Classifications

• • G—PHYSICS
  • G04—HOROLOGY
  • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
  • G04B37/00—Cases
  • G04B37/22—Materials or processes of manufacturing pocket watch or wrist watch cases
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
  • C22C33/0285—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5% with Cr, Co, or Ni having a minimum content higher than 5%
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Definitions

• the present invention relates to stainless steel ferritic nickel free, as well as an external part of clothing for watch.
• Iron the basic element of all steels, presents the disadvantage of being sensitive to corrosion.
• the essays of this type lead to a ferritic structure, in particular identifiable by the fact that the alloy thus obtained is ferromagnetic, that is, it is attracted to magnets.
• ferromagnetic that is, it is attracted to magnets.
• This structure is indeed known to have better properties than ferritic structure, particularly in terms of resistance to corrosion, and be non-magnetic.
• this technique requires a high sintering temperature to lead to parts dense, free of porosity.
• this temperature of sintering is usually very close, or even better, at the maximum allowable temperature to obtain a austenitic structure. It is thus difficult, even impossible, to obtain under industrial conditions, both porous and austenitic parts after sintering.
• experience shows that it is very difficult to reform the austenite on a structural part ferritic formed at high temperature.
• the object of the present invention is to remedy the problems and disadvantages above, by proposing a steel with no allergenic character, resistant well corrosion, and can be advantageously put shaped by powder metallurgy.
• the present invention relates to a stainless steel alloy with structure ferritic and magnetic, characterized in that it contains at least 0.4% by weight of nitrogen, and at most 0.5% by weight nickel, the balance being made up of iron and unavoidable impurities.
• the invention also relates to such a steel alloy produced by powder metallurgy.
• the invention finally relates to an external part of clothing for a watch made of such an alloy of steel.
• the present invention proposes to start from a ferritic structure free of nickel, whose corrosion resistance is known for be less good, and improve this resistance to corrosion in a completely original way, adding new alloying elements and retaining the structure ferritic.
• the alloy which is the subject of the present invention is a ferritic alloy based on iron, chromium, manganese and nitrogen.
• the composition of the alloy according to the invention is similar to certain compositions of the prior art, its ferritic structure and magnetic is totally different, and results in extremely advantageous new properties.
• the alloy according to the invention is magnetic, that is, it is attracted by magnets. This property is particularly interesting when the invention is applied to boxes of watch. Indeed, watch movements are particularly sensitive to fields magnetic, and a case made of an alloy magnetic can provide shielding against fields magnetic exterior.
• Another advantage of the alloy according to the invention lies in the removal of the temperature constraint maximum treatment imposed on art alloys earlier, especially when the metallurgy of powders is used. Indeed, in accordance with the invention, to reach the ferritic structure you need a high temperature, perfectly compatible with the sintering temperature required for obtain dense parts, free of porosity.
• Another advantage of the alloy according to the invention is that the amount of nitrogen and added manganese can be reduced to the minimum necessary to obtain sufficient corrosion resistance for the application considered, while a concentration high is essential to obtain alloys with an austenitic structure. It is so possible to make alloys with a much better machinability than high alloys nitrogen and manganese content, elements which are known to significantly increase hardness, strength, and the toughness of the alloy.
• This powder is mixed with an organic binder to 60% by volume of powder for 40% by volume of binder, and injected according to the so-called "MIM" process (Metal Injection Molding).
• MIM Metal Injection Molding
• the parts thus obtained are freed from their binder by a thermochemical process said to be dewaxing, and sintered in an atmosphere of formiergaz comprising 8% hydrogen and 92% nitrogen, at one temperature of 1350 ° C for one hour. During the sintering, the nitrogen diffuses rapidly in the alloy, until its concentration reaches about 1% in weight, which is confirmed by the chemical analyzes carried out thereafter on the samples thus produced.
• the parts obtained are dense (only about 0.1% of porosities) and magnetic, indicating that their structure is ferritic.
• Ferritic parts obtained by means of the alloy according to the invention have been subjected to a corrosion test consisting of submerging them for seventy-two hours contact with a mist made from salt water, then putting them for seventy-two hours in a synthetic sweat solution. After the test, the parts show no trace of corrosion, indicating that unlike most other steels ferritic, their corrosion resistance is at least as good as a good stainless alloy austenitic. This is due to the presence of nitrogen and manganese which improve the properties of the phase ferritic.
• a mechanical watch movement has been set up in a watch case made by means of the alloy according to the invention.
• Standard watchmaking resistance tests to magnetic fields showed a shielding effect beneficial for movement in the presence of a field magnetic outside. No harmful influence of the magnetic alloy on the march of mechanical movement has not been observed even after subjecting the box to fields of five Tesla, a thousand times more powerful than magnetic fields normally used.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Powder Metallurgy (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

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Citations (4)

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• 1998
  • 1998-06-12 EP EP98110813A patent/EP0964071A1/fr not_active Withdrawn
• 1999
  • 1999-06-09 JP JP11162265A patent/JP2000017403A/ja active Pending
  • 1999-06-10 US US09/329,793 patent/US6093233A/en not_active Expired - Fee Related
  • 1999-06-11 CN CN99109480.8A patent/CN1239153A/zh active Pending

Patent Citations (4)

Non-Patent Citations (1)

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