KR950008687B1 - Making method of sintering tappet for diesel and gasoline engine and tip composite - Google Patents

Abstract

A green compact as a chip material, composed of (by wt.) 2.0-2.5% C, 10-14% Cr, 0.5-2.0% Mo, 0.3-0.9% P, 0.1-0.5% Nb and balance Fe with inevitable imprities and formed to disc shape, is joined to the top surface of a cold-rolled low or medium carbon alloy steel tappet body by diffusion bonding method. The method comprises putting the tip on the top surface of the tappet body and maintaining at 1110-1190 deg.C of sintering temperature for 1hr. under reducing atmosphere, and tempering for oil-cooling after maintaining at 580-630 deg.C for 1hr. under reducing atmosphere, if a cooling rate is rapid enough to appear a quenching effects.

Description

Manufacturing method and tip composition of sintered tappet for diesel and gasoline engine

(A), (b), (c) and (d) of FIG. 1 are enlarged 250 times microscope views according to the sintering temperature for the first sample of Example 1 of the present invention.

Figure 2 (a) (b) (c) (d) is a state of the tappet surface after the second test and the present invention.

The present invention relates to a method for producing a tappet having excellent corrosion resistance and wear resistance, and in particular, tappets of all engine types that can be manufactured by diffusion bonding of a body made of cold forging and a powder molded tip. The present invention relates to a method for preparing a sintered tappet for diesel and gasoline engines and a tip composition.

First, the engine tappet is a part which opens and closes the intake and exhaust valves by making linear contact with the cam portion of the cam shaft.

As such a conventional tappet, a chill cast product or a carburized steel product made by casting gray cast iron on a chill plate is used. However, defects such as pitting and scuffing, which are caused by the contact portions falling off both the cam shaft and the tappet due to the cyclic contact load with the cam shaft, occur consistently. Countermeasures against these defects are very difficult and the process control is not easy.

Therefore, the object of the present invention is to improve the engine performance by manufacturing a tappet having superior corrosion resistance and wear resistance than the conventional tappet, as well as to improve productivity and throughput by manufacturing the cold forging (forming) and the molded body tip of the body by diffusion bonding To reduce costs and reduce processing costs.

Hereinafter, described in detail by the accompanying drawings as follows.

The invention consists of a cold forging of the tappet body and a diffusion bonding process of the molded body tip. Here, the tip of the tappet, which is in contact with the cam shaft, from 1 to 3 mm is called the tip of the tappet, and the body part refers to the rest. In other words, after the powder compact is molded into a disk shape of about 1 to 3 mm, and then placed on the body and sintered in a reducing atmosphere, the tip is sintered and diffusion-bonded to the body. At this time, since the liquid phase sintering is performed by the addition of P (phosphorus), the sintering part (Tip) becomes very dense. The tappet shape is shown in FIG.

The composition (weight%) of the molded body tip in the present invention is as follows.

C: 2.0 to 2.5% Cr: 10 to 14%

Mo: 0.5-2.0% P: 0.3-0.9%

Nb: 0.1-0.5% Ni: 0.2-2.5%

Fe: 77-86.9%

In view of the effect of each element on the alloy, C is a carbide forming element to improve the abrasion resistance and strength, less than 2.0% of the carbide amount is reduced, if it exceeds 2.5% to form a large amount of carbide Rather vulnerable.

Cr is a carbide forming element and a matrix strengthening element. Less than 10% is good sintering ability to obtain a high density, but in the present invention, since the carbide appears as a coarse mesh at the sintering temperature forming the tip and the body, Cr should be more than 10% and if the sinterability is more than 14% Falls.

Mo, together with Cr, is a carbide forming element and a matrix strengthening element. Less than 0.5% is meaningless, and above 2.0% is no longer effective for wear resistance.

P is an element that forms a process liquid phase together with Fe, etc., less than 0.3% is difficult to cause diffusion bonding with the body due to the small amount of liquid phase, when more than 0.9%, a large amount of liquid phase is generated, severe dimension change occurs at the sintering temperature of the present invention, and also fragile Done.

Nb is a carbide-forming and fine grain element, meaning less than 0.1% and less than 0.5% sinterability.

Ni is a matrix-reinforced element, less than 0.2% is meaningless, and when it exceeds 2.5%, strength no longer occurs and wear resistance is inferior.

The tip powder of the above-mentioned composition is compacted in the form of a disk having a thickness of 1 to 3 mm, and then placed on a cold forged body with a cold forging material (general medium carbon steel or structural medium carbon alloy steel) and sintered in a reducing atmosphere. The sintering temperature is set at 1110 to 1190 ° C, and low vacuum using Ar partial pressure, decomposed NH ₃ gas or N _2, H ₂ mixed gas is used as the reducing atmosphere. When the sintering time is about 1 hour at the sintering temperature, the tip is sintered and diffusion bonded to the body at the same time.

If the sintering temperature is 1110 ℃ or less, the liquid phase formation is insufficient, resulting in poor bonding. Above 1190 ℃, the bonding is good, but network carbides are formed and fatigue life is low. In this case, when the thickness of the tip molded body is 1 mm or less, the thickness of the friction surface after bonding becomes undesirable, and when it exceeds 3 mm, it is not preferable because it is uneconomical in terms of cost.

When the sintering process is completed as described above, to enter the heat treatment step to secure the structure, if the cooling rate is slow after sintering, it is subjected to a quenching process to cool the oil after maintaining for 1 hour at 1000 ℃ in a vacuum or reducing atmosphere, 1000 Below ℃, the matrix structure does not become austenite and does not become martensite of cooling (remaining pearlite). Above 1050 ℃, particles grow and become brittle, and a liquid phase is formed, which may cause cracks upon cooling.

Tempering treatment is then carried out for oil cooling after holding for 1 to 1.5 hours at 580 to 630 캜 in a reducing atmosphere. If the tempering treatment is not performed or the temperature is 580 ° C. or less or 1 hour or less, abrasive cracking may occur during processing or dimensional deformation due to residual stress may be performed. On the other hand, tempering is performed at a high temperature of 630 ° C. or higher for a long time. If the base tissue is softened, wear resistance is reduced.

On the other hand, if the cooling rate after sintering is fast, only the tapering treatment is performed under the above conditions. When the heat treatment is carried out as described above, the tappet obtains a good product as desired by the present invention formed of a tampered martensite matrix and carbide and pore tissue.

The present invention will be described in more detail with reference to examples.

Example 1

After molding the powder for the tip molded body in the form of disc of 2mm thickness at the composition ratio as shown in Table 1,

TABLE 1

On the body made by cold forging the cold forging steel (here SM 45C), the tip molded body of each composition is placed and sintered at different sintering temperatures as shown in Table 2 under N ₂ and H ₂ mixed gas sulfuric atmosphere, and then reducing Heat treatment was performed in an atmosphere.

TABLE 2

As a result, in Samples 1 and 2, the sintering temperature was best at 1170 ℃ and 118 ℃, and especially the sample structure was strengthened by adding Ni.

In Sample 3, a large amount of P (0.65%) was added, thereby achieving good bonding at the sintering temperatures of 1110 ° C and 1130 ° C.

On the other hand, samples 1, 2, 3 showed a weak carbide structure coarse at the sintering temperature of 1200 ℃.

1 is a micrograph showing the diffusion bonding state of the body and the tip according to the sintering temperature of each sample 1.

Experimental Example

A rig test was performed on the inventive tappet and the conventional tappet taken out from Example 1 as shown in Table 3.

TABLE 3

Tappet surface conditions for the experimental results are shown in FIG.

As shown in Table 3, the engine tappet of the present invention has excellent corrosion resistance and wear resistance than conventional tappet types. Therefore, it is possible to achieve high performance and high output of the engine, and to improve the quality of the engine because it can prevent the problem of sticking and abrasion, which is a problem of the conventional tappet and cap shaft.

In the engine tappet of the present invention, since the manufacturing process is diffusion-bonding a tip in the form of a disk having a thickness of 1 to 3 mm only to a part made of a cold carbon forging, such as a medium carbon steel, in contact with a gam shaft, Compared with productivity, mass production is also possible. In addition, since the body is cold forged close to the dimensions of the product, compared to the conventional tappets, the amount of machining is less, and the machining cost is much reduced because only the polishing process is performed. The tappet of the present invention produced according to this can achieve a cost reduction compared to the conventional tappet.

Claims (8)

C: 2.0 to 2.5%, Cr: 10 to 14%, Mo: 0.5 to 2.0%, P: 0.3 to 0.9%, Nb: 0.1 to 0.5%, by weight ratio to the body made by cold forging of medium or heavy carbon alloy steel After forming the powder for the tip molded body consisting of the remaining Fe in the form of a disk and placed on one end of the body and maintained for 1 hour at a sintering temperature of 1110 ~ 1190 ℃ in a reducing atmosphere, the tip is diffusion-bonded to the body, the cooling rate The method of manufacturing a sintered tappet for diesel and gasoline engines, characterized in that if the quenching effect is fast enough to be tempered to maintain the oil after cooling for 1 hour at 580 ~ 630 ℃ in a reducing atmosphere. The method for producing a sintered tappet for a diesel and gasoline engine according to claim 1, wherein Ni: 0.2% to 2.5% is added to the powder for the tip molded body. The method of claim 1, wherein the tip has a thickness of 1 to 3 mm. The method of claim 1, wherein the reducing atmosphere is one of decomposition NH ₃ , gas atmosphere, or N ₂ and H ₂ mixed gas atmosphere in a low vacuum atmosphere using Ar partial pressure. The method of claim 1, wherein the heat treatment step after sintering is a diesel and gasoline engine having a step of quenching after holding for about 1 hour at 1000 to 1050 ° C. in a vacuum or reducing atmosphere when the cooling rate is slow. Method for producing sintered tappets The method of claim 1, wherein the tip is made of Tampered Martensite matrix and carbide and pores. Tappet for diesel and gasoline engines, characterized by C: 2.0 to 2.5%, Cr: 10 to 14%, Mo: 0.5 to 2.0%, P: 0.3 to 0.9%, Nb: 0.1 to 0.5, remaining Fe Tip composition. The tip composition of the tappet for diesel and gasoline engines according to claim 7, wherein Ni is added in an amount of 0.2 to 2.5%.