Martensitic wear-resistant alloy strengthened by aluminum nitride

Abstract

An iron-based alloy comprising, in weight percent, about 0.75 to about 2% carbon; about 0.1 to about 1% manganese; about 0.1 to about 1% silicon; about 3 to about 6% chromium; up to about 4% nickel; about 1 to about 3% vanadium; about 4 to about 7% molybdenum; about 4 to about 7% tungsten; about 4 to about 7% cobalt; up to about 0.1% boron; about 0.001 to about 0.15% nitrogen, about 0.001 to about 0.6% aluminum, about 0.1 to about 1% copper, up to about 0.3% sulfur, up to about 0.3% phosphorus, up to about 5% total of tantalum, titanium, hafnium, and zirconium; about 65 to about 80% iron; and incidental impurities. The alloy is suitable for high temperature applications, such as valve seat inserts for combustion engines.

Description

Technical Field

[0001] This disclosure relates to iron-based alloys, and in particular to corrosion-resistant and wear-resistant iron-based alloys with high hardenability that can be used, for example, in valve seat inserts. Background Technology

[0002] Stricter emissions regulations for diesel engines have driven changes in engine design, including the need for high-pressure electronic fuel injection systems. Engines built according to the new designs use higher combustion pressures, higher operating temperatures, and require less lubrication than previous designs. Components in the new designs, including valve seat inserts (VSIs), are subjected to significantly higher wear rates. For example, exhaust and intake valve seat inserts and valves must be able to withstand a large number of valve impact events and combustion events with minimal wear (e.g., erosion, adhesive, and corrosive wear). This has prompted a shift in material selection towards materials that offer improved wear resistance compared to valve seat insert materials traditionally used by the diesel and natural gas engine industry.

[0003] Another emerging trend in diesel and natural gas engine development is the use of EGR (Exhaust Gas Recirculation). With EGR, exhaust gases are partially redirected back into the intake airflow to reduce nitrogen monoxide (NOx) emissions. x The content of EGR is important. Using EGR in diesel engines alters engine combustion characteristics, thus changing the valve / VSI operating environment. Therefore, low-cost exhaust valve seat inserts with suitable metallurgical and mechanical properties are needed for diesel and natural gas engines using EGR.

[0004] Furthermore, because exhaust gases contain compounds of nitrogen, sulfur, chlorine, and other elements that can potentially form acids, diesel and natural gas engines using EGR require improved corrosion resistance for alloys used in intake and exhaust valve seat inserts. Acids can attack valve seat inserts and valves, leading to premature engine failure.

[0005] There is a need for improved iron-based alloys for valve seat inserts that exhibit sufficient hardness, mechanical strength, toughness, corrosion resistance, and wear resistance suitable for applications such as intake and exhaust valve seat inserts. Summary of the Invention

[0006] In an embodiment, this disclosure provides an iron-based alloy containing, by weight percentage, about 0.75 to about 2% carbon; about 0.1 to about 1% manganese; about 0.1 to about 1% silicon; about 4 to about 7% cobalt; about 3 to about 6% chromium; up to about 4% nickel; about 1 to about 3% vanadium; about 4 to about 7% molybdenum; about 4 to about 7% tungsten; about 0.001 to about 0.15% nitrogen; about 0.001 to about 0.6% aluminum; about 0.1 to about 1% copper; up to about 0.05% boron; up to about 0.3% sulfur; up to about 0.3% phosphorus; about 65 to about 80% iron, and the balance being incidental impurities, together with up to about 5% of total additional elements including niobium, tantalum, titanium, zirconium and hafnium.

[0007] In an embodiment, this disclosure provides an iron-based alloy containing, by weight percentage: about 0.75 to about 1.6% carbon; about 0.2 to about 0.8% manganese; about 0.2 to about 0.8% silicon; about 4.5 to about 5.5% cobalt; about 4 to about 5.5% chromium; about 0.05 to about 2.5% nickel; about 1.2 to about 2% vanadium; about 5.5 to about 7% molybdenum; about 4.5 to about 5.5% tungsten; and 0.05 to about 0.12% tungsten. % nitrogen; about 0.01 to about 0.6% aluminum; about 0.2 to about 0.6% copper; about 0.003 to about 0.01% boron; up to about 0.3% sulfur; up to about 0.3% phosphorus; about 70 to about 76% iron; and the balance being incidental impurities, wherein the alloy has an as-cast microstructure having about 50 to about 80 vol% intradendritic martensite and about 20 to about 50 vol% interdendritic eutectoid phase.

[0008] In a further embodiment, this disclosure also provides a valve seat insert for an internal combustion engine. In this embodiment, the valve seat insert is made of an iron-based alloy containing: by weight percentage, about 0.75 to about 2% carbon; about 0.1 to about 1% manganese; about 0.1 to about 1% silicon; about 4 to about 7% cobalt; about 3 to about 6% chromium; up to about 4% nickel; about 1 to about 3% vanadium; about 4 to about 7% molybdenum; about 4 to about 7% tungsten; about 0.001 to about 0.15% nitrogen; about 0.001 to about 0.6% aluminum; about 0.1 to about 1% copper; up to about 0.1% boron; up to about 0.3% sulfur; up to about 0.3% phosphorus; about 65 to about 80% iron; the balance being impurities, together with up to about 5% of total additional elements including niobium, tantalum, titanium, zirconium, and hafnium.

[0009] In one embodiment, the valve seat insert is a cast alloy comprising, by weight percentage, about 0.8 to about 1.2% carbon; about 0.3 to about 0.7% manganese; about 0.3 to about 0.7% silicon; about 4.5 to about 5.5% cobalt; about 4 to about 5.5% chromium; about 0.15 to about 2.5% nickel; about 1.2 to about 1.6% vanadium; about 5.5 to about 7% molybdenum; and about 4.5 to about 5%. 5% tungsten; about 0.3 to about 0.5% copper; about 0.075 to about 0.1% nitrogen; about 0.01 to about 0.6% aluminum; about 0.003 to about 0.01% boron; up to about 0.3% sulfur; up to about 0.3% phosphorus; about 70 to about 76% iron; the balance being up to about 5% of total additional elements and incidental impurities including niobium, tantalum, titanium, zirconium, hafnium, wherein the amount of nickel plus cobalt is 8% by weight or less. Attached Figure Description

[0010] Figure 1 An exemplary valve system is shown, which includes a valve seat insert that may be made of an alloy called J137 disclosed herein.

[0011] Figure 2 This is a comparison chart of the radial crush toughness of various J137 alloys and J120V.

[0012] Figure 3 This is a graph showing the relationship between the hardness and tempering temperature of various J137 alloys.

[0013] Figure 4 This is a graph showing the relationship between radial crush toughness and tempering temperature for various J137 alloys.

[0014] Figure 5 This is a graph showing the compressive yield strength and tensile strength of various J137 alloys.

[0015] Figure 6 This is a graph showing the relationship between the hot hardness and temperature of various J137 alloys.

[0016] Figure 7 These are thermal expansion diagrams for various J137 alloys.

[0017] Figure 8 It is a 100x magnified micrograph of the cast J137 alloy and Figure 9 This is a 100x magnified micrograph of the cast contrast alloy.

[0018] Figure 10 This is a comparison chart of the immersion and condensation corrosion test results of J137 alloy and J120V alloy at 1.2 pH.

[0019] Figure 11 This is a comparison chart of the immersion and condensation corrosion test results of J137 alloy and J120V alloy at 2.8 pH.

[0020] Figure 12A It is a wear diagram of the pin sample. Figure 12B It is a wear diagram of the plate sample, and Figure 12C This is a comparison chart of the total wear of J137 and other alloy systems. Detailed Implementation

[0021] This document discloses an iron-based alloy for use as a valve seat insert, which will now be described in detail with reference to several embodiments thereof as shown in the accompanying drawings. Numerous specific details are set forth in the following description to provide a thorough understanding of the iron-based alloy. However, it will be apparent to those skilled in the art that the embodiments described herein can be practiced without some or all of these specific details.

[0022] Unless otherwise stated, all figures indicating quantities, conditions, etc., in this disclosure and claims should be understood to be modified by the term "about" in all cases. The term "about" refers to a numerical value, for example, covering a range of ±10%. The modifier "about" used in combination with a quantity includes the stated value. In this specification and the following claims, unless expressly specified otherwise, singular forms such as "a," "an," and "the" include plural forms.

[0023] The terms “room temperature,” “ambient temperature,” and “ambient” refer to temperatures, for example, from about 20°C to about 25°C.

[0024] Figure 1 An exemplary valve assembly 2 according to this disclosure is shown. Valve assembly 2 may include a valve 4, which may be slidably supported within the inner bore of a valve stem guide 6 and a valve seat insert 18. The valve stem guide 6 may be a tubular structure fitted into a cylinder head 8. Arrows indicate the direction of movement of valve 4. Valve 4 may include a valve seat face 10 inserted between a cap 12 and a neck 14 of valve 4. A valve stem 16 may be positioned above the neck 14 and may be received within the valve stem guide 6. The valve seat insert 18 may include a valve seat insert face 10' and may be mounted, for example, within the cylinder head 8 of an engine by press fitting. In an embodiment, the cylinder head 8 may comprise a casting, for example, cast iron, aluminum, or an aluminum alloy. In an embodiment, the insert 18 (shown in cross-section) may be annular in shape, and the valve seat insert face 10' may engage the valve seat face 10 during movement of valve 4.

[0025] In this embodiment, the present disclosure relates to an iron-based alloy (hereinafter referred to as "J137 alloy" or "J137"). The bulk hardness, hot hardness, high-temperature strength, corrosion resistance, and wear resistance of the J137 alloy make it suitable for a variety of applications, including, for example, valve seat inserts in internal combustion engines, and for use in ball bearings, coatings, etc. In this embodiment, the alloy is used as a valve seat insert in an internal combustion engine.

[0026] In the embodiments, the J137 alloy comprises, by weight percentage, about 0.75 to about 2 wt% carbon (C); about 0.1 to about 1 wt% manganese (Mn); about 0.1 to about 1 wt% silicon (Si); about 4 to about 7% cobalt (Co); about 3 to about 6 wt% chromium (Cr); up to about 4 wt% nickel (Ni); about 1 to about 3 wt% vanadium (V); about 4 to about 7 wt% molybdenum (Mo); about 4 to about 7 wt% tungsten (W); about 0.1 to about 1% copper (Cu); about 0.001 to about 0.15% nitrogen (N); and about 0.001 to about 0.6% aluminum (Al). Up to 0.1% boron (B); up to about 0.3% phosphorus (P); up to about 0.3% sulfur (S); about 65 to about 80% iron (Fe); the balance being up to about 5% total additional elements and incidental impurities including niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), hafnium (Hf), which may contain up to about 1% by weight of other elements such as magnesium (Mg), lead (Pb), antimony (Sb), tin (Sn), zinc (Zn), arsenic (As), bismuth (Bi), calcium (Ca), cerium (Ce), selenium (Se), oxygen (O), yttrium (Y) and rare earth elements (lanthanides).

[0027] In the embodiments, the J137 alloy is substantially composed of the following: by weight percentage, about 0.75 to about 1.6% carbon; about 0.2 to about 0.8% manganese; about 0.2 to about 0.8% silicon; about 4.5 to about 7% cobalt; about 3.5 to about 5.5% chromium; about 0.05 to about 2.5% nickel; about 1.2 to about 1.6% vanadium; about 5 to about 7% molybdenum; about 4 to about 7% tungsten; about 0.2 to about 0.6% copper; about 0.05 to about 0.12% nitrogen; about 0.01 to about 0.6% aluminum; about 0.001 to about 0.05% boron; up to 0.3% phosphorus; up to 0.3% sulfur; about 70 to about 76% iron; the balance being up to about 5% of total additional elements and incidental impurities including niobium, tantalum, titanium, zirconium, and hafnium. As used herein, the terms “consistently composed of” or “consistently made of” have a partially closed meaning—that is, such terms do not include steps, features, or components that would significantly and adversely alter the fundamental and novel properties of the alloy (i.e., steps, features, or components that would adversely affect the desired properties of the J137 alloy). The fundamental and novel properties of the J137 alloy may include at least one of the following: hardness, coefficient of thermal expansion, compressive yield strength, ultimate tensile strength, wear resistance, corrosion resistance, and microstructure (i.e., substantially about 50 to about 80 vol% intradendritic martensite and about 20 to about 50 vol% interdendritic eutectoid phase).

[0028] In the embodiments, the J137 alloy can be machined to achieve a combination of hardness, wear resistance, and corrosion resistance suitable for valve seat inserts in the as-cast or stress-relieved heat-treated or hardened and tempered conditions. In the embodiments, the J137 alloy can be machined according to any suitable method; for example, in the embodiments, J137 can be machined using conventional techniques including powder metallurgy, casting, thermal / plasma spraying, weld overlay, etc.

[0029] In this embodiment, the J137 alloy can be formed into a metal powder using any suitable technique. Various techniques for forming the alloy into a metal powder include, for example, ball milling the elemental powder or atomization to form a pre-alloyed powder. In this embodiment, the powder material can be compacted into a desired shape and sintered. The sintering process can be used to achieve the desired properties in the resulting part.

[0030] In one embodiment, the valve seat insert can be manufactured by casting, which involves melting the alloy composition and pouring the molten mixture into a mold. In another embodiment, the alloy casting can be subsequently heat-treated before machining into its final shape. Alternatively, the valve seat insert can be manufactured by machining a J137 alloy casting.

[0031] In embodiments, J137 alloy can be used to manufacture valve seat inserts, such as those for use in diesel engines (e.g., diesel engines with or without EGR). In embodiments, J137 alloy can be used in other applications, including valve seat inserts for example, gasoline, natural gas, dual-fuel, or alternative fuel internal combustion engines. Such valve seat inserts can be manufactured using conventional techniques. Furthermore, J137 alloy can be used in other applications, including those where its high-temperature properties are advantageous, such as wear-resistant coatings, internal combustion engine components, and diesel engine components.

[0032] In the embodiments, J137 has a microstructure in the as-cast, quenched, and tempered states, the microstructure comprising about 50 to about 80 vol% intradendritic tempered martensite and about 20 to about 50 vol% interdendritic eutectic phase. After heat treatment of the cast alloy, the microstructure may comprise about 75 to about 90 vol% tempered martensite and about 10 to about 25 vol% carbide / eutectoid phase.

[0033] In embodiments, the J137 alloy may have a microhardness suitable for valve seat insert applications (such as that obtained under vacuum conditions using a Vickers HV10 scale). In embodiments, the J137 alloy may have a high hardness ranging from room temperature to high temperatures. For example, in embodiments, the J137 alloy may have a hardness HV(10) exceeding 600 at room temperature and exceeding 400 at temperatures between room temperature and 1000°F.

[0034] The thermal conductivity of the valve seat insert material affects its performance, because valve seat insert materials with high thermal conductivity can more effectively remove heat from the engine valve in order to prevent overheating.

[0035] In embodiments, the J137 alloy may have high ultimate tensile strength and compressive yield strength suitable for valve seat insert applications. Generally, a higher ultimate tensile strength corresponds to greater resistance to insertion cracking, and a higher compressive yield strength corresponds to higher valve seat insert retention force. In embodiments, the J137 alloy may have a compressive yield strength greater than about 199 ksi and a tensile strength greater than about 139 ksi at a temperature of about 75°F. In embodiments, the tensile strength at 1200°F may be greater than about 132 ksi, for example, greater than about 130 ksi. In embodiments, the difference between the tensile strength at 75°F and 1200°F may be less than about 10 ksi, for example, less than about 7 ksi. In embodiments, the difference between the tensile strength at 75°F and 1000°F may be less than about 28 ksi, for example, less than about 25 ksi, or less than about 23 ksi.

[0036] In the implementation, the J137 alloy may have radial crush toughness and thermal expansion suitable for valve seat insert applications.

[0037] Carbon (C) is an alloying element in J137 alloy, which can affect the alloy's castability, microstructure, solidification substructure, and mechanical and metallurgical properties. Increasing the carbon content can generally improve the hardenability of martensitic iron-based alloys. Carbon can form primary and secondary carbides with chromium, molybdenum, tungsten, and vanadium, and the carbon content can be used to obtain the desired amount of martensite. For example, to increase the volume percentage of tempered martensite, J137 alloy may contain carbon at the upper end of the carbon range. J137 contains a relatively large amount of carbon, which contributes to the high wear resistance of J137 alloy. In embodiments, carbon may be present in J137 alloy in an amount of about 0.75 to about 2% by weight, for example, about 0.8 to about 1.6% by weight, or about 0.8 to about 1.2% by weight.

[0038] In embodiments, small amounts of boron (B) can also be used in the J137 alloy as an effective alloying element to increase the hardness level of the iron-based alloy system. Boron can also be used for solidification substructure honeycomb size refinement. In embodiments, the J137 alloy may contain, for example, up to about 0.1% boron, about 0.001 to about 0.05% boron by weight, about 0.003 to about 0.01% boron by weight, or about 0.003 to about 0.009% boron by weight. Boron has very low solubility in iron (e.g., about 0.01 wt.%), which can be used to achieve high levels of hot hardness. Small amounts of boron can improve the strength of the J137 alloy and can improve grain refinement through precipitation processes (e.g., boron carbide, boron nitride, boron carbonitride). The distribution of boron can be both intragranular (within grains) and intergranular (along grain boundaries). However, excessive boron can segregate to grain boundaries and reduce the toughness of the steel. By controlling the addition of boron along with other alloying elements, intragranular saturation of boron can be achieved, which promotes the formation of boron compounds at grain boundaries. These boron compounds can effectively enhance grain boundary strength. Without being bound by theory, it is believed that boron, whether in solid solution or through the formation of boron compounds (e.g., compounds with C, Fe, Cr, and / or Mo), can advantageously strengthen steel through solid solution hardening and precipitation hardening (preferably along solidification substructure boundaries and pre-austenite grain boundaries). Furthermore, boron can suppress eutectoid reactions in the J137 alloy system.

[0039] Manganese (Mn) is an austenite-forming element and may be present in the J137 alloy in amounts such as about 0.1 to about 1 wt%, about 0.2 to about 0.8 wt%, or about 0.3 to about 0.7 wt%. Manganese, as a solute in the iron-based matrix, promotes austenite formation, which enhances the strength of the J137 alloy through solid solution strengthening and increases its oxidation resistance. When the J137 alloy is cast into parts, the addition of manganese can contribute to the deoxidation, desulfurization, and / or degassing of the J137 alloy.

[0040] In the embodiments, the silicon (Si) content in the J137 alloy is from about 0.1 to about 1% by weight, for example, from about 0.2 to about 0.8% by weight, or from about 0.4 to about 0.7% by weight. In the embodiments, silicon can enhance the liquid metal fluidity and solidification mode of the alloy by significantly altering the compositional undercooling conditions in the solid-liquid interface region during the solidification process, thereby affecting castability. Silicon can form a solid solution with iron and improve the strength of the J137 alloy through solid solution hardening, as well as increase oxidation resistance. When the J137 alloy is formed into parts by casting, the addition of silicon can contribute to the deoxidation and / or degassing of the J137 alloy.

[0041] In the embodiments, the alloy may contain chromium (Cr), carbides, and ferrite-forming elements in amounts of about 3 to about 6% by weight, for example, about 3.5 to about 5.5% by weight of chromium, or about 4 to about 5.5% by weight of chromium. Therefore, with a carbon content, chromium carbide is expected to be present in the hardened and tempered J137 alloy matrix, which is one of the fundamental strengthening mechanisms of the J137 alloy. Furthermore, the chromium content preferably provides the desired combination of corrosion resistance, hardenability, wear resistance, and oxidation resistance. Not wishing to be bound by theory, chromium in the J137 alloy can form a dense, protective chromium oxide layer on the surface of the J137 alloy, which inhibits high-temperature oxidation and minimizes wear and corrosion.

[0042] In the embodiments, nickel (Ni), as an austenite-forming element, may be present in the J137 alloy in amounts such as up to about 4% by weight, about 0.05 to about 2.5% by weight, or about 0.15 to about 2.5% by weight. Nickel may be present in the J137 alloy in an amount that does not adversely affect the desired properties of the J137 alloy. Nickel can advantageously increase oxidation and corrosion resistance, and can also increase the hardness and strength of the J137 alloy via secondary phase strengthening. Nickel can be an austenite-forming element, and excessive nickel can enlarge the size of the austenite regions in the J137 alloy, which can lead to an increase in the coefficient of thermal expansion and a decrease in low-temperature wear resistance. Therefore, the role of nickel is to strengthen the matrix phase through solid solution strengthening. Although nickel does not form carbides in iron-based alloys, the addition of nickel to the J137 alloy can be used to enhance high-temperature strength and hot hardness.

[0043] Vanadium (V) is a carbide-forming element and may be present in the J137 alloy in an amount of, for example, about 1 to about 3% by weight, such as about 1.2 to about 2% by weight, or about 1.2 to about 1.6% by weight. Vanadium may be included in the iron-based alloy in an effective amount to improve the wear resistance and corrosion resistance of the iron-based alloy.

[0044] In the implementation, molybdenum (Mo), which is also a carbide-forming element, may be present in the J137 alloy in amounts such as about 4 to about 7 wt%, about 5 to about 7 wt%, or about 5.5 to about 7 wt%. Molybdenum is a carbide-forming element and is likely to combine with chromium to form primary carbides. The addition of molybdenum can also improve the localized corrosion resistance of the J137 alloy. Molybdenum can help reduce intergranular stress corrosion, stress corrosion cracking, and / or pitting corrosion.

[0045] In the embodiments, the J137 alloy may contain tungsten (W) in amounts such as about 4 to about 7% by weight, about 4.5 to about 6% by weight, or about 4.5 to about 5.5% by weight. Tungsten is a very effective solid solution alloying element for iron-based alloys such as J137. Tungsten is also a carbide-forming element and can be included in iron-based alloys in amounts that effectively improve the wear resistance and corrosion resistance of the alloys.

[0046] In embodiments, the J137 alloy may contain an appropriate amount of cobalt (Co). For example, in embodiments, the J137 alloy may contain about 4 to about 7% by weight of cobalt, such as about 4.5 to about 6% by weight of cobalt, or about 4.5 to about 5.5% by weight of cobalt. Preferably, the total content of cobalt plus nickel is up to about 8% by weight or about 5 to about 8% by weight. Cobalt may be included in the iron-based alloy in an effective amount to improve the high-temperature wear resistance and high-temperature corrosion resistance of the iron-based alloy.

[0047] In embodiments, the J137 alloy may further contain aluminum (Al) in amounts of about 0.001 to about 0.6 wt%, or about 0.01 to about 0.6 wt%, and nitrogen may be present in amounts of about 0.001 to about 0.15 wt%, or about 0.05 to about 0.12 wt%, or about 0.075 to about 0.1 wt%. The aluminum is preferably combined with nitrogen to form aluminum nitride (AlN) particles in amounts of about 0.005 to about 0.05 vol%, or about 0.01 to about 0.05 vol%. The aluminum nitride particles have a hexagonal close-packed structure and a particle size of about 0.5 to about 10 micrometers or about 1 to about 5 micrometers, randomly distributed throughout the alloy.

[0048] In an embodiment, the J137 alloy may contain about 0.1 to about 1% by weight of copper (Cu). For example, the copper content may be about 0.2 to about 0.6% by weight or about 0.3 to about 0.5% by weight of copper. The copper may exist as a fine and uniform distribution of precipitated ε-copper.

[0049] The J137 alloy may optionally contain other alloying elements, or may not contain any such intentionally added elements. In an embodiment, the balance of the J137 alloy is iron (Fe), in an amount of about 65 to about 80% by weight or about 70 to about 76% by weight of iron and incidental impurities. The J137 alloy may contain up to about 5% of total additional elements including niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf). In an embodiment, the total amount of additional elements may be up to about 3% or up to about 1%. Incidental impurities may contain up to about 1.5% of other elements, such as arsenic (As), bismuth (Bi), calcium (Ca), magnesium (Mg), oxygen (O), lead (Pb), tin (Sn), yttrium (Y), and rare earth elements (REM, also known as lanthanides), zinc (Zn), and selenium (Se). In an embodiment, the J137 alloy contains less than about 0.5% by weight of impurities, for example less than about 0.3% by weight of impurities.

[0050] In the implementation scheme, the J137 alloy is free of intentionally added phosphorus (P), sulfur (S), arsenic, bismuth, calcium, magnesium, oxygen, lead, tin, yttrium, rare earth elements, zinc, selenium, niobium, tantalum, titanium, hafnium, and zirconium. "Free of intentionally added" means, for example, that such an element was not intentionally added but may be present accidentally due to processing materials and conditions. For example, additional impurities may be present in the inventory used to manufacture the alloy. Furthermore, since sulfur and phosphorus are common impurities removed during alloy preparation, completely removing these elements from the alloy may not be cost-effective. In the implementation scheme, the alloy may contain less than about 0.3% by weight of sulfur and / or less than about 0.3% by weight of phosphorus.

[0051] In the embodiments, the sulfur content is preferably less than about 0.1% by weight and the phosphorus content is preferably less than about 0.1% by weight. For example, phosphorus and sulfur may each be present in the alloy in amounts of less than about 0.06% by weight, such as up to about 0.05% by weight, or about 0.001% to about 0.03% by weight, or about 0.01% to about 0.02% by weight.

[0052] In an embodiment, the J137 alloy can be cast into the desired shape, such as a valve seat insert, which is heat-treated by heating to a temperature in the austenitic range (e.g., to about 1700°F), quenching to transform the microstructure into about 50 to about 80 vol% martensite and about 20 to about 50 vol% eutectoid phase, and then tempered (e.g., at about 1100 to about 1350°F) to toughen the alloy.

[0053] Example

[0054] The embodiments described below illustrate different compositions and conditions that can be used to practice the embodiments of this disclosure. Unless otherwise stated, all proportions are by weight. However, it will be apparent that the embodiments can be practiced with a variety of types of compositions and have a variety of uses based on the above disclosure and as indicated below.

[0055] J137 alloy can be used to manufacture valve seat inserts by forming a melt containing alloying components, deoxidizing the melt by adding aluminum shortly before casting, casting the alloy, and then tempering the casting to obtain a microstructure containing dendritic tempered martensite and interdendritic eutectoid phases. Because aluminum nitride nuclei form in the liquid metal prior to the solidification of the bulk matrix, the aluminum nitride nuclei effectively reduce the size of the solidified substructure. Furthermore, the precipitation of ε-copper occurs during hot soaking in the hardening and temperature working processes, which reduces grain growth during hardening and tempering, thus achieving the desired uniform and fine porous microstructure.

[0056] In one embodiment, the J137 alloy can be characterized as a fine-grained martensitic alloy with copper precipitation hardening, a pre-austenitization process, and dispersed aluminum nitride strengthening design. The three main differences between the J137 alloy and M2 tool steel and the J120V alloy are: (1) the addition of required amounts of cobalt and nickel to ensure adequate austenitization; (2) the addition of sufficient copper for precipitation hardening and pre-austenite grain size control; and (3) the addition of aluminum as an aluminum nitride forming element. By combining these three alloy design criteria, the J137 alloy can be provided with grain size refinement, matrix strengthening, and nitride distribution formation suitable for engine valve mechanism components [e.g., valve seat insert (VSI) applications].

[0057] Alloy J137, under the desired hardening and tempering conditions, possesses a tempered martensitic matrix with a small amount of retained austenite. The amount of tempered martensite in the air-quenched and tempered state is approximately 50 to approximately 80% by volume. Another portion of the alloy consists of approximately 10 to approximately 50% by volume of a eutectic / eutectoid thin-layer phase from the J137 matrix. During the solidification process of J137, the intradendritic region consists of a solid solution phase (austenite / ferrite / martensite). The interdendritic region consists of solidified phases and eutectic reaction phases (austenite and thin-layered carbides). At lower temperatures, a eutectoid reaction occurs to form thin-layered ferrite and carbides.

[0058] During quenching, the ferrite portion of the preeutectoid reactants transforms into a martensitic structure through a solid-state phase transformation, which is subsequently converted into tempered martensite after tempering. Therefore, under hardening and tempering conditions, the J137 alloy can contain approximately 5 to 25 vol% eutectoid carbides rich in chromium, molybdenum, tungsten, and vanadium.

[0059] Aluminum nitride (AlN) possesses high thermal conductivity (around 160 W / mK in ambient conditions), high microhardness (HK1200 in ambient conditions), and a compatible coefficient of thermal expansion that complements its carbide and tempered martensitic crystal structures. AlN synthesized from aluminum and nitrogen can exhibit a wurtzite crystal structure. The covalently bonded nitride structure remains stable at temperatures up to 2000°C in oxygen-depleted environments. AlN can be successfully introduced into J137 to enhance the alloy's wear resistance under adhesive and abrasive conditions. Due to the designed process for AlN formation in the J137 alloy system, AlN formation occurs at high temperatures while the bulk alloy metal is in a liquid state. AlN nuclei initially form at random locations within the liquid J137 metal (with both aluminum and nitrogen as solutes). Therefore, uniform AlN size and random distribution are expected.

[0060] In iron-based alloy systems, ε-copper precipitation can readily occur at the boundary between eutectoid ferrite and carbides. ε-copper precipitation typically occurs at or around the eutectoid temperature, which strengthens the matrix and refines grain size. ε-copper, as an interphase in the iron-based matrix, is highly stable and resists both precipitation dissolution and grain growth within the operating temperature range of engine valve mechanisms. A small amount of copper can be included in the J137 alloy to introduce ε-copper precipitation.

[0061] Table 1 lists the composition of seven J137 experimental heats, with a total cobalt and nickel content of less than 8.0 wt.% and copper content ranging from 0.30 to 0.50 wt.%. Heats included various aluminum contents to explore the effects of nitride formation on the mechanical and metallurgical responses in the alloy system. Aluminum nitride formation was designed for the alloy to enhance its wear resistance, particularly to minimize high-temperature adhesive wear. The heats contained up to approximately 1% incidental impurities, including up to approximately 0.03% Mg, up to approximately 0.015% Pb, up to approximately 0.05% Sb, up to approximately 0.03% Sn, up to approximately 0.02% Zn, up to approximately 0.02% As, up to approximately 0.1% Bi, up to approximately 0.001% Ca, up to approximately 0.1% Ce, up to approximately 0.02% Zr, up to approximately 0.003% La, and up to approximately 0.03% Se.

[0062] Table 1. Composition of the J137 experiment

[0063] Furnace 0B12R 0H28XA 0I02XA 0I08XA 0J07XA 0J12XA 0L02XB 0L22XB C 1.2 1.27 1.13 1 0.94 0.85 1.16 1.18 Mn 0.384 0.8 0.64 0.365 0.383 0.372 0.433 0.560 Si 0.65 0.76 0.81 0.56 0.78 0.71 0.61 0.63 Ni 0.148 0.483 0.146 0.236 1.96 1.66 0.5 0.479 Cr 4.26 4.68 4.74 4.37 5.09 5.3 4.53 4.53 Mo 5.98 6.53 6.11 6.15 5.85 6.15 6.51 6.67 Cu 0.387 0.464 0.381 0.409 0.364 0.395 0.479 0.442 W 4.62 5.49 5.27 5.23 5.41 4.95 5.17 4.56 V 1.27 1.53 1.4 1.41 1.57 1.5 1.38 1.4 Co 4.82 5.08 4.81 4.92 5.22 5.41 4.96 4.86 Al 0.042 0.272 0.162 0.078 0.445 0.236 0.457 0.540 B 0.0094 0.011 0.0081 0.0081 0.011 0.01 0.0082 0.0077 N 0.084 0.054 0.064 0.064 0.061 0.068 0.073 0.051 P 0.037 0.034 0.032 0.032 0.032 0.031 0.031 0.031 S 0.021 0.014 0.016 0.016 0.015 0.015 0.015 0.016 Nb 0.025 0.059 0.085 0.042 0.91 0.7 0.134 0.121 Ti 0.041 0.028 0.036 0.024 0.046 0.047 0.037 0.023 Ta 0.11 0.1 0.092 0.11 0.01 0.067 0.089 0.153 Fe 75.7 72 73.8 74.7 70.7 71.3 73.2 73.5

[0064] Radial crushing tests were used to evaluate the toughness of the alloy using a tensile testing apparatus. During testing, a ring-shaped experimental specimen with dimensions of 1.935” OD, 1.750” ID, and 0.3050” height was pressed onto the OD surface until it fractured. The radial crushing toughness was then calculated using the fracture load and deformation. Five specimens and one standard J120V alloy were tested under as-cast conditions from six of the J137 alloy heats. The standard J120V alloy had a composition of 1.32% C, 0.36% Mn, 0.428% Si, 0.08% Ni, and 3% MgO. The alloy composition is 0.9% Cr, 6.68% Mo, 0.08% Cu, 5.46% W, 1.42% V, 0.1% Co, 0.0268% N, 0.001% Al, and 80.2% Fe. For the J137 alloy, different amounts of aluminum plunger material were applied to the molten metal in different heats just before the casting samples were poured. The different amounts of aluminum plunger introduced different amounts of aluminum nitride particles into the alloy matrix. The alloy solidification mode was designed to facilitate the formation of a finely dispersed distribution of aluminum nitride.

[0065] The radial crush test results of these furnaces are shown in Figure 2 The radial crush toughness of alloy J137 is most likely a function of aluminum content. Results show that, under as-cast conditions, all J137 experimental heats exhibit higher radial crush toughness than the standard J120V alloy. Therefore, the casting cracking tendency of J137 should be lower than that of J120V.

[0066] Compare the tempering response performance of the J137 with Figure 3 Comparing it with the J120V, Figure 3 The bulk hardness was plotted as a function of tempering temperature. Generally, the J137 alloy exhibits the same or higher bulk hardness as J120V in the tempering temperature range from room temperature to 1500°F.

[0067] Figure 4 The radial crush toughness as a function of tempering temperature was shown. All J137 experimental heats exhibited the same or better radial crush toughness compared to alloy J120V (a classic VSI alloy). Therefore, alloy J137 can be expected to possess sufficient toughness for valve mechanism component applications.

[0068] Figure 5 This comparison shows the compressive yield strength and tensile strength at break among J120V, JP23, and J137. For compressive yield strength, J137 exhibits the desired high-temperature performance from 600°F to 1200°F compared to JP23 (PMVSI material) and J120V. In terms of tensile properties, J137 has the highest tensile strength at break among J120V, JP23, and J137.

[0069] Figure 6 The comparison of hot hardness between J120V and J137 is shown, and it is clear that J137 has a higher overall hot hardness than J120V. Therefore, considering hot hardness, J137 has high potential for high-temperature applications (including VSI). From a tribological application perspective, higher hot hardness corresponds to better high-temperature wear resistance. Therefore, J137 is expected to have the required higher wear resistance potential.

[0070] Figure 7 This is a comparison of the coefficients of thermal expansion among J120V, JP23, and J137. Alloy J137 has a coefficient of thermal expansion between that of J120V and JP23. Figure 7 The coefficient of thermal expansion shown is applicable to valve mechanism component applications.

[0071] Figure 8 and Figure 9 The microstructure of J137 alloy with and without aluminum plungers is shown. Figure 8 The distribution of aluminum-rich nitrides in the J137 experiment (furnace 0H28XA) is shown at 100X magnification, with an aluminum plunger of 0.208 wt.%. At approximately 0.208 wt.% aluminum plunger, a significant amount (~0.01 vol.%) of aluminum nitride is randomly distributed within the J137 matrix, typically ranging in size from 1 to 5 micrometers. Figure 8 As shown. Figure 9 The distribution of aluminum-rich nitrides in the J137 experiment (0B12R) is shown when experiments are conducted on low aluminum content at 100X magnification.

[0072] The corrosion resistance of J137 under test solution conditions of 1.2 pH and 2.8 pH is shown in the following figures. Figure 10 and 11 The corrosion test includes two parts: vapor corrosion test and immersion corrosion test. For the 1.2 pH test, the solution consists of 3.4 ml nitric acid, 1.4 ml sulfuric acid, and 1.65 g NaCl contained in 500 ml H2O. Figure 10 As shown, J137 exhibits slightly lower corrosion resistance and abrasion resistance than LE Jones alloy J160, but significantly higher than J120V. Furthermore, J137 heats with aluminum additives (plungers) demonstrate significantly better corrosion resistance than J137 heats without aluminum plungers. Figure 11 The corrosion test results are shown under test conditions of 2.8 pH, where the solution consists of sodium sulfate (7800 ppm SO42-). -2 ) and sodium nitrate (1800ppm NO3) - The composition is adjusted to the designed pH value with acetic acid. Generally, J137 exhibits higher corrosion resistance between J120V and J160.

[0073] The J137 alloy system can be designed to achieve a refined pre-austenite grain size and the desired aluminum nitride distribution, which enhances wear resistance under as-cast, quenched, and tempered conditions. Figures 12A to 12C The display shows a comparison of J137 alloy with several valve materials, as well as a comparison of JP23 and J120VN (J120V nitride). The results of the Plat wear test show that the J137 alloy exhibits good overall conventional wear resistance, while in this case, the J137 alloy compares with the VAT... It exhibits the highest wear resistance. Figure 12A It is a wear diagram of the pin sample. Figure 12B It is a wear diagram of a plate sample, and Figure 12C This is a total wear diagram of J137 compared to other alloy systems.

[0074] The J137 alloy exhibits excellent wear resistance and good mechanical properties, such as hot hardness, compressive yield strength, ultimate tensile strength, and radial fracture toughness, thanks to its microstructure featuring fine-grained pre-austenite, copper precipitation hardening, and dispersed aluminum nitride. It is also clearly demonstrated that J137 has better corrosion resistance than J120V. Therefore, the J137 alloy is expected to have better general applicability than J120V for valve mechanism applications.

[0075] Those skilled in the art will understand that the invention may be practiced in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments currently disclosed are to be considered illustrative rather than restrictive in all respects. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all variations in their meaning and scope, as well as their equivalents, are intended to be included therein.

Claims

1. An iron-based alloy comprising, by weight percentage: 0.75% to 2% carbon; 0.1% to 1% manganese; 0.1% to 1% silicon; 3 to 6% chromium; Up to 4% nickel; 1 to 3% vanadium; 4 to 7% molybdenum; 4 to 7% tungsten; 4 to 7% cobalt; Up to 0.1% boron; 0.001 to 0.15% nitrogen; 0.001 to 0.6% aluminum; 0.1% to 1% copper; Sulfur content as high as 0.3%; Phosphorus content as high as 0.3%; The total content is as high as 5% of niobium, tantalum, titanium, hafnium, and zirconium; 65 to 80% iron; and The remaining amount contains impurities. The alloy exhibits improved properties due to aluminum nitride strengthening and copper precipitation hardening.

2. The alloy according to claim 1, wherein the alloy substantially comprises the following: composition: 0.75% to 1.6% carbon; 0.2% to 0.8% manganese; 0.2% to 0.8% silicon; 3.5% to 5.5% chromium; 0.05% to 2.5% nickel; 1.2% to 2% vanadium; 5 to 7% molybdenum; 4.5% to 7% tungsten; 4.5% to 7% cobalt; 0.001 to 0.05% boron; 0.05% to 0.12% nitrogen; 0.01 to 0.6% aluminum; 0.2% to 0.6% copper; Sulfur content as high as 0.3%; Phosphorus content as high as 0.3%; The total content is as high as 3% of niobium, tantalum, titanium, hafnium, and zirconium; 70 to 76% iron; and The balance contains impurities, with nickel and cobalt totaling 8% or less.

3. The alloy according to claim 1, comprising: 0.75% to 1.4% carbon; 0.3% to 0.7% manganese; 0.3% to 0.7% silicon; 4 to 5.5% chromium; 0.15% to 2.5% nickel; Vanadium content of 1.2% to 1.6%; 5.25% to 7% molybdenum; 4 to 6% tungsten; 4.5% to 6% cobalt; 0.003 to 0.015% boron; 0.07% to 0.1% nitrogen; 0.01 to 0.6% aluminum; 0.3% to 0.5% copper; Sulfur content as high as 0.3%; Phosphorus content as high as 0.3%; The total content is up to 1% of niobium, tantalum, titanium, hafnium, and zirconium; 70 to 76% iron; and The remainder contains impurities, of which nickel and cobalt together account for 5 to 8%.

4. The alloy according to claim 1, comprising: 0.8% to 1.2% carbon; 0.4% to 0.7% manganese; 0.4% to 0.7% silicon; 4 to 5.5% chromium; 0.05% to 2% nickel; Vanadium content of 1.2% to 1.6%; 5.5% to 7% molybdenum; 4 to 5.5% tungsten; 4.5% to 5.5% cobalt; 0.005% to 0.015% boron; 0.05% to 0.1% nitrogen; 0.01 to 0.6% aluminum 0.3% to 0.5% copper; Sulfur content as high as 0.3%; Phosphorus content as high as 0.3%; Up to 1% niobium; Up to 0.1% titanium; 70 to 76% iron; as well as The balance includes impurities, wherein the alloy contains a total of 15 to 27% cobalt, tungsten, molybdenum and chromium.

5. The alloy of claim 4, wherein the total amount of cobalt, tungsten, molybdenum and chromium is 19 to 24%.

6. The alloy according to claim 1, wherein the alloy has an as-cast microstructure of 50 to 80 vol% intradendritic phase and 20 to 50 vol% interdendritic phase, and the aluminum nitride reinforcement is provided by aluminum nitride particles in a content of 0.005-0.05 vol%.

7. The alloy according to claim 1, wherein the alloy has a quenched and tempered microstructure of 75 to 90 vol% tempered martensite and 10 to 25 vol% eutectoid phase.

8. The alloy of claim 1, wherein the alloy is in a hardened and tempered state, and wherein the amount of aluminum nitride and copper precipitates is sufficient to provide a hardness of at least 45 Rockwell C.

9. The alloy of claim 1, wherein the alloy has a microhardness (HV10) of at least 350 at a temperature of 1000°F, and the aluminum nitride reinforcement is provided by aluminum nitride particles with a particle size of 0.5 to 10 micrometers.

10. The alloy of claim 1, wherein the alloy is substantially composed of the following ingredients by weight percentage: composition: 0.8% to 1.2% carbon; 0.3% to 0.7% manganese; 0.4% to 0.7% silicon; 4 to 5.5% chromium; 0.05% to 2.5% nickel; Vanadium content of 1.2% to 1.6%; 5.5% to 7% molybdenum; 4 to 5.5% tungsten; 4.5% to 5.5% cobalt; 0.003 to 0.015% boron; 0.08% to 0.1% nitrogen; 0.01 to 0.6% aluminum; 0.3% to 0.5% copper; Sulfur content as high as 0.3%; Phosphorus content as high as 0.3%; The total content is up to 1% of niobium, tantalum, titanium, hafnium, and zirconium; 70 to 76% iron; and Impurities are present.

11. A valve seat insert for an internal combustion engine, the valve seat insert comprising the alloy according to claim 1.

12. A casting comprising the alloy according to claim 1, wherein the casting has a fully ferritic microstructure.

13. A valve seat insert for an internal combustion engine, the valve seat insert being made of an iron-based alloy, the iron-based alloy comprising, by weight percentage: 0.75% to 2% carbon; 0.1% to 1% manganese; 0.1% to 1% silicon; 3 to 6% chromium; Up to 4% nickel; 1 to 3% vanadium; 4 to 7% molybdenum; 4 to 7% tungsten; 4 to 7% cobalt; Up to 0.1% boron; 0.001 to 0.15% nitrogen; 0.001 to 0.6% aluminum; 0.1% to 1% copper; Sulfur content as high as 0.3%; Phosphorus content as high as 0.3%; The total content is as high as 5% of niobium, tantalum, titanium, hafnium, and zirconium; 70 to 80% iron; and The remaining amount contains impurities. The alloy exhibits improved properties due to aluminum nitride strengthening and copper precipitation hardening.

14. The valve seat insert according to claim 13, wherein the alloy is substantially composed of the following: composition: 0.8% to 1.6% carbon; 0.2% to 0.8% manganese; 0.2% to 0.8% silicon; 3.5% to 5.5% chromium; 0.05% to 2.5% nickel; 1.2% to 2% vanadium; 5 to 7% molybdenum; 4.5% to 6% tungsten; 4.5% to 6% cobalt; 0.001 to 0.05% boron; 0.05% to 0.12% nitrogen; 0.01 to 0.6% aluminum; 0.3% to 0.5% copper; Sulfur content as high as 0.3%; Phosphorus content as high as 0.3%; The total content is up to 1% of niobium, tantalum, titanium, hafnium, and zirconium; 70 to 76% iron; and The remaining amount contains impurities. The aluminum nitride reinforcement is provided by aluminum nitride particles, the content of which is 0.005-0.05% by volume and the particle size is 0.5 to 10 micrometers.

15. The valve seat insert of claim 13, wherein the alloy is substantially composed of the following by weight percentage: composition: 0.8% to 1.2% carbon; 0.3% to 0.7% manganese; 0.4% to 0.7% silicon; 4 to 5.5% chromium; 0.15% to 2.5% nickel; Vanadium content of 1.2% to 1.6%; 5.5% to 7% molybdenum; 4 to 5.5% tungsten; 4.5% to 5.5% cobalt; 0.003 to 0.015% boron; 0.05% to 0.1% nitrogen; 0.01 to 0.6% aluminum; 0.3% to 0.5% copper; Sulfur content as high as 0.3%; Phosphorus content as high as 0.3%; The total content is up to 1% of niobium, tantalum, titanium, hafnium, and zirconium; 70 to 76% iron; and The remainder contains impurities.

16. A method of manufacturing a valve seat insert as claimed in claim 13, the method comprising: Cast the iron-based alloy; as well as Machining castings.

17. A method of manufacturing a valve seat insert as claimed in claim 13, the method comprising: The iron-based alloy is heated to a temperature of at least 1700°F; as well as The hardened alloy is quenched and tempered at temperatures ranging from 1100°F to 1350°F.

18. A method of manufacturing an internal combustion engine, the method comprising inserting a valve seat insert as claimed in claim 13 into the cylinder head of the internal combustion engine.

19. The method of claim 18, wherein the internal combustion engine is selected from the group consisting of a diesel engine and a natural gas engine.

20. A method of operating an internal combustion engine, the method comprising: The cylinder of the internal combustion engine is closed by means of the valve seat insert according to claim 13; as well as The fuel in the cylinder is ignited to operate the internal combustion engine.

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