JPH11221663A - Fitting part strengthening method of cast iron member to other member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strengthening method for strengthening a local part which is a fitting part of a cast iron member to other members. SOLUTION: In a fitting part strengthening method to other members in a cast iron member to reinforce a fitting part to other members through the solid solution of much Ni which is a metallic element for strengthening, a porous body 5 of Ni is installed in a mold 1 in advance, a molten metal of the temperature higher than the melting point of the porous body 5 is poured in the mold 1 to melt the porous body 5, and Ni is solid-solved to a local part of a casting, and a martensitic phase is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an attachment of a cast iron member to another member in which a large amount of a reinforcing metal element is dissolved in the attachment portion to the other member to strengthen the attachment portion to the other member. It relates to the method of strengthening the department.

[0002]

2. Description of the Related Art As a technique for dissolving a large amount of a specific metal element in a local portion of a metal member to impart excellent properties such as heat resistance and wear resistance to the local portion,
Attach metal powder to local parts of metal members (place on the surface,
Irradiating and applying high-density energy by laser beam, electron beam, TIG arc, etc. to melt the metal powder and the local part of the metal member.
There is known a method of solidifying and solidifying a reinforcing metal element in the local part (for example, JP-A-62-86178,
JP-A-62-88876.

However, in this method, high-density energy is used, so that the cost is increased and only the surface portion is reinforced.

Further, in order to strengthen the surface of cast iron and cast steel products, a powder of a reinforcing metal element is mixed in a solvent, applied to the inner surface of a mold, and the metal is poured by a molten metal poured into the mold. A method is known in which a powder is melted to form a solid solution in a local part of a casting (eg, Japanese Patent Application Laid-Open No. 50-7727).
The drawback of this method is that it is difficult to apply a large amount of powder to the inner surface of the mold, and the applied powder is dispersed throughout by the injected molten metal, often failing to achieve the purpose of strengthening the local part. Is a point.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the drawbacks of these methods, wherein the reinforcing metal element is Ni and the metal to be reinforced is a cast iron member. The present invention relates to a method for strengthening an attachment part with another member in a cast iron member in which a local part of the metal to be strengthened is an attachment part with another member, and dissolving a large amount of Ni, which is a metal element for strengthening, into an attachment part with another member. In the method of strengthening the attachment part with another member in a cast iron member for strengthening, a porous body of Ni is previously set in a mold, and a molten metal having a temperature higher than the melting point of the porous body is poured into the mold. Dissolve the porous body,
Thus, the above-mentioned Ni is solid-dissolved in a local part of the casting and a martensite phase is formed.

In the present invention, a porous body of Ni is placed in a mold in advance, and a molten metal having a temperature higher than the melting point of the porous body is poured into the mold to dissolve the porous body. The solid solution of Ni and the formation of a martensitic phase in the local area of the cast iron increase the amount of Ni, which is a metal element for strengthening, which is solid-solved in the Ni strengthened portion of the casting, thereby strengthening the local area. it can.

Here, the porous body refers to a foamed body, a green compact (a body using an organic binder may be used), a fiber molded body, and the like. These porous bodies have a large contact surface area with the molten metal. Because of its small heat capacity, it easily melts on contact with the molten metal (assuming that the melting point of the porous body is lower than the pouring temperature of the cast metal), and because the porous body is a lump, However, it is easy to install it at a desired position in the mold, the amount of use can be sufficiently increased, and unlike powdered metal, it is not washed away by the molten metal injected into the mold.

[0008] Therefore, it is possible to always stably contain a large amount of the reinforcing metal element at the target location (local) of the casting, and in addition to this, even if this target location is inside the casting. However, it is also possible to strengthen only the interior. In addition,
The porous body easily melts into the molten metal on the side in contact with the molten metal in a sufficient depth range, but the surface of the anti-melt side is relatively hard to melt into the molten metal. The content tends to be larger than that of the inner layer. Also,
The addition depth range of the reinforcing metal element can be adjusted by appropriately changing the porosity, melting point or shape of the porous body.

In addition, in the conventional partial solid solution strengthening method, only the surface can be strengthened in the case of strengthening the bolt hole serving as a mounting portion with another member. Therefore, a bolt hole is prepared in advance to strengthen the portion. According to the method of the present invention, a porous body of Ni is previously set in the vicinity of the bolt hole, and a molten metal is poured into the solid solution to form a solid solution. Since the bolt hole can be formed by machining after completion, it is particularly effective to apply the method of the present invention to a member in which a large load acts on the peripheral wall of the bolt hole in use.

[0010] Further, a bolt hole peripheral wall portion where stress concentration is likely to occur,
Alternatively, by adding a reinforcing metal element to a mounting portion with another member such as a predetermined range including the bolt hole peripheral wall portion, the local thickness of the cast product can be made smaller than usual while ensuring the required strength, and The weight of the entire cast product can be reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific examples (see FIGS. 1 to 6). A mold 1 and a core 4 for obtaining a cast iron cylinder having an outer diameter of 87 mm, a length of 115 mm, and a thickness of 10 mm were prepared. The material of the cylinder is a material equivalent to JIS FCD50 (spheroidal graphite cast iron), and its composition is total carbon content = 3.45%, Si = 3.50
%, Mn = 0.34%, P = 0.03%, S = 0.01
3%, Mo = 0.25%, balance Fe and inevitable impurities (all by weight).

Ni foam 5 (thickness 3 mm, length 205 m)
m and a width of 60 mm), which were wound around the core 4 and fixed as shown in FIG. The Ni foam 5 is manufactured by Sumitomo Electric Industries, Ltd., Celmet # 2 (trade name) (cell number 11 to 17).
Pieces / inch, specific surface area 1,000 m ² / m ³ , porosity 9
5% and a density of 0.40 gr / cm ³ ). * However, the porosity is represented by the following equation. Porosity = {1-weight of cermet (gr) / volume of cermet cm ³ × density} × 100%

With the core 4 around which the band-shaped Ni foam 5 is wound around set in the mold 1 as shown in FIG. 1, the molten metal of the JIS FCD50 equivalent material is poured into the cavity 3 through the gate 2. Injected.

The surface of the inner wall portion A of the obtained cylindrical casting 6 (FIG. 2) (a local portion of the cylindrical casting 6 in which the Ni foam 5 is set: shown by a virtual line in FIG. 2). When the Ni content (% by weight) was examined toward the center of the wall thickness, it was 5% Ni at the outermost surface and 1% Ni at a depth of 0.5 mm. FIG. 4 is a graph showing the relationship between the depth from the surface of the inner wall portion A and the Ni content (% by weight).

As a comparative example, the inner wall A of the obtained cylindrical casting 6 and the other conditions were all the same as in the case of the cylindrical casting 6 without using the band Ni foam. The metal structure of the inner wall portion B (* note: B is not shown in the figure) of the cylindrical casting was examined from the surface toward the center of the wall thickness (cross-sectional macro etching).
The results shown in FIG. 6 (inner wall portion A) and FIG. 6 (inner wall portion B) were obtained.

The structure of the inner wall portion A shown in FIG. 5 (base phase)
Is in the range where the amount of Ni is relatively large (from the surface to about 0.3 mm).
Depth), a mixed phase of martensite, pearlite and ferrite in a range where the amount of Ni added is relatively small (about 0.3 to 0.5 mm depth), and pearlite and ferrite at a depth of 0.5 mm or more. (The outer wall side is also a mixed phase of pearlite and ferrite).

The structure of the inner wall portion B shown in FIG. 6 was all a mixed phase of pearlite and ferrite (the outer wall side was also a mixed phase of pearlite and ferrite).

The cylindrical casting 6 and the cylindrical casting as a comparative example were separately charged into a heating furnace, heated at 900 ° C. for 3 hours, and then cooled twice in the furnace over 10 hours. Hot oxidation. As a result of this high-temperature oxidation treatment, the thickness (layer thickness from the surface) of the oxide layer on the inner wall portion A (example of the present invention) to which Ni was added was 300 μm, and the oxide layer was less likely to fall off. The thickness of the oxide layer on the inner wall portion B (comparative example) to which no oxide was added was 650 μm, and the oxide layer was severely dropped.

<Evaluation of Test Results in Examples> From the above items, it is understood that a sufficiently large amount of Ni can be added to a desired position of the cylindrical casting 6 by using the Ni foam 5.

The results of the high-temperature oxidation treatment of the cylindrical casting 6 and the cylindrical casting as a comparative example (see the above item);
It was confirmed that Ni can be added to the surface layer of the casting to improve its oxidation resistance.

The fact that Ni was added to the inner wall portion of the cylindrical casting 6 in an appropriate thickness range (surface to 0.5 mm depth)
It was also confirmed by examining the metal structure (see the above item). In the as-cast state, the structure of the portion where Ni is not added is a mixed phase of pearlite and ferrite,
It can be seen that the structure of the surface portion to which Ni is added is a martensite phase, which can strengthen the surface layer of the cast product and improve the wear resistance.

In the above embodiment, the Ni foam 5 is wound around the core 4 and fixed by utilizing the plasticity of the Ni foam 5, but Ni is applied to the outer peripheral surface layer of the cylindrical casting 6. When adding, a plurality of support pins 7 are planted on the inner wall of the mold 1 as shown in FIG. 3, and the Ni foam 5 can be held by the support pins 7 in a skewered state.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a mold structure for carrying out the method of the present invention.

FIG. 2 is a longitudinal sectional view of a cast iron cylinder obtained by the mold of FIG.

FIG. 3 is a cross-sectional view of a main part of a mold showing a method of installing a foam in the mold of FIG.

4 is a graph showing a relationship between a depth from a surface of an inner wall portion to which Ni is added and a Ni content (% by weight) in the cast iron cylindrical body of FIG. 2;

5 is a photograph (magnification: 50) showing the metal structure of the inner wall portion to which Ni is added in the cast iron cylindrical body of FIG. 2 together with the depth from the surface.

FIG. 6 is a photograph (magnification: 50) showing a metal structure of an inner wall portion of a cast iron cylindrical body to which Ni is not added according to a comparative example, together with a depth from a surface.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mold, 2 ... Gate, 3 ... Cavity, 4 ... Core, 5 ...
Ni foam, 6: cylindrical casting, 7: support pin.

Claims (1)

[Claims] 1. A method for strengthening an attachment part to another member in a cast iron member for strengthening an attachment part to another member by dissolving a large amount of Ni which is a metal element for reinforcement, wherein a porous body of Ni is previously placed in a mold. The molten metal having a temperature higher than the melting point of the porous body is poured into the casting mold to dissolve the porous body, so that the Ni is solid-dissolved in a local part of the casting and a martensite phase is formed. A method for strengthening an attachment portion of a cast iron member with another member.