JPS62156262A - Production of sliding contact member - Google Patents

Abstract

PURPOSE:To obtain a crack-free sliding contact member having superior sliding characteristics by heat treating a stock having a sliding part made of chilled cast iron at a prescribed temp. for a prescribed time. CONSTITUTION:Stock for a sliding contact member having a sliding part made of chilled cost iron is prepd. by chilling. The stock is heat treated at 850-870 deg.C for 10-30min to spheroidize carbide in the sliding part made of chilled cast iron. The surface of the sliding part is then nitrided to form a nitride layer and the stock is slowly cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a sliding contact member such as a cam shirt i., particularly a sliding contact member made of chilled cast iron and having a compound layer on its sliding surface.

(Prior art) Sliding members used under extremely harsh sliding conditions, such as camshafts used in engine valve mechanisms, generally have excellent behavior characteristics. Therefore, when manufacturing this type of sliding contact member using cast iron material, for example, by chilling the part of the product that will become the sliding part using a cold metal etc. at the time of &63a, The hardness, that is, the wear resistance of the sliding portion is improved in advance.

By the way, the improvement in the hardness or wear resistance of the sliding part by such chilling treatment is due to the chilled sliding part (
Highly hard carbide (t:!mentite: F
This is due to the generation of a large amount of c 3 C), and it is known that in this case, if a compound layer is formed on the surface of the chilled portion, performance such as wear resistance can be further improved. Therefore, in the past, the 13th part chilled as described above is subjected to nitriding treatment, or in some cases, after the nitriding treatment, further oxidation treatment is performed to form a compound layer on the surface of the sliding part. However, in this case, the following problems have arisen.

That is, since the above-mentioned nitriding treatment and oxidation treatment are usually performed under heated conditions, after the treatment, it is necessary to cool the material of the sliding contact member by immersing it in hot water of, for example, 80°C. However, at that time, cracks had occurred in the delta part, that is, the sliding part of the indirect member. This is because cementite (carbide) in the chilled structure is formed into dendritic dendrites during the chilling treatment of the part that is to become the sliding part, and the notch action of each separate tip of the dendrite and the dendrite described above occur. Cementite and barley in 4111i]
This is caused by the difference in thermal expansion that exists between the two.

In addition, if a crack occurs in the chilled sliding part of a cast iron sliding member as described above, □ The cracks formed on the surface (sliding surface) of the sliding part by the above nitriding or oxidation treatment. The cracks propagate to the surface of the compound layer, resulting in various problems such as peeling of the compound layer during sliding and significantly deteriorating sliding properties.

(Object of the Invention) The present invention addresses the above-mentioned problems related to the manufacture of sliding contact members such as camshafts, particularly l3 contact members made of chilled cast iron and having a compound layer on the sliding part. By granulating the acicular light QW portion of the carbide in the chilled structure of the moving part, the notching effect is prevented or suppressed, and the thermal distortion in the boule coarse weave that is likely to occur in the final cooling process is also prevented. This prevents the generation of cracks in the sliding part due to the notch action of the carbide tip and the thermal strain, and creates an IFI without this type of crack.
It is an object of the present invention to provide a sliding contact member with excellent JJ characteristics.

(Structure of the Invention) In order to achieve the above object, the method for manufacturing a sliding contact member according to the present invention is characterized by having the following structure.

That is, using a material for a sliding member having a sliding part made of chilled vJ iron, the part of which should become the sliding part has been chilled, and heating this material at a temperature of 850°C to 870°C for 10 to 30 minutes. Hold and slowly cool.

As a result, the shape of the gentrite tip in the chill structure of the sliding part, that is, the shape of the carbide tip changes from a set shape to a granular shape, so that the notch effect of the carbide tip is eliminated. . Next, after performing the carbide granulation treatment in this way, a nitride layer is formed by performing a nitriding treatment on the surface of the chilled cast iron sliding part of the above material, and then the material is slowly cooled. (e.g. cooled in the atmosphere).

In that case, this slow cooling helps or prevents the thermal distortion of the cementite and pearlite in the chilled structure, which have different coefficients of thermal expansion, so that the notching effect due to the granulation of the tip of the carbide is eliminated, and the sliding This effectively prevents the occurrence of cracks in the moving parts. Here, after the above-mentioned nitriding treatment, an oxidation treatment may be further performed as necessary, and then the material may be slowly cooled. In addition, it is preferable that the cooling rate after this nitriding treatment or oxidation treatment be 5°C/second or less, but if the cooling rate exceeds 5°C/second, the cement in the chilled structure will This is because thermal distortion occurs due to the difference in thermal expansion between pearlite and pearlite, and cracks are likely to occur in the chilled structure and thus in the compound layer on the surface.

For the above nitriding treatment, for example, a salt bath nitriding method using cyanides such as NaCN, KCN, etc. is adopted, and in that case, the treatment temperature is 500°C to 630°C, and the treatment time is 0.
．． The duration is 5 to 3 hours. The reason is that at a processing temperature below 500°C, the reaction is slow and a sufficient compound layer cannot be obtained.
Furthermore, if the treatment temperature exceeds 630°C, the matrix structure will decompose and the hardness will decrease. Furthermore, if the treatment time is less than 0.5 hours, the compound layer will not be formed sufficiently, and if the treatment time exceeds 3 hours, the hardness will decrease. This is because the thickness of the compound layer hardly changes even if the compound layer is subjected to the treatment.

Further, as the above-mentioned oxidation treatment, for example, KO)I.

Using a hydroxide whose main component is NaOH, it is carried out at a temperature higher than the melting point of the component (360.4°C for K O+-1, 328°C for NaOH1) or in a KCJl salt bath at 380°C. This is done by soaking for 10 minutes, but in that case,
It is desirable to set the upper limit of the treatment temperature to 500°C or less. This is because if the treatment temperature exceeds 500°C, the compound layer formed by the above salt bath nitriding treatment may decompose, and the old oxide formed on the surface does not change even after treatment for more than 1 hour. It is from.

(Effects of the Invention) As described above, according to the manufacturing method of the present invention, when manufacturing a cast iron sliding contact member having a compound layer on the active surface, the chill structure of the material portion that is to become the sliding part is reduced. Since the tip of the carbide formed inside is granulated, its notching effect is prevented, and the thermal distortion within the chilled structure that tends to occur during the final cooling process of the material after the compound layer is formed is prevented or alleviated. will be done.

As a result, it is possible to prevent cracks from occurring in the chilled sliding portion, and it is possible to obtain a sliding contact member that is free of this type of crack and has excellent sliding characteristics.

(Example) The present invention will be described in detail below. Note that this embodiment relates to the manufacture of a camshaft having a sliding portion made of chilled cast iron.

First, carbon (C): 3.5%, silicon (Si):
1.4 weight R%, manganese (Mn): 0.6 sets a%,
Chromium (Cr): 0.3% by weight, phosphorus (P): 0.0
8 [F1%, sulfur (S): 0.03% by weight, and the balance is iron (Fe) J, a part of which is shown in Fig. 1, is used as cast iron material A. At this time, the active surface A1 is cast by using a cold metal on the part of the camshaft material Δ corresponding to the cam sliding part A1.
Chilling treatment is applied to the parts that should become . As a result, the portion A1 is chilled, and its tissue structure is
A chilled structure is formed in which carbide (carbide represented by 3G) and barley 1- coexist, but in this case, cementite exists in the form of dendrites with needle-shaped tips.

However, the camshaft material A cast as described above
Next, by heating and holding at a temperature of 860° C. for 15 minutes, a granulation treatment is performed as indicated by the symbol ■ in FIG. As a result, the above l! ! The shape of the tip of the dendrite existing in the chilled structure of the moving part A1 changes from needle-like to granular, and as a result, the notch action by the tip of the dendrite is prevented. At this time, heating at a temperature of less than 850° C. for less than 10 minutes is not preferable because the dendrite tips will not be sufficiently granulated and needle-like portions will remain in some portions. Also, the heating temperature is 87
If the temperature exceeds 0° C. and the heating time exceeds 30 minutes, the chilled structure will decompose, making it impossible to ensure sufficient hardness. Therefore, the heat treatment in this case is 850°C to 870°C.
It is necessary to heat for a short time of 10 minutes to 30 minutes in the temperature range of °C.

Next, the material subjected to the heat treatment (granulation treatment) (1) is left to cool in the atmosphere, and then machined to produce a secondary material with a more precise camshaft shape. After degreasing the entire secondary material produced in this way, it was preheated at a temperature of 360°C for 60 minutes, and then the first
As shown by the symbol ■ in the figure, this was nitrided by immersing it in a cyanide salt bath at 600°C for 90 minutes to form a nitride layer on the surface of the chilled weave of the sliding part A1. form. Furthermore, in this example, after the above-mentioned nitriding treatment, the secondary material was immersed in a potassium chloride salt bath at 380°C for 10 minutes to perform an oxidation treatment as indicated by the symbol ■ in Fig. 1, and then exposed to the atmosphere. Allow to cool (indicated by reference numeral IV in the figure). At this time, specifically, by setting the cooling rate to 5° C./second or less, the thermal strain of cementite 1 to pearlite in the chilled structure with a coefficient of thermal expansion of n is relaxed.

The sliding r on the camshaft obtained as above
Microscopic photograph of the metal structure of A (chilled part) (()1 ratio 400
Fig. 2 shows the double version. In this photograph, the compound layer formed on the top layer of the coarse metal weave in the chilled part is omitted. From the photograph in Figure 2, it can be seen that according to the above configuration, the tips of the dendrites (the thin, white parts shown in multiple places in the same photograph) are granulated, resulting in a chilled part of the metal structure without cracks. It was confirmed that

For comparison, Fig. 3 shows a micrograph (400x magnification) of the metal structure of the chilled cast iron sliding part when a camshaft was manufactured under conditions partially different from the method of the present invention.
indicates 1°. This photo shows a sample similar to the above example, except that the dendrites were not granulated as described above, and the final cooling process was rapid cooling (immersion in 80°C warm water) instead of slow cooling. In this case, the dendrites shown in white in the same photo have a C1 shape, and there are many large and small cracks (parts shown in black). The compound layer at the top of the metal structure where the crack is the chilled part (approximately 1/2 inch from the top in the same photo)
At the bottom of 3, it was observed that the black part and white part, which appear to extend parallel to each other in the horizontal direction, had reached the bottom.

Furthermore, FIGS. 4 and 5 show micrographs at the same magnification as above of the metal structure in the sliding part (chill part) when the dendrite granulation treatment was carried out under conditions different from those of the present invention. Of these, the photo in Figure 4 shows carbon: 3.1% by weight, silicon: 1.8% by weight, manganese 20.5% by weight,
This is obtained by heating and holding a chilled cast iron camshaft material at 840°C for 5 minutes, consisting of 0.2% chromium, 0.08% sulfur, 1% sulfur, and the balance being diiron. However, in this case, rKI confirmed that the granulation of the tip of the dendrite in the metal structure in the chilled part was incomplete, leaving nail-shaped dendrites. In addition, the photograph in Figure 5 shows carbon = 3.81m%, GJ Ii"18:
1, 1 flfffi%, mankan: 0.8 weight 1%,
When a chilled cast iron camshaft material consisting of 0.4% chrome co, 0.06% phosphorus, 0.05% sulfur, and 0% di-iron was heated and held at 880°C for 40 minutes. However, in this case, the tip of the dendrite does not become granular, and it is observed that part of the metal structure in the chilled part decomposes and graphite (black part in the photo) is precipitated in the structure. Ta. From these results, it has been found that short-time heating for 10 minutes to 30 minutes in the temperature range of 850° C. to 870° C., as described above, is appropriate for the granulation treatment of dendrites.

[Brief explanation of drawings]

1 and 2 show embodiments of the present invention.
The figure shows a chilled cast iron camshaft (
A process diagram showing a part of the material (sliding contact member) and each step after chilling treatment, FIG. This is a micrograph with a magnification of 400 times showing an enlarged view of the metal structure in a longitudinal cross section of (omitted). In addition, Figures 3 to 5 are photographs in place of drawings showing comparative examples in which sliding contact members were manufactured under conditions different from those of the present invention, and the longitudinal cross-sections of the metal structure in the surface layer of the active part are shown as above. These are micrographs shown enlarged at the same magnification. A...Cast iron sliding contact member (camshaft) just before granulation treatment, Δ1...)2! Choribe.

Claims (1)

[Claims] (1) A method of manufacturing a sliding contact member made of cast iron having a compound layer on the sliding surface, wherein the sliding member has a sliding part made of chilled cast iron where the portion to become the sliding part is chilled. Using the material of the contact member, perform a granulation treatment to granulate the carbide in the chilled cast iron sliding part by heating and holding this material at a temperature of 850 ° C to 870 ° C for 10 to 30 minutes, and then, A method for manufacturing a sliding contact member, characterized in that the surface of the sliding portion is subjected to nitriding treatment to form a nitride layer, and then the material is slowly cooled to obtain the sliding contact member.