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
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

Definitions

• the invention relates to an austenitic stainless steel for hot use.
• Alloy 286 is an austenitic superalloy containing approximately 26% Nickel, 15% Chromium, 1.25% Molybdenum and 2% Titanium. Titanium is intended to form hardening precipitates of ⁇ phase ⁇ These alloys can be used up to 700 ° C but not beyond because, above this temperature, the ⁇ 'phase is unstable and tends to transform into ⁇ phase which is less hardening. In addition, the nickel content being high, these alloys are expensive.
• Martensitic stainless steels contain around 12% chromium and little or no nickel, so that their price is significantly lower than that of alloys of type 286, but on the other hand, they can only be used up to 600 ° C, which is insufficient for some applications.
• the object of the present invention is to remedy these drawbacks by proposing a stainless steel for hot use which is more economical than alloys of type 286 and which has hot mechanical characteristics comparable to or even superior to those of these alloys.
• the invention relates to an austenitic stainless steel for hot use, the chemical composition, by weight, comprises:
• the chemical composition, by weight is such that: 0.45% ⁇ Al ⁇ 1.2% and
• the invention also relates to the use of a steel according to the invention for the manufacture of bolts for hot use intended in particular for beings mounted on automobile engines.
• the steel according to the invention is a stainless steel consisting of a stable ⁇ austenitic matrix, hardened by precipitates of ⁇ 'phase Ni3Ti, or better, Ni3 (Ti, Al) of cubic structure, containing enough Aluminum to limit the transformation of phase ⁇ 'into phase ⁇ of the same composition, but of hexagonal structure, and not containing too much Aluminum so as not to form the phase
• the steel In order to be able to form sufficient hardening precipitates, the steel must contain more than 1% of titanium, but the content of this element must remain below 3.5% ⁇ and preferably at 3%, because beyond it deteriorates the aptitude for hot plastic deformation which makes shaping operations by rolling or forging difficult. In addition, when the titanium content is too high, the steel must be remelted under vacuum to limit segregation and this operation is very expensive.
• the aluminum content should not exceed 1.5% and preferably
• the aluminum content must be between 0.45% and 1.2%.
• the titanium and aluminum contents are such that:
• the nickel content must be between 16% and 25% and preferably be less than 23%, and the chromium content must be between 16% and 18.5%) and preferably be less than 18%, for that, after formation of the precipitates, the matrix remains austenitic, and to limit the formation of ferrite which decreases the hot resistance, or of phase ⁇ or phase ⁇ , which weaken the steel.
• nickel which is a very expensive element, has no significant effect on the properties of the steel according to the invention, given the upper limits of the titanium and aluminum contents. .
• the austenitic matrix has an optimal composition, it is preferable that:
• Ni is the nickel content of the steel
• Cr is the chromium content
• F is calculated by the formula:
• the steel When the steel is produced by reflow of scrap alloys or steel, it may also contain residual elements such as Silicon, Copper, Cobalt, or Vanadium, in contents of less than 0.5% for each of these.
• the rest of the chemical composition consists of Iron and impurities resulting from the production.
• This steel can be manufactured in any desired form: sheet metal, bar, profile, wire, forgings.
• a heat treatment consisting for example of dissolution by heating between 850 ° C and 1050 ° C for about an hour, followed by rapid cooling to avoid uncontrolled precipitation, for example by quenching with water, then an income by holding for 10 to 24 hours at a temperature between 680 ° C and 760 ° C followed by quenching in air.
• steels A to G are manufactured, the chemical compositions of which, in% by weight, are given by the following table
• t R is the breaking time
• a R is the elongation at break
• ⁇ R is the necking.
• the properties of the steel according to the invention make it particularly suitable for the manufacture of connecting parts and in particular of bolts for hot use, in particular for assembling parts of a heat engine, and for example, for fixing a turbo compressor on the exhaust manifold of an automobile engine.
• the steel according to the invention is also very well suited to the manufacture of components for boilers or for steam turbines of thermal power plants, such as casings, exchangers or rotors.

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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 Articles (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)

Priority Applications (5)

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Publications (1)

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Citations (6)

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• 1994
  • 1994-12-13 FR FR9414942A patent/FR2727982A1/fr active Granted
• 1995
  • 1995-12-07 KR KR1019960704185A patent/KR100215531B1/ko not_active Expired - Fee Related
  • 1995-12-07 JP JP8518353A patent/JPH09506933A/ja active Pending
  • 1995-12-07 EP EP95941782A patent/EP0742845A1/fr not_active Ceased
  • 1995-12-07 WO PCT/FR1995/001617 patent/WO1996018750A1/fr not_active Ceased
  • 1995-12-07 US US08/687,423 patent/US5753178A/en not_active Expired - Fee Related
  • 1995-12-08 TW TW084113091A patent/TW381121B/zh not_active IP Right Cessation
• 1996
  • 1996-08-12 FI FI963149A patent/FI112872B/fi active

Patent Citations (6)

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