Nanocarbide precipitation strengthened ultrahigh-strength, corrosion resistant, structural steels

Abstract

A nanocarbide precipitation strengthened ultrahigh-strength, corrosion resistant, structural steel possesses a combination of strength and corrosion resistance comprising in combination, by weight, about: 0.1 to 0.3% carbon (C), 8 to 17% cobalt (Co), 0 to 10% nickel (Ni), 6 to 12% chromium (Cr), less than 1% silicon (Si), less than 0.5% manganese (Mn), and less than 0.15% copper (Cu), with additives selected from the group comprising about: less than 3% molybdenum (Mo), less than 0.3% niobium (Nb), less than 0.8% vanadium (V), less than 0.2% tantalum (Ta), less than 3% tungsten (W), and combinations thereof, with additional additives selected from the group comprising about: less than 0.2% titanium (Ti), less than 0.2% lanthanum (La) or other rare earth elements, less than 0.15% zirconium (Zr), less than 0.005% boron (B), and combinations thereof, impurities of less than about: 0.02% sulfur (S), 0.012% phosphorus (P), 0.015% oxygen (O) and 0.015% nitrogen (N), the remainder substantially iron (Fe), incidental elements and other impurities. The alloy is strengthened by nanometer scale MZC carbides within a fine lath martensite matrix from which enhanced chemical partitioning of Cr to the surface provides a stable oxide passivating film for corrosion resistance. The alloy, with a UTS in excess of 280 ksi, is useful for applications such as aircraft landing gear, machinery and tools used in hostile environments, and other applications wherein ultrahigh-strength, corrosion resistant, structural steel alloys are desired.

1 . A carbide strengthened alloy composition comprising in combination, by weight, about: 0.1-0.3% carbon (C), 8 to 17% cobalt (Co), at least about 1.7% to about 5% nickel (Ni), greater than 6 and less than 11% chromium (Cr), and less than 3% molybdenum (Mo) including Mo as a precipitated carbide having the composition M 2 C, the balance essentially iron (Fe) and incidental elements and impurities.  
     
     
         2 . The alloy of  claim 1  or  claim 127  having an ultimate tensile strength (UTS) greater than about 240 ksi.  
     
     
         3 - 4 . (canceled)  
     
     
         5 . The alloy of  claim 1  or  claim 127  having an ultimate tensile strength (UTS) greater than about 240 ksi and a yield strength (YS) greater than about 200 ksi.  
     
     
         6 - 7 . (canceled)  
     
     
         8 . The alloy of  claim 1  or  claim 127 , having a martensite start (M s ) temperature as measured by quenching dilatometry and 1% transformation fraction, greater than about 150° C.  
     
     
         9 - 10 . (canceled)  
     
     
         11 . The alloy of  claim 1  or  claim 127 , having more than about 85% by weight of the carbon (C) content of the alloy comprising M 2 C carbides smaller than about ten nanometers, where M is selected from the group consisting of Cr, Mo, V, W, Nb, Ta and combinations thereof.  
     
     
         12 - 29 . (canceled)  
     
     
         30 . The alloy of  claim 1  or  claim 127  having an ultimate tensile strength (UTS) greater than about 240 ksi, more than about 85% by weight of the carbon content of the alloy is found in M 2 C carbides smaller than about ten nanometers, where M is selected from the group consisting of Cr, Mo, V, W, Nb, Ta and combinations thereof, where the martensite start (M s ) temperature of the alloy as measured by quenching dilatometry and 1% transformation fraction, is greater than about 150° C., and an annual corrosion rate, as measured by linear polarization measurements in a 3.5% by weight aqueous sodium chloride solution, less than about 250% of the rate determined for 15-5PH (H900 Condition) stainless steel.  
     
     
         31 . (canceled)  
     
     
         32 . The alloy of  claim 1  or  claim 127  wherein said alloy contains one or more elements comprising less than 1% silicon (Si), less than 0.3% niobium (Nb), less than 0.8% vanadium (V), less than 3% tungsten (W), less than 0.2% titanium (Ti), less than 0.2% lanthanum (La) or other rare earth elements, less than 0.15% zirconium (Zr), and less than 0.005% boron (B), percentages being by weight.  
     
     
         33 . The alloy of  claim 1  or  claim 127  wherein said alloy contains less than about: 0.02% sulfur (S), 0.012% phosphorus (P), 0.015% oxygen (0) and 0.015% nitrogen (N), percentages being by weight.  
     
     
         34 . The alloy of  claim 1  or  claim 127  wherein said alloy comprises a substantially lath martensite phase.  
     
     
         35 . The alloy of  claim 1  or  claim 127  wherein said alloy comprises Cr and Co in combination with M 2 C carbides to provide a Cr rich corrosion resistant passivation layer.  
     
     
         36 - 58 . (canceled)  
     
     
         59 . A method of producing an ultrahigh-strength, corrosion resistant, structural steel carbide strengthened alloy product comprising the steps of: 
 combining a mixture of elements in a melt comprising, by weight, about: 0.1 to 0.3% carbon (C), 8 to 17% cobalt (Co), more than 1.7% and less than 5% nickel (Ni), greater than 6 and less than 11% chromium (Cr), and less than 3% molybdenum (Mo), the balance essentially iron (Fe) and incidental elements and impurities; and    processing said melt mixture to form an article of manufacture.    
     
     
         60 - 110 . (canceled)  
     
     
         111 . A carbide strengthened alloy composition comprising, in combination, by weight, about: 0.18 to 0.25% carbon (C), 6 to 10% cobalt (Co), 4.0 to 8.0% nickel (Ni), 8.0 to 10.0% chromium (Cr), 1.0 to 3.0% molybdenum (Mo), less than 3.0% tungsten (W), less than 1.0% silicon (Si), and less than 0.8% vanadium (V), the balance essentially iron (Fe) and incidental elements and impurities.  
     
     
         112 . A carbide strengthened alloy composition comprising, in combination, by weight, about: 0.1 to 0.3% carbon (C), 0 to 17% cobalt (Co), 0 to 5% nickel (Ni), 6 to 12% chromium (Cr), less than 1% silicon (Si), less than 0.5% manganese (Mn), and less than 0.15% copper (Cu), with additives selected from the group comprising about: less than 3% molybdenum (Mo), less than 0.3% niobium (Nb), less than 0.8% vanadium (V), less than 0.2% tantalum (Ta), less than 3% tungsten (W), and combinations thereof, with additional additives selected from the group comprising about: less than 0.2% titanium (Ti), less than 0.2% lanthanum (La) or other rare earth elements, less than 0.15% zirconium (Zr), less than 0.005% boron (B), and combinations thereof, and the balance essentially iron (Fe) and incidental elements and impurities.  
     
     
         113 . A carbide strengthened alloy composition comprising in combination, by weight, about: 0.1 to 0.3% carbon (C), 8 to 17% cobalt (Co), 0 to 5% nickel (Ni), 6 to 12% chromium (Cr), less than 1% silicon (Si), less than 0.5% manganese (Mn), and less than 0.15% copper (Cu), with additives selected from the group comprising about: less than 3% molybdenum (Mo), less than 0.3% niobium (Nb), less than 0.8% vanadium (V), less than 0.2% tantalum (Ta), less than 3% tungsten (W), and combinations thereof, with additional additives selected from the group comprising about: less than 0.2% titanium (Ti), less than 0.2% lanthanum (La) or other rare earth elements, less than 0.15% zirconium (Zr), less than 0.005% boron (B), and combinations thereof, impurities of about less than 0.02% sulfur (S), 0.012% phosphorus (P), 0.015% oxygen (O) and 0.015% nitrogen (N), the balance essentially iron (Fe) and incidental elements and impurities.  
     
     
         114 . A carbide strengthened alloy composition comprising, in combination, by weight, about: 0.1 to 0.3% carbon (C), 8 to 17% cobalt (Co), 0 to 10% nickel (Ni), 6 to 12% chromium (Cr), less than 1% silicon (Si), less than 0.5% manganese (Mn), and less than 0.15% copper (Cu), with additives selected from the group comprising about: less than 3% molybdenum (Mo), less than 0.3% niobium (Nb), less than 0.8% vanadium (V), less than 0.2% tantalum (Ta), less than 3% tungsten (W), and combinations thereof, with additional additives selected from the group comprising about: less than 0.2% titanium (Ti), less than 0.2% lanthanum (La) or other rare earth elements, less than 0.15% zirconium (Zr), less than 0.005% boron (B), and combinations thereof, and the balance essentially iron (Fe) and incidental elements and impurities.  
     
     
         115 . A carbide strengthened alloy composition comprising in combination, by weight, about: 0.1 to 0.3% carbon (C), 8 to 17% cobalt (Co), 0 to 10% nickel (Ni), 6 to 12% chromium (Cr), less than 1% silicon (Si), less than 0.5% manganese (Mn), and less than 0.15% copper (Cu), with additives selected from the group comprising about: less than 3% molybdenum (Mo), less than 0.3% niobium (Nb), less than 0.8% vanadium (V), less than 0.2% tantalum (Ta), less than 3% tungsten (W), and combinations thereof, with additional additives selected from the group comprising about: less than 0.2% titanium (Ti), less than 0.2% lanthanum (La) or other rare earth elements, less than 0.15% zirconium (Zr), less than 0.005% boron (B), and combinations thereof, impurities of about less than 0.02% sulfur (S), 0.012% phosphorus (P), 0.015% oxygen (O) and 0.015% nitrogen (N), the balance essentially iron (Fe) and incidental elements and impurities.  
     
     
         116 - 119 . (canceled)  
     
     
         120 . An alloy as set forth in any of claims  105 - 115  including metal (M) carbide particles dispersed therein, said particles having the formula MXC where X≦2 for the majority of weight percent of said particles, and wherein said alloy is predominantly in the martensitic phase.  
     
     
         121 . An alloy as set forth in any of claims  105 - 115 , wherein said alloy is in the martensitic phase and includes metal carbides dispersed therein, said metal carbides having a nominal dimension less than about ten nanometers in diameter and having a metal ion to carbon ion ratio predominantly in the range of about two to one or less.  
     
     
         122 - 126 . (canceled)  
     
     
         127 . A carbide strengthened alloy composition comprising in combination, by weight, about: 0.1 to 0.3% carbon (C), 8 to 17% cobalt (Co), less than 10% nickel (Ni), greater than 6 and less than 11% chromium (Cr), and less than 3% molybdenum (Mo), the balance essentially iron (Fe) and incidental elements and impurities.  
     
     
         128 . A method of producing an ultrahigh-strength, corrosion resistant, structural steel alloy product comprising the steps of: 
 combining a mixture of elements in a melt comprising, by weight, about: 0.1 to 0.3% carbon (C), 8 to 17% cobalt (Co), less than 10% nickel (Ni), greater than 6 and less than 11% chromium (Cr), and less than 3% molybdenum (Mo), the balance essentially iron (Fe) and incidental elements and impurities; and    processing said melt mixture to form an article of manufacture.    
     
     
         129 - 173 . (canceled)