JP2000042721A - Composite casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the corrosion resistance on the outer peripheral surface of a cast product most effectively produced by a pouring casting method into a mold. SOLUTION: Metallic powder A of Ni base alloy, stainless steel or ferrous alloy containing at least >=10 wt.% Cr and metallic powder B composed of Cu base with the m.p. adjusted to a value clearly lower than that of the metallic powder A by containing 5-12 wt.% P, are mixed and stuck to a target position and molten metal having higher m.p. than the m.p. of the metallic powder B. At the time of pouring the molten metal into the mold, firstly, the metallic powder B is melted and the molten metal is started to impregnate into the stuck layer by the static pressure of the molten metal, and a microscopic liquid phase sintering is started in the state of enclosing the metallic powder A having higher m.p. than the metallic powder B and intensely pushed to the inner surface of the mold with the molten metal pressure in this state, and the integrally strong composite phase is formed by cooling and solidifying.

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 specific properties is added to the entire surface or a part thereof to enhance the functionality in the metal casting method.

[0002]

2. Description of the Related Art As a method of imparting corrosion resistance and wear 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 carbonitriding, to the cast product itself. There is a problem that the man-hour is definitely increased. Therefore, a specific metal that imparts specific physical properties is attached to a desired portion of the cavity surface of the mold before casting, a molten metal is poured, the attached metal layer is welded by the heat, and the desired portion is solidified after solidification. Various casting methods for forming a hardened layer have been proposed.

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,
The filler was selected from copper and had a melting point of 1300 ° C. or less. Alternatively, an embodiment in which the melting point of the molten cast iron is selected to be 1150 ° C. or lower is also shown.

According to the prior art disclosed in Japanese Patent Application Laid-Open No. 5-77019, a powder layer for accelerating solidification is formed in a mold with a mixed powder of Ni, Cr, or an alloy thereof and Ca or Si for almost the same purpose. Was presented. It states that this powder layer prevents defects by the heat insulating action at the time of pouring, and prevents pinholes from being generated by the rapid solidification of 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]

In casting into a mold, in order to form a metal layer having excellent corrosion resistance and abrasion resistance at a desired portion of a product, a metal powder imparting desired properties is applied into the mold. Or, the spraying itself is already known, and the two prior arts cited above also belong to that category. However, the gist of this is, for example, in the case of corrosion resistance, the focus is on the control of components so as to shift the melting point of the corrosion-resistant metal to the lower temperature side, and the reinforcement level of the outer peripheral surface protective layer itself to be coated is still thorough Maybe not.

[0006] If it is primarily desired to lower the melting point of the reinforcing layer, it must follow the form of a kind of metal brazing. It means that the metal is diffused into the metal and the concentration of the components on the surface is largely lost, and if the melting point is lost at a high level, there is a doubt 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, a molten metal is injected into a mold cavity, and a specific metal powder or an alloy powder B that imparts specific physical properties to A by a casting method having a desired shape after solidification has a lower melting point than the metal constituting A. Using a metal powder having the following formula: kneading an appropriate amount of the organic binder C and attaching it to a desired position, and injecting a molten metal having a higher melting point than the metal constituting B into the void portion By adopting such a configuration, first, the low melting point metal powder 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. Then, diffusion welding is performed through the layer surface with the injected metal.

[0008] Since the wear-resistant material is strong and is consumed from the outer surface with the passage of time, a certain thickness of a reinforcing layer is required. Ni-Cr-Si-Fe powder, formed of polyvinyl acetate or the like as C, poured molten cast iron as a base material, and demonstrated the results of locally strengthening particularly the wear surface of wear-resistant cast iron parts. .

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 it is only one point how the protective layer integrally welded to the base material can form a dense and robust composite layer. . For example, if another type of metal film deposited on the surface of the base metal is Ni-based metal or stainless steel,
When there is a difference in the crystal conditions to be formed, such as a variation in the crystal grain size, a structurally different part or a difference in density, if there is a difference between the grain boundary and the grain, a lattice defect and a normal lattice structure, a fine grain and a coarse grain, etc. During this period, the corrosion battery is formed and the characteristic of generating a potential difference is strong. Regardless of the thickness of the protective layer, the progress of corrosion unique to Ni-based alloys and austenitic stainless steel such as polarization, pitting, pitting, grain boundary corrosion, etc. It is a well-known fact that, despite its inherently excellent corrosion resistance, localized corrosion is concentrated and some of the base material quickly loses its function. An object of the present invention is to provide a method for most effectively improving the corrosion resistance of the outer peripheral surface of the above-mentioned corrosion-resistant member, particularly a cast product obtained by casting into a mold.

[0010]

SUMMARY OF THE INVENTION A composite casting method according to the present invention is a casting method in which a molten metal is poured into a mold having a cavity in which a desired shape has been transferred. In a composite casting method in which a specific metal is pre-attached to a corresponding position on the inner surface of the mold in order to apply the
Alternatively, one or a plurality of metal powders A selected from a Ni-based alloy, stainless steel containing Ni and / or Cr, or an iron-based alloy containing at least 10% by weight or more of Cr, and P
By mixing with a metal powder B made of a Cu-based alloy whose melting point has been clearly adjusted to a lower temperature than that of the metal powder A by mixing and adhering to the above position, and being higher than the melting point of the metal powder B. Pouring a molten metal consisting of a melting point and integrally forming a strong and dense sintered layer at a desired position of the product by liquid phase sintering developed by the correlation of the melting points and static pressure of the molten metal This has solved the above-mentioned problem.

In the above-described configuration, a mode in which an appropriate amount of an organic binder C is added to the metal powder A and the metal powder B, and the three are mixed in a slurry form and adhered to a desired location on the mold surface to a desired thickness. desirable. Further, it is desirable that the mixing ratio of A and B is A / B = 40/60 to 90/10.

When A and B charged in the mold come into contact with the molten metal, the low melting point metal powder B is first melted by the heat of the molten metal, and the molten metal injected therein is melted. The metal powder A undergoes liquid phase sintering via the layer portion, and a rich layer of the metal powder A having excellent corrosion resistance is formed on the surface layer. At this time, solid-phase diffusion also partially occurs and is firmly joined to the base material, so that the metal powders A, B,
In this case, a layer having excellent corrosion resistance in which a part of the base material cast iron is melted is formed.

The most important feature of the function is that the corrosion-resistant layer is not formed straight, but the low melting point metal powder B is first melted by the heat of the molten metal, and the metal powder A is firmly contained. This is the point of causing so-called liquid phase sintering, which is performed in cooperation with the molten metal. Therefore, as will be shown in a later example, the reaction layer embraces the metal powder A governing the physical properties and combines with the metal powder B and the molten metal base material. Diffusion bonding to the base material over a depth of

Therefore, 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 ℃. Regarding the blending of the metal powders A and B, it is difficult to sinter the molten metal by the heat of fusion only with the metal powder A having a high melting point. Further, when the metal powder A is 40% or less, the corrosion resistance is insufficient. A / B is 40/60
A larger value is the lower limit of the sintering process. On the other hand, only the metal powder B having a low melting point is completely melted due to the heat of melting together with the pouring of the molten metal and diffused into the molten metal, thereby achieving the purpose of forming a layer having excellent corrosion resistance on the surface. If the mixing ratio of the metal powder B is less than 10%, the function of complementing the sintering action of the metal powder A is insufficient, and the original purpose of forming a robust and dense liquid phase sintered layer cannot be achieved. , A / B smaller than 90/10 is the upper limit of the sintering process.

The main object of the present invention is to improve the corrosion resistance of the outer surface of a ductile iron casting, as will be clearly described 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 ℃)
First, the metal powder B (for example, Cu-P, melting point limited to about 720 ° C. to about 900 ° C.) is melted, and the molten cast iron enters the adhering layer by the static pressure of the molten metal from the product part itself or the riser. Starting with impregnation, micro-phase liquid phase sintering starts in a state in which powder metal A (eg, nickel, melting point 1450 ° C.) having a melting point higher than that of metal powder B is wrapped. In this state, they are strongly pressed against the inner surface of the mold while being held together by the pressure of the molten metal, and are cooled to form a solid composite phase integrally.
The structure after solidification is, for example, when the heat capacity of the molten cast iron is large,
A large amount of Fe, C, and the like infiltrated from the molten cast iron, and a matrix having a high concentration of Ni and Cu, which are austenite-forming components, was found to be too high.
When a structure similar to a stained niresist is obtained, and when the molten cast iron is less molten, F
An austenite structure in which the diffusion of e, C, etc. is small and the concentration of Ni and Cu is higher (specifically, Cu + Ni is 20% by weight or more) is obtained, and a corrosion-resistant outer layer portion is formed.

The adhering layer mixes the above A, B, and C into a slurry state and adheres it to a desired portion on the surface of the casting to a desired thickness, thereby freely changing the shape thickness, thereby forming a portion having excellent corrosion resistance. Can be manufactured. This method is used when the thickness of the casting varies, or when it is difficult to set an effective impregnated layer in the mold, where the casting surface requiring corrosion resistance is not a flat surface but an uneven curved surface. This is a particularly excellent method of handling, and has a great advantage that the corrosion resistance can be easily set for a complicated shape. Further, even for a simple shape, the adhering layer is formed into a thin plate after kneading A, B and C,
By adhering as a thin plate of a desired thickness to a desired portion of the mold casting surface, it is often recognized that in mass production, the advantage of producing a product having a certain thickness is obtained.
The melting point is adjusted to an optimum temperature of 720 to 900 ° C. by appropriately selecting the P weight% of the metal powder B within the range of 5 to 12, or the mixing ratio of A and B is set to A / B = 40/60 ~
By making appropriate changes within the range of 90/10, it is possible to form the optimal liquid phase sintering, and to add corrosion resistance with different performance according to the purpose of use of the product and the difference in the corrosive atmosphere to be used. It cannot be overlooked that the merit of the implementation of the present invention is further enhanced by flexible measures. Also, when facing not only corrosion resistance but also aggressive wear action, a relatively low P is used to avoid brittleness.
Side, for example, P: Limiting to 5-10% by weight may lead to desirable results.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to prove the corrosion resistance of the present invention, the present invention was carried out in the following modes. The used mold is shown in FIG. 2 with a flange 11, a cylindrical part 12, a main mold 1 to be formed, as shown in a state where the divided surfaces (parting surfaces) of the upper mold and the lower mold are overlooked.
A hollow 2 and a core 2 composed of both baseboards 22 and 23 are fitted to each other, and a vertical gate 3, a runner 4, a weir 5, and a riser 6 are used as main parts, and the whole is furan-based self-hardening sand. Molded.
A heating sleeve is applied to the feeder, a flanged short tube with a nominal diameter of 150 (inner diameter 170 mm, outer diameter 190 mm, casting weight is about 30 kg, material is ductile cast iron, casting temperature is 13
50 ° C.). After casting, the mold was separated, and a test piece was cut out after shot blasting.

[0018] The range of corrosion resistance that is particularly necessary for this casting is:
It was determined for the entire length of the outer peripheral surface of the cylindrical portion 12 in FIG.
For this purpose, as shown in the figure, a paste-like attachment layer 7 made by kneading three kinds of powder materials selected from a group of metals having particularly excellent corrosion resistance was attached to the outer peripheral surface of the cylindrical portion 12. The adhering layer for confirming the results is obtained by kneading a mixture of three types of A, B, and C and applying the mixture on the surface of the mold, and has a thickness of about 500 microns. Table 1 shows the components of A, B, and C and the mixing ratio in the examples. Binder C is polyvinyl acetate (PVAC)
It was used.

[0019]

[Table 1] Note) Binder C was set to 5 for A + B = 100.
The powder was kneaded to a coating thickness of 500 microns. In addition, only in Example (5), the casting temperature was 1450 ° C.
It is. Table 2 is a list of chemical compositions of various materials used for forming the powder layer of Table 1. Ideally the powder is less than 200 microns, preferably less than 150 microns, and even less than 50 microns.

[0020]

[Table 2]

The test piece thus cast was processed into an appropriate size, and the following test was performed. A. The observation of the metal structure under a microscope and the conditions are as follows. Magnification: 100 times B, quantitative analysis by EPMA (measures 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. C, Corrosion resistance test According to the method described in JIS K 5400, JIS
A salt spray test of 5% NaClaq was performed at 35 ° C. using an apparatus specified in Z2371. The test piece had a size of 45 mm × 45 mm × 10 mmt, exposing the surface on which the coating layer was formed, and sealing the other surface.

FIG. 5 shows the result of observation of the metallographic structure using a microscope.
(A) and (B) show. That is, (A) shows the Ni-based embodiment (1) and (B) shows the SUS304L-based embodiment (4), respectively, and a high corrosion resistant composite layer formed by completely integrated welding by liquid phase sintering. This is effective as data supporting the dense structure and the robust structure near the weld boundary without defects.

3 and 4, 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 is recognized to a depth of 0 to 600 μm, and forms a dense composite phase with high corrosion resistance due to the coexistence of Cu, which is an austenitizing component of iron, like Ni, and is a spherical graphitized structure similar to the structure of knee resist ductile cast iron. The austenitic phase is well matched with the microscopic structure of FIGS.

In the corrosion resistance test, as shown in Table 3, different metal powders A and Cu-P were mixed at a ratio of 50/50, and the weight loss of each sample which progressed with the lapse of the test days was weighed to indicate the corrosion resistance. It has become.

[0025]

[Table 3]

FIG. 1 shows that each of the samples was treated with saline (5% NaCl).
aq) Its corrosion loss by spray test (mg / cm2)
And the immersion period (day). This chart shows that the conventional ductile cast iron (FC)
The difference in corrosion weight loss spreads proportionally with time with respect to D). In particular, the Ni / Cu-P embodiment (2) is about 9 times as large as the conventional FCD, and SUS304L / Cu-P
Example (4) of SUS430L / C
Example (5) of u-P also proves that it has about four times the corrosion resistance. It is clear from this figure that this difference significantly increases with the passage of time.

[0027]

According to the composite casting method of the present invention, the corrosion-resistant coating layer of the prior art, which is planned and implemented for almost the same purpose, is mainly composed of a single coating, and has the welding property of the base metal behind and the physical properties of the layer itself. The composite layer of the present invention is based on the original idea of liquid phase sintering, while the dense and robust composite layer with outstanding corrosion resistance is integrated. Since it is formed by fusion welding, there is a far superior effect on durability after use.

[Brief description of the drawings]

FIG. 1 is a chart showing a comparative display of corrosion resistance by a salt spray test among the effects of the present invention.

FIG. 2 is a partial cross-sectional front view of a centrifugal casting mold used for carrying out the present invention.

FIG. 3 is a table showing a relationship between a depth and a component from the surface in Example (1).

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

5 (A) and 5 (B) show metallographic photographs by microscope in two examples.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main mold 2 Core 3 Gate 4 Runner 5 Weir 6 Feeder 7 Adhesion layer 11 Flange part 12 Cylindrical part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kimio Nakamura 1-112-19 Kitahorie, Nishi-ku, Osaka-shi, Osaka Inside Kurimoto Ironworks Co., Ltd. (72) Inventor Shigenori Tanabe 2--15 Nishiyamadai, Osaka Sayama-shi, Osaka No. 3

Claims (3)

[Claims] 1. A casting method of pouring a molten metal into a mold having a cavity in which a desired shape has been transferred, in order to impart specific physical properties to a desired position of the casting, In a composite casting method in which a specific metal is previously attached to a corresponding position, Ni or a Ni-based alloy, Ni and / or Cr
At least 10% by weight of stainless steel or Cr containing
One or more metal powders A selected from the above-mentioned iron-based alloys, and a metal made of a Cu-based alloy containing P in an amount of 5 to 12 wt. The powder B is mixed and adhered to the above position, a molten metal having a melting point higher than the melting point of the metal powder B is poured, and liquid phase sintering and melting expressed by the correlation between the three melting points are performed. A composite casting method wherein a strong and dense sintered layer is integrally formed at a desired position on a product by static pressure of a metal. 2. The composite casting method according to claim 1, wherein the mixing ratio of the metal powder A and the metal powder B is A / B = 40/60 to 90/10. 3. A metal powder A and a metal powder B, to which an appropriate amount of an organic binder C is added and mixed in a slurry form, and the resultant mixture is attached to a desired portion of a mold surface at a desired thickness.
The described composite casting method.