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
  • C23C8/60—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 solids, e.g. powders, pastes
  • C23C8/62—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 solids, e.g. powders, pastes only one element being applied
  • C23C8/68—Boronising
  • C23C8/70—Boronising of ferrous surfaces

Definitions

• the invention relates to a borating agent in the form of a paste for the production of boride layers on metallic Materials. This is used in particular for generation single-phase, hard and adhesive boride layers Iron materials to increase wear resistance and corresponding to improve the corrosion resistance Workpieces.
• Boronizing for wear protection of iron, 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 creates 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 they are Most borides are very hard, corrosion-resistant and therefore extremely wear-resistant. Due to their generation by diffusion and solid-state reaction, the boride layers are firmly connected to the base material. With regard to their wear resistance, borated steels, for example, are sometimes superior to steels treated by nitriding or carburizing.
• boriding is predominantly in solid Borating agents applied.
• the ones to be treated Parts packed in iron boxes in powder mixtures which in the essentially from boron-releasing substances, activating Substances and the rest of refractory, inert Extenders exist.
• the closed boxes are for annealed for a while, being in direct Solid state reaction or by transporting the boron over the Gas phase on the parts the desired boride layers be formed.
• Boronization is usually carried out at temperatures between 800 and 1100 ° C and especially between 850 and 950 ° C carried out.
• the achievable layer thicknesses of the Boride layers are usually in the range between 30 and 300 ⁇ m.
• boriding agents come as boron-releasing substances amorphous and crystalline boron, ferroboron, boron carbide and Borates like Borax in question.
• Chlorine- or fluoride-releasing compounds are suitable such as alkali and alkaline earth chlorides or fluorides.
• Fluoroborates such as are commonly used as activators especially potassium tetrafluoroborate.
• Typical extenders are aluminum oxide, silicon dioxide and silicon carbide. Borating agents of this type are described, for example, in DE-PS 17 96 216.
• a typical composition that extends up to proven today as a borating agent contains about 5% by weight Boron carbide, 5% by weight potassium tetrafluoroborate and 90% by weight Silicon carbide.
• the boron-rich FeB phase is much more brittle than the Fe 2 B phase, which has a negative effect on the wear resistance of the borated components.
• boride layers over 50 ⁇ m an FeB surface layer is easily formed, which should be avoided for the reason mentioned.
• boron pastes are among the usual ones Process conditions for single-phase layers only To achieve layer thicknesses below 50 microns.
• Boride layers have to be elaborately annealed in a vacuum or Salt bath can be used for subsequent diffusion or it is special borating agents (e.g. after the German Patent application 198 30 654.7) is required.
• fluoride emissions in the exhaust gas determine. Both through the post-diffusion as well the fluoride emission becomes a porosity in the layer causes that adversely affect the layer properties effect.
• the well-known Borierpaste is used in many Materials a corrosion attack on the coated Workpiece effected during the drying phase. Thereby paste residues adhere so firmly to the skin after treatment Workpiece surface that a cleaning of the components with Water is insufficient and an additional Blasting process is required, and also the There is a risk that the boride layer produced in Is affected.
• the corrosion attack can do so be pronounced that the application of the So far, paste boriding has not been possible with certain types of steel is possible because there are real gnawings.
• the known Borier pastes have storage instabilities, in particular at elevated temperatures, which is caused by the dissociation of the activator KBF 4 with a lowering of the pH.
• the invention was therefore based on the object of developing a borating agent in the form of a paste with which, in particular on iron materials, practically exclusively single-phase, Fe 2 B-containing boride layers can be produced. Furthermore, the content of water-soluble fluorides in this paste-like boronizing agent should be reduced and, when used as intended, there should be a reduced fluoride emission. In particular, the porosity of the boride layer formed should also be reduced. Furthermore, the corrosion attacks should be prevented and the cleaning of the components should be made easier. In addition, the storage stability of the stock exchange paste should be improved.
• the porosity of the boride layer can be significantly reduced. This results in a longer service life for the components.
• the hydrogen fluoride emissions are also reduced by binding fluorides, for example HF, as CaF 2 .
• the CaF 2 which may arise also has the positive effects described in German patent application 198 30 654.7.
• the borating paste according to the invention preferably contains based on the solids content, 0.1-5% by weight Compounds according to (a), 0.1-2% by weight of compounds according to (b) and 0.1-2% by weight of compounds according to (c).
• the boron paste contains, based on the Solids content, 1-3% by weight of compounds according to (a), 0.2-1 % By weight of compounds according to (b) and 0.2-1% by weight Compounds according to (c).
• the compounds according to (a) include in particular Carbonates of sodium, potassium, calcium and magnesium in Question. Calcium carbonate is particularly preferred.
• Preferred compounds according to (b) are Alkali nitrites such as sodium and potassium nitrite in particular Question. Sodium nitrite is particularly preferred.
• alkali borates such as in particular sodium and Potassium borate in question.
• the borating paste according to the invention preferably contains as Boron-releasing substance Boron carbide, as an activating substance Potassium tetrafluoroborate and as an extender silicon carbide.
• the Borier paste as an activating substance a combination of Potassium tetrafluoroborate and calcium fluoride.
• a conventional borating agent to which calcium fluoride is added as a further activating substance in addition to the usual activator substances, can be used to specifically influence and control the type of boride formation in the workpiece surface.
• practically FeB-free, single-phase Fe 2 B layers can be produced without further ado.
• the borating paste according to the invention expediently contains as a activating substance a combination of 1 to 15 % By weight potassium tetrafluoroborate and 5 to 40% by weight Calcium fluoride, each based on the solids content.
• the pasty boroning agent according to the invention can contain the usual boron-releasing substances, such as amorphous or crystalline ferroboron and in particular boron carbide (B 4 C). It preferably contains 1 to 15% by weight of boron carbide, based on the solids content.
• the borating paste according to the invention contains the rest the usual extenders, in particular silicon carbide (SiC), further water and possibly auxiliary substances.
• SiC silicon carbide
• the borating paste according to the invention preferably contains based on the solids content, 8 to 10% by weight boron carbide, 5 to 10% by weight potassium tetrafluoroborate, 10 to 30% by weight Calcium fluoride, 1-3% by weight calcium carbonate, 0.2-1% by weight Sodium nitrite, 0.2-1% by weight sodium tetraborate and the rest as an extender silicon carbide, water and optionally auxiliary substances.
• a typical composition consists of approximately 10% by weight Boron carbide, 7% by weight potassium tetrafluoroborate, 15% by weight Calcium fluoride, 1.5% by weight calcium carbonate, 0.5% by weight Sodium nitrite, 0.5% by weight sodium tetraborate and the rest Silicon carbide, based on the solids content.
• Borating agent can be added by adding water and if necessary, minor amounts of auxiliaries, such as e.g. commercially available binders and / or Thickener, from the corresponding powder mixture respectively.
• auxiliaries such as e.g. commercially available binders and / or Thickener
• the water content based on the total amount, 25 to 40% by weight.
• the paste preferably contains 30 to 35% by weight and in particular about 30% by weight of water.
• Thickeners may be used as other auxiliary substances and binders as used in the formulation of pastes are common in question.
• a particularly suitable one Bentonite is a thickening agent. This will decrease Amount, typically about 1% by weight, based on the total amount used in the borier paste.
• the borating paste according to the invention can be very advantageous for Generation of boride layers on metallic workpieces be used.
• the addition of carbonate reduces the porosity of the boride layer and thus increases the durability of the components.
• the addition of nitrite eliminates the tendency of known boron pastes to corrode the component. This results in a very good surface appearance.
• the agent according to the invention is considerably less critical with regard to fluoride emissions, which in particular means the disposal of waste water after washing the borated components and of depleted borating agent concerns.
• a reduced KBF 4 content is also advantageous when the agent is used as intended, since correspondingly lower fluoride-containing gas emissions occur.
• By adding carbonate these emissions are further reduced, which leads to an increased environmental compatibility of the process.
• the problems of known borating pastes with regard to storage stability are eliminated by adding borate.
• the borate, together with the nitrite additive leads to a much easier cleaning of the components than known boron pastes.
• a particular process advantage of the boron paste according to the invention is that single-phase, Fe 2 B-containing, low-pore boride layers can be easily and easily produced on workpieces made of ferrous materials. This is due to the preferred choice of a combination of 1 to 15% by weight of potassium tetrafluoroborate and 5 to 40% by weight of calcium fluoride, based on the amount of solids in the borating paste, as the activating substance.
• the surface of the workpieces is covered with the borating paste and this is then treated at temperatures between 800 and 1100 ° C. until a boride layer of the desired size Has formed thickness.
• the surface of the parts is coated with the borating agent paste. This is particularly advantageous when a partially borated surface is desired.
• the borating agent can also be applied by immersing the parts in the paste or by spraying the paste.
• Boronation is preferably carried out at temperatures between 850 and 980 ° C. over a period of 20 minutes to 2 hours.
• single-phase Fe 2 B layers with a thickness of 30 to 150 ⁇ m can be obtained.
• the borating agent was left after the heat treatment remove easily and residue-free with water, the Components showed no corrosion attacks or stains on.
• the boride layer was FeB-free, low in pores and had one 50 ⁇ m thick.
• the paste also showed after a long time Storage at elevated temperature does not change the Processing properties.
• the pH was around 7.5.
• Example 2 (comparative example )
• the borating agent was acceptable after the heat treatment Do not remove water completely without residue, only after The components were sufficient for brushing or blasting cleaned. The components showed slight corrosion attacks and a strong spotting.
• the boride layer had a thickness of about 50 microns, but was two-phase; the FeB needles reached to a depth of 14 ⁇ m. It was opposite Example 1 to recognize stronger pore hem. After a long time Storage at elevated temperature was the viscosity of the Paste dropped and it had a stronger settling of the Solids occurred. The pH of the paste was approx. 4.
• the borating agent was left after the heat treatment remove easily and residue-free with water, the Components showed no corrosion attacks or stains on.
• the boride layer was FeB-free, low in pores and had one 70 ⁇ m thick.
• the borating agent was left after the heat treatment remove easily and residue-free with water, the Component showed no corrosion attacks or stains.
• the boride layer was FeB-free, low in pores and had one Thickness of approx. 140 ⁇ m.
• the borating agent was left after the heat treatment remove easily and residue-free with water, the Components showed no corrosion attacks or stains on.
• the boride layer was FeB-free, low in pores and had one 52 ⁇ m thick.
• the emissions of fluorine compounds were approx. 25% higher than those from example 1.
• the borating agent was left after the heat treatment remove easily and residue-free with water, the Components showed no corrosion attacks or stains on.
• the approximately 50 ⁇ m thick boride layer was two-phase, the FeB needles reached a depth of 10 ⁇ m.
• the shift was more porous than in example 5.
• the emissions of fluorine compounds were approximately 40% higher than those from example 1.

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• Chemical & Material Sciences (AREA)
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• 1999
  • 1999-02-05 DE DE19904629A patent/DE19904629C2/de not_active Expired - Lifetime
  • 1999-12-30 TR TR1999/03326A patent/TR199903326A2/xx unknown
• 2000
  • 2000-01-12 EP EP00100550A patent/EP1026282B1/de not_active Expired - Lifetime
  • 2000-01-12 AT AT00100550T patent/ATE234946T1/de active
  • 2000-01-12 DE DE50001473T patent/DE50001473D1/de not_active Expired - Lifetime
  • 2000-02-01 CZ CZ2000366A patent/CZ295247B6/cs not_active IP Right Cessation
  • 2000-02-02 BR BRPI0000249-6A patent/BR0000249B1/pt not_active IP Right Cessation
  • 2000-02-04 CA CA002298046A patent/CA2298046A1/en not_active Abandoned
  • 2000-02-04 JP JP2000028339A patent/JP4360728B2/ja not_active Expired - Lifetime

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