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
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • 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
  • C21D6/001—Heat treatment of ferrous alloys containing 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
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0236—Cold rolling
• • 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

Definitions

• the present invention relates to a cobalt-free and titanium-free maraging steel having a high yield strength and good resistance to fatigue.
• Maraging steels are self-hardening steels likely to acquire by air cooling a soft martensitic structure which can be considerably hardened by an aging heat treatment causing formation of intermetallic precipitates.
• these steels contain 10% to 30% of nickel intended to allow a martensitic structure to be obtained by air cooling, low carbon to get martensite soft and additives intended to allow hardening by formation of intermetallic precipitates.
• Additions intended to obtain precipitation hardening include titanium, aluminum and molybdenum whose effects are significantly enhanced by the presence of cobalt. We can also add niobium to fix the carbon and thus soften the non-aged martensitic structure.
• the steel does not contain titanium. Indeed, due to the development, the steel always contains a little nitrogen which forms with the titanium nitrides unfavorable to good resistance to fatigue.
• the object of the present invention is to provide a maraging steel having the properties indicated above.
• the subject of the invention is a maraging steel without cobalt (that is to say, without voluntary addition of Co, there may be small quantities, generally less than 0.2%), the chemical composition of which comprises, in weight : 14% ⁇ Ni ⁇ 23% 4% ⁇ Mo ⁇ 13% 1% ⁇ Al ⁇ 3.5% C ⁇ 0.01% the remainder being iron and impurities resulting from processing; the chemical composition satisfying, in addition, the following conditions: 23% ⁇ Ni + Mo ⁇ 27% and: Ni + 2.5 x Mo +2.3 x Al ⁇ 38%
• This steel has a yield strength Re greater than or equal to 1900 MPa and a elongation greater than or equal to 4% in the aged state after annealing in solution above 800 ° C or in the aged state directly after cold work hardening, the rate work hardening then being between 0% and 30%.
• Maraging steel contains from 14% to 23%, and preferably more than 16% nickel, on the other hand from 4% to 13%, and preferably from 5% to 8%, of molybdenum.
• Preferred areas provide the characteristics mechanical desired under better economic conditions; indeed, the molybdenum costing 2 to 4 times more expensive than nickel, it is better to use more nickel and less molybdenum.
• the sum of the nickel and in molybdenum must be between 23% and 27%, and preferably between 24% and 26%, so as to have a martensitic transformation start temperature neither too high nor too low, and to obtain a sufficient hardening effect of the molybdenum.
• Steel also contains 1% to 3.5% aluminum, to achieve an effect hardening by precipitation while limiting the risk of default during hot rolling. It does not contain titanium (i.e., less than 0.01%) for avoid the formation of nitrides unfavorable to fatigue resistance.
• Ni, Mo and Al contents are such that: Ni + 2.5 x Mo +2.3 x Al ⁇ 72%, so as to obtain the desired yield strength.
• the carbon content is limited to a maximum of 0.01% to obtain a Martensite sufficiently soft before aging.
• the rest of the composition is consisting of iron and impurities resulting from the production.
• This steel is produced, then poured and hot rolled in accordance with the state of art. In addition, it can be cold rolled, for example to obtain a strip of less than 1.5 mm thick.
• cold rolling can be performed in several stages separated by annealing at a temperature greater than or equal to 800 ° C.
• the last cold rolling step corresponds to a hardening rate between 0% and 30%.
• the mechanical characteristics are obtained after an aging treatment between 450 ° C and 540 ° C. This treatment can be carried out either immediately after solution annealing above 800 ° C, ie after the last stage of cold rolling.
• the yield strength Re obtained is greater than 1900 MPa and the elongation at break A% is greater than 4%.
• castings 1, 2, 3, 4 and 5 were produced in accordance with the invention.
• cold rolled strips were produced with variable work hardening rates during the last cold rolling step, this one being preceded by annealing on parade at 1020 ° C.
• These strips were then hardened by aging at 510 ° C for 4 hours, then the characteristics were measured mechanical by a tensile test.
• This maraging steel is particularly suitable for the manufacture of parts watchmaking and belts.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Heat Treatment Of Steel (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (2)

Publications (2)

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Cited By (2)

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Citations (6)

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• 1998
  • 1998-02-04 FR FR9801241A patent/FR2774396B1/fr not_active Expired - Fee Related
• 1999
  • 1999-01-28 DE DE69903201T patent/DE69903201T2/de not_active Expired - Fee Related
  • 1999-01-28 EP EP99400192A patent/EP0935007B1/de not_active Expired - Lifetime
  • 1999-01-28 ES ES99400192T patent/ES2185295T3/es not_active Expired - Lifetime
  • 1999-02-02 JP JP11025527A patent/JPH11264054A/ja not_active Withdrawn
  • 1999-02-03 US US09/243,492 patent/US6136102A/en not_active Expired - Fee Related

Patent Citations (8)

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