Copper alloy for valve seat

Abstract

The present invention provides a copper alloy for valve seats, and more specifically, provides a copper alloy for valve seats with improved wear resistance, which contains 12 to 24% by weight of Ni, 2 to 4% by weight of Si, 7 to 13% by weight of Cr, 20 to 35% by weight of Fe, the balance being Cu and other impurities.

Description

Technical Field

[0001] The present invention relates to a copper alloy for a valve seat, and more particularly to a copper alloy for a valve seat having improved wear resistance. Background Art

[0002] A cylinder head of an engine is provided with engine valves such as intake valves or exhaust valves. Combustion explosion heat and mechanical shock generated during engine operation are transmitted from the engine valves to the cylinder head. However, an ordinary cylinder head is made of an aluminum (Al) material, and thus there is a problem of being damaged by high temperature and shock.

[0003] Therefore, in a conventional method of manufacturing a cylinder head, a valve seat made of an Fe-based powder sintered material is usually installed in a region in contact with the engine valve.

[0004] However, the valve seat made of the Fe-based powder sintered material must be installed on the cylinder head through a mechanical coupling. This causes a problem of requiring a separate fastening device, and has a disadvantage that a linear flow passage cannot be achieved because the valve seat needs to be formed to a certain thickness or greater thickness. In addition, there is a problem of the valve seat coming off during engine operation.

[0005] Meanwhile, since the valve seat needs to withstand conditions including contact with and friction against the engine valve and exposure to exhaust gas, the valve seat requires excellent heat resistance and wear resistance.

[0006] Therefore, recently, in the process of manufacturing a cylinder head, by using a laser cladding method of a Cu-based material, the corresponding region is strengthened by directly cladding a cladding layer on the region in contact with the engine valve.

[0007] However, a disadvantage of the cladding layer formed by using the laser cladding method of the Cu-based material is that its wear resistance is significantly lower than that of the valve seat made of the Fe-based powder material.

[0008] Therefore, in order to overcome the problems of the Cu-based material, a method of forming a valve seat by using a laser cladding method of an Fe-based material can be considered. However, in this case, the Fe-based material having a melting point of about 1400 °C or higher requires more heat input than the Cu-based material having a lower melting point of about 1000 °C. Therefore, a greater heat input may cause greater thermal damage to the cylinder head made of aluminum (Al). Due to the enlarged heat affected zone, this results in interfacial cracks and thermal cracks in the cladding region, thereby disadvantageously making it difficult to form a cladding layer having a leak-free and intact valve seat shape.

[0009] The above information disclosed in the background art section is only intended to deepen the understanding of the background art of the present disclosure, and thus it may include information that does not constitute the prior art known to those skilled in the art. Summary of the Invention

[0010] Therefore, in view of the above problems, the present disclosure is made, and an object of the present disclosure is to provide a copper alloy for a valve seat, which can improve wear resistance by forming a duplex clad layer in which a Cu matrix structure and an Fe matrix structure are formed together.

[0011] According to the present disclosure, the above and other objects can be achieved by providing a copper alloy for a valve seat, the copper alloy for a valve seat containing 12 to 24 wt% of Ni, 2 to 4 wt% of Si, 7 to 13 wt% of Cr, 20 to 35 wt% of Fe, the balance being Cu and other impurities.

[0012] The matrix structure of the copper alloy can be a duplex matrix structure including a Cu matrix structure and an Fe matrix structure formed together.

[0013] The copper alloy can form (Ni,Cr)Si-based hard phases in the matrix structure.

[0014] The area fraction of the Fe matrix structure in the copper alloy can be 20% to 40% of the total area.

[0015] The copper alloy can satisfy the following relational expression 1:

[0016] 20.7 < 1.27[Fe] - 0.36[Cr] < 42.0… (Relational expression 1)

[0017] where [Fe] and [Cr] represent the contents (wt%) of Fe and Cr.

[0018] The copper alloy does not form a Cr phase with a body-centered cubic structure (BCC).

[0019] The wear amount of the copper alloy measured under the following conditions in a high-temperature friction and wear test may be less than 20,000 μm 2 :

[0020] (Conditions of the high-temperature friction and wear test)

[0021] - Pin material: Inconel

[0022] - Load: 50 N

[0023] - Temperature: 200 °C

[0024] - Stroke: 7 mm

[0025] - Frequency: 6 Hz

[0026] - Atmosphere: Air

[0027] - Time: 10 minutes.

[0028] After laser cladding, the copper alloy can have a heat affected zone with a thickness of 1 mm or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, features, and other advantages of the present disclosure will be more clearly understood from the following detailed description presented in conjunction with the accompanying drawings, in which:

[0030] Figure 1 is a microstructural image of a cladding layer made of Cu-17Ni-3Si-30Fe material;

[0031] Figures 2A through 2I is a graph showing the calculation results of phase diagrams for respective contents of Fe depending on the added alloying elements;

[0032] Figure 3 is a graph showing the calculation results of phase diagrams for respective contents of Cr;

[0033] Figure 4A and Figure 4B are microstructural images of Example 2 and Comparative Example 17; and DETAILED DESCRIPTION

[0034] Now, embodiments of the present disclosure will be described in detail. Examples of the embodiments are shown in the accompanying drawings. However, the present disclosure is not limited to these embodiments and can be implemented in various different forms. These embodiments are provided only to fully illustrate the present disclosure and to enable those skilled in the art to fully understand the scope of the present disclosure.

[0035] The copper alloy for a valve seat according to an embodiment of the present disclosure is an alloy that can be used for laser cladding. For example, a cladding layer having improved heat resistance and wear resistance can be formed in a region where an engine valve contacts an engine cylinder head. This cladding layer serves as a conventional valve seat fixed to the cylinder head. Hereinafter, the layer formed by the laser cladding method using the copper alloy for a valve seat according to an embodiment of the present disclosure is referred to as a "cladding layer".

[0036] In the present embodiment, in order to improve the heat resistance and wear resistance of the cladding layer made of the copper alloy, the type and composition of the alloy are adjusted to form a (Ni,Cr)Si-based hard phase in the matrix structure, while forming a duplex matrix structure in which a Cu matrix structure and an Fe matrix structure are formed together. In addition, by adjusting the type and composition of the alloy, while controlling the area ratio of the Fe matrix structure, the formation of a body-centered cubic structure (BCC) Cr phase is prevented.

[0037] In particular, by adjusting the type and composition of the alloy, liquid immiscibility is induced, so that the Fe matrix structure is formed into a circular structure instead of a needle-like or reticular structure.

[0038] Specifically, the copper alloy for a valve seat according to an embodiment of the present disclosure contains 12 to 24 wt% of Ni, 2 to 4 wt% of Si, 7 to 13 wt% of Cr, 20 to 35 wt% of Fe, and the balance of Cu and other impurities.

[0039] Next, the reasons for defining the alloy components and their content ranges are described below. Hereinafter, unless otherwise specified, the percentage (%) refers to the weight percentage (%), which is the unit of the content range.

[0040] In some cases, the content of nickel (Ni) is or can be 12% to 24%. Nickel (Ni) forms a Cu-Ni-Si based solid state structure and forms strengthening phases that can be expressed as Ni x Si y (such as NiSi, NiSi2, Ni2Si, Ni3Si, Ni 31 Si 12 , Ni3Si2, and Ni5Si2), thereby improving the strength of the cladding layer made of the alloy. Therefore, maintaining the content of nickel (Ni) at 12% or more can maintain the excellent strength and wear resistance of the cladding layer. However, when the content of nickel (Ni) exceeds 24%, problems may occur, that is, the interfacial bonding between the cladding layer and the cylinder head as the base material may be reduced.

[0041] In some cases, the content of silicon (Si) is or can be 2% to 4%. Silicon (Si) forms a Cu-Ni-Si based solid state structure and forms strengthening phases that can be expressed as Ni x Si y (such as NiSi, NiSi2, Ni2Si, Ni3Si, Ni 31 Si 12 , Ni3Si2, and Ni5Si2), thereby improving the interfacial bonding between the cladding layer and the cylinder head as the base material. Therefore, maintaining the content of silicon (Si) at 2% or more can form appropriate strengthening phases while improving the interfacial bonding between the cladding layer and the cylinder head. However, when the content of silicon (Si) exceeds 4%, the increase in the fraction of the Cu-Ni-Si solid state structure will reduce the ductility of the cladding layer, causing problems of cracking.

[0042] In some cases, the content of chromium (Cr) is or can be 7% to 13%. Chromium (Cr) is an element that causes liquid immiscibility and inhibits the formation of acicular or reticular structures. Therefore, when the content of chromium (Cr) is less than 7%, liquid immiscibility may not be obtained or may not be obtained during solidification, resulting in the formation of acicular and reticular structures, thus leading to the problem of poor crack resistance. In addition, when the content of chromium (Cr) exceeds 13%, a body-centered cubic structure (BCC) Cr phase may be formed or may be formed, thus unfavorably causing brittleness.

[0043] In some cases, the content of iron (Fe) is or can be 20% to 35%. Iron (Fe) is an element that forms a hard Fe matrix structure and improves wear resistance. Therefore, when the content of iron (Fe) is less than 20%, due to the reduced proportion of the Fe matrix structure, there is a problem that the wear resistance cannot or may not be maintained at the desired level. When the content of iron (Fe) exceeds 35%, the following problems may occur: the cladding layer may crack and the thickness of the heat-affected zone will be greater than or equal to 1 mm.

[0044] Meanwhile, the balance, in addition to the above components, also includes copper (Cu) and impurities.

[0045] In particular, in this embodiment, the copper alloy defines the relative contents of iron (Fe) and chromium (Cr) to adjust the area fraction of the Fe matrix structure to 20% to 40% of the total area. Specifically, the relative contents between iron (Fe) and chromium (Cr) satisfy the following relational expression 1:

[0046] 20.7 < 1.27[Fe] - 0.36[Cr] < 42.0… (Relational expression 1)

[0047] Wherein, [Fe] and [Cr] represent the contents (wt%) of Fe and Cr.

[0048] Hereinafter, the present disclosure will be described with reference to the following comparative examples and examples.

[0049] The cladding layer formed by the laser cladding method using a Cu-Ni-Si-based material (the Cu-Ni-Si-based material is an alloy material commonly used in the laser cladding method) has or may have the following disadvantages: its wear resistance is significantly lower than that of a conventional valve seat made of an Fe-based powder material.

[0050] Therefore, first, in order to improve the wear resistance of the Cu-Ni-Si-based material, an experiment was conducted to form an Fe matrix structure and a Cu matrix structure by adding Fe to the Cu-Ni-Si-based material.

[0051] More specifically, a clad layer was formed on an aluminum (Al) base material by a laser cladding method using a Cu-17Ni-3Si-30Fe material, and the microstructure of the clad layer was observed. The results are shown in Figure 1 . Here, the Cu-17Ni-3Si-30Fe material refers to a copper alloy material containing 17 wt% of Ni, 3 wt% of Si, 30 wt% of Fe, and the balance of Cu and other impurities.

[0052] From Figure 1 it can be seen that when only Fe is added to the component system of Cu-17Ni-3Si, a duplex matrix structure including a Cu matrix structure and an Fe matrix structure is formed as the matrix structure, but the Fe matrix structure is formed into a needle-like and reticular structure. In Figure 1 , the structure with a relatively darker color represents the Fe matrix structure, and the structure with a relatively lighter color represents the Cu matrix structure.

[0053] The reason why the Fe matrix structure is formed into a needle-like and reticular structure is that liquid immiscibility cannot be obtained or may not be obtained. Even if the Fe matrix structure is formed, it will not or may not be randomly distributed, but takes the form of a needle-like and reticular structure.

[0054] When the Fe matrix structure has the needle-like and reticular structure as shown in Figure 1 , due to the increase in the size of the interface between the matrices and the fact that this interface provides a fracture path, the wear resistance of the clad layer will be significantly reduced.

[0055] Next, in order to induce liquid immiscibility, the following experiment was carried out: an Fe matrix structure together with a Cu matrix structure was formed using a Cu-17Ni-3Si-aFe-20Y material, where a represents the content of Fe (wt%), and Y is an alloy element added together with Fe. In this experiment, any one of the alloy elements of Mn, Cr, W, Co, Nb, Ti, V, Al, and Zr was selectively added as Y. Accordingly, the calculation results of the Fe content phase diagram for each material were determined, and the results are shown in Figures 2A through 2I . In Figures 2A through 2I , the region represented by the dark color is the region of liquid immiscibility (separation).

[0056] From Figures 2A through 2I 's results, it can be seen that liquid immiscibility occurs when Cr, V, and Zr are added, and liquid immiscibility does not occur when Mn, W, Co, Nb, Ti, and Al are added. Due to the addition of Cr, V, and Zr, the solubility of liquid Fe relative to Cu is reduced, so liquid immiscibility between the Cu-based component and the Fe-based component can be obtained or may be obtained, and thus the above results can be obtained or can be obtained.

[0057] Accordingly, it was confirmed that when Cr, V, and Zr were added, the Fe matrix structure was a circular structure rather than a needle-like or reticular structure, and a duplex structure in which the Cu matrix structure and the Fe matrix structure were formed together was obtained.

[0058] However, among the added components, V is a relatively expensive alloying element, and Zr has a small liquid immiscibility region and thus does not effectively cause a structural change. Therefore, it can be seen that by adding Fe and Cr to the Cu-Ni-Si-based material, liquid immiscibility between the Fe-based matrix structure and the Cr-based matrix structure can be caused.

[0059] Next, in order to determine the appropriate Cr content, experiments were conducted to confirm the change in the alloy state of the Cu-17Ni-3Si-25Fe-bCr material, where b represents the content of Cr (wt%). Therefore, the calculation results of the phase diagram depending on the Cr content were obtained, and the results are shown in Figure 3 .

[0060] From Figure 3 it can be seen that in the region where the Cr content is 5 wt%, in some cases where it is less than 7 wt%, the temperature region where liquid immiscibility occurs is narrow or may be narrow, so it may be difficult to avoid the formation of needle-like and reticular structures. In addition, in the region where the Cr content is 15 wt%, in some cases where it is greater than 13 wt%, a body-centered cubic structure (BCC) Cr phase is formed or may be formed, which may cause a problem of poor impact toughness. Therefore, in some cases, the Cr content is or can be 7 wt% - 13 wt%.

[0061] Next, in order to determine the appropriate contents of Fe and Cr in the Cu-Ni-Si-based material, as shown in Table 1, a clad layer was formed on an aluminum (Al) base material by a laser cladding method using copper alloys with adjusted component contents. The occurrence of cracks, the thickness of the heat-affected zone, the amount of wear, and the microstructure in the clad layer were measured and observed, and the results are shown together in Table 1. In addition, the microstructures of Example 2 and Comparative Example 16 in Table 1 are shown in Figure 4A and Figure 4B respectively.

[0062] Table 1: Components and experimental results of comparative examples and examples

[0063]

[0064] At this time, a dye penetrant inspection method (ISO3452-1, Non-destructive testing - Penetrant testing) was used to evaluate whether cracks occurred.

[0065] More particularly, dye penetrant inspection (DPI) is a method that utilizes capillary action. First, the specimen is washed with a washing solution, the penetrant solution is sprayed onto the area to be inspected and dried for 5 minutes, and then the penetrant solution on the surface of the specimen is removed with the washing solution. Then, the developer solution is sprayed onto the surface of the specimen to determine if there are any areas where the colored penetrant solution remains. Since the penetrant solution remains in the cracks, the areas where the colored penetrant solution is determined to be present correspond to the cracks.

[0066] In addition, the wear amount is measured by a high-temperature friction and wear test, and the test conditions are as follows.

[0067] (Conditions of the high-temperature friction and wear test)

[0068] - Needle material: Inconel

[0069] - Load: 50 N

[0070] - Temperature: 200 °C

[0071] - Stroke: 7 mm

[0072] - Frequency: 6 Hz

[0073] - Atmosphere: Air

[0074] - Time: 10 minutes.

[0075] As can be seen from Table 1, Figure 4A and Figure 4B Examples 1 to 8, which are examples that satisfy the alloy components and their contents proposed in the present disclosure, all avoid cracking and satisfy the requirements for the thickness (1 mm or less), wear amount (less than 20,000 μm 2 ) and area ratio (20% - 40%) of the heat-affected zone of the Fe matrix structure proposed in the present disclosure.

[0076] Moreover, as can be seen from Figure 4A the microstructure image of Example 2 shows a duplex structure in which the Cu matrix structure and the Fe matrix structure are formed together as the matrix structure. Specifically, each microstructure is shown to be circular.

[0077] In addition, Comparative Examples 1 to 6, which are comparative examples where the content of Fe is less than the content proposed in the present disclosure, avoid cracking and have a smaller thickness of the heat-affected zone. However, it can be confirmed that since the Fe matrix structure is not formed or not sufficiently formed, the wear amount increases significantly.

[0078] In addition, Comparative Examples 7 to 9 are comparative examples in which the content of Fe exceeds the content recommended in the present disclosure. Since the Fe matrix structure is excessively formed, cracks are formed and the thickness of the heat-affected zone also increases. At this time, the wear amount cannot be measured.

[0079] In particular, the reason for cracking is as follows. As the heat input increases, an intermetallic compound layer such as AlCu2 may be formed or is likely to be formed at the interface of the clad layer formed of an aluminum (Al)-based material and alloy, and its thickness increases. The thickened intermetallic compound layer may be brittle. Therefore, the stress generated during the solidification and shrinkage of the alloy forming the clad layer causes crack formation. Therefore, in order to avoid cracking, the intermetallic compound layer can be formed to be thin. For this purpose, the heat input amount can be reduced, and the content of Fe as a high melting point element can be limited.

[0080] In addition, Comparative Examples 10 to 12, as comparative examples in which the content of Cr exceeds the content recommended in the present disclosure, avoid cracking and have a smaller thickness of the heat-affected zone. However, with the formation of the body-centered cubic structure (BCC) Cr phase, it is found that the wear amount increases significantly. In addition, small holes are generated in Comparative Examples 10 to 12.

[0081] In addition, Comparative Examples 13 to 15 are comparative examples in which the content of Cr is less than the content recommended in the present disclosure. The thickness of the heat-affected zone is thin, and a duplex phase is formed as the matrix structure, which includes a Cu matrix structure and an Fe matrix structure formed together. However, it can be confirmed that deep cracks are formed due to the formation of a needle-like or reticular Fe matrix structure, and the wear amount also increases significantly.

[0082] In addition, Comparative Example 16 is a comparative example in which Fe is added alone to the component system of Cu-17Ni-3Si. As in Comparative Examples 13 to 15, the heat-affected zone is thinner, and a duplex phase is formed as the matrix structure, in which the Cu matrix structure and the Fe matrix structure are formed together. However, it can be confirmed that with the formation of a needle-like or reticular Fe matrix structure, deep cracks are formed and the wear amount also increases significantly.

[0083] In addition, from Figure 4B it can be seen that the microstructural image of Comparative Example 16 shows a duplex structure in which the Cu matrix structure and the Fe matrix structure are formed together as the matrix structure. However, it can be confirmed that liquid immiscibility does not occur properly, so a needle-like or reticular Fe matrix structure is formed.

[0084] Meanwhile, in the present disclosure, in order to adjust the area fraction of the Fe matrix structure to 20% to 40% of the total area, the relative contents between the Fe content and the Cr content are restricted as shown in the following relational expression 1:

[0085] 20.7 < 1.27[Fe] - 0.36[Cr] < 42.0…(Relationship 1)

[0086] Wherein, [Fe] and [Cr] represent the contents of Fe and Cr (wt%).

[0087] Therefore, in order to determine the applicability of the above Relationship 1, in the component system of Cu - 17Ni - 3Si, alloys with varying Fe and Cr contents as shown in Table 2 were formed, and the values of 1.27[Fe] - 0.36[Cr] and the area fraction of the Fe matrix structure for each alloy were determined. The results are shown together in Table 2.

[0088] Table 2: Relationship between the area fraction of the Fe matrix structure varying with Fe and Cr contents and Relationship 1

[0089]

[0090] As can be seen from Table 2, alloys 1 to 9 that satisfy the Fe and Cr contents recommended in the present disclosure satisfy Relationship 1 and the area fraction of the Fe matrix structure.

[0091] However, alloys 10 to 18 that satisfy the Fe content recommended in the present disclosure neither satisfy Relationship 1 nor the area fraction of the Fe matrix structure.

[0092] In addition, alloy 19 that satisfies the Cr content recommended in the present disclosure neither satisfies Relationship 1 nor the area fraction of the Fe matrix structure.

[0093] It is obvious from the foregoing that according to the embodiments of the present disclosure, a hard Fe matrix structure can be formed on the Cu matrix structure with an area ratio of 20% to 40%, thereby forming a cladding layer with excellent wear resistance.

[0094] As a result, compared with the cladding layer obtained by the method of separately manufacturing a valve seat and fixing it to the cylinder head, this cladding layer is thinner. Therefore, an improved intake and exhaust efficiency effect can be obtained by realizing the linear intake and exhaust channels of the engine.

[0095] As a result, by achieving a high tumble effect in the cylinder, an effect of improving the fuel efficiency of the engine can be obtained.

[0096] Although the embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art should understand that various modifications, additions, and deletions are possible without departing from the scope and spirit of the present invention disclosed in the appended claims.

Claims

1. A copper alloy for a valve seat, which consists of the following: 17 to 24 wt% of Ni; 2 to 4 wt% of Si; 7 to 13 wt% of Cr; 20 to 35 wt% of Fe; The balance of Cu and other impurities; wherein the matrix structure of the copper alloy is a duplex matrix structure comprising a Cu matrix structure and an Fe matrix structure formed together; wherein the copper alloy forms (Ni,Cr)Si-based hard phases in the matrix structure; wherein the copper alloy satisfies the following relationship 1: 20.7 < 1.27[Fe] - 0.36[Cr] < 42.0 ··· Relationship 1 where [Fe] and [Cr] represent the wt% contents of Fe and Cr; wherein the area fraction of the Fe matrix structure in the copper alloy is 20% to 40% of the total area.

2. The copper alloy for a valve seat according to claim 1, wherein, The copper alloy does not form a Cr phase with a body-centered cubic structure.

3. The copper alloy for a valve seat according to claim 1, wherein, The wear amount of the copper alloy measured under the following conditions in the high-temperature friction and wear test is less than 20,000 µm 2 : Conditions of the high-temperature friction and wear test - Pin material: Inconel alloy, - Load: 50 N, - Temperature: 200 °C, - Stroke: 7 mm, - Frequency: 6 Hz, - Atmosphere: Air, and - Time: 10 minutes.

4. The copper alloy for a valve seat according to claim 1, wherein, After laser cladding, the copper alloy has a heat-affected zone with a thickness of 1 mm or less.

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