KR890003408B1 - Manufacturing method of fe sintering alloy for valve seat - Google Patents

Abstract

Sintering alloy is produced by pressing the powder mixture, consisting of (in wt.%) 1.0-2.0% C, 2.0-3.0% Cr, 0.2-0.4% Mo, 0.2- 0.4% V, 5-20% WC and balance Fe, to 5-7 ton/cm2, sintering the pressed element for 30-60 minutes at 1100-1200 deg.C under reduction atmosphere, infitrating copper into the sintered element, and high- temp. quenching for 60-120 minutes at 500-700 deg.C. The sintering alloy is used for valve seat and has an improved wearresistance.

Description

Manufacturing method of wear-resistant iron-based alloy for valve seat

1 shows (Fe-Cr-Mo-V)-10% WC-1.5% C sintering and post-infiltration optical microscope structure of the test specimen (magnification × 200) where 1 is a dispersion wear-resistant WC particles, 2 is for Cu Infiltration, 3 represents martensite matrix, respectively.

2 shows the optical microscope structure (magnification × 200) 2-1 of the structure subjected to the sintering and tempering heat treatment of the test specimen of the first composition 2 × is the WC particles of the dispersion wear-resistant material, 2-2 is the Cu infiltration material 2-3 Each temper heat treatment structure is shown.

The present invention relates to a method for producing a wear resistant small alloy alloy for valve seats of an internal combustion engine. The valve sheet is in direct contact with the valve in a high temperature oxidizing atmosphere, and rotates, and at the same time, it is used under a condition that is subject to hot shock, so heat and wear resistance are required.

In recent years, the internal combustion engine has become smaller and higher power, and the use of lead-free gasoline to prevent pollution has increased the demand for wear resistance.

In particular, valve seats of diesel engines have higher combustion pressure and temperature than gasoline engines, and are used in more severe conditions because wear phenomenon accompanied by chemical corrosion caused by sulfur or vanadium in fuel occurs. For this reason, blue-metal sintered alloys having excellent durability have been developed for gasoline engine valve seats even when using lead-free gasoline or LPG as fuel, but they do not have sufficient durability for valve seats of diesel engines. .

Therefore, the characteristics of the present invention is to prevent wear due to severe contact rotation between the valve and the valve seat by using spherical hard particles of WC as a dispersion antiwear material in order to have sufficient durability even for the valve seat of a diesel engine. By using alloy steel powder containing 2.0-3.0% Cr, 0.2-0.4% Mo, 0.2-0.4% V furnace, it gives heat resistance and corrosion resistance to the base, improves thermal conductivity, improves machinability, and Cu oxide on the surface by infiltrating Cu. The purpose of the present invention is to improve wear resistance due to film formation and to prevent internal corrosion by infiltration of combustion atmosphere through pores by filling pores with Cu. That is, the present invention relates to an iron-based alloy for valve sheet having a composition of C 1.0-2.0%, Cr 2.0-3.0%, Mo 0.2-0.4%, V 0.2-0.4%, WC 5-20%, Cu 10-20% will be.

In addition, the manufacturing method of the valve seat using the alloy of this invention is as follows. Iron alloy steel powder containing Cr2.0-3.0%, Mo 0.2-0.4%, V 0.2-0.4%, 5-20% WC powder 1.0-2% graphite powder and 0.5-0.8% zinc stearate Molding is performed at a molding pressure of ⁷ ton / cm ² .

Sintering is carried out in a reducing atmosphere (hydrogen or decomposed ammonia gas) to assist in the reduction of Cr, and the sintering temperature is 1100-1200 ° C. Cu infiltration is preferably a method of infiltration after sintering in order to improve strength, hardness, and dimensional change, and infiltration temperature is 1100-1150 ° C. At the time of sintering, the structure is sorbite (SORBITE) or truesite (TROOSITE) structure, but after infiltration, the entire matrix structure becomes martensite even at a relatively slow cooling rate under the influence of infiltration Cu.

In general, martensite is mild and fragile, so it is necessary to perform tempering heat treatment in order to improve toughness and machinability. Tempering heat treatment temperature is 500-700 ° C., so that HV 300-500 is appropriately adjusted.

The following is described by way of examples.

EXAMPLE

This test specimen is based on a mixed powder obtained by adding 1.3% of natural earth graphite powder having an average particle size of -100 mesh to Cr-Mo-V steel powder, and 5,10,15% of WC is added as a wear-resistant dispersion.

0.6% zinc stearate powder (-325 mesh) is added to the mixed powder, mixed, and molded at a pressure of ⁶ ton / cm ² .

The molded body is cooled at a rate of 20 ° C./min after sintering at 1150 ° C. for 50 minutes in a decomposed ammonia atmosphere. The sintered compact thus obtained is infiltrated with Cu. The infiltration amount was about 15% of the weight of the sintered body, and the infiltration temperature and infiltration time were 1120 ° C. and 50 minutes. After infiltration, the hardness of the specimen is about HRc 40, which leads to machinability. Therefore, the tempering heat treatment for 30 minutes at 700 ℃ to lower the hardness. The changes in the compressive strength and the hardness change after infiltration and infiltration are shown in Tables 1 and 2.

Also, matrix structures and WC distributions during tempering and tempering after tempering are shown in FIGS. 1 and 2.

The endurance test was performed on the valve sheet manufactured as described above using a valve seat wear tester, and the test conditions and test results are shown in Table 3.

Table 1

[Table 2]

Table 3

VALVE MATERIAL: SUH 36 (Ni-Cr Heat Resistant Steel) (HRC 30-40)

The basic idea of the present invention is to disperse coarse WC particles having an average particle size of 40-100 μm on a matrix, unlike the reinforcing mechanism of dispersion-reinforced alloys, whereby wear caused by contact rotation with the valve acts as a distributed wear material It occurs in the particles to protect the matrix from abrasion. The reasons why the WC particles can protect the matrix from wear are as follows.

If the observation surface is very smooth on the naked eye, the actual contact area is the projection part due to the unevenness of the contact surface. Therefore, the area where wear is mainly occurred is not limited to the projection area between the contact surfaces but the entire visual contact area.

In the surface grinding of the valve sheet or in the initial wear process, the harder WC particles are projected onto the valve sheet surface, so that the WC becomes the actual contact point. On the other hand, the WC particles as the actual contact area are superior to the wear resistance than the alloy steel having a known phase.

In the case of valve seats, wear occurs mainly due to wear, welding, corrosion and surface fatigue wear. The main factor of wear is hardness, and WC is significantly harder than ordinary steel, which can protect the matrix structure from wear and tear.

In the case of adhesion wear, hardness and adhesion degree are important factors, so the adhesion of carbide WC to metal valve surface is lower than that of base structure, thus protecting the base structure from adhesion wear.

In addition, corrosion wear is an important factor of corrosion resistance, WC is better corrosion resistance than ordinary steel can protect the base structure from corrosion wear.

Therefore, the WC particles can protect the base tissue from three types of abrasion. In the case of surface fatigue wear, the WC particles absorb the base tissues that resist the impact of the WC particles, thereby reducing the amount of wear.

For the above reason, the alloy of the present invention is excellent in wear resistance. Next will be mentioned the role and optimum composition of the chemical components used in the present invention.

Cr: Cr combines with carbon on a matrix to form carbides to stabilize the structure and increase hardenability. In addition, stable and solid oxide film is formed during use, contributing to improvement of corrosion resistance and heat resistance. However, when excessively added, surface oxidation rapidly occurs and becomes brittle, thereby impairing machinability. Therefore, the optimum content of Cr on the matrix is 2.0-3.0%.

Mo: Mo is one of the carbide forming elements, which forms complex carbides together with Cr, V, and C in Fe base to improve high temperature wear resistance, and also improve heat treatment to stabilize the structure after heat treatment. Mo is a carbide forming element, and at the same time, it is dissolved in ferrite to improve processability and creep strength, and to increase impact value and fatigue strength.

However, 0.2-0.4% is suitable for excessive addition because it impairs workability due to excessive precipitation.

V: Vanadium is one of the carbide forming elements to refine carbides, and these carbides are stable at high temperatures and effectively fix and hinder movement of the mouth, thereby improving heat resistance.

However, 0.2-0.4% is suitable for over-addition because it impairs machinability.

Carbon: Carbon combines with known carbide forming elements Cr, Mo, and V to form carbides to increase the hardenability. If there are enough carbide forming elements in the matrix, the hardenability increases as the amount of carbon increases. If the added carbon content of the matrix is less than 1.0%, a low-strength ferrite (FERRITE) structure is generated, and if the added carbon content is more than 2%, the precipitated amount of cementite becomes excessive, and thus becomes vulnerable. Therefore, the optimum carbon addition amount is 1.0-2.0%.

5-20% of the amount of WC added as a wear-resistant dispersant to the matrix structure of the composition mentioned above is appropriate. This is not preferable because the added amount of WC, which is a dispersion wear resistant material, is more than 5%, so that sufficient abrasion resistance can be obtained.

Claims (1)

Sintering a compact (5-7ton / cm ² ) of a mixed raw material powder composed of C 1.0-2.0%, Cr 2.0-3.0%, Mo 0.2-0.4%, and WC 5-20% remaining Fe in a reducing atmosphere (1100-1200 ° C) 30-60 minutes), and the obtained sintered body was infiltrated with 10-20% Cu by weight ratio (1100-1150 deg. Method for producing a wear-resistant iron-based alloy for sheets.

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