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

Abstract

The invention relates to an impregnation liquid comprising diacetone alcohol, at a content of between 20 wt.%. and 50 wt.%, glycerol trioleate, at a content of between 20 wt.%. and 50 wt.%, castor oil, at a content of between 10 wt.%. and 40 wt.%, acetone, at a content of between 3 wt.%. and 5 wt.%, and at least one sulfonate, at a content of between 0 wt.%. and 1.5 wt.%. The invention also relates to a method for surface treatment of a ferrous part, comprising a step of impregnation with such an impregnation liquid, and to a treated part obtained.

Description

[0001] Impregnating liquid, method of treatment with such an impregnating liquid, and resulting treated part

[0002] The present invention relates to an impregnation liquid and to a method for surface treatment of a ferrous part comprising a step of impregnation with such an impregnation liquid.

[0003] Many parts, due to their intended application, require corrosion resistance, possibly across the entire part, and wear resistance, while also needing improvement in their frictional, or anti-scaling, properties.

[0004] To do this, they undergo, for example, nitriding, oxidation and impregnation treatment, for example as described in document W02016 / 102813. Impregnation completes the part's protection against corrosion and can sometimes improve other properties such as the coefficient of friction.

[0005] 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 of steel, for example XC10 or 1.0335, forged and locally machined), it appeared that certain impregnation products caused incompatibility of the treated part with brake fluids, in particular of the DOT4 type, which is a commonly used brake fluid.

[0006] Furthermore, it has been found that some products tend to cause gaskets to swell, for example EPDM (ethylene-propylene-diene monomer) gaskets, when used with parts treated in this way.

[0007] Since the treated part is in contact with the brake fluid, it is also desirable that the treatment avoids generating two distinct phases in the brake fluid.

[0008] The object of the present application is to improve at least in part the aforementioned disadvantages, further leading to other advantages.

[0009] For this purpose, according to a first aspect of the invention, an impregnation liquid is proposed comprising: - diacetone alcohol (4-hydroxy-4-methylpentan-2-one, C6H12O2), at a content of between 20 wt.% and 50 wt.%,

[0010] - glycerol trioleate (C57H104O6), at a content between 20 wt.% and 50 wt.%,

[0011] - castor oil (ricinolein (major component of castor oil): C57H104O9), at a content of between 10 wt.% and 40 wt.%,

[0012] - acetone (CsHeO), at a content between 3 wt.% and 5 wt.%, and

[0013] - at least one sulfonate (R-SO3- (ion), RI -SO2-O-R2 (ester)), at a content between 0 wt.% and 1.5 wt.%;

[0014] The total makes 100%.

[0015] The percentages here refer to mass percentages, also noted as “wt.%”.

[0016] Such an impregnation liquid is basically an oily liquid kept fluid by the presence of solvents, in particular here diacetone alcohol and acetone.

[0017] Sulfonate, for example, is a thickener used in the formulation of high-performance greases and contributes to corrosion resistance.

[0018] To promote compatibility with brake fluid, the impregnation fluid here is devoid of an aqueous phase (i.e. without water (H2O)), because an aqueous phase is generally incompatible with a brake fluid, in particular of the DOT4 type.

[0019] Such an impregnation liquid is then, for example, miscible with such a brake fluid, which limits the risk of formation of distinct phases.

[0020] Such a liquid is also compatible with EPDM, a material frequently used to make seals for a brake piston.

[0021] For example, the diacetone alcohol content is at least 30 wt.% and / or at most 40 wt.%.

[0022] For example, the glycerol trioleate content is at least 30 wt.% and / or at most 40 wt.%.

[0023] For example, the castor oil content is at least 20 wt.% and / or at most 30 wt.%. For example, the acetone content is at least 3.5 wt.% and / or at most 4.5 wt.%.

[0024] For example, the content of the at least one sulfonate is at least 0.01 wt.%.

[0025] For example, the content of the at least one sulfonate is between 1 wt.% and 1.5 wt.%.

[0026] For example, the at least one sulfonate comprises at least one of calcium sulfonate, barium sulfonate, magnesium sulfonate, aluminum sulfonate, and sodium sulfonate, preferably calcium sulfonate.

[0027] The present invention also relates to a method of surface treatment of a ferrous part to give it high resistance to wear and corrosion.

[0028] For this purpose, a method of surface treatment of a ferrous part is also proposed, comprising a step of impregnation with an impregnation liquid as described previously.

[0029] Such a process relates more particularly to a steel part, for example at least partly machined.

[0030] Such a process also concerns other ferrous parts, possibly not forged, but preferably machined.

[0031] The part is for example a low carbon steel part.

[0032] Low carbon steel here refers to steel with a carbon content of between 0.05 wt.% and 0.8 wt.%, or even between 0.05 wt.% and 0.2 wt.%, relative to the mass of the iron.

[0033] The part is for example in particular a brake piston.

[0034] For example, the impregnation liquid is used at room temperature, i.e. for example at a temperature between 10°C and 45°C, or for example at least 15°C and / or at most 30°C.

[0035] This impregnation liquid is applied by dipping or spraying. Thus, in an example of implementation, 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] Immersion is typically done on a load consisting of several parts, for example directly after a nitriding step and, possibly, after an oxidation step as described later.

[0038] The immersion stage lasts for example between 10 minutes and

[0039] 15 minutes.

[0040] However, the immersion step can be very short, for example lasting a few seconds at most, for example 1 s, especially if complete filling of the pores of a surface of the part is not desired.

[0041] Otherwise, especially if complete filling of the pores is desired, the immersion step can last several minutes or even several hours, for example 1 hour.

[0042] According to an interesting option, the process can include a bath agitation step.

[0043] For example, agitation can be mechanical or ultrasonic.

[0044] In another exemplary implementation, the impregnation step comprises a step of spraying the impregnation liquid onto at least a portion of the part.

[0045] The spraying step lasts for example a few seconds, for example between 1 s and 60 s.

[0046] Spray impregnation is, for example, implemented when the treatment process includes an individual treatment sub-step, i.e. which is then a treatment more often carried out piece by piece, for example a polishing treatment.

[0047] In this case, spraying is carried out after this processing sub-step, and the part can, for example, automatically move from this processing sub-step to the spray impregnation step.

[0048] The impregnation step is, for example, a final treatment step here, specially 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 process to a brake piston.

[0049] In an exemplary implementation, the method may comprise, after the impregnation step, a drying step, the drying being natural and / or accelerated by steaming.

[0050] The part to be treated may undergo other surface treatments before the impregnation stage, in order to improve certain properties of the material, or to complete the protection of the part against certain attacks, or even to improve the adhesion of an impregnation layer.

[0051] Thus, in an exemplary implementation, the method comprises a nitriding or nitrocarburizing step (hereinafter referred to more simply as the “nitriding step”) configured to form a combination layer.

[0052] Such a step is for example implemented before the impregnation step.

[0053] Such a nitriding step (also called “nitrocarburizing”) consists, for example, of enriching the part material with nitrogen and carbon; this step provides very high layer homogeneity and good repeatability.

[0054] For example, the nitriding step is configured to form a combination layer having a thickness at least equal to 8 micrometers (pm), for example between 8 pm and 30 pm, or even between 10 pm and 30 pm, or even between 15 pm and 30 pm, and preferably around 20 pm.

[0055] For example, the nitriding step is configured to form a combination layer formed of nitrides, for example iron nitride of £ and / or y' phases.

[0056] This nitriding can be obtained by different methods such as nitriding in ionic liquid medium (salt bath), plasma nitriding or gas nitriding.

[0057] In an exemplary implementation, the nitriding / nitrocarburizing step is carried out at a temperature 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).

[0058] In an exemplary implementation, the nitriding / nitrocarburizing step is carried out for a period of between 45 minutes and 200 minutes.

[0059] For example, nitriding / nitrocarburizing treatment is carried out at a temperature of 590°C for a duration of between 60 minutes and 200 minutes.

[0060] For example, nitriding / nitrocarburizing treatment is carried out at a temperature of 630°C for a duration of between 30 minutes and 150 minutes.

[0061] In an exemplary implementation, the nitriding step includes a step of immersing the part in a nitriding or nitrocarburizing bath (hereinafter referred to as a nitriding bath for simplification).

[0062] The nitriding bath here refers to a liquid, ionic medium.

[0063] 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.

[0064] For example, the nitriding bath contains cyanates (CNO ) and carbonates (CO 2- ).

[0065] For example, the nitriding bath contains 14 wt.% to 90 wt.%, or even 20 wt.% to 80 wt.%, of alkali cyanates.

[0066] An alkali compound here means a compound of sodium, potassium or lithium.

[0067] For example, the nitriding bath contains, in mass percentage:

[0068] - lithium ions (Li+) between 0 wt.% and 5 wt.%,

[0069] - sodium ions (Na+) between 5 wt.% and 25 wt.%,

[0070] - potassium ions (K+) between 15 wt.% and 50 wt.%,

[0071] - carbonate ions (CO3 2- ) between 10 wt.% and 50 wt.%, and

[0072] - cyanate ions (CNO ) between 10 wt.% and 50 wt.%. According to an interesting option, the bath contains between 10 wt.% and 40 wt.% of chloride ions.

[0073] In an exemplary implementation, the nitriding or nitrocarburizing step is carried out 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 of between 10 Pa and 1000 Pa and at a temperature of between approximately 350°C and 600°C.

[0074] According to another example of implementation, the nitriding step is carried out in a gaseous medium.

[0075] For example, it includes a step of immersing the part in a nitriding (or nitrocarburizing) gas.

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

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

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

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

[0080] According to an interesting implementation option, after the salt bath nitriding step, the process also includes a part rinsing step.

[0081] In an exemplary implementation, the method comprises an oxidation step configured to generate an oxide layer.

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

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

[0084] For example, the oxidation step, also called post-oxidation, can be carried out in a liquid medium, i.e. by immersing the part in a bath, then called an oxidation bath. In an exemplary implementation, the part is immersed in an oxidation bath for a period of between 10 minutes and 90 minutes, for example for at least 10 minutes and / or a maximum of 20 minutes.

[0085] For example, the oxidation bath is an ionic liquid medium containing:

[0086] - sodium nitrate (NaNOs), in particular between 10 wt.% and 40 wt.%,

[0087] - at least one carbonate, for example at least one lithium, potassium or sodium carbonate, between 5 wt.% and 30 wt.%, and

[0088] - sodium hydroxide (NaOH), between 20 wt.% and 45 wt.%.

[0089] The temperature of such a bath is for example maintained between 400°C and 500°C, typically around 450°C.

[0090] In one example, the oxidation bath is an aqueous bath that includes alkali hydroxides, alkali nitrates, and alkali nitrites (i.e., sodium, potassium, and lithium).

[0091] Such a bath is typically maintained at a temperature between 110°C and 130°C.

[0092] According to yet another example, the oxidation step is carried out in a gaseous medium consisting mainly of water vapor.

[0093] For example, the oxidation step in gaseous media is then carried out at a temperature between approximately 450°C and 550°C.

[0094] For example, the oxidation step in gaseous media is then carried out for a duration of between approximately 30 min and 120 min.

[0095] For example, the oxidation step is configured to generate an oxide layer with a thickness of between approximately 0.1 pm and 3 pm.

[0096] According to an interesting implementation option, after the oxidation step in an oxidation bath, the process also includes a step of rinsing the part.

[0097] Optionally, the process also includes a step of polishing a surface of the part.

[0098] For example, the polishing step is configured to produce a roughness adapted to the need, in particular a roughness Ra between 0.05 and 0.40, and a roughness Rz between 1.5 and 3.0. Ra and Rz denote roughness parameters very commonly used in industry. Roughness parameters are for example defined in the ISO 21920-2:2021 standard. In particular, Ra is the arithmetic mean of the height of a profile and Rz the mean of the total deviations.

[0099] A corresponding measuring device is a roughness meter. The roughness meter directly provides the parameters according to the aforementioned standard.

[0100] For example, the polishing step includes a so-called “centerless” polishing step.

[0101] A “centerless” polishing here refers to a specific polishing for a cylindrical part of a part.

[0102] Polishing is often done by belt or wheel.

[0103] The choice of grinding wheel, rotation and / or pressure parameters are then chosen on a case-by-case basis.

[0104] For example, here, for a part made of low carbon steel, polishing is advantageously carried out with a wheel of compressed non-woven abrasive, for example polymer.

[0105] For example, the grinding wheel has a diameter between 200 mm and 500 mm.

[0106] For example, a pressure of the grinding wheel on the part is between 0.5 bar and 2 bar (with 1 bar = 10 5 Pa).

[0107] For example, a grinding wheel rotation frequency is between 20 Hz and 50 Hz.

[0108] In an exemplary implementation, the impregnation step is coupled with the polishing step.

[0109] For example, polishing can be done piece by piece on a processing line and the part passes, on this line, from polishing to impregnation, especially when impregnation takes place by spraying. Everything can then, for example, be automated.

[0110] In one exemplary implementation, the polishing step includes a brushing step. In another exemplary implementation, the polishing step is performed between the nitrocarburizing step and the impregnation step, or even between the oxidation step and the impregnation step.

[0111] Also provided, according to another aspect, is a treated part obtained by a process comprising all or part of the steps described above.

[0112] For example, such a treated part comprises at least the ferrous part, for example made of steel, forming a substrate.

[0113] For example, the ferrous part is at least partly machined.

[0114] The steel part is, for example, made of low-carbon steel.

[0115] Low carbon steel here refers to steel with a carbon content of between 0.05 wt.% and 0.8 wt.%, or even between 0.05 wt.% and 0.2 wt.%, relative to the mass of the iron.

[0116] For example, the part being treated is a brake piston.

[0117] For example, the treated part has an impregnation layer forming a surface of the treated part.

[0118] For example, the impregnation layer has a greasy appearance.

[0119] For example, the impregnation layer comprises at least one of glycerol trioleate, and / or castor oil, optionally a sulfonate of calcium, barium, sodium, aluminum or magnesium sulfonate.

[0120] Glycerol trioleate tends to leave a greasy film on the surface of the part, giving it a greasy appearance.

[0121] The sulfonate is possibly present on the surface, although in small quantities; it contributes to conferring anti-corrosion and anti-oxidation properties to the treated part.

[0122] For example, the treated part has a diffusion zone.

[0123] The diffusion zone extends for example to a depth of at least 50 pm, for example between 50 pm and 500 pm.

[0124] The diffusion zone extends, for example, from an initial surface of the ferrous part forming the substrate. For example, the diffusion zone comprises nitrogen.

[0125] For example, the treated part has a combination layer.

[0126] For example, the combination layer is formed on the surface of the substrate; that is, it at least partially covers the diffusion zone.

[0127] For example, the combination layer comprises nitrides, for example, iron nitrides of £ and / or y' phases.

[0128] For example, the combination layer has a thickness of at least 8 pm, for example between 8 pm and 30 pm, or even between 10 pm and 30 pm, or even between 15 pm and 30 pm, and preferably approximately 20 pm.

[0129] For example, the treated part has a layer of oxides.

[0130] The oxide layer contains, for example, iron oxides (FesCU).

[0131] For example, the oxide layer is formed on the combination layer.

[0132] For example, the oxide layer has a thickness between 0.1 pm and 3 pm.

[0133] Thus, according to an exemplary embodiment, the treated part comprises, in order, the basic ferrous part forming the substrate, the diffusion zone, the combination layer, the oxide layer, then the impregnation layer.

[0134] In order to verify the corrosion resistance of a part treated according to the present invention, two parts were treated: a brake piston in cold forged 1.0335 steel and a piston in machined XC 10.

[0135] After degreasing, the parts were rinsed and then dried before undergoing a nitriding treatment.

[0136] Nitriding was carried out in a molten salt bath containing the following ions, in mass percentage: lithium ions (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 23 wt.%, carbonate ions (COs 2- ) from 38 wt.% to 43 wt.%, cyanate ions (CNO ) from 12 wt.% to 17 wt.%.

[0137] The bath temperature is maintained at approximately 590°C (± 5°C) and the duration of the nitriding step is 120 minutes.

[0138] Then, the parts are immersed in a bath of oxidation salts containing sodium nitrate (NaNOs), in particular between 35 wt.% and 40 wt.%, carbonates (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.

[0139] After rinsing and drying, the pieces were polished for about 1 second by passing between a grinding wheel and a rubber wheel. The grinding wheel, for example, is rotated by the movement of the wheel and is therefore not fixed in its center.

[0140] The grinding wheel is for example a compressed non-woven abrasive wheel (for example marketed under the name Norton 7 SF) at a pressure of 0.8 bar to 1.4 bar, and a rotation frequency of the wheel between 30 Hz and 50 Hz.

[0141] The parts were then spray impregnated with a liquid containing 35 wt.% diacetone alcohol, 35 wt.% glycerol trioleate, 25 wt.% castor oil, 4.2 wt.% acetone, and 0.8 wt.% calcium sulfonate.

[0142] These parts were then subjected to a salt spray corrosion test, and the following results were obtained:

[0143] - For the forged part:

[0144] • On an edge: resistance to salt spray validated for up to 120 hours,

[0145] • On a smooth area: resistance to salt spray validated for at least 240 hours.

[0146] - For the machined part:

[0147] • On an edge: resistance to salt spray validated for up to 240 hours,

[0148] • On a smooth area: resistance to salt spray validated for at least 300 hours.

[0149] This corrosion resistance was considered very satisfactory for the two types of parts mentioned above.

[0150] The compatibility of the impregnation liquid with EPDM gaskets was checked by immersing such gaskets in the impregnation liquid for 24 hours.

[0151] No swelling of the joint was then observed.

Claims

CLAIMS 1. Impregnation liquid comprising: - diacetone alcohol, at a content between 20 wt.% and 50 wt.%, - glycerol trioleate, at a content between 20 wt.% and 50 wt.%, - castor oil, at a content of between 10 wt.% and 40 wt.%, - acetone, at a content between 3 wt.% and 5 wt.%, and - at least one sulfonate, at a content between 0 wt.% and 1.5 wt.%; the total being 100%.

2. Liquid according to claim 1, wherein the diacetone alcohol content is at least 30 wt.% and / or at most 40 wt.%.

3. Liquid according to any one of claims 1 or 2, wherein the glycerol trioleate content is at least 30 wt.% and / or at most 40 wt.%.

4. Liquid according to any one of claims 1 to 3, wherein the castor oil content is at least 20 wt.% and / or at most 30 wt.%.

5. Liquid according to any one of claims 1 to 4, wherein the acetone content is at least 3.5 wt.% and / or at most 4.5 wt.%.

6. Liquid according to any one of claims 1 to 5, in which the content of the at least one sulfonate is between 1 wt.% and 1.5 wt.%.

7. Liquid according to any one of claims 1 to 6, wherein the at least one sulfonate comprises at least one sulfonate from among a calcium sulfonate, a barium sulfonate, a magnesium sulfonate, an aluminum sulfonate and a sodium sulfonate.

8. Liquid according to claim 7, wherein the at least one sulfonate comprises calcium sulfonate.

9. Method for surface treatment of a ferrous part comprising a step of impregnation with an impregnation liquid according to any one of claims 1 to 8.

10. Method according to claim 9, in which the impregnation liquid has a temperature between 10°C and 45°C.

11. Method according to any one of claims 9 or 10, in which the step of impregnation with the impregnation liquid comprises a step of immersing the part in the impregnation liquid.

12. Method according to any one of claims 9 or 10, in which the impregnation step comprises a step of spraying the impregnation liquid onto at least a portion of the part.

13. A method according to any one of claims 9 to 12, wherein the method comprises a nitriding step configured to form a combination layer, the nitriding step being carried out before the impregnation step.

14. Method according to any one of claims 9 to 13, in which the method comprises an oxidation step configured to generate a layer of oxides, the oxidation step being carried out before the impregnation step.

15. Treated part obtained by a method according to any one of claims 9 to 14.

16. Treated part according to claim 15 forming a brake piston, the treated part comprising an impregnation layer forming a surface of the treated part, the impregnation layer comprising at least one of glycerol trioleate, and / or castor oil, and / or a sulfonate from a calcium, barium, sodium, aluminum or magnesium sulfonate.