JP3061332B2 - Casting surface modification 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 method for modifying a casting surface, and more particularly to a technique for modifying a casting surface which forms a modified layer having excellent wear resistance and heat resistance on the casting surface.

[0002]

2. Description of the Related Art Various surface modification methods have been conventionally proposed in order to improve wear resistance, heat resistance, and the like at a specific portion of a casting surface.

For example, there are measures for improving wear resistance by surface quenching, carburizing, nitriding, etc., and measures for improving wear resistance and heat resistance by welding of dissimilar metals such as thermal spraying or brazing. Dissimilar metals used for thermal spraying or brazing differ depending on the required properties. For example, carbide constituent elements such as Cr for improving wear resistance, and N for improving heat resistance.
i and Mo are used.

[0004]

However, surface quenching, carburizing, nitriding or thermal spraying of a casting requires special equipment and complicated steps, and has the disadvantage of increasing the cost. In addition, since the brazing contains a large amount of carbon in the casting, the bonding strength with the casting is weak, and the brazing is easily peeled off when a strong bonding pressure or impact is applied.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 60-82263, a welding material is applied to a predetermined shape made of a modifying alloy by utilizing the properties of a casting, and is then placed in a mold. There is known a so-called cast-in technique in which a molten metal is set and cast into a casting to form a casting. According to this method, the casting and the modified alloy layer on the surface are integrated by the solidification of the molten metal, so that the adhesion of the modified layer is far superior to brazing or the like.

However, in this method, it takes time and effort to form a cast-in material, and a large amount of expensive modifying alloys are required. Furthermore, since the welding material used is generally of an organic type, it emits gas upon contact with the molten metal during casting,
There are many problems such as the occurrence of defects such as pinholes at the boundary of the cast-in.

[0007] The problem to be solved by the present invention is to further develop a casting surface modification technique by a cast-in method and to improve the casting surface modification technique which is relatively simple and has improved characteristics such as excellent wear resistance. Is to get

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a method for modifying a casting surface according to the present invention provides a WC having a weight of 70 to 98 wt.
%, 30 to 2% by weight of Co and particle size of 100 to 250 μm
Of cemented carbide powder and mixed 2.0% to 3.5% of the molar ratio of water glass-based welding material at a ratio of 1:10 with paste, this surface modification corresponding parts in the mold 1 0.0 to 6.0
After coating and curing to a thickness of mm , an iron-based molten metal is cast into the same mold to form a modified layer on the surface of the casting.

[0009] In order to improve the wear resistance of the cast piece surface is, WC70～98 wt%, Co30～2 wt%, Ru using the above cemented carbide powder particle size 100 [mu] m.

The reason why the amount of Co is 30 to 2% by weight is that 30% by weight.
If the content is more than 2% by weight, the wear resistance is excessively reduced, and if the content is less than 2% by weight, the strength becomes insufficient.

As the water glass-based welding material, a material which is easy to mix with a metal powder and does not easily flow out by application to a mold is desirable, and has a molar ratio of 2.0 to 3.5%. Use something. The water glass and the metal powder are mixed at a weight ratio of 10: 1 to form a paste.

The paste can be applied by brushing or spraying, and the applied thickness is 1.0-6.
0 mm is desirable. If the coating thickness is less than 1.0 mm, the impact resistance will be low, and if it exceeds 6.0 mm, it will be difficult to form a sound superhard layer.

For the purpose of improving heat resistance, metal powder of Ni or Mo can be used. For the purpose of improving corrosion resistance, metal powder of Cr or Ni can be used.

[0014] In this case, the conditions are as follows:
A Ni or Mo powder of 0 to 200 μm is mixed with water glass having the above molar ratio to form a paste, applied to a mold by brush or spray, and cast an iron-based molten metal. It is assumed that 250 μm of Cr or Ni powder is applied to a mold and cast in the same manner as in the case of heat resistance.

[0015]

The paste-like mixture of the metal powder and the water glass-based welding material applied in the mold is securely held at the application location by viscousness of the water glass, and the metal powder applied by contact with the molten metal is applied. It melts and forms a modified layer integrated with the casting on the casting surface. At that time, the water glass-based welding material is dehydrated and melted and slag flows out, and does not burn because it is inorganic, and unlike conventional organic welding materials, for example, acrylic or phenol-based materials, generates extremely little gas. In addition, there is no possibility that a defect such as a pinhole or a blowhole occurs at the boundary of the base material.

In particular, the metal powder composed of WC and Co is
It alloys with the iron base material at the temperature of the iron-based molten metal. At that time, since WC has relatively low solubility, most of the WC remains in the form of particles and remains as an aggregate, and Co alloys with Fe to form a solution. A surface modified layer having a strong structure is formed.

[0017]

FIG. 1 is a sectional view of a mold used for carrying out the present invention.

In the figures, 1a and 1b denote organic self-hardening lower and upper dies, 2 denotes a cavity for forming a casting, 3 denotes a modified layer,
Indicates a gate.

WC93.
5% by weight, Co 6.5% by weight, particle size 125 to 250 μm
The cemented carbide powder of particles of the above and water glass having a concentration of 50% and a molar ratio of 2.3 are mixed at a weight ratio of 10: 1 to form a paste, which is applied with a brush to a thickness of about 1.5 mm. Thus, a modified layer 3 was formed.

Then, this is left to cure at room temperature for about 5 hours, and is further covered with an upper mold 1b of the same material provided with a gate 4 to assemble a mold, and a molten ductile cast iron having the components (% by weight) shown in Table 1 is obtained. Was cast at 1320 ° C. by this,
A casting was obtained in which the modified layer 3 made of an alloy of WC and Co was deposited on the entire surface.

[0021]

[Table 1] ★

FIG. 2 is a structural diagram of the modified surface, and FIG. 3 is an enlarged structural diagram of the cemented carbide portion.

As is apparent from the figure, the hard WC exists in a lump, and it can be seen that the base of the ductile cast iron and the alloyed Co are buried in a cement-like space therebetween and are well welded.
Further, the water glass used as the welding agent remains in a spherical shape. The cemented carbide of this example is composed of WC and Co, and most of the C alloyed with ductile iron is crystallized as graphite, but when C is included, its carbides are formed, contributing to wear resistance. Therefore, the cemented carbide component can be adjusted depending on the application.

As described above, when the cemented carbide powder comes into contact with the molten metal, most of the high melting point WC remains as particles, and the low melting point Co melts with the base iron to form the WC.
, And diffuses into the ductile cast iron base to form a strong bonding structure.

When a steel ball of φ3 mm was projected on the casting with improved wear resistance by shot blasting for a factory,
No peeling was observed and no abrasion was observed.

Further, as shown in FIG. 4, a SiC-based polishing cloth having a roughness of # 60 (width 100 mm, length 1525 mm) 2
0 was moved at a speed of 920 m / min, a sample A was placed thereon, a load of 3.0 kg / cm ² was applied, and the weight loss was measured at regular intervals. As a comparative example, a surface chilled ductile cast iron having the components shown in Table 1, which was subjected to austempering AD
I and those obtained by brazing a cemented carbide material having the same components as in the examples were used. The results are as shown in FIG. 5, and it can be seen that this example is excellent.

FIG. 6 shows still another test example, in which the particle size is 70 to 70%.
20 weight% of 100 mesh flattery sand, about 1 diameter
0 × 20 mm, mixed in a pebble of 0 mm, put in a container 22, and immersed in water up to the surface to form a muddy liquid 23. × 10
A sample A of 0 mm is fixed with a bolt 26 and rotated. The same comparative example as described above was fixed on a concentric circle on a rotating disk 25. FIG. 7 is a graph plotting the weight loss at regular time intervals at a rotation speed of 300 rpm. In this test, the wear resistance of this example was excellent.

In each of the abrasion measurement examples, the brazed sample peeled off at a short time in the cemented carbide portion, and could not withstand severe test conditions as in this experiment.

In this embodiment, the weight loss is much smaller than that of the chill casting or ADI, and the surface structure after the test is stable as shown in FIG. 8, there is no peeling, and the surface modified layer works effectively. . Examples of applications of the casting having such excellent wear resistance include teeth for construction vehicles and disk rotors.

For the purpose of improving the corrosion resistance, nickel was used as the metal powder in the same procedure as described above. The particle size was 170-200 μm and other conditions such as water glass were the same. As a result, a casting excellent in corrosion resistance was manufactured.

For the purpose of improving heat resistance, a particle size of 120
When a molybdenum powder having a thickness of about 170 μm was used, a casting having excellent heat resistance could be produced.

Although a ductile cast iron melt is used as an example here, it is a matter of course that similar results can be obtained by using a normal cast iron melt or a low alloy cast iron melt.

[0033]

According to the present invention, the following effects can be obtained.

(1) Since the modified layer can be integrally welded to the surface of the cast iron casting by casting, it is inexpensive, unlike the conventional method of surface quenching or spraying or brazing a wear-resistant alloy.
It is possible to obtain a casting that is strong and has excellent reforming properties without requiring an extra step.

(2) Since an inorganic water glass material is used as the welding material, there is no generation of pinholes in the boundary portion or the reformed layer due to the combustion gas or the like.

(3) By using the metal powder composed of WC and Co, a strong surface-modified layer having a stone wall structure in which WC as an aggregate is surrounded by Co is formed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold used for carrying out the present invention.

FIG. 2 is a photograph showing a metal structure on the surface of a modified layer.

FIG. 3 is a partially enlarged view of FIG. 2;

FIG. 4 is a schematic diagram of a weight loss test apparatus.

FIG. 5 shows a test result obtained by the test apparatus shown in FIG.

FIG. 6 is a schematic diagram of another test apparatus.

FIG. 7 is a test result obtained by the test apparatus of FIG.

FIG. 8 is a structural diagram of the surface of the modified layer after the test.

[Explanation of symbols]

 1a Lower mold 1b Upper mold 2 Cavity for casting 3 Modified layer 4 Gate

Continuation of the front page (72) Inventor Shinya Detsu 25-25, Egasaki-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Automobile Casting Co., Ltd. (56) References JP-A-53-146928 (JP, A) JP-A-56 JP-A-134047 (JP, A) JP-A-62-199256 (JP, A) JP-A-57-85668 (JP, A) JP-A-63-33143 (JP, A) JP-B-43-9992 (JP, B1) (58) Fields surveyed (Int. Cl. ⁷ , DB name) B22D 27/18 B22C 3/00 B22D 19/08

Claims (1)

(57) [Claims] 1. WC 70 to 98% by weight and Co 30 to 2% by weight having characteristics according to the purpose of modification such as abrasion resistance and heat resistance.
Carbide powder having a particle size of 100 to 250 μm and 2.0
To 3.5% of the molar ratio of glass-based welding material and the 1:10 water
The mixture is mixed in a ratio to form a paste, which is applied to a portion corresponding to the surface modification in the mold in a thickness of 1.0 to 6.0 mm and cured, and then the molten iron is poured into the mold and the surface of the casting is cast. A method for modifying a casting surface for forming a modified layer.