is approximately 150°C. Good results can be obtained by adjusting the

Casting of carbide particles (carbide grains) may be started at the same time as the start of casting of molten metal, but after an appropriate amount of molten metal has been cast, especially the area in the mold where the composite phase portion is formed (product forming area) is filled with molten metal. Starting later is preferable to improve the cleanliness of the product. If carbide particles are poured from the beginning of molten metal casting, the temperature of the molten metal will drop and become viscous due to heat absorption by the carbide particles (this is noticeable in the early stages of casting when the amount of molten metal is small).
Therefore, scum inside the mold (such as scum that flows from the ladle accompanying the molten metal or generated by oxidation of the molten metal during casting)
However, it is necessary to start casting particles after the molten metal surface has been poured to the top of the product forming section (plane (B) in Figure 7 above). For example, even if flotation and separation of scum is prevented, scum remains in the metal phase part (Bl) and in the product part (3).
) will be avoided. It is preferable that the casting of the particles is completed at approximately the same time as the casting of the molten metal.

The ratio of the casting speed of the molten metal and the particles (casting speed of the particles/casting speed of the molten metal) may generally be about 0.4 to 1.2.

The types of metal and carbide particles used in the casting of the present invention are appropriately selected depending on the intended use and required performance of the composite casting. Typical examples of metals include iron-based alloys, such as nihard cast iron, but other metals include cobalt (C
o), nickel (Ni), iron (Fe), Co-based alloy, Ni-based alloy, etc. are used. Typical examples of carbide particles include tungsten carbide (WC, W2C) particles and tungsten-titanium double carbide particles.

These may be used alone or as a mixture in any combination.

Preheating of the particles for controlling the casting temperature of the carbide particles may be performed by an appropriate method. If the oxidation of the particle surface causes the lid to open during heating, heat treatment may be performed in an inert gas atmosphere, and more preferably, the particle surface may be coated with N1-
B: Those coated with an anti-oxidation coating such as electroless plating are used.

The larger the particle size of the carbide particles is, the more advantageous it is in terms of promoting sedimentation and aggregation in the molten metal, but in consideration of the material of the composite structure to be formed, those in the range of about 44 to 350 μm are preferable.

The amount of carbide particles cast in the present invention may be sufficient to form the desired composite phase (product), and the proportion of carbide particles in the composite phase depends on the type and size of the particles, Although it depends on the difference in specific gravity with the molten metal, the ratio of particles to metal is approximately 65:35 to 75:25 in terms of volume ratio. On the other hand, as shown in the figure, the molten metal is cast in an excess amount that exceeds the amount sufficient to form the product part. This is mainly intended to replenish the molten metal against solidification shrinkage in the product part, but if a larger number of holes are cast, the heat retained in the molten metal in the mold will increase, and the molten metal will continue to flow until the deposition of carbide particles is completed. Advantageously, the viscosity of the particles is delayed, and complete agglomeration of the particles and densification of the structure are promoted.

In the casting of carbide particles and molten metal in the present invention, for example, as shown in FIG.
The molten metal (M') from 3) and the carbide particles (Pl) from the carbide particle dosing jig (4) are mixed in the hopper under appropriate control of their flow rates (casting speeds), or the particles are This is done by placing the dosing jig (4) directly into the opening of the mold (1) and casting the molten metal and particles separately into the mold.Also, promoting sedimentation and agglomeration of the particles in the molten metal. In order to improve the compactness of the composite structure, it is also effective to connect an appropriate vibration device to the mold and apply vibration continuously or intermittently during the casting process.

Of course, the shape of the cast body is not limited to a solid body; for example, a hollow cylindrical body can also be cast.

FIG. 4 shows an example. The casting procedure does not need to be particularly different from that described above, but care should be taken to ensure an even distribution of carbide particles in the circumferential direction within the mold and equalization of the molten metal temperature. (1) is installed on a rotary table (5), and a spindle (5) is mounted on a rotary drive device (not shown).
1) It is preferable to perform casting while rotating at an appropriate rotational speed. In this way, the carbide particles (Pi) can be evenly distributed and administered in the circumferential direction within the mold, and it is also possible to avoid unevenness in the temperature distribution in the circumferential direction.

As an alternative method for casting hollow cylindrical castings, as shown in Fig. 5, a mold (1) equipped with a core αB having a hemispherical top O2 is used, and the molten metal flowing down from a hopper (2) is used. Casting can also be carried out with the particles directed toward the center of the hemispherical top of the core.

The molten metal and particles collided with the center of the top of the core are continuously dispersed radially from the center of the top to each part of the mold in the circumferential direction, so that the carbide particles and the temperature of the molten metal are uniformly distributed in the circumferential direction. You can complete the casting based on the original. If there is a slight deviation in the radial distribution from the center of the top of the core, the rotation of the mold as shown in FIG. 4 may be used in combination to equalize the deviation in the circumferential direction.

2. In each of the casting modes mentioned above, the carbide particles are preheated by, for example, changing the heating temperature over time with a heating source (not shown) attached to the particle dosing jig (4), or heating the carbide particles at a predetermined temperature outside the particle dosing jig (4). The casting temperature of the particles may be adjusted as described above by sequentially replenishing the heated particles into the jig and casting them. Furthermore, the casting speed of particles can be set to a desired value by a flow rate regulator (41) provided in the dosing jig, and the casting speed of molten metal can be set to a desired value by adjusting the tilting angle of the ladle (3). .

Although there are no restrictions on the material of the mold, for example, a firing mold (1) used for precision casting is placed in a case (7) together with a back sand (6) as shown in the figure above, and this is placed in a heating furnace. It can also be used as a heat-retaining mold that is preheated to, for example, 500 to 900°C.

Next, examples of the present invention will be described.

Example In the casting apparatus shown in Fig. 5, molten nihard cast iron and tungsten carbon (W2C) particles were cast under the following casting conditions to obtain a cast body having the shape shown in Fig. 6.
), the metal phase portion (Bl) was cut and removed, and the composite phase portion (Al) was collected as a hollow cylindrical cast product.

[1] Casting mold (firing mold) (1) Set in the case (7) with back sand (6) and preheat in a heating furnace. Temperature 600°C just before casting.

(II) Shape (see Figure 6): Outer diameter (Dl) 180mm
,.

Core diameter (D 2 ) 100 m mo [2] Nihard cast iron molten metal (1) Chemical composition: C3, 10%, SiO, 73%,
Mn 0.68%, Cr 1.52%, Ni 4.46%
,M.

0.38%, balance Fe (11) Molten metal temperature: 1600°C C3] W2C particles (1) Particle size: Average 280 mesh (11) Casting R = Product forming part between (a) and (b) in the mold (H1=80mm) with composite phase (particles: metal-70=
30 (volume ratio) is formed.

[4] Casting procedure Start casting the molten metal first, and make sure that the surface of the molten metal reaches the top surface (b) of the product forming part.
The casting of particles is started from the moment when the melt level reaches β)(H
2=350 mm), the casting of the molten metal/particles was stopped. The particle casting temperature was 450°C at the start of casting.
When 1/4 has passed: 400°C, when 2/4 has passed = 350°C, and at the end: 300°C. Note that the particle/molten metal casting speed ratio is a constant value of approximately 0.9.

The obtained composite cast product has a homogeneous composite structure with a healthy grain size layer throughout from the bottom (face) to the top (mouth face). The decay rate of carbide particles at the center of the wall thickness 10 mm below the top is only 596.

As a control, a composite cast product was obtained under the same casting conditions as above, except that the casting temperature of carbide particles was always set at a constant value of 450°C. The particle disintegration rate in the same part of this casting as above was 45%, and structural non-uniformity was observed due to the disintegration of a large amount of particles.

As described above, according to the present invention, it is possible to substantially eliminate the disintegration of carbide particles and the resulting non-uniform structure, and to produce composite castings with excellent soundness at a high yield. The composite castings obtained by the present invention are suitable for rolls and other applications requiring wear resistance, toughness, etc., and their excellent homogeneity contributes to improved durability and stability.

[Brief explanation of the drawing]

1 and 2 are graphs schematically showing an example of controlling the casting temperature of carbide particles in the present invention, FIG. 3 is a longitudinal cross-sectional view showing an example of the casting procedure, and FIGS. Figure [■] is a vertical cross-sectional view of another example of the casting procedure, Figure 4C
rD, Fig. 5 CrI] is a plan view of the mold part, Figs. 6 and 7 are explanatory longitudinal cross-sectional views of the mold and the cast body, and Figs. 8 and 9 are schematic enlarged views of the composite structure. 1: Mold, 2: Casting hopper, 4: Particle dosing jig, M:
Metal, P: Carbide particles, A: Composite phase part (composite cast product), B: Metal phase part. Agent Patent Attorney Miyazaki Shinshikibu (161 Figure 6 Figure 7 Figure 8 Figure 9-338=

Claims (3)

[Claims] (1) Metal elution and carbide particles having a higher specific gravity than the molten metal are poured into a mold, and the carbide particles are allowed to settle due to the difference in specific gravity, so that the carbide particles are placed under the separated metal phase of the molten metal. In the casting method, a composite phase consisting of precipitated and agglomerated carbide particles and molten metal is formed, and after solidification, the metal phase portion is cut and removed to obtain the lower composite phase portion as a composite cast product. , a method for manufacturing composite castings characterized by casting while lowering the casting continuously or intermittently from the initial stage to the final stage of casting. (2) The method for manufacturing a composite casting according to item 2, item (1), characterized in that casting of the carbide particles is started after the molten metal is filled into the part of the mold where the composite phase is formed. (3) The method for producing a composite casting according to item 2, item (1) or item (2), wherein the metal is an iron-based metal and the carbide particles are tungsten carbide and/or tungsten titanium double carbide. .