Methods for performing processing on parts made of ferrous metals and parts made of iron.

Abstract

Essentially, an invention deals with a method for performing a process on a part. (P) which is made from a group of ferrous metals consisting of: The nitriding action that forms on the part(P) is a composite layer(2) of considerable thickness. Between 5 and 30 micrometers and the diffusion area (3) which is located below and Contact with the composite layer (2) with a thickness between 100 micrometers and 500 micrometers; Next, The operation of wet hardening of part (P) by induction at high frequency throughout. A deep induction hardening of 0.5 mm or more is required for this process. The part (P) and it is to make that part (P) have: Surface hardness greater than or equal to 50HRC. Hardness of the aggregate layer (2) greater than or equal to 400HV0.0s, The hardness of the part is greater than or equal to 500HV0.05 at a depth of 500. micrometer, And since the high-frequency induction hardening process is performed without... Apply a protective film to the part (P) before induction hardening. The invention also involves a part (P) which is made of ferrous metals. Significant resistance to wear by abrasion and adhesion; possesses friction properties. And it has improved scratch resistance and excellent corrosion resistance;

Description

[0001] METHOD FOR TREATMENT OF A FERROUS METAL PART AND A PART IN

[0002] FERROUS METAL

[0003] TECHNICAL FIELD

[0004] The field of the invention is that of the surface treatment of ferrous metal parts, in particular very low or low alloy steel.

[0005] EARLIER ART

[0006] In automotive, aeronautical or industrial applications, mechanical parts are generally subjected to significant stresses in service.

[0007] Typically, parts can receive one or more treatments to improve some of their performance characteristics, including friction properties, wear resistance, fatigue resistance, flaking resistance, corrosion resistance, etc.

[0008] However, it is difficult to achieve a good compromise between the different properties of the part.

[0009] As an example, document WO2011013362A1 describes a process for treating a part, comprising a nitriding operation, a coating operation with a chemical conversion film (sol-gel), and an induction hardening operation. However, such a process is prohibitively expensive due to the cost of the film and the need to perform three successive operations.

[0010] DESCRIPTION OF THE INVENTION

[0011] The aim of the present invention is to remedy the above disadvantages, while maintaining a good compromise between the different properties of the part.

[0012] To this end, the invention relates to a process for treating a ferrous metal part, comprising:

[0013] - a nitriding operation forming a compound layer on the part with a thickness between 5 µm and 30 µm, and a diffusion zone arranged under and in contact with the compound layer with a thickness between 100 µm and 500 µm; then - a high-frequency induction hardening operation of the part, with an induction depth greater than or equal to 0.5 mm, causing hardening of the part and providing said part with:

[0014] • a surface hardness greater than or equal to 50 HRC,

[0015] • a hardness of the combination layer greater than or equal to 400 HV0.05,

[0016] • a hardness of the part greater than or equal to 500 HV0.05 at a depth of 500 pm, and in which the high-frequency induction hardening operation is carried out without application of a protective film on the part prior to the induction hardening operation.

[0017] The process of the invention makes it possible to obtain a part exhibiting both high resistance to wear by abrasion and adhesion, improved friction and flaking resistance properties, and good corrosion resistance. Furthermore, the process of the invention is simpler to implement and less expensive than prior art processes because it eliminates the need for applying a protective film to the composite layer, as well as the potential removal of said protective film.

[0018] The protective film can be of any type suitable to prevent degradation of the combination layer during high-frequency induction quenching, this degradation being manifested by flaking, cracking, or fracturing of the combination layer.

[0019] In particular, the protective film can be a sol-gel film. Therefore, the high-frequency induction hardening operation is carried out without a sol-gel film.

[0020] In other respects, the treatment process according to the invention has the following characteristics, taken individually or in technically feasible combinations: the nitriding operation is carried out using gas, plasma, or molten salts; the nitriding operation is carried out at a temperature between 500°C and 630°C, for a duration between 15 minutes and 3 hours; the induction hardening operation is not followed by a tempering operation; the high-frequency induction hardening of the workpiece is carried out in such a way as to retain ferrite within the workpiece between the diffusion zone / combination layer interface and a depth of 500 µm, preferably between the diffusion zone / combination layer interface and a depth of 300 µm. The diffusion zone / combination layer interface means the contact surface between the diffusion zone and the overlying combination layer.The quenching process is rapid and does not completely transform the ferrite in the part into martensite to its treatment depth, so some ferrite remains at the depth treated by HF quenching at the end of the process. The 500 pm depth corresponds to an induction depth where hardening and / or changes in the metallurgical structure of the part are observed; the high-frequency induction quenching operation of the part is carried out in such a way as to have a residual ferrite content in the part, between the diffusion zone / combination layer interface and a depth of 500 pm, of between 1% and 50% by volume, preferably between 1% and 30%, and even more preferably between 5% and 30%.The residual ferrite content is volumetric and corresponds to the ratio of the ferrite volume to the volume of the rest of the part in the area considered. The high-frequency induction hardening operation is carried out so as to have a residual ferrite content in the part, between the diffusion zone / combination layer interface and a depth of 500 µm, of between 5% and 20% by volume, preferably between 5% and 15%. The process includes an impregnation step after the high-frequency induction hardening operation. If a tempering step is performed, impregnation is carried out after tempering. It can be done, for example, by dipping or spraying.Impregnation protects the part by delaying the onset of corrosion, reducing the corrosion rate, and thus increasing the part's lifespan; the process provides the part with corrosion resistance exceeding 80 hours in a neutral salt spray test. Corrosion resistance is measured by a neutral salt spray test, sometimes also called a standard salt spray test, according to EN ISO 9227; the high-frequency induction hardening operation is carried out with the following parameters:

[0021] • a frequency between 50 and 400 kHz,

[0022] • a linear energy between 4.6 and 5.8 J / mm.

[0023] This dual requirement for frequency and linear energy allows for the production of a ferrous metal part with significantly improved mechanical properties compared to state-of-the-art parts, particularly resistance to abrasion and adhesion wear, friction, and spalling, while maintaining good corrosion resistance. The frequency and linear energy are adjusted according to the part's morphology, such as its diameter; the high-frequency induction hardening operation is performed with a feed rate between 5 and 40 mm / s.

[0024] The invention also relates to a ferrous metal part, comprising a compound layer having a thickness of between 5 µm and 30 µm, and a diffusion zone arranged under and in contact with the compound layer, having a thickness of between 100 µm and 500 µm, said part having:

[0025] - a surface hardness greater than or equal to 50 HRC,

[0026] - a hardness of the combination layer greater than or equal to 400 HV0.05,

[0027] - a hardness of the part greater than or equal to 500 HV0.05 at a depth of 500 pm, said part comprising ferrite and martensite between the diffusion zone / combination layer interface and a depth of 500 pm.

[0028] According to other aspects, the ferrous metal part according to the invention has the following characteristics, taken individually or in technically feasible combinations: the hardness of the part at a depth of 0.5 mm is greater than or equal to a core hardness + 100 HV0.05; the hardness of the part at a depth of 0.25 mm is greater than or equal to a core hardness + 350 HV0.05; the part is made of very low-alloy steel, from the C10-C70 family, with a manganese content of less than 1%. Under these conditions, the steel does not contain any significant alloying elements, i.e., any element exceeding 5% by mass relative to the total mass of the steel. Preferably, the part is made of C45 grade steel. The term "grade," commonly used in the field of steels, designates a specific steel within a family.In particular, this refers to grade C45 chosen from the C10 to C70 steel family; the part is made of low-alloy steel, without any alloying element exceeding 5% by mass. More preferably, the part is made of 31CrMo4 grade steel; the part comprises ferrite and martensite between the diffusion zone / combination layer interface and a depth of 300 µm; the part comprises a ferrite content, between the diffusion zone / combination layer interface and a depth of 500 µm, of between 1% and 50% by volume, preferably between 1% and 30%, and more preferably between 5% and 30%; the part comprises a ferrite content, between the diffusion zone / combination layer interface and a depth of 500 µm, of between 5% and 20% by volume, preferably between 5% and 15%; The part exhibits corrosion resistance of over 80 hours in a neutral salt spray test.

[0029] In this text, "thickness" means the distance between the upper and lower limits of a given layer or zone within the ferrous metal part. The thickness is perpendicular to the average surface of said upper and lower limits.

[0030] The term "depth" refers to the distance between the surface of the part, also called the free surface, and a given point within the part. The depth is perpendicular to the average area of ​​the free surface. For example, "a diffusion zone hardness greater than or equal to 500 HV0.05 at a depth of 500 pm" means that at a distance of 500 pm within the part, measured from the free surface of the part, the diffusion zone hardness is greater than or equal to 500 HV0.05.

[0031] Terms such as "on," "above," "above," and "under," "below," refer to the relative positions of layers or areas within the room. These terms do not necessarily imply contact between the layers or areas in question.

[0032] Nitriding, as is well known, involves immersing a ferrous metal part in a nitrogen-releasing medium. In this text, nitriding encompasses nitrocarburizing, a variant of nitriding in which carbon is introduced into the part in addition to nitrogen. The ARCOR process described later in this text is a preferred example of a nitrocarburizing process.

[0033] Within the treated part, the diffusion zone is located beneath the combination layer and extends towards the core of the part (away from the free surface) from said combination layer. The combination layer itself can be on the surface of the part or at a given depth.

[0034] An induction depth of 0.5 mm or greater means that the hardening and / or changes in the metallurgical structure of the part, caused by the induction hardening step, extend from the surface of the part to a depth of at least 0.5 mm. Beyond a certain depth, the thermal effect gradually diminishes until it no longer has a measurable effect on the microstructure and hardness of the part.

[0035] The high-frequency induction hardening process provides a part hardness greater than or equal to 500 HV0.05 at a depth of 500 µm, and preferably, corrosion resistance exceeding 80 hours in a standard salt spray test. Indeed, surprisingly, the high-frequency induction hardening according to the invention enhances the mechanical properties, particularly the hardness, of the previously nitrided part, while preserving the compound layer. Thus, the corrosion resistance of the parts is maintained without the need for additional treatments such as a sol-gel film or paint. Eliminating the need for a sol-gel film reduces processing costs.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which:

[0038] Figure 1 is a graph illustrating the hardness profile of two parts, respectively conforming (ARCOR FLASH, i.e. ARCOR nitriding treatment followed by high-frequency induction hardening) and not conforming to the invention (ARCOR alone, without high-frequency induction hardening).

[0039] Figure 2 is a table describing a series of tests carried out on steel parts, in order to characterize the process according to the invention.

[0040] Figure 3 is a graph illustrating a series of tests corresponding to the table in Figure 2.

[0041] Figure 4 is a micrograph of a part treated by the process according to the invention.

[0042] Figure 5 is a close-up view of Figure 4.

[0043] Figure 6 is a micrograph of a part treated according to the prior art (ARCOR treatment followed by induction hardening according to the prior art).

[0044] Figure 7 is a micrograph of a part treated after ARCOR treatment, without induction hardening.

[0045] Figure 8 is a micrograph of a ferrous metal part according to the invention (ARCOR FLASH treatment).

[0046] Figure 9 is a montage of a micrograph of a ferrous metal part according to the invention and a hardness profile obtained by measurement on the same part.

[0047] Figure 10 is a graph illustrating the evolution of the coefficient of friction of rings, for a ring according to the invention (ARCOR FLASH treatment) and a prior art ring (ARCOR treatment alone). Figure 11 is a photograph of a ferrous metal part that has undergone ARCOR treatment alone.

[0048] Figure 12 is a photograph of a ferrous metal part according to the invention, having undergone ARCOR FLASH treatment (ARCOR nitriding followed by high-frequency induction quenching).

[0049] Figure 13 is a close-up view of the micrograph of Figure 4, centered on the induction layer.

[0050] DETAILED DESCRIPTION OF THE INVENTION

[0051] The inventors' approach was to carry out several series of tests implementing different treatments of a ferrous metal part.

[0052] In particular, the inventors studied the effects of the following two treatments.

[0053] The ARCOR nitrocarburizing treatment (trademark registered by the Applicant) creates, from the surface towards the core of the part, a juxtaposed combination layer 2 and diffusion zone 3 (see Figure 4). The combination layer 2 typically has a thickness of approximately 20 µm, while the diffusion zone 3 typically has a thickness of a few tens or hundreds of microns, for example 300 µm.

[0054] High-frequency hardening (frequency > 20 kHz) creates a martensitic structure on the surface of the part, on an induction layer typically around 1 mm deep. In other words, induction hardening extends from the surface of the part to a depth of approximately 1 mm, and is superimposed on the hardening profile already obtained by nitriding. The induction layer comprises Fe(a') martensite resulting from the transformation of Fe(a) ferrite, as well as remaining untransformed Fe(a) ferrite, and offers significant hardness, considered highly beneficial for resistance to abrasive wear and fatigue.

[0055] The combination layer 2 offers, among other things, good friction properties, high resistance to adhesive wear and good corrosion resistance.

[0056] The diffusion zone 3 offers a hardness gradient, between the combination layer 2 and the base material 1 located below the diffusion zone 3, which is favorable to a certain resistance to wear (abrasive and adhesive) and to fatigue resistance.

[0057] Table 1 below describes different series of tests:

[0058] Legend :

[0059] 0: Non-existent property +: Moderate improvement of the property ++: Good property +++: Excellent property -: Degraded property

[0060] Comments on the results of the series of tests:

[0061] - Series 1: Shallow underlayer hardness depth (“0.3 mm”), therefore resistance to abrasive wear and moderate fatigue.

[0062] - Series 2: Lack of anti-seize and corrosion resistance. - Series 3: ARCOR nitriding temperature ( «590°C) has a tempering effect on the martensitic structure brought about by HF quenching. This results in a significant decrease in hardness. The results are comparable to those of Series 1.

[0063] - Series 4: The time / temperature parameter of HF quenching degrades the ARCOR combination layer. Corrosion resistance properties and tribological behavior are therefore degraded.

[0064] - Series 5: Surprisingly, HF FLASH hardening minimizes or even eliminates degradation of the ARCOR Combination Layer 2 (oxidation or flaking that leads to losses of corrosion resistance and the tribological properties associated with Combination Layer 2). Compared to Series 4, the part retains its basic properties provided by ARCOR. Compared to Series 1, HF FLASH hardening increases the hardness below Combination Layer 2, as well as the depth of hardening.

[0065] The development of the invention required, firstly, identifying the unexpected advantages of HF FLASH quenching compared to conventional HF quenching, and secondly, characterizing the parameters of HF FLASH quenching in order to be able to implement the ARCOR treatment process + HF FLASH quenching = ARCOR FLASH on all types of ferrous parts.

[0066] Figure 1 is a graph comparing the hardness profile of two parts: one receiving ARCOR treatment alone (Series 1) and the other receiving ARCOR FLASH treatment according to the invention (Series 5). The ARCOR FLASH treatment increases the hardness below the combination layer 2, particularly in the diffusion zone, as well as the hardening depth. For the sample in Figure 1, the diffusion zone 3 has a thickness between 400 µm and 500 µm, and the induction depth is approximately 1 mm.

[0067] Figure 2 is a table describing a series of tests carried out on steel parts, in order to characterize the ARCOR FLASH treatment process according to the invention.

[0068] The parts are steel bars with a diameter of 38 mm, having received an ARCOR treatment creating a combination layer with a thickness between 15 and 20 µm.

[0069] Tests E1-E9 are performed on C45 steel bars, tests E10 and E11 on C10 steel bars, test E12 on a C70 steel bar, and test E13 on a 42CD4 steel bar. The tests consist of high-frequency induction hardening operations performed with variable parameters. The speed of the magnetic inductor moving along the workpiece is determined by its translational speed.

[0070] Comments on the test results:

[0071] - E1 (comparative): Low frequency and high power. Combination layer degraded by induction.

[0072] - E2 (according to the invention): Optimal linear energy. Satisfactory results.

[0073] - E3 (comparative): Scrolling speed a little too fast. Linear energy a little too low. Surface hardness and induction depth too low.

[0074] - E4 (conforming to the invention): Results less good than E2 but better than E3.

[0075] - E5 (comparative): Scrolling a little too slow. Linear energy a little too high. Surface hardness and induction depth satisfactory, but combination layer degraded by induction.

[0076] - E6, E7, E8 and E9 (all in accordance with the invention): Tests aimed at determining the influence of frequency and scrolling speed. Satisfactory results.

[0077] - E10, E11 and E12: Tests illustrating the influence of the steel grade on the results of the treatment.

[0078] - E10 (comparative): The parameters of test E5, tested on a C10 steel, give a non-compliant result.

[0079] - E11 (according to the invention): The parameters of test E2, tested on a C10 steel, allow us to obtain satisfactory results.

[0080] - E12 (according to the invention): The parameters of test E2 also allow satisfactory results to be obtained with C70 steel.

[0081] - E13 (according to the invention): The parameters of test E8, applied to a 42CD4 steel, allow satisfactory results to be obtained.

[0082] Figure 3 is a graph showing the results of tests E1-E9 from Figure 2, carried out on C45 steel bars.

[0083] On the graph, linear energy (in Ws / mm) is represented on the x-axis and induction frequency (in kHz) is represented on the y-axis.

[0084] Linear energy is defined as the induction power divided by the throughput speed of the parts P during induction. This quantity is related to the geometry of the parts P being treated. Another, more general quantity could be the surface power density applied over a certain time, that is, the induction power divided by the surface area of ​​the part absorbing the induction, and divided by the throughput speed. It would thus be possible, starting from optimal quenching parameters for a part of a first dimension, to easily find the optimal quenching parameters for a part of a second dimension (for example, with a larger diameter), assuming all other parameters are equal (same material, same nitriding).

[0085] According to figures 2 and 3, it can be noted that the tests carried out on C45, C10, C70 and 42CD4 steels for which the frequency (F) is between 50 kHz and 400 kHz and the linear energy (E) is between 4.6 and 5.8 J / mm (we are then in the area modeled by the dotted rectangle on figure 3), make it possible to obtain after induction: a combination layer of satisfactory quality, a combination layer with a hardness greater than or equal to 400 HV0.05, an induction depth greater than or equal to 0.5 mm, a surface hardness greater than or equal to 50 HRC, and satisfactory corrosion resistance.

[0086] Moreover, these results are obtained without the need to pre-coat the part in a protective film before high-frequency induction quenching, such as a sol-gel film, which reduces the complexity and costs of the treatment.

[0087] For tests 2, 4, and 6-9 and 11-12, all in accordance with the invention, the following advantageous properties: the hardness of the diffusion zone at a depth of 0.25 mm is greater than or equal to a core hardness + 350 HV0.05, and the hardness of the diffusion zone at a depth of 0.5 mm is greater than or equal to the core hardness + 100 HV0.05.

[0088] The treatment according to the invention is therefore effective up to a great depth in the diffusion zone.

[0089] These tests were carried out on C45, C10, C70, and 42CD4 steel bars. In practice, the frequency (F) and linear energy (E) of the high-frequency induction hardening are adapted to the ferrous metal of the part P. It may be necessary to proceed by trial and error to determine the appropriate parameters. For the production of the micrographs of the metal parts illustrated in Figures 4 to 8, and described below, the parts were subjected to chemical etching with a solution of nitric acid and alcohol called "Nital." Nital thus acts as a revealer of the part's microstructure, making it visible under an optical microscope.

[0090] Figures 4 and 5 are micrographs of a C45 steel part P that has received the ARCOR FLASH treatment (ARCOR + HF induction hardening, according to the invention) with a combination layer 2 of 18 pm, a diffusion zone 3 of about 300 pm and an induction depth of about 0.5 mm.

[0091] Part P comprises a steel substrate 1, an induction layer 4, a combination layer 2, and a diffusion zone 3. An aluminum foil 5 and an encapsulation 6 were added to create the cross-section necessary for micrographing. In Figure 4, segment [AB] represents the distance (thickness) between an average surface of the combination layer 2 (interface between the diffusion zone 3 and the combination layer 2) and an average surface of the steel substrate 1.

[0092] The combination layer 2 and the diffusion zone 3 are obtained here by ARCOR nitrocarburization.

[0093] Induction layer 4 is obtained by high-frequency induction. It is composed of fine martensite Fe(a') and ferrite Fe(a). Figure 5 clearly shows the presence of ferrite Fe(a) remaining in the hardened zone of the part obtained at the end of the process, after hardening. This microstructure conforms to the invention.

[0094] Figure 6 illustrates a micrograph of a nitrided steel that has subsequently undergone conventional high-frequency quenching: all the ferrite Fe(a) has been transformed into martensite Fe(a') during quenching. Therefore, no ferrite remains in the treated area. This microstructure is thus not in accordance with the invention.

[0095] Figure 7 illustrates a ferrous metal part that has received ARCOR nitrocarburizing alone (without quenching), and Figure 8 illustrates a part according to the invention, therefore having received nitrocarburizing then HF quenching (ARCOR + HF induction quenching, according to the invention).

[0096] In Figure 8, it can be seen that the compound layer 2 of part P has a black top layer 2a measuring approximately ten micrometers. This top layer 2a has been rendered porous by high-frequency quenching and is clearly revealed by Nital. This demonstrates that, following the treatment process according to the invention, the compound layer is slightly degraded by high-frequency quenching but remains present and retains its structural integrity, at least in its lower portion 2b. Such a top layer 2a is not observed in Figure 7. The structure of the compound layer has not been modified since no quenching has taken place.

[0097] The part P according to the invention therefore does indeed have a combination layer 2 giving the part wear and friction resistance properties, and corrosion resistance, despite the fact that the HF quenching was carried out without a protective film.

[0098] Figure 9 shows a montage juxtaposing a micrograph of a part P according to the invention and a hardness profile obtained by measurements on the same part. Hardness measurement points are visible on the micrograph, and measurement intervals corresponding to the different layers are outlined.

[0099] In this figure, the partially oxidized combination layer 2 and the induction layer 4 are particularly visible. Hardness measurements taken just below the combination layer show a hardness of up to 900 HV. Moving away from the surface of the part and towards its core, the hardness decreases almost linearly, allowing the thickness of the diffusion zone 3 to be estimated at approximately 175 µm, a depth at which the hardness reaches 775 HV.

[0100] For depths ranging from 200 µm to 500 µm, the hardness is generally stable at values ​​between 550 and 600 HV. These depths are located within the induction treatment zone, which is visually detectable on the micrograph due to the crystallography of the part.

[0101] Measurements taken from a depth of 600 µm and beyond are located in the base material of the part, i.e., the core of the part, which has not undergone any treatment. The recorded hardness values ​​are approximately 250 HV.

[0102] With reference to Figures 10 to 12, the Applicant then carried out mechanical aging tests on parts to characterize the performance of the resulting parts. A smooth 42CD4 steel ring with ARCOR nitrocarburization alone, hereinafter referred to as the "ARCOR ring," is compared with a smooth 42CD4 steel ring with ARCOR nitrocarburization and HF quenching according to the invention.

[0103] These two bushings were mounted on 16NC6 CT steel shafts, with the addition of commercial lubricant. The applied load induced a contact pressure of 50 MPa, and the rotational speed of the bushings relative to the shaft was 7.8 mm / s.

[0104] Figure 10 is a graph illustrating the evolution of the friction coefficient of these two rings as a function of the number of revolutions. The y-axis represents the friction coefficient m (unitless), and the x-axis represents the number of revolutions Rev (in revolutions) that the ring undergoes. It can be seen that the ARCOR ring alone has a friction coefficient m of approximately 0.15 at nine revolutions, and that this coefficient begins to increase steadily from only 2000 revolutions, reaching high values ​​of around 0.6 at approximately 9000 revolutions.

[0105] The part P according to the invention has, in its new condition, a coefficient of friction slightly lower than that of the ARCOR ring alone, on the order of 0.1, and remains stable up to approximately 11,000 rpm. It is only from this value that the coefficient of friction begins to increase, reaching a value of 0.6 at approximately 125,000 rpm, similar to that of the ARCOR ring alone.

[0106] Figures 11 and 12 are photographs, respectively, of the ARCOR ring alone and of part P according to the invention, after these tests. They show that the ARCOR ring alone exhibits marked wear, with material having been torn away by seizing. Part P, on the other hand, shows less pronounced wear.

[0107] Figure 13 is a close-up view of the micrograph in Figure 4, centered on induction layer 4. The thickness of induction layer 4 is represented by segment [AB]. Processing the image in Figure 13 allows us to estimate the proportion of areas composed of ferrite Fe(a) in the induction layer, that is, relative to the sum of the areas of ferrite Fe(a) and martensite Fe(a'). More precisely, by defining lower and upper gray-level thresholds, we can estimate the area occupied by the mid-gray zone of the martensite phase and thus determine the ferrite content. It is necessary to use two thresholds and vary them to arrive at this estimate, because although the ferrite appears light, the phase interfaces can appear dark, and for small ferrites, this cannot be negligible.

[0108] In the example of Figure 13, the residual ferrite content relative to the rest of the layer delimited by segment [AB] is between 1% and 15%, with this content tending towards 1% near the combination layer (point A), and towards 15% near the core (point B). The residual ferrite content is volumetric.

[0109] In general, the treatment process according to the invention makes it possible to obtain a residual ferrite rate in the part, between the diffusion zone interface 3 / combination layer 2 and a depth of 500 pm (segment [AB]), greater than or equal to 1%, preferably greater than or equal to 5%.

[0110] Similarly, the treatment process according to the invention makes it possible to obtain a residual ferrite rate in the part, between the diffusion zone 3 / combination layer 2 interface and a depth of 500 pm (segment [AB]), less than or equal to 50%, preferably less than or equal to 30%, more preferably less than or equal to 20%, and more preferably less than or equal to 15%.

[0111] Preferably, the residual ferrite content is between 1% and 20%, preferably between 5% and 15%.

[0112] The manufacturing process may optionally include an impregnation step, in order to improve the corrosion resistance of part P.

[0113] Preferably, impregnation takes place after induction hardening.

[0114] Impregnation itself is a well-known technique to those skilled in the art, and a particular method is described, for example, in document EP3237648. Impregnation can be done by dipping or by spraying.

[0115] Impregnation protects the part because it delays the start of corrosion, reduces the rate of corrosion and thus increases the part's lifespan.

[0116] An evaluation of the corrosion resistance of parts can be carried out by tests under a corrosive atmosphere, for example, a salt spray. The EN ISO 9227 standard, "Corrosion tests in artificial atmospheres — Salt spray tests," describes such tests. By adding an impregnation step to the process according to the invention, it is possible to obtain a part P whose corrosion resistance in a neutral salt spray test exceeds 80 hours.

[0117] In light of the foregoing, and somewhat unexpectedly, numerous advantages can be obtained by implementing a nitriding operation followed by a high-frequency induction hardening operation according to the invention. These operations make it possible to obtain ferrous material parts exhibiting significant resistance to wear by abrasion and adhesion, and improved friction properties, resistance to spalling combined with adequate corrosion resistance, without the need to coat the part before HF hardening.

Claims

<h2>1. Methods for performing processing on parts (P) which are made of ferrous metals.< / h2> <h2> Consisting of:< / h2> <h2> -The nitriding operation that forms on the part(P) is a composite layer(2) that is of considerable thickness.< / h2> <h2> Between 5 micrometers and 30 micrometers and the diffusion area (3) which is located< / h2> <h2> Below and in contact with the aggregate layer (2) which has a thickness between 100 micrometers and< / h2> <h2> 500 micrometers: Next.< / h2> <h2> -Induction hardening of damp parts (P) at high frequency throughout the depth.< / h2> <h2> Induction hardening of 0.5 mm or greater means the process is considered hardened.< / h2> <h2> The part (P) and it is to make that part (P) have:< / h2> <h2> Surface hardness greater than or equal to 50HRC.< / h2> <h2> ?The hardness of the overall layer (2) is greater than or equal to 400HV0.05.< / h2> <h2> The hardness of the part is greater than or equal to 500HV0.05 at depth.< / h2> <h2> 500 micrometers< / h2> <h2> And since the high-frequency induction hardening operation is performed without...< / h2> <h2> Application of protective film on parts (P) prior to induction hardening.< / h2> <h2> 2. The method under Claim 1, which is characterized by a hardening operation based on...< / h2> <h2> Induction is not followed by temper operation.< / h2> <h2>3. The method under Claim 1 or Claim 2, which is characterized by the operation of...< / h2> <h2> High-frequency induction hardening of parts is performed in a pathway where the Ferrite pathway is preserved.< / h2> <h2> Part(P) between the contact surface of the diffusion area(3), the combined layer(2), and at a depth of 500.< / h2> <h2> The desired micrometer is between the contact surfaces of the diffusion area (3), the combined layer (2), and< / h2> <h2> At a depth of 300 micrometers.< / h2> <h2> 4. The method based on any one of the preceding claims, which has the following characteristics:< / h2> <h2> The induction hardening process at high frequency is performed in a way that provides quantity.< / h2> <h2> Ferrite residues are found in the fragment (P) at the contact of the diffusion region (3) / combination layer (2) and at the< / h2> <h2> The desired depth is between 1 percent and 50 percent by volume.< / h2> <h2> That's between 1 percent and 30 percent, and the more desirable is between 5 percent.< / h2> <h2> And 30 percent.< / h2> <h2> 5. The method based on any one of the preceding claims, which has a specific characteristic, is:< / h2> <h2> The induction hardening process at high frequency is performed in a way that provides quantity.< / h2> <h2>Ferrite residues are found in the fragment (P) between the diffusion zone (3) / combination layer (2) and< / h2> <h2>< / h2> <h2> At a depth of 00 micrometers, the percentage is between 5 percent and 20 percent by volume.< / h2> <h2> The desirable percentage is between 5 percent and 15 percent.< / h2> <h2> 6. The method according to any one of the preceding claims which has a specific characteristic is:< / h2> <h2> This method incorporates an impregnation step following the hardening process.< / h2> <h2> High-frequency induction type.< / h2> <h2> 7. The method according to the claim, which is characterized by the fact that such method has resulted in a component (P).< / h2> <h2> It has corrosion resistance of more than 80 hours as tested using salt spray.< / h2> <h2> Neutral< / h2> <h2> 8. The method under any one of the preceding claims that has a specific characteristic is:< / h2> <h2> High-frequency induction hardening was performed with the following parameters:< / h2> <h2> Frequency (F) of 50 to 400 kHz,< / h2> <h2> Linear energy (E) at 4.6 to 5.8 micrometers / mm².< / h2> <h2> 1. Nitriding parts (P) which are made from ferrous metals combined with a composite layer (2)< / h2> <h2> with a thickness between 5 micrometers and 30 micrometers and a diffusion area (3) which is< / h2> <h2>Placed underneath and in contact with the aggregate layer (2) which has a thickness between 100 micrometers and 500 micrometers.< / h2> <h2> Micrometers, where the part (P) has:< / h2> <h2> Surface hardness greater than or equal to 50 HRC.< / h2> <h2> ?The hardness of the overall layer (2) is greater than or equal to 400HV0.05,< / h2> <h2> The hardness of the part is greater than or equal to 500HV0.0 at a depth of< / h2> <h2> 00 micrometers in which the particle (P) is composed of ferrite and< / h2> <h2> The martensite lies between the contact surface of the diffusion region (3) / combination layer (2) and< / h2> <h2> The depth is 500 micrometers.< / h2> <h2> 10. The component (P) under claim 9, which is characterized by the hardness of the component (P).< / h2> <h2> At a depth of 0.5 mm, the axial hardness is greater than or equal to +100HV0.05.< / h2> <h2> 11. Part (P) under claim 9 or claim 10, which is characterized by hardness.< / h2> <h2> The part (P) at a depth of 0.25 mm has a axial hardness greater than or equal to +350HV0.05.< / h2> <h2> 12. A component (P) under any one of the claims in Claims 9 through 11 that has a specific characteristic.< / h2> <h2> The part in question is made from very low alloy steel of the C10-C70 family with a high manganese content.< / h2> <h2> Less than 1 percent< / h2> <h2> 13. A component (P) under any one of the claims in Claims 1 through 12 which has the following characteristics:< / h2> <h2>Specifically, the component consists of ferrite and martensite located between the contacts.< / h2> <h2> The diffusion area (3), the total layer (2), and the depth are 300 micrometers.< / h2> <h2>< / h2> <h2> 14. A component (P) under any one of the claims in Claims 9 through 13 that has a specific characteristic.< / h2> <h2> This component consists of a quantity of ferrite located between the contact surfaces of the diffusion region.< / h2> <h2> (3) The total layer (2) and at a depth of 500 micrometers is between 1 percent and 50 percent by< / h2> <h2> The desired volume is between 1 percent and 30 percent, and even more desirable is...< / h2> <h2> Between 5 percent and 30 percent.< / h2> <h2> 15. A component (P) under any one of the claims in Claims 9 through 13 that has a specific characteristic.< / h2> <h2> This component consists of a quantity of ferrite located between the contact surfaces of the diffusion region.< / h2> <h2> (3) The total layer (2) and at a depth of 00 micrometers is between 5 percent and 20 percent.< / h2> <h2> By volume, the desirable percentage is between 5 percent and 15 percent.< / h2> <h2> 16. The claim (P) shall be based on one of the specific claims of Claims 9 through 1.< / h2> <h2> The component in question has corrosion resistance of over 80 hours according to testing using spraying.< / h2> <h2> With neutral saline solution.< / h2>;