Classifications

• • 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
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/14—Treatment of metallic powder
  • B22F1/145—Chemical treatment, e.g. passivation or decarburisation
• • 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
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/24—Nitriding
  • C23C8/26—Nitriding of ferrous surfaces

Definitions

• the chromium containing steel alloy it achieves its aim by melting the chromium containing steel alloy, forming from the melt a powder by atomization and annealing the powder at atmospheric pressure in a nitrogen atmosphere at temperatures ranging between about 800 C. and 1100 C.
• a powder Prior to the annealing step in the nitrogen atmosphere it may be advantageous to compress the powder to a porous body. The compression step may be carried out by simple pressure or by rolling. It may also be advantageous to introduce another annealing step prior to the nitrogen atmosphere annealing by exposing the powder, either in its powder form or after compression as a porous body, to reduced pressure (vacuum) at temperatures exceeding the maximum temperature used in the nitrogen atmosphere annealing, which is 1100 C. This prior annealing step reduces the oxygen and carbon content of the alloy prior to the contact with the nitrogen atmosphere. Suitable illustration for the temperature used in the prior annealing step is, for example, 1150 to 1200 C.
• nitrogen contents of up to 2%, or even more, can be produced, whereas prior art processes ranged from about 0.2% to about 0.8% nitrogen.
• Nickel may be present in the chromium containing alloys and the high nitrogen content permits the reduction of the nickel content without adverse effects.
• the invention relates to the production of metal alloys having a high nitrogen content.
• nitrogen While the presence of nitrogen in pure carbon steel is looked upon as disadvantageous, nitrogen has in a variety of metals achieved importance as an alloying element. A nitriding with ammonia at relatively low temperatures leads to hard wear-resistant surfaces that furthermore improve the corrosion resistance, particularly at porous sintered parts. It is furthermore possible to substitute in chromium nickel steels nitrogen at least in part for the expensive nickel, and to achieve thereby an improvement in heat resistance.
• metal alloys having a high nitrogen content by methods as follows: Adding to the metal bath of salts, for instance calcium cyanamide, which give off nitrogen at high temperatures; use of nitrided alloying elements, such as ferrochromium; or melting of the metal under increased nitrogen pressure.
• the first and second methods lead to melting with nitrogen contents that correspond to air saturation, for instance leading at the melting of an 18-8 chromium nickel steel to a nitrogen content of about .2%.
• the nitrogen concentrations achieved with the first two mentioned methods are for most purposes too low.
• the melting under high nitrogen pressure on the other hand, under the third method, is very expensive, particularly when even higher nitrogen pressures above the aforesaid twenty atmospheres overpressure need to be used to achieve a nitrogen content of about the aforesaid .8%.
• metal alloys particularly iron and steel alloys may be produced having a high nitrogen content, preferably above .5
• the instant invention provides for pulverizing a metal to obtain solid metal powder, for instance by pulverizing a molten metal alloy with pressurized water; thereafter, either the powder or a body formed by pressing or rolling from the powder, for instance a block or a sheet of metal, is subjected to a decarburizing and/ or reducing annealing at a rarefied atmospheric pressure at a temperature of above 1100 C.; immediately after the cooling to a temperature of between about 1100 C. and about 800 (1., preferably at normal atmospheric pressure, the powder or body, respectively, is annealed in a nitrogen containing atmosphere.
• the invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, all as exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.
• either the powder or the body which is formed from the carbon containing powder is nitrided for achieving a desired nitrogen content only after a preceding decarburizing annealing in a vacuum.
• This may be done in such a manner that after the vacuum annealing, that is carried out preferably at a temperature range of between about 1150 C. and 1200 C., nitrogen gas is led into the annealing furnace, which is still at a high temperature though its temperature has receded to a range of from about 1100" C. to about 800 C.
• the decarbuizing first annealing step serves the following purposes:
• the surfaces of the grains of the powder can absorb the nitrogen during the subsequent annealing in the nitrogen atmosphere faster, so that there will be achieved already within a few minutes the desired nitrogen content in uniform distribution.
• the porous body formed of the steel powder will be annealed, in the aforesaid second nitrogen annealing step, in accordance with the invention, at a temperature of between 800 C. and 1100 C., preferably 950 C., with the aid of a gaseous nitrogen at a pressure of about one atmosphere.
• EXAMPLE II The table below shows the results of several nitridings of various chromium containing steels, in accordance with the invention.
• the table contains the analysis of the steel alloys and their nitrogen contents after an annealing of three hours at 950 C. with nitrogen gas:
• EXAMPLE III For the production of tubes of 18-8 chromium nickel steel with a high nitrogen content, there was first produced a steel powder by atomizing the steel melt with pressure water, with a stoichiometrical relation of carbon to oxygen, which was thereafter pressed into blocks each weighing 20 kilograms at a pressure of 2 tons per square centimeter. The blocks were subsequently annealed in vacuum at 1150 C. for eight hours, for removing the carbon and oxygen. Thereafter, the furnace was cooled to 950 C. and the nitrogen was admitted. After an annealing time of twenty minutes, these blocks showed throughout their entire cross section uniformly distributed a nitrogen content of .8%. Subsequently, the blocks were heated under nitrogen to 1150 C. and shaped into tubes in an extrusion press.
• step (b) is carried out by the aid of pressurized water.
• step (b) is compressed by mechanical means into a porous body prior to the annealing step of (c).
• step (b) is compressed by mechanical means into a porous body and prior to the annealing step of (c) is also exposed to another annealing step under vacuum and at temperatures exceeding that of the annealing step of (c) in order to reduce the carbon and oxygen content of the alloy.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Powder Metallurgy (AREA)

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Citations (5)

• 1966
  • 1966-05-27 GB GB23854/66A patent/GB1146712A/en not_active Expired
  • 1966-05-31 US US558540A patent/US3357827A/en not_active Expired - Lifetime
  • 1966-06-01 BE BE681925D patent/BE681925A/xx unknown

Patent Citations (5)

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