Manufacturing method of nitrided valve seat ring with supersaturated nitrogen surface layer and product thereof

Abstract

A pre-surface hardened valve seat ring and a method of forming the same, the valve seat ring may be used for embedding a cylinder head or an engine block of an internal combustion engine. The method includes the steps of: (a) forming the valve seat ring by casting an iron-chromium alloy containing no more than 75 wt.% (weight percent) of iron and at least 25 wt.% of alloying elements including at least 9 wt.% of chromium; (b) the valve seat ring is precisely machined to the precise tolerance, so that the valve seat ring can be installed in a cylinder cover or an engine cylinder body, and no matter whether additional seat ring machining is needed or not; and (c) treating the valve seat ring to form an exposed wear resistant surface layer free of supersaturated nitrogen of nitride.

Description

BACKGROUND 1. TECHNICAL FIELD

[0001] The present invention relates to an internal combustion engine valve seat insert and method of making the same, and more particularly, to a valve seat insert that is precision formed and surface treated prior to being inserted into an internal combustion engine.

[0002] 2. RELATED PRIOR ART

[0003] Valve seat inserts produced by known monolithic or composite methods can experience wear in certain engine applications or can cause wear to other engine components, such as mating valves. With monolithic or composite valve seat inserts, the surface of the insert is finished after being inserted into the cylinder head or engine block. In order to finish the surface, the material used for the insert must be machinable, which in turn reduces the wear resistance of the material.

[0004] With monolithic materials, it is common practice to produce the monolithic material into a valve seat insert by casting, forging or powder metallurgy processes. The valve seat insert is then inserted into the cylinder head or engine block and the surface of the insert is machined. Thus, the wear resistance of the surface of the insert is the same as the bulk monolith from which the insert is made and is typically susceptible to wear problems.

[0005] Composite inserts have also been used that employ a cladding or bimetallic powder metallurgy product that coats a low alloy content substrate with a wear resistant material. However, this type of valve seat is first inserted into the cylinder head or engine block and then the surface of the insert is finished after being inserted. Finishing after the wear resistant material is applied wears away the wear resistant material and makes the valve seat insert more susceptible to wear. Another approach is to nitride the valve seat insert as described in commonly owned U.S. Patent Nos. 6,519,847 and 7,216,427.

[0006] A problem with conventional nitriding of valve seat inserts is that a nitride "white layer" forms above the nitride diffusion zone. The thermal expansion coefficient of the white layer (nitride zone) is significantly different from the thermal expansion coefficient of the underlying base material, and thus, separation between the compound zone and the base can occur at high temperatures or cyclic thermal environments. The broken pieces of the compound zone can cause high wear rates during engine operation. Thus, there is a need in the art for improved valve seat inserts that have higher wear resistance under engine operating conditions.

[0007] Nitriding is a common surface treatment method for iron-based alloys, which can improve surface hardness and thus enhance wear resistance. Ferritic nitrocarburizing can be achieved using salt bath methods, vapor phase methods, and ion nitriding methods. Ferritic nitriding is usually carried out in the temperature range of 560 to 580°C, which is lower than the A1 temperature of common iron-based alloy systems.

[0008] During the nitriding process, iron-based alloy parts form several different iron-nitrogen phases, including α phase, α′ phase, γ phase, γ′ phase, ε phase, η phase, and γ″ phase. Among them, the ε phase nitride (Fe) 2-3 Nitrogen (N) or ε-phase + γ′-phase (Fe4N) is generally considered to be the basic component of the white nitride layer (compound region). In most cases, a lower diffusion layer consisting of a nitrogen-rich matrix and nitride precipitates is formed. The thickness of the compound layer is typically no more than 10 μm, while the thickness of the diffusion region can be significantly increased, depending on the alloy matrix to which the nitriding is applied. Summary of the Invention

[0009] This invention represents a significant improvement over existing valve seat manufacturing processes. By eliminating the white layer typically formed during valve seat nitriding and instead creating an exposed supersaturated nitrogen surface area on the valve seat (this area will not crack under engine operating conditions), this invention overcomes the aforementioned limitations of the prior art.

[0010] In one embodiment, a method for forming a surface-hardened valve seat ring suitable for embedding in a cylinder head or engine block of an internal combustion engine includes the following steps: casting the valve seat ring with an iron-chromium alloy containing no more than 75 wt.% iron and at least 25 wt.% of an alloying element, said alloying element including at least 9 wt.% chromium; precision machining the valve seat ring to achieve precise tolerances such that the valve seat ring can be installed in the cylinder head or engine block, regardless of whether additional seat ring machining is required; and nitriding the valve seat ring to produce an exposed supersaturated nitrogen region free of nitride white layer.

[0011] In various embodiments, the nitriding step includes ferritic carburizing, carbonitriding, or gas nitriding of the valve seat. In a preferred embodiment, the alloy is melted and formed into the shape of the valve seat during the casting step.

[0012] According to the implementation plan, the iron-chromium alloy comprises 0.15-2.00 wt.% C, 0.3-1.0 wt.% Mn, 0.10-2.15 wt.% Si, 0.35-2.25 wt.% Ni, 9.0-33.5 wt.% Cr, up to 15.3 wt.% Mo, up to 2.6 wt.% V, up to 2.3 wt.% Nb, up to 4 wt.% W, up to 19 wt.% Co, up to 0.23 wt.% B, with the balance being incidental impurities and 50-75 wt.% Fe.

[0013] According to the implementation plan, the iron-chromium alloy comprises 0.1-2.2 wt.% C, 0.1-1.5 wt.% Mn, 0.1-2.5 wt.% Si, 0.15-3.00 wt.% Ni, 9-35 wt.% Cr, up to 17 wt.% Mo, up to 3 wt.% V, up to 2.5 wt.% Nb, up to 5 wt.% W, up to 21 wt.% Co, up to 0.3 wt.% B, with the balance being incidental impurities and 50-75 wt.% Fe.

[0014] According to the implementation plan, the iron-chromium alloy comprises 1.45-1.60 wt.% C, 0.35-0.45 wt.% Mn, 0.1-0.6 wt.% Si, 0.35-1.00 wt.% Ni, 9.8-13.0 wt.% Cr, 5.40-9.15 wt.% Mo, 1.25-1.30 wt.% V, 1.9-2.0 wt.% Nb, up to 4 wt.% W, up to 3.7 wt.% Co, up to 0.23 wt.% B, with the balance being incidental impurities and 67.5-71.0 wt.% Fe.

[0015] According to the implementation plan, the iron-chromium alloy comprises 1.3-1.7 wt.% C, 0.3-0.5 wt.% Mn, 0.1-0.8 wt.% Si, 0.3-2.0 wt.% Ni, 9-15 wt.% Cr, 5-10 wt.% Mo, 1.0-1.5 wt.% V, 1.8-2.2 wt.% Nb, up to 5 wt.% W, up to 4 wt.% Co, up to 0.3 wt.% B, with the balance being incidental impurities and 67-71 wt.% Fe.

[0016] According to the implementation scheme, the iron-chromium alloy comprises 0.1-0.2 wt.% C, 0.3-0.5 wt.% Mn, up to 0.2 wt.% Si, up to 2 wt.% Ni, 14-16 wt.% Cr, 14-16 wt.% Mo, 2-3 wt.% V, 1-3 wt.% Nb, up to 0.1 wt.% W, up to 1 wt.% Co, up to 0.2 wt.% B, the balance being incidental impurities, and 60-64 wt.% Fe.

[0017] According to the implementation plan, the iron-chromium alloy comprises 1.8-2.1 wt.% C, 0.1-0.5 wt.% Mn, 0.3-0.8 wt.% Si, 2-3 wt.% Ni, 14-18 wt.% Cr, 10-14 wt.% Mo, up to 0.2 wt.% V, up to 0.05 wt.% Nb, up to 0.3 wt.% W, 17-21 wt.% Co, up to 0.1 wt.% B, with the balance being incidental impurities and 48-52 wt.% Fe.

[0018] According to the implementation plan, the iron-chromium alloy comprises 1.55-2.00 wt.% C, 0.35-0.40 wt.% Mn, 0.1-2.0 wt.% Si, 1.1-2.0 wt.% Ni, 20.0-33.5 wt.% Cr, up to 2 wt.% Mo, up to 0.05 wt.% V, up to 2.3 wt.% Nb, up to 1.5 wt.% W, up to 0.05 wt.% Co, up to 0.2 wt.% B, with the balance being incidental impurities and 54-75 wt.% Fe.

[0019] According to the implementation plan, the iron-chromium alloy comprises 1.5-2.1 wt.% C, 0.3-0.5 wt.% Mn, 0.1-2.1 wt.% Si, 1.0-2.5 wt.% Ni, 20-35 wt.% Cr, up to 3 wt.% Mo, up to 0.1 wt.% V, up to 2.5 wt.% Nb, up to 2 wt.% W, up to 0.1 wt.% Co, up to 0.3 wt.% B, with the balance being incidental impurities and 50-75 wt.% Fe.

[0020] According to the implementation scheme, a valve seat ring is cast from an iron-chromium alloy having no more than 75 wt.% Fe and at least 25 wt.% of alloying elements, said alloying elements including at least 9 wt.% chromium.

[0021] According to the implementation plan, the nitrogen content in the supersaturated nitrogen region is 1-5 wt.%.

[0022] According to the implementation plan, the valve seat ring is cast from an iron-chromium alloy melt containing 1.45-1.60 wt.% C, 0.35-0.45 wt.% Mn, 0.1-0.6 wt.% Si, 0.35-1.00 wt.% Ni, 9.8-13.0 wt.% Cr, 5.40-9.15 wt.% Mo, 1.25-1.30 wt.% V, 1.9-2.0 wt.% Nb, up to 4 wt.% W, up to 3.7 wt.% Co, up to 0.23 wt.% B, with the balance being incidental impurities and 67.5-71.0 wt.% Fe.

[0023] According to the implementation plan, the valve seat ring is cast from an iron-chromium alloy melt containing 1.3-1.7 wt.% C, 0.3-0.5 wt.% Mn, 0.1-0.8 wt.% Si, 0.3-2.0 wt.% Ni, 9-15 wt.% Cr, 5-10 wt.% Mo, 1.0-1.5 wt.% V, 1.8-2.2 wt.% Nb, up to 5 wt.% W, up to 4 wt.% Co, up to 0.3 wt.% B, with the balance being incidental impurities and 67-71 wt.% Fe.

[0024] According to the implementation plan, the valve seat ring is cast from an iron-chromium alloy melt containing 0.1-0.2 wt.% C, 0.3-0.5 wt.% Mn, up to 0.2 wt.% Si, up to 2 wt.% Ni, 14-16 wt.% Cr, 14-16 wt.% Mo, 2-3 wt.% V, 1-3 wt.% Nb, up to 0.1 wt.% W, up to 1 wt.% Co, up to 0.2 wt.% B, with the balance being incidental impurities and 60-64 wt.% Fe.

[0025] According to the implementation plan, the valve seat ring is cast from an iron-chromium alloy melt containing 1.8-2.1 wt.% C, 0.1-0.5 wt.% Mn, 0.3-0.8 wt.% Si, 2-3 wt.% Ni, 14-18 wt.% Cr, 10-14 wt.% Mo, up to 0.2 wt.% V, up to 0.05 wt.% Nb, up to 0.3 wt.% W, 17-21 wt.% Co, up to 0.1 wt.% B, with the balance being incidental impurities and 48-52 wt.% Fe.

[0026] According to the implementation plan, the valve seat ring is cast from an iron-chromium alloy melt containing 1.5-2.1 wt.% C, 0.3-0.5 wt.% Mn, 0.1-2.1 wt.% Si, 1.0-2.5 wt.% Ni, 20-35 wt.% Cr, up to 3 wt.% Mo, up to 0.1 wt.% V, up to 2.5 wt.% Nb, up to 2 wt.% W, up to 0.1 wt.% Co, up to 0.3 wt.% B, with the balance being incidental impurities and 50-75 wt.% Fe.

[0027] According to the implementation plan, the valve seat ring is made of an iron-chromium alloy that can be nitrided at low temperatures to form an exposed supersaturated nitrogen surface area without a nitride white layer. Attached Figure Description

[0028] Figure 1A (100x) Figure 1B (200x) and Figure 1C (500x) is a micrograph of J120V after ion nitriding at 560℃ for 15 hours.

[0029] Figure 2A (100x) Figure 2B (200x) and Figure 2C (500x) is a micrograph of the product after salt bath nitriding at 580℃ for 3 hours at 120V.

[0030] Figure 3A (100x) and Figure 3B (500x) is a micrograph of J160 after ion nitriding at 500℃ for 10 hours.

[0031] Figure 4A (100x) and Figure 4B (500x) is a micrograph of J160 after ion nitriding at 560℃ for 10 hours.

[0032] Figure 5A (100x) and Figure 5B (500x) is an image of J155 after ion nitriding at 500℃ for 15 hours.

[0033] Figure 6A (100x) and Figure 6B (500x) is an image of J122 after ion nitriding at 500℃ for 15 hours.

[0034] Figure 7A (100x) and Figure 7B (500x) is an image of J125 after ion nitriding at 500℃ for 15 hours.

[0035] Figure 8A (100x) and Figure 8B (500x) is an image of J130 after ion nitriding at 500℃ for 15 hours.

[0036] Figure 9A (100x) and Figure 9B (500x) is an image of J303 after ion nitriding at 500℃ for 15 hours.

[0037] Figure 10A (100x) and Figure 10B (500x) is an image of J513 after ion nitriding at 500℃ for 15 hours.

[0038] Figure 11 This is a graph showing the relationship between iron content and diffusion zone depth.

[0039] Figure 12A To display the microhardness curve of the J120V sample after salt bath nitriding at 580℃ for 3 hours, Figure 12B To display the microhardness curve of the J160N sample after gas nitriding at 571℃ for 3 hours. Detailed Implementation

[0040] In general, the valve seat ring and its manufacturing method according to the present invention can be divided into two aspects: first, the valve seat ring is precision formed; second, before the precision formed valve seat ring is embedded into the engine cylinder block, it is treated to improve wear resistance.

[0041] In one embodiment, the valve seat ring is formed by sand casting of a high-alloy iron-based alloy (e.g., an iron-chromium alloy) containing no more than 75 wt.% iron and at least 25 wt.% of an alloying element, including at least 9 wt.% chromium. Sand casting techniques known in the art are employed. However, it should be understood that other techniques may also be considered for producing rough-machined valve seat rings.

[0042] J120V nitrided steel (M2 tool steel produced by assignee LE Jones) has been used in valve seat applications, with typical nitriding temperatures in the range of 560-580°C. Figure 1A -C are micrographs at 100x, 200x, and 500x magnification, respectively, of J120V after ion nitriding at 560°C for 15 hours. At this ion nitriding temperature, an exposed compound layer (white layer) is formed on the surface.

[0043] Figure 2A -C are micrographs at 100x, 200x, and 500x, respectively, of J120V after salt bath nitriding at 580°C for 3 hours. At this salt bath nitriding temperature, an exposed surface compound layer (white layer) is formed.

[0044] The nitriding response study of J120V indicates that the formation of a compound layer in J120V reduces the tendency for diffusion layer formation in the alloy system. The nitriding process is a diffusion-controlled process; therefore, the nitriding temperature is a key factor affecting compound layer formation, besides the base alloy system.

[0045] Compared to J120V, the J160 alloy (produced by the assignee LE Jones) has a significantly higher total alloy element content and a unique microstructure. In J160, the interdendritic region constitutes a significant portion of the matrix, while in J120V, only a thin layer of network carbides exists between the dendrites.

[0046] Figure 3A (100x) and Figure 3B (500x) are micrographs of the J160 after 10 hours of ion nitriding at 500°C. These images show only the diffusion layer. Notably, the diffusion layer consists of two distinct regions: a dark area and a bright area beneath it. The dark area likely contains supersaturated nitrogen and iron nitride precipitates, while the bright area is primarily composed of a matrix containing supersaturated nitrogen. Unlike the compound region, the thickness of the supersaturated nitrogen surface layer can be significantly increased; for example, depending on the matrix system and nitriding conditions, the depth can reach 0.5 mm. Therefore, after installing VSI in the engine cylinder head or block, only a small amount of removal of the seat ring surface is required. Furthermore, the bonding strength between the supersaturated nitrogen layer and the underlying matrix is ​​significantly higher than that between the nitride layer and the matrix.

[0047] Figure 4A (100x) and Figure 4B (500x) is a micrograph of J160 after ion nitriding at 560℃ for 10 hours. When the nitriding temperature is increased to 560℃, the size of the diffusion layer is essentially the same as that of the sample nitrided at 500℃. Therefore, the surface nitriding response of J160 differs significantly from that of J120V. Thus, the compositional differences between the J120V and J160 alloys are considered the main reason for their different nitriding responses.

[0048] To verify the above hypothesis, the nitriding response of six additional alloys was evaluated. The nominal compositions of all evaluated alloys are summarized in Table 1. Of these eight iron-based alloys, J120V, J122, and J125 are tempered martensitic matrix alloys; J130 and J160 are martensitic + eutectoid matrix alloys; J155 is a ferrite + primary carbide matrix alloy; J303 is a ferrite matrix alloy; and J513 is an intermetallic compound + martensitic matrix alloy.

[0049] Table 1: Composition of the alloy systems being evaluated Alloy C Mn Si Ni Cr Mo v Nb W Co P S B Fe J120V 1.35 0.45 0.45 - 3.90 6.50 1.50 - 5.50 - - - - ～80.0 J122 0.90 0.70 2.00 - 3.00 4.50 - - - - - - - ～88.5 J125 1.55 0.40 2.15 1.10 20.0 - - - - - - - - ～75.0 J130 1.60 0.45 0.10 1.00 9.80 9.15 1.30 1.90 - - - - 0.23 ～71.0 J155 2.00 0.35 2.00 2.00 33.5 2.00 - 2.30 1.50 - - - 0.15 ～54.0 J160 1.45 0.35 0.60 0.35 13.0 5.40 1.25 2.00 4.00 3.70 - - - ～67.5 J303 0.155 0.45 0.10 1.00 15.3 15.3 2.60 2.00 - 0.55 - - 0.15 ～62.0 J513 1.95 0.30 0.50 2.25 16.0 12.0 0.10 - 0.145 19.0 - - 0.05 ～50.0

[0050] Figures 5 to 10 are micrographs of J155, J122, J125, J130, J303, and J513 after ion nitriding, respectively. All six alloys underwent ion nitriding at 500°C for 15 hours. Of the six alloys, only J122 formed a compound layer with a thickness of approximately 2 μm. The other five ion-nitrided alloys did not form a compound layer.

[0051] The diffusion layers of J155, J125, J130, J160, J303 and J513 are approximately 50 μm, 70 μm, 75 μm, 75 μm and 45 μm, respectively. Figure 5A (100x) and Figure 5B (500x) is an image of J155 after ion nitriding at 500℃ for 15 hours. Figure 6A (100x) and Figure 6B (500x) is an image of J122 after ion nitriding at 500℃ for 15 hours. Figure 7A (100x) and Figure 7B (500x) is an image of J125 after ion nitriding at 500℃ for 15 hours. Figure 8A (100x) and Figure 8B (500x) is an image of J130 after ion nitriding at 500℃ for 15 hours. Figure 9A (100x) and Figure 9B (500x) is an image of J303 after ion nitriding at 500℃ for 15 hours. Figure 10A (100 times) and Figure 10B (500x) is an image of J513 after ion nitriding at 500℃ for 15 hours.

[0052] Figure 11 The relationship between iron content and diffusion zone depth was shown. Among the eight iron-based alloys tested, the diffusion layer was most pronounced when the iron content was approximately 65 wt.%. Furthermore, the tendency to form a nitride compound layer was significantly suppressed when the iron content was below approximately 75 wt.% (preferably below 70 wt.%) and the chromium content was above approximately 9 wt.% (preferably above approximately 9.8 wt.%). Therefore, J130 and J160 are highly likely to form a significant diffusion layer without a compound region during nitriding. For many engineering applications, such as valve seat rings, nitride components with only a diffusion layer are superior to those with a surface compound layer because the surface compound layer is more easily separated from the underlying substrate by thermal action.

[0053] In the implementation scheme, suitable alloys for ion nitriding without a white layer (compound-free region) include the J125, J130, J155, J160, J303 and J513 alloys listed in Table 1, with the following compositions: 0.15-2.00 wt.% C, 0.3-1.0 wt.% Mn, 0.10-2.15 wt.% Si, 0.35-2.25 wt.% Ni, 9.8-33.5 wt.% Cr, up to 15.3 wt.% Mo, up to 2.6 wt.% V, up to 2.3 wt.% Nb, up to 4 wt.% W, up to 19 The alloys contain wt.% Co, up to 0.23 wt.% B, with the balance being occasional impurities and 50-75 wt.% Fe; or more generally, 0.1-2.2 wt.% C, 0.1-1.5 wt.% Mn, 0.1-2.5 wt.% Si, 0.15-3.00 wt.% Ni, 9-35 wt.% Cr, up to 17 wt.% Mo, up to 3 wt.% V, up to 2.5 wt.% Nb, up to 5 wt.% W, up to 21 wt.% Co, up to 0.3 wt.% B, with the balance being occasional impurities and 50-75 wt.% Fe. These iron-chromium alloys can be cast to have a matrix microstructure, such as tempered martensitic matrix, martensite + eutectoid matrix, ferrite + primary carbide matrix, ferrite matrix, or intermetallic compound + martensitic matrix alloys.

[0054] In embodiments covering J130 and J160 alloys, the alloy composition suitable for nitriding includes: 1.45-1.60 wt.% C, 0.35-0.45 wt.% Mn, 0.1-0.6 wt.% Si, 0.35-1.00 wt.% Ni, 9.8-13.0 wt.% Cr, 5.40-9.15 wt.% Mo, 1.25-1.30 wt.% V, 1.9-2.0 wt.% Nb, up to 4 wt.% W, up to 3.7 wt.% Co, and up to 0.23 wt.% B. The balance is for incidental impurities and 67.5-71.0 wt.% Fe; or more generally, 1.3-1.7 wt.% C, 0.3-0.5 wt.% Mn, 0.1-0.8 wt.% Si, 0.3-2.0 wt.% Ni, 9-15 wt.% Cr, 5-10 wt.% Mo, 1.0-1.5 wt.% V, 1.8-2.2 wt.% Nb, up to 5 wt.% W, up to 4 wt.% Co, up to 0.3 wt.% B, with the balance being for incidental impurities and 67-71 wt.% Fe.

[0055] In embodiments covering the J303 alloy, which differs from other alloys in that it has a very low carbon content, the alloy suitable for nitriding comprises: 0.1-0.2 wt.% C, 0.3-0.5 wt.% Mn, up to 0.2 wt.% Si, up to 2 wt.% Ni, 14-16 wt.% Cr, 14-16 wt.% Mo, 2-3 wt.% V, 1-3 wt.% Nb, up to 0.1 wt.% W, up to 1 wt.% Co, up to 0.2 wt.% B, the balance being incidental impurities and 60-64 wt.% Fe.

[0056] In embodiments covering the J513 alloy, the alloy differs from other alloys in that it has a very high Co content. The alloys suitable for nitriding include: 1.8-2.1 wt.% C, 0.1-0.5 wt.% Mn, 0.3-0.8 wt.% Si, 2-3 wt.% Ni, 14-18 wt.% Cr, 10-14 wt.% Mo, up to 0.2 wt.% V, up to 0.05 wt.% Nb, up to 0.3 wt.% W, 17-21 wt.% Co, up to 0.1 wt.% B, with the balance being incidental impurities and 48-52 wt.% Fe.

[0057] In embodiments covering J125 and J155 alloys, the alloys suitable for nitriding include: 1.55-2.00 wt.% C, 0.35-0.40 wt.% Mn, 0.1-2.0 wt.% Si, 1.1-2.0 wt.% Ni, 20.0-33.5 wt.% Cr, up to 2 wt.% Mo, up to 0.05 wt.% V, up to 2.3 wt.% Nb, up to 1.5 wt.% W, up to 0.05 wt.% Co, up to 0.2 wt.% B, and the balance. The composition consists of incidental impurities and 54-75 wt.% Fe; or more typically, 1.5-2.1 wt.% C, 0.3-0.5 wt.% Mn, 0.1-2.1 wt.% Si, 1.0-2.5 wt.% Ni, 20-35 wt.% Cr, up to 3 wt.% Mo, up to 0.1 wt.% V, up to 2.5 wt.% Nb, up to 2 wt.% W, up to 0.1 wt.% Co, up to 0.3 wt.% B, with the balance being incidental impurities and 50-75 wt.% Fe.

[0058] Figure 12AThe image shows the microhardness curve of the J120V sample after salt bath nitriding at 580℃ for 3 hours. Analysis of the J120V sample revealed the presence of a compound layer and the formation of a soft spot at the center of the cross-section. Elemental lattice scanning of the J120V sample showed that the nitrided surface was directly composed of oxides / carbides, with a compound region extending to a depth of approximately 20 μm. The surface oxide layer was in contact with the vertically oriented oxide / carbide phases, with no obvious nitrogen diffusion region. Furthermore, the interdendritic phase was largely minimized in the region near the nitride surface, likely due to its dissolution into the matrix.

[0059] Figure 12B This is a microhardness distribution map of the J160N sample after gas nitriding at 571℃ for 3 hours. Analysis of the J160 sample shows that no compound layer exists, only a diffusion region. Elemental lattice scanning of the J160 sample shows that no compound region was formed, and the diffusion region extends to a depth of approximately 45 μm. Compared with the underlying matrix, the microstructure of the diffusion region did not show significant changes.

[0060] Referring to commonly assigned U.S. Patents US Patent Nos. 6,519,847 and 7,216,427 (both incorporated herein by reference), a precision machining process can be used to produce valve seats with seat surfaces where the seat angle, seat surface finish, seat profile, and seat runout relative to the outer diameter (OD) and bottom surface of the valve seat are controlled within very precise tolerances. These controls produce pre-machined valve seats that can be installed in the cylinder head or engine block, regardless of whether additional seat machining is required.

[0061] In one implementation, the following machining process is used. After rough casting the valve seat ring, any remaining gates from the casting process are first ground away. Next, the top and bottom surfaces of the insert are rough ground using a double-disc grinder to approximate the finished size. Depending on the size and material of the insert, multiple grinding operations may be used. Then, the outer diameter (OD) of the insert is ground to approximate the finished size using centerless grinding. Next, if necessary, the inner diameter (ID) is bored using a lathe, and a guide chamfer is machined on the outer diameter (OD). The surface is now finish ground to the finished width (W) using a double-disc grinder, followed by finish grinding to the finished outer diameter (OD). The part is then vibratory finished to clean and remove burrs. The final machining operation is the precision machining of the seat ring surface. Turning is a common machining method, requiring control of the seat ring angle, runout between the seat ring and the outer diameter, and the surface finish of the seat ring to achieve the aforementioned tolerances. Another possible manufacturing method is to grind the precision seat ring.

[0062] After the valve seat ring is precision-formed, it needs to undergo nitriding to improve the wear resistance of the insert. However, the wear resistance treatment should minimize the dimensional deformation of the precision-formed valve seat ring. In a preferred embodiment, the wear resistance treatment typically results in a dimensional change of less than 0.05 mm on the insert surface.

[0063] Wear-resistant treatment preferably includes any of the following processes: ferritic carburizing, carbonitriding, gas nitriding, plasma nitriding, or other suitable techniques known in the field of nitriding. The nitriding treatment should result in the pre-machined valve seat ring having an exposed supersaturated nitrogen region without a white layer. For gas nitriding, a mixture of ammonia (NH3, approximately 91 vol.%) and carbon dioxide (CO2, 9 vol.%) is used; when the ammonia comes into contact with the surface of the metal part at the nitriding temperature, the ammonia decomposes into hydrogen and nitrogen. For ionic (plasma) nitriding, a mixture of 85 vol.% N2 and 15 vol.% H2 can be used.

[0064] Although some embodiments of the invention have been discussed above, alternative embodiments will be apparent to those skilled in the art and are within the scope of the invention.

Claims

1. A method for forming a surface hardened valve seat ring that can be used for embedding in a cylinder head or engine block of an internal combustion engine, the method comprising the steps of: casting the valve seat ring from an iron-chromium alloy containing no more than 75 weight percent (wt.%) iron and at least 25 wt.% of alloying elements, the alloying elements including at least 9 wt.% chromium; precision machining the valve seat ring to precise tolerances such that the valve seat ring can be installed in the cylinder head or engine block without the need for additional seat machining; and nitriding the valve seat ring to produce an exposed supersaturated nitrogen region free of nitride white layers.

2. The method of claim 1, wherein the nitriding step comprises ferritic nitrocarburizing the valve seat ring.

3. The method of claim 1, wherein the nitriding step comprises carbonitriding the valve seat ring.

4. The method of claim 1, wherein the nitriding step comprises ionitriding the valve seat.

5. The method of claim 1, wherein in the casting step, the alloy is melted and formed into the shape of a valve seat ring.

6. The method of claim 5, wherein the iron-chromium alloy includes 0.15-2.00 wt.% C, 0.3-1.0 wt.% Mn, 0.10-2.15 wt.% Si, 0.35-2.25 wt.% Ni, 9.8-33.5 wt.% Cr, up to 15.3 wt.% Mo, up to 2.6 wt.% V, up to 2.3 wt.% Nb, up to 4 wt.% W, up to 19 wt.% Co, up to 0.23 wt.% B, balance incidental impurities, and 50-75 wt.% Fe.

7. The method of claim 5, wherein the iron-chromium alloy includes 0.1-2.2 wt.% C, 0.1-1.5 wt.% Mn, 0.1-2.5 wt.% Si, 0.15-3.00 wt.% Ni, 9-35 wt.% Cr, up to 17 wt.% Mo, up to 3 wt.% V, up to 2.5 wt.% Nb, up to 5 wt.% W, up to 21 wt.% Co, up to 0.3 wt.% B, balance incidental impurities, and 48-75 wt.% Fe.

8. The method of claim 5, wherein the iron-chromium alloy includes 1.45-1.60 wt.% C, 0.35-0.45 wt.% Mn, 0.1-0.6 wt.% Si, 0.35-1.00 wt.% Ni, 9.8-13.0 wt.% Cr, 5.4-9.15 wt.% Mo, 1.25-1.30 wt.% V, 1.9-2.0 wt.% Nb, up to 4 wt.% W, up to 3.7 wt.% Co, up to 0.23 wt.% B, balance incidental impurities, and 67.5-71.0 wt.% Fe.

9. The method of claim 5, wherein the iron-chromium alloy comprises 1.3-1.7 wt.% C, 0.3-0.5 wt.% Mn, 0.1-0.8 wt.% Si, 0.3-2.0 wt.% Ni, 9-15 wt.% Cr, 5-10 wt.% Mo, 1.0-1.5 wt.% V, 1.8-2.2 wt.% Nb, up to 5 wt.% W, up to 4 wt.% Co, up to 0.3 wt.% B, balance incidental impurities, and 67-71 wt.% Fe.

10. The method of claim 5, wherein the iron-chromium alloy comprises 0.1-0.2 wt.% C, 0.3-0.5 wt.% Mn, up to 0.2 wt.% Si, up to 2 wt.% Ni, 14-16 wt.% Cr, 14-16 wt.% Mo, 2-3 wt.% V, 1-3 wt.% Nb, up to 0.1 wt.% W, up to 1 wt.% Co, up to 0.2 wt.% B, balance incidental impurities, and 60-64 wt.% Fe.

11. The method of claim 5, wherein the iron-chromium alloy comprises 1.8-2.1 wt.% C, 0.1-0.5 wt.% Mn, 0.3-0.8 wt.% Si, 2-3 wt.% Ni, 14-18 wt.% Cr, 10-14 wt.% Mo, up to 0.2 wt.% V, up to 0.05 wt.% Nb, up to 0.3 wt.% W, 17-21 wt.% Co, up to 0.1 wt.% B, balance incidental impurities, and 48-52 wt.% Fe.

12. The method of claim 5, wherein the iron-chromium alloy comprises 1.55-2.00 wt.% C, 0.35-0.40 wt.% Mn, 0.1-2.0 wt.% Si, 1.1-2.0 wt.% Ni, 20.0-33.5 wt.% Cr, up to 2 wt.% Mo, up to 0.05 wt.% V, up to 2.3 wt.% Nb, up to 1.5 wt.% W, up to 0.05 wt.% Co, up to 0.2 wt.% B, balance incidental impurities, and 54-75 wt.% Fe.

13. The method of claim 5, wherein the iron-chromium alloy comprises 1.5-2.1 wt.% C, 0.3-0.5 wt.% Mn, 0.1-2.1 wt.% Si, 1.0-2.5 wt.% Ni, 20-35 wt.% Cr, up to 3 wt.% Mo, up to 0.1 wt.% V, up to 2.5 wt.% Nb, up to 2 wt.% W, up to 0.1 wt.% Co, up to 0.3 wt.% B, balance incidental impurities, and 50-75 wt.% Fe.

14. A valve seat insert made by the method of claim 1.

15. The valve seat insert of claim 14, wherein the supersaturated nitrogen region has a nitrogen content of 1 to 5 wt.%.

16. The valve seat insert of claim 14 wherein, The valve seat insert is cast from an iron-chromium alloy melt comprising: 1.45-1.60 wt.% C, 0.35-0.45 wt.% Mn, 0.1-0.6 wt.% Si, 0.35-1.00 wt.% Ni, 9.8-13.0 wt.% Cr, 5.40-9.15 wt.% Mo, 1.25-1.30 wt.% V, 1.9-2.0 wt.% Nb, up to 4 wt.% W, up to 3.7 wt.% Co, up to 0.23 wt.% B, balance incidental impurities, and 67.5-71.0 wt.% Fe.

17. The valve seat insert of claim 14 wherein, The valve seat insert is cast from an iron-chromium alloy melt comprising: 1.45-1.60 wt.% C, 0.35-0.45 wt.% Mn, 0.1-0.6 wt.% Si, 0.35-1.00 wt.% Ni, 9.8-13.0 wt.% Cr, 5.40-9.15 wt.% Mo, 1.25-1.30 wt.% V, 1.9-2.0 wt.% Nb, up to 4 wt.% W, up to 3.7 wt.% Co, up to 0.23 wt.% B, balance incidental impurities, and 67.5-71.0 wt.% Fe.

18. The valve seat insert of claim 14, wherein the valve seat insert is cast from an iron-chromium alloy melt comprising: 0.1-0.2 wt.% C, 0.3-0.5 wt.% Mn, up to 0.2 wt.% Si, up to 2 wt.% Ni, 14-16 wt.% Cr, 14-16 wt.% Mo, 2-3 wt.% V, 1-3 wt.% Nb, up to 0.1 wt.% W, up to 1 wt.% Co, up to 0.2 wt.% B, balance incidental impurities, and 60-64 wt.% Fe.

19. The valve seat insert of claim 14, wherein the valve seat insert is cast from an iron-chromium alloy melt comprising: 1.8-2.1 wt.% C, 0.1-0.5 wt.% Mn, 0.3-0.8 wt.% Si, 2-3 wt.% Ni, 14-18 wt.% Cr, 10-14 wt.% Mo, up to 0.2 wt.% V, up to 0.05 wt.% Nb, up to 0.3 wt.% W, 17-21 wt.% Co, up to 0.1 wt.% B, balance incidental impurities, and 48-52 wt.% Fe.

20. The valve seat insert of claim 14, wherein the valve seat insert is cast from a ferrochrome alloy melt comprising 1.5-2.1 wt. % C, 0.3-0.5 wt. % Mn, 0.1-2.1 wt. % Si, 1.0-2.5 wt. % Ni, 20-35 wt. % Cr, up to 3 wt. % Mo, up to 0.1 wt. % V, up to 2.5 wt. % Nb, up to 2 wt. % W, up to 0.1 wt. % Co, up to 0.3 wt. % B, balance incidental impurities, and 50-75 wt. % Fe.

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