Classifications

• • 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
  • C23C8/40—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 liquids, e.g. salt baths, liquid suspensions

Definitions

• the invention relates to a salt bath based on alkali and / or alkaline earth metal halides for the currentless production of wear-resistant boride layers on metallic materials at 650 to 1100 ° C. It is used in particular for the production of single-phase, hard and adhesive boride layers on steels to increase wear resistance and improve corrosion resistance.
• Boronizing for wear protection of steel and refractory metals has been a well-known process. Diffusion of the element boron into the surface of the treated workpiece and reaction with the base material results in dense, uniform layers of the respective boride, on iron, for example, the borides FeB Fe 2 B.
• the borides have significantly changed properties compared to the pure metals, in particular most are Borides are very hard, corrosion-resistant and therefore extremely wear-resistant.
• the boride layers are firmly connected to the base material by diffusion.
• borated steels for example, are partly superior to steels treated by nitriding or carburizing. A large number of technical process variants have therefore been developed in the past according to which boride layers, in particular on steel, can be produced.
• boriding in solid boriding agents is used almost exclusively.
• the parts to be treated are packed in iron boxes in a boron-releasing powder, usually mixtures of boron carbide, aluminum oxide, silicon oxide and the like, with activating additives such as ammonium fluoride or potassium borofluoride (e.g. DE-PS 1,796,216).
• activating additives such as ammonium fluoride or potassium borofluoride (e.g. DE-PS 1,796,216).
• the boxes are tightly sealed and annealed for a while, the desired boride layers being formed in direct solid-to-solid reactions or by transporting the boron over the gas phase.
• paste processes are only modifications of powder boriding and have the additional disadvantage that large amounts of stubborn residues have to be dissolved from the parts after the treatment and that even application of the paste is extremely difficult, particularly in the case of parts of complex shape.
• Electroless borating salt baths which contain boric acid and fluoborates in addition to boron carbide (GB-PS 959533) or an alkali or alkaline earth metal halide and fluoborate (U.S. Patent 3,634,145).
• these salt baths have also not been able to establish themselves in practice.
• the salt bath contains boron monofluoride or compounds from which boron monofluoride is formed as an intermediate under bath conditions.
• the boron monofluoride which acts as a borating agent can be added to the melt from the outside or can advantageously be generated in the melt itself.
• the gaseous boron monofluoride produced in a known manner by heating boron trifluoride with finely divided boron is introduced into the salt melt during the boronization process.
• Electroless boronation baths that are particularly easy to operate are obtained when the boron monofluoride is generated in the molten salt itself.
• the required trifluoroboroxol (BOF) 3 is also generated in the melt itself. This is based on the knowledge that (BOF) 3 can be produced very well in an inert melt from alkali / alkaline earth chlorides by reacting boron oxide or borates with alkali / alkaline earth fluorides, the presence of barium ions in particular having a positive influence.
• the trifluoroboroxol that is produced in this way in a very slow reaction and in a concentration that is barely measurable converts with the boron carbide suspended in the melt to form the boronizing agent, the boron monofluoride BF.
• molten salts which, in addition to alkali and / or alkaline earth halides, contain 1 to 30% by weight of a boron-oxygen compound, 1 to 30% by weight of alkali and / or alkaline earth fluorides and 1 to 15% by weight of boron carbide.
• the trifluoroboroxol formed by reacting boron-oxygen compounds with fluorides brings about a slow, controlled digestion of the boron carbide, wherein boron-active boron monofluoride is released, which boron can release on the workpiece surface through decay.
• boron carbide instead of boron carbide, other known borating agents, such as amorphous boron or calcium boride, can also be used.
• the boriding effect of the melts can be influenced above all by variations in the concentration of boron oxide or borate and in alkali metal / alkaline earth metal fluoride, as well as by changing the temperature and - to a small extent - by changing the concentration of the boron carbide. It has been shown that the inventive Salt melting is possible to produce layers of Fe 2 B on steel without the undesirable boron-rich phase FeB occurring.
• Salt melts which are composed of 30-60% by weight BaCl2, 10-20% by weight B 2 0 3 , alkali and / or alkaline earth borates, 10-30% by weight NaF, 10-25% by weight N aCl and 1-15% by weight are preferably used.
• B 4 C exist.
• Salt melts with 40-55% by weight BaCl, 5-15% by weight B 203 , alkali and / or alkaline earth borate, 18-25% by weight NaF, 15-20% by weight NaCl and 4-10% by weight B are particularly advantageous 4 C.
• the molten salts according to the invention enable one. extremely simple work in practice.
• the salt mixture is melted in a melting crucible made of heat-resistant steel and the B 4 C is kept in suspension by introducing an inert gas stream, for example nitrogen.
• the workpieces to be borated are attached to a charging frame, preheated to 350 C with hot air, for example, and then hung in the melt.
• Steels produce uniform, very wear-resistant, single-phase layers of Fe 2 B, whereby the layer thickness can be varied depending on the base material and the duration of treatment.
• the parts are removed from the melt and quenched, for example in a quenching bath made of sodium and potassium nitrate, which is customary in hardening technology, and then rinsed with water. In this way, no fluoride gets into the waste water.
• the method according to the invention can thus be easily integrated into the existing infrastructure of a salt bath hardening plant without significant investments or additional wastewater treatment being required.
• the method of operation largely corresponds to that of salt bath coal or Salt bath nitriding.
• the melts are composed of relatively cheap components.
• a boriding process is thus available which can compete with the known large-scale processes of salt bath nitriding and salt bath coaling in terms of operation and costs.
• 100 kg of a salt mixture of 50 kg BaCl 2 , 15 kg NaF, 20 kg NaCl, 5 kg B 2 O 3 and 10 kg B 4 C powder are melted in a crucible furnace of size 30/80 and the boron carbide is suspended by introducing a stream of inert gas .
• a treatment temperature of 900 ° C. an FeB-free boride layer of Fe 2 B of 60 ⁇ m thickness is obtained on CK 15 steel with a treatment time of 2 hours.
• 100 kg of a salt mixture of 50 kg BaCl 2 , 25 kg KF, 15 kg NaCl, 5 kg B 2 0 3 and 5 kg B 4 C powder are melted in a crucible furnace of size 30/80 and the boron carbide is introduced by introducing an inert gas stream, eg nitrogen, kept in suspension.
• an inert gas stream eg nitrogen
• an FeB-free Fe 2 B boride layer of 30 ⁇ m thick is obtained on CK-15 steel.
• Particularly good boride layers provide molten salts with the following composition: 50 kg BaCl 2 , 16 kg NaCl, 10 kg B 2 O 3 , 18 kg NaF and 6 kg B 4 C.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Chemically Coating (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Ceramic Products (AREA)
• Coating By Spraying Or Casting (AREA)
• Physical Vapour Deposition (AREA)
• Electrolytic Production Of Metals (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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Publications (2)

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• 1983
  • 1983-07-26 DE DE19833326863 patent/DE3326863A1/de not_active Withdrawn
• 1984
  • 1984-06-26 DE DE8484107296T patent/DE3462272D1/de not_active Expired
  • 1984-06-26 EP EP84107296A patent/EP0132602B1/fr not_active Expired
  • 1984-06-26 AT AT84107296T patent/ATE25267T1/de not_active IP Right Cessation
  • 1984-07-04 ZA ZA845139A patent/ZA845139B/xx unknown
  • 1984-07-12 US US06/630,302 patent/US4536224A/en not_active Expired - Fee Related
  • 1984-07-24 ES ES534584A patent/ES534584A0/es active Granted
  • 1984-07-25 CA CA000459631A patent/CA1224389A/fr not_active Expired
  • 1984-07-25 BR BR8403695A patent/BR8403695A/pt unknown
  • 1984-07-25 JP JP59153298A patent/JPS6070169A/ja active Pending

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