JPH0264211A - Rocker arm - Google Patents

Abstract

PURPOSE:To improve abrasion resistance and scaffing resistance by adapting cast iron composed of specified amounts of elements, and in which carbide mainly made of Cr is evenly precipitated in perlite and/or mertensite base to an abutting part. CONSTITUTION:Elementary composition of cast iron is 2.5 to 3.7wt% of C, 2.1 to 3.5wt% of Si, 1.1 to 1.5wt% of Mn, 10 to 20wt% of Cr, 0.3 to 0.7wt% of Ni, 0.3wt% or less of P, 0.1wt% or less of S and remainder, Fe and inevitable impurity. Carbide mainly having Cr is evenly precipitated in perlite and/or mertensite base. The thus produced cast iron is adapted at least to an abutting part, so that excellent abrasion resistance and scaffing resistance are obtained. Excellent ability is showed particularly when the cast iron is used for an engine on which high load is exerted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a rocker arm made of cast iron material with high wear resistance and scuffing resistance.

[Prior Art] Rocker arms that come into contact with camshafts and valves under high surface pressure must have high wear resistance. Conventionally, the rocker arm body or the tip of the contact area has been made of chilled cast iron, cast steel, sintered alloy, etc. is used.

[Problems to be Solved by the Invention] However, in the case of rocker arms manufactured from these materials, in the case of sintered alloys, sintered chips are brazed or sintered to a cold forged steel body; Costs were rising. Furthermore, in the case of chilled cast iron and cast steel, when used in today's engines that are becoming increasingly high-performance and high-load, significant wear occurs due to increased contact surface pressure, and the wear resistance of these conventional materials is no longer sufficient. It's coming.

On the other hand, 25~
There is cast iron containing 35% Cr, but because of its tendency to precipitate ferrite, it still has poor wear resistance when used in high-speed, high-load engines.

[Means for solving the problems] The present invention has a component composition of C: 2.5 to 3.7% by weight.
, Si: 2.1~3.5%,)In: 1.1~
1.5%, Cr: 10-20%, Ni: 0.3-0.
7%, P: 0.3% or less, S: 0.1% or less, and W as necessary) 10, V, Nb, Ta, Ti,
13: '1 to 10% of one or more types, balance Fe
The above-mentioned problem is solved by providing a rocker arm in which at least the abutting part is made of a cast iron material consisting of C and unavoidable impurities and in which carbide mainly composed of C is uniformly precipitated in a pearlite and/or martensite base. be.

In the rocker arm of the present invention, the tip of the contact part with the camshaft or valve can be made of cast iron and combined with the steel body or aluminum body by means such as brazing or casting, but it is preferable to reduce the manufacturing cost. It is integrally molded by casting using a shell mold or lost wax mold in order to lower the weight.

In addition, cast iron has sufficiently excellent wear resistance in its as-cast state with a pearlite base, but when it is hardened with a quenched martensite base, a mixed base of pearlite and martensite, or as-cast or nitrided after quenching, the surface becomes highly wear resistant. Even higher wear resistance can be obtained by forming a hard nitride compound layer.

The reason why the component composition was limited as described above will be explained below.

The C component solidly dissolves in the base to strengthen it, and (Cr-F
e) Forms hard carbides mainly composed of Cr such as 703 and other carbides, which have the effect of improving wear resistance.

If it is less than 2.5%, the amount of carbide precipitated is insufficient and wear resistance cannot be obtained, and if it exceeds 3.7%, the amount of carbide precipitated is excessive, resulting in excessive aggressiveness to the mating material, or machining. Sex also gets worse.

The Si component is well known as an element that suppresses the precipitation of carbides and promotes graphitization, but it has been found that when added to high Cr cast iron, it has the effect of granulating carbides. If it is less than 2.1%, the effect of carbide granulation cannot be obtained, and if it exceeds 3.5%, the base becomes ferrite, which reduces wear resistance and also causes embrittlement of the material.

) The In component solidly dissolves in the matrix to strengthen it, toughen the material, and at the same time increase the tendency of cementite and Fe-Cr composite carbide to become granular. If it is less than 1.1%, these effects cannot be obtained, and if it exceeds 1.5%, there is no significant improvement in the effect even if it is added beyond 1.5%, which is economically disadvantageous, and also causes embrittlement of the material during quenching.

The Cr component solid-solves in the matrix to strengthen it and improve heat and corrosion resistance. Furthermore, the cast iron material of the present invention is characterized by a high Cr content, and forms carbides mainly composed of Cr such as (Cr-Fe) 703, which has high hardness and exhibits excellent wear resistance. . If it is less than 10%, the amount of carbide precipitated is small and the wear resistance is poor.

Moreover, if it exceeds 20%, the base tends to become ferrite, resulting in a decrease in wear resistance.

The old component has the effect of densifying and strengthening the matrix and improving hardenability. If it is less than 0.3%, these effects cannot be obtained, and if it exceeds 0.7%, the effect is saturated and it becomes economically disadvantageous.

The P component is 0.3% or less, and the S component is 0.1% or less, but if both exceed these ranges, the material becomes brittle.

If the cast iron material of the present invention is manufactured as a rocker arm or rocker arm chip from the above components and the balance Fe and unavoidable components normally included in cast iron, it will become a pearlite base in the as-cast state, and it will become a martensite base by quenching or a martensite base by nitriding treatment. Surface hardening provides good sliding performance with cams and valves. However, if higher wear resistance is required depending on the sliding environment with these mating materials, WSNo, V, Ni), ra, Ti, 3
1 to 1 or more carbide-forming elements such as
Contain 10%. If it is less than 1%, there will be no effect of improving wear resistance, and if it exceeds 10%, it will be economically disadvantageous.

[Example] The present invention will be explained below using examples.

(Test method) Molten metals of 1450 to 1550°C with different blending compositions were cast into lost wax molds, and the cast iron materials of the present invention having compositions of Nα1 to 12 shown in Table 1 and comparative cast iron materials having compositions of Nα13 to 16 were cast. Manufactured a rocker shaft type rocker arm. (
In the comparative material, the portion marked with an X is out of the composition range of the present invention. ) These were left as cast and then oil quenched on the entire surface at 900°C for 60 minutes, and after quenching, they were nitrocarburized in a salt bath at 580°C for 90 minutes.
Base structure observation, hardness measurement, and actual machine durability test were conducted. The durability test was conducted using a 4-cylinder OHC engine with each rocker arm and a cast iron camshaft with a chilled nose (C: 3.3
, Si: 2.2, Mn: 0.75, P: 0
．． 18, S: 0°06, Cu: 0.21, Cr: 0
．． 85.80: 0.19, [3:0.04, Fe:
Incorporated with the remaining weight% or more, oil used: 5A
E10W, rotation speed: 11000rp, test time:
It was operated for 200 hours, and the wear R on the pad surface of the rocker arm made of the sample material and the amount of wear on the nose surface of the camshaft, which was the mating material, were measured.

(Test results) As can be seen from the measurement results shown in Table 1, in the comparison materials, there was a large amount of friction in either or both of the rocker arm itself and the camshaft, which is the mating material, resulting in scuffing. In contrast, in the material of the present invention, the amount of wear on the rocker arm is small, and the amount of wear on the camshaft is also relatively small.

As for the base hardness, the materials of the present invention that have been quenched have an HRC of 62 or higher, and those that have been tempered by nitriding after quenching have a softened base, but the nitrided layer on the surface becomes extremely hard, as is well known.

Regarding the base structure in Table 1, pearlite is represented by P, martensite is represented by M1, and ferrite is represented by F. P+F is a mixture of pearlite and ferrite.

(Structural Photograph) FIG. 1 shows a microscopic structural photograph (Nital liquid corrosion, 400x magnification, hereinafter the same) of the Nα3 sample material in Table 1.

Carbide (white part) is distributed in the martensite base (black part).

FIG. 2 is a photograph of the structure of Nα4. A nitride compound layer (about 13 μm in thickness) is formed on the surface, and a mesh-like nitride diffusion layer is formed below it. Carbide (white part) is observed in the tempered martensite matrix (black part) in the base material below the diffusion layer.

FIG. 3 is a photograph of the structure of Nn1O. Carbide (white part) is distributed in the martensite base (black part). N
Compared to α2, the carbide becomes finer grained due to the influence of W, )lo, 3.

[Effects of the Invention] As mentioned above, the rocker arm of the present invention has excellent wear resistance,
It has scuffing resistance and exhibits excellent performance especially when used in engines under high load.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are microscopic metallographic photographs of cast iron materials used for the rocker arm of the present invention.

Claims (2)

[Claims] (1) Component composition in weight%, C: 2.5-3.7%, S
i: 2.1-3.5%, Mn: 1.1-1.5%, Cr
:10~20%, Ni:0.3~0.7%, P:0.3
% or less, S: 0.1% or less, the balance consists of Fe and unavoidable impurities, and a cast iron material in which carbides mainly composed of Cr are uniformly precipitated in a pearlite and/or martensite base is used at least in the contact part. rocker arm. (2) Component composition in weight%, C: 2.5 to 3.7%, S
i: 2.1-3.5%, Mn: 1.1-1.5%, Cr
:10~20%, Ni:0.3~0.7%, and W, M
o, V, Nb, Ta, Ti, B: 1 type or 2 or more types
~10%, P: 0.3% or less, S: 0.1% or less, the balance consists of Fe and unavoidable impurities, and cast iron has uniformly precipitated carbides mainly composed of Cr in a pearlite and/or martensite base. A rocker arm in which at least the contact portion is made of wood.