Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/02—Hardening by precipitation
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/04—Hardening by cooling below 0 degrees Celsius
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2201/00—Treatment for obtaining particular effects
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• the present invention relates to ultra-high strength steels and, more particularly, to ultra-high strength steels that are air castable and that provide improved properties of strength, ductility, toughness, and corrosion resistance when compared to conventional ultra-high strength steels.
• Maraging steels and other types of ultra-high strength precipitation hardening steels are melted and poured under vacuum conditions in an inert environment to protect essential and very reactive elements used in making such steels, such as titanium and aluminum, from exposure with atmospheric air. Air exposure during the melting and pouring process is intentionally avoided for the purpose of preventing the reactive elements from undergoing oxidation reactions. Presence of the reactive elements in the oxidized state is known to severely degrade the desired mechanical properties of the resulting steels.
• Titanium and aluminum are mandatory ingredients that are used in making maraging steels for the purpose of providing properties of increased strength and hardness to the resulting steel.
• any steels that are made using titanium and aluminum cannot be melted in air (as explained above) because of their susceptibility to form embrittling compounds.
• ultra-high strength steels formed using titanium and aluminum must be subjected to vacuum melting and pouring.
• Ultra-high strength maraging steels on the other hand are known to possess good properties of toughness and weldability. However, as discussed above, maraging steels are sensitive to atmospheric corrosion and related stress corrosion cracking. These steels are also are very expensive to acquire.
• new ultra-high strength steels be developed that provide improved combined properties of strength, toughness, ductility and resistance to atmospheric corrosion when compared to those conventional ultra-high strength steels noted above. It is also desired that such new ultra-high strength steels be capable of being made without the need for expensive and time consuming vacuum melt and pour processing, in a manner that permits air casting.
• an air-cast ultra-high strength stainless steel prepared by combining Si, Cr, Mo, Ni, Co, Cu, W, and Fe, wherein the steel has a yield strength of greater than about 215,000 psi, a tensile strength of greater than about 240,000 psi, and an elongation of greater than about 6 percent.
• the air-cast ultra-high strength stainless steel may additionally include one or more ingredient selected from the group consisting of C, Mn, V, and mixtures thereof.
• ultra-high strength stainless steels of this invention may comprise in the range of from about 0.3 to 1.5 percent by weight Si, in the range of from about 9 to 13 percent by weight Cr, in the range of from about 2.5 to 4.5 percent by weight Mo, in the range of from about 4 to 7 percent by weight Ni, in the range of from about 7 to 13 percent by weight Co, in the range of from about 0.3 to 3 percent by weight Cu, and in the range of from about 0.2 to 2 percent by weight W. Additionally, C may be present up to about 0.08 percent by weight, Mn may be present up to about 1.5 percent by weight, and V may be present up to about 0.5 percent by weight. Fe is present in a remaining amount.
• ultra-high strength stainless steels of this invention may comprise in the range of from about 0.4 to 1.2 percent by weight Si, in the range of from about 10.5 to 13 percent by weight Cr, in the range of from about 2.75 to 4.25 percent by weight Mo, in the range of from about 4.5 to 6 percent by weight Ni, in the range of from about 8 to 12.5 percent by weight Co, in the range of from about 0.4 to 1.5 percent by weight Cu, and in the range of from about 0.2 to 1 percent by weight W.
• C may be present up to about 0.05 percent by weight
• Mn may be present in the range of from about 0.2 to 1 percent by weight
• V may be present up to about 0.25 percent by weight.
• Fe is present in a remaining amount.
• an ultra-high strength stainless steel including in the range of from about 0.4 to 0.9 percent by weight Si, in the range of from about 10.5 to 12 percent by weight Cr, in the range of from about 3.5 to 4.1 percent by weight Mo, in the range of from about 4.5 to 5.5 percent by weight Ni, in the range of from about 8.3 to 10.6 percent by weight Co, in the range of from about 0.4 to 1 percent by weight Cu, in the range of from about 0.3 to 0.6 percent by weight W, and a remaining amount Fe. Additionally, C may be present up to about 0.03 percent by weight, Mn may be present in the range of from about 0.2 to 0.6 percent by weight, and V may be present up to about 0.15 percent by weight. Fe is present in a remaining amount.
• a casting made from a stainless steel that is prepared according to the steps of melting the combined ingredients to form a stainless steel mixture and pouring the stainless steel mixture to form the cast part, which can both be conducted in an open air environment; homogenating the cast part at a temperature of above about 2,100°F for a period of from about 1 to 6 hours; solution heat treating the cast part at a temperature in the range of from about 1,600° to about 2,100°F for about 1 to 4 hours, followed by cooling to room temperature; cooling the cast part by refrigeration for about 1 to 8 hours at a temperature below about -50°F; and aging the cast part at a temperature of between about 800°F and about 1,000°F for about 4 to about 5 hours; if required to further enhance the mechanical properties of this alloy a hot isostatic pressing of a cast part made from this stainless steel at a temperature of above about 1,900°F for about 3 to 5 hours at a pressure of greater than about 14,000 psi, is acceptable. This should be performed prior to
• Ultra-high strength steels prepared in accordance with the principles of this invention provide an air-castable product that demonstrates improved combined properties of strength, toughness, ductility and resistance to atmospheric corrosion when compared to those conventional ultra-high strength steels noted above. Additionally, such new ultra-high strength stainless steels of this invention can be made in an open air environment, thereby obviating the need for employing expensive and time consuming vacuum melt, and multiple melt and pour processing.
• the present invention is directed to ultra-high strength stainless steels (hereafter "stainless steel”) and methods of making the same.
• Stainless steels of this invention generally comprise silicon, chromium, molybdenum, nickel, cobalt, copper, and tungsten as principle alloying elements along with small additions of carbon, manganese and vanadium if so desired, with the remaining ingredient being iron.
• the specific constitution of the alloying ingredients used to form stainless steels of this invention, and the thermal treatments used for processing the same provide an air castable steel having improved combined properties of strength, ductility, toughness, and resistance to atmospheric corrosion when compared to conventional ultra-high strength steels, and results in a predominantly martensitic microstructure that is subsequently hardened by precipitation of intermetallic compounds.
• stainless steels of this invention can be vacuum melted and poured directly into a mold (investment cast) or made into ingots that could be subsequently forged to further improve its toughness and fatigue properties.
• a key feature of stainless steels of this invention is the ability to achieve such performance improvements while intentionally avoiding use of reactive elements such as titanium and/or aluminum.
• the use of these elements is common in making typical maraging steels for the purpose of providing contributions in hardness. Therefore, the ability to provide a stainless steel having a high level of hardness while intentionally avoiding the use of these elements was something unexpected, surprising, and not before thought possible.
• Stainless steels can be formed from the following atomic elements: Fe, Si, Cr, Mo, Ni, Co, Cu, and W.
• a key feature distinguishing steels of this invention from conventional ultra-high strength steels, such as maraging steels or the like, is the intentional avoidance of the reactive elements titanium and aluminum.
• Stainless steels of this invention comprise alloying elements provided in respective weight percent ranges as recited below in Table 3. It is to be understood that all provided values are approximate.
• Table 3 Element Example Range Preferred Range Most Preferred Range C Up to 0.08 Up to 0.05 Up to 0.03 Si 0.3 to 1.5 0.4 to 1.2 0.4 to 0.9 Cr 9 to 13 10.5 to 13 10.5 to 12 Cu 0.3 to 3 0.4 to 1.5 0.4 to 1 Mo 2.5 to 4.5 2.75 to 4.25 3.5 to 4.15 Ni 4 to 7 4.5 to 6 4.5 to 5.5 Mn Up to 1.5 0.2 to 1 0.2 to 0.6 Co 7 to 13 8 to 12.5 8.3 to 10.6 V Up to 0.5 Up to 0.25 Up to 0.15 W 0.2 to 2 0.2 to 1 0.2 to 0.6 S 0.01 Max 0.01 Max 0.01 Max P 0.03 Max 0.03 Max 0.03 Max N 0.05 Max 0.05 Max 0.05 Max Fe Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance Balance
• stainless steels of this invention may comprise the usual impurities found in commercial grades of maraging steels.
• stainless steels of this invention may include the presence of trace elements such as up to about 0.01 percent by weight S, up to about 0.03 percent by weigh P, and up to about 0.05 percent by weight.
• Silicon is used for the purpose of providing improved properties of castability and fluidity during processing of the steel.
• Stainless steels of this invention may comprise in the range of from about 0.3 to 1.5 percent by weight Si. Chromium is used for the purpose of providing improved properties of corrosion resistance, strength and hardenability. Stainless steels of this invention comprise in the range of from about 9 to 13 percent by weight Cr. Copper is used for the purpose of providing improved corrosion resistance and weatherability to the finished steel product. It, works along with Cr, Ni and Mo, to provide the desired degree of corrosion resistance.
• Stainless steels of this invention comprise in the range of from about 0.3 to 3 percent by weight Cu.
• Molybdenum is used for the purpose of improving the hardenability of stainless steels of this invention.
• stainless steels of this invention comprise in the range of from about 2.5 to 4.5 percent by weight Mo.
• Nickel is used for the purpose of adding strength and toughness to the alloy.
• Stainless steels of this invention comprise in the range of from about 4 to 7 percent by weight Ni.
• Cobalt is used for the purpose of increasing strength.
• stainless steels of this invention comprise in the range of from about 7 to 13 percent by weight Co.
• Tungsten is used for the purpose of providing improved properties of strength and hardness.
• Stainless steels of this invention comprise in the range of from about 0.2 to 2 percent by weight W.
• alloying elements C, Mn and V are understood to be optional. Carbon is used for the purpose of increasing strength & hardenability of the alloy by heat treatment. Thus, stainless steels of this invention may comprise up to about 0.08 percent by weight C. Manganese is used for the purpose of castability. Stainless steels of this invention may comprise up to about 1.5 percent by weight Mn. Vanadium is used for the purpose of increasing hardness, or to enhance toughness at a given hardness level. Stainless steels of this invention may comprise up to about 0. 5 percent by weight V.
• Stainless steels of this invention are rendered more robust against atmospheric corrosion by substitution of the highly reactive elements, e.g., aluminum and/or titanium, contained in conventional maraging or other ultra-high strength precipitation hardening alloys with more benign elements. Purposeful substitution of the highly reactive elements with less reactive elements results in the creation of an alloy that can be single melted and poured in air while exhibiting superior stability and castability (fluidity).
• highly reactive elements e.g., aluminum and/or titanium
• stainless steels of this invention are investment cast into a desired form.
• the stainless steel is melted and poured in a single operation that, unlike conventional maraging steel, does not have to take place in a non-reactive environment. It will be appreciated that stainless steels, prepared according to the principles of the invention, can be readily air cast into complex configurations.
• a protective atmosphere can also be used.
• Argon used as either a liquid or in a gas state, can be applied over the surface of the charge material during melting in order to enhance its castability. Additionally, during the first ten minutes or so of the solidification of the casting, if air is eliminated from around the cooling shell by placing a can over the cooling shell a better casting surface may be obtained.
• this is not a limitation on the invention.
• stainless steels of this invention display the following desired combined mechanical properties: (i) yield strength of greater than about 215,000 psi, preferably in the range of from about 230,000 to 260,000 psi; (ii) tensile strength of greater than about 240,000 psi, preferably in the range of from about 250,000 to 280,000 psi; and (iii) elongation of over about 6 percent, preferably from 8 to 14 percent.
• stainless steels of this invention also display good properties of castability, fluidity, weldability, and resistance to atmospheric corrosion.
• Stainless steels of this invention can be formulated to provide desired levels of strength, toughness, elongation, and corrosion resistance within the above-noted ranges as needed to accommodate a particular steel application.
• the different levels of performance in these areas can be obtained by selective use of alloying ingredients and/or by varying the amounts of such alloying ingredients.
• stainless steels of this invention can be melted and poured in an air environment, i.e., air melted, poured, and air cast into a desired configuration.
• the typical process for processing the stainless steel includes the following steps: (a) homogenation; (b) solution heat treating; (c) cooling; and (d) aging; (e) a high-temperature/high-pressure consolidation can be performed if desired, but should be done prior to the homogenation step.
• the step of high-temperature/high-pressure consolidation is preferably carried out by hot isostatic pressing (hipping).
• hipping hot isostatic pressing
• the investment cast product is placed in a special pressure vessel that is capable of heating the product to specific temperatures under inert gas pressures of over about 14,000 psi.
• the high temperatures and pressures used in this process cause the collapse of internal casting discontinuities within the product, such as voids, gas, or shrinkage porosity. Thereby, resulting in a casting that has substantially lower internal defects and better mechanical properties.
• the cast product is preferably Hipped at a pressure of about 15,000 psi, and at a temperature of greater than about 1,900°F and, more preferably within the range of from about 1,900°F to 2,250°F in an inert gas-filled chamber, e.g., using argon gas.
• a pressure chamber is filled or charged with argon gas to a specific pressure range before the chamber is heated.
• the temperature within the chamber is raised to a desired temperature, causing the pressure within the chamber to increase to a desired level.
• the desired temperature is held for a period of from about 3 to 5 hours followed by cooling of the castings to room temperature.
• Products are normally inspected after hipping to evaluate pore closure.
• the homogenation step is conducted in a neutral atmosphere at a temperature range of from about 2,000°F and about 2,225°F for a period of about 1 to 6 hours.
• the homogenation step serves to reverse and or neutralize the micro-structural changes produced during the hip cycle and minimizes any chemical segregation caused during casting.
• the solution heat treating step is conducted in a neutral atmosphere at a temperature in the range of from about 1,600°F to 2,100°F for a period of from about 1 to 4 hours, followed by rapid gas fan cooling to room temperature.
• the solution heat treating step serves to put the micro-structure in an Austenitic condition and by rapid cooling transforming the structure into Martensite.
• the cooling step is conducted by refrigerating the room temperature cast product within 24 hours of completing the solution heat treat for a period of from about 1 to 4 hours at a temperature below about -50°F preferably (-90°F to -100°F) to complete the transformation of the Austenite into Martensite.
• the aging step is conducted at a temperature range of from about 800°F to 1,000°F for a period of from about 1 to 6 hours to achieve the desired combination of above-described mechanical properties.
• Table 4 sets forth preferred, more preferred and most preferred ranges of the processing parameters used for making stainless steel according to the principles of this invention. It will be understood that all values are approximate.
• Table 4 Process Step Preferred More Preferred Most Preferred Hipping (optional) 1,900°F to 2,250°F @ 14,000 to 16,000 psi for 3 to 5 Hours 2,000°F to 2,240°F @ 14,000 to 16,000 psi for 3 to 5 Hours 2,125°F to 2,220°F @ 14,000 to 16,000 psi for 3 to 5 Hours Homogenation 2,100°F to 2,225°F for 1 to 6 Hours 2,150°F to 2,220°F for 2 to 5 Hours 2,205°F to 2220°F for 4 Hours ⁇ 15 Minutes Solution Heat Treating 1,600°F to 2,100°F for 1 to 4 Hours 1,800°F to 1,950°F for 1 to 3 Hours 1,875°F to 1,925°F for 1 Hour ⁇ 15 Minutes Cooling -350°F to -50°F for
• a number of example embodiments of stainless steels of this invention were prepared according to the practice of this invention. These examples are designated MR04-1, MR04-2, MR04B, MR04C, MR04D, MR04E, MR04L, MR04C, MR08A, MR08B, in Table 5 provided below. These examples were prepared by combining alloying ingredients within the amounts presented in Table 5, and air melting, pouring and casting the combined alloy mixture into a desired cast part.
• the example stainless steels of this invention were tested and were shown to provide properties of yield strength and tensile strength that are comparable to conventional vacuum melted wrought ultra-high strength stainless steel alloys. However, the example stainless steels of this invention were provided in the form of investment castings that were air melted and air cast.
• Table 6 below provides physical properties of the example stainless steels prepared as described above along with the heat treatment process data for each of the samples.
• the cast part was homogenized for a period of about 4 hours at a temperature in the range of from 2,100°F to about 2,220°F (see the table for each sample), followed by solution heat treating at a temperature of about 1,900°F for a period of about 1.5 hours.
• the solution heat treated part was then rapid gas fan cooled to room temperature, and subsequently refrigerated at a temperature of about 100°F for a period of about 4 to about 6 hours (see the table for each sample) to transform retained austenite to martensite.
• the part was then aged at a temperature of about 950°F for a period of from 4 to 6 hours to achieve the desired mechanical properties.
• the first time and temperature numbers represent the homogenization data
• the second time and temperature numbers represent the solution heat treating data
• the third time and temperature numbers represent the refrigeration data
• the fourth time and temperature numbers represent the aging data.
• Table 6 Specimen Yield KSI UTS KSI %EL %RA Heat Treatment MR04-1 231. 5 253.5 13 40 2220°F 4 hrs,1900°F 1.
• Table 7 below provides data comparing the physical/mechanical properties of the example stainless steels prepared as described above with other conventional steels: Table 7 Alloy YS, PSI UTS, PSI % El Density Strength to Weight Corrosion Rating Castability Rating MR04-1 Avg. 231,500 253,500 13 0.285 889474 8 8 MR04-2 Avg. 236,000 257,000 10.3 0.285 901754 8 8 MR04B Avg. 235,000 254,600 10.2 0.285 893333 8 8 MR04C Avg. 231,600 252,000 10.8 0.285 884211 8 8 MR04D Avg. 232,400 251,200 10.2 0.285 881403 8 8 MR04E Avg.
• stainless steels of this invention display combined properties of yield strength and tensile strength that are both superior to other compared conventional steels, while at the same time providing properties of percent elongation and corrosion resistance that are comparable to the other compared conventional steels.
• the present invention provides stainless steels that are air-castable and that are specially designed to overcome the noted drawbacks of conventional ultra-high strength steels discussed above.
• Stainless steels of this invention are more resistant to atmospheric corrosion than their martensitic and maraging counterparts, and offer a better combination of mechanical properties than most wrought hardened and precipitation hardened stainless steels, providing a yield strength of over about 215,000 psi and tensile strength of more than about 240,000 psi with over 6% elongation and 20 % reduction in area.
• Stainless steels of this invention exhibit excellent fluidity and castability, which permits their use in being cast into complex thin-walled configurations.
• Stainless steels are less reactive than other maraging steels, enabling air melting and pouring, and achieving the desired combination of mechanical properties without the need for multiple vacuum melting and wrought processing. The less reactive nature of such steels results in less metal-mold reaction and porosity.
• stainless steels of this invention can be produced to near net shape directly via investment casting. These alloys are significantly cheaper and easier to obtain than conventional maraging alloys. They can achieve their desired mechanical properties without the need for high purity raw material. They can easily be recycled to reduce costs and help the environment. They exhibit better weldability than their low-alloy martensitic counterparts (4140 or 300M alloys). They do not require chrome or cadmium plating for most applications, in comparison to conventional ultra high strength steels, thereby making them more environmentally friendly.
• Stainless steels of this invention can be single melted, thereby significantly reducing processing costs. They can be air melted and air cast into complex configurations, thereby reducing the capital expenditure needed for vacuum casting furnaces. As an air cast alloy, productivity (output per hour) is significantly higher than that associated with using vacuum melted alloys. Stainless steels require lower acquisition lead-times, faster production cycle times, and lower manufacturing costs. Due to their simpler processing and faster production throughput and cycle times (set up and run times), less inventory is required. Since they achieve their properties without the need for wrought processing, they do not require progressive dies to achieve the desired shape and mechanical properties. Wrought processing and vacuum melting can improve their properties for certain applications, at the expense of acquisition and processing costs.

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• 2005
  • 2005-05-12 EP EP05090140A patent/EP1722000A1/fr not_active Withdrawn

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