Impregnation liquid, method of treatment with such an impregnation liquid, and treated part obtained

Abstract

An impregnation liquid comprises diacetone alcohol, in a proportion of between 20 wt. % and 50 wt. %, glycerol trioleate, in a proportion of between 20 wt. % and 50 wt. %, castor oil, in a proportion of between 10 wt. % and 40 wt. %, acetone, in a proportion of between 3 wt. % and 5 wt. %, and at least one sulfonate, in a proportion of between 0 wt. % and 1.5 wt. %. A method for surface treatment of a ferrous part includes an impregnation step by such an impregnation liquid, and the treated part obtained.

Description

[0001] This application is the U.S. national phase of PCT application PCT / FR2023 / 051733, filed Nov. 6, 2023, which claims priority of French patent application no. 2211562 filed Nov. 7, 2022, the entire contents of each of which are hereby incorporated by reference.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The present invention relates to an impregnation liquid and a method for the surface treatment of a ferrous part including a step of impregnation by such an impregnation liquid.2. Description of Related Art

[0003] Many parts, because of the application for which they are intended, require corrosion resistance, optionally over the entire part, and resistance to wear, while also needing improvement to their friction and anti-scaling property. For this purpose, they undergo for example a nitriding, oxidation and impregnation treatment, for example as described in the document WO2016 / 102813. The impregnation completes the corrosion protection of the part and can sometimes improve other properties such as the coefficient of friction.

[0004] In the context of a treatment applied to a brake part (such as for example a brake caliper piston, which is a ferrous part, typically made from steel, for example XC10 or 1.0335, forged and locally machined), it became clear that some impregnation products caused incompatibility of the treated part with some brake fluids, in particular of the DOT4 type, which is a frequently used brake fluid.

[0005] Furthermore, it became clear that some products had a tendency to make seals swell, for example seals made from EPDM (ethylene propylene diene monomer), used with parts thus treated.

[0006] The treated part being in contact with the brake fluid, it is also desirable that the treatment avoids generating two distinct phases in the brake fluid.SUMMARY

[0007] The object of the present application aims to improve at least partly the aforementioned drawbacks, furthermore leading to other advantages.

[0008] For this purpose, it is proposed, according to a first aspect of the invention, an impregnation liquid including:

[0009] diacetone alcohol (4-hydroxy-4-methylpentan-2-one, C6H12O2), in a proportion of between 20 wt. % and 50 wt. %, glycerol trioleate (C57H104O6), in a proportion of between 20 wt. % and 50 wt. %,

[0010] castor oil (ricinolein (the main component of castor oil): C57H104O9), in a proportion of between 10 wt. % and 40 wt. %,

[0011] acetone (C3H6O), in a proportion of between 3 wt. % and 5 wt. %, and

[0012] at least one sulfonate (R—SO3— (ion), R1-SO2—O—R2 (ester)), in a proportion of between 0 wt. % and 1.5 wt. %;

[0013] The total amounting to 100%.

[0014] The percentages herein refer to weight percentages, also denoted “wt. %”.DETAILED DESCRIPTION

[0015] Such an impregnation liquid is based on an oily liquid kept fluid by the presence of solvents, in particular here diacetone alcohol and acetone. Sulfonate is for example a thickener that participates in the formulation of high-performance greases and contributes to corrosion resistance.

[0016] To promote compatibility with the brake fluid, the impregnation liquid is here devoid of any aqueous phase (i.e. without water (H2O)), since an aqueous phase is generally incompatible with a brake fluid, in particular of the DOT4 type.

[0017] Such an impregnation liquid is then for example miscible with such a brake fluid, which limits the risk of the formation of distinct phases.

[0018] Such a liquid is furthermore compatible with EPDM, a material frequently used for producing seals for a brake piston.

[0019] For example, the proportion of diacetone alcohol is at least 30 wt. % and / or no more than 40 wt. %.

[0020] For example, the proportion of glycerol trioleate is at least 30 wt. % and / or no more than 40 wt. %.

[0021] For example, the proportion of castor oil is at least 20 wt. % and / or no more than 30 wt. %.

[0022] For example, the proportion of acetone is at least 3.5 wt. % and / or no more than 4.5 wt. %.

[0023] For example, the proportion of the at least one sulfonate is at least 0.01 wt. %.

[0024] For example, the proportion of the at least one sulfonate is between 1 wt. % and 1.5 wt. %.

[0025] For example, the at least one sulfonate includes at least one sulfonate chosen from a calcium sulfonate, a barium sulfonate, a magnesium sulfonate, an aluminium sulfonate and a sodium sulfonate, preferably calcium sulfonate.

[0026] The present invention also relates to a method for surface treatment of a ferrous part to confer thereon a high resistance to wear and to corrosion.

[0027] For this purpose, a method for surface treatment of a ferrous part including an impregnation step by an impregnation liquid as described previously is also proposed.

[0028] Such a method more particularly relates to a steel part, for example at least partly machined.

[0029] Such a method also relates to other ferrous parts, optionally not forged, but preferably machined.

[0030] The part is for example a part made from steel with a low carbon content.

[0031] A steel with a low carbon content here designates a steel with a carbon content which is between 0.05 wt. % and 0.8 wt. %, or even between 0.05 wt. % and 0.2 wt. %, with respect to the mass of the iron.

[0032] The part is for example in particular a brake piston.

[0033] For example, the impregnation liquid is used at ambient temperature, i.e. for example at a temperature of between 10° C. and 45° C., or even for example at at least 15° C. and / or no more than 30° C.

[0034] This impregnation liquid is applied by dipping or spraying.

[0035] Thus, in an example embodiment, the step of impregnation by the impregnation liquid includes a step of immersing the part in the impregnation liquid.

[0036] The impregnation liquid then constitutes an impregnation bath.

[0037] The immersion is typically done on a load consisting of a plurality of parts, for example directly after a nitriding step and, optionally, after an oxidation step as both described subsequently.

[0038] The immersion step lasts for example for between 10 minutes and 15 minutes.

[0039] However, the immersion step may be very short, for example may last for a few seconds at a maximum, for example 1 s, in particular if total filling of the pores of a surface of the part is not sought.

[0040] Otherwise, in particular if total filling of the pores is sought, the immersion step may last for several minutes, or even several hours, for example 1 h.

[0041] According to an interesting option, the method may include a step of stirring the bath.

[0042] For example, the stirring may be mechanical or by ultrasound.

[0043] In another example embodiment, the impregnation step includes a step of spraying the impregnation liquid onto at least a portion of the part.

[0044] The spraying step lasts for example for a few seconds, for example between 1 s and 60 s.

[0045] Impregnation by spraying is for example implemented when the treatment method includes a substep of individual treatment, i.e. which is then a treatment usually implemented part by part, for example a polishing treatment.

[0046] In this case, the spraying is implemented after this treatment substep, and the part can for example automatically pass from this treatment substep to the step of impregnation by spraying.

[0047] The impregnation step is for example here a final treatment step, especially developed to be compatible with a brake system, i.e. compatible with brake fluid and a seal in particular, for a particular application of the method to a brake piston.

[0048] In one example embodiment, the method may include, after the impregnation step, a drying step, the drying being natural and / or accelerated by heat (drying oven).

[0049] The part to be treated may undergo other surface treatments before the impregnation step, for the purpose of improving certain properties of the material, or supplementing the protection of the part against certain attacks, or in order to improve the adhesion of an impregnation layer.

[0050] Thus, in an example embodiment, the method includes a nitriding or nitrocarburising step (hereinafter designated more simply as “nitriding step”) configured to form a combination layer.

[0051] Such a step is for example implemented before the impregnation step.

[0052] Such a nitriding step (also referred to as “nitrocarburising”) consists for example in enriching the material of the part with nitrogen and with carbon; this step confers very high layer homogeneity and good repeatability.

[0053] For example, the nitriding step is configured to form a combination layer having a thickness of at least 8 micrometers (μm), for example between 8 μm and 30 μm, or even between 10 μm and 30 μm, or even between 15 μm and 30 μm, and preferably approximately 20 μm.

[0054] For example, the nitriding step is configured to form a combination layer formed by nitrides, for example iron nitride of & and / or y′ phases.

[0055] This nitriding can be obtained by various methods such as nitriding in an ionic liquid medium (salt bath), plasma nitriding or gas nitriding.

[0056] In an example embodiment, the nitriding / nitrocarburising step is implemented at a temperature of between 500° C. and 650° C., or even between 550° C. and 650° C., or even between 550° C. and 635° C., or even preferably between 580° C. and 630° C., preferably at approximately 590° C. (i.e. for example between 585° C. and 595° C.).

[0057] In an example embodiment, the nitriding / nitrocarburising step is implemented for a period of between 45 minutes and 200 minutes.

[0058] For example, the nitriding / nitrocarburising treatment is implemented at a temperature of 590° C. for a period of between 60 minutes and 200 minutes.

[0059] For example, the nitriding / nitrocarburising treatment is implemented at a temperature of 630° C. for a period of between 30 minutes and 150 minutes.

[0060] In an example embodiment, the nitriding step includes a step of immersing the part in a nitriding or nitrocarburising bath (next designated nitriding bath for simplification).

[0061] The nitriding bath here designates an ionic liquid medium.

[0062] For example, the part is immersed in the nitriding bath for at least 45 minutes, for example between 45 minutes and 200 minutes, preferably between 90 minutes and 150 minutes.

[0063] For example, the nitriding bath includes cyanates (CNO) and carbonates (CO32−).

[0064] For example, the nitriding bath includes 14 wt. % to 90 wt. %, or even 20 wt. % to 80 wt. %, of alkali cyanates.

[0065] An alkali compound here designates a sodium, potassium or lithium compound.

[0066] For example, the nitriding bath includes, as a mass percentage:

[0067] lithium ions (Li+) between 0 wt. % and 5 wt. %,

[0068] sodium ions (Na+) between 5 wt. % and 25 wt. %,

[0069] potassium ions (K+) between 15 wt. % and 50 wt. %,

[0070] carbonate ions (CO32−) between 10 wt. % and 50 wt. %, and

[0071] cyanate ions (CNO−) between 10 wt. % and 50 wt. %.

[0072] According to an interesting option, the bath includes between 10 wt. % and 40 wt. % of chloride ions.

[0073] In an example embodiment, the nitriding or nitrocarburising step is implemented in an ionic medium forming a plasma, in an atmosphere comprising at least nitrogen (N2) and hydrogen (H2) under reduced pressure, i.e. at a pressure between 10 Pa and 1000 Pa and at a temperature of between approximately 350° C. and 600° C.

[0074] According to another example embodiment, the nitriding step is implemented in a gaseous medium.

[0075] It includes for example a step of immersing the part in a nitriding (or nitrocarburising) gas.

[0076] For example, the nitriding gas includes ammonia (NH3).

[0077] In an example embodiment, the nitriding gas in which the part is immersed has a temperature of between approximately 500° C. and 630° C.

[0078] According to an interesting implementation option, before the nitriding step, the method furthermore includes a step of degreasing the part.

[0079] According to an interesting implementation option, before the nitriding step, the method furthermore includes a step of preheating the part.

[0080] According to an interesting implementation option, after the salt-bath nitriding step, the method furthermore includes a step of rinsing the part.

[0081] In an example embodiment, the method includes an oxidation step configured to generate a layer of oxides.

[0082] Such a step is for example implemented before the impregnation step.

[0083] Such a step is for example implemented after the nitriding / nitrocarburising step.

[0084] For example, the oxidation step, also referred to as post-oxidation, can be implemented in a liquid medium, i.e. by immersing the part in a bath, then referred to as an oxidation bath.

[0085] In an example embodiment, the part is immersed in an oxidation bath for a period of between 10 minutes and 90 minutes, for example for at least 10 min and / or at a maximum for 20 min.

[0086] For example, the oxidation bath is an ionic liquid medium containing:

[0087] sodium nitrate (NaNO3), in particular between 10 wt. % and 40 wt. %,

[0088] at least one carbonate, for example at least one lithium, or potassium, or sodium, carbonate, between 5 wt. % and 30 wt. %, and

[0089] sodium hydroxide (NaOH), between 20 wt. % and 45 wt. %.

[0090] The temperature of such a bath is for example maintained between 400° C. and 500° C., typically around 450° C.

[0091] According to one example, the oxidation bath is an aqueous bath that includes alkali hydroxides, alkali nitrates and alkali nitrites (i.e. of sodium, potassium and lithium).

[0092] Such a bath is typically maintained at a temperature of between 110° C. and 130° C.

[0093] According to yet another example, the oxidation step is implemented in a gaseous medium mainly consisting of steam.

[0094] For example, the oxidation step in gaseous medium is then implemented at a temperature of between approximately 450° C. and 550° C.

[0095] For example, the oxidation step in gaseous medium is then implemented for a period of between approximately 30 min and 120 min.

[0096] For example, the oxidation step is configured to generate a layer of oxides with a thickness of between approximately 0.1 μm and 3 μm.

[0097] According to an interesting implementation option, after the oxidation step in an oxidation bath, the method furthermore includes a step of rinsing the part.

[0098] Optionally, the method also includes a step of polishing a surface of the part.

[0099] For example, the polishing step is configured to produce a roughness adapted to requirements, in particular a roughness Ra of between 0.05 and 0.40 and a roughness Rz of between 1.5 and 3.0.

[0100] Ra and Rz designate roughness parameters very often used in industry. The roughness parameters are for example defined in ISO 21920-2:2021. In particular, Ra is the arithmetic mean of the height of the profile and Rz the mean of the total differences.

[0101] A corresponding measurement means is a roughness meter. The roughness meter directly supplies the parameters in accordance with the aforementioned standard.

[0102] For example, the polishing step includes a so-called “centreless” polishing step.

[0103] A “centreless” polishing designates here a specific polishing for a cylindrical portion of the part.

[0104] The polishing is often done by belt or by wheel.

[0105] The selection of the polishing wheel, the rotation and / or pressure parameters are then selected on a case-by-case basis.

[0106] For example, here, for a part made from steel with a low carbon content, the polishing is advantageously implemented with a compressed non-woven abrasive wheel, for example made from polymer.

[0107] The wheel has for example a diameter of between 200 mm and 500 mm.

[0108] For example, a pressure of the wheel on the part is between 0.5 bar and 2 bar (with 1 bar=105 Pa).

[0109] For example, a rotation frequency of the wheel is between 20 Hz and 50 Hz.

[0110] In an example embodiment, the impregnation step is coupled with the polishing step.

[0111] For example, the polishing may be done part by part on a treatment line and the part passes, on this line, from the polishing to the impregnation, in particular when the impregnation takes place by spraying. Everything can then for example be automated.

[0112] In an example embodiment, the polishing step includes a brushing step.

[0113] In another example embodiment, the polishing step is implemented between the nitrocarburising step and the impregnation step, or even between the oxidation step and the impregnation step.

[0114] A treated part obtained by a method including all or some of the steps described above is also proposed according to another aspect.

[0115] For example, such a treated part includes at least the ferrous part, for example made from steel, forming a substrate.

[0116] For example, the ferrous part is at least partly machined.

[0117] The steel part is for example made from steel with a low carbon content.

[0118] A steel with a low carbon content here designates a steel with a carbon content which is between 0.05 wt. % and 0.8 wt. %, or even between 0.05 wt. % and 0.2 wt. %, with respect to the mass of the iron.

[0119] For example, the treated part is a brake piston.

[0120] For example, the treated part includes an impregnation layer forming a surface of the treated part.

[0121] For example, the impregnation layer has a fatty appearance.

[0122] For example, the impregnation layer includes at least one from glycerol trioleate, and / or castor oil, optionally a sulfonate chosen from a calcium, barium, sodium, aluminium or magnesium sulfonate.

[0123] Glycerol trioleate has a tendency to leave a fatty film on the surface of the part, thus giving it a fatty appearance.

[0124] The sulfonate is possibly present on the surface, although in a small quantity; it contributes to conferring anticorrosion and anti-oxidation properties to the treated part.

[0125] For example, the treated part includes a diffusion zone.

[0126] The diffusion zone extends for example over a depth of at least 50 μm, for example between 50 μm and 500 μm.

[0127] The diffusion zone extends for example from an initial surface of the ferrous part forming the substrate.

[0128] For example, the diffusion zone comprises nitrogen.

[0129] For example, the treated part includes a combination layer.

[0130] For example, the combination layer is formed on the surface of the substrate; in other words, it at least partly covers the diffusion zone.

[0131] For example, the combination layer includes nitrides, for example iron nitrides of & and / or y′ phases.

[0132] For example, the combination layer has a thickness of at least 8 μm, for example between 8 μm and 30 μm, or even between 10 μm and 30 μm, or even between 15 μm and 30 μm, and preferably approximately 20 μm.

[0133] For example, the treated part includes a layer of oxides.

[0134] The oxide layer includes for example iron oxides (Fe3O4).

[0135] For example, the layer of oxides is formed on the combination layer.

[0136] For example, the oxide layer has a thickness of between 0.1 μm and 3 μm.

[0137] Thus, according to one example embodiment, the treated part includes, in the following order, the base ferrous part forming the substrate, the diffusion zone, the combination layer, the layer of oxides, and then the impregnation layer.

[0138] In order to check the corrosion resistance of a part treated according to the present invention, two parts were treated: a brake piston made from cold-forged 1.0335 steel and a piston made from machined XC 10.

[0139] After degreasing, the parts were rinsed and then dried before undergoing nitriding treatment.

[0140] The nitriding was implemented in a molten-salt bath containing the following ions, as a mass percentage: ions lithium (Li+) from 2.8 wt. % to 4.2 wt. %, sodium ions (Na+) from 16 wt. % to 19 wt. %, potassium ions (K+) from 20 wt. % to à 23 wt. %, carbonate ions (CO32−) from 38 wt. % to 43 wt. %, cyanate ions (CNO−) from 12 wt. % to 17 wt. %.

[0141] The temperature of the bath is maintained at substantially 590° C. (+5° C.) and the duration of the nitriding step is 120 minutes.

[0142] Next, the parts are immersed in an oxidation salt bath containing sodium nitrate (NaNO3), in particular between 35 wt. % and 40 wt. %, carbonates (of lithium, potassium and sodium) between 15 wt. % and 20 wt. %, sodium hydroxide (NaOH) between 40 wt. % and 45 wt. %, at a temperature of 450° C. for 15 minutes.

[0143] After rinsing and drying, the parts underwent polishing of approximately 1 second by passing between a polishing wheel and a rubber wheel. The polishing wheel is for example rotated by the movement of the rubber wheel and is therefore not fixed at its centre.

[0144] The polishing wheel is for example a compressed nonwoven abrasive wheel (for example sold under the name Norton 7 SF) at a pressure of 0.8 bar to 1.4 bar, and a rotation frequency of the polishing wheel between 30 Hz and 50 Hz.

[0145] The parts were next impregnated by spraying with a liquid containing 35 wt. % of diacetone alcohol, 35 wt. % of glycerol trioleate, 25 wt. % of castor oil, 4.2 wt. % of acetone and 0.8 wt. % of calcium sulfonate.

[0146] These parts were next subjected to a salt-spray corrosion test, and the following results were obtained:

[0147] For the forged part:

[0148] On an edge: resistance to salt spray validated up to 120 hr,

[0149] On a smooth zone: resistance to salt spray validated over at least 240 hr.

[0150] For the machined part:

[0151] On an edge: resistance to salt spray validated up to 240 hr,

[0152] On a smooth zone: resistance to salt spray validated over at least 300 hr.

[0153] This corrosion resistance was judged very satisfactory for the aforementioned two types of part.

[0154] Compatibility of the impregnation liquid with the EPDM seals was checked by immersing such seals in the impregnation liquid for 24 hours.

[0155] No swelling of the seals was then observed.

Claims

1. -16. (canceled)17. An impregnation liquid, comprising:diacetone alcohol, in a proportion of between 20 wt. % and 50 wt. %,glycerol trioleate, in a proportion of between 20 wt. % and 50 wt. %,castor oil, in a proportion of between 10 wt. % and 40 wt. %,acetone, in a proportion of between 3 wt. % and 5 wt. %, andat least one sulfonate, in a proportion of between 0 wt. % and 1.5 wt. %.

18. The impregnation liquid according to claim 17, wherein the recited ingredients constitute 100% of said impregnation liquid.

19. The impregnation liquid according to claim 17, wherein the proportion of diacetone alcohol is at least 30 wt. %.

20. The impregnation liquid according to claim 17, wherein the proportion of glycerol trioleate is at least 30 wt. %.

21. The impregnation liquid according to claim 17, wherein the proportion of castor oil is at least 20 wt. %.

22. The impregnation liquid according to claim 17, wherein the proportion of acetone is at least 3.5 wt. % and no more than 4.5 wt. %.

23. The impregnation liquid according to claim 17, wherein the proportion of the at least one sulfonate is between 1 wt. % and 1.5 wt. %.

24. The impregnation liquid according to claim 17, wherein the at least one sulfonate includes at least one sulfonate selected from the group consisting of calcium sulfonate, barium sulfonate, magnesium sulfonate, aluminium sulfonate and sodium sulfonate.

25. The impregnation liquid according to claim 24, wherein the at least one sulfonate comprises calcium sulfonate.

26. The impregnation liquid according to claim 17, wherein the proportion of diacetone alcohol is no more than 40 wt. %.

27. The impregnation liquid according to claim 17, wherein the proportion of glycerol trioleate is no more than 40 wt. %.

28. The impregnation liquid according to claim 17, wherein the proportion of castor oil is no more than 30 wt. %.

29. A method for surface treatment of a ferrous part, comprising impregnating the ferrous part with an impregnation liquid comprising:diacetone alcohol, in a proportion of between 20 wt. % and 50 wt. %,glycerol trioleate, in a proportion of between 20 wt. % and 50 wt. %,castor oil, in a proportion of between 10 wt. % and 40 wt. %,acetone, in a proportion of between 3 wt. % and 5 wt. %, andat least one sulfonate, in a proportion of between 0 wt. % and 1.5 wt. %.

30. The method according to claim 29, wherein the impregnation liquid has a temperature of between 10° C. and 45° C.

31. The method according to claim 29, wherein the impregnation step by the impregnation liquid comprises immersing the ferrous part in the impregnation liquid.

32. The method according to claim 29, wherein the impregnation step comprises spraying the impregnation liquid onto at least a portion of the ferrous part.

33. The method according to claim 29, further comprising a nitriding step configured to form a combination layer, the nitriding step being implemented before the impregnation step.

34. The method according to claim 29, further comprising an oxidation step configured to generate a layer of oxides, the oxidation step being implemented before the impregnation step.

35. A treated ferrous part obtained by the method according to claim 29.

36. The treated ferrous part according to claim 35, configured as a brake piston, the treated ferrous part comprising an impregnation layer forming a surface of the treated ferrous part, the impregnation layer including at least one of glycerol trioleate, castor oil, and a sulfonate chosen from a calcium, barium, sodium, aluminium and magnesium sulfonate.