JPH01273661A - Method for forming sintered layer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming a sintered layer, and in particular, a method for forming a wear-resistant sintered layer by casting an iron-based eutectic alloy sintered material into an iron-based metal. It's about how to do it.

[Prior art]

Conventionally, in order to improve the wear resistance of the cam and journal parts of cast iron camshafts for automobile engines, a chilled metal was incorporated as part of the mold during casting, and the molten metal that came into contact with the chilled metal was rapidly solidified. A method of improving wear resistance by creating a fine del structure has been widely put into practical use. However, this method has limitations in improving wear resistance, complicates the structure of the mold, and requires a large number of expensive chillers.

Therefore, a sintered member made by molding and sintering a wear-resistant alloy powder is attached to a mold, and then molten cast iron is poured in, and the sintered member is diffusion bonded to the cast iron, and the sintered member is cast. Cast-in camshaft technology is being adopted.

For example, in Japanese Patent Application Laid-open No. 60-76268, a wear-resistant sintered cam piece and a journal piece are set in a mold, molten cast iron is poured into the mold to form a shaft part, and the shaft part and cam piece are set in a mold. A method for manufacturing a camshaft in which a camshaft and a journal piece are integrally coupled is described.

In this case, the materials for the sintered body of the cam piece include Cr: 2 to 15% and Mo: 0°5 to 15% by weight.
5%, V: 0.5-5%, C: O, 5-3% and the balance substantially Fe, or Cr:
2-10%, Mo: 0.1-0.5%, ■2 0.1-0
．． 5%, C: 0.5-3.0%, P: 0.3-0°7
It is said that an alloy powder material consisting of % Fe and the balance Fe is effective.

The sintered cam piece is manufactured by molding a material having the above composition into the shape of a cam piece and sintering it in a non-oxidizing atmosphere.

[Problems to be Solved by the Invention] In the technology described in the above-mentioned publication G, the mass of the cam piece is large and M contained in the material of the cam piece is
Due to the small amounts of O and P, there is less crystallization of the liquid phase from the sintered cam piece during casting of cast iron materials, and for other reasons, the molten metal that comes into contact with the cam piece during casting is rapidly cooled and solidified, resulting in the formation of cast iron materials. There is a problem in that poor connection between the cam piece and the cam piece occurs.

In order to reduce the mass of the cam piece, it is not preferable to form the entire cam part with a sintered member, and it is desirable to use only the sintered member in the vicinity of the cam forming part of the cam part.

Therefore, when attempting to form a wear-resistant sintered layer by casting a relatively thin sintered material on the surface layer near the cam forming part of the cam part, the sintered material with a small heat capacity suddenly melts when molten metal is poured. There is a problem that cranking occurs in the sintered material due to the thermal shock caused by the temperature rise, making it difficult to form the desired sintered layer.

[Means to solve the problem]

The method for forming a sintered layer according to the present invention involves forming a compact with an iron-based eutectic alloy powder containing Fe, P, Mo, and C, and converting the compact into a co-material of a Fe-P-C-based eutectic alloy. Crystal temperature and Fe-M
o - Form a sintered material by sintering at a temperature between the eutectic temperature of the C-based eutectic alloy, then attach the sintered material to a mold, and then pour molten iron-based metal into the mold. The sintered material is supplied and integrally joined to the ferrous metal.

The iron-based eutectic alloy powder containing Fe, P%Mo, and Cr has p:o, s~2.0% by weight.
, Mo1.5-7.0%, C:1.5-3.0%, Cr
:5.0 to 10.0%, and the balance is preferably Fe.

To explain C, C combines with Fe and P to form Fe
- Forms a P-C system eutectic alloy (melting point 950°C), which is useful for alloying, and combines with Fe and MO to form Fe-Mo
- Forms a C-based eutectic alloy (melting point 1070°C) that is useful for alloying, while strengthening the matrix structure and
A hardened phase consisting of carbides such as Mo and Cr is formed. C months, if it is less than 5%, the formation of low melting point crystallized substances decreases,
It becomes difficult to react with molten iron-based metals. In addition, C is 3.0%
If it exceeds this, too many hardened phases will precipitate, resulting in a decrease in toughness and a tendency to crack.

To explain P, P combines with Fe and C to form Fe.
-A P-C system eutectic alloy is formed to improve wear resistance, lower the melting point of the alloy, and crystallize a liquid phase. P is 0.
If it is less than 8%, the amount of liquid phase decreases, and the density of the alloy does not increase, and at the same time, it becomes difficult to react with the molten iron-based metal, resulting in poor bonding.

Moreover, if P exceeds 2.0%, the amount of liquid phase becomes excessive and melts during casting.

Regarding MO, MO contributes to the formation of a hardened phase by strengthening the matrix, especially strengthening the thermal shock resistance, and precipitation of its carbide, and combines with Fe and C to form a Fe-Mo-C eutectic alloy. It serves to crystallize the liquid phase and lower the melting point. If the MO content is less than 3.5%, the hardened phase will be small and the liquid phase (2) will also be small.

Moreover, if it exceeds 7.0%, the amount of liquid phase will be too large and will be easily melted in the molten metal.

Regarding Cr, it is effective as a secondary element that improves wear resistance through the precipitation of carbides, and is useful for strengthening the base, particularly improving toughness and thermal shock resistance. If the Cr content is less than 5.0%, sufficient wear resistance cannot be obtained, and if it exceeds 10.0%, the melting point increases, making it difficult to react with molten iron-based metal.

In addition to the above elements, B is effective as an element that promotes liquid phase crystallization by molten metal, and B combines with Fe- and C to form a Fe-B-C system eutectic alloy and lower the melting point. It has the effect of crystallizing the lowered liquid phase and the effect of forming a hardened phase. In addition, as elements for improving wear resistance, ■, W, , Nb, Ta, Ti
The inclusion of these elements is also effective, and these elements are useful for strengthening the matrix, particularly improving toughness, and are preferable elements for combining with C to form a hard phase. Further, in order to improve thermal shock resistance, Ni, Co, Cu, and W may be added.

Next, the temperature at which the compact formed from the iron-based eutectic alloy powder is sintered will be explained.

This sintering temperature is very important in preventing cranking of the sintered material due to thermal shock of the molten metal. That is, Fe-P-C
When sintered below the eutectic temperature (950°C) of the system eutectic alloy,
Since the liquid phase of the Fe-P-C-based eutectic alloy is not crystallized, the density of the sintered material is not increased, many pores are present, the strength is low, and the occurrence of cracks cannot be prevented.

On the other hand, the eutectic temperature (10
If the steel is sintered at a temperature of 70° C. or higher, carbides will grow and the crystal grains of the metal structure will become larger, resulting in a decrease in toughness and thermal shock resistance.

As a result, when the molten metal is poured, cracks occur due to thermal shock caused by the heat from the molten metal.

Next, the above-mentioned sintered material is attached to the mold, and when molten iron-based metal is supplied to the mold, the above-mentioned sintered material does not crack due to thermal shock, and when it comes into contact with the molten iron-based metal, it sinters. The material is at least Fe-M.

- Since it is heated above the eutectic temperature (1070°C) of the C-based eutectic alloy, the liquid phase of the eutectic alloy crystallizes, and the sintered material and the cast iron-based metal are diffusion bonded. Unify.

[Effect]

In the method for forming a sintered layer according to the present invention, a molded body made of the above-mentioned iron-based eutectic alloy powder is adjusted to the eutectic temperature of the Fe-P-C-based eutectic alloy and the Fe-Mo-C-based eutectic Since sintering is carried out at a temperature between the eutectic temperature of
Pores in the sintered material are reduced, increasing density and improving strength. Moreover, since sintering is performed at a relatively low temperature, carbides do not grow much and crystal grains do not become coarse. Therefore, the sintered material has high strength, toughness, and thermal shock resistance.

Next, when the sintered material is attached to a mold and molten iron-based metal is poured into it, the sintered material that comes into contact with the molten metal absorbs heat from the molten metal and at least produces a Fe-Mo-C-based eutectic alloy. It is heated above the eutectic temperature. As a result, the liquid phase of the Fe-Mo-C-based eutectic alloy crystallizes, and the sintered material and the cast iron-based metal are strongly diffusion-bonded and integrated. The sintering at this time advances the growth of carbides and forms a wear-resistant hardened phase.

As mentioned above, the sintered material before pouring has high strength, toughness, and thermal shock resistance, so there is no cranking in the sintered material due to thermal shock during pouring, and the desired sintered material has excellent wear resistance. Each time a layer is formed.

〔Effect of the invention〕

According to the method for forming a sintered layer according to the present invention, as explained above, when sintering a compact, the crystallization effect of the liquid phase of the Fe-P-C eutectic alloy is effectively utilized to make the sintered layer relatively By performing sintering at low temperatures, a sintered material with excellent strength, toughness, and thermal shock resistance can be formed. Since molten ferrous metal is poured with this sintered material attached to the mold, it is not only possible to reliably prevent the occurrence of cranks in the sintered material due to thermal shock during pouring. , Fe-M during pouring.

By utilizing the crystallization effect of the liquid phase of the -C-based eutectic alloy, it is possible to strongly diffuse bond the sintered material and the cast iron-based metal.

In this way, it is possible to form a sintered layer that does not contain cracks and is strongly bonded to the iron-based metal and has excellent wear resistance.

Moreover, considering that it is necessary to sinter the molded body before attaching it to the mold, the present invention does not increase the number of steps, so it can be easily and economically done without using special machinery. It can be implemented.

〔Example〕

Examples of the present invention will be described below.

This example is an example in which a sintered layer made of a wear-resistant iron-based eutectic alloy is formed on the sliding contact portion of a tappet of an automobile engine with a cam.

Example 1 C: 2.0%, P: 0.9%, Cr: 9°1 in weight%
%, Mo: 4.1% and the balance essentially consisting of Fe, 97% by weight of wear-resistant iron-based eutectic alloy powder with a powder particle size of 200 mesh or less, and 3% by weight of an acrylic adhesive binder diluted with acetone. After kneading with a kneader, it was formed into a sheet with a thickness of 1.5+n, and this sheet 1 was punched out to a size of 40 mm to produce a powder compact 1a (Fig. 1 (a), (b)). reference).

Next, as a dewaxing treatment (preliminary sintering treatment), the powder compact 1a was heated to 300°C in an H2 gas atmosphere.
After holding for 0 minutes, it was cooled (see FIG. 1(c)).

Next, as a sintering process, the powder compact was placed in a vacuum furnace and heated to a boundary temperature of 1040"C at a rate of 10℃/departure temperature, held for 20 minutes, and then lowered to 900℃ and maintained at this temperature. After holding for 30 minutes, it was rapidly cooled with N2 gas to produce a sintered member IA (see FIG. 1(d)).

Next, as shown in FIG. 1(e), a part of the casting cavity 2a of the split shell mold 2 for casting the tappet of an automobile engine, which corresponds to the sliding contact part with the cam of the tappet, is baked. The connecting member IA is arranged, and then the spheroidal graphite cast iron FCD4 at 1410°C is placed in the casting cavity 2a of the mold 2.
The molten metal No. 5 was poured and the sintered member IA was cast. During casting, the sintered member IA is heated to a temperature of approximately 1250°C, which is higher than the eutectic temperature (1070°C) of the Fe-Mo-C based alloy, and is then subjected to main sintering.

As a result, the sintered member IA did not melt and no cracks occurred.

The metal structure of the sintered member IA, which has been subjected to the above dewaxing treatment and sintering treatment (preliminary sintering) at 1410°C, was examined with an optical microscope at 40°C.
A 0x magnification is shown in FIG. 2(a).

On the other hand, a plurality of sintered members IA that had been subjected to the above pre-sintering were prepared, and two of the samples were placed in a vacuum furnace without being cast and heated to 1080° at a heating rate of 10°C/min. After heating to C and holding at that temperature for 20 minutes,
The temperature was lowered to 00°C, held at 900°C for 30 minutes, and then rapidly cooled with N2 gas. FIG. 2(b) shows the metal structure of the sintered member subjected to the main sintering treatment, magnified 400 times using an optical microscope.

As is clear from a comparison of FIGS. 2(a) and (b) above, in the pre-sintered sintered member IA, white precipitated carbide does not become coarse, whereas in the main sintered member IA, the white precipitated carbide does not become coarse. White carbide, which contributes to wear resistance, grows and becomes coarser in the member. In addition, the black part is the base (macrisox).

The above cast sintered member IA and spheroidal graphite cast iron FCD
Fig. 2(c) shows the metal structure near the joint with FCD45, magnified 400 times in the same manner as above, where A indicates the metal structure of the sintered member IA, and B indicates the metal weave of FCD45. be. It can be seen from FIG. 2(c) that the sintered member IA and the FCD 45 are well bonded.

Example 2 As wear-resistant iron-based eutectic alloy powder, C:2 in weight%
．． 2%, P: 1.1%, Cr: 8.3%, Mo: 4
．． 8% and the balance essentially consists of Fe, powder particle size 200
97% by weight of wear-resistant iron-based eutectic alloy powder of less than 100% by weight and 3% by weight of acrylic adhesive binder diluted with toluene.
After kneading with a kneader, the powder was formed into a sheet with a thickness of 2.0 gm, and this sheet was punched out to a diameter of 40 mm to produce a powder compact, and this powder compact was demolded under the same conditions as in Example 1. After waxing, the temperature was heated to 990°C at a rate of 10°C/min in a vacuum furnace and held for 20 minutes, then lowered to 900°C and held at this temperature for 30 minutes, then rapidly cooled with N2 gas and calcined. A sintered member is manufactured, and this sintered member is set in the same mold as in Example 1, and then cast iron FC2 is placed in the mold.
The molten metal of No. 5 at 1360°C was poured and the sintered parts were cast into cast iron.

As a result, the sintered member and cast iron were bonded well, no cracks were generated in the sintered member, and a wear-resistant sintered layer made of an iron-based eutectic alloy was formed on the surface layer of the cast iron.

Comparative Example 1 A powder compact made of the same material as in Example 1 and subjected to dewaxing treatment in the same manner was subjected to 1080°C instead of pre-sintering.
A sintered member was produced by performing main sintering at ℃, and this sintered member was set in a mold in the same manner as in Example 1, and the spheroidal graphite cast iron FCD
The sintered parts are cast by pouring 1410°C molten metal.

As a result, cracks (two cracks with a length of five fins extending from the ends toward the center) were generated in the sintered member due to thermal shock.

This is because the main sintering temperature was high, which caused the carbides to become coarser, resulting in a decrease in toughness, thermal shock resistance, etc.

Comparative Example 2 As a wear-resistant iron-based eutectic alloy powder, C in weight %; 1
．． 8%, p:o, 9%, Cr: 8.9%, MO: 4.8
% and the remainder consists essentially of Fe, and 97% by weight of wear-resistant iron-based eutectic alloy powder with a powder particle size of 200 mesh or less and 3% by weight of an acrylic adhesive binder diluted with toluene are kneaded in a kneader. After that, it was formed into a sheet with a thickness of 1.5 mm, and this sheet was punched to a diameter of 39.5 mm to produce a powder compact. After dewaxing the powder compact under the same conditions as in Example 1,
The temperature was raised to 940°C at a heating rate of 10'c/min in a vacuum furnace, held for 20 minutes, then lowered to 900°C, held at this temperature for 30 minutes, and then rapidly cooled with N2 gas.

The sintered member pre-sintered as described above was set in the same mold as in Example 1, and molten cast iron FC25 at 1360° C. was poured in the same manner to cast the sintered member.

As a result, the sintered member is affected by the thermal shock of the heat transmitted from the molten metal.
A book and two with five fins in length) were occurring.

This is because the temperature during preliminary sintering was lower than the eutectic temperature (950°C) of the Fe-P-C eutectic alloy, so the liquid phase of the eutectic alloy was not crystallized and the number of pores increased. This is because the strength has decreased.

As explained above, according to the present invention, Fe, P, Mo
By using the iron-based eutectic alloy powder containing Cr and Cr, it is possible to reliably form a wear-resistant sintered layer on the surface layer of cast iron or spheroidal graphite cast iron castings. Although the above embodiment is for manufacturing a tappet for an automobile engine, a wear-resistant sintered layer can be similarly formed on the cam forming portion of the cam portion of the camshaft of the same engine. However, in this case, a sintered member having a shape that follows the curved shape of the cam forming portion may be manufactured and then cast. It goes without saying that the present invention can also be applied to the manufacture of various mechanical parts other than tappets and camshafts that require wear-resistant sliding parts.

In addition, as a method similar to the present invention, Fe, P, B and C
A compact is formed from an iron-based eutectic alloy powder containing
It is also possible to form a sintered material by sintering at a temperature between the eutectic temperature of the system eutectic alloy, and then cast it in molten iron-based metal and join it integrally, as in the present invention. , also F
It is also conceivable to use iron-based eutectic alloy powder containing e % Mo, B, and C for processing based on the same concept.

[Brief explanation of the drawing]

The drawings relate to the implementation side skin of the present invention, and are shown in Figs.
In is a process explanatory diagram of Example 1, and Figures 2 (a) to (c) are 400 times enlarged photographs of the metal structure of the sintered member pre-sintered in Example 1, and the sintered member subjected to main sintering. Metal structure 4
These are a 00x enlarged photograph and a 400x enlarged photograph of the metal structure near the joint between the sintered member and the spheroidal graphite cast iron. 1a...Powder compact, IA...Sintered member, 2...Mold.

Claims (1)

[Claims] (1) Form a compact with iron-based eutectic alloy powder containing Fe, P, Mo, and C, and compare the above compact with the eutectic temperature of the Fe-P-C-based eutectic alloy and the Fe-Mo-C system. A sintered material is formed by sintering at a temperature between the eutectic temperature of the eutectic alloy, then the sintered material is attached to a mold, and then molten iron-based metal is supplied to the mold and sintered. A method for forming a sintered layer characterized by integrally joining a binder to a ferrous metal.