JPH0436439A - Camshaft of valve train for internal combustion engine and method for manufacturing the same - Google Patents

Abstract

PURPOSE:To form a sliding member also excellent in workability, in the sliding member in this invention, by forming the structure of the surface layer of the sliding part into a one excellent in wear resistance, toughness or the like and forming the structure of the part to be softened into the one similar to that of a core part. CONSTITUTION:Alloy cast iron contg. the components of cast iron equivalent to JIS FC20 to FC30 or contg. the compositional components of, by weight, 0.4 to 0.6% Ni, 0.5 to 1.0% Cr and 0.5 to 1.0% Mo is used as a structural material, by which a sliding member in which the surface layer part of the sliding part has a mixed structure of a ledeburite one and a tempered martensite one or a tempered sorbite one and has >=55HRC surface hardness as well as the prescribed part of the other surface part has a graphite, ledeburite and sorbite structure and has <=35HRC surface hardness is formed. Furthermore, a casting stage of casting cast iron or alloy cast iron having the above compsn. in a metal mold, an intermediate stage of the hardening stage of the sliding part and the local softening treatment of the part to be softened, and a tempering stage of executing tempering are carried out in order to form the above each structure on the surface layer part of the sliding part and the part to be softened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sliding member having a sliding portion, such as a camshaft which is a valve train component of an internal combustion engine, and a method for manufacturing the same.

(Prior Art) Conventionally, a sliding member such as a camshaft used as a valve mechanism of a vehicle engine has characteristics such as wear resistance and toughness because the cam part makes sliding contact with a tappet, etc. For example, camshafts are formed by chilling the surface layer of a cast iron camshaft cast using a mold. At this time, as shown in Fig. 6, the surface layer of the molten metal filled in the mold cavity is rapidly cooled to form a shell-like solidified layer, and then the mold is released and allowed to cool, so that the rapidly cooled surface layer becomes highly hard. A method of chilling the tissue is known. The steel structure of the chill layer thus formed is a mixed structure of pearlite structure and ledebrite structure.

(Problem to be Solved by the Invention) However, when forming a chill layer using such a mold, unlike when setting a chilled metal in a sand mold, the surface layer of the cast member is chilled over the entire area, and the spline is formed after casting. When cutting grooves, etc., the hardness of the machined part becomes too hard and reduces the life of the cutting tool, so it is necessary to locally soften the necessary parts to improve the life of the cutting tool. .

On the other hand, if the sliding part is a sliding part such as a cam part of a camshaft, it is necessary to further improve the sliding characteristics in order to keep up with the trend of higher speed rotation and higher output of engines.

In other words, in sliding parts such as the contact between the cam part and the tappet, which are lubricated with lubricating oil but cannot be expected to have good fluid lubrication, such as bearings, the hardness of the member itself, self-lubricating property, Pitching (
It is necessary to suppress defects such as small hole scratches on the shaft, scuffing (galling scratches), and abnormal wear as much as possible.

For this reason, in sliding parts, the mixed structure of pearlite and ledebrite in the chill layer obtained by conventional die casting is
A mixed structure of ledebrite and sorbite structures or a mixed structure of ledebrite and tempered martensitic structures with excellent toughness and wear resistance is created, and the surface hardness is increased to improve pitting resistance and scuffing resistance, while softening It was desirable that the surface hardness of the target portion be reduced by forming a structure similar to that of the non-chilled core.

(Means for solving the problem) In order to solve the problem, the present invention complies with JISFC20~
Cast iron component equivalent to FC30 or Ni 0.4~O5wt
%, Cr 0. ! +~1.0wt%, Mo
0.5-1. (The constituent material is alloyed cast iron containing a composition of
5 or more, other predetermined parts of the surface layer have graphite, ledebrite, and solbite structures, and the surface hardness is H.
A sliding member with an RC of 35 or less was constructed.

In addition, a casting process in which cast iron or alloyed cast iron having the above composition is cast in a mold, an intermediate process in which sliding parts are quenched and parts to be softened are locally softened, and a tempering process in which tempering is performed are sequentially performed. Each of the above-mentioned structures was formed in the surface layer part of the sliding part and the part to be softened.

The intermediate process of quenching is performed immediately after releasing the mold from the mold casting.
A. The sliding part, which is in a red-hot state in the temperature range above the transformation point and below 950°C, is treated by forced air cooling, and the local softening treatment is carried out at the same time as the above-mentioned quenching, so that the temperature of the part to be softened is 6.
While the part is in a red-hot state in the temperature range of 00°C to A1 transformation point, the part is heated and held at 1000°C to 1100°C to graphitize a part of the cementite constituting the ledebrite eutectic of the chill layer and to form the chill layer. While the temperature of the part to be austenitized or softened is within the temperature range of A1 transformation point or higher and 950°C or lower, the same part is heated to 10
Heat and hold at 00°C to 1100°C to graphitize a part of the cementite constituting the ledebrite eutectic and keep the residual austenite in an austenite state, and then let it cool or forcefully cool it to turn the austenite into martensite. did.

In addition, in the tempering process, the hardened sliding parts are tempered,
The martensitic portion of the softened portion is tempered at the same time.

As the sliding portion of such a sliding member, a cam of a camshaft of a valve mechanism for an internal combustion engine was used.

(Function) Toughness and fatigue strength can be improved by making the sliding part a mixed structure of a ledebrite structure obtained by chilling and a tempered martensite or tempered sorbite structure obtained by quenching and tempering, and by setting a specific surface hardness. or,
The cam portion of the camshaft also has improved scuffing resistance, pitting resistance, and wear resistance, increasing durability.

On the other hand, by decomposing and graphitizing a part of the ledebrite structure in the portion to be softened, the hardness of the surface layer is reduced and cutting becomes easier. Further, by performing these processes in parallel almost simultaneously, work efficiency can be improved.

(Example) An example of a sliding member having a sliding portion and a manufacturing method of the present invention will be described based on the attached drawings.

Figures 1 and 2 are partial cross-sectional views of a camshaft which is an example of the sliding member of the present invention. Figure 1 shows the chill layer structure after casting, and Figure 2 shows the structure after quenching and softening treatment. Surface layer structure, FIGS. 3 to 5 are process diagrams showing the manufacturing method.

As is well known, a plurality of cam parts 2 are formed in the axial direction of the camshaft 1 shown in Figure N1, and a journal part 3 is integrally formed between each cam part 2.2 and at the end of the shaft. It is set in. The cam portion 2 is provided with a cam lifter portion for raising the valve lift of the intake valve of the engine, and the contact pressure applied from a tappet etc. that slides into contact with the cam portion is particularly high at this cam lifter portion.

Such a camshaft 1 is obtained by die casting, and in the case of this example, Ni 0.4 to 0.6 wt%, Cr00
A molten cast iron alloy containing components of 5 to 1.0 wt% and Mo of 0.5 to 1.0 wt% is poured into a mold, and the surface is rapidly cooled to form a chill layer on the surface layer 1a. For this reason, the mold used for casting is, for example, 0.8 to 4.0 wt%
The mold is made of a material with high thermal conductivity such as a Cu-(:r alloy) containing Cr, and a cooling path is formed in a predetermined part inside the mold in order to rapidly cool the surface part.Then, such a mold is cast. After the cast member processed in the process is released, the cam part 2, which is a sliding part, is removed in the intermediate process shown in FIG. 3, and the journal parts 3 at both ends of the shaft are removed in the intermediate process shown in FIG. 4. Processed in parallel.

That is, the cam portion 2 is formed at 930 after being released from the mold as shown in FIG.
A hardening process is performed by forced air cooling from a red-hot state in the temperature range of .degree. C. to 980.degree. C., and a mixed structure of a ledebrite structure and a martensitic structure is formed in the chilled layer of the cam portion 2.

Meanwhile, as shown in FIG. 4, the journal parts 3 at both ends are heated by the high-frequency induction heating coil 4 for 10 minutes while the temperature range of the parts is above the A1 transformation point and below 950°C.
Locally heat from 00℃ to 1100℃ for 20 seconds to 30 seconds.
After holding it for a second, it is left to cool or forced air to soften.

Therefore, during heating and holding, a part of the cementite constituting the ledebrite eutectic in the chill layer in the same part becomes Fe5C-*3
Fe1C changes and becomes graphite (carbon C), and the retained austenite in the chill layer remains in the austenite state. Then, by cooling by air or forced air,
The austenite turns into martensite, and a structure of graphite, ledebrite, and martensite is formed in the chill layer in the same part.

After completing the intermediate process in which the cam portion 2 is hardened and the journal portion 3 at the end of the shaft is subjected to a softening process as described above, the entire camshaft 1 is subjected to a tempering process. That is, this tempering process is performed by heating in an electric furnace as shown in FIGS.
Processing is carried out by heating and holding at 0° C. for 2 hours. Therefore, the martensitic structure of the cam portion 2 changes to a tempered sorbite structure, and the surface layer structure after treatment becomes a mixed structure of a ledebrite structure and a tempered sorbite structure. For example, when tempering is performed at a low tempering temperature of about 180°C, the martensite structure changes to tempered martensite (β-martensite), and the surface layer of the same part becomes a ledebrite structure and a tempered martensite structure. The surface hardness can be HRC55 or higher.

On the other hand, in the journal parts 3 at both ends, martensite is similarly changed to a tempered sorbite structure by tempering at 600°C for 2 hours, and the surface layer structure is composed of graphite, ledebrite, and sorbite, similar to the structure of the core part 1b, as shown in FIG. The surface hardness becomes HRC35 or less.

Next, FIG. 5 is a process diagram showing the second method of softening treatment in the intermediate process of the journal part 3. In this case, the temperature range is 600°C after the cast member is released from the mold after the casting process and left to cool. High frequency induction heating is performed from a temperature below the A1 transformation point. In this case, as the temperature drops below the A1 transformation point, the pearlite part formed on the surface layer becomes austenite by high-frequency induction heating, and a part of the cementite that makes up the ledebrite eutectic becomes graphitized, resulting in the same structure as in the previous case. I can do it. Therefore, the final surface structure and surface hardness obtained by the following tempering process substantially match the structure and hardness of the core portion 1b, as in the previous example.

In this way, the structure of the cam part 2 after the quenching and tempering treatment has excellent toughness such as impact value, wear resistance, and is tough and resistant to fatigue fracture, while the workability of the softened journal part 3 is improves.

(Effects of the Invention) As described above, the sliding member of the present invention has a surface layer structure of the sliding portion with excellent wear resistance, toughness, etc., and a structure of the portion to be softened that is similar to that of the core portion. By forming a structure, a sliding member with excellent workability can be constructed. Therefore, by particularly applying it to the camshaft of a valve mechanism for an internal combustion engine, it is possible to meet the demands for higher performance of the engine.

In addition, in the manufacturing method, the hardening of the sliding part and the local softening of the part to be softened are performed at the same time, and the tempering is also performed at the same time, so that the processing work is smooth.
Productivity is also good.

In particular, as a quenching treatment, immediately after release from the mold, the A1 transformation point or higher is 95
A method of rapidly cooling and quenching a sliding part in a temperature range below 0°C, and a method of heating from a red-hot state without cooling it to room temperature in local softening treatment enable efficient processing. .

[Brief explanation of drawings]

Figures 1 and 2 are partial cross-sectional views of a camshaft, which is an example of the sliding member of the present invention. Figure 1 shows the chill layer structure after mold casting, and Figure 2 shows the quenching and softening treatment. The subsequent surface layer structure, FIGS. 3 to 5 are process diagrams showing the manufacturing method of the present invention, and FIG.
The figure is a process diagram showing a conventional manufacturing method. In the figure, 1 is a camshaft, 1a is a surface layer part, 1b is a core part, 2 is a cam part, 3 is a journal part, and 4 is a high-frequency induction heating coil.

Claims (6)

[Claims] (1) Cast iron component equivalent to JISFC20~FC30 or N
i0.4-0.6wt%, Cr0.5-1.0wt%,
The constituent material is alloyed cast iron containing a composition of 0.5 to 1.0 wt% Mo, and the surface layer of the sliding part has a mixed structure of a ledebrite structure and a tempered martensite structure or a tempered sorbite structure, and has a surface hardness. HRC55 or higher, other predetermined parts of the surface layer have graphite, ledebrite, and sorbite structures, and the surface hardness is HRC35.
A sliding member having a sliding portion as follows. (2) Cast iron component or N equivalent to JISFC20~FC30
i0.4-0.6wt%, Cr0.5-1.0wt%,
A casting process in which a sliding member made of alloyed cast iron containing a composition of M00.5 to 1.0 wt% is cast in a mold, and an intermediate process in which the sliding part is quenched and the parts to be softened are locally softened. , a tempering process is performed sequentially, and the surface hardness of the surface layer of the sliding part is changed to a mixed structure of a ledebrite structure obtained by die casting and a tempered martensite structure or a tempered sorbite structure obtained by quenching and tempering. A method for manufacturing a sliding member, characterized in that the surface hardness of the sliding member is HRC55 or higher, and the surface hardness of the portion to be softened is made of graphite, ledebrite, and sorbite structure to have a surface hardness of HRC35 or lower. (3) The quenching treatment in the intermediate step is characterized in that the sliding part, which is in a red-hot state in a temperature range of A_1 transformation point or higher and 950° C. or lower, is subjected to the treatment by forced air cooling immediately after mold release from mold casting. A method for manufacturing a sliding member according to claim 2. (4) The local softening treatment in the intermediate step is carried out in parallel with the quenching treatment, and the part to be softened is heated to 1000°C while the temperature of the part to be softened is in a red-hot state in the temperature range of 600°C to A_1 transformation point. ℃ ~ 1100 ℃ to graphitize a part of the cementite constituting the ledebrite eutectic of the chill layer and turn the pearlite part of the chill layer into austenite, or the temperature of the part to be softened is above A_1 transformation point and below 950 ℃ 1000 ml of the same part while the temperature is within the
It is characterized by heating and holding at a temperature of ℃ to 1100 ℃ to graphitize a part of the cementite constituting the ledebrite eutectic and keeping the residual austenite in an austenite state, and then cooling the austenite by cooling or forced air cooling to turn the austenite into martensite. The method for manufacturing a sliding member according to claim 2. (5) Manufacturing the sliding part according to claim 2, wherein in the tempering step, the martensitic portion of the softened part is tempered simultaneously with the tempering of the hardened sliding part. Method. (6) The sliding member is a camshaft of a valve mechanism for an internal combustion engine, and the sliding part is a cam according to claim 2, 3, 4, or 5. A method for manufacturing a sliding member.