JP6929313B2 - Iron-based sintered alloy for high-temperature wear resistance - Google Patents

Description

The present invention relates to an iron-based sintered alloy for high-temperature wear resistance applied to a valve seat for an internal combustion engine. In particular, the composition of the iron-based sintered alloy is changed to have heat resistance as well as wear resistance. The present invention relates to an iron-based sintered alloy for high-temperature wear resistance that maximizes the amount of gold, and a method for manufacturing a valve seat using the same.

Generally, the valve seat for an internal combustion engine is a ring-shaped sintered body that maintains the airtightness of the intake / exhaust valves in the process of opening and closing the intake valve and the exhaust valve, and the valve seat 18 is a cylinder head as shown in FIG. In a state of being inserted into the 24 by an insert type, it contacts the head portions of the intake valve and the exhaust valve to perform the sealing function.

The valve seat 18 comes into contact with the intake / exhaust valve in the process of closing the exhaust valve, and performs a function of preventing leakage of exhaust gas in the process of opening the exhaust valve. In connecting, physical conditions such as wear resistance and heat resistance that can withstand continuous friction with the intake / exhaust valve and continuous chemical reaction with the exhaust gas are required. ..

Therefore, many studies have been conducted to improve the wear resistance and heat resistance of the valve seat, and as an example, a method of dispersing cobalt-based or chromium-based carbides in an iron matrix, or a ferrochrome-based (Fe-Cr) or A method of dispersing hard particles in the form of a ferro-molybdenum-based (Fe-Mo) intermetallic compound is known.

In addition, as another example of improving the wear resistance and heat resistance of the valve seat, a penetration method using a powder metallurgy method in which various types of alloys having excellent wear resistance and heat resistance are added to the iron matrix. And the addition method of adding hard particles, the manufacturing method by controlling the base alloy, and the sintering step forming method are known.

However, the internal combustion engine applies a method of burning gas fuel as well as liquid fuel, and since the liquid and gas fuel form more various forms of combustion products, combustion of the liquid and gas fuel Physical conditions such as abrasion resistance and heat resistance that can withstand the product need to be further strengthened.

Korean Publication No. 10-2004-0025003 Korean Publication No. 10-2012-0125817 Korean Registered Patent No. 10-0461304

Therefore, the present invention is for solving the above-mentioned problems, and the life of the valve seat is extended by maximizing not only wear resistance but also heat resistance by changing the composition of the iron-based sintered alloy. It is an object of the present invention to provide an iron-based sintered alloy for high temperature wear resistance and a method for manufacturing a valve seat using the same.

The composition for achieving the above purpose is 100 parts by weight of cobalt powder, 5.0 to 9.0 parts by weight of molybdenum powder, and 1.5 to 4 parts by weight of chromium powder with respect to 100 parts by weight of iron powder. .1 parts by weight, carbon powder 0.7 to 1.3 parts by weight, manganese powder 1.0 to 1.8 parts by weight, silicon powder 0.4 to 1.2 parts by weight, sulfur powder 0.2 to 0.8 It is a composition of a sintered alloy containing 0.1 to 0.7 parts by weight of vanadium powder by weight.

The manufacturing method for achieving the above object is formed in the mixing step of uniformly mixing the composition of the sintered alloy, the pressurizing step of pressurizing the mixture formed in the mixing step at the setting pressure, and the pressurizing step. In the sintering step where the molded body is sintered together with the infiltrating material and copper is infiltrated into the molded body, the sintered body formed in the sintering step is subjected to low temperature treatment to change the residual austenite into martensite. It includes a low-temperature treatment step and a heat treatment step of tempering the low-temperature treatment body formed in the low-temperature treatment step to remove residual stress.

The present invention includes at least the following four effects as described below.
First, by adding cobalt, molybdenum, chromium and a strength-increasing component to the composition of the valve seat to form a composite carbide, the amount of precipitated particles and the amount of solid solution is increased in the iron matrix of the valve seat, and the valve seat Life is extended.

Next, by adding silicon or vanadium to the composition of the valve seat to disperse the fine spherical particles in the iron matrix, the carbide particles are less likely to fall off during the wear process of the valve seat, and the amount of wear is reduced. And the life is extended.

Then, by adding manganese, sulfur, or the like to the valve seat composition to improve self-lubricating property, not only the machinability of the valve seat is improved, but also wear is performed in the friction process with the intake / exhaust valve. Is minimized and the life is further extended.

Finally, by sintering the composition of the valve seat while impregnating the copper powder, wear resistance and heat resistance are improved as compared with the conventional valve seat, and the liquid fuel as well as the gaseous fuel can be used. It can be applied to all internal combustion engines used.

It is a drawing which shows the installation state of the valve seat by a prior art. It is an optical micrograph of Embodiment 1 by this invention (magnification 500 times). It is an optical micrograph of Embodiment 2 by this invention (magnification 500 times). It is an optical micrograph of Embodiment 3 by this invention (magnification 500 times).

Hereinafter, the composition according to the present invention will be described. As shown in FIGS. 2 to 4, the iron-based sintered alloy according to the present invention is a sintered alloy applied to the internal combustion engine, and in particular, the intake / exhaust in the process of opening and closing the intake valve and the exhaust valve. It is applied to valve seats that not only maintain the airtightness of the valve but also minimize damage during the contact process with the combustion products.

At this time, the present application has been limited to the application of the high-temperature wear-resistant iron-based sintered alloy to the valve seat, but the technical scope of the present application may be applied to a cylinder liner, a valve guide, or the like. It is natural to be included in.

Iron-based sintered alloy according to the invention comprises the composition of the iron powder sintered alloy composed mainly of and infiltrant is infiltrated into the sintered alloy of the composition, the sintered alloy of the composition Is 100 parts by weight of iron powder, 10.0 to 14.0 parts by weight of cobalt powder, 5.0 to 9.0 parts by weight of molybdenum powder, 1.5 to 4.1 parts by weight of chromium powder, and 0 parts by weight of carbon powder. 7 to 1.3 parts by weight, manganese powder 1.0 to 1.8 parts by weight, silicon powder 0.4 to 1.2 parts by weight, sulfur powder 0.2 to 0.8 parts by weight, vanadium powder 0.1 to 1 part Including 0.7 parts by weight, the infiltrating material means 10.0 to 20.0 parts by weight of copper powder with respect to 100 parts by weight of the iron powder.

At this time, by infiltrating the infiltrant in the sintered alloy of the composition, the iron-based sintered alloy composition of cobalt-based hard particulate or molybdenum-based hard particulate and chromium-based hard martensite matrix Composite carbides such as particulate matter are uniformly dispersed, and in particular, the manganese and sulfur or the intermetallic compound of manganese and carbon perform the role of a lubricant, and the silicon and vanadium make the particles finer.

That is, the reason why the infiltrating material is impregnated into the composition of the sintered alloy to produce the valve seat is that the high temperature heat resistance, high temperature wear resistance and corrosion resistance of the contact portion in contact with the intake / exhaust valve are further increased. It is for doing.

The valve seat produced in the iron-based sintered alloy composition (hereinafter referred to as the composition) has a hardness (HRA) of at least 71 to 81 of the final product and a density (g / cm3) of the final product. It is a high-strength material that maintains at least 7.4 to 8.1.

On the other hand, the cobalt (Co) reacts with iron, molybdenum and carbon to precipitate composite carbides, so that the cobalt (Co) is uniformly dispersed in the matrix and contributes to wear resistance, and a part of the cobalt is solidified in the matrix. When it is melted to increase heat resistance and the cobalt content is less than 10.0 parts by weight, the amount of solid dissolved particles and matrix is small and the wear resistance and heat resistance are lowered, and the cobalt content is 14. If it exceeds .0 parts by weight, the matrix metal is weakened due to the excess of precipitated particles, and the machinability is deteriorated.

Further, the molybdenum (Mo) is dissolved in the matrix or forms an intermetallic compound in a composite carbide state to improve wear resistance and heat resistance, and the content of the molybdenum is less than 5.0 parts by weight. In the case of, the amount of solid solution of the matrix and the amount of intermetallic compound are small, and the abrasion resistance and heat resistance are lowered. If the content of molybdenum exceeds 9.0 parts by weight, the amount of solid solution of the matrix metal is excessive. It becomes a fragile factor of matrix metal.

Further, the chromium (Cr) reacts with the carbon in the matrix to form a composite carbide to improve the wear resistance, and is also dissolved in the matrix to improve the heat resistance. The content is preferably 1.5 parts by weight to 4.1 parts by weight.

When the chromium content is less than 1.5 parts by weight, the amount of the composite carbide is small and the abrasion resistance and heat resistance are lowered, and when the chromium content exceeds 4.1 parts by weight, the matrix metal The amount of solid solution is excessive and the product becomes weak.

Further, the carbon (C) is a component that not only strengthens the matrix by being solidified or diffused in the matrix but also forms a composite carbide by reacting with the cobalt, chromium and molybdenum, and is a component of the matrix. It not only performs the function of increasing strength and hardness, but also performs the function of increasing wear resistance and heat resistance.

When the carbon content is less than 0.7 parts by weight, ferrite is excessively formed in the matrix metal together with pearlite, so that the matrix is softened and the strength and abrasion resistance are lowered, and the carbon content is reduced. When is in excess of 1.3 parts by weight, the residual carbon required for pearlite formation forms cementite and weakens the matrix metal.

Further, the manganese (Mn) is a component that improves self-lubricating property by reacting with sulfur (S) existing in the iron matrix to form MnS, and the content of the manganese is 1.0 weight by weight. If it is less than a portion, the self-lubricating function is deteriorated by forming the MnS, and if the manganese content exceeds 1.8 parts by weight, segregation may occur in addition to the formation of the MnS.

Further, the silicon (Si) is a component added for the purpose of improving the corrosion resistance and heat resistance as well as adjusting the crystal grains of the iron matrix to make it finer, and the content of the silicon is 0. 4 to 1.2 parts by weight is desirable.

Further, the sulfur (S) is a component that is added to the iron matrix and dispersed in the grain boundaries of the matrix in the form of MnS, and the MnS is not decomposed into compounds at high temperatures and maintains a stabilized state. After the sintering process is completed, it remains at the grain boundaries of the sintered body and lowers the coefficient of friction in the process of processing the final product to increase machinability. In particular, the sulfur content is 0.2. ~ 0.8 parts by weight is desirable.

It is desirable to increase the efficiency by forming the MnS by mixing the manganese and the sulfur in a ratio of approximately 6: 4.

If the MnS content (Mn + S) is less than 1.25 parts by weight, the role of remaining in the matrix of the sintered body is weak, and if the MnS content (Mn + S) exceeds 2.6 parts by weight, the matrix It becomes weak and causes damage to the valve seat.

Further, the vanadium (V) is a component added for the purpose of improving heat resistance as well as adjusting the crystal grain adjustment of the iron matrix to make it finer, and the content of the vanadium is 0. .1 to 0.7 parts by weight is desirable, and if the vanadium exceeds a specified value, the crystal grains are coarsened and cause damage to the final valve seat product.

Hereinafter, the production method according to the present invention will be described. First, the present invention includes a mixing step of mixing the compositions to produce a mixture, a pressurizing step of pressurizing, a sintering step of sintering, a low temperature treatment step of changing residual austenite into martensite, and residual stress. It is a heat treatment stage to remove.

Further, the mixing step is a step in which the iron alloy powder is contained in the mixer and the high-speed tool steel powder, the superalloy powder, the manganese sulfide powder, the carbon powder and the like are uniformly mixed in a predetermined amount.

Further, the pressurization step is a step of compressing the mixture formed in the mixing step to form a density suitable for the valve seat, and pressurizing the mixture to a surface pressure of 6 to 10 t / cm2 for compactness. Means the stage of improving.

Further, the sintering step means a step of sintering a molded body formed in the pressurizing step in a temperature range of 1120 ± 20 ° C. for 30 ± 10 minutes to form a sintered body, and the sintered body is formed. The step of infiltrating 10.0 to 20.0 parts by weight of the copper powder is included.

If the sintering temperature at the sintering stage is less than 1100 ° C, the diffusion of powder particles is not smooth and the matrix structure is weakened, and if the sintering temperature exceeds 1140 ° C, the crystal grains are coarsened and the mechanical properties are deteriorated. It will be lowered.

By sintering with the addition of 10.0 to 20.0 parts by weight of the copper powder in the sintering step and infiltrating the copper particles into the pores of the matrix structure, the strength of the matrix is not only strengthened but also lubricated. Become more sexual.

The low temperature treatment step is a step of cooling the sintered body formed in the sintering step to a temperature range of −120 ± 10 ° C. for 20 ± 5 minutes to change the remaining austenite into martensite. It induces aging deformation prevention, mechanical property improvement and tissue stabilization of the composition.

Further, the heat treatment step is a step of tempering the low temperature treated body formed in the low temperature treatment step to remove residual stress, and by heating in a temperature range of 600 ± 20 ° C. for 120 ± 10 minutes. This is the stage of imparting toughness to the matrix structure.

Further, as a post-processing step of the heat treatment step, a step of removing foreign substances such as burr of the final product or a step of obtaining a finished product through a machining process such as forging or polishing can be included. The description about this is omitted.

The finished product of the valve seat that has undergone the above steps has a hardness (HRA) of about 71 to 81 and a density (g / cm3) of about 7.4 to 8.1. It can be seen that it provides hardness and density suitable for use.

Hereinafter, embodiments according to the present invention will be described.

First, the compositions having the composition ratios of Examples 1 to 3 in Table 1 are mixed with a mixer to produce a mixture, and then the mixture is pressurized to a surface pressure of 10 t / cm 2 and heated from 1120 ° C. in the heat treatment furnace. Sintered and soaked for 30 minutes.

Next, the sintered body that has undergone sintering and copper infiltration in the sintering step is rapidly cooled in a temperature range of −120 ° C. for 20 minutes to produce a low-temperature treated body, and then the low-temperature treated body is placed in a temperature range of 600 ° C. The mixture was heated for 120 minutes and tempered.

Subsequently, after drawing out the heat-treated body that has undergone the heat treatment step, samples 1 to 3 are manufactured, respectively, and then a wear tester (Rig Tester, nitrogen atmosphere; 0.2 mm Offset; SUH35 + Tuff valve, rotation speed: 3, The amount of wear was measured using 500 rpm, temperature: 350 ° C., time: 2 hours).

As a result, in the case of the first to third embodiments (samples 1 to 3), the total wear amount of the valve and the valve seat was 48 μm on average, and it was found that the valve seat was suitable as a material.

That is, as shown in FIGS. 2 to 4, the samples 1 to 3 represent numerical values having similar densities and hardnesses, and in particular, hard particles and workability improving elements are uniformly distributed in the martensite matrix structure. You can know that you are.

In particular, it has been known that the wear resistance and heat resistance of the valve seat are increased by filling the pores in the matrix structure with the copper alloy.

As described above, the present invention is not limited to the above-described embodiment, does not deviate from the technical idea of the present invention claimed within the scope of the claim, and is obvious to a person having ordinary knowledge in the technical field to which the invention belongs. Deformation can be performed, and such modification is within the scope of the present invention.

Claims (1)

With respect to 100 parts by weight of iron powder, 10.0 to 14.0 parts by weight of cobalt powder, 5.0 to 9.0 parts by weight of molybdenum powder, 1.5 to 4.1 parts by weight of chromium powder, 0.7 by weight of carbon powder. ~ 1.3 parts by weight, manganese powder 1.0 to 1.8 parts by weight, silicon powder 0.4 to 1.2 parts by weight, sulfur powder 0.2 to 0.8 parts by weight, vanadium powder 0.1 to 0 A feature of the composition of an iron-based sintered alloy consisting of .7 parts by weight is that 10.0 to 20.0 parts by weight of copper powder is infiltrated into 100 parts by weight of the iron powder as an infiltrating material. High temperature wear resistant iron-based sintered alloy.

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