Precipitation hardenable martensitic stainless steel alloy, method for manufacturing a metal part or component and article of manufacture
Patent Information
- Application Number
- BR112022016765
- Authority / Receiving Office
- BR · BR
- Patent Type
- Patents
- Current Assignee / Owner
- Publication Date
- 2026-09-01
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Abstract
Description
1 / 27 “PRECIPITATION HARDENABLE MARTENSITIC STAINLESS STEEL ALLOY, METHOD FOR MANUFACTURING A METAL PART OR COMPONENT AND ARTICLE OF MANUFACTURE Background of the invention Field of invention
[001] This invention relates to a precipitation-hardenable martensitic stainless steel alloy that is capable of providing very high fracture strength and toughness along with corrosion resistance. The superior combination of fracture strength and toughness combined with corrosion resistance makes this alloy particularly suitable for aerospace components, specifically for aircraft landing gear. The alloy can be used to manufacture other articles that require the combination of high strength and fracture toughness provided by the alloy. Description of the Related State of the Art
[002] The aerospace industry has been searching for many years for a high-strength stainless steel alloy for use in aircraft landing gear. One alloy currently known and used for commercial aircraft landing gear applications is alloy 300M. Alloy 300M can be quenched and tempered to provide an ultimate tensile strength of approximately 280 ksi (1930 MPa) with good ductility, as represented by an elongation greater than 10%. Alloy 300M also provides a fracture toughness KIc of 50-60 ksiVm (55-66 MPaVm). However, alloy 300M does not offer effective corrosion resistance. Therefore, it was necessary to coat the landing gear components with a corrosion-resistant metal. Petition 870260070122, dated 07 / 15 / 2026, page 8 / 72 2 / 27 Corrosion, such as cadmium. Cadmium is a highly toxic and carcinogenic material, and its use has presented significant health and environmental risks in the manufacture and maintenance of aircraft landing gear and other exposed components made of alloy 300M. The desired corrosion resistance for aircraft landing gear applications includes general corrosion resistance, pitting corrosion resistance, and stress corrosion cracking resistance.
[003] Furthermore, for critical applications involving high strength and high toughness, such as in the case of aerospace landing gear, the relevant material specifications require a design based on a critical failure size. Many of these specifications require a fracture toughness to ultimate tensile strength ratio, KIc:UTS, which must be met by the qualified material. Although some of the known corrosion-resistant and precipitation-hardenable alloys are capable of meeting the strength, ductility, and corrosion resistance requirements for landing gear applications, they have not been able to provide fracture toughness greater than about 50 ksiVin (55 MPaVm), or greater than about 60 ksiVin (65 MPaVm). Nor are they able to provide a fracture toughness to UTS ratio equivalent to or better than 300M.For example, alloy 300M is known to provide a fracture strength to tensile strength ratio of about 0.20–0.26 Vin, and examples of the alloy disclosed in US2016 / 02898056A1 provide ratios of only about 0.20 Vin and 0.21 Vin.
[004] Consequently, there is a need for a league Petition 870260070122, dated 07 / 15 / 2026, p. 9 / 72 3 / 27 of corrosion-resistant steel to qualify as a direct substitute for alloy 300M without a major design modification in terms of mechanical functionality, and which provides the combination of strength and fracture toughness required for aerospace landing gear applications and conventionally provided by alloy 300M. Brief summary of the invention
[005] According to a first aspect of the present invention, a precipitation-hardenable martensitic stainless steel is provided having the following broad, intermediate and preferred compositions in weight percent. Preferred Broad Intermediate Ni 10.5-12.5 11.0-12.2 11.4-12.0 Co 1, 0-6, 0 1.5-5.5 2.0-5.0 Mo 1.0-4.0 2.0-3.0 2.25-2.75 Ti 1.5-2.0 1.55-1.8 1.60-1.75 Cr 8.5-11.5 8.75-10.5 9.0-10.0 Al Up to 0.5 Up to 0.3 Up to 0.2 C 0.03 max. 0.02 max. 0.015 max. Mn 1.0 max. 0.25 max. 0.10 max. Si 0.75 max. 0.25 max. 0.10 max. Nb 0.10 max. 0.10 max. 0.10 max. P 0.04 max. 0.015 max. 0.01 max. S 0.02 0 max. 0.01 max. 0.005 max. B 0.01 max. 0.001-0.005 0.0015-0.0035 N 0.03 max. 0.015 max. 0.010 max.
[006] The balance of the alloy is iron and the usual impurities found in commercial grades of precipitation-hardenable martensitic stainless steels, as is known to those skilled in the art in the practice of melting for such steels.
[007] The preceding tabulation is provided as a convenient summary and is not intended to restrict the lower and upper values of the ranges of the individual alloy elements of this invention for use in combination. Petition 870260070122, dated 07 / 15 / 2026, page 10 / 72 4 / 2Ί among themselves, or restrict the element ranges for use only in combination with each other. Thus, one or more of the element ranges of the broad composition may be used with one or more of the other ranges for the remaining elements in the preferred composition. Furthermore, a minimum or maximum for an element of a broad, intermediate, or preferred embodiment may be used with the maximum or minimum for that element of another broad, intermediate, or preferred embodiment. In addition, the alloy according to this invention may comprise, consist essentially of, or consist of the constituent elements described above and as described throughout this descriptive report.
[008] According to another aspect of this invention, a method is provided for manufacturing a metal part or component made of the precipitation-hardenable martensitic stainless steel alloy described above. The method includes the step of providing an ingot with the composition of the precipitation-hardenable martensitic stainless steel alloy described above. The method also includes the steps of heating the ingot to a temperature of about 2,000 °F (1,093 °C) to about 2,400 °F (1,315 °C) for a time sufficient to homogenize said ingot. The homogenized ingot is then hot-worked to provide a nearly liquid-shaped part or an intermediate product form. The method further includes heat-treating the part or intermediate product form by annealing the nearly liquid-shaped part by heating the part or product form to a temperature of about 100 °F (92 °C) to about 1900 °F (1038 °C). Petition 870260070122, dated 07 / 15 / 2026, p. 11 / 72 5 / 27 for a pre-selected period of time. The part or product shape is then tempered from annealing temperature below approximately -100°F (-73°C) to ensure complete martensitic transformation of the alloy matrix. The method also includes an aging hardening step of the tempered part by heating it to a temperature of 900°F (482°C) to approximately 1150°F (621°C) for a selected time to obtain a combination of high tensile strength, good fracture toughness, and good corrosion resistance.
[009] According to a further aspect of this invention, a fabricated article made from the alloy described in the preceding table is provided. The article is characterized by having high strength and high fracture toughness, along with good corrosion resistance. The article according to the invention provides an ultimate tensile strength of at least about 280 ksi (1930 MPa), a plane strain fracture toughness of at least about 60 ksiVin (65 MPaVm), and a fracture strength to tensile strength ratio of about 0.25-0.3 Vin (Vm), in the solution annealed and age-hardened condition.
[010] Here and throughout this patent application, the term percentage or the symbol % means percentage by weight or percentage by mass, unless otherwise indicated. The term tensile strength means ultimate tensile strength, as this property is generally defined and understood by those skilled in the art. With respect to fracture toughness, the symbol KI refers to fracture toughness measured under predominantly Petition 870260070122, dated 07 / 15 / 2026, page 12 / 72 6 / 27 linear elastic and plane strain. The symbol KQ refers to fracture toughness measured under predominantly linear elastic conditions. Under the experimental conditions applied, the difference between these two quantities is similar to the reproducibility standard deviation of the method (ASTM E399). Thus, the term fracture strength is used in this document as a general term to indicate both KIc and KQ. Brief description of the drawings
[011] Figure 1 illustrates graphs of fracture toughness (MPaVm) as a function of ultimate tensile strength (MPa), for example, alloys described in US2016 / 02899805A1 and for examples of the alloy according to the present invention.
[012] Figure 2 illustrates graphs of fracture toughness (ksiVin) as a function of ultimate tensile strength (ksi) for examples of the alloy according to the present invention and, for example, alloys described in US2016 / 02899805A1, US8097098B2, US2016 / 0319406A1 and US5855844. Detailed description of the invention
[013] The alloy according to the present invention contains at least about 10.50% nickel because nickel contributes to the stabilization of the austenite phase. A stable austenite phase facilitates the transformation of the alloy into a dense displacement martensite during quenching, preventing the formation of delta ferrite in the alloy. A sufficient concentration of nickel is also necessary because nickel participates in the formation of the primary reinforcing phase, Ni3Ti. In addition, nickel ensures good toughness by promoting a reversed austenite, “interlat” austenite and retained austenite during aging and Petition 870260070122, dated 07 / 15 / 2026, p. 13 / 72 7 / 27 alloy tempering. Nickel also reduces the ductile-brittle transition temperature (DBTT) to well below room temperature to provide the good impact toughness that is a characteristic of the alloy. Preferably, the alloy contains at least about 11.0% nickel, and even better, at least about 11.4% nickel. Too much nickel results in the suppression of the initial martensitic transformation temperature (Ms) to undesirably well below room temperature, which prohibits sufficient transformation to achieve the desired mechanical properties. Therefore, the alloy contains no more than about 12.5% nickel. Preferably, the alloy contains no more than about 12.2% nickel, and even better, no more than about 12.0% nickel.
[014] At least about 1.0%, preferably at least about 1.5%, and even better, at least about 2.0% of cobalt is present in this alloy. Cobalt benefits the alloy properties in several important ways. More specifically, cobalt delays the dislocation recovery that occurs during the aging heat treatment of the alloy. Delaying the dislocation recovery phenomenon benefits the heterogeneous nucleation of a fine dispersion of reinforcing precipitates in the alloy matrix. In addition, cobalt interacts with molybdenum to reduce the solubility of molybdenum in the alloy, leading to better coherence between the matrix and the precipitates. The improved coherence benefits the fracture toughness provided by the alloy. Furthermore, cobalt stabilizes the austenite in the alloy at elevated temperatures and contributes to the strengthening of the alloy at Petition 870260070122, dated 07 / 15 / 2026, page 14 / 72 8 / 27 solid solution. On the other hand, when more than about 6% cobalt is present in the alloy, the corrosion resistance provided by the alloy is adversely affected. Cobalt interacts with chromium to form Cr-rich phases during aging heat treatment, thus depleting the chromium from the matrix material. Consequently, cobalt is limited to no more than about 6.0%, preferably no more than about 5.5%, and for best results, no more than about 5.0% in this alloy.
[015] This alloy contains at least about 1.5% titanium to benefit the strength provided by the alloy. Titanium combines with nickel to form the primary strengthening phase, Ni3Ti, during an age hardening heat treatment. Preferably, the alloy contains at least about 1.55% titanium and, for best results, at least about 1.6% titanium. Too much titanium causes an undesirable increase in the soIvus temperature of the Laves phase that forms in the alloy, to the point where it is not possible to sufficiently dissolve the Laves phases without undesirable grain growth. Therefore, titanium is restricted to no more than about 2.0%, preferably no more than about 1.8%, and for best results, no more than about 1.75% in this alloy.
[016] Chromium enhances the corrosion resistance provided by the alloy of this invention. To this end, the alloy contains at least about 8.5% chromium. Preferably, the alloy contains at least about 8.75%, and even better, at least about 9.0% chromium. Excess chromium reduces the Ms temperature of the alloy, which inhibits the Petition 870260070122, dated 07 / 15 / 2026, p. 15 / 72 9 / 27 Martensite formation in the alloy matrix during quenching negatively affects the tensile strength provided by the alloy. Consequently, chromium is limited to no more than about 11.5% in this alloy. Preferably, the alloy contains no more than about 10.5%, and even better, no more than about 10.0% chromium.
[017] At least about 1.0% molybdenum is present in this alloy to benefit the strength provided by the alloy by participating in the precipitation of reinforcing phases, such as the R phase, during the aging hardening of the alloy. Molybdenum also contributes to the pit and crevice corrosion resistance provided by the alloy. For these ends, the alloy preferably contains at least about 2.0% and for best results, at least about 2.25% molybdenum. Excess molybdenum causes a reduction in the Ms temperature such that complete martensitic transformation is inhibited. In addition, too much molybdenum can promote the formation of topologically closed phases (TCPs) rich in Mo that reduce the availability of molybdenum for localized corrosion resistance. For this reason, the alloy contains no more than about 4.0%, better yet no more than about 3.0%, and preferably no more than about 2.75% molybdenum.
[018] Up to about 0.5% or up to about 0.3% aluminum may be present in this alloy as a residue from deoxidizing additions during the primary melting of the alloy. Aluminum may improve the fluidity of the alloy during casting. It is believed that a small amount of aluminum increases the Ms temperature of the alloy, which helps to ensure the Petition 870260070122, dated 07 / 15 / 2026, p. 16 / 72 10 / 27 complete transformation to the martensite phase. The alloy may optionally contain at least about 0.15% aluminum to benefit the yield and tensile strength provided by the alloy. Too much aluminum is detrimental to the fracture toughness provided by the alloy. Therefore, when added positively, aluminum is restricted to no more than about 0.25% and preferably no more than about 0.20% in this alloy. For applications requiring maximum toughness, the alloy contains no more than about 0.025% aluminum.
[019] Other elements such as boron, manganese, and silicon may be present in controlled amounts to benefit other desirable properties provided by this alloy. More specifically, up to about 0.01% boron, better yet up to about 0.005% boron, and preferably up to about 0.0035% boron may be present in the alloy to benefit the hot workability of the alloy. In order to provide the desired effect, at least about 0.001% and preferably at least about 0.0015% boron is present in the alloy. Up to about 1.0%, better yet up to about 0.5%, and even better up to about 0.25% manganese may be present in the alloy as a residue of filler additions during melting. Up to about 0.75%, better still up to about 0.5%, or even better, up to about 0.25% of silicon may be present in the alloy as residual scrap filler materials or deoxidizing additions. Such additions are beneficial when the alloy is not vacuum melted.Manganese and / or silicon are preferably kept at low levels because they can adversely affect toughness and corrosion resistance. Petition 870260070122, dated 07 / 15 / 2026, page 17 / 72 11 / 27 provided by the alloy. Excess manganese and / or silicon also negatively affects the austenite-martensite phase balance in the matrix material. Therefore, manganese and silicon are preferably limited to no more than about 0.10% each in this alloy. Furthermore, the amount of Nb should be limited to no more than about 0.10% to reduce the adverse influence of Nb on the alloy's toughness or to increase the tendency of the alloy to segregate by promoting high-temperature Laves phases.
[020] The alloy balance is essentially iron and the usual impurities found in commercial alloys intended for similar services or uses. The levels of such elements are controlled so as not to impair the combination of properties provided by the alloy.
[021] In particular, too much carbon and / or nitrogen impairs corrosion resistance and negatively affects the toughness provided by this alloy. Consequently, no more than about 0.03%, better still no more than about 0.02%, and preferably no more than about 0.015% of carbon is present in the alloy. Furthermore, no more than about 0.030%, better still no more than about 0.015%, and no more than about 0.010% of nitrogen is present in the alloy. When carbon and / or nitrogen are present in larger quantities, the carbon and / or nitrogen binds to titanium to form titanium-rich nonmetallic inclusions. This reaction inhibits the formation of the nickel-titanium-rich phase, which is a primary factor in the high strength provided by this alloy.
[022] Phosphorus and sulfur are also inevitably present in the alloying additions made during melting. Petition 870260070122, dated 07 / 15 / 2026, p. 18 / 72 12 / 27 primary. However, the amounts of phosphorus and sulfur are controlled. In particular, phosphorus is kept at a low level due to its side effect on the toughness and corrosion resistance properties provided by the alloy. In this respect, no more than about 0.04%, better yet no more than about 0.015%, and preferably no more than about 0.01% of phosphorus is present in this alloy. Sulfur is restricted to no more than about 0.020%, better yet no more than about 0.01%, and preferably no more than about 0.005% in this alloy. Higher amounts of sulfur promote the formation of titanium-rich nonmetallic inclusions that inhibit the strengthening effect provided by titanium because less titanium is available to form the primary strengthening phase during aging heat treatment.Furthermore, amounts of sulfur exceeding these limits adversely affect the hot workability and corrosion resistance provided by the alloy. Additionally, such amounts of sulfur negatively affect the alloy's toughness, particularly in the transverse direction.
[023] When present, sulfur and phosphorus tend to segregate to the grain boundaries of the alloy. Such segregation reduces grain boundary adhesion, which adversely affects the fracture toughness, notch toughness, and notch tensile strength of the alloy. A product form of this alloy having a cross-section greater than about 0.7 in² (4 cm²) does not undergo sufficient thermomechanical processing to homogenize the alloy and neutralize the adverse effect of sulfur concentration and Petition 870260070122, dated 07 / 15 / 2026, page 19 / 72 13 / 27 Phosphorus at grain boundaries. For these large cross-sectional products, a small addition of cerium is preferably made to the alloy during melting to benefit the fracture toughness, notch toughness, and notch tensile strength of the alloy by combining with sulfur and phosphorus to facilitate their removal from the alloy. For sulfur and phosphorus to be adequately removed from the alloy, the ratio of cerium to sulfur present in the alloy (Ce:S) is at least about 1:1, better yet at least about 2:1, and preferably at least about 3:1. Only a small amount (i.e., <0.001%) of cerium needs to be retained in the alloy for the cerium addition to be carried out. However, to ensure that sufficient cerium has been added and to prevent too much sulfur and phosphorus from being retained in the final product, at least about 0.001% and better yet at least about 0.002% of cerium is preferably present in the alloy.Excess cerium can adversely affect the hot workability of the alloy and its fracture toughness. Therefore, cerium is restricted to no more than about 0.025%, better still to no more than about 0.015%, and preferably no more than about 0.010% in the alloy. Alternatively, the cerium-sulfur ratio of the alloy is not more than about 15:1, better still not more than about 12:1, and preferably not more than about 10:1. Other rare earth metals, such as lanthanum and yttrium, as well as calcium and magnesium, may be present in the alloy in place of some or all of the cerium.
[024] No special techniques are required for melting, smelting, or mechanically working the alloy of the present design. Petition 870260070122, dated 07 / 15 / 2026, p. 20 / 72 14 / 27 invention. The alloy of this invention is preferably produced by vacuum induction melting (VIM). When desired, the alloy can be refined by a double melting process in which the VIM ingot is remelted by electroconductive slag (esc) melting (ESR) or by vacuum arc melting (VAR). For more critical applications, a triple melting process consisting of VIM followed by ESR and then VAR can be used. Alternatively, a melting process consisting of VIM followed by multiple VAR melting, or any combination of ESR and VAR melting in an appropriate sequence, as may be known to those skilled in the art, can be used.
[025] The alloy can be cast as an ingot which is hot worked to provide a product form close to the liquid form, such as a billet or bar. Although the alloy of the present invention can be hot or cold worked, cold working increases the mechanical strength of the alloy. Before hot working, the alloy ingot is preferably homogenized by heating the ingot to a temperature of about 2,000 °F to about 2,400 °F for a time selected to equalize the temperature of the ingot.
[026] Hot working is preferably carried out from the homogenization temperature up to a finishing temperature of about 1900 °F (1038 °C). If further reduction in cross-sectional area is required, the alloy may be reheated to about 1900 °F–2400 °F (1038 °C–1315 °C) before continuing hot working. Hot working may be carried out by techniques such as press forging and rotary forging. Petition 870260070122, dated 07 / 15 / 2026, p. 21 / 72 15 / 27
[027] The precipitation-hardenable alloy of the present invention is solution-annealed (re-annealed) and then age-hardened to develop the desired strength. The solution annealing temperature must be high enough to bring sufficient titanium and molybdenum into solution to produce the desired hardening response during the age heat treatment. However, if the solution annealing temperature is too high, this will impair the fracture toughness of the alloy, promoting excessive grain growth. Typically, the alloy of the present invention is solution-annealed at about 1700 °F - 1900 °F (927 °C - 1038 °C) for 1 hour and then quenched. Quenching can be carried out with any known medium, including, but not limited to, water, oil, or inert gas.Preferably, the extinguishing medium is selected to provide an extinguishing rate of about 60 °C / second (°C / s), better still about 80 °C / s, and most preferably about 100 °C / s.
[028] Preferably, this alloy is subjected to a deep quenching treatment after quenching to further develop the alloy's high strength. The deep quenching treatment cools the alloy to a temperature sufficiently below the martensite finishing temperature (Mf) to ensure the completion of the martensite transformation. Typically, a deep quenching treatment consists of cooling the alloy below about -73 °C (-100 °F) for about 1 hour. However, the need for a deep quenching treatment will be affected, at least in part, by the temperature of Petition 870260070122, dated 07 / 15 / 2026, page 22 / 72 16 / 27 Martensite finish of the alloy. If the martensite finish temperature is sufficiently high, the transformation to a martensitic structure will occur without the need for deep cooling treatment. Furthermore, the need for deep cooling treatment may also depend on the cross-sectional size of the part being manufactured. As the cross-sectional size of the part increases, segregation in the alloy becomes more significant, and the use of deep cooling treatment becomes more beneficial. Additionally, the cooling time may need to be increased for large parts in order to complete the martensite transformation. For example, it has been found that in a part with a large cross-sectional area (i.e., 0.7 in² or more), a deep cooling treatment lasting approximately 8 to 16 hours is preferred to develop the high strength characteristic of this alloy.
[029] The alloy of the present invention is age-hardened according to techniques used for known precipitation hardening of stainless steel alloys, techniques which are known to those skilled in the art. For example, the alloys can be aged at a temperature between about 900°F (482°C) and about 1150°F (621°C) for about 4 to about 24 hours. After the aging treatment, the material is cooled in a selected medium to produce a cooling rate of about 60°C / s, or preferably about 80°C / s, or more preferably about 100°C / s. A slower cooling rate may be used, although the Petition 870260070122, dated 07 / 15 / 2026, p. 23 / 72 17 / 27 mechanical properties cannot be guaranteed. The alloy according to the invention is capable of providing an ultimate tensile strength of at least about 280 ksi and a fracture toughness of at least about 60 ksi in the solution annealed and age-hardened condition. The alloy is further characterized by having good general corrosion resistance as determined by the salt spray test (ASTM B117).
[030] The alloy of the present invention can be formed into a variety of product shapes for a wide range of uses and lends itself to the formation of billets, bars, rods, wires or plates using conventional practices. In the annealed solution condition, this alloy is processable and sufficiently ductile to be processed into small gauge sheets and strips. Furthermore, cold working into sheets and strips followed by aging will lead to greater mechanical strength, but at some cost to toughness and ductility properties. In addition, the alloy can be produced by powder metallurgy techniques. The metal powder made from the alloy according to the present invention can be processed into a complex semi-finished state close to the final product as is known to those skilled in the art. In this respect, the metal powder can be processed or manufactured into a semi-finished part by powder metallurgy or additive manufacturing techniques.
[031] The alloy of the present invention is useful in a wide range of practical applications requiring an alloy with a good combination of corrosion resistance, high strength and good toughness. In particular, the alloy of the present invention can be used to produce structural members. Petition 870260070122, dated 07 / 15 / 2026, p. 24 / 72 18 / 27 for aircraft, including but not limited to landing gear components, flap tracks, and fasteners. The alloy is also suitable for use in medical and dental applications, such as dental tools, medical scrapers and cutters, as well as suture needles. The alloy is also suitable for use in consumer sporting applications, such as golf club heads. Examples of work
[032] In order to demonstrate the novel combination of high strength and fracture toughness provided by the alloy according to this invention, Examples 1-13, which incorporate the alloy of this invention, were vacuum induction cast (VIM). The compositions of Examples 1-13 are shown in Table 1 below in weight percent. Petition 870260070122, dated 07 / 15 / 2026, page 25 / 72 19 / 27 Table 1 Example By Cr Mo Ti Co Al Other 1 11, 88 9, 24 2.48 1, 73 2.79 0, 17 2 11, 8 9.5 2 1.7 2.5 0, 19 3 11, 4 9.5 2.75 1, 65 3 0, 2 4 12, 9.2 2 1.7 2 0 5 11, 7 9.2 3 1.7 2 0 6 11, 1 9.2 3 1.7 5 0 7 11, 6 9.2 2 1.7 5 0 8 12, 1 9 2.5 1.7 1.4 0 9 11, 2 9.2 2.5 1.7 5. 6 0 10 11. 9 9.2 1.79 1.7 3. 5 0 11 11. 2 9.2 3.21 1.7 3. 5 0 12 11. 6 9.2 2.5 1.7 3. 5 0 13 11. 5 9.8 2.4 1.7 3 0 A 11.47 10.14 1.99 1.16 5 1.32 B 12.21 9.12 2.05 1.22 3.09 1.31 C 12.21 9.12 2.05 1.22 3.09 1.31 D 12.21 9, 12 2.05 1, 22 3, 09 1, 31 E 12.43 8, 98 2.08 1, 23 3, 12 1, 38 F 12.43 8, 98 2.08 1, 23 3, 12 1, 38 G 11, 82 9.00. 6 2.03 1.45 3.06 1.09 H 11.82 9.6 2.03 1.45 3.06 1.09 I 11.16 11.36 1.94 1.03 0 1.35 J 10.58 11.4 1.98 0.09 . 961 0 1. 38 K 10. 85 10.89 2. 45 1. 02 0 1.41 L 11. 84 9 2. 96 0. 842 0 1.41 M 10. 95 10.35 2. 85 1. 22 0 1. 33 N 10 2 1, 09 0 1.41 O 11, 91 7, 74 0, 98 0.71 9, 95 0, 27 P 13, 45 8, 67 0, 82 0, 57 13, 9 0, 39 Q 11, 04 11.42 0, 63 0.98 0.55 0.5 Nb R 10.66 11.50.49 0.95 1.63 0.98 0.57 0.51 Nb S 7.97 10.96 5 0 8.55 1.21 T 8.01 11.14 4.99 0 8.62 1.22 1.56 0 0 V 11 11.6 1.26 1.63 0 0 W 11.03 11.59 1.26 1.6 0 0, Petition 870260070122, dated 07 / 15 / 2026, p. 26 / 72 20 / 27
[033] The balance of each example was iron and usual impurities. For Examples 1-13, the impurities included less than 0.01% manganese, a maximum of 0.01% silicon, less than 0.005% phosphorus, less than 0.001% sulfur, 0.002-0.004% carbon, less than 0.01% nitrogen, and less than 0.01% niobium.
[034] The AW examples correspond to examples described in issued U.S. patents and published U.S. patent applications. The alloys corresponding to the AW Examples in the various references are identified in Table 2 below. Table 2 Example Application. Example of ID Reference A 9 US 2016 / 0289805 B 10 C 10 D 10 E 12 F 12 G 14 H 14 IE US 8.097.098 JFKGLHMINJO M52S-1A US 7.879.159 P M52S-2C Q 1 US 2016 / 0319406 R 2 S 2A US 6.630.103 T 2B U 25 US 5.855.844 V 26 W 27
[035] The batteries in Examples 1–13 were cast in 4-inch (10.2 cm) tapered square ingots. The Petition 870260070122, dated 07 / 15 / 2026, p. 27 / 72 21 / 27 ingots were homogenized at 2300 °F (1260 °C) for 24 hours. The ingots were then heated to 2000 °F (1093 °C) for a time sufficient to equalize the temperature and then pressure forged into 2¼ inch (5.7 cm) square bars. The forged bars were cut and then reheated to 2000 °F (1093 °C). The square bars were then pressure forged into 1 ¼ inch (3.175 cm) square bars, cut, and then reheated to equalize the temperature at 2000 °F (1093 °C). The bars were then single-end press forged into 17.5 mm (11 / 16 inch) square bars and then air-cooled to room temperature. The bars were then relieved of stress by heating at 1250 °F (677 °C) for 4 hours followed by air cooling to room temperature.
[036] After super-aging heat treatment, longitudinal specimens were roughly machined from the bars for mild tensile, Charpy V-Notch (CVN) impact, and four-point bending fracture strength testing. Test specimens from Examples 1 to 13 were solution annealed at temperatures in the range of 1750 to 1900 °F (927–1030 °C) for 1 hour and then cooled in oil to room temperature. After solution annealing, the test specimens were cooled to -100 °F (-73 °C) for at least 8 hours and then warmed to room temperature. The specimens were then milled to their respective sizes, heated to 925 °F (496 °C) for 12 hours, and then cooled in water to room temperature before testing.
[037] The AW examples were prepared, processed Petition 870260070122, dated 07 / 15 / 2026, page 28 / 72 22 / 27 thermally and tested as described in the respective published patents and patent applications identified in Table 2.
[038] The results of the mechanical tests are shown in Table 3 below, including 0.2% displacement flow resistance (YS) and ultimate tensile strength in ksi, percent elongation (%El.), percent reduction in area (%RA), Charpy V-notch impact energy (CVN) in ft-lbs and fracture toughness (KQ / KIc) in ksiVin. Table 3 also shows the ratio of fracture toughness to ultimate tensile strength in Vin (Ratio) for each example. Petition 870260070122, dated 07 / 15 / 2026, p. 29 / 72 23 / 27 Table 3 And. YS UTS %El %RA CVN Kq* / Kic** Ratio 1 269 284 12 53 9 75* 0.26 2 262 281 12 53 6 63* 0. 11 54 13 79, 8* 0.29 5 255 274 12 56 13 83, 3* 0.30 6 261 282 11 56 10 69, 7* 0.25 7 267 704,1 255 275 11 53 15 78, 6* 0.29 9 263 283 7 52 8 67.2* 0.24 10 262 278 12 54 13 _ 1 * 68 1*7 0.27 12 263 280 12 53 13 71.6* 0.26 13 252 274 11 53 17 84.8* 0.31 A 256, 4 278, 2 13 57 11 53, 7** 0.19 C 264.3 282.7 13 54 9, 6 _ „ _ * * 57.3 0.20 D 262.8 281, 8 12 2 53 7.3 52.8** E 0.5 55 10, 3 47.3 0, 16 F 264.2 283, 3 13 57 9, 6 51, 8 0, 18 G 265, 6 281, 8 9 38 5.9 54.6 0, 2,5 2 H 4 28 — * * 50 0, 18 I 255 273, 8 9.5 53 6, 6 / 9, 5 *** J 261 275 9, 14 56 4.4 / 5 *** K 264 278 9.2 53 5.9 / 84 L 6 2.6 51 55 5.9 *** M 275 282 9.1 50 4.4 *** N 240 267 11, 7 51 83, 5 0.31 O 266 278 7 *** P 256 280 14 *** 0, 1**02 8 4 6 Q 0,16 R 264 282 10.2 46.6 47.25** 0.17 249 13, 8 55.7 10 72, 6 0.29 W 224 246, 4 14.8 59 21 90, 9** 0. 37, *** Not reported in the reference.
[039] The salt spray corrosion test was performed Petition 870260070122, dated 07 / 15 / 2026, page 30 / 72 24 / 27 in duplicate samples of Examples 1-13 in the solution-treated and age-hardened condition. All samples were aged at 925 °F (496 °C) for 12 hours and then quenched with water to room temperature before testing. Samples were tested according to ASTM B117, using a 5% NaCl concentration, natural pH, at 95 °F for the durations shown in Table 4 below. Samples were surface-ground with a SiC paper finish using 1200 grit for Examples 1-3 and 120 grit for Examples 4-13 before salt spray exposure. Salt spray test results are shown in Table 4 below, including solution heat treatment parameters, surface finish grit, test duration, and ratings based on visual inspection of the tested samples.The classification scale is as follows: 1 = no rust, 2 = 1 to 3 rust points, 3 = up to 5% of the surface rusted, 4 = 5-10% of the surface rusted, 5 = 10-20% of the surface rusted, and 6 = 20-24% of the surface rusted. Table 4 Example No. Solution Treatment Finished Surface Duration (hours) Classification 1 1850 °F / 1hr / OQ1 1200 grit 1000 1 / 1 2 1850 °F / 1hr / OQ 1200 grit 1000 1 / 1 3 1850 °F / 1hr / OQ 1200 grit 1000 1 / 1 4 1850 °F / 1hr / OQ 120 grit 408 1 / 1 5 1875 °F / 1hr / OQ 120 grit 408 32 / 1 6 1825 °F / 1hr / OQ 120 grit 408 1 / 62 7 1775 °F / 1hr / OQ 120 grit 408 1 / 1 8 1875 °F / 1hr / OQ 120 grit 408 1 / 1 9 1800 °F / 1hr / OQ 120 grains 408 1 / 1 10 1825 °F / 1hr / OQ 120 grains 408 2 / 22 11 1875 °F / 1hr / OQ 120 grains 408 1 / 1 12 1850 °F / 1hr / OQ 120 grains 408 1 / 1 13 1850 °F / 1hr / OQ 120 grains 408 1 / 1 Petition 870260070122, dated 07 / 15 / 2026, page 31 / 72 25 / 271OQ = quenched oil 2After further inspection of the rusted sample, it was determined that the rust was initiated in foreign media, such as sand embedded in the surface of the sample, not in the matrix metal itself.
[040] Example 1 above provided the best combination of tensile strength, fracture toughness, and corrosion resistance. Therefore, a 400-lb. (181.4 kg) heat with a chemistry essentially equal to that of Example 1 was vacuum induction melted (VIM) and cast as a 6-inch (15.2 cm) VAR electrode. The weight percent composition of the heat is shown as Example 14 in Table 5 below in weight percent. Table 5 Elmt. Ni Cr Mo Ti Co Al Ex. 14 11.88 9.25 2.47 1.75 2.74 0.18 Mn Si PSCN <0.01 0.01 <0.005 <0.001 0.005 0.002
[041] The composition's balance consisted of iron and other impurities that were not analyzed.
[042] The electrode ingot was vacuum remelted (VAR) into an 8-inch (20.3 cm) ingot. The VAR ingot was homogenized at 2300 °F (1260 °C) for 36 hours and then equalized at 2000 °F (1093 °C). The 8-inch (20.3 cm) ingot was pressure forged at 2000 °F (1093 °C) to a 6-inch (15.2 cm) square ingot. The billet was reheated to 2000 °F (1093 °C), temperature equalized, and then pressure forged to a 3.75-inch (9.5 cm) square bar. A length of the 3.75-inch (9.5 cm) bar was reduced to 1.5 inches x 2.75 inches. (3.8 cm x 6.9 cm) slab. Petition 870260070122, dated 07 / 15 / 2026, page 32 / 72 26 / 27
[043] Standard longitudinal smooth tensile specimens and standard longitudinal Charpy V-Notch impact (CVN) specimens were prepared from 3.75 in. (9.5 cm) square bar material (Examples 14A and 14B) and 1.5 in. x 2.75 in. (3.8 cm x 6.9 cm) slab material (Examples 14C and 14D). Standard 1-inch (2.54 cm) longitudinal fracture strength blocks were prepared from the bar material and slab material according to ASTM Standard Test Procedure E399. The tensile, CVN, and fracture strength specimens from Examples 14A, 14B, 14C, and 14D were solution annealed as described in Table 5 below. The specimens were hardened by aging by heating at 925 °F (496 °C) for 12 hours and then tempered with water.
[044] The room temperature mechanical test results for Examples 14A, 14B, 14C, and 14D are shown in Table 6 below, including 0.2% displacement flow resistance (YS) and ultimate tensile strength in ksi, percent elongation (%El.), percent reduction in area (%RA), Charpy Vnotch impact energy (CVN) in ft-lbs, and fracture toughness (KIc) in ksiVin. Table 5 also shows the ratio of fracture toughness to ultimate tensile strength (Ratio) in Vin for each example. Table 5 Example: Treatment of solution YS UTS %El %RA CVN Kic Ratio 14A 1750F / 1Hr / OQ1 261 282 8 26 9 75 0.27 14B 1850F / 1Hr / OQ 258 280 9 37 9 72 0.26 14C 1750F / 1Hr / OQ1 266 284 12 56 14 68 0.24 14D 1850F / 1Hr / OQ 259 280 11 52 13 73.5 0.26 1OQ = oil tempering Petition 870260070122, dated 07 / 15 / 2026, p. 33 / 72 27 / 27
[045] The significant advantage provided by the alloy claimed by the Applicant is illustrated in Figures 1 and 2. Figure 1 illustrates graphs of fracture toughness as a function of ultimate tensile strength provided by Examples 14A-14D of the claimed alloy (A's) and provided by the example alloys described in US 2016 / 0289805 (o's). Figure 2 illustrates graphs of fracture toughness as a function of ultimate tensile strength provided by Examples 14A-14D of the claimed alloy (A's), Comparative Examples U, V and W (x's), Comparative Examples K and N (O's), Comparative Examples AH (o's) and Comparative Examples Q and R (—'s).
[046] The salt spray corrosion test according to ASTM B117 was performed on duplicate coupon samples prepared from a 0.25-inch (6.35 mm) thick slice of 3.75-inch thickness. Square bar. The salt spray coupons were ground on the surface and exposed to a mist of 5% saline solution (NaCl) at 35 °C.No rust formation was observed on any of the coupon samples after 200 hours of exposure.
[047] The terms and expressions used in this specification are used as descriptive terms and not as limiting terms. There is no intention in using such terms and expressions to exclude any equivalents of the features shown and described or parts thereof. It is acknowledged that various modifications are possible within the invention described and claimed herein. Petition 870260070122, dated 07 / 15 / 2026, page 34 / 72
Claims
1 / 5 CLAIMS 1. Precipitation-hardenable martensitic stainless steel alloy, characterized in that it consists of, in weight percent: Ni, about 10.5 to about 12.5; Co, about 1.0 to about 6.0; Mo, about 1.0 to about 4.0; Ti, about 1.5 to about 2.0; Cr, about 8.5 to about 11.5; Al, up to 0.2; Mn, up to about 1.0 maximum; Si, up to about 0.75 maximum; B, up to about 0.01 maximum; and the balance of the alloy is iron and the usual impurities, including not more than about 0.03% carbon, not more than about 0.03% nitrogen, not more than about 0.04% phosphorus and not more than about 0.020% sulfur.
2. Alloy, the claim characterized by the fact that the aluminum content is at least 0.15%.
3. Alloy, according to claim 1, characterized in that the nickel content is at least 11.0%.
4. Alloy, according to claim 1, characterized in that the cobalt content is at least 1.5%.
5. Alloy, according to claim 4, characterized in that the cobalt content is no more than about 5.5%.
6. Alloy according to claim 1, characterized in that the molybdenum content is at least 2.0%.
7. Alloy according to claim 6, characterized in that the molybdenum content is no more than about 3.0%.
8. Alloy, according to claim 1, characterized by the fact that titanium is at least 1.55%.
9. Alloy, according to claim 8, characterized in that the titanium content is no more than about 1.8%.
10. Alloy, according to claim 1, characterized in that the chromium content is at least 8.75%.
11. Alloy, according to claim 10, characterized in that the chromium content is no more than about 10.5%.
12. Alloy, according to claim 1, characterized in that it contains, in weight percent: Ni about 11.0 to about 12.2; Co about 1.5 to about 5.5; Mo about 2.0 to about 3.0; Ti about 1.55 to about 1.8; Cr about 8.75 to about 10.5; Al up to 0.2; Mn up to about 0.25 maximum; Si up to about 0.25 maximum; B 0.001-0.005; and the balance of the alloy is iron and the usual impurities, including not more than about 0.02% carbon, not more than about 0.015% nitrogen, not more than about 0.015% phosphorus, and not more than about 0.01% sulfur.
13. Alloy, according to claim 12, characterized in that it contains at least about 0.15% aluminum.
14. Alloy, according to claim 12, characterized in that it contains at least about 11.4% nickel.
15. Alloy, according to claim 12, characterized in that it contains at least about 2.0% cobalt.
16. Alloy, according to claim 15, characterized in that it contains no more than about 5.0% cobalt. Petition 870260070122, dated 07 / 15 / 2026, p. 36 / 72 3 / 5 17. Alloy, according to claim 12, characterized in that it contains at least about 2.25% molybdenum.
18. Alloy, according to claim 17, characterized in that it contains no more than about 2.75% molybdenum.
19. Alloy, according to claim 12, characterized in that it contains at least about 1.60% titanium.
20. Alloy, according to claim 19, characterized in that it contains no more than about 1.75% titanium.
21. Alloy, according to claim 12, characterized in that it contains at least about 9.0% chromium.
22. Alloy, according to claim 21, characterized in that it contains no more than about 10.0% chromium.
23. Alloy, according to claim 1, characterized in that it contains, in weight percent: Ni about 11.4 to about 12.0; Co about 2.0 to about 5.0; Mo about 2.25 to about 2.75; Ti about 1.60 to about 1.75; Cr about 9.0 to about 10.0; Al up to 0.2; Mn up to about 0.10 maximum; Si up to about 0.10 maximum; B 0.0015-0.0035; and the balance of the alloy is iron and the usual impurities, including not more than about 0.015% carbon, not more than about 0.010% nitrogen, not more than about 0.01% phosphorus, and not more than about 0.005% sulfur.
24. Alloy, according to claim 23, characterized in that it contains at least about 0.15% aluminum. Petition 870260070122, dated 07 / 15 / 2026, p. 37 / 72 4 / 5 25. Method for manufacturing a metal part or component, made of precipitation-hardenable martensitic stainless steel alloy as defined in claim 1, characterized in that it comprises the steps of: - providing an ingot having the composition of precipitation-hardenable martensitic stainless steel alloy as defined in claim 1, by melting and casting said alloy; - heating the ingot to a temperature of about 2000 °F (1093 °C) to about 2400 °F (1315 °C) for a time sufficient to homogenize said ingot; - hot working the homogenized ingot to provide a part in near-liquid form; - annealing the part in near-liquid form by heating the part to a temperature of about 1700 °F (927 °C) to about 1900 °F (1038 °C) for a pre-selected period of time;- Temper the annealed part at an annealing temperature below approximately -100 °F (-73 °C) to ensure complete martensitic transformation of the alloy matrix; and then: - Age harden the annealed part by heating it at a temperature of 900 °F (482 °C) to approximately 1150 °F (621 °C) for a time selected to obtain a combination of tensile strength, fracture toughness, and corrosion resistance.
26. A manufactured article, made of precipitation-hardenable martensitic stainless steel alloy as defined in claim 1, said manufactured article being characterized by having a tensile strength of at least 280 ksi (1930 MPa), a plane strain fracture toughness of at least 60 ksiVin (66 MPa Vm), and overall corrosion resistance defined by a rating of about 1 when tested in accordance with ASTM B117 Standard Test Procedure.
27. Article of manufacture, according to claim 26, characterized in that the article is a structural member for an aircraft.
28. Article of manufacture according to claim 27, characterized in that the structural member is selected from the group consisting of landing gear, landing gear components, flap rails and fasteners.
29. Article of manufacture, according to claim 26, characterized in that the article is a medical or dental device.
30. Article of manufacture, according to claim 29, characterized in that the medical or dental device is selected from the group consisting of dental tools, medical scrapers, cutters and suture needles.
31. Article of manufacture, according to claim 26, characterized in that the article comprises sporting equipment.
32. Article of manufacture, according to claim 31, characterized in that the sporting equipment comprises a golf club head. Petition 870260070122, dated 15 / 07 / 2026, pp. 39 / 72