Steel with excellent wear resistance, corrosion resistance, and toughness

Abstract

A powder metallurgy steel which can be used to make tools, and tools made from such steel. Tools made from the inventive steel exhibit corrosion resistance, wear resistance, and toughness. These properties make the invention well suited for cutting implements, and may be well suited in plastic processing operations, such as injection molding, because many plastics are abrasive and corrosive. This desirable combination of properties may be achieved by keeping the amount of carbon, chromium, vanadium, niobium, molybdenum, nitrogen, silicon, manganese, cobalt, and tungsten within certain ranges.

Description

103415.00011Page 1 of 25Steell With Excellent Wear Resistance,Corrosion Resistance, And ToughnessCross-Reference to Related Application

[0001] This application claims the benefit of priority to U. S. provisional patent application serial number 63 / 679,215, filed on August 5, 2024.Incorporation By Reference

[0002] The disclosure of U. S. patent application 63 / 679,215 is hereby incorporated into this document.Field of the Invention

[0003] The present invention pertains generally to steel alloys known as stainless steel, articles of manufacture (such as a sintered body) made from such steel, and methods for making such steel.Background of the Invention

[0004] Stainless steels are often selected for applications in which corrosion resistance is needed. However, other characteristics are also important. For example, in selecting a stainless steel for a particular application, there is often a tradeoff to be made between desired characteristics such as corrosion resistance, toughness, hardness, and wear resistance. Often, a desired characteristic can be achieved only at the expense of a different characteristic. A consequence of such tradeoffs is that there are many different grades of stainless steel, each having a particular set of characteristics that may be suitable for a particular use. For example, when used for cutting implements, it is desirable that the edges of the cutting implement have high resistance to wear, with high hardness and high toughness often being important secondary considerations. As such, the desired characteristics of a stainless steel (e.g. corrosion resistance, edge wear resistance, hardness, toughness) may be achieved by carefully selecting thePage 1 of 2567637633v3103415.00011Page 2 of 25components of the steel to achieve acceptable levels (but not necessarily the desired levels) of the desired characteristics. Below is a brief overview of some of the tradeoffs.

[0005] Stainless steel is "stainless" because chromium is available to form a chromium oxide layer at the surface, which prevents rust. Approximately 10.5% chromium by weight "in solution" is often targeted in order to achieve a level of rust prevention normally associated with stainless steel. If some vanadium / niobium carbide is present in the microstructure, there will be less steel matrix to contain the chromium, and so it may be possible in such a situation to have less than 10.5% chromium by weight and yet achieve the level of rust-prevention normally associated with stainless steel. With higher levels of chromium, higher corrosion resistance can be obtained, but the achievable hardness is lower after the amount of carbon is reduced to avoid chromium-rich carbide.

[0006] Pitting is a type of corrosion. Molybdenum improves "pitting resistance," as well as "secondary' hardening," and "hardenability." Secondary hardening means the steel goes up in hardness at elevated temperatures, allowing the steel to be operated at higher temperatures.Hardenability is how slowly the steel can be cooled during heat treating and still achieve full hardness. However, if the concentration of molybdenum is too high, the steel will not harden during heat treating because the steel does not fully transform to austenite in the high temperature process before quenching. Instead, the high temperature "delta ferrite" phase is still present.

[0007] Tungsten behaves similarly to molybdenum, but requires roughly twice as much for the same effect. Therefore, molybdenum is typically used in stainless steels rather than tungsten.

[0008] Vanadium leads to the formation of very high hardness carbides that contribute greatly to wear resistance. More vanadium necessitates more carbon to form the high-hardness carbides. However, although more vanadium-rich carbide means higher wear resistance, a corresponding decrease in toughness is realized.

[0009] Niobium also forms very high hardness carbides. Its advantage in powder metallurgy stainless tool steels is that it is a "stronger" carbide former than vanadium. With high chromium steels, the vanadium tends to combine with chromium and form a complex chromium-richPage 2 of 2567637633v3103415.00011Page 3 of 25carbide instead, which is softer and contributes less to wear resistance. When niobium is too high it leads to niobium carbide formation in the "melt" and clogs the nozzle during atomization when forming the powder.

[0010] Nitrogen behaves similarly to carbon, increasing hardness of steel and forming hard nitrides. Complex carbonitrides (carbon and nitrogen) may also form. Nitrogen is less prone to forming chromium nitrides than carbon is to form chromium carbides. Thus, nitrogen is less detrimental to corrosion resistance than carbon. However, nitrogen is not very soluble in liquid steel, and so in order to add nitrogen in amounts greater than about 0.4 weight % more complex methods are needed.

[0011] Cobalt is an "austenite stabilizer", which can help prevent delta ferrite in heat treating so that the steel is fully austenitized. Chromium, molybdenum, tungsten, vanadium, and niobium are all ferrite stabilizers. Carbon and nitrogen are also austenite stabilizers, but excess carbon leads to chromium-rich carbides, and high nitrogen is difficult to add (see above). Adding cobalt can be a good idea in cases where high chromium and molybdenum is desired for high corrosion resistance, with reduced carbon to avoid chromium-rich carbide formation.

[0012] Manganese forms with sulfur so that detrimental iron sulfides are avoided. However, manganese is an austenite stabilizer, so it contributes to retained austenite after quenching.Retained austenite is austenite that does not convert to hard martensite on quenching. Excess retained austenite reduces hardness.

[0013] Nickel is also an austenite stabilizer, and improves toughness, but it also increases retained austenite after quenching.

[0014] Silicon helps increase hardness of steel after tempering, and helps to deoxidize alloys in the melting process. It is a "ferrite stabilizer" and so the amount is limited to avoid delta ferrite.

[0015] A particularly useful method of forming steel alloy is as a powder. Powdered metal is often produced by atomizing liquid steel, and then cooling to form a fine powder. The atomization and rapid solidification results in a finer, and more consistent microstructure. ForPage 3 of 2567637633v3103415.00011Page 4 of 25example, carbides are hard particles formed in steel that resist wear, but are detrimental to toughness. The use of powder metallurgy to minimize the size of these carbides results in greater toughness without a related decrease in wear resistance. Tool steels and stainless steels produced by powder-metallurgy techniques result in better and more consistent properties in the finished products.

[0016] For example, the use of powder metallurgy results in finer and more consistent carbide distribution, which in turn leads to more consistent properties, particularly with respect to corrosion resistance. For example, in processes not using powder metallurgy, large chromium- rich carbides are more difficult to dissolve, leading to some locations in the steel-matrix having reduced chromium content. Those locations having reduced chromium content are more prone to rust because the presence of chromium in the steel matrix facilitates the formation of a chromium oxide layer at the surface, which prevents rust. Smaller chromium-rich carbides found in powder metallurgy steels are still detrimental to corrosion resistance, but to a lesser extent than in conventional steels.

[0017] The powder produced by atomization of the liquid steel can be formed into an ingot by hot isostatic pressing(" HIP"). The ingot may be hot rolled and processed in the same manner as steel that is prepared via traditional methods.

[0018] Cutting implements, including knives, require high strength and hardness to avoid deformation of sharp edges, high toughness to avoid chipping of edges, high corrosion resistance for avoiding rusting of edges, and high wear resistance to avoid wear of edges. Processing of reinforced plastics and other materials that are both abrasive and corrosive also benefit from steel having a combination of high wear resistance and corrosion resistance.

[0019] Previous powder metallurgy steels designed for high wear resistance have high vanadium contents because vanadium-rich carbides are among the hardest carbide types that form in steel. Niobium-rich carbides are also similar in hardness. A complex vanadium and niobium-rich carbide can also form in steels with both alloying elements. Compared to softer carbides, harder carbides contribute more to wear resistance for a given volume fraction of carbide. Minimizing the volume fraction of the carbide leads to higher toughness. However,Page 4 of 2567637633v3103415.00011Page 5 of 25prior art powder metallurgy stainless steels have a significant volume fraction of chromium-rich carbides which are much softer than vanadium-rich carbides, leading to a worse combination of toughness and wear resistance. Furthermore, chromium-rich carbides coarsen more rapidly during high temperature operations such as HIPing and hot rolling, so in powder metallurgy steels the chromium-rich carbides are typically larger than vanadium- and niobium-rich carbides. The larger chromium-rich carbides are more detrimental to toughness than the small vanadium- and niobium-rich carbides.

[0020] A prior-art powder metallurgy stainless steel known as “MagnaCut” is designed to avoid the formation of chromium-rich carbide. Prior to MagnaCut, powder metallurgy stainless steels had 14% by weight or more of chromium for corrosion resistance leading to a significant volume fraction of chromium-rich carbide. However, after heat treatment only about 9-12% of the chromium is present in solution for corrosion resistance, with the remaining chromium present as carbides. MagnaCut reduced chromium while controlling other alloying elements so that most, if not all, of its chromium is present in solution, and most, if not all, carbides present for wear resistance are of the harder vanadium and niobium type. Chromium-rich carbides create local regions with reduced chromium content in the matrix, leading to preferential sites for corrosion, and eliminating the chromium-rich carbides improved corrosion resistance. A microstructure composed of only the small, high hardness vanadium- and niobium-rich carbides, and free from chromium-rich carbides, leads to superior corrosion resistance and toughness. However, MagnaCut has insufficient wear resistance for some applications. What is needed is a material with high wear-resistance, high corrosion resistance, and high toughness. MagnaCut does not provide all three characteristics. It will be shown herein that other stainless steels having high wear resistance, do not also provide high toughness and / or high corrosion resistance.Summary of the Invention[00211 The steel that is the subject of this disclosure provides high corrosion resistance by avoiding the formation of chromium-rich carbides through careful control of chromium, and high wear resistance by forming hard vanadium-rich, niobium-rich, and vanadium-niobium-rich carbides. Chromium-rich carbides are typically M7C3 or M23C6 where “M” is the metal elementPage 5 of 2567637633v3103415.00011Page 6 of 25and “C” is carbon. M7C3 refers to 7 atoms of a metal with 3 atoms of carbon, vanadium -rich, niobium-rich, and vanadium-niobium-rich carbides are more typically MC carbides.

[0022] Furthermore, this disclosure includes an equation for establishing a minimum and / or maximum carbon content for a given content of other alloying elements, which allows for selecting from a range of potential compositions that will achieve a desired wear resistance that is greater than the prior art product known as MagnaCut. The equation can be used to simultaneously:(a) avoid producing a steel having a carbon content that is too low, which cannot be heat treated to the desired strength and hardness level; and(b) avoid having a carbon content that is too high, which would lead to formation of chromium-rich carbides, which in turn would reduce the chromium available for corrosion resistance; and(c) identify a need to increase the vanadium and / or niobium content so that the desired wear resistance is achieved.

[0023] The result is an ability to achieve desired corrosion-resistance and toughness in the finished steel that is not present in prior art formulations such as stainless steels known as CPM S90V, M390, and CPM SHOW

[0024] With those general comments about the invention, a more complete summary of the invention is provided via the following Statements.Statement 1. An iron-based alloy powder, comprising:carbon: 1.3 to 3.4 weight %, including all 0.01 weight % values and ranges therebetween; chromium: 9.0 to 13.9 weight %, including all 0.01 weight % values and ranges therebetween;vanadium: 4.1 to 12.0 weight %, including all 0.01 weight % values and ranges therebetween;niobium: 0.0 to 4.0 weight %, including all 0.01 weight % values and ranges therebetween; molybdenum: 1.0 to 4.0 weight %, including all 0.01 weight % values and ranges therebetween;Page 6 of 2567637633v3103415.00011Page 7 of 25nitrogen: 0.05 to 0.4 weight %, including all 0.01 weight % values and ranges therebetween, silicon: 0.1 to 1.0 weight %, including all 0.01 weight % values and ranges therebetween; manganese: 0.1 to 1.0 weight %, including all 0.01 weight % values and ranges therebetween;cobalt: 0.0 to 5.0 weight %, including all 0.01 weight % values and ranges therebetween; and tungsten: 0.0 to 5.0 weight %, including all 0.01 weight % values and ranges therebetween; with the balance being iron and, optionally, other impurities.Statement 2. The iron-based alloy powder of Statement 1, wherein the carbon content is 1.5 to 2.5 v / eight %, including all 0.01 weight % values and ranges therebetween.Statement 3. The iron-based alloy powder of Statement 1, wherein the carbon content is 1.7 to 2.3 v / eight %, including all 0.01 weight % values and ranges therebetween.Statement 4. The iron-based alloy powder of any one of Statement 1, 2, or 3, wherein the chromium content is 10.0 to 12.0 weight %, including all 0.01 weight % values and ranges therebetween.Statement 5. The iron-based alloy powder of any one of Statement 1, 2, or 3, wherein the vanadium content is 5.5 to 10.5 weight %, including all 0.01 weight % values and ranges therebetween.Statement 6. The iron-based alloy powder of any one of Statement 1, 2,.3, or 4, wherein the vanadium content is 7.0 to 9.0 weight %, including all 0.01 weight % values and ranges therebetween.Statement 7. The iron-based alloy powder of any one of Statements 1 through 6, wherein the niobium content is 0.0 to 3.0 weight %, including all 0.01 weight % values and ranges therebetween.Statement 8. The iron-based alloy powder of any one of Statements 1 through 7, wherein the molybdenum content is 1.5 to 2.5 weight %, including all 0.01 weight % values and ranges therebetween.Page 7 of 2567637633v3103415.00011Page 8 of 25Statement 9. The iron-based alloy powder of any one of Statements 1 through 8, wherein the nitrogen content is 0.18 to 0.28 weight %, including all 0.01 weight % values and ranges therebetween.Statement 10. The iron-based alloy powder of Statement 1, wherein:the carbon content is about 2.04 weight %;the chromium content is about 10.47 weight %;the vanadium content is about 7.9 weight %;the niobium content is about 2.52 weight %;the molybdenum content is about 2.0 weight %;the nitrogen content is about 0.22 weight %;the silicon content is about 0.41 weight %; andthe manganese content is about 0.51 weight %.Statement 11. The iron-based alloy powder of Statement 1, where the minimum and / or maximum carbon content in weight % fit the following equations:Min. carbon for invention = 0.82 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% — 0.261 * N%Max. carbon for invention = 1.15 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% — 0.261 * N%where “%” means “weight percent” of the element indicated.Statement 12. A sintered body derived from an iron-based alloy powder, the powder comprising:carbon: 1.3 to 3.4 weight %, including all 0.01 weight % values and ranges therebetween; chromium: 9.0 to 13.9 weight %, including all 0.01 weight % values and ranges therebetween;vanadium: 4.1 to 12.0 weight %, including all 0.01 weight % values and ranges therebetween;niobium: 0.0 to 4.0 weight %, including all 0.01 weight % values and ranges therebetween;Page 8 of 2567637633v3103415.00011Page 9 of 25molybdenum: 1.0 to 4.0 weight %, including all 0.01 weight % values and ranges therebetween;nitrogen: 0.05 to 0.4 weight %, including all 0.01 weight % values and ranges therebetween; silicon: 0.1 to 1.0 weight %, including all 0.01 weight % values and ranges therebetween; manganese: 0.1 to 1.0 weight %, including all 0.01 weight % values and ranges therebetween;cobalt: 0.0 to 5.0 weight %, including all 0.01 weight % values and ranges therebetween; and tungsten: 0.0 to 5.0 weight %, including all 0.01 weight % values and ranges therebetween; with the balance being iron and optionally, other impurities.Statement 13. The sintered body of Statement 12, wherein the carbon content of the powder is 1.5 to 2.5 weight %, including all 0.01 weight % values and ranges therebetween.Statement 14. The sintered body of Statement 12, wherein the carbon content of the powder is 1.7 to 2.3 weight %, including all 0.01 weight % values and ranges therebetween.Statement 15. The sintered body of any one of Statement 12, 13, or 14, wherein the chromium content of the powder is 10.0 to 12.0 weight %, including all 0.01 weight % values and ranges therebetween.Statement 16. The sintered body of any one of Statement 12, 13, 14, or 15, wherein the vanadium content of the powder is 5.5 to 10.5 weight %, including all 0.01 weight % values and ranges therebetween.Statement 17. The sintered body of any one of Statement 12, 13, 14, or 15, wherein the vanadium content of the powder is 7.0 to 9.0 weight %, including all 0.01 weight % values and ranges therebetween.Statement 18. The sintered body of any one of Statements 12 through 17, wherein the niobium content of the powder is 0.0 to 3.0 weight %, including all 0.01 weight % values and ranges therebetween.Page 9 of 2567637633v3103415.00011Page 10 of 25Statement 19. The sintered body of any one of Statements 12 through 18, wherein the molybdenum content of the powder is 1.5 to 2.5 weight %, including all 0.01 weight % values and ranges therebetween.Statement 20. The sintered body of any one of Statements 12 through 19, wherein the nitrogen content of the powder is 0.18 to 0.28 weight %, including all 0.01 weight % values and ranges therebetween.Statement 21. The sintered body of Statement 12, wherein the powder comprises:about 2.04 weight % carbon,about 10.47 weight % chromium;about 7.9 weight % vanadium;about 2.52 weight % niobium;about 2.0 weight % molybdenum;about 0.22 weight % nitrogen;about 0.41 weight % silicon; andabout 0.51 weight % manganese.Statement 22. The sintered body of Statement 12, where the minimum and / or maximum carbon content of the powder fit the following equations:Min. carbon for invention - 0.82 - 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 *V% + 0.0248 * Mo% - 0.261 * N%Max. carbon for invention - 1.15 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% — 0.261 * N%where “%” means “weight percent” of the element indicated.Statement 23. The sintered body of any one of Statements 12 through 22, comprising not more than 3 weight % chromium-rich carbide after final heat treatment.Statement 24. The sintered body of any one of Statements 12 through 22, comprising at least 10% carbide after final heat treatment.Page 10 of 2567637633v3103415.00011Page 11 of 25Statement 25. The sintered body of any one of Statements 12 through 22, comprising vanadium- rich carbide.Statement 26. The sintered body of any one of Statements 12 through 22, comprising niobium- rich carbide.Statement 27. The sintered body of any one of Statements 12 through 22, comprising vanadium- rich carbide and niobium-rich carbide.Statement 28, The sintered body of any one of Statements 12 through 22, which has been formed into a cuting implement.Statement 29. The sintered body of Statement 28, wherein the cutting implement is a knife.Statement 30. The sintered body of Statement 28, wherein the cutting implement is a saw blade.Statement 31. The sintered body of Statement 28, wherein the cutting implement is a pair of scissors.Statement 32. A method of forming an iron-based alloy powder, comprising:forming a liquid comprising:carbon: 1.3 to 3.4 weight %, including all 0.01 weight % values and ranges therebetween; chromium: 9.0 to 13.9 weight %, including all 0.01 weight % values and ranges therebetween;vanadium: 4.1 to 12.0 weight %, including all 0.01 weight % values and ranges therebetween;niobium: 0.0 to 4.0 weight %, including all 0.01 weight % values and ranges therebetween;molybdenum: 1.0 to 4.0 weight %, including all 0.01 weight % values and ranges therebetween;nitrogen: 0.05 to 0.4 weight %, including all 0.01 weight % values and ranges therebetween;silicon: 0.1 to 1.0 weight %, including all 0.01 weight % values and ranges therebetween;Page 11 of 2567637633v3103415.00011Page 12 of 25manganese: 0.1 to 1.0 weight %, including all 0.01 weight % values and ranges therebetween,cobalt: 0.0 to 5.0 weight %, including all 0.01 weight % values and ranges therebetween;andtungsten: 0.0 to 5.0 weight %, including all 0.01 weight % values and ranges therebetween;with the balance being iron and optionally, other impurities; andatomizing the liquid.Statement 33. The method of Statement 32, wherein the carbon content of the liquid is 1.5 to 2.5 weight %, including all 0.01 weight % values and ranges therebetween.Statement 34. The method of Statement 32, wherein the carbon content of the liquid is 1.7 to 2.3 weight %, including all 0.01 weight % values and ranges therebetween.Statement 35. The method of any one of Statement 32, 33, or 34, wherein the chromium content of the liquid is 10.0 to 12.0 weight %, including all 0.01 weight % values and ranges therebetween.Statement 36. The method of any one of Statement 32, 33, 34, or 35, wherein the vanadium content of the liquid is 5.5 to 10.5 weight %, including all 0.01 weight % values and ranges therebetween.Statement 37. The method of any one of Statement 32, 33, 34, or 35, wherein the vanadium content of the liquid is 7.0 to 9.0 weight %, including all 0.01 weight % values and ranges therebetween.Statement 38. The method of any one of Statements 32 through 37, wherein the niobium content of the liquid is 0.0 to 3.0 weight %, including all 0.01 weight % values and ranges therebetween.Statement 39. The method of any one of Statements 32 through 37, wherein the molybdenum content of the liquid is 1.5 to 2.5 weight %, including all 0.01 weight % values and ranges therebetween.Page 12 of 2567637633v3103415.00011Page 13 of 25Statement 40. The method of any one of Statements 32 through 37, wherein the nitrogen content of the liquid is 0.18 to 0.28 weight %, including all 0.01 weight % values and ranges therebetween.Statement 41. The method of Statement 32, wherein the liquid comprises:about 2,04 weight % carbon;about 10.47 weight % chromium;about 7.9 weight % vanadium;about 2.52 weight % niobium;about 2.0 weight % molybdenum;about 0.22 weight % nitrogen;about 0.41 weight % silicon; andabout 0.51 weight % manganese.Statement 42. The iron-based alloy powder of Statement 32, where the minimum and / or maximum carbon content fit the following equations:Min. carbon for invention = 0.82 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% — 0.261 * N%Max. carbon for invention = 1.15 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% — 0.261 * N%where “%” means “weight percent” of the element indicated.Brief Description Of The Drawings[00251 For a fuller understanding of the nature and objects of the invention, reference should be made to the accompanying drawings and the subsequent description. Briefly, the drawings are:Figure 1, which is a table showing components of some existing stainless steel alloys and a stainless steel alloy that is in keeping with the invention.Figure 2, which is a table showing toughness measurements obtained via acharpy impact of unnotched specimens with dimensions 2.5 x 10 x 55 mm.Page 13 of 2567637633v3103415.00011Page 14 of 25The toughness of the steel formulated according to the invention issignificantly higher than prior art stainless steels having high wearresistance. In Figure 2, the stainless steel is lower in toughness than MagnaCut, though MagnaCut has significantly lower wear resistance (see Figure 3).Figure 3, which is a table showing wear resistance obtained via a CATRA edge retention test BS EN ISO 8442-5: 2004. The knives used in the test hadthe same sharpening and edge geometry. The stainless steel formulated according to the invention exhibits characteristics similar to those stainless steels having high edge retention / wear resistance (e.g. CPM SI 10V and M390), and is significantly more wear resistant than MagnaCut.Figure 4, which is a table showing the results of corrosion tests by spraying I x1.5 meh polished coupons with 1% saltwater solution every eight hours and evaluated after 48 hours. The steel formulated according to the invention showed no rust spots in this test.Figure 5, which is a table showing results of hardness tests after different heat treatments of steel formulated according to the invention in comparisonwith MagnaCut. Higher than 60 Rockwell C was achieved with theinventive steel, and the inventive steel heat treated similarly to MagnaCut. The inventive steel was austenitized at the temperature shown in the table, quenched, and tempered at 350 degrees Fahrenheit.Figure 6, which depicts an article of manufacture that is a sintered body formedfrom steel formulated according to the invention. In Figure 6, the article of manufacture is a knife.Figure 7, which is a flow diagram depicting steps of a method that is in keeping with the invention.Further Description of the InventionPage 14 of 2567637633v3103415.00011Page 15 of 25

[0026] It has been discovered that an improved powder metallurgy corrosion-resistant steel can be produced using a combination of reduced chromium content and high vanadium and / or niobium content. The high vanadium content provides improved wear resistance and a corresponding reduction in chromium-rich carbides, as well as an ability to reduce the amount of chromium, while also achieving corrosion resistance equivalent to stainless steel commonly known as MagnaCut, which is a counterintuitive result because of the importance of chromium for corrosion resistance.

[0027] This disclosure describes an iron-based alloy, which may be formed as a powder. The alloy comprises:carbon: 1.3 to 3.4 weight %, including all 0.01 weight % values and ranges therebetween, and preferably 1.5 to 2.5 weight %, including all 0.01 weight % values and ranges therebetween, and more preferably 1.7 to 2.3 weight %, including all 0.01 weight % values and ranges therebetween;chromium: 9.0 to 13.9 weight %, including all 0.01 weight % values and ranges therebetween, and preferably 10 to 12 weight %, including all 0.01 weight % values and ranges therebetween;vanadium: 4.1 to 12 weight %, including all 0.01 weight % values and ranges therebetween, and preferably 5.5 to 10.5 weight %, including all 0.01 weight % values and ranges therebetween, and more preferably 7.0 to 9.0 weight %, including all 0.01 weight % values and ranges therebetween;niobium: 0.0 to 4.0 weight %, including all 0.01 weight % values and ranges therebetween, and preferably 0,0 to 3.0 weight %, including all 0.01 weight % values and ranges therebetween;molybdenum: 1.0 to 4.0 weight %, including all 0,01 weight % values and ranges therebetween, and preferably 1,5 to 2.5 weight %, including all 0.01 weight % values and ranges therebetween;nitrogen: 0.05 to 0.4 weight %, including all 0.01 weight % values and ranges therebetween, and preferably 0.18 to 0.28 weight %, including all 0.01 weight % values and ranges therebetween,silicon: 0.1 weight % to 1.0 weight %;Page 15 of 2567637633v3103415.00011Page 16 of 25manganese: 0.1 weight % to 1.0 weight %;cobalt 5.0 weight % or lesstungsten 5.0 weight % or less;with the balance being iron and optionally, other impurities.

[0028] A particular example of an iron-based alloy that is in keeping with the invention, comprises:about carbon: 2.04 weight %;about chromium: 10.47 weight %;about vanadium: 7.9 weight %;about molybdenum: 2.0 weight %;about niobium: 2.52 weight %;about nitrogen: 0.22 weight %;about manganese: 0.51 weight %;about silicon: 0.41 weight %;with the balance being iron and optionally, other impurities, which may be inevitable.

[0029] Carbon is required for achieving high hardness after heat treatment, by achieving 0.35-0.60% carbon "in solution" to contribute to hardness. The remaining carbon forms carbides with one or more alloying elements. If the carbon content is too high in the steel, chromium-rich carbide will be present in the heat-treated microstructure, which will reduce toughness and corrosion resistance. If carbon content is too low in the steel, the steel is too soft after heat treating.

[0030] In particular, some carbon is needed so that the steel can be hardened to 60 Rockwell C or higher. However, a maximum level of carbon should be adhered to so as to avoid formation of chromium-rich carbides. To achieve these aspects, the following equations may be used to calculate a desired level of carbon for a steel alloy that is in keeping with the invention:Min. carbon for invention = 0.82 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% — 0.261 * N%Page 16 of 2567637633v3103415.00011Page 17 of 25Max. carbon for invention = 1.15 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% — 0.261 * N%where “%” means “weight percent” of the element indicated. For clarity: Cr = chromium, Nb = niobium, V = vanadium, Mo = molybdenum, and N = nitrogen.

[0031] Such an alloy can be used to produce an article of manufacture. Such articles made from the inventive alloy may exhibit a combination of corrosion resistance, wear resistance, and toughness, which together have not been seen in the prior art. These properties make the inventive alloy well suited for use as a cutting implement, such as a knife. Cutting implements require high strength and hardness to avoid deformation of sharp edges, high toughness to avoid chipping of edges, high corrosion resistance for avoiding rusting of edges, and high wear resistance to avoid wear of edges. Achieving all of these characteristics in one metal is difficult. This desirable combination of properties, which is embodied by the inventive iron-based alloy disclosed herein, may be achieved by controlling the composition of the iron-based alloy, and in particular, keeping within certain ranges the amount of carbon, chromium, vanadium, niobium, molybdenum, nitrogen, manganese, silicon, cobalt, and tungsten.

[0032] It will now be recognized that the invention is an improvement over the prior art. Figure 3 identifies the following stainless steels as having high wear resistance: the invention, CPM S110V, and CPM S90V. Of those three, Figure 4 identifies two of those as having high resistance to corrosion, specifically: the invention and CPM S110V. Of those two, Figure 2 identifies only the invention as having high toughness. Only the invention provides high wear resistance, high corrosion resistance, and high toughness.

[0033] In addition, because many plastics are abrasive and corrosive, the inventive iron¬ based alloy may be well suited for use in manufacturing operations involving the formation of plastic objects, such as molds used in injection molding.

[0034] Herein, “impurities” are mentioned. Such impurities may be naturally occurring, or may occur as a result of processing. Such impurities may include, but are not limited to sulfur, phosphorus, and oxygen.Page 17 of 2567637633v3103415.00011Page 18 of 25

[0035] Embodiments of the invention may consist essentially of the aforementioned ranges of carbon, chromium, vanadium, niobium, molybdenum, nitrogen, manganese, silicon, cobalt, and tungsten.

[0036] In the foregoing description, the word “comprises” is used to describe the invention. In those instances, the description is intended to describe the invention in such a way that the description includes an example of the invention in which the word “comprises” means “comprises”, an example of the invention in which the word “comprises” means “consists of’, and also an example of the invention in which the word “comprises” means “consists essentially of”.

[0037] As used herein, unless otherwise indicated, “about”, “substantially”, or “the like”, when used in connection with a measurable variable (such as, for example, a parameter, an amount, a temporal duration, or the like) or a list of alternatives, is meant to encompass variations of and from the specified value including, but not limited to, those within experimental error (which can be determined by, e.g., a given data set, an art accepted standard, etc. and / or with, e.g., a given confidence interval (e.g. 90%, 95%, or more confidence interval from the mean), such as, for example, variations of 4-7-10% or less, -<- / -5% or less, + / -!% or less, and + / - 0.1% or less of and from the specified value), insofar such variations in a variable and / or variations in the alternatives are appropriate to perform in the instant disclosure. As used herein, the term “about” may mean that the amount or value in question is the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, compositions, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error, or the like, or other factors known to those of skill in the art such that equivalent results or effects are obtained. In general, an amount, size, composition, parameter, or other quantity or characteristic, or alternative is “about” or “the like,” whether or not expressly stated to be such. It is understood that where “about,” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.Page 18 of 2567637633v3103415.00011Page 19 of 25

[0038] All references to “weight %” or “weight percent” are relative to the total weight of the alloy, and represent the proportion of a specific component's weight within the alloy, expressed as a percentage of the total weight.

[0039] Although the present invention has been described with respect to one or more particular examples, it will be understood that other embodiments of the present invention may be made without departing from the spirit and scope of the present invention. Hence, the present invention is deemed limited only by the appended claims and the reasonable interpretation thereof.Page 19 of 2567637633v3

Claims

103415.00011Page 20 of 25What is claimed is:

1. An iron-based alloy powder, comprising:carbon: 1.5 to 2.5 weight %;chromium: 9.0 to 13.9 weight %;vanadium: 5.5 to 10.5 weight %;niobium: 0.0 to 3.0 weight %;molybdenum: 1.0 to 4.0 weight %;nitrogen: 0.05 to 0.28 weight %;silicon: 0.1 to 1.0 weight %;manganese: 0.1 to 1.0 weight %;cobalt: 0.0 to 5.0 weight %; andtungsten: 0.0 to 5.0 weight %;with the balance being iron and optionally, other impurities.

2. The iron-based alloy powder of Claim I, wherein the carbon content is 1.7 to 2.3 weight %.

3. The iron-based alloy powder of Claim 1, wherein the vanadium content is 7.0 to 9.0 weight %.

4. The iron-based alloy powder of Claim 1, wherein:the carbon content is about 2.04 weight %;the chromium content is about 10.47 weight %;the vanadium content is about 7.9 weight %;the molybdenum content is about 2.0 weight %;the niobium content is about 2.52 weight %;the nitrogen content is about 0.22 weight %;the manganese content is about 0.51 weight %; andthe silicon content is about 0.41 weight %.

5. The iron-based alloy powder of Claim I, where the minimum and maximum carbon content fit the following equations:Page 20 of 2567637633v3103415.00011Page 21 of 25Min. carbon for invention = 0.82 ■■■■ 0,0875 * Cr% + 0.1669 * Nb% + 0.1964 *V% + 0.0248 * Mo% - 0.261 * N%Max. carbon for invention ~ 1.15 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0,0248 * Mo% - 0.261 * N%where “%” means “weight percent” of the element indicated.

6. A sintered body derived from an iron-based alloy powder, the powder comprising:carbon: 1.5 to 2.5 weight %;chromium: 9.0 to 13.9 weight %;vanadium: 5.5 to 10.5 weight %;niobium: 0.0 to 3.0 weight %;molybdenum: 1.0 to 4.0 weight %;nitrogen: 0.05 to 0.28 weight %;silicon: 0.1 to 1.0 weight %;manganese: 0.1 to 1.0 weight %;cobalt: 0.0 to 5.0 weight %; andtungsten: 0.0 to 5.0 weight %;with the balance being iron and optionally, other impurities.

7. The sintered body of Claim 6, wherein the carbon content of the powder is 1.7 to 2.3 weight %.

8. The sintered body of Claim 6, wherein the vanadium content of the powder is 7.0 to 9.0 weight %.

9. The sintered body of Claim 6, wherein the powder comprises:about 2.04 weight % carbon;about 10.47 weight % chromium;about 7.9 weight % vanadium;about 2.0 weight % molybdenum;about 2.52 weight % niobium;Page 21 of 2567637633v3103415.00011Page 22 of 25about 0.22 weight % nitrogen,about 0.51 weight % manganese; andabout 0.41 weight % silicon.

10. The sintered body of Claim 6, where the minimum and maximum carbon content of the powder fit the following equations:Min. carbon for invention = 0.82 ■■■■ 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 *V% + 0.0248 * Mo% - 0.261 * N%Max. carbon for invention = 1.15 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% - 0.261 * N%where “%” means “weight percent” of the element indicated.

11. The sintered body of Claim 6, comprising not more than 3 weight % chromium-rich carbide after final heat treatment.

12. The sintered body of Claim 6, comprising at least 10% carbide after final heat treatment.

13. The sintered body of Claim 6, comprising vanadium-rich carbide.

14. The sintered body of Claim 6,comprising niobium-rich carbide.

15. The sintered body of Claim 6, comprising vanadium-rich carbide and niobium-rich carbide.

16. The sintered body of Claim 6, which has been formed into a cutting implement.

17. The sintered body of Claim 16, wherein the cutting implement is a knife.

18. The sintered body of Claim 16, wherein the cutting implement is a saw blade.

19. The sintered body of Claim 16, wherein the cutting implement is a pair of scissors.

20. A method of forming an iron-based alloy powder, comprising:forming a liquid comprising:carbon: 1.5 to 2.5 weight %;Page 22 of 2567637633v3103415.00011Page 23 of 25chromium: 9.0 to 13.9 weight %;vanadium: 5.5 to 10.5 weight %;niobium: 0.0 to 3.0 weight %;molybdenum: 1.0 to 4.0 weight %;nitrogen: 0.05 to 0.28 weight %;silicon: 0.1 to 1.0 weight %;manganese: 0.1 to 1.0 weight %;cobalt: 0.0 to 5.0 weight %; andtungsten: 0.0 to 5.0 weight %;with the balance being iron and optionally, other impurities; andatomizing the liquid.

21. The method of Claim 20, wherein the carbon content of the liquid is 1.7 to 2.3 weight %.

22. The method of Claim 20, wherein the vanadium content of the liquid is 7.0 to 9.0 weight %.

23. The method of Claim 20, wherein the liquid comprises:about 2.04 weight % carbon;about 10.47 weight % chromium;about 7.9 weight % vanadium;about 2.0 weight % molybdenum;about 2.52 weight % niobium;about 0.22 weight % nitrogen;about 0.51 weight % manganese; andabout 0.41 weight % silicon.

24. The iron-based alloy powder of Claim 20, where the minimum and maximum carbon content fit the following equations:Min. carbon for invention = 0.82 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% — 0.261 * N%Page 23 of 2567637633v3103415.00011Page 24 of 25Max. carbon for invention = 1.15 — 0.0875 * Cr% + 0.1669 * Nb% + 0.1964 * V% + 0.0248 * Mo% - 0.261 * N%where “%” means “weight percent” of the element indicated.Page 24 of 2567637633v3

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