Classifications

• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
  • C21D1/76—Adjusting the composition of the atmosphere
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
  • B22F3/1003—Use of special medium during sintering, e.g. sintering aid
  • B22F3/1007—Atmosphere
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

• the invention relates to a method for sintering or annealing of metal components in a furnace atmosphere comprising one or more of the gases nitrogen, hydrogen and argon.
• Metal sintering is defined as the thermal treatment of a metal powder or a mixture of metal powders at an enhanced temperature for the purpose of increasing its strength by bonding together of the particles. During sintering atomic diffusion takes place and the powder particles are welded together. The sintering operation has normally to be carried out under a protective atmosphere in order to prevent oxidation and to promote the reduction of surface oxides.
• Annealing is a heat treatment that alters the micro structure of a metal causing changes in properties such as strength and hardness.
• the controlled atmosphere for sintering may be produced by blending pure nitrogen with pure hydrogen. In practice such atmospheres contain about 90% nitrogen and 10% hydrogen, sometimes with small additions of CH 4 .
• the controlled atmosphere for annealing may be produced by blending pure nitrogen with pure hydrogen. In practice such atmospheres contain about 95% nitrogen and 5% hydrogen for carbon steel and 75 to 100% hydrogen and rest nitrogen for stainless steel.
• the sintering atmosphere is often produced by the reaction of a hydrocarbon gas with a limited amount of air. Since this reaction is endo-thermic, external heat has to be supplied, and the resulting atmosphere is called endogas. That endogas may contain up to 40% of hydrogen, some carbon monoxide and carbon dioxide with the remainder being nitrogen.
• This object is achieved by a method for heat treating of metal components in a furnace atmosphere comprising one or more of the gases nitrogen, hydrogen and argon, which is characterized in that said furnace atmosphere comprises a gaseous hydride.
• Gaseous hydrides such as silane are known to have a very high reactivity with oxygen containing substances or compounds.
• silane or mono silane undergoes a spontaneous reaction with oxygen as well as with air: SiH 4 + O 2 ----> SiO 2 + 2 H 2 SiH 4 + 2 H 2 O ----> SiO 2 + 4 H 2
• the invention relates to the heat treatment of metal components.
• heat treatment shall mean a method alter the physical or chemical properties of the metal component, in particular sintering, annealing, hardening, tempering and quenching.
• heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally.
• silanes or boranes are added to the furnace atmosphere.
• Silanes are chemical compounds of silicon and hydrogen.
• the lowest silanes, mono silane with the chemical formula SiH 4 and di silane with the chemical formula Si 2 H 6 are gaseous and thus are particularly suitable for the invention.
• Boranes are chemical compounds of boron and hydrogen.
• the two smallest members of the borane group are mono borane or simply borane BH 3 and di borane B 2 H 6 . All these compounds are known to be very reactive with oxygen and air.
• these boranes are also preferably used for reducing the oxygen content in the furnace atmosphere.
• the amount of the gaseous and reactive hydride which is added to the furnace atmosphere is preferably between 0.00001 % and 2 %, most preferably between 0.001 % to 0,05%.
• the amount of hydride is determined based on one or more of the following factors:
• furnace temperature between 300 and 1500 °C for the inventive sintering or annealing application.
• the invention it is possible to extremely decrease the oxygen and moisture level in the furnace atmosphere.
• metals it is possible to subject metals to a heat treatment process which could not have been treated in this way before.
• the invention allows to sinter or anneal metal components, in particular steel, without getting the material oxidized or/and discouloured.
• the invention is useful for the heat treatment of all kind of metals.
• preferred metals and metal powders to be used with the inventive method are iron, low alloyed steel, austenitic, ferritic and duplex stainless steel, copper and copper alloys, nickel and nickel alloys.
• controlled atmosphere for annealing may be produced by blending pure nitrogen with pure hydrogen.
• atmospheres contain about 95% nitrogen and 5% hydrogen for carbon steel and 75 to 100% hydrogen and rest nitrogen for stainless steel.
• a little amount of silane is added to the furnace atmosphere.
• the hydrogen content of the atmosphere can be essentially reduced.
• the atmosphere will preferably contain pure nitrogen with addition of silane, and for the heat treatment of stainless steel the furnace atmosphere will consist of about 5-10% hydrogen, a small amount of silane and the remainder being nitrogen.
• the inventive furnace atmosphere is either plain nitrogen, plain hydrogen, plain argon or a mixture of these gases blended with a gaseous hydride.
• Preferred furnace atmospheres are
• the mixture of nitrogen and hydrogen or the mixture of argon and hydrogen are preferably produced by blending pure nitrogen with hydrogen or pure argon with hydrogen, respectively.
• Nitrogen/hydrogen mixtures may also be produced by endothermic generators or ammonia dissociation.
• the invention is particularly advantageous for the production of a controlled atmosphere in industrial furnaces, for example in a continuous furnace for heat treatment of metals.
• industrial furnaces for example in a continuous furnace for heat treatment of metals.
• there is always some leak air entering the furnace increasing the oxygen and water vapour content of the furnace atmosphere.
• a gaseous reactive hydride any ingress of air and moisture reacts with the hydride so that within the furnace a high quality atmosphere is permanently guaranteed.
• the inventive method is not only useful to decrease the oxygen and water vapour content in a furnace atmosphere but can also be used as a reducing agent to react with other impurities in the atmosphere, for example organic compounds.
• Annealing of steel in the inventive atmosphere is a good alternative to pickling of stainless steel.
• the amount of oxides on the surface of the steel can be essentially reduced.
• Another preferred application of the invention is sintering of powder containing easily oxidised elements like chromium, manganese and silicon.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)
• Furnace Details (AREA)

Priority Applications (1)

Applications Claiming Priority (1)

Publications (1)

Family

ID=39427512

Family Applications (1)

Country Status (1)

Cited By (2)

Citations (1)

• 2007
  • 2007-10-18 EP EP07020457A patent/EP2050526A1/fr not_active Withdrawn

Patent Citations (1)

Similar Documents

Legal Events