Metal treatment – Process of modifying or maintaining internal physical... – Producing or treating layered – bonded – welded – or...
Reexamination Certificate
1999-12-06
2001-11-13
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Producing or treating layered, bonded, welded, or...
C148S525000, C148S528000, C148S529000, C228S903000
Reexamination Certificate
active
06315843
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a sliding member such as a valve train part, a cam follower, or a rocker arm of an automobile engine and, more particularly, to a sliding component which has a structure of a base metal and, joined thereto, a ceramic sliding member and which exhibits an effect when used in a tappet, and to a method of manufacturing the same.
BACKGROUND ART
Sliding components have been selected from the viewpoint of good abrasion resistance on the sliding face and low sliding resistance. A single material having excellent properties has been employed or a composite has been prepared therefrom for practical utilization as a sliding component.
Attention has been drawn to ceramics having excellent sliding properties in recent years. Especially, examples of actual use are found in which a ceramic is joined to a metal material in a manner such that the ceramic is positioned in sliding parts where sliding conditions are severe.
For example, there is an application where a silicon nitride ceramic having good sliding properties is joined to a cam sliding portion of an engine tappet as practiced for a high-powered engine or in compliance with exhaust gas regulations.
The above sliding component is occasionally required to exhibit sliding properties at sliding zones other than the ceramic zone or on the whole body of the component, so that hardening treatment is performed for improving the sliding properties of the metal material.
Thus, the metal part is hardened by the use of the heating and cooling effected when the ceramic is joined to the metal by heating in the previous Japanese,Patent Application Laid-Open Nos. 2-55807, 2-55809, 2-199073 and 4-2672.
However, the above hardening relying on the heat joining has encountered the problems that the heating temperature applied to the sliding part of the body is different from that employed in the conventional heat hardening treatment of steel, thereby occasionally disenabling attainment of a hardness required for the sliding performance, and that the cooling method is special, the variety of metallic material suitable therefor is limited and the cost is increased. For example, the above Japanese Patent Application Laid-Open No. 2-55809 describes the use of a specific steel which is capable of being hardened by martensitic transformation induced by air-cooling after the heat joining. Further, in the Japanese Patent Application Laid-Open No. 2-55807, a main body of a tappet is constituted of a top half part of a carburized steel and a bottom half part of another steel and these parts are hardened by the heating and cooling effected when a ceramic member is brazed to the bottom half part. Therefore, a complicated carburization step is required for the top half part before heat-joining the ceramic member to the main body.
With respect to the above mentioned conventional problem, the present invention is directed to provide a method of manufacturing a sliding component of higher practicability.
DISCLOSURE OF THE INVENTION
In order to achieve the above mentioned object, the present invention provides a method of manufacturing a sliding component comprising a main body made of a non-carburized heat-hardened steel and a member adapted to form at least one sliding face of sliding faces of the sliding component and heat-joined to the main body, in which the steel-made main body is heat-hardened before heat-joining to the member and the heat-joining between the main body made of the heat-hardened steel and the member is conducted at a lower temperature than the temperature at which the heat-hardened main body has been heat-hardened.
Constituent members of the sliding component of the present invention are the steel-made main body thereof which has been heat-hardened before the heat-joining, and one or more slide faces. At least one of the slide faces is joined to the main body by means of heat-joining.
The main body of the sliding component before joining has a surface hardened by means of the heat-hardening. In addition, the temperature of the steel portion during the joining is lower than the heat-hardening temperature for that steel, so that the hardness of the steel joined is almost the same hardness as the one during the heat-hardening. Accordingly, the sliding properties of the sliding component of the present invention is significantly improved as compared with conventional material, which have been hardened during the above mentioned heat-joining, without requiring carburization treatment before the heat-joining or the use of any special steel capable of being transformed into a martensitic structure by air-cooling after the heat-joining, as referred to in the above-mentioned prior art.
A hardness of the steel main body after the joining is 45 or higher in Rockwell hardness (H
R
C) scale. With H
R
C of lower than 45, abrasion becomes large and no durability is given, so that sufficient sliding properties cannot be obtained. The hardness of the steel body before the joining is preferably 50 or higher in H
R
C scale because a slight reduction in hardness is caused as the heat-joining.
The material of the main body of the sliding component is steel, and the type thereof is not specifically limited as long as it exhibits 50 or higher in H
R
C by the heat-hardening. However, carbon steels or alloy steels including additive alloying elements such as Ni, Cr, or Mo, which are widely used as machine structural steels are preferable from the viewpoints of strength, and costs for the material and working.
A junction area between the member adapted to form the sliding face and the steel main body is preferably 50% or larger of an interface area therebetween. An area smaller than this increases a load applied to the junction portion as compared with the breaking load at that junction portion, increasing the possibility of the member at the sliding face to be stripped off.
The member heat-joined to the main body of the sliding component to form the sliding face is preferably made of a silicon nitride ceramic, and a strength and a Charpy impact value thereof at a room temperature are 130 kg/mm
2
or higher and 15 kJ/m
2
or larger, respectively.
In this event, the ceramic having the strength of 130 kg/mm
2
or higher makes it possible to withstand a thermal tensile stress caused inside the ceramic due to the difference in coefficient of thermal expansion between the steel and the ceramic during the heat-joining and to thereby avoid any cracks without any difficulty.
In addition, considering actual state of usage, a shock loading may act from, for example, a metal cam in a valve train system for an engine as illustrated in FIG.
2
. In order to avoid damages of the ceramic thereupon, it is preferable that the Charpy impact value is 15 kJ/m
2
or larger.
Furthermore, it is preferable that the temperature of the steel during the joining is as lower as possible than the heat-hardening temperature for that steel in order to inhibit temper softening of the steel due to the heat applied during the joining. For example, for a hypo-eutectoid steel, an appropriate heating temperature during the heat-hardening is around 800° C., which is from 30° C. to 50° C. higher than an AC3 or AC1 transformation temperature at which the steel has only an austenite phase during the heating. Accordingly, the temperature of the steel portion during the joining is preferably as lower as possible than 800° C. Any joining methods may be used if the joining temperature satisfies the above mentioned condition, and a known method may be used such as brazing and diffusion joining.
When the member to be heat-joined is ceramic, joining by means of brazing is conducted. For a brazing filler material, it is preferable to use a brazing filler material of which joining temperature is lower than the heat-hardening temperature. For example, when an Al alloy brazing filler material is used, the joining temperature is 580° C., allowing the joining at the significantly lower temperature than the heat-hardening temperature.
In addition, when a brazing filler material s
Matsuura Takashi
Yamakawa Akira
Bierman, Muserlian and Lucas
Sumitomo Electric Industries Ltd.
Wyszomierski George
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