EP2683845B1 - Salt bath for nitriding of steel workpieces and its related production method - Google Patents
Salt bath for nitriding of steel workpieces and its related production method Download PDFInfo
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- EP2683845B1 EP2683845B1 EP12713208.2A EP12713208A EP2683845B1 EP 2683845 B1 EP2683845 B1 EP 2683845B1 EP 12713208 A EP12713208 A EP 12713208A EP 2683845 B1 EP2683845 B1 EP 2683845B1
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- EP
- European Patent Office
- Prior art keywords
- sodium
- bath
- nitriding
- alkali metal
- carbonate
- Prior art date
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- 238000005121 nitriding Methods 0.000 title claims description 49
- 229910000831 Steel Inorganic materials 0.000 title claims description 18
- 239000010959 steel Substances 0.000 title claims description 18
- 150000003839 salts Chemical class 0.000 title description 21
- 238000004519 manufacturing process Methods 0.000 title 1
- XFXPMWWXUTWYJX-UHFFFAOYSA-N Cyanide Chemical compound N#[C-] XFXPMWWXUTWYJX-UHFFFAOYSA-N 0.000 claims description 32
- 229910052708 sodium Inorganic materials 0.000 claims description 30
- 239000011734 sodium Substances 0.000 claims description 30
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 29
- 235000002639 sodium chloride Nutrition 0.000 claims description 29
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical class [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 claims description 26
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 18
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 17
- ZVCDLGYNFYZZOK-UHFFFAOYSA-M sodium cyanate Chemical compound [Na]OC#N ZVCDLGYNFYZZOK-UHFFFAOYSA-M 0.000 claims description 16
- 235000011164 potassium chloride Nutrition 0.000 claims description 15
- 229910052783 alkali metal Inorganic materials 0.000 claims description 12
- 229910052744 lithium Inorganic materials 0.000 claims description 12
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical class [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 12
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 11
- 239000001103 potassium chloride Substances 0.000 claims description 11
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 11
- 229910001514 alkali metal chloride Inorganic materials 0.000 claims description 9
- -1 alkali metal cyanates Chemical class 0.000 claims description 8
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 8
- 238000000034 method Methods 0.000 claims description 8
- 229910000288 alkali metal carbonate Inorganic materials 0.000 claims description 7
- 150000008041 alkali metal carbonates Chemical class 0.000 claims description 7
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 238000005498 polishing Methods 0.000 claims description 6
- 230000015572 biosynthetic process Effects 0.000 claims description 5
- 238000010002 mechanical finishing Methods 0.000 claims description 2
- 230000001747 exhibiting effect Effects 0.000 claims 1
- 238000011282 treatment Methods 0.000 description 25
- 229910052700 potassium Inorganic materials 0.000 description 22
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 21
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 20
- 239000011591 potassium Substances 0.000 description 20
- XLJMAIOERFSOGZ-UHFFFAOYSA-M cyanate Chemical compound [O-]C#N XLJMAIOERFSOGZ-UHFFFAOYSA-M 0.000 description 16
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 15
- 150000001805 chlorine compounds Chemical class 0.000 description 15
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 13
- 230000007797 corrosion Effects 0.000 description 12
- 238000005260 corrosion Methods 0.000 description 12
- 150000002825 nitriles Chemical class 0.000 description 12
- 150000001913 cyanates Chemical class 0.000 description 11
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 8
- 150000004767 nitrides Chemical class 0.000 description 8
- 239000012071 phase Substances 0.000 description 8
- 229910001337 iron nitride Inorganic materials 0.000 description 7
- 239000011780 sodium chloride Substances 0.000 description 7
- 235000011181 potassium carbonates Nutrition 0.000 description 6
- 150000001340 alkali metals Chemical class 0.000 description 5
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 229910000027 potassium carbonate Inorganic materials 0.000 description 5
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 230000007935 neutral effect Effects 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- 239000007921 spray Substances 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical group [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 238000005255 carburizing Methods 0.000 description 3
- 150000001768 cations Chemical class 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 238000000399 optical microscopy Methods 0.000 description 3
- GKKCIDNWFBPDBW-UHFFFAOYSA-M potassium cyanate Chemical compound [K]OC#N GKKCIDNWFBPDBW-UHFFFAOYSA-M 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 230000008929 regeneration Effects 0.000 description 3
- 238000011069 regeneration method Methods 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 150000004679 hydroxides Chemical class 0.000 description 2
- 239000003112 inhibitor Substances 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 150000002823 nitrates Chemical class 0.000 description 2
- 230000035515 penetration Effects 0.000 description 2
- 238000005482 strain hardening Methods 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- 239000011593 sulfur Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910000599 Cr alloy Inorganic materials 0.000 description 1
- 235000008612 Gnetum gnemon Nutrition 0.000 description 1
- 240000000018 Gnetum gnemon Species 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 1
- 239000012670 alkaline solution Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- WDIHJSXYQDMJHN-UHFFFAOYSA-L barium chloride Chemical compound [Cl-].[Cl-].[Ba+2] WDIHJSXYQDMJHN-UHFFFAOYSA-L 0.000 description 1
- 229910001626 barium chloride Inorganic materials 0.000 description 1
- 238000005256 carbonitriding Methods 0.000 description 1
- KXZJHVJKXJLBKO-UHFFFAOYSA-N chembl1408157 Chemical compound N=1C2=CC=CC=C2C(C(=O)O)=CC=1C1=CC=C(O)C=C1 KXZJHVJKXJLBKO-UHFFFAOYSA-N 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- XLJMAIOERFSOGZ-UHFFFAOYSA-N cyanic acid Chemical compound OC#N XLJMAIOERFSOGZ-UHFFFAOYSA-N 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 239000012948 isocyanate Substances 0.000 description 1
- 150000002513 isocyanates Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000005226 mechanical processes and functions Effects 0.000 description 1
- 238000000386 microscopy Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000001603 reducing effect Effects 0.000 description 1
- 238000009877 rendering Methods 0.000 description 1
- 229910052711 selenium Inorganic materials 0.000 description 1
- 239000011669 selenium Substances 0.000 description 1
- 150000004760 silicates Chemical class 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000011182 sodium carbonates Nutrition 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
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
- C23C8/42—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 only one element being applied
- C23C8/48—Nitriding
- C23C8/50—Nitriding of ferrous surfaces
-
- 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
- C23C8/52—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 more than one element being applied in one step
- C23C8/54—Carbo-nitriding
- C23C8/56—Carbo-nitriding of ferrous surfaces
Definitions
- the invention relates to the nitriding of mechanical parts made of steel.
- nitriding treatment sometimes accompanied by a carburation, in which case it is often referred to as nitrocarburizing.
- nitrocarburizing a nitriding treatment
- the concept of nitriding includes both nitriding alone, in a bath with a very low cyanide content (typically less than 0.5%), as well as nitrocarburization for cyanide contents above this threshold.
- This nitriding can be done from a gas phase or a plasma phase or from a liquid phase.
- Nitriding in the liquid phase has the advantage of allowing a significant hardening to a thickness of several microns in hours of barely a few hours, but has the important disadvantage of involving the use of molten salt baths, at temperatures of the order of 600 ° C (or more), containing in practice cyanides, in combination with cyanates and carbonates (the cations are in practice cations of alkali metals, such as lithium, sodium, potassium, etc ).
- the cyanates are decomposed to form in particular cyanides, carbonates and nitrogen which is thus available to diffuse into the part to be nitrided.
- low cyanide baths should consist essentially of potassium or sodium cyanates, potassium and sodium carbonates, with more potassium than sodium (which lowered the temperature of the salt baths). ); the objective was to reduce the cyanide content to no more than 5% or even 3%); the decrease in cyanide content was to be offset by cyanates; there was no particular explanation for the role of chlorides apart from the fact that, in carburizing baths, barium chloride is a melting flux.
- nitriding-carburizing baths could contain alkaline chlorides, saving cyanides and cyanates, which are much more expensive, or lowering the melting temperature; this document concerned salt baths containing from 30% to 60% of cyanides and taught to maximize the content of n-cyanates relative to isocyanates (there were no chlorides in the example described).
- carburizing baths (used at temperatures of 800 ° C to 950 ° C) containing, by weight, from 35% to 82% of alkali metal carbonates, from 15% to 35% of alkali metal cyanides, from 3% to 15% of alkali metal anhydrous silicates and up to 15% of alkaline chlorides; it was indicated that it is preferable that alkaline chlorides be present, preferably up to 10%, without giving any explanation (it seems however that the presence of chlorides has contributed to the preparation of cyanides in a usable form ).
- nitride ferrous parts To nitride ferrous parts, it has been proposed by the document US - 6,746,546 (published in 2004 ) a molten salt bath containing alkali metal cyanates and alkali metal carbonates, with 45% to 53% cyanate ion (preferably between 48% and 50%), maintained between 750 ° F and 950 ° F that is, between 400 ° C and 510 ° C, to impart good corrosion resistance.
- the alkali metals were preferably sodium and / or potassium (when both were present, the potassium content was preferably 3.9: 1 relative to the sodium content); in use, this bath contained 1% to 4% cyanide (no details were given as to the presence of any other elements in the bath).
- nitriding treatments with a low cyanide content should be followed by a finishing treatment as long as a low roughness is sought, which contributes to increasing the cost treatment (labor, polishing equipment) as well as the overall duration of treatment.
- a low roughness can be obtained with nitriding baths with a high cyanide content (more than 5%), but after periods of several hours (typically 4 to 6 hours), which may seem too long on an industrial scale.
- the subject of the invention is a nitriding bath with a low cyanide content capable of, at most of the order of a few hours, of nitriding mechanical parts made of iron or steel while giving them a very low roughness (ie without porosity significant), rendering unnecessary a subsequent mechanical recovery (polishing or tribofinishing), all for a moderate cost.
- composition ranges are generally given for a new bath, but that one seeks in practice to stay as far as possible in these ranges; thus, there is in practice no cyanide ion in the starting bath, and it is in service that one seeks to remain at not more than 3% of cyanide ions.
- the alkali metal chlorides are lithium, sodium and / or potassium chlorides, which corresponds to chlorides which have proved effective, while having a moderate cost, and not requiring heavy constraints from the point of view of handling. .
- the chloride content is between 40% and 50%, preferably at least approximately equal to 45% (+/- 2%, even +/- 1%). This range of contents has been found to lead, in a reasonable time, to good nitriding and low roughness.
- the cyanate content is between 20% and 40%, or even between 20% and 35%, preferably between 20% and 30%. Even more advantageously, this content is between 25% and 40%, or even between 25% and 35%, preferably between 25% and 30%.
- These cyanates may in particular be sodium cyanates (or potassium cyanates).
- alkali metal carbonates is from 20% to 30%, preferably from 25% to 30%.
- These carbonates may in particular be sodium, potassium and / or lithium carbonates; it is advantageously a mixture of sodium carbonate and lithium.
- the invention also proposes a process for nitriding mechanical parts made of iron or steel, according to which these parts are immersed in a bath of the aforementioned composition at a temperature of between 530 ° C. and 650 ° C. for at most 4 hours.
- the parts are immersed in the bath at a temperature of between 570 ° C. and 590 ° C. for at most 2 hours.
- the duration of a nitriding treatment is conventionally of the order of 90 minutes, but it is understood that the duration of treatment depends on the nature and / or the destination of the parts; this is how one can go from some 30 minutes for valves or tool steels, up to 4 hours when one seeks to nitride on important thicknesses (layers of several tens of micrometers of thickness), or in the case of alloy steels.
- the invention is advantageously implemented with processing times of the order of 60 to 120 minutes.
- the invention also relates to mechanical parts of iron or steel nitrided according to the aforementioned method, recognizable in particular by the absence of traces of subsequent mechanical finishing process such as polishing (including the absence of fine polishing scratches).
- compositions tested are compared with standard baths (which are the same for the various examples) which do not conform to the invention.
- the iron nitride layer thus formed had a thickness of 10 +/- 1 ⁇ m.
- composition according to the invention of this example appeared to be favorable to a good stability of the bath over time, in particular as regards the cyanide content.
- the samples thus nitrided were then oxidized in a bath of molten salts containing carbonates, hydroxides and nitrates of alkali metals.
- the purpose of this oxidation was to passivate the surface of the nitride layer forming an iron oxide layer of 1 to 3 microns thick.
- the parts were immersed in a corrosion protection oil (containing corrosion inhibitors) as is usual with nitriding processes.
- the corrosion resistance (measured on 10 neutral salt spray parts according to ISO 9227) of the samples treated according to the invention was between 150 and 250 hours.
- the corrosion resistance (measured on 10 pieces of neutral salt spray according to ISO 9227) of the samples treated in the standard bath was between 120 and 290 hours.
- a nitriding of ferrous parts made according to the invention thus makes it possible to obtain corrosion resistance comparable to that obtained with standard bath nitriding, while improving the roughness of the surfaces, compared with a treatment in such a standard bath. .
- Such a bath has proved not usable industrially since its melting temperature is greater than 600 ° C., which prevents any ferritic phase nitriding treatment (the majority of the parts are generally nitrided in the ferritic phase, ie at a temperature below 600 ° C). Only the austenitic phase nitriding is then possible, but only for temperatures above 630 ° C and with a high salt entrainment rate (high bath viscosity), which is economically unattractive.
- this composition appeared to have a higher viscosity than the composition of Example 1, which results in a greater consumption of salts.
- the degree of porosity of the nitride layers obtained according to the invention is less than 5%, whereas the degree of porosity of the nitride layers obtained with a standard bath is between 25 and 35%.
- Such a bath has proved not usable for a nitriding treatment since its liquidus temperature is greater than 600 ° C. It is recalled that the temperature of the liquidus is the temperature from which the bath is fully melted and homogeneous composition (unlike the melting temperature which is the temperature from which the bath begins to be liquid, possibly in several phases.
- the iron nitride layer formed in the bath according to the invention is of the ⁇ (Fe 2-3 N) type and has a porosity of less than 5% (measured by optical microscopy) and has a hardness of 840 ⁇ 40 HV. 0.01 .
- the iron nitride layer formed in the standard bath (not in accordance with the invention) is of the ⁇ (Fe 2-3 N) type and has a porosity of between 25 and 35% (measured by optical microscopy) and has a hardness of 700 ⁇ 40 HV 0.01 .
- a lower apparent hardness of the layers obtained with a standard bath is explained by their higher porosity rate. Indeed, it is well known that the presence of porosity (ie holes) reduces the resistance of the layers to the penetration of the indenter used for the measurement of hardness.
- the layer formed has a thickness of 10 +/- 1 ⁇ m
- the degree of porosity of the nitride layers obtained according to the invention is between 5 and 10%, whereas the degree of porosity of the nitride layers obtained with a standard bath is between 55 and 65%. It is known that cold-impacted steels have a high degree of work hardening which has a detrimental effect on the porosity of the layers (the higher the degree of work hardening, the more porous the layers). The invention makes it possible to obtain layers with a low porosity rate, even for strongly hardened steels.
- the samples thus nitrided were then oxidized in a bath of molten salts containing carbonates, hydroxides and nitrates of alkali metals.
- the purpose of this oxidation is to passivate the surface of the nitride layer forming an iron oxide layer of 1 to 3 microns thick.
- the parts are immersed in a corrosion protection oil (containing corrosion inhibitors) as is usual with nitriding processes.
- the corrosion resistance (measured on 10 pieces in neutral salt spray according to ISO 9227) of the treated samples according to the invention is between 310 and 650 hours.
- the corrosion resistance (measured on 10 pieces of neutral salt spray according to ISO 9227) of samples treated in a standard bath is between 240 and 650 hours.
- the iron nitride layer formed in the bath according to the invention is of the ⁇ (Fe 2-3 N) type and has a porosity of less than 5% (measured by optical microscopy) and has a hardness of 1020 ⁇ 40 HV. 0.01 .
- the layer of iron nitride formed in the standard bath is ⁇ -type (Fe 2-3 N) and has a porosity of between 30 and 40% (measured by light microscopy) and has a hardness of 830 ⁇ 40 HV 0 , 01 .
- a lower apparent hardness of the layers obtained with a standard bath is explained by their higher porosity rate. Indeed, it is well known that the presence of porosity (ie holes) reduces the resistance of the layers to the penetration of the indenter used for the measurement of hardness.
- compositions indicated in the abovementioned examples define the new bath, it being specified that the indications of contents for the cyanide ions are valid in service, taking into account the reactions occurring during the nitriding (it is then sought to maintain the composition bath as stable as possible).
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Description
L'invention concerne la nitruration de pièces mécaniques en acier.The invention relates to the nitriding of mechanical parts made of steel.
Par pièces mécaniques on entend des pièces destinées à assurer, en service, une fonction mécanique, ce qui implique généralement que ces pièces aient une dureté importante, une bonne résistance à la corrosion et à l'usure ; on peut ainsi citer, de manière non exhaustive :
- des axes d'essuie-glace,
- des tiges de vérin hydraulique ou à gaz,
- des soupapes de moteur à combustion,
- des bagues d'articulation.
- wiper shafts,
- hydraulic or gas cylinder rods,
- combustion engine valves,
- hinge rings.
La gamme des aciers dans lesquels ces pièces sont réalisées, au moins à proximité de leur surface susceptible de subir du frottement ou de la corrosion, est large, allant des aciers non alliés à des alliages dits inoxydables, notamment des alliages au chrome ou au nickel.The range of steels in which these parts are made, at least close to their surface susceptible to friction or corrosion, is wide, ranging from unalloyed steels to so-called stainless alloys, especially chromium or nickel alloys. .
Pour durcir superficiellement de telles pièces, il est connu d'appliquer un traitement de nitruration (parfois accompagné d'une carburation, auquel cas on parle volontiers de nitrocarburation). En fait, la notion de nitruration englobe à la fois la nitruration seule, dans un bain à très faible teneur en cyanures (typiquement inférieure à 0,5%), ainsi que la nitrocarburation pour des teneurs en cyanures supérieures à ce seuil. Dans la suite on regroupe ces deux types de traitement sous le terme de nitruration.To surface harden such parts, it is known to apply a nitriding treatment (sometimes accompanied by a carburation, in which case it is often referred to as nitrocarburizing). In fact, the concept of nitriding includes both nitriding alone, in a bath with a very low cyanide content (typically less than 0.5%), as well as nitrocarburization for cyanide contents above this threshold. In the following we group these two types of treatment under the term nitriding.
Cette nitruration peut se faire à partir d'une phase gazeuse ou d'une phase plasma ou à partir d'une phase liquide.This nitriding can be done from a gas phase or a plasma phase or from a liquid phase.
La nitruration en phase liquide a pour avantage de permettre un durcissement important sur une épaisseur de plusieurs microns en des temps d'à peine quelques heures, mais a pour inconvénient important d'impliquer de mettre en oeuvre des bains de sels fondus, à des températures de l'ordre de 600°C (voire plus), contenant en pratique des cyanures, en combinaison avec des cyanates et des carbonates (les cations sont en pratique des cations de métaux alcalins, tels que le lithium, le sodium, le potassium, etc...). En pratique les cyanates se décomposent pour former notamment des cyanures, des carbonates et de l'azote qui est ainsi disponible pour diffuser dans la pièce à nitrurer. Du fait de la consommation des cyanates et de l'enrichissement en carbonates, il faut prévoir une régénération des bains par introduction de compléments permettant de ramener leurs teneurs en cyanures et en cyanates dans des gammes en garantissant l'efficacité. Dans la suite, les teneurs des bains sont exprimées en pourcentage en poids.Nitriding in the liquid phase has the advantage of allowing a significant hardening to a thickness of several microns in hours of barely a few hours, but has the important disadvantage of involving the use of molten salt baths, at temperatures of the order of 600 ° C (or more), containing in practice cyanides, in combination with cyanates and carbonates (the cations are in practice cations of alkali metals, such as lithium, sodium, potassium, etc ...). In practice the cyanates are decomposed to form in particular cyanides, carbonates and nitrogen which is thus available to diffuse into the part to be nitrided. Due to the consumption of cyanates and the enrichment of carbonates, it is necessary to provide a regeneration of baths by introduction of supplements to reduce their cyanide and cyanate contents in ranges ensuring efficiency. In the following, the contents of the baths are expressed in percentage by weight.
Or, ainsi qu'on le sait, la mise en oeuvre de cyanures est dangereuse pour les opérateurs ainsi que pour l'environnement, de sorte que cela fait des décennies qu'on cherche à minimiser la quantité de cyanures à mettre en oeuvre dans les procédés de nitruration de pièces mécaniques en acier en bains de sels fondus.However, as we know, the use of cyanide is dangerous for the operators as well as for the environment, so it has been decades since we wanted to minimize the amount of cyanide to be used in nitriding processes of mechanical steel parts in molten salt baths.
Ainsi, dès les années 1974-75, il a été proposé de chercher à minimiser la teneur en cyanures des bains de nitruration, notamment en évitant les produits toxiques au moment de la régénération, (
Préalablement (voir le document
Il avait également été mentionné (voir le document
Pour la nitruration d'aciers inoxydables, il a été proposé (
Plus récemment, il a été proposé (voir notamment le document
Il a aussi été proposé de durcir des pièces ferreuses en utilisant un bain contenant de fortes teneurs en chlorures (voir le document
Pour nitrurer des pièces ferreuses, il a été proposé par le document
Encore plus récemment, en vue de minimiser l'entraînement des sels fondus à la sortie de pièces ferreuses nitrurées, le document
Il apparaît ainsi que diverses compositions de bains de sels fondus ont été proposées en vue de permettre une nitruration de pièces ferreuses sans mettre en oeuvre de teneurs significatives en cyanures.It thus appears that various molten salt bath compositions have been proposed with a view to enabling nitriding of ferrous parts without implementing significant levels of cyanides.
Toutefois, en règle générale, les traitements de nitruration à faible teneur en cyanures (moins de 3%, typiquement) doivent être suivis d'un traitement de finition dès lors que l'on recherche une faible rugosité, ce qui contribue à augmenter le coût de traitement (main d'oeuvre, équipements de polissage) ainsi que la durée globale de traitement.However, as a general rule, nitriding treatments with a low cyanide content (typically less than 3%) should be followed by a finishing treatment as long as a low roughness is sought, which contributes to increasing the cost treatment (labor, polishing equipment) as well as the overall duration of treatment.
Une faible rugosité peut être obtenue avec des bains de nitruration à forte teneur en cyanures (plus de 5 %), mais après des durées de plusieurs heures (typiquement 4 à 6 heures), ce qui peut paraître trop long à l'échelle industrielle.A low roughness can be obtained with nitriding baths with a high cyanide content (more than 5%), but after periods of several hours (typically 4 to 6 hours), which may seem too long on an industrial scale.
L'invention a pour objet un bain de nitruration à faible teneur en cyanures capable, en au plus de l'ordre de quelques heures, de nitrurer des pièces mécaniques en fer ou en acier tout en leur conférant une rugosité très faible (donc sans porosité significative), rendant inutile une reprise mécanique ultérieure (par polissage ou tribofinition), le tout pour un coût modéré.The subject of the invention is a nitriding bath with a low cyanide content capable of, at most of the order of a few hours, of nitriding mechanical parts made of iron or steel while giving them a very low roughness (ie without porosity significant), rendering unnecessary a subsequent mechanical recovery (polishing or tribofinishing), all for a moderate cost.
L'invention propose à cet effet un bain de nitruration selon la revendication 1 essentiellement constitué (les teneurs sont exprimées en poids) :
- de 40% à 60% de chlorures de métal alcalin,
- de 10% à 40% de carbonates de métal alcalin, et
- de 20% à 40% de cyanates de métal alcalin,
- un maximum de 3% d'ions cyanures (formés en service),
- from 40% to 60% of alkali metal chlorides,
- from 10% to 40% of alkali metal carbonates, and
- from 20% to 40% of alkali metal cyanates,
- a maximum of 3% cyanide ion (formed in service),
Il mérite d'être noté que les plages de composition sont généralement données pour un bain neuf, mais que l'on cherche en pratique à rester autant que possible dans ces plages ; ainsi, il n'y a en pratique aucun ion cyanure dans le bain de départ, et c'est en service qu'on cherche à rester à pas plus de 3% d'ions cyanures.It should be noted that the composition ranges are generally given for a new bath, but that one seeks in practice to stay as far as possible in these ranges; thus, there is in practice no cyanide ion in the starting bath, and it is in service that one seeks to remain at not more than 3% of cyanide ions.
La présence selon l'invention de composés chlorés en quantité significative (NaCl, KCl, LiCl, ...) permet d'obtenir lors de la nitruration des couches non poreuses, non poudreuses et donc peu rugueuses, après des durées de traitement d'à peine de l'ordre d'une à deux heures ; les chlorures étant moins chers que les autres composants habituels des bains de nitruration, un bain selon l'invention est donc plus économique qu'un bain standard, tout en évitant d'avoir recours à un traitement ultérieur de polissage. On peut rappeler que des temps de traitement d'au plus de l'ordre de deux heures (2h +/-5mn) sont considérés comme des temps compatibles avec des rendements satisfaisants à l'échelle industrielle.The presence according to the invention of chlorine compounds in a significant amount (NaCl, KCl, LiCl,...) Makes it possible to obtain, during nitriding, non-porous, non-powdery and therefore not very rough layers, after treatment times of barely of the order of one to two hours; the chlorides being less expensive than the other usual components of nitriding baths, a bath according to the invention is therefore more economical than a standard bath, while avoiding the need for a subsequent polishing treatment. It can be recalled that processing times of at most about two hours (2h +/- 5mn) are considered as times compatible with satisfactory yields on an industrial scale.
On peut noter que, dans les bains utilisés dans le passé, il avait déjà été proposé de combiner des cyanates et des carbonates avec des chlorures dans des bains de nitruration, y compris lorsqu'ils sont sensiblement dépourvus de cyanures, mais les chlorures (dont aucun rôle n'était reconnu dans la nitruration) n'apparaissaient pas en pratique à des teneurs supérieures à 10-15% en l'absence de cyanures (ou avec des teneurs faibles en ions cyanures, typiquement inférieures ou égales à 3%). En outre, aucun document n'avait suggéré la moindre corrélation entre la présence de chlorures et la rugosité finale.It may be noted that, in baths used in the past, it had already been proposed to combine cyanates and carbonates with chlorides in nitriding baths, including when they are substantially free of cyanides, but chlorides (of which no role was recognized in nitriding) did not appear in practice at levels greater than 10-15% in the absence of cyanides (or with low levels of cyanide ions, typically less than or equal to 3%). In addition, no document suggested any correlation between the presence of chlorides and the final roughness.
Les chlorures de métal alcalin sont des chlorures de lithium, de sodium et/ou de potassium, ce qui correspond à des chlorures qui se sont révélés efficaces, tout en ayant un coût modéré, et ne nécessitant pas de contraintes lourdes du point de vue manutention.The alkali metal chlorides are lithium, sodium and / or potassium chlorides, which corresponds to chlorides which have proved effective, while having a moderate cost, and not requiring heavy constraints from the point of view of handling. .
De manière avantageuse, la teneur en chlorures est comprise entre 40% et 50%, de préférence au moins approximativement égale à 45% (+/-2%, voire +/- 1%). Cette plage de teneurs s'est révélée aboutir, en un temps raisonnable, à une bonne nitruration et à une rugosité faible.Advantageously, the chloride content is between 40% and 50%, preferably at least approximately equal to 45% (+/- 2%, even +/- 1%). This range of contents has been found to lead, in a reasonable time, to good nitriding and low roughness.
On comprend que :
- la teneur en cyanates doit être suffisante pour permettre un effet de nitruration,
- la teneur en carbonates ne doit pas devenir trop importante au risque d'empêcher les réactions chimiques qui conduisent à la nitruration.
- the cyanate content must be sufficient to allow a nitriding effect,
- the carbonates content must not become too high at the risk of preventing the chemical reactions that lead to nitriding.
C'est ainsi que la teneur en cyanates est comprise entre 20% et 40%, voire entre 20% et 35%, de préférence comprise entre 20% et 30%. De manière encore plus avantageuse, cette teneur est comprise entre 25% et 40%, voire entre 25% et 35%, de préférence comprise entre 25% et 30%. Ces cyanates peuvent notamment être des cyanates de sodium (ou des cyanates de potassium).Thus, the cyanate content is between 20% and 40%, or even between 20% and 35%, preferably between 20% and 30%. Even more advantageously, this content is between 25% and 40%, or even between 25% and 35%, preferably between 25% and 30%. These cyanates may in particular be sodium cyanates (or potassium cyanates).
De manière également avantageuse, la teneur en carbonates de métal alcalin est de 20% à 30%, de préférence comprise entre 25% et 30%. Ces carbonates peuvent notamment être des carbonates de sodium, de potassium et/ou de lithium ; il s'agit avantageusement d'un mélange de carbonates de sodium et de lithium.Also advantageously, the content of alkali metal carbonates is from 20% to 30%, preferably from 25% to 30%. These carbonates may in particular be sodium, potassium and / or lithium carbonates; it is advantageously a mixture of sodium carbonate and lithium.
Ainsi, de manière particulièrement avantageuse, le bain de sels fondus est essentiellement constitué de (à +/- 2%, voire +/- 1% près) :
- 25% à 30% de cyanate de sodium,
- 25% à 30% de carbonates de sodium et de lithium,
- 40% à 50% de chlorures de potassium,
- un maximum de 3% d'ions cyanures (formés en service),
- 25% to 30% sodium cyanate,
- 25% to 30% of sodium and lithium carbonates,
- 40% to 50% potassium chloride,
- a maximum of 3% cyanide ion (formed in service),
De manière préférée, le bain de sels fondus est essentiellement constitué, avant formation de cyanures jusqu'à un maximum de 3, de (à +/- 2%, voire +/- 1% près) :
- 28% de cyanate de sodium,
- 22% de carbonate de sodium,
- 5% de carbonate lithium,
- 45% de chlorure de potassium,
- 28% sodium cyanate,
- 22% sodium carbonate,
- 5% lithium carbonate,
- 45% potassium chloride,
L'invention propose également un procédé de nitruration de pièces mécaniques en fer ou en acier, selon lequel on immerge ces pièces dans un bain de composition précitée, à une température comprise entre 530°C et 650°C pendant au plus 4h.The invention also proposes a process for nitriding mechanical parts made of iron or steel, according to which these parts are immersed in a bath of the aforementioned composition at a temperature of between 530 ° C. and 650 ° C. for at most 4 hours.
De manière préférée, les pièces sont immergées dans le bain à une température comprise entre 570°C et 590°C pendant au plus 2h.Preferably, the parts are immersed in the bath at a temperature of between 570 ° C. and 590 ° C. for at most 2 hours.
En pratique, la durée d'un traitement de nitruration est classiquement de l'ordre de 90 minutes, mais on comprend que la durée de traitement dépend de la nature et/ou de la destination des pièces ; c'est ainsi qu'on peut aller de quelques 30 minutes pour des soupapes ou des aciers à outils, jusqu'à 4 h lorsque l'on cherche à nitrurer sur des épaisseurs importantes (couches de plusieurs dizaines de micromètres d'épaisseur), ou dans le cas d'aciers alliés. Toutefois, l'invention est avantageusement mise en oeuvre avec des temps de traitement de l'ordre de 60 à 120 minutes.In practice, the duration of a nitriding treatment is conventionally of the order of 90 minutes, but it is understood that the duration of treatment depends on the nature and / or the destination of the parts; this is how one can go from some 30 minutes for valves or tool steels, up to 4 hours when one seeks to nitride on important thicknesses (layers of several tens of micrometers of thickness), or in the case of alloy steels. However, the invention is advantageously implemented with processing times of the order of 60 to 120 minutes.
L'invention concerne également des pièces mécaniques en fer ou en acier nitrurées selon le procédé précité, reconnaissables notamment par l'absence de traces de procédé ultérieur de finition mécanique tel que polissage (notamment l'absence de fines rayures de polissage).The invention also relates to mechanical parts of iron or steel nitrided according to the aforementioned method, recognizable in particular by the absence of traces of subsequent mechanical finishing process such as polishing (including the absence of fine polishing scratches).
Dans la suite, les compositions testées sont comparées à des bains standard (qui sont les mêmes pour les divers exemples) qui ne sont pas conformes à l'invention.In the following, the compositions tested are compared with standard baths (which are the same for the various examples) which do not conform to the invention.
Des échantillons en un acier de type C45 recuit, pouvant être utilisé pour des axes d'essuie-glace, des tiges de vérin hydraulique ou à gaz, ou des bagues d'articulation, ont été traités comme suit.Samples of annealed C45 type steel, usable for wiper shafts, hydraulic or gas cylinder rods, or hinge rings, were treated as follows.
Ces échantillons ont fait l'objet d'un dégraissage dans une solution alcaline, d'un rinçage à l'eau puis d'un préchauffage à 350°C.These samples were degreased in an alkaline solution, rinsed with water and then preheated to 350 ° C.
Ils ont ensuite été immergés, pendant 60 min, dans un bain de sels fondus maintenu à 580°C et contenant :
- 28% de cyanate de sodium,
- 22% de carbonate de sodium, et
- 45% de chlorures de potassium
- 5% de carbonate de lithium.
- 28% sodium cyanate,
- 22% sodium carbonate, and
- 45% potassium chlorides
- 5% lithium carbonate.
Les échantillons ainsi nitrurés ont ensuite été rincés à l'eau.The samples thus nitrided were then rinsed with water.
Des échantillons identiques ont fait l'objet du même traitement, à ceci près que le traitement de nitruration de 60 mn à 580°C a été fait dans un bain de nitruration standard (non-conforme à l'invention) essentiellement constitué de :
- 58% de cyanate de sodium,
- 36% de carbonate de potassium, et
- 6% de carbonate de lithium
- 58% sodium cyanate,
- 36% potassium carbonate, and
- 6% lithium carbonate
Dans les deux cas, la couche de nitrures de fer ainsi formée a eu une épaisseur de 10+/-1 µm.In both cases, the iron nitride layer thus formed had a thickness of 10 +/- 1 μm.
Il a été constaté que, la rugosité des échantillons ayant été initialement de Ra = 0.2 micromètres, elle est devenue Ra = 0.52 micromètres après le traitement dans un bain standard mais Ra = 0.25 micromètres après le traitement dans le bain selon l'invention, c'est-à-dire une rugosité à peine supérieure à la rugosité de départ.It was found that, the roughness of the samples having been initially of Ra = 0.2 micrometers, it became Ra = 0.52 micrometers after the treatment in a standard bath but Ra = 0.25 micrometers after the treatment in the bath according to the invention, c that is to say a roughness barely greater than the initial roughness.
La composition conforme à l'invention de cet exemple est apparue être favorable à une bonne stabilité du bain au cours du temps, en particulier en ce qui concerne le taux de cyanures.The composition according to the invention of this example appeared to be favorable to a good stability of the bath over time, in particular as regards the cyanide content.
Les échantillons ainsi nitrurés ont été ensuite oxydés dans un bain de sels fondus contenant des carbonates, des hydroxydes et des nitrates de métaux alcalins. Le but de cette oxydation a été de passiver la surface de la couche de nitrure en formant une couche d'oxyde de fer de 1 à 3 µm d'épaisseur. Après oxydation, les pièces ont été immergées dans une huile de protection contre la corrosion (contenant des inhibiteurs de corrosion) comme il est d'usage avec les procédés de nitruration.The samples thus nitrided were then oxidized in a bath of molten salts containing carbonates, hydroxides and nitrates of alkali metals. The purpose of this oxidation was to passivate the surface of the nitride layer forming an iron oxide layer of 1 to 3 microns thick. After oxidation, the parts were immersed in a corrosion protection oil (containing corrosion inhibitors) as is usual with nitriding processes.
La résistance à la corrosion (mesurée sur 10 pièces en brouillard salin neutre suivant la norme ISO 9227) des échantillons traités suivant l'invention a été comprise entre 150 et 250 heures.The corrosion resistance (measured on 10 neutral salt spray parts according to ISO 9227) of the samples treated according to the invention was between 150 and 250 hours.
La résistance à la corrosion (mesurée sur 10 pièces en brouillard salin neutre suivant la norme ISO 9227) des échantillons traités dans le bain standard a été comprise entre 120 et 290 heures.The corrosion resistance (measured on 10 pieces of neutral salt spray according to ISO 9227) of the samples treated in the standard bath was between 120 and 290 hours.
Une nitruration de pièces ferreuses réalisée suivant l'invention permet donc bien d'obtenir une résistance à la corrosion comparable à celle obtenue avec une nitruration en bain standard, tout en améliorant la rugosité des surfaces, par rapport à un traitement dans un tel bain standard.A nitriding of ferrous parts made according to the invention thus makes it possible to obtain corrosion resistance comparable to that obtained with standard bath nitriding, while improving the roughness of the surfaces, compared with a treatment in such a standard bath. .
Des échantillons en acier C45 recuits, préparés comme précédemment, ont été nitrurés pendant 1 heure à 590°C dans un bain contenant :
- 20 % de chlorures de métal alcalin (NaCl, KCI)
- 40 % de cyanate de sodium
- 30 % de carbonate de potassium
- 10 % de carbonate de lithium
- 20% alkali metal chlorides (NaCl, KCl)
- 40% sodium cyanate
- 30% potassium carbonate
- 10% lithium carbonate
Dans les deux cas, la couche formée a une épaisseur de 10 +/- 1 µm
Il a été constaté que, la rugosité des échantillons ayant été initialement de Ra = 0.2 micromètres, elle est devenue Ra = 0.48 micromètres après le traitement dans ce bain contre Ra = 0.52 micromètres après le traitement dans un bain standard.In both cases, the layer formed has a thickness of 10 +/- 1 μm
It was found that, the roughness of the samples having been initially of Ra = 0.2 micrometers, it became Ra = 0.48 micrometers after the treatment in this bath against Ra = 0.52 micrometers after the treatment in a standard bath.
Cela conduit à conclure qu'une teneur trop faible en chlorures ne permet pas de faire baisser la rugosité finale des pièces de façon significative par rapport à un bain standard (non conforme à l'invention).This leads to the conclusion that a too low chlorides content does not make it possible to lower the final roughness of the parts significantly compared to a standard bath (not in accordance with the invention).
Il a été préparé un bain contenant
- 65 % de chlorure de sodium
- 25 % de cyanate de potassium
- 10 % de carbonate de potassium.
- 65% sodium chloride
- 25% potassium cyanate
- 10% potassium carbonate.
Un tel bain s'est révélé non utilisable industriellement puisque sa température de fusion est supérieure à 600°C, ce qui empêche de réaliser tout traitement de nitruration en phase ferritique (la majorité des pièces est généralement nitrurée en phase ferritique, c'est à dire à une température inférieure à 600°C). Seule la nitruration en phase austénitique est alors envisageable, mais uniquement pour des températures supérieures à 630°C et avec un fort taux d'entraînement de sels (viscosité du bain élevée), ce qui est économiquement peu intéressant.Such a bath has proved not usable industrially since its melting temperature is greater than 600 ° C., which prevents any ferritic phase nitriding treatment (the majority of the parts are generally nitrided in the ferritic phase, ie at a temperature below 600 ° C). Only the austenitic phase nitriding is then possible, but only for temperatures above 630 ° C and with a high salt entrainment rate (high bath viscosity), which is economically unattractive.
Le traitement d'échantillons en C45 recuits, dans des conditions similaires à celles de l'exemple 1, mais dans un bain contenant
- 35 % de cyanate de sodium
- 20 % de carbonate de sodium
- 20 % de carbonate de potassium
- 25 % de chlorure de potassium
- 35% sodium cyanate
- 20% sodium carbonate
- 20% potassium carbonate
- 25% potassium chloride
Quoique satisfaisante du point de vue rugosité, cette composition est apparue avoir une viscosité plus importante que la composition de l'exemple 1, ce qui se traduit par une consommation de sels plus importante.Although satisfactory from the point of view of roughness, this composition appeared to have a higher viscosity than the composition of Example 1, which results in a greater consumption of salts.
Le taux de porosité des couches de nitrures obtenues suivant l'invention est inférieur à 5 %, alors que le taux de porosité des couches de nitrures obtenues avec un bain standard est compris entre 25 et 35 %.The degree of porosity of the nitride layers obtained according to the invention is less than 5%, whereas the degree of porosity of the nitride layers obtained with a standard bath is between 25 and 35%.
Il a été préparé un bain contenant
- 45 % de chlorure de potassium
- 10 % de cyanate de sodium
- 45 % de carbonate de sodium.
- 45% potassium chloride
- 10% sodium cyanate
- 45% sodium carbonate.
Un tel bain s'est révélé non utilisable pour un traitement de nitruration puisque sa température de liquidus est supérieure à 600 °C. Il est rappelé que la température du liquidus est la température à partir de laquelle le bain est entièrement fondu et homogène en composition (à la différence de la température de fusion qui est la température à partir de laquelle le bain commence à être liquide, éventuellement en plusieurs phases.Such a bath has proved not usable for a nitriding treatment since its liquidus temperature is greater than 600 ° C. It is recalled that the temperature of the liquidus is the temperature from which the bath is fully melted and homogeneous composition (unlike the melting temperature which is the temperature from which the bath begins to be liquid, possibly in several phases.
Comme expliqué dans l'exemple 3, un tel bain ne peut être utilisé industriellement de façon avantageuse car il rend impossible tout traitement en phase ferritique et les entraînements de sels entre 600 et 650°C sont très importants.As explained in Example 3, such a bath can not be used industrially advantageously because it makes impossible any ferritic phase treatment and salt entrainment between 600 and 650 ° C are very important.
Le traitement d'échantillons en C45 recuits, dans des conditions similaires à celles de l'exemple 1, mais dans un bain contenant :
- 45 % de chlorure de potassium
- 30 % de cyanate de sodium
- 25 % de carbonate de sodium
- 45% potassium chloride
- 30% sodium cyanate
- 25% sodium carbonate
La couche de nitrure de fer formée dans le bain suivant l'invention est de type ε (Fe2-3N) et a un taux de porosité inférieur à 5 % (mesuré par microscopie optique) et a une dureté de 840 ± 40 HV0,01.The iron nitride layer formed in the bath according to the invention is of the ε (Fe 2-3 N) type and has a porosity of less than 5% (measured by optical microscopy) and has a hardness of 840 ± 40 HV. 0.01 .
La couche de nitrure de fer formée dans le bain standard (non-conforme à l'invention) est de type ε (Fe2-3N) et a un taux de porosité compris entre 25 et 35 % (mesuré par microscopie optique) et a une dureté de 700 ± 40 HV0,01. Une plus faible dureté apparente des couches obtenues avec un bain standard s'explique par leur taux de porosité plus important. En effet, il est bien connu que la présence de porosité (c'est à dire des trous) réduit la résistance des couches à la pénétration de l'indenteur utilisé pour la mesure de dureté.The iron nitride layer formed in the standard bath (not in accordance with the invention) is of the ε (Fe 2-3 N) type and has a porosity of between 25 and 35% (measured by optical microscopy) and has a hardness of 700 ± 40 HV 0.01 . A lower apparent hardness of the layers obtained with a standard bath is explained by their higher porosity rate. Indeed, it is well known that the presence of porosity (ie holes) reduces the resistance of the layers to the penetration of the indenter used for the measurement of hardness.
Dans les deux cas, la couche formée a une épaisseur de 10 +/- 1 µmIn both cases, the layer formed has a thickness of 10 +/- 1 μm
Des échantillons en C45 usinés par frappe à froid puis ayant subi une trempe hyper fréquence avec une rugosité initiale de Ra = 0,74 µm ont été nitrurés (après une préparation similaire à celle de l'exemple 1) pendant deux heures à 590°C dans un bain identique à celui de l'exemple 1, contenant :
- 28 % de cyanate de sodium
- 22 % de carbonate de sodium
- 45 % de chlorure de potassium
- 5 % de carbonate de lithium
- 28% sodium cyanate
- 22% sodium carbonate
- 45% potassium chloride
- 5% lithium carbonate
Une couche de 20 +/- 1 µm a été formée avec une rugosité finale de Ra = 0,79 µm. En comparaison, des échantillons identiques qui ont été traités pendant la même durée, deux heures, dans un bain standard (non-conforme à l'invention) ont une couche une rugosité finale de Ra = 1,23 µm pour une couche de 17 +/- 1 µm d'épaisseur.A layer of 20 +/- 1 μm was formed with a final roughness of Ra = 0.79 μm. In comparison, identical samples which have been treated for the same duration, two hours, in a standard bath (not in accordance with the invention) have a final roughness layer of Ra = 1.23 μm for a layer of 17 + / - 1 μm thick.
Le taux de porosité des couches de nitrures obtenues suivant l'invention est compris entre 5 et 10 %, alors que le taux de porosité des couches de nitrures obtenues avec un bain standard est compris entre 55 et 65 %. Il est connu que les aciers ayant subi une frappe à froid ont un taux d'écrouissage important qui a un effet néfaste sur la porosité des couches (plus le taux d'écrouissage est important, plus les couches sont poreuses). L'invention permet d'obtenir des couches avec un faible taux de porosité, même pour des aciers fortement écrouis.The degree of porosity of the nitride layers obtained according to the invention is between 5 and 10%, whereas the degree of porosity of the nitride layers obtained with a standard bath is between 55 and 65%. It is known that cold-impacted steels have a high degree of work hardening which has a detrimental effect on the porosity of the layers (the higher the degree of work hardening, the more porous the layers). The invention makes it possible to obtain layers with a low porosity rate, even for strongly hardened steels.
Les échantillons ainsi nitrurés ont été ensuite oxydés dans un bain de sels fondus contenant des carbonates, des hydroxydes et des nitrates de métaux alcalins. Le but de cette oxydation est de passiver la surface de la couche de nitrure en formant une couche d'oxyde de fer de 1 à 3 µm d'épaisseur. Après oxydation, les pièces sont immergées dans une huile de protection contre la corrosion (contenant des inhibiteurs de corrosion) comme il est d'usage avec les procédés de nitruration.The samples thus nitrided were then oxidized in a bath of molten salts containing carbonates, hydroxides and nitrates of alkali metals. The purpose of this oxidation is to passivate the surface of the nitride layer forming an iron oxide layer of 1 to 3 microns thick. After oxidation, the parts are immersed in a corrosion protection oil (containing corrosion inhibitors) as is usual with nitriding processes.
La résistance à la corrosion (mesurée sur 10 pièces en brouillard salin neutre suivant la norme ISO 9227) des échantillons traités suivant l'invention est comprise entre 310 et 650 heures.The corrosion resistance (measured on 10 pieces in neutral salt spray according to ISO 9227) of the treated samples according to the invention is between 310 and 650 hours.
La résistance à la corrosion (mesurée sur 10 pièces en brouillard salin neutre suivant la norme ISO 9227) des échantillons traités dans un bain standard est comprise entre 240 et 650 heures.The corrosion resistance (measured on 10 pieces of neutral salt spray according to ISO 9227) of samples treated in a standard bath is between 240 and 650 hours.
Des échantillons en 42CrMo4 trempés-revenus puis rectifiés avec une rugosité initiale de Ra = 0,34 µm ont été nitrurés (après une préparation similaire à celle de l'exemple 1) comme ceux de l'exemple 7, c'est-à-dire pendant deux heures à 590°C dans un bain identique à celui de l'exemple 1, contenant :
- 28 % de cyanate de sodium
- 22 % de carbonate de sodium
- 45 % de chlorure de potassium
- 5 % de carbonate de lithium
- 28% sodium cyanate
- 22% sodium carbonate
- 45% potassium chloride
- 5% lithium carbonate
Une couche de nitrure de fer de 16 +/- 1 µm a été formée avec une rugosité finale de Ra = 0,44 µm. En comparaison, des échantillons identiques qui ont été traités deux heures dans un bain standard (non-conforme à l'invention) ont une couche de nitrures de fer avec une rugosité finale de Ra = 0,85 µm pour une couche de 14 +/- 1 µm d'épaisseur.An iron nitride layer of 16 +/- 1 μm was formed with a final roughness of Ra = 0.44 μm. In comparison, identical samples which have been treated for two hours in a standard bath (not in accordance with the invention) have a layer of iron nitrides with a final roughness of Ra = 0.85 μm for a layer of 14 + / cm. - 1 μm thick.
La couche de nitrure de fer formée dans le bain suivant l'invention est de type ε (Fe2-3N) et a un taux de porosité inférieur à 5 % (mesuré par microscopie optique) et a une dureté de 1020 ± 40 HV0,01.The iron nitride layer formed in the bath according to the invention is of the ε (Fe 2-3 N) type and has a porosity of less than 5% (measured by optical microscopy) and has a hardness of 1020 ± 40 HV. 0.01 .
La couche de nitrure de fer formée dans le bain standard est de type ε (Fe2-3N) et a un taux de porosité compris entre 30 et 40 % (mesuré par microscopie optique) et a une dureté de 830 ± 40 HV0,01. Une plus faible dureté apparente des couches obtenues avec un bain standard s'explique par leur taux de porosité plus important. En effet, il est bien connu que la présence de porosité (c'est à dire des trous) réduit la résistance des couches à la pénétration de l'indenteur utilisé pour la mesure de dureté.The layer of iron nitride formed in the standard bath is ε-type (Fe 2-3 N) and has a porosity of between 30 and 40% (measured by light microscopy) and has a hardness of 830 ± 40 HV 0 , 01 . A lower apparent hardness of the layers obtained with a standard bath is explained by their higher porosity rate. Indeed, it is well known that the presence of porosity (ie holes) reduces the resistance of the layers to the penetration of the indenter used for the measurement of hardness.
Des échantillons en C45 recuits avec une rugosité initiale de Ra = 0,20 µm ont été préparés et nitrurés comme dans l'exemple 1, c'est à dire pendant 1 heure à 580°C dans un bain contenant :
- 28 % de cyanate de sodium
- 22 % de carbonate de sodium
- 45 % de chlorure de potassium
- 5 % de carbonate de lithium
- 28% sodium cyanate
- 22% sodium carbonate
- 45% potassium chloride
- 5% lithium carbonate
Une couche de 10 +/- 1 µm a été formée avec une rugosité finale de Ra = 0,25 µm. En comparaison, des échantillons identiques qui ont été traités trois heures dans un bain standard fonctionnant avec un taux de cyanures élevé (5,2 %) ont une couche une rugosité finale de Ra = 0,27 µm pour une couche de 7 +/- 1 µm d'épaisseur.A 10 +/- 1 μm layer was formed with a final roughness of Ra = 0.25 μm. In comparison, identical samples which have been treated for three hours in a standard bath with a high cyanide level (5.2%) have a final roughness layer of Ra = 0.27 μm for a layer of 7 +/- 1 μm thick.
Il apparaît ainsi qu'à rugosité finale équivalente, bien que le temps de traitement soit plus important, l'épaisseur des couches obtenues dans un bain standard à taux de cyanure élevé est plus faible que l'épaisseur des couches obtenues dans un bain suivant l'invention. Ceci est expliqué par le fait que, en plus d'être plus polluant, un bain à forte teneur en cyanure est également carburant, c'est à dire que du carbone va diffuser conjointement à l'azote dans l'acier. Or, le carbone et l'azote sont en compétition lors de la diffusion puisqu'ils occupent les mêmes sites dans le réseau cristallin du fer. La présence de carbone limitera donc la diffusion de l'azote, ce qui entraînera des couches de plus faible épaisseur.It thus appears that at equivalent final roughness, although the treatment time is greater, the thickness of the layers obtained in a standard bath with a high cyanide content is lower than the thickness of the layers obtained in a bath following 'invention. This is explained by the fact that, in addition to being more polluting, a bath with a high cyanide content is also fuel, that is to say that carbon will diffuse together with nitrogen in the steel. However, carbon and nitrogen compete during diffusion because they occupy the same sites in the crystal lattice of iron. The presence of carbon will limit the diffusion of nitrogen, which will result in layers of smaller thickness.
Comme indiqué ci-dessus, les compositions indiquées dans les exemples précités définissent le bain neuf, étant précisé que les indications de teneurs pour les ions cyanures valent en service, compte tenu des réactions intervenant lors de la nitruration (on cherche alors à maintenir la composition du bain aussi stable que possible).As indicated above, the compositions indicated in the abovementioned examples define the new bath, it being specified that the indications of contents for the cyanide ions are valid in service, taking into account the reactions occurring during the nitriding (it is then sought to maintain the composition bath as stable as possible).
Claims (11)
- Molten-salt bath for nitriding mechanical parts made of steel, essentially constituted by (the contents are expressed by weight):- 40% to 60% alkali metal chlorides,- 10% to 40% alkali metal carbonates, and- 20% to 40% alkali metal cyanates,- a maximum of 3% cyanide ions,the total of the contents being 100%,
in which the alkali metal chlorides are lithium, sodium and/or potassium chlorides. - Molten-salt bath according to claim 1, in which the alkali metal chloride content is comprised between 40% and 50%.
- Molten-salt bath according to claim 2, in which the alkali metal chloride content is at least approximately equal to 45%.
- Molten-salt bath according to any one of claims 1 to 3, in which the alkali metal cyanate content is comprised between 25% and 30%.
- Molten-salt bath according to any one of claims 1 to 4, in which the alkali metal carbonate content is comprised between 20% and 30%.
- Molten-salt bath according to claim 5, in which the alkali metal carbonate content is comprised between 25% and 30%.
- Molten-salt bath according to claim 1, essentially constituted by:- 25% to 30% sodium cyanate,- 25% to 30% sodium and lithium carbonates,- 40% to 50% potassium chlorides,- a maximum of 3% cyanide ions,the sum of these contents being 100%.
- Molten-salt bath according to claim 7, essentially constituted, before formation of cyanide ions up to a maximum of 3%, by:- 28% sodium cyanate,- 22% sodium carbonate,- 5% lithium carbonate,- 45% potassium chloride.
- Process for nitriding mechanical parts made of iron or steel, according to which these parts are immersed in a bath of the abovementioned composition, at a temperature comprised between 530°C and 650°C for a maximum of 4 h.
- Process according to claim 9, according to which the parts are immersed in the bath at a temperature comprised between 570°C and 590°C for a maximum of 2 h.
- Mechanical part made of nitrided steel obtained by the process according to either one of claims 9 and 10, not exhibiting any trace of a subsequent mechanical finishing process such as polishing.
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FR1152020A FR2972459B1 (en) | 2011-03-11 | 2011-03-11 | FOUNDED SALT BATHS FOR NITRIDING STEEL MECHANICAL PARTS, AND METHOD FOR IMPLEMENTING THE SAME |
PCT/FR2012/050479 WO2012146839A1 (en) | 2011-03-11 | 2012-03-07 | Molten-salt bath for nitriding mechanical steel parts, and implementation method |
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CN103882370A (en) * | 2014-03-24 | 2014-06-25 | 合肥美桥汽车传动及底盘系统有限公司 | 42CrMo or 40Cr steering knuckle nitrocarburizing treatment process |
FR3030578B1 (en) | 2014-12-23 | 2017-02-10 | Hydromecanique & Frottement | PROCESS FOR SUPERFICIAL TREATMENT OF A STEEL PART BY NITRURATION OR NITROCARBURING, OXIDATION THEN IMPREGNATION |
CA3068747A1 (en) * | 2017-07-07 | 2019-01-10 | Industries Mailhot Inc. | A method and system for cooling metal parts after nitriding |
RU2688428C1 (en) * | 2018-10-01 | 2019-05-22 | Открытое акционерное общество "Завод бурового оборудования" | Method of surface hardening of thread joints of thin-walled drilling pipes |
CN111500974A (en) * | 2020-04-30 | 2020-08-07 | 海门金锋盛厨房设备有限公司 | Salt bath nitriding system and nitriding method for wear-resistant and corrosion-resistant stainless steel |
CN113416918A (en) * | 2021-05-28 | 2021-09-21 | 昆山三民涂赖电子材料技术有限公司 | Nitrocarburizing process for extremely-thin parts |
US11668000B1 (en) | 2021-11-29 | 2023-06-06 | Fluid Controls Pvt. Ltd. | Method of treating an article |
FR3133394A1 (en) | 2022-03-14 | 2023-09-15 | Hydromecanique Et Frottement | METHOD FOR TREATING AN IRON ALLOY PART TO IMPROVE ITS CORROSION RESISTANCE |
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FR2972459A1 (en) | 2012-09-14 |
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CA2825652C (en) | 2019-02-19 |
BR112013018061A2 (en) | 2020-03-31 |
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MX2013010431A (en) | 2013-10-03 |
KR20190011318A (en) | 2019-02-01 |
MY164965A (en) | 2018-02-28 |
AU2012247317A1 (en) | 2013-09-19 |
AU2012247317B2 (en) | 2017-03-09 |
WO2012146839A1 (en) | 2012-11-01 |
MA34884B1 (en) | 2014-02-01 |
ZA201306476B (en) | 2014-05-28 |
SG192765A1 (en) | 2013-09-30 |
US20130327445A1 (en) | 2013-12-12 |
PL2683845T3 (en) | 2020-01-31 |
FR2972459B1 (en) | 2013-04-12 |
KR20140010141A (en) | 2014-01-23 |
CA2825652A1 (en) | 2012-11-01 |
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