KR20010011266A - Sintered steel alloy and fabrication method of valve-seat using the same - Google Patents

Abstract

PURPOSE: Provided are iron-based sintered alloy and preparation of valve seat using the same, which are excellent in abrasion resistance and heat resistance against a high-powered engine, are applicable for use in a valve seat for a suction and exhaust valve of internal-combustion engine of all sorts. CONSTITUTION: The iron-based sintered alloy contains 0.5-2.0pts.wt. of Cr, 6.0-10.0pts.wt. of Mo, 0.1-2.0pts.wt. of Si, 9.0-14.0pts.wt. of Co, 0.5-2.0pts.wt. of Ni, 2.0-6.0pts.wt. of Cu, 0.6-1.2pts.wt. of C, 5.0-15.0pts.wt. of Pb and up to 3.0pts.wt. and the rest composed of iron. The iron-based sintered alloy is characterized by being distributed homogeneously Co-based hard phase and Mo-based hard phase over mixture matrix of sorbite and bainite. Preparation of valve seat using the iron-based sintered contains the steps of: i) mixing step that mix homogeneously the components of the iron-based sintered alloy; ii) compression-molding step that compression-mold the composition to make a molded article; iii) pre-sintering step that make the molded article sintered to give a little hardness at temperature that carbon is not diffused in mixture gas of N2 + H2 atmosphere; iv) cold forging step that inject the pre-sintered body into a mold and press it under a pressure of 10-15TON/cm2 at the upper and lower sides to make a matrix high-density by being increased density of the pre-sintered body; v) a second sintering step that sinter the cold gorging article under a temperature of not more than melting point in the mixture gas atmosphere to be diffused homogeneously to be joined the Co-based hard phase and the Mo-based hard phase over the matrix, and making the sorbite and the bainite formed by the matrix; vi) Pb impregnation step that impregnate Pb having excellent lubrication property into a void formed at the mixture matrix or the hard phases to be lubricated the sintered body; and then vii) barrel step that remove a wire after manufacturing.

Description

Sintered steel alloy and fabrication method of valve-seat using the same}

The present invention provides a valve seat for intake / exhaust valves of various internal combustion engines that can be used in common in response to the use conditions of unleaded gasoline, diesel, and LPG fuels according to fuel conditions, displacements, and camshaft types (DOHC, SOHC). The present invention relates to an iron base alloy having excellent wear resistance and heat resistance and a method of manufacturing a valve sheet using the same.

In general, the engine is provided with an intake valve for sucking the mixed gas into the combustion chamber and an exhaust valve for discharging the combustion gas to the outside. The valve seat is in close contact with the face of the intake and exhaust valve, so that the pressure in the combustion chamber is leaked. It is a component that keeps the airtightness by preventing it.

The valve seat is made of an iron base alloy having wear resistance and heat resistance corresponding to an increase in operating pressure and temperature as the internal combustion engine has become smaller and higher in power. In other words, it must have strong wear resistance that will not be damaged even if it repeatedly collides with the valve which accelerates during engine operation and also opens and closes several hundred thousand times per hour. do.

For example, since the valve seat is operated under high impact and high temperature gases, the wear and corrosion resistance at high temperatures up to about 700 ° C. is very severe because the operating conditions that must withstand contact and friction with the valve and exposure to exhaust gases are very harsh. Further, there is a need for further improvement in oxidation resistance and high temperature characteristics. In addition, in recent years, due to the nature of automobiles as an international product, there is a need for a small bond alloy for valve seat that can cope with a wide range of conditions that differ from region to region.

In addition, the conventional iron-based ferrous alloy for valve seats has a different application material according to the use conditions such as the displacement, cam-shaft type (DOHC, SOHC) and the type of fuel used. In particular, they have not been used in low cost LPG fueled engines with severe combustion conditions. Thus, not only can the material be shared in all the above use conditions, but there is an increasing demand for a ferrous base alloy for valve seat that can be applied to an LPG fuel engine.

The present invention has been made to improve the above problems, has a wear resistance and heat resistance that can cope with high engine power output, excellent performance even in LPG fuel, as well as unleaded gasoline or diesel fuel, and can be shared under various other conditions. An object of the present invention is to provide an iron-based small alloy and a method for producing a valve sheet using the same.

1 is a micrograph (× 200) showing an enlarged structure of the iron-based small alloy according to the present invention,

2 is a flow chart for explaining a method for manufacturing a valve sheet using an iron-based small alloy according to the present invention.

<Explanation of symbols for main parts of drawing>

A ... sorbite / bainite mixed base tissue

B ... Co hard phase

C ... Mo hard phase

D ... impregnation Pb

In order to achieve the above object, the iron-based small alloy alloy according to the present invention is employed in an engine of an internal combustion engine, and is applied to an engine valve sheet for improving heat efficiency in a combustion chamber by maintaining airtightness with the valve when opening and closing an intake / exhaust valve. 0.5-2.0 parts by weight Cr, 6.0-10.0 parts by weight Mo, 0.1-2.0 parts by weight Si, 9.0-14.0 parts by weight Co, 0.5-2.0 parts by weight Ni, 2.0-6.0 Cu, 0.6-1.2 Parts by weight C, 5.0-15.0 parts by weight Pb, 3.0 parts by weight or less The other and the remainder are provided with a composition made of Fe, uniformly dispersed Co-based and Mo-based hard particles in the mixed base structure of sorbite and bainite Characterized in that it comprises a.

In addition, in order to improve machinability during machining, MnS of 2.0 parts by weight or less is preferably added to the composition, and pores formed on the mixed base or hard particles are impregnated with Pb to enable self-lubrication. It is desirable to have.

In addition, in order to achieve the above object, the manufacturing method of the valve seat using the iron-based sintered alloy according to the present invention is employed in the engine of the internal combustion engine, when opening and closing the intake / exhaust valve, maintaining airtightness with the valve and thermal efficiency in the combustion chamber In the method for producing an iron base alloy applied to an engine valve seat for improving the pressure, 0.5 to 2.0 parts by weight Cr, 6.0 to 10.0 parts by weight Mo, 0.1 to 2.0 parts by weight Si, 9.0 to 14.0 parts by weight Co, 0.5 to 2.0 Parts by weight Ni, 2.0 to 6.0 Cu, 0.6 to 1.2 parts by weight C, 5.0 to 15.0 parts by weight Pb, 3.0 parts by weight or less The other and the remainder are blended with raw materials to mix the composition uniformly in a mixer fair; A molding step of forming a molded body by compression molding the mixed composition; A pre-sintering step of sintering the molded body in a mixed gas atmosphere of N ₂ + H ₂ at a temperature at which carbon does not diffuse; Cold forging step (S4) to charge the pre-sintered body into a mold and to increase the density of the pre-sintered body by applying a pressure of 10 ~ 15TON / ㎠ in the upper and lower (S4); The cold forging is sintered in a mixed gas atmosphere of N ₂ + H ₂ at a temperature below the melting point, whereby Co-based hard particles and Mo-based hard particles are uniformly diffused and joined to the base, and the base forms sorbite and bainite. Secondary sintering process; A Pb impregnation process for impregnating Pb having excellent lubricating properties in pores formed on the mixed base or hard particles for self lubrication of the sintered body; And a post process of obtaining a finished product of the valve seat by subjecting it to a barrel process for removing iron bark after machining and machining.

The pre-sintering process is preferably sintered at 723 ℃ to 910 ℃ the temperature between the A ₁ transformation point and the A ₃ transformation point.

In the Pb impregnation process, the sintered body is heated in a vacuum state, the sintered body is charged in a Pb melt in a vacuum state, and then, N ₂ gas is added at 4 atmospheres or more for 10 minutes to 60 minutes to increase Pb impregnation efficiency. It is preferable to impregnate the Pb melt in the pores of the sintered compact.

Therefore, the iron base alloy of the present invention and the valve sheet manufactured using the same have wear resistance and heat resistance that can cope with high engine output, and lead-free gasoline or diesel fuel, as well as LPG fuel, have excellent performance and Its feature is that it can be shared under different conditions.

The iron-based small alloy according to the present invention having such a feature will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the iron-based small alloy according to the present invention is employed in an engine of an internal combustion engine, and is applicable to an engine valve sheet for improving heat efficiency in a combustion chamber by maintaining airtightness with the valve when opening and closing an intake / exhaust valve. Do.

Thus, the iron-based small alloy is 0.5 to 2.0 parts by weight Cr, 6.0 to 10.0 parts by weight Mo, 0.1 to 2.0 parts by weight Si, 9.0 to 14.0 parts by weight Co, 0.5 to 2.0 parts by weight Ni, 2.0 to 6.0 Cu, 0.6 to 1.2 Parts by weight C, 5.0-15.0 parts by weight Pb, 3.0 parts by weight or less, and others are provided with a composition made of Fe, have a surface hardness of HRA 55-75, a density of 7.7-8.2 g / cc, and mHv (100 g). In the mixed base structure (A) of sorbite and bainite having a microhardness of 350 to 550, mHv (100 g) and a Co-based hard particle phase (B) having a microhardness of 600 to 900 and mHv (100 g) of 1000 to 1500 Mo-based hard particle phase (C) having a fine hardness of has a uniformly dispersed structure.

In addition, MnS of 2.0 parts by weight or less may be further added to the composition to improve machinability during machining, and self-lubrication is performed in the pores formed in the mixed base structure (A) or the hard particle phase (B, C). Pb (D) is impregnated to improve abrasion resistance and heat resistance.

When the valve seat is manufactured from this small alloy, it has abrasion resistance and heat resistance to cope with high engine output, and shows excellent performance that can be shared in harsh conditions such as an unleaded gasoline engine and a diesel or LPG fuel engine. do. In addition, since the application material can be shared according to the use amount of each displacement and cam-shaft type (DOHC, SOHC), etc., as a result, the production line is simplified, resulting in cost reduction.

When explaining the effect of the composition and the reason for the composition limitation in detail as follows.

In the iron-based small alloy according to the present invention, Co-based hard particles and Mo-based hard particles (B, C) are uniformly dispersed in the mixed base structure (A) of sorbite and bainite, and Pb is impregnated into the pores. The base material is an alloy of Fe-Co-MO-Ni. In other words, Co added to the base contributes to wear resistance by precipitating hard particles, which are complex carbides with Fe, Mo, and C, to be uniformly dispersed in the base metal, and contributes to the wear resistance. . Here, the content is regulated to 6.0 to 7.0 parts by weight.

Ni added to the base is diffused and dissolved in the base metal to improve heat resistance and high temperature characteristics. Thus, if the content is less than 0.5 parts by weight, the above effect is insignificant, and if it exceeds 2.0 parts by weight, the whole of the matrix structure is changed to martensite and the hardness becomes larger than necessary, and the machinability is lowered. Here, the content is 0.5 to 2.0 parts by weight.

Mo added to the base forms a complex carbide together with Fe, Co and C to obtain excellent wear resistance and heat resistance, and diffuses in the base contributes to high temperature stability. If the content is less than 1.0 parts by weight, the wear resistance of the precipitated particles are weak, and if the content exceeds 2.0 parts by weight, the base metal is vulnerable, and the machinability decreases, so that the enhanced effect cannot be expected. Therefore, the content is 1.3 to 1.7 parts by weight.

The Cu (90 parts by weight) -Sn (10 parts by weight) alloy added to the substrate is used to improve the strength by solid solution in the substrate. Since the thermal conductivity is excellent, the thermal load is reduced during high temperature operation and the flexibility of the sintered sintered body is reduced. Is improved. In addition, by solid solution in Fe during the sintering process to fine precipitate on the base during cooling contributes to the improvement of wear resistance. If the content is less than 2.0 parts by weight, the amount of the solid solution to the base is not enough to expect the above effects, and if the content exceeds 6.0 parts by weight, the tissue is uneven due to the remaining unemployed particles and the dimensional change is also the same phenomenon Dimensional management becomes difficult. Therefore, Cu content is set to 2.0 to 6.0 parts by weight, and Sn is regulated by other components.

C added to the matrix forms carbides with other elements and diffuses into the matrix, thereby improving wear resistance according to the improvement of the strength and hardness of the material, and C dissolved in the Fe matrix improves the strength of the matrix. If the content is less than 0.4 part by weight, the ferrite is excessively formed together with the ferrite in the base metal, so that the base is softened, thereby reducing the strength and wear resistance. On the other hand, if the content exceeds 1.2 parts by weight, the carbon remaining in the pearlite forms cementite having a network structure, thereby making the base metal vulnerable. Therefore, 0.4-1.2 weight part is suitable.

Since the MnS added to the matrix is stable and does not decompose as a compound even at a high temperature, it remains in the sintered compact in the form of MnS after sintering to obtain a sintered compact with good machinability during machining, but when the content exceeds 2.0 parts by weight, the matrix becomes brittle. The above effect is lowered.

Co-based hard particle phase (B) added as hard particles has a fine hardness mHv (100 g) of 600 to 900 and does not soften even at high temperature, and is a hard particle phase having excellent room temperature and high temperature wear resistance. Do it. The Co-based hard particle phase (B) is composed of 27.0 to 30.0 parts by weight Mo, 7.5 to 9.5 parts by weight Cr, 2.30 to 2.80 parts by weight Si, 0.05 or less parts by weight C, and the remaining Co, and the addition amount is 10.0 to 15.0 parts by weight. To wealth.

Mo-based hard particle phase (C) added as a hard particle phase has a fine hardness mHv (100g) 1000 to 1500, and is a hard particle phase having excellent abrasion resistance at room temperature and serves to propagate to the base under the load of the valve. The composition of the Mo-based hard particle phase (C) is composed of 60.0 to 65.0 parts by weight of Mo and the remaining Fe, and the addition amount is 5.0 to 10.0 parts by weight.

Hereinafter, a method of manufacturing a valve sheet using an iron-based small alloy according to the present invention will be described in detail with reference to the accompanying drawings.

As shown in Fig. 2, first, 0.5 to 2.0 parts by weight Cr, 6.0 to 10.0 parts by weight Mo, 0.1 to 2.0 parts by weight Si, 9.0 to 14.0 parts by weight Co, 0.5 to 2.0 parts by weight Ni, prepared through strict inspection, 2.0 to 6.0 Cu, 0.6 to 1.2 parts by weight C, 5.0 to 15.0 parts by weight Pb, 3.0 parts by weight or less After mixing the other and the raw material composition of the metal powder of Fe, these compositions are mixed in a double cone. Mix uniformly for about 40 minutes (S1).

Next, the mixed composition is compression molded at room temperature with an automatic molding machine using a high precision mold to form a molded body (S2). The density here is between 6.8 and 7.0 g / cc.

The subsequent step is a pre-sintering step (S3), which is a pretreatment operation of the cold forging step (S4) described later, and the A1 transformation point (723 ° C.) to the A3 transformation point (910 ° C.) in the Fe-C state diagram in which carbon is not diffused. The compacts compressed at a temperature are sintered in a gas atmosphere composed of a mixture gas of N ₂ , which is a neutral gas, and H _{2, which} is a reducing gas, and socialized to have some strength to perform cold forging (S3). Here, the reason for sintering using a mixed gas of (N ₂ + H ₂ ) during sintering is to prevent the sintered body from being affected by external environmental conditions.

Next, for densification of the mixed base structure (A) is carried out a cold forging process to increase the density to 7.2 ~ 7.5g / cc (S4). The cold forging process (S4) is charged to the pre-sintered body into the mold to apply a pressure of 10 ~ 15TON / ㎠ in the top and bottom to increase the density of the pre-sintered body to have a known densification. Here, the reason for carrying out the pre-sintering step (S3) and cold forging step (S4) as described above is to increase the density to 7.2 ~ 7.5g / cc.

When the cold forging process S4 as described above is completed, the cold forging body is sintered in a mixed gas atmosphere of (N ₂ + H ₂ ) at a temperature below the melting point (1130 ° C.) to form a Co-based hard particle (B). And Mo-based hard particle phase (C) is uniformly diffused and bonded to the matrix, and the matrix is subjected to secondary sintering to form sorbite and bainite (S5). As a result, the sintered compact has mechanical properties.

In the next step, the step (S6) of impregnating the excellent Pb in the pores formed on the mixed substrate (A) or hard particles (B, C) for self-lubrication of the sintered body, which is a vacuum state Use a batch-type Pb impregnation furnace that is heated while maintaining. That is, after the container on which the sintered body is mounted is charged in a Pb melt of the Pb impregnating furnace under vacuum, N ₂ gas is added at 4 atmospheres or more for 10 minutes to 60 minutes to increase the Pb impregnation efficiency into the pores of the sintered body. The Pb melt is impregnated. Then, the sintered body impregnated with Pb is taken out of the Pb melt and then cooled by cooling in the furnace.

Thereafter, the valve sheet as a finished product is obtained by going through the post-process of the barrel process for removing the iron bark after machining and machining (S7). The post-process described above is a general process for processing a sintered body to match the drawing dimensions, and the processing method according thereto is a high-polishing to match the height dimension, an outer-polishing to match the outer diameter, and the valve seat of the sintered body is press-fitting in the head. Chamfering is performed to facilitate this.

Finally, after removing the remainder of the jagged edge portion after the processing as described above is completed the manufacture of the valve sheet of the iron base alloy according to the present invention.

The valve sheet thus prepared has a surface hardness of HRA 55-75, mHv (100 g) mHv (100 g) 600-900 in a mixed base structure (A) of sorbite and bainite having a microhardness of 350-550. Co-based hard particle phase (B) having fine hardness and Mo-based hard particle phase (C) having fine hardness of 1000-1500 mHv (100 g) are uniformly distributed.

In addition, the self-lubrication of the product itself is excellent due to the impregnation of Pb, and the abrasion resistance, heat resistance, corrosion resistance, oxidation resistance, and high temperature characteristics against the harsh conditions of use that must withstand contact with the valve, friction, and exposure to exhaust gas. This is improved.

Meanwhile, the present invention has been described only with respect to the valve sheet to which the iron-based small alloy is applied, but is not limited thereto. The present invention is applicable to other parts requiring sufficient wear resistance and heat resistance.

As described above, the iron base alloy according to the present invention and a method for manufacturing a valve seat using the same have wear resistance and heat resistance that can cope with high engine output, and lead-free gasoline or diesel fuel, as well as LPG fuel At the same time, it has the advantage that it can be shared under different conditions.

Claims (6)

In the iron-based sintered alloy which is employed in the engine of the internal combustion engine and is applied to the engine valve sheet for maintaining the airtightness with the valve when opening and closing the intake and exhaust valve, and improving the thermal efficiency in the combustion chamber, 0.5 to 2.0 parts by weight Cr, 6.0 to 10.0 parts by weight Mo, 0.1 to 2.0 parts by weight Si, 9.0 to 14.0 parts by weight Co, 0.5 to 2.0 parts by weight Ni, 2.0 to 6.0 Cu, 0.6 to 1.2 parts by weight C, 5.0 to 15.0 Parts by weight Pb, not more than 3.0 parts by weight Others and the rest are provided with a composition made of Fe, the Co-based hard particles and Mo-based hard particles (B, C) uniformly in the mixed base structure (A) of sorbite and bainite An iron-based small alloy comprising a dispersion. The method of claim 1, Iron-based small bonds, characterized in that the addition of more than 2.0 parts by weight of MnS to the composition. The method of claim 1, The pores formed in the mixed base tissue (A) or the hard particle phase (B, C) is iron-based small alloy characterized in that the impregnated with Pb (D). In the method of manufacturing a valve sheet using an iron-based sintered alloy which is employed in an engine of an internal combustion engine and is applied to an engine valve sheet for maintaining an airtightness with the valve when opening and closing an intake / exhaust valve, thereby improving thermal efficiency in the combustion chamber. 0.5 to 2.0 parts by weight Cr, 6.0 to 10.0 parts by weight Mo, 0.1 to 2.0 parts by weight Si, 9.0 to 14.0 parts by weight Co, 0.5 to 2.0 parts by weight Ni, 2.0 to 6.0 Cu, 0.6 to 1.2 parts by weight C, 5.0 to 15.0 Parts by weight of Pb, 3.0 parts by weight or less, and the other and the rest are mixed with Fe and the composition is uniformly mixed in a mixer in a raw material mixture (S1); A molding step of forming a molded body by compression molding the mixed composition (S2); Pre-sintering step (S3) of sintering the molded body in a mixed gas atmosphere of N ₂ + H ₂ at a temperature at which carbon does not diffuse (S3); Cold forging step (S4) to charge the pre-sintered body into a mold and to increase the density of the pre-sintered body by applying a pressure of 10 ~ 15TON / ㎠ in the upper and lower (S4); The cold forging body is sintered in a mixed gas atmosphere of N ₂ + H ₂ at a temperature below the melting point, whereby Co-based hard particle phase (B) and Mo-based hard particle phase (C) are uniformly diffused and joined to the base, and the base is sorbite. And secondary sintering step (S5) to form bainite; A Pb impregnation process (S6) for impregnating Pb (D) having excellent lubricating properties in pores formed in the mixed base (A) or hard particle phases (B, C) for self lubrication of the sintered body; And A post-process (S7) of obtaining a finished product of the valve sheet by performing a barrel process for removing iron bark after machining and machining. The method of manufacturing a valve sheet using an iron-based small alloy. The method of claim 4, wherein The pre-sintering step (S3), A method of manufacturing a valve sheet using an iron-based small alloy, which is sintered at 723 ° C. to 910 ° C., which is a temperature between the A ₁ transformation point and the A ₃ transformation point. The method of claim 4, wherein The Pb impregnation step (S6), In the Pb impregnation process, the sintered body is heated in a vacuum state, the sintered body is charged in a Pb melt in a vacuum state, and then, N ₂ gas is added at 4 atmospheres or more for 10 minutes to 60 minutes to increase Pb impregnation efficiency. A method of manufacturing a valve sheet using an iron-based small alloy, characterized in that the Pb melt is impregnated in the pores of the sintered body.