Surface treatment method for steel machine parts to improve wear resistance and corrosion resistance under severe stress.

Abstract

The present invention relates to a surface treatment method for improving the wear resistance and corrosion resistance of steel machine parts, the method comprising at least one step of nitriding or soft nitriding the part to form a nitrided surface layer, followed by a step of impregnating the nitrided surface layer with a solution comprising at least one hydrophobic wax, wherein the wax is a carbon-containing organic compound having a molecular weight of less than 500, preferably between 200 and 500.

Description

[Technical Field]

[0001] The present invention relates to the field of surface treatment for steel machine parts to improve wear resistance and corrosion resistance. More specifically, the present invention relates to a treatment process involving nitriding or soft nitriding, optionally followed by oxidation, and impregnation with hydrophobic wax. [Background technology]

[0002] EP0524037 discloses a surface treatment method for improving the corrosion resistance of machine parts.

[0003] This document describes techniques for improving the friction resistance and corrosion resistance of ferrous metal parts. The disclosed techniques encompass a series of processes including nitriding, oxidation, and the application of a final coating.

[0004] This final coating is a hydrophobic wax, specifically an organic carbon-based compound with a high molecular weight, particularly between 500 and 10,000. The application of this high molecular weight wax helps improve the corrosion resistance of the component and minimize rebound effects.

[0005] These processes are advantageous because they are easy to implement at low cost, even in the industrial-scale production of mass-produced parts. Furthermore, they impart high technical performance to the processed parts, even those with complex shapes.

[0006] Publication WO2016 / 102813 discloses a process using PVD coating to enhance the durability of machine parts.

[0007] This document describes a method for treating the surface of steel machine parts to impart high wear resistance and corrosion resistance. The process includes the following steps: - A nitriding or soft nitriding step to form an iron nitride layer with a thickness of at least 8 micrometers; - Oxidation step to produce an oxide layer with a thickness of 0.1 to 3 micrometers; - An impregnation step by immersing in an impregnation bath for at least 5 minutes. The bath consists of ±1% of at least 70% by weight of a hydrocarbon solvent, ±1% of at least one paraffin oil in a concentration of 10% to 30% by weight, and ±0.1% of at least one synthetic phenolic additive in a concentration of 0.01% to 3% by weight.

[0008] This method achieves a significant improvement in corrosion resistance compared to conventional oil-based or acid-based baths. Furthermore, the treated parts have a dry feel, which means they do not transfer oil to other surfaces and do not attract surrounding dust. This also makes post-processing, such as overmolding, possible.

[0009] However, in any of the above-mentioned technologies, the corrosion resistance of the treated and impregnated parts will decrease if they are subjected to harsh conditions such as high-pressure washing or repeated mechanical stress (e.g., friction from seals).

[0010] To address this problem, certain coating techniques, such as electroless nickel plating or hard chrome coating, are known to be used. However, these techniques have drawbacks, including: - Fluctuations in raw material costs: Nickel, for example, is susceptible to significant price fluctuations due to economic and geopolitical factors, making coating costs unpredictable and potentially expensive. - REACH Regulation: The European Regulation on Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) requires prior authorization for the use of certain materials, such as hard chromium. This can lead to production delays and increased costs. There are also environmental and health concerns associated with these substances.

[0011] Therefore, while these coating technologies can improve the wear resistance and corrosion resistance of steel machine parts, they face challenges in terms of cost and regulatory compliance.

[0012] Publication No. FR3030578 also describes the current prior art. [Overview of the project] [Problems that the invention aims to solve]

[0013] One of the objectives of the present invention is to overcome the shortcomings of the prior art by providing a surface treatment process for steel machine parts that improves the wear resistance and corrosion resistance of steel machine parts and maintains this resistance even when exposed to aggressive and harsh environmental conditions such as repeated high-pressure washing, exposure to sand and weather, or repeated mechanical friction. [Means for solving the problem]

[0014] The present invention solves the problems of the prior art by proposing a surface treatment method for steel machine parts that includes at least one nitriding or soft nitriding step to form a nitrided surface layer, which includes, for example, a dense internal sublayer and a porous external sublayer. The external sublayer contains more than 60% Fe 2-3 It contains a N solid phase and has a hardness of 550-650HV0.1. Its roughness is 0.3-1.5 micrometers, which further improves the adhesion and corrosion resistance of the wax. This nitriding or soft nitriding step is followed by an impregnation step of this layer with a solution containing at least one hydrophobic wax.

[0015] According to the present invention, the wax is an organic carbon compound having a low molecular weight, specifically less than 500, preferably 200 to 500.

[0016] This feature provides effective corrosion protection while remaining economically viable.

[0017] Furthermore, in contrast to prior art teachings that recommended the use of high molecular weight organic carbon compounds, the applicant found that, provided that nitriding or soft nitriding is performed properly, low molecular weight organic carbon compounds enhance the retention of protective waxes and reduce their susceptibility to cleaning or degradation under harsh operating conditions.

[0018] Under these conditions, the present invention ensures excellent corrosion resistance and high resistance to high-pressure washing / cleaning, exposure to sand and weather, or repeated mechanical friction.

[0019] The present invention regards corrosion resistance exceeding 1600 hours in a salt spray test for parts immediately after treatment, and corrosion resistance exceeding 500 hours for parts exposed to simulated high-pressure washing after treatment, as satisfactory corrosion resistance.

[0020] The impregnation according to the present invention does not impair the appearance or handling of the part, and provides a surface with a dry touch.

[0021] The process may further comprise an oxidation step after nitriding or nitrocarburizing, resulting in the formation of a porous surface layer containing iron oxide. This oxide layer improves corrosion resistance and wax retention.

[0022] The impregnation can be carried out at room temperature by immersion in a bath or spraying of the solution, which makes the process flexible and adaptable to different part geometries.

[0023] The immersion time is at least 2 minutes, which provides an effective balance between treatment time and protection quality.

[0024] In view of the confirmed performance, the impregnation solution may contain wax diluted to 50%, 75%, or 80% with a solvent, and still achieve very excellent corrosion resistance under severe conditions. When diluted to 90%, the wax maintains its protective properties under normal conditions, but is no longer suitable for severe conditions.

[0025] Advantageously, the process does not require oven drying, and air-drying the impregnated solution at room temperature for at least 5 minutes is sufficient to ensure good wax adhesion.

[0026] The solution advantageously contains 1% to 30% by mass, preferably 1% to 20% by mass, of calcium sulfonate, improving corrosion resistance while being environmentally friendly.

[0027] Calcium sulfonate also acts as a lubricant, reducing friction and wear between moving surfaces (sliding surfaces). When added to wax, it improves the lubricating properties of the wax, promoting smoother movement and reducing friction, for example, between seals on a hydraulic rod.

[0028] The addition of calcium sulfonate also improves the oxidation resistance of the wax, acting as an antioxidant to prevent deterioration in the presence of oxygen, thereby extending the wax's lifespan.

[0029] Calcium sulfonate further provides water stability and forms a protective layer on metal surfaces, preventing corrosion and maintaining lubricity even in humid environments.

[0030] In one embodiment, the solution comprises a wax essentially consisting of C20-C35 alkane fractions and calcium sulfonate.

[0031] This provides excellent corrosion resistance while using economical and readily available raw materials.

[0032] The wax can be diluted with a solvent containing mainly C8-C12 alkanes (especially C9, C10, and C11), or with white spirits.

[0033] The present invention also relates to a steel machine part subjected to such surface treatment, wherein the steel machine part comprises a nitrided surface layer impregnated with a hydrophobic wax-based solution, the wax being an organic carbon compound having a molecular weight of less than 500, preferably 200 to 500.

[0034] Preferably, based on the confirmed performance, the treated and impregnated mechanical parts have a density of 5-60 g / m². 2 Preferably 30-60 g / m²2 It can have a low wax coating weight with a mass per unit area, resulting in reduced product consumption, lower costs, and limited environmental impact. [Modes for carrying out the invention]

[0035] The present invention relates to a surface treatment process for improving the wear resistance and corrosion resistance of steel machine parts. This process is based on a surface treatment based on nitriding or soft nitriding, followed by impregnation with a solution containing at least one specific hydrophobic wax.

[0036] The present invention is particularly advantageous for processing parts that require high corrosion resistance, as evaluated by salt spray testing (ISO 9227), and that are used under harsh conditions such as weather, exposure to sand, or repeated high-pressure washing.

[0037] One example of a processed part is the tailgate cylinder rod located at the rear of the truck body, which is often subjected to environmental stress and friction from the cylinder inlet seal (in an extended state).

[0038] The nitriding or soft nitriding step allows for the diffusion of nitrogen (or nitrogen and carbon) into the steel surface, forming a nitrided layer that improves wear resistance.

[0039] In some embodiments, this step is followed by oxidation to further enhance corrosion resistance by forming a protective oxide barrier.

[0040] Nitriding and subsequent oxidation form a layer comprising a dense inner sublayer and a porous outer sublayer (5-25 μm thick) with open pores of 0.2-3 μm. The steel parts thus treated are then impregnated with a hydrophobic wax-based solution having a molecular weight of 200-500 and a solid surface energy of 29-35 mN / m.

[0041] Surface energy is measured by the contact angle in three polished samples immersed in 50%, 75%, and 87.5% wax solutions (wax content 50%, 25%, and 12.5%) and dried for 24 hours. The energy is largely independent of concentration.

[0042] The wax according to the present invention provides excellent impregnation and resistance under harsh exposure. Impregnation may be achieved by immersion or spraying at ambient temperature.

[0043] Immersion should continue for at least 2 minutes. The wax is generally diluted to 50-80% with a solvent (C8-C12 alkanes or white spirits). After impregnation, the process is completed by air drying for at least 5 minutes.

[0044] The wax solution advantageously contains 1-30%, preferably 2-20%, calcium sulfonate, and the wax is based on a C20-C35 alkane fraction. Optionally, to enhance cohesiveness, 1,1'-biphenyl 4,4'-dibromo(C) 12 Plasticizers such as H8Br2 may be added.

[0045] The resulting steel components have a nitrided layer impregnated with hydrophobic wax, significantly improving wear resistance and corrosion resistance under harsh conditions.

[0046] The outer sublayer has over 60% Fe 2-3 This includes N phase, hardness of 550-650 HV0.1, and surface roughness of 0.3-1.5 μm CLA.

[0047] The wax may be natural or synthetic (polyethylene, polypropylene, polyester, fluorinated wax, or modified petroleum wax).

[0048] The composition, thickness, and hardness of the nitride layer are optimized to withstand wear without becoming brittle or prone to delamination. Fe 2-3The hexagonal close-packed structure of N provides good deformability and excellent friction performance.

[0049] The use of a molten salt bath for nitriding treatment, as described in document FR-A-2171993, is a notable advantage of the present invention. This bath consists essentially of carbonates and cyanates of the alkali metals K, Na and Li. The weight proportion of alkali cations, relative to the total weight of the bath, is Na + is 25 to 42.6% for K + is 42.6 to 62.5% for, and Li + is 11.3 to 17.1% for.

[0050] The oxidation treatment also improves corrosion resistance and optimizes the surface structure for efficient wax impregnation.

[0051] Oxidation is generally carried out in a molten salt bath at 350 to 450°C, similarly as in FR-A-2525637.

Examples

[0052] Corrosion resistance tests were carried out on both cleaned and uncleaned parts treated according to the present invention and comparative parts.

[0053] The nitriding and oxidation steps were identical, only the type of wax differed.

[0054] The nitrided layer (dense sublayer + porous sublayer) had a thickness of 20 to 30 μm (with a 5 to 10 μm porous surface). The oxide layer had a thickness of about 1 to 2 μm. All impregnations were carried out by immersion.

[0055] High-pressure cleaning was carried out at a distance of 50 cm using a 180 bar cold water jet for 30 seconds.

[0056] The results of these tests are summarized in the table below.

[0057] [Table 1]

[0058] For each test, trials were conducted on 10 parts, and the time it took for corrosion to occur in 50% of the parts was measured.

[0059] Parts 0, 0bis, and 0ter, treated according to the present invention and not cleaned, were observed to exhibit improved corrosion resistance and achieve exposure to salt spray for over 1600 hours without any corrosion occurring.

[0060] Parts 0, 0bis, and 0ter, processed according to the present invention and subjected to high-pressure cleaning, have a relatively low amount of wax present in the layer, i.e., 60 g / m². 2 Less than 35g / m² 2 Despite being less than [amount missing], it withstood exposure to salt spray for over 500 hours, and even over approximately 1600 hours, without any signs of corrosion, which is very satisfactory.

[0061] Conversely, it should be noted that the corrosion resistance of parts treated with waxes in the form of organic carbon compounds having a molecular weight of 500 to 10,000 (see Tests 1, 2, 3, and 4) is less than 500 hours after high-pressure cleaning, and is therefore not considered satisfactory in the sense of the present invention.

[0062] Furthermore, it was observed that increasing the wax coating weight in Examples 2 and 4 somewhat improved corrosion resistance after high-pressure washing, but did not reach a satisfactory level of resistance.

[0063] As is clear from the above description, the present invention provides a surface treatment method for steel machine parts to improve wear resistance and corrosion resistance under harsh operating conditions, and also provides parts obtained by this process.

Claims

1. A surface treatment method for steel machine parts to improve wear resistance and corrosion resistance, The process includes at least one nitriding or soft nitriding step to form a nitrided surface layer, followed by impregnation of the nitrided layer with a solution containing at least one hydrophobic wax, The wax is characterized by being an organic carbon compound having a molecular weight of less than 500, preferably 200 to 500. method.

2. After the nitriding or soft nitriding step, oxidation is performed. The method according to claim 1.

3. Impregnation is carried out by immersion or spraying at ambient temperature. The method according to claim 1 or claim 2.

4. The immersion and impregnation will continue for at least two minutes. The method according to claim 3.

5. The impregnation solution comprises wax diluted with a solvent to a concentration of 50%, 75%, or 80%. The method according to any one of claims 1 to 4.

6. The impregnated part is air-dried at ambient temperature for at least 5 minutes. The method according to any one of claims 1 to 5.

7. The aforementioned solution contains 1% to 30% by mass of calcium sulfonate. The method according to any one of claims 1 to 6.

8. The solution contains the hydrophobic wax which is essentially composed of C20-C35 alkane fractions and calcium sulfonate. The method according to any one of claims 1 to 7.

9. The above solution is 1,1'-biphenyl 4,4'-dibromo (C １２ H ８ Br ２ ) further includes, The method according to any one of claims 1 to 8.

10. Steel machine parts that have been surface-treated to improve wear resistance and corrosion resistance, It has a nitrided surface layer impregnated with a hydrophobic wax-based solution, The wax is an organic carbon compound having a molecular weight of less than 500, preferably 200 to 500. Machine parts.

11. The aforementioned wax-based layer is 5 to 60 g / m² ２ Having a coating weight, The machine part according to claim 10.

12. The wax-based layer contains calcium sulfonate in an amount of 1% to 30% by mass. The machine part according to claim 10 or claim 11.

13. The wax-based solution comprises the wax, which is essentially composed of C20-C35 alkane fractions and calcium sulfonate. A machine part according to any one of claims 10 to 12.

Images