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
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
  • C22C38/105—Ferrous alloys, e.g. steel alloys containing cobalt containing Co and Ni

Definitions

• the present invention relates to maraging steels, particularly to maraging steels of improved yield strength and ductility.
• maraging steels of the present invention consist essentially of, in percent by weight, about 15% to 20% nickel, about 8% to 16% cobalt, about 2.5% to 5% molybdenum, about 1.3% to 2.25% titanium, up to about 0.8% aluminum, the sum of the titanium plus aluminum being at least 1.6% and not more than 2.5 up to 0.05% carbon, up to 0.5% manganese, up to 0.5% silicon, and the balance essentially iron.
• iron in referring to iron as constituting the balance or essentially the balance of the steels, it is to be understood, as will be readily appreciated by those skilled in the art, that the presence of other elements is not excluded, such as those commonly present as incidental elements, deoxidation and cleansing elements, and impurities ordinarily associated therewith in small amounts which do not adversely affect the basic characteristics of the steels.
• Elements such as phosphorus, sulfur, hydrogen, oxygen and nitrogen should be kept at levels as low as is consistent with commercial steelmaking practice. Sulfur and phosphorus should not exceed 0.02% each and preferably should not exceed 0.01% each.
• Auxiliary constituents which can be present, include the following: up to 1% vanadium, up to 1% columbium, up to 5% chromium, up to 1% tantalum, up to 2% copper, up to 0.2% beryllium, up to 0.01% boron and up to 0.1% zirconium.
• the total amount of these auxiliary elements should not exceed about 7%.
• Calcium, cerium and the like can be used in amounts up to 0.1% for purposes of deoxidation and the like.
• the martensitic transformation temperature (Ms)
• Ms martensitic transformation temperature
• Molybdenum generally speaking, exerts a marked influence on lowering the Ms temperature, the result of which is incomplete transformation to martensite and low strength. However, provided that transformation would otherwise be complete, relatively high amounts of molybdenum (not above about 5%) can be used. It is advantageous that the molybdenum not exceed 4.25% and more advantageously it should not exceed about 4%. While the molybdenum content should not fall below 2.5%, for enhanced ductility and notch toughness at least 3% molybdenum should be present.
• the following alloying ranges are most advantageous: about 17% to 18% nickel, about 12% to 13% cobalt, about 3.5% to 4% molybdenum, about 1.6% to 2% titanium, about 0.1% to 0.2% aluminum, up to 0.02% carbon, up to 0.1% manganese, up to 0.1% silicon and the balance essentially iron.
• An exemplary steel contains about 17.5% nickel, 12.5% cobalt, 3.7% molybdenum, 1.7% titanium, 0.15% aluminum, up to 0.02% carbon, up to 0.1% manganese, up to 0.1% silicon, balance essentially iron.
• the hot working operation should generally be conducted over the range of about 1500 F. to 2000 F., e.g., 1700 F. to 1900 F., and it is preferred that the finishing temperature be as close to 1500 F. as is practicable.
• the steels are preferably directly aged, although an annealing temperature can be employed prior thereto.
• a suitable aging temperature is from 800 F. to 1000 F. for a period up to about 24 hours, a shorter time period being used at the higher temperature.
• a temperature range of 850 F. to 950 F. is preferred, the time period being from about one half hour to ten hours.
• a most satisfactory maraging temperature is about 900 F. for about three hours.
• Temperatures above 1000 F. are unnecessary and not recommended in view of the possibility of occurrence of austenite reversion; however, an additional attribute of the steels is that they manifest substantial resistance to austenite reversion even at temperatures as high as 1050 F.
• an annealing operation should not be carried out at a temperature above 1700 F. and it is most preferred that the temperature be about 1400 F. Generally speaking, a loss of yield strength is experienced as a consequence of an annealing operation, the loss being greater the higher the annealing temperature.
• Alloys Nos. 1 through 11 being within the invention and Alloys A, B and C being outside the scope thereof.
• the steels were produced by vacuum induction melting using aluminum deoxidation. Ingots were soaked one hour at 2300 F., forged and reheated to 2300 F., reforged to 2 x 2 inch or 1 x 3 inch bars, air cooled to room temperature, reheated to about 1800 F. to 1900 F. and hot rolled to inch bar.
• Alloys Nos. 5 and 7 contained 0.69% and 0.5% vanadium, respectively. Manganese and 51110011 contents of each alloy less than 0.05%.
• Alloys A, B and C are illustrative of the adverse effects encountered with low molybdenum, particularly with high cobalt (Alloy A) and nickel (Alloy B) contents. Further, Alloy C contained a comparatively low amount of titanium and this alloy exhibited about the lowest yield strength, notwithstanding that it contained 0.76% aluminum. This reflects that it is not only the sum of titanium and aluminum which is important but that with titanium contents below those recommended herein, inferior results can ensue irrespective of the fact that the total sum of titanium plus aluminum might otherwise be suflicient.
• alloys within the invention also possess attractive high temperature characteristics.
• Alloy No. 1 subjected to Heat Treatment II and tested at 1000 F., exhibited a yield strength of 194,000 p.s.i., an ultimate tensile strength of 229,000 p.s.i., a tensile elongation of and a reduction in area of 70% when tested at 1000 F.
• This alloy also showed remarkable resistance to austenite reversion, the alloy containing only 5.8% (X-ray determination) austenite after the application of an intentionally high aging treatment of three hours at 1050" F.
• Alloy No. 1 when drawn to wire (0.025 inch diameter) and aged was 431,000 p.s.i. Further, wire has been drawn to 99.5% reduction in area without intermediate annealing and nominal thickness), Alloy No. 1 when given Heat Treatment III exhibited a yield strength of 350,000 p.s.i., and an autogenous, full penetration weld on the sheet material had a yield strength of 321,000 p.s.i. (after aging for three hours at 900 F.), a strength representing 92% of the base sheet.
• the steels of the subject invention can also be used for fasteners and bearings.
• a high strength maragin-g steel consisting essentially of from 15% to 20% nickel, from 11% to 16% cobalt, from 2.5% to 5% molybdenum, from 1.3% to 2.25% titanium, up to 0.8% aluminum, the sum of the titanium plus aluminum being from about 1.6% to 2.5 up to 0.05% carbon, up to 0.5% manganese, up to 0.5 silicon, up to 1% vanadium, up to 1% columbium, up to 5% chromium, up to 1% tantalum, up to 21% copper, up to 0.2% beryllium, up to 0.01% boron, up to 0.1% zirconium, the total amount of vanadium, columbium, chromium, tantalum, copper, beryllium, boron and zirconium not exceeding 7%, and the balance essentially 1I'OI1.
• a high strength maraging steel consisting essentially of from 15% to 20% nickel, from 8% to 16% cobalt, from 2.5% to 4.25% molybdenum, from 1.3% to 2.25% titanium, up to 0.8% aluminum, the sum of the titanium plus aluminum being from about 1.6% to 2.5%, up to 0.05% carbon, up to 0.5% manganese, up to 0.5% silicon, up to 1% vanadium, up to 1% columbium, up to 5% chromium, up to 1% tantalum, up to 2% copper, up to 0.2% berryllium, up to 0.01% boron, up to 0.1% zirconium, the total amount of vanadium, columbium, chromium, tantalum, copper, beryllium, boron and zirconium not exceeding 7%, and the balance essentially won.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)

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Citations (3)

• 1966
  • 1966-03-08 US US532597A patent/US3453102A/en not_active Expired - Lifetime
• 1967
  • 1967-02-28 GB GB9391/67A patent/GB1118689A/en not_active Expired
  • 1967-03-07 FR FR97792A patent/FR1513183A/fr not_active Expired
  • 1967-03-07 AT AT215167A patent/AT270724B/de active
  • 1967-03-07 DE DE19671558509 patent/DE1558509A1/de active Pending
  • 1967-03-08 BE BE695186D patent/BE695186A/xx unknown
  • 1967-03-08 SE SE3175/67A patent/SE310428B/xx unknown
  • 1967-03-08 JP JP42014234A patent/JPS4942572B1/ja active Pending

Patent Citations (3)

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