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

a technology of nanocarbide precipitation and structural steel, which is applied in the field of nickel, chromium stainless martensitic steel alloy, can solve the problems of poor general corrosion resistance of ultrahigh-strength steels, and inability to meet the requirements of use, so as to achieve easy work

Inactive Publication Date: 2005-05-19
KUEHMANN CHARLES J +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0011] The alloys of the subject invention can achieve an ultimate tensile strength (UTS) of about 300 ksi with a yield strength (YS) of about 230 ksi and also provide corrosion resistance with greater than about 6% and less than about 11%, preferably less than about 10% by weight chromium. The alloys of the invention provide a combination of the observed mechanical properties of structural steels, that are currently cadmium coated and used in aerospace applications, and the corrosion properties of stainless steels without special coating or plating. Highly efficient nanoscale carbide (M2C) strengthening of the described alloys provides ultrahigh strengths with lower carbon and alloy content while improving corrosion resistance due to the ability of the nanoscale carbides to oxidize and supply chromium as a passivating oxide film. This combination of ultrahigh strength and corrosion resistance properties in a single material eliminates the need for cadmium coating without a weight penalty relative to current structural steels. Additionally, alloys of the subject invention reduce environmental embrittlement driven field failures because they no longer rely on an unreliable coating for protection from the environment.
[0017] Yet another object of the invention is to provide ultrahigh-strength, corrosion resistant, structural steel alloys which may be easily worked to form component parts and articles while maintaining its ultrahigh strength and noncorrosive characteristics.

Problems solved by technology

Main structural components in aerospace and other high-performance structures are almost exclusively made of ultrahigh-strength steels because the weight, size and, in some cases, cost penalties associated with use of other materials is prohibitive.
However, ultrahigh-strength steels with a tensile strength in the range of at least 240 ksi to 300 ksi have poor general corrosion resistance and are susceptible to hydrogen and environmental embrittlement.
These coatings have disadvantages from a cost, manufacturing, environmental and reliability standpoint.
However, the lack of general corrosion resistance requires cadmium coating, and the low stress corrosion cracking resistance results in significant field failures due to environmental embrittlement.
This limits the application to components that are not strength limited.
These stainless steels use higher chromium levels to maintain corrosion resistance and therefore compromise strength.
This large gap between yield and ultimate limits the applications for which these steels can be used.

Method used

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

Examples

Experimental program
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Effect test

example 1

[0084] Alloy 1 in TABLE 1 was vacuum induction melted (VIM) to a six inch diameter electrode which was subsequently vacuum arc remelted (VAR) to a eight inch diameter ingot. The material was homogenized for seventy-two hours at 1200° C., forged and annealed according to the preferred processing techniques described above and depicted in FIGS. 2A and 2B. Dilatometer samples were machined and the Ms temperature was measured as 175° C. by quenching dilatometry and 1% transformation fraction.

[0085] Test samples were machined, solution heat treated at 1025° C. for one hour, oil quenched, immersed in liquid nitrogen for one hour, warmed to room temperature and tempered at 482° C. for eight hours. The measured properties are listed in TABLE 2 below.

TABLE 2Various measured properties for Alloy 1PropertyValueYield Strength205ksiUltimate Tensile Strength245ksiElongation10%Reduction of Area48%Hardness51HRC

example 2

[0086] Alloy 2A in TABLE 1 was vacuum induction melted (VIM) to a six inch diameter electrode which was subsequently vacuum arc remelted (VAR) to a eight inch diameter ingot. The ingot was homogenized for twelve hours at 1190° C., forged and rolled to 1.500 inch square bar starting at 1120° C., and annealed according to the preferred processing techniques described above and depicted in FIGS. 2A and 2B. Dilatometer samples were machined and the Ms temperature was measured as 265° C. by quenching dilatometry and 1% transformation fraction.

[0087] Test samples were machined from the square bar, solution heat treated at 1050° C. for one hour, oil quenched, immersed in liquid nitrogen for one hour, warmed to room temperature, tempered at 500° C. for five hours, air cooled, immersed in liquid nitrogen for one hour, warmed to room temperature and tempered at 500° C. for five and one-half hours. The measured properties are listed in TABLE 3 below. The reference to the corrosion rate of 15-...

example 3

[0089] Alloy 2B in TABLE 1 was vacuum induction melted (VIM) to a six inch diameter electrode which was subsequently vacuum arc remelted (VAR) to a eight inch diameter ingot. The ingot was homogenized for twelve hours at 1190° C., forged and rolled to 1.000 inch diameter round bar starting at 1120° C. and annealed according to the preferred processing techniques described above and depicted in FIGS. 2A and 2B. Dilatometer samples were machined and the Ms temperature was measured as 225° C. by quenching dilatometry and 1% transformation fraction.

[0090] Test samples were machined from the round bar, solution heat treated at 1100° C. for 70 minutes, oil quenched, immersed in liquid nitrogen for one hour, warmed to room temperature and tempered at 482° C. for twenty-four hours. The measured properties are listed in TABLE 5 below.

TABLE 5Various measured properties for Alloy 2BPropertyValueYield Strength211ksiUltimate Tensile Strength247ksiElongation17%Reduction of Area62%Hardness51HRC...

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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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This international application is based upon U.S. Ser. No. 10 / 071,688, filed Feb. 8, 2002, which is based on the following provisional applications which are incorporated herewith by reference and for which priority is claimed: U.S. Ser. No. 60 / 267,627, filed Feb. 9, 2001, entitled, “Nano-Precipitation Strengthened Ultra-High Strength Corrosion Resistant Structural Steels” and U.S. Ser. No. 60 / 323,996 filed Sep. 21, 2001 entitled, “Nano-Precipitation Strengthened Ultra-High Strength Corrosion Resistant Structural Steels”. BACKGROUND OF THE INVENTION [0002] In a principal aspect, the present invention relates to cobalt, nickel, chromium stainless martensitic steel alloys having ultrahigh strength and corrosion resistance characterized by nanoscale sized carbide precipitates, in particular, M2C precipitates. [0003] Main structural components in aerospace and other high-performance structures are almost exclusively made of ultrahigh-streng...

Claims

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Application Information

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IPC IPC(8): C22C38/52
CPCC21D2201/03C21D2211/003C22C38/52C22C38/46C22C38/44
Inventor KUEHMANN, CHARLES JOLSON, GREGORY BLOU, HERNG-JENG
Owner KUEHMANN CHARLES J
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