JP3283003B2 - Composite centrifugal casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal casting method in which a metal or an alloy exhibiting a specific property is added to the whole or part of the metal to enhance the functionality.

[0002]

2. Description of the Related Art As a method of imparting corrosion resistance to a specific part of a cast product, there is a method of applying a surface treatment after casting, such as thermal spraying or partial quenching and carbonitriding, to the cast product itself. There is an increasing problem. Therefore, a hardening material layer containing a specific substance is provided at a desired portion of the cavity surface of the mold before casting, molten metal is poured, the hardening material layer is welded by the heat, and after solidification, it is transferred to a desired department. Various casting methods have been proposed to form a hardened layer.

In the prior art disclosed in Japanese Patent Publication No. 5-20184, for example, a filler made of a Ni alloy having a Ni content of 80% by weight or more is charged as a powder into a mold immediately before casting. The main point is to form a corrosion-resistant layer on the outer peripheral surface by pouring, and boron, silicon, chromium,
A filler having a melting point of 1300 ° C. or less was selected from copper.
Alternatively, an embodiment in which the melting point of the molten cast iron is selected to be 1150 ° C. or lower is also shown.

In the prior art disclosed in Japanese Patent Application Laid-Open No. 5-77019, a powder layer for accelerating solidification is placed in a mold for almost the same purpose.
It has been shown that it is formed by a mixed powder of i, Cr, or an alloy thereof and Ca, Si. It is stated that the heat insulation effect at the time of pouring by the powder layer prevents the occurrence of pinholes by preventing defects, protecting the mold, and rapidly solidifying the cast molten metal. That is, Ca and Si in this case are intended to have a kind of deoxidizing inoculation effect and an effect of lowering the melting point of the mixed powder layer.

[0005]

SUMMARY OF THE INVENTION In centrifugal die casting, a layer having excellent corrosion resistance is formed on the outer peripheral surface of a product.
The application or spraying of the corrosion resistant metal powder into the mold is already known, and the two prior arts cited above also belong to that category. However, the main point is to focus on controlling the components so that the melting point of the metal imparting corrosion resistance is shifted to the lower temperature side, and the reinforcement level of the outer peripheral surface protective layer itself to be coated is still perfect. Isn't it?

[0006] If it is primarily desired to lower the melting point of the powder layer, it must follow the form of a kind of metal brazing. It means that it diffuses into the metal and the concentration of components on the surface is greatly lost, and if the melting point is too high, there remains a question about the integral welding with the base metal.

[0007] The applicant of the present invention previously filed Japanese Patent Publication No. Hei 5-201.
No. 87 discloses a completely new composite integration by liquid phase sintering mainly aimed at locally strengthening wear-resistant steel. That is, by injecting a molten metal into the mold cavity and casting it into a desired shape after solidification, a specific metal or alloy imparting specific physical properties to A, and B is more clearly defined than the metal constituting A. Using a metal powder having a low melting point, C is an appropriate amount of an organic binder, and the three are kneaded together and attached at a desired position, and the melting point of the void is higher than the metal constituting B. Casting method to inject metal. With this configuration, first, the low melting point metal B is melted by the retained heat of the injected molten metal, and the three components A, B and the injected metal are integrated by liquid phase sintering, and then the injected metal and the layer are integrated. Diffusion welds through the surface.

[0008] Since the wear-resistant material is strong and is consumed from the outer surface with the passage of time, a certain thickness of the reinforcing layer is required.
Of Ni-Cr-Si-Fe powder as C and polyvinyl acetate as C, and pouring molten cast iron as a base material, especially in abrasion-resistant cast iron parts, the results of locally strengthening the wear surface Indicated.

On the other hand, regarding the corrosion-resistant material, the thickness itself of the reinforcing layer on the outer surface is not the main subject, and one point is how the protective layer integrally welded with the base material can form a dense and robust composite layer. run out. For example, when there is variation in the crystal grain size of different kinds of metal films deposited on the surface of the base metal, or when there are structurally different parts or differences in density, grain boundaries and intragranules, lattice defects and normal lattice structure, etc. When a corrosion battery is formed and a potential difference is generated, regardless of the thickness of the protective layer, the unique corrosion of the metal such as polarization, pitting, pitting, and intergranular corrosion progresses extremely, and local corrosion concentrates. It is a well-known fact that some of the base materials lose their functions quickly. An object of the present invention is to provide a method for most effectively improving the corrosion resistance of the above-described corrosion-resistant member, particularly the outer peripheral surface of a cast iron pipe formed by centrifugal casting.

[0010]

According to the composite centrifugal casting method of the present invention, in order to improve specific physical properties, specific metals and the like are added into a mold, and molten metal is poured while rotating at a high speed. In the composite centrifugal casting method in which the outer peripheral surface is
i or a Ni-based alloy, one or more metal powders A selected from stainless steel containing Ni and / or Cr or an iron-based alloy containing at least 10% by weight of Cr , and 5 to 12% by weight of P , A metal powder B of Cu-P adjusted to a melting point at a lower temperature than that of the metal powder A more clearly.
And the mixing ratio is in the range of A / B = 40/60 to 90/10
Create a powder uniformly mixed within, while rotating the mold at high speed, immediately before pouring the molten metal having a melting point higher than the melting point of the metal powder B, or at the same time the powder in the mold By spraying, liquids A and B having a higher specific gravity than the molten metal form a powder layer which is separated and attached to the inner surface of the mold due to a difference in centrifugal force, heat is received from the molten metal, and a liquid developed by the interrelation of the three melting points The above-mentioned problem has been solved by forming a strong and dense sintered layer integrally on the outer peripheral surface of the product by phase sintering and centrifugal action.

In the above configuration, instead of spraying the mixed powder on the inner surface of the mold, the metal powder A, the metal powder B and the organic binder C are mixed and applied onto the inner surface of the mold. While rotating at a high speed, a molten metal having a melting point higher than the melting point of the metal powder B is poured and subjected to liquid phase sintering and centrifugal action developed by the interrelation of the three melting points. A method of converting the powder layer or the adhering layer into a sintered layer that is firmly and densely formed on the outer peripheral surface of the product may be used.

When a mixed powder of the metal powders A and B is sprayed immediately before or simultaneously with injection of a target welding metal into a mold rotating at a high speed, heat is applied to the molten metal to form the mixed powder B.
The powder reaches its melting point and begins to melt. At this time, the powder metal A has three modes: a case where it is dissolved by the compounded material, a case where it is dissolved only near a part of the surface, and a case where it is not dissolved at all. This depends on the balance between the components of the powdered metal A and the temperature of the molten metal to be injected.
These are elements that can be calculated and formulated in advance. The most important feature of the operation is that the dispersed or applied metal powder is separated from the molten metal by the difference in centrifugal force based on the difference in specific gravity, transferred to the inner peripheral surface of the mold, and adhered to the annular powder layer. Rather than dissolving and dispersing all in the molten metal as it is to form a reaction layer straight, the powder metal B having a low melting point is first melted by receiving the heat of the molten metal, and the powder metal A is firmly embraced, and the molten metal A This is the point where so-called liquid phase sintering occurs in which welding is performed in cooperation. Therefore, as will be shown in a later embodiment, the reaction layer embraces the powder metal A, which controls the physical properties, and combines with the powder metal B and the molten metal base material. Diffusion bonding to the base material over a depth of

Accordingly, the difference between the melting points of the metal powders A and B,
In addition, the mixing ratio is an important point in promoting favorable liquid phase sintering. FIG. 6 is a binary phase diagram of Cu-P. As can be read from the correlation between the weight% in the upper column of the horizontal axis and the temperature ° C. in the vertical axis, P has a eutectic point at about 8% by weight and has a eutectic point. The temperature is around 720 ° C. The Cu-P alloy forms the lowest melting temperature at this eutectic point, moves away from this eutectic point, and moves to a high temperature side in a sharp curve. Therefore, P
It is important to determine the extent to which P can dissolve in Cu. However, when the phase diagram reading and the results of the field test are performed, P is limited to 5 to 12% by weight, and the melting temperature is set to 900%. The critical significance of obtaining the best liquid phase sintering for practical use could be determined by setting the temperature below ℃. Also, when facing not only mere corrosion resistance but also aggressive wear action, it may lead to a desirable result to limit to a relatively low P side, for example, P: 5 to 10% by weight in order to avoid brittleness. . Regarding the composition, sintering of the molten metal by the heat of fusion is difficult with only A having a high melting point, and further, when A is 40% or less, the corrosion resistance is insufficient, so that A / B is 40/60.
A larger value is the lower limit of the sintering process. On the other hand, B alone having a low melting point alone completely melts and diffuses into the molten metal due to the heat of melting together with the pouring of the molten metal, so that the purpose of forming a layer having excellent corrosion resistance on the surface cannot be achieved. If the compounding ratio of B is less than 10%, the function of complementing the sintering action of A is insufficient and the original purpose of forming a robust and dense liquid phase sintered layer cannot be fulfilled.
B is smaller than 90/10, which is the upper limit of the sintering process.

The component C is used only in the case where the coating film is formed by applying it to the inner surface of the mold, and keeps the bond with the mold surface. It does not peel off, but serves to grip until solidification starts at the surface.

The main object of the present invention is to improve the corrosion resistance of the outer surface of a ductile cast iron pipe, as will be clearly shown in the embodiments described later. Specifically, the operation in this case will be described.
Melt of ductile cast iron into mold (melting point about 1150 ℃)
When the molten metal is poured, the mixed metal powder sprayed due to the difference in centrifugal force due to the difference in specific gravity moves to the inner peripheral surface of the mold and separates and adheres in a layer form.
u-P, melting point limited to the range of about 900 to about 720 ° C)
Is melted, and the molten cast iron is pushed into the powder layer by centrifugal force to start impregnation, and powder metal A having a melting point higher than powder metal B (for example, nickel, melting point of about 1450).
℃), microscopic liquid phase sintering starts.
In this state, they are strongly pressed against the inner surface of the mold while being held together by the centrifugal force, and are rapidly cooled to form a solid composite layer integrally. In the solidified structure, for example, when the heat capacity of the cast iron melt is large, Fe, C, and the like infiltrate much from the cast iron melt, and Ni, which is an austenitization promoting component, is both used.
In the case where the base having a high total concentration of Cu and Cu is similar to an austenitized niresist, and the molten cast iron is less molten, the diffusion of Fe, C, etc. in the surface layer is small, and the Ni and Cu concentrations are low. Higher (specifically, Ni + C
u is 20% by weight or more) An austenite structure is obtained and a corrosion-resistant outer layer is formed. In the case of the form in which the metal powders A and B are mixed and adjusted in advance and applied in the mold, the progress of the liquid phase sintering is basically the same, and the A component is rich on the outer peripheral surface of the solidified product. To obtain a rigid and dense corrosion-resistant composite layer.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to prove the corrosion resistance of the present invention, a confirmation test was performed in the following manner. FIG. 3 is a partial cross-sectional view of a centrifugal casting mold. The centrifugal casting mold 1 is horizontally supported by a rotary bearing 2, and while being rotated at a low speed, the mixed powder is sprayed from a supply pipe 4 to have a uniform thickness over the entire length. Thus, a powder layer 3 was formed. Using the mold shown in FIG. 3, a centrifugal cast iron tube (outer diameter 169 m) was used.
m, length 1080 mm, thickness 7.5 mm).
The molten metal used was 1350 ° C. ductile cast iron. After casting, it is refined (980 ° C x 1hr + 730 ° C x 1h)
r) Then, the test piece was cut out. Metal powder A, B
The particles having a particle diameter of 150 μm or less were used and mixed and sprayed on the inner surface of the mold immediately before pouring of the molten metal or simultaneously with an average thickness of about 500 μm. Table 1 shows the components and mixing ratios of the metal powders A and B in Examples (1) to (5).

[0017]

[Table 1] Note) In the case of spraying, the binder C is not used, but in the case of application, it is used in a ratio of about 5 with respect to A + B = 100, and polyvinyl acetate (PVAc) is preferable. Table 2 is a list of chemical compositions of various materials used for forming the powder layer of Table 1. The particle size of the powder is less than 200 microns, preferably less than 150 microns,
Most preferably, it is 50 microns or less.

[0018]

[Table 2]

The cast test piece was processed into an appropriate size, and the following test was performed. A, Quantitative analysis by EPMA, measuring the chemical composition ratio of elements contained near the surface. That is, it is significant to know the fluctuation of the concentration of the additive component mainly composed of Ni and Cu to determine the effective depth of corrosion resistance from the surface. B, Corrosion resistance test According to the method described in JIS K 5400, JIS
Using a device specified in Z2371 and a salt spray test of 5.0% NaClaq in an atmosphere of 35 ° C. and 3.0%
A salt water immersion test of NaClaq was performed. In the case of the immersion test, the test solution is newly changed every two weeks, and the weight is measured every predetermined time to record the weight loss and charted.
The relationship with time was plotted. The test piece is 45
The surface having the coating layer formed thereon was exposed in a size of mm × 45 mm × thickness 7.5 mm, and the other surfaces were sealed.

4 and 5, the horizontal axis represents the distance (μm) from the surface of the casting, and the vertical axis represents the results obtained by EPMA (X-ray micro-analyzer). The quantitative analysis values of the obtained Fe, Ni and Cu components are plotted to show the mutual relationship. In both figures, Ni and Cu are 50
It was observed to a depth of 0 to 600 μm, suggesting that a dense composite phase with high corrosion resistance was formed by the coexistence of Cu, which is an austenitizing component of iron, like Ni.

Table 3 shows that each of the samples was treated with saline (5.0% NaC).
laq) By spray test, its corrosion weight loss (mg / cm
FIG. 1 shows the relationship between 2) and the immersion period (day), and FIG. 1 plots the passage of time and the progress of corrosion based on this table. Table 4 shows that 3.0% NaC
The relationship between weight loss and time when a test piece is immersed in a saline test solution of laq is shown, and FIG. 2 is a representation of this data in the figure.

[0022]

[Table 3]

[Table 4]

It can be seen from this table and figure that the difference in corrosion weight loss spreads proportionally over time for all test pieces with respect to the ductile cast iron (FCD) of the comparative example as the prior art, and the test conditions are severe. In the case of continuous spraying, the corrosion resistance of the Ni / Cu-P example (1) was about 8 times or more, and the Ni-Sn / Cu-P example (4) was 6 times or more. Even Example (5), which applied the economical SUS304L powder, recorded more than 4 times the corrosion resistance. It can be easily estimated from this figure that the difference increases almost proportionally with the passage of time, and appears as a marked difference in the service life in actual use.

[0024]

According to the composite centrifugal casting method of the present invention, the conventional anti-corrosion coating layer, which is planned and implemented for almost the same purpose, comprises a single coating as a main component and the weldability of the base metal behind,
While some concerns had to be denied in consideration of the physical properties of the layer itself, the composite layer of the present invention is a dense, dense, highly corrosion-resistant alloy based on the original idea of liquid phase sintering. Since the solid composite layer is formed by integrally welding, there is an effect that the durability after use is far superior.

[Brief description of the drawings]

FIG. 1 is a view comparatively showing the corrosion resistance by a salt spray test among the effects of the present invention.

FIG. 2 is a diagram showing a comparative display of corrosion resistance by a salt water immersion test among the effects of the present invention.

FIG. 3 is a partially sectional front view of a centrifugal casting mold used for carrying out the present invention.

FIG. 4 is a table showing a relationship between a depth from a surface and a component in the embodiment (1).

FIG. 5 is a table showing a relationship between a depth and a component from the surface in Example (3).

FIG. 6 is a Cu-P binary phase diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Centrifugal casting die 2 Rotation bearing 3 Powder layer 4 Supply pipe

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigenori Tanabe 2- 15-3 Nishiyamadai, Osaka Sayama City, Osaka Prefecture (56) References JP-A-10-272547 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) B22D 13/02

Claims (2)

(57) [Claims] 1. A composite centrifugal casting method in which a specific metal or the like is added into a metal mold and molten metal is poured while rotating at a high speed, and the outer peripheral surface is compositely strengthened in order to improve specific physical properties. , Ni or a Ni-based alloy, stainless steel containing Ni and / or Cr, or one or more metal powders A selected from iron-based alloys containing at least 10% by weight or more of Cr
And 5 to 12% by weight of P to make the metal powder A
A / B = 40/60 to 90/1 when the mixing ratio with the metal powder B made of Cu-P, which is more clearly adjusted to a low melting point, is used.
0, and a powder mixed uniformly within a range of 0 is prepared. While the mold is being rotated at a high speed, immediately before or simultaneously with pouring a molten metal having a melting point higher than the melting point of the metal powder B, the powder is mixed with a metal. By dispersing in the mold, A and B having a higher specific gravity than the molten metal form a powder layer separated and attached to the inner surface of the mold due to a difference in centrifugal force. Due to the liquid phase sintering and centrifugal action that appears,
A composite centrifugal casting method characterized by integrally forming a strong and dense sintered layer on the outer peripheral surface of a product. 2. The method according to claim 1, wherein the metal powder A, the metal powder B, and the organic binder C are mixed and dispersed on the inner surface of the mold instead of spraying the mixed powder on the inner surface of the mold. A liquid layer having a melting point higher than the melting point of the metal powder B is poured by pouring a molten metal having a melting point higher than the melting point of the metal powder B while forming a powder layer or an adhering layer by coating. A composite centrifugal casting method characterized by converting the powder layer or the adhering layer into a sintered layer which is firmly and densely formed on the outer peripheral surface of the product by phase sintering and centrifugal action.