JPS62161941A - Sliding member having superior sliding characteristic - Google Patents

Abstract

PURPOSE:To improve the durability and sliding characteristics by combining a sliding member made of a sintered alloy consisting of specified amounts of C, P, Mo, B, Cr, NbC, TaC and Fe with other sliding member having a nitride layer. CONSTITUTION:The titled sliding member is obtd. by slidably combining the 1st sliding member 1a made of a sintered alloy having >=7g/cm<3> density with the 2nd iron-base sliding member 2 having a nitride layer formed on the sliding surface 2a. The sintered alloy consists of, by weight, 1-4% C, one or more among 0.5-2% P, 2-6% Mo and 0.5-3% B, 4-7% Cr, 5-20% NbC and/or TaC and the balance Fe.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to sliding members that require excellent surrounding characteristics, such as rocker arms and camshafts used in engine valve mechanisms. Regarding improvement of members.

(Prior art) For example, in an engine valve mechanism, the rocker arms (or tappets) and camshafts must undergo harsh sliding movements in order to maintain or fully utilize engine performance. It must be able to withstand the conditions, but especially in recent years, with the adoption of FR mechanisms such as multiple valve n structures and variable valve timing mechanisms, and increases in valve lift, it is necessary to have better sliding than ever before. There is a growing need for sliding members that have dynamic performance and durability. Therefore, even though sliding parts such as rocker arms and V-lifts used to have sufficient durability, in recent years, engines have become more complex or have higher performance. Although it depends on other conditions such as the quality of the oil, generally speaking, the wear of the sliding parts becomes noticeable, and in extreme cases, it even causes a decrease in engine performance.

On the other hand, in recent years, composite rocker arms such as aluminum alloy rocker arms have been manufactured in order to reduce the weight of each component. The main body of the rocker arm, which was conventionally made of cast iron, is made of aluminum alloy, and a wear-resistant chip material is fixed to only the sliding part of the rocker arm. This makes it possible to reduce the weight of the entire engine and, by extension, the weight of the engine. In that case, a highly durable sintered alloy is usually used as the tip material for the rocker arm, but even with this type of sintered alloy tip material, for example, an engine with low speed and low oil/water temperature is used. It has been confirmed that when engine oil of inferior quality is used under certain conditions, the degree of wear of the tip material is several orders of magnitude greater than under normal conditions.

Conventionally, it has been known that in order to deal with such problems, it is sufficient to disperse a large amount of hard particles in the material of the above-mentioned sintered alloy chip material. There is a sliding member made of a tA-based smoked alloy disclosed in Japanese Patent No.-118859. This is due to the specific composition of c,
According to this, it has a structure in which WC (tungsten carbide) and NbC (obcarbide) are uniformly dispersed in a sintered alloy matrix consisting of cr, x+, Mo, P, and Fc. Above WC,N
Since hard particles such as bC are dispersed and uniformly present in the structure, wear resistance is improved compared to a sliding member simply made of a sintered alloy.

However, l! made of iron-based sintered alloy made by dispersing WC etc. as mentioned above! When the No. 11 member is employed as a tip material for a rocker arm sliding portion, for example, the following problem arises in relation to the cam sliding surface of a camshaft serving as a mating member. In other words, conventionally, in order to improve the wear resistance of the left side of the force cam, the sliding surface of the cam is subjected to nitriding treatment such as soft nitriding treatment to form a nitride layer. When a camshaft having a nitride layer on the sliding surface and a chip material containing the above-mentioned WC etc. are slid together, the WC present in the structure of the chip material and the cam sliding surface Since it is not compatible with the nitride layer, the wear resistance of the chip material and the cam sliding surface decreases, making it impossible to ensure sufficient durability.

(Object of the Invention) The present invention addresses the above-mentioned conventional situation by combining one sliding member made of a sintered alloy and the other sliding member having a nitride layer in the sliding direction. In such cases, by adopting a sintered alloy that is compatible with the nitride layer as the material for one of the sliding members, a sliding member with excellent sliding properties and sufficient wear resistance as a whole can be realized. The purpose is to

(Structure of the Invention) In order to achieve the above object, the present invention provides a first sliding member made of a sintered alloy and a second sliding member made of iron having a nitride layer formed in the sliding direction. The sliding members that can be combined together are characterized by the following structure. That is, the sintered alloy constituting the first sliding member has a weight C: 1.0 to 4.
．． 0%, P: 0.5-2.0%, Mo: 2. 0
~6.0%, and at least one of B: 0.5 to 3.0%, Cr: 4.0 to 7.0%, NbC and T.
A sintered alloy containing 5.0 to 20.0% of one or both of aC, the remainder being substantially iron, and having a density of 7.0Q/at or more is used.

In that case, this sintered alloy contains V, Co, Ni, and Cu as components other than the above components, as will be described later.

Any one or two or more of 3n is 0.5 to 8.0
It is preferred to add % deuterium. Further, the content of Si and Mn contained as unavoidable components is 1.0% by weight or less.

Here, the reason why the composition and density of the sintered alloy are limited as described above is as follows.

C (carbon): 1.0 to 4.0% (heavy metal %: same below).

If the C content is less than 1.0%, there will be insufficient liquid phase during the production of the sintered alloy, and the sintered density will be less than 7.0 g/cIIi, resulting in a sharp decline in the wear resistance of the finished product. . on the other hand,
If the content exceeds 4.0%, there will be too many liquid phase protrusions, which will cause deformation during sintering, and the number of carbide gaps will increase, making the material brittle, making it unsuitable for practical use.

P (phosphorus) = 0.5-2.0%.

P forms a ternary eutectic alloy of Fe-P-C, and the P content m
If it is less than 0.5%, the sintered density will be 7.5% due to insufficient liquid phase. OQ/cI+! If it becomes less than 100%, the wear resistance will decrease rapidly. On the other hand, if the above content exceeds 2.0%, liquid phase m
If there is too much of it, it will deform during sintering and become brittle, making it unusable.

MO (molybdenum): 2.0 to 6.0%.

While MO strengthens the base metal, it forms a composite carbide with Fe to improve wear resistance. Also, Fe-MO
By heating above the eutectic temperature of -C, a liquid phase is generated, which improves sinterability. However, if the content of MO is less than 2.0%, the above effect is not achieved, and if it exceeds 6.0%, the carbide becomes coarse and brittle, and the wear resistance is rather reduced.

B (boron) = 0.5-3.0%.

B forms a ternary eutectic mother alloy of Fe-B-C, and Fe'
, is an element that combines with C to form a hard phase and lowers the melting point, and if it is less than 0.51%, Fe -
Since the ternary eutectic thickness of B-C decreases, wear resistance and seizure resistance deteriorate. If it exceeds 3゜0*lff1%, it becomes very brittle and becomes impractical. Therefore, 0.
It is necessary that the content be in the range of 5 to 3.0% by weight.

Cr (chromium): 4.0 to 7.0%.

Cr is useful for strengthening the base, particularly improving toughness, and is preferable because it combines with C to form a hard layer (carbide). In this case, if the Cr content m is less than 4.0%, the formation group of the hard layer will be insufficient, and if it exceeds 7%, the effects such as improving toughness will be saturated and the excess will be wasted.

Nb C (obcarbide) and Ta C (tantalum carbide): 5°0 to 20 for either one or both
．． 0%.

NbC and TaC exist as carbides and improve wear resistance. In particular, since these have good compatibility with the nitride layer, they have excellent wear resistance even when the nitride layer is formed on the sliding surface of the mating member. Also, Nb C, T
The particle size of aC is preferably 10 μm or less. The reason is that in the case of NbC and TaC, when dispersed in FO-based sintered alloy and sintered,
This is because it is extremely stable at a sintering temperature of 0.degree. C., and exists with the same particle size as when it was added. In the case of other carbides such as chromium carbide and molybdenum carbide, they become composite carbides with Fe at the above sintering temperature, or partially melt to become coarse carbides.

If the content of Nb C and Ta C is less than 5.0%, wear resistance is insufficient, and if this content exceeds 2.0%, the liquid phase ratio decreases relatively and the density decreases to 7.0%. (Since it is less than 1/ctA, wear resistance decreases and it is also economically disadvantageous.

Density near, 0g/ctA or more.

The density of the fired crystal is 7. If it is less than Oa/d, the number of pores increases and the wear resistance decreases.

■ (Vanadium), Co (Cobalt), Ni Nickel)
, Cu (copper), Sn (tin): 0.5 to 8.0% of one or more of them.

If part of the liquid phase sintering is performed, the structure of the base metal becomes coarse and the wear resistance, especially the seizure resistance, decreases, but in that case, the above-mentioned V
, Co 2 , Ni 2 , Cu 2 , and Sn make the structure of the base metal finer, so that it is possible to prevent the above-mentioned decrease in wear resistance.

Among these, V is also effective in increasing the tempering resistance and preventing secondary hard cavities due to tempering. If the content of these elements is less than 0.5%, the above effects will be reduced;
Since the effect does not change even if the amount exceeds 8%, it is more economical to suppress the chain content to 8% or less.

Incidentally, the above-mentioned sintered alloy is manufactured, for example, as follows. That is, an alloy powder material with a particle size of 150 mesh or less (containing each component except Nb C and Ta C in the above configuration) and Nb C and Ta C with an average particle size of 10 μm or less
are mixed so that the composition of the sintering material is as described above, and then 1 to 10% of camphor or paraffin is added as a binder.
Add 2% by weight and mix, and add this to 1 to 6 j/ct
After compacting at a pressure of A, pre-sintering is performed at a temperature of 300 to 800°C for 30 to 90 minutes in a non-oxidizing atmosphere such as hydrogen gas or inert gas, and then at a temperature of 1050 to 1150°C.
Sintering is performed for 10 to 90 minutes in a non-oxidizing atmosphere such as hydrogen gas or vacuum. If heat treatment is necessary, it is further heated in a vacuum at 850 to 1000°C, then quenched by nitrogen gas cooling, and then tempered in nitrogen gas at a temperature of 500 to 650°C for 30 to 120 minutes. I do.

(Effects of the Invention) According to the present invention, in a configuration in which a first sliding member made of a sintered alloy and a second sliding member having a nitride layer formed on the sliding surface are combined, the first sliding member described above is combined. Nb contained in the sintered alloy of the sliding member
The hard particles made of C or TaC exhibit extremely good compatibility with the nitride layer of the second oscillating member and have excellent wear resistance. ! ! This results in a significant reduction in wear on the decoy portion of the moving member. As a result, a surrounding member with excellent durability and sliding properties can be realized.

(Example) Examples of the present invention will be described below. In addition, each of the following examples is based on a sintered alloy chip material (the first
The present invention is applied to a sliding member) 1a and an iron-based camshaft (second sliding member) 2 having a nitride layer on a cam sliding surface 2a in sliding contact therewith.

First, the rocker arm chip material 1a was manufactured as follows. That is, the particle size is 200 mesh or less, Cr: 12.5% (1,000 m%, less than 1), Mn: 0
．． 1%, Si: 0.05%, and the balance is Fe.
Alloy powder material with a particle size of 150 mesh or less and C
:4.2%, P:2.4%, MO:9.5%, Si
:0.2%, Mn:0.05%, and the balance is Fe, and NbC or T having an average particle size of 1 μm.
At least one type of aC powder was blended so that the chemical components and composition after sintering were as shown in Tables 1 (I) and (II), respectively, to be described later. At this time, one or more of V, Co, Ni, CO, and Sn were added as necessary, but these are shown in Table 1 (I), (IF
) in the "Others" section (Examples 5 to 1)
1). Next, after completing the above formulation, 1.5 times R of camphor dissolved in toluene was added as a binder.
% was added, kneaded, and dried. And this is 4.5
Compacting into a predetermined chip shape with a compression pressure of t/cd,
After that, it was placed in a hydrogen gas atmosphere furnace and heated at 10°C/min.
The temperature was raised to 300°C at a heating rate and held for 30 minutes, then further raised to 1090°C at a heating rate of 10°C/min, held for 20 minutes, and then furnace cooled to obtain the results shown in Table 1 (
Chip materials for rocker arms according to Examples 1 to 3 shown in I) were obtained. In addition, for the chip materials of Examples 4 to 11, after completing the above steps, the chip materials were further vacuumed at a degree of vacuum of 5
In a 10-2 TOrr vacuum furnace, the temperature was increased to 900°C at a heating rate of 7°C/min. After being held in that state for 60 minutes, nitrogen gas quenching was performed, and the temperature was raised again at 10°C/min. After raising the temperature to 570°C at a temperature rate and holding it for 90 minutes,
It was slowly cooled.

On the other hand, the camshaft 2 was manufactured as follows.

First, a cast iron camshaft material (composition C: 3.5%, Si: 1.85%,
Mn: 0. 72%, Cr: 0°2%, P: 0.0
2%, S: 0.05%, balance: iron), each part of the material is processed into a predetermined shape and dimension, and then the sliding surface 2a of the cam part is subjected to nitrocarburizing treatment using a salt bath. This formed a nitride layer, thereby obtaining the camshafts of Examples 1 and 2.

Further, in the case of the camshafts of Examples 3 to 11, an oxidation treatment was further performed after the above-mentioned nitriding treatment.

For the above nitriding treatment, a salt bath soft nitriding treatment method using cyanides such as Na CN and KCN was adopted, but the treatment temperature in that case was 500°C to 630°C, and the treatment time was 0.5°C.
3 hours. The reason for this is that if the treatment temperature is less than 500°C, the reaction will be slow and a sufficient compound layer will not be obtained, and if the temperature exceeds 680°C, the base material structure will decompose and the hardness will decrease. This is because the compound layer is not sufficiently formed if the treatment time is less than 0.5 hours, and on the contrary, the thickness of the compound layer hardly changes even if the treatment time is more than 3 hours.

Further, as the above-mentioned oxidation treatment, for example, KOH is used.

Using a hydroxide whose main component is NaOH at a temperature higher than the melting point of the component (360.4°C for KOH, 328°C for NaO2), or KC at 380°C.
The treatment was carried out by immersion in a J2 salt bath 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 salt bath nitriding treatment may decompose.
This is also because the amount of oxide formed on the surface does not change even if the treatment is performed for more than one hour.

Finally, the compositions of the rocker arm tip material 1a and the camshaft 2 obtained as described above, and the test results obtained by assembling these parts into an actual automobile and examining their effects on wear resistance, will be discussed in this section. Tables 1 (1) and (I) show a comparative example (the sintered alloy constituting the chip material contains neither NbC nor TaC) in Table 1 (I [[)]. In this case, the operating conditions for the wear test are as follows. Engine speed: 200O
rpm.

Oil temperature: Low oil temperature around 50℃, Oil: Commercially available product, Test car: 1800cc PG car. Also, Table 1 (D) ~ (II
The symbol ☆ shown in I) as the material of the camshaft is
Hand ratio: C: 3.5%, Si: 1.85%, Mn: 0
．． 72%, Cr: 0.2%, P: 0.02%, S: 0
．． 05%, balance: indicates lunar quality consisting of Fe.

(Hereinafter, blank space) As shown in these tables, according to the present invention, even in the case of Example 1, which has the largest amount of wear among the Examples, the comparative example has the least back wear ■. It was observed that the wear resistance was better overall than in Example 4, and in the opposite case, for example, when comparing Example 11 and Comparative Example 1, the difference was clear. did.

[Brief explanation of drawings]

Talented 1f! 5 is a front view showing an example in which the present invention is applied to a rocker arm chip material and a camshaft. 1a...First sliding member (chip material for rocker arm)
, 2... second sliding member (camshaft), 2a...
Murderous side.

Claims (1)

[Claims] (1) C: 1.0 to 4.0% and P: 0.5 to 4.0% by weight
2.0%, Mo: 2.0~6.0%, and B: 0.5~
At least one of 3.0% and Cr: 4.0 to 7.
0%, and 5.0 to 20.0% of either or both of NbC and TaC, the balance being substantially iron and having a density of 7.0 g/cm^3 or more. A sliding characteristic characterized by a sliding combination of a first sliding member made of a bonded metal and a second iron-based sliding member having a nitride layer formed on the sliding surface. Excellent sliding member.