Metal material and preparation method and application thereof

Abstract

The invention discloses a metal material and a preparation method and application thereof, and relates to the technical field of surface treatment. The metal material comprises a metal base material, wherein a hardened layer is arranged on the surface of the metal base material; the surface hardness of the hardened layer is Vickers hardness of 550-700, and the depth of the hardened layer is 20-50 microns; the hardness of the hardened layer is gradually reduced from outside to inside; the inward fingers face the direction of the metal base material; and the metal base material and the hardened layer are metallurgically bonded. The metal material has excellent frictional wear performance, the problem of binding force failure is avoided through the metallurgical bonding mode, and in the aspect of products, the durability life is prolonged, and the precision degradation rate is increased. When the metal material is used in the flexible gear or the harmonic speed reducer, the service life of the flexible gear or the harmonic speed reducer can be effectively prolonged, the precision retentivity of the flexible gear or the harmonic speed reducer can be effectively improved, and the harmonic speed reducer product has the advantages of being long in service life, low in abrasion, high in precision retentivity and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of surface treatment, and in particular to a metal material and a preparation method and application thereof. Background Art

[0002] Harmonic reducers are core components of industrial robots and are widely used in robot automation, aerospace and other fields. They have the characteristics of compact structure, light weight, strong load-bearing capacity and high transmission accuracy. Among the components of harmonic reducer products, the flexible wheel is the core component of the harmonic reducer products. The fatigue performance and tribological performance of the flexible wheel play an important role in improving the service life and other performance of the harmonic reducer. Therefore, in order to improve the use effectiveness of the flexible wheel parts of the harmonic reducer, after the raw material bar forging heat treatment and machining, the flexible wheel parts are usually subjected to surface strengthening treatment to improve the tooth root fatigue strength of the flexible wheel parts. However, this strengthening treatment has a very limited effect on the improvement of the friction and wear performance of the flexible wheel parts.

[0003] The friction and wear performance of the flexwheel parts plays a vital role in the service life and precision retention of the harmonic reducer. It directly affects the friction and wear behavior of the two key friction pairs, the inner wall of the flexwheel and the outer ring of the flexible bearing, and the tooth surface of the flexwheel and the tooth surface of the rigid wheel, during service. Among them, friction and wear performance mainly refers to friction reduction and wear resistance. Friction reduction refers to the reduction of friction coefficient, and wear resistance is related to wear rate. Therefore, improving friction and wear performance means that it is necessary to reduce friction coefficient and wear rate. However, the existing technology still lacks an effective solution that can effectively balance the friction coefficient and wear rate, improve the friction and wear performance of flexwheel parts, achieve high-precision retention, and ensure long service life. Summary of the invention

[0004] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, one of the purposes of the present invention is to provide a metal material provided with a hardened layer having a moderate surface hardness range and depth to reduce the friction coefficient and wear rate and improve the friction and wear performance of the metal material.

[0005] A second object of the present invention is to provide a method for preparing a metal material.

[0006] A third object of the present invention is to provide a flexible spline.

[0007] A fourth object of the present invention is to provide a harmonic reducer.

[0008] A fifth object of the present invention is to provide a joint component of an industrial robot.

[0009] A first aspect of the present invention provides a metal material, comprising a metal substrate, wherein a hardened layer is provided on the surface of the metal substrate; the surface hardness of the hardened layer is 550 to 700 Vickers hardness and the depth is 20 to 50 μm;

[0010] The hardness of the hardened layer is distributed decreasing from the outside to the inside; the inside refers to the direction toward the metal substrate;

[0011] The metal substrate and the hardened layer are metallurgically bonded.

[0012] The metal material in the embodiment of the present invention has at least the following beneficial effects:

[0013] The metal material includes a metal substrate, and a hardened layer is arranged on the surface of the metal substrate. The surface hardness of the hardened layer is 550 to 700 Vickers hardness. Within this hardness range, the friction and wear performance of the hardened layer can be effectively improved, and the friction coefficient and wear rate can be reduced. For the workpiece formed by the metal material, it has the effects of high precision retention and long life. The control of the depth of the hardened layer can ensure that the hardened layer can play its effect of improving the friction and wear performance, so that the surface of the metal material still has a hardened layer of sufficient depth after wear, which is beneficial to improving the service life of the metal material. If the depth is too large, it will affect the properties of the metal material itself.

[0014] At the same time, there is a metallurgical bond between the metal substrate and the surface hardened layer, so there is no problem with bonding strength. After long-term friction, it will not fall off due to failure of bonding strength, which is beneficial to improving the service life of the metal material.

[0015] According to some embodiments of the present invention, the measurement range of the depth of the hardened layer is a range where the Vickers hardness of the hardened layer is greater than or equal to 500.

[0016] According to some embodiments of the present invention, the core hardness of the metal substrate is 400-450 in Vickers hardness.

[0017] According to some embodiments of the present invention, the metal substrate comprises an alloy.

[0018] According to some embodiments of the present invention, the friction coefficient of the hardened layer is 0.08 to 0.13.

[0019] The second aspect of the present invention provides a method for preparing the metal material according to the first aspect of the present invention, comprising the following steps:

[0020] Providing a metal substrate, and performing nitrocarburizing on at least a portion of the surface of the metal substrate to form a hardened layer on at least a portion of the surface;

[0021] The surface hardness of the hardened layer is 550 to 700 Vickers hardness and the depth is 20 to 50 μm;

[0022] The hardness of the hardened layer decreases from the outside to the inside; the inside refers to the direction toward the metal substrate.

[0023] The preparation method according to the embodiment of the present invention has at least the following beneficial effects:

[0024] The preparation method of metal materials mainly includes a surface chemical heat treatment method for metal substrates, namely, a nitrocarburizing process, which can introduce a hardened layer with a hardness gradient on the surface of the metal substrate. The hardened layer has excellent friction and wear properties, and there is no problem of failure of bonding force with the metal substrate. Moreover, this preparation method will not cause significant deformation of the metal substrate. From the product level, this preparation method can effectively reduce the wear rate of metal products, making the products have the characteristics of long life, low wear, and high precision retention.

[0025] According to some embodiments of the present invention, during the nitrocarburizing process, the treatment temperature is 380-470°C.

[0026] In some embodiments of the present invention, during the nitrocarburizing process, the treatment time is 4 to 8 hours.

[0027] According to some embodiments of the present invention, the nitrocarburizing process is performed in an atmosphere into which ammonia, nitrogen and carbon dioxide are introduced.

[0028] According to some embodiments of the present invention, during the process of introducing gas, the ventilation rate of ammonia is 160-200 L / min; the ventilation rate of nitrogen is 60-100 L / min; and the ventilation rate of carbon dioxide is 2-3 L / min.

[0029] According to some embodiments of the present invention, before the metal substrate is subjected to nitrocarburizing, a preheating step is further included; and / or the preheating temperature is 200-300°C.

[0030] According to some embodiments of the present invention, the nitrocarburizing further includes a cooling step; the cooling is inert gas cooling.

[0031] A third aspect of the present invention provides a flexible spline, comprising the metal material described in the first aspect of the present invention.

[0032] The flexible wheel in the embodiment of the present invention has at least the following beneficial effects:

[0033] The flexible wheel made of metal material has a metallurgically bonded hardened layer on its surface, which can improve the surface hardness while ensuring the flexibility of the flexible wheel itself, and can effectively improve the friction and wear performance of the flexible wheel. The metallurgical bonding method of the hardened layer and the flexible wheel substrate prevents it from failing and falling off due to repeated deformation. In addition, in the process of preparing and forming the hardened layer of this metal material, it can also prevent the flexible wheel from being significantly deformed during the processing process, which affects its use.

[0034] According to some embodiments of the present invention, at least one side of the flexspline is provided with a hardened layer; the depth of the hardened layer is 10 to 25% of the minimum wall thickness of the flexspline.

[0035] A fourth aspect of the present invention provides a harmonic reducer, comprising the metal material described in the first aspect of the present invention, or the flexible spline described in the third aspect of the present invention.

[0036] The harmonic reducer according to the embodiment of the present invention has at least the following beneficial effects:

[0037] The harmonic reducer contains parts formed by a metal substrate, such as a flexible wheel. The surface of the metal substrate is provided with a hardened layer, which has excellent friction and wear performance, a low friction coefficient, and a low wear rate. In addition, the hardened layer and the metal substrate are metallurgically bonded, and there is no problem of bonding failure. Therefore, the wear rate of the flexible wheel parts and the accuracy degradation rate after durability can be effectively reduced, so that the harmonic reducer has the characteristics of long life, low wear, and high precision retention.

[0038] The fifth aspect of the present invention provides an industrial robot joint component, comprising the metal material described in the first aspect of the present invention, or the flexible spline described in the third aspect of the present invention, or the harmonic reducer described in the fourth aspect of the present invention.

[0039] The industrial robot joint includes the harmonic reducer, flexible wheel or metal material of the present invention. Since the durability and precision retention are improved, the positioning accuracy and service life of the industrial robot are also improved.

[0040] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. DETAILED DESCRIPTION

[0041] The embodiments of the present invention are described in detail below. The described embodiments are exemplary and are only used to explain the present invention, but should not be understood as limiting the present invention.

[0042] In the description of this specification, the description with reference to the terms "some embodiments", "some examples", "some specific embodiments", "some examples" or "some specific examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0043] The term "core hardness" refers to the hardness of a substrate (in this specification, a metal substrate or a flexspline) at half the thickness, that is, the hardness at the center of the substrate.

[0044] The term "depth" refers to the depth of the hardened layer, which refers to the surface of the substrate, that is, the range of the hardened layer Vickers hardness ≥ 500. In other words, it refers to the vertical distance from the Vickers hardness of 500 to the surface of the hardened layer.

[0045] The term "nitrocarburizing" refers to a nitrocarburizing process, which is a chemical surface heat treatment process for simultaneously infiltrating carbon and nitrogen into the surface of a substrate (in this specification, a metal substrate or a flexspline).

[0046] "Metal substrate" generally refers to a material with metal as the main component.

[0047] "Friction and wear performance" includes a reduction in the coefficient of friction and a reduction in the wear rate.

[0048] “Vickers hardness” can be represented by “HV”. In some embodiments of the present invention, the value of the Vickers hardness is represented by “value+HV”, for example, 550HV represents a Vickers hardness of 550.

[0049] The term "metallurgical bonding" as used herein refers to a bond formed by mutual diffusion of atoms at the interface between the hardened layer and the metal substrate.

[0050] The embodiment of the first aspect of the present invention provides a metal material, comprising a metal substrate, wherein a hardened layer is provided on the surface of the metal substrate; the surface hardness of the hardened layer is 550 to 700 Vickers hardness, and the depth is 20 to 50 μm;

[0051] The hardness of the hardened layer is distributed decreasing from the outside to the inside; the inside refers to the direction toward the metal substrate;

[0052] The metal substrate and the hardened layer are metallurgically bonded.

[0053] The metal material includes a metal substrate, and a hardened layer is provided on the surface of the metal substrate through metallurgical bonding. This metallurgical bonding method eliminates the problem of bonding force between the inside of the metal substrate and the surface hardened layer. After long-term accumulation of friction and wear, there will be no problem of bonding force failure leading to falling off. For workpieces obtained using this metal material, such as flexible wheels, the durability of the workpiece is greatly improved.

[0054] Controlling the surface hardness and depth of the hardened layer of the metal substrate is critical to improving the friction and wear properties of metal materials. Changes in the surface hardness of the hardened layer will affect the friction coefficient and wear rate, that is, the friction and wear properties of the metal material. For specific application products, such as flexible wheels, it is related to its service life and precision retention rate. When the surface hardness of the hardened layer is low, the wear resistance is poor, the wear rate increases, and the friction coefficient will also increase. After long-term accumulation of friction and wear, the precision degradation rate is large and the service life of the product is short; when the surface hardness of the hardened layer is high, the high surface hardness and the core hardness of the metal substrate are quite different. When the metal material is deformed during use, the contradiction caused by the hardness difference between the inside and the surface can easily cause damage to the material and affect the durability. As for the depth of the hardened layer, the control of the depth of the hardened layer is not only to ensure that the hardened layer can play its ideal effect, that is, to provide a depth sufficient to support wear on the surface, so that the metal material still has a hardened layer sufficient to improve the friction and wear performance after wear, but also to avoid excessive impact on the flexibility of the metal substrate itself. When the depth is too large, the hardened layer occupies more of the thickness of the metal substrate, resulting in the metal substrate being harder as a whole, which is not conducive to the flexible deformation of the overall metal material.

[0055] In some embodiments of the present invention, the hardened layer comprises nitride and carbide. In some embodiments of the present invention, the hardened layer is formed by a nitrocarburizing process.

[0056] In some embodiments of the present invention, the measurement range of the depth of the hardened layer is a range in which the Vickers hardness of the hardened layer is greater than or equal to 500.

[0057] In some embodiments of the present invention, the core hardness of the metal substrate is in the range of Vickers hardness of 400 to 450. Alternatively, the core hardness of the metal substrate may be in the range of Vickers hardness of 400, 410, 420, 430 or 450.

[0058] Controlling the core hardness of the metal substrate containing the hardened layer can ensure that the metal substrate does not lose the flexibility of the material itself while the hardened layer increases the surface hardness.

[0059] In some embodiments of the present invention, the surface hardness of the hardened layer, the depth of the hardened layer and the core hardness of the metal substrate are all tested according to the method in "GBT 9450-2005 Determination and Verification of the Depth of Carburizing and Quenching Hardened Layer of Steel Parts".

[0060] In some embodiments of the present invention, the metal substrate comprises an alloy. Further, the alloy can be an alloy structural steel, such as SNCM439 material. It is understandable that when the metal substrate is an alloy structural steel, the alloy structural steel can be any shape available to those skilled in the art, such as a rectangle, a square, a pie, an oval, etc.

[0061] In some specific embodiments of the present invention, the metal substrate may be a flexible metal part, such as a flexible wheel.

[0062] In some embodiments of the present invention, the friction coefficient of the hardened layer is 0.08 to 0.13. Optionally, in the present invention, the friction coefficient of the hardened layer may be 0.08, 0.1, 0.11, 0.12 or 0.13. In some embodiments of the present invention, the friction coefficient of the hardened layer may be 0.1 to 0.13. Further, it may be 0.1 to 0.12.

[0063] In some embodiments of the present invention, the friction coefficient is tested under lubrication conditions. In some specific embodiments of the present invention, the lubrication condition is to add grease for harmonic reducer products.

[0064] A low friction coefficient is beneficial to improving friction and wear performance. When the friction coefficient is low, the friction force generated under the same normal pressure is small, which helps to reduce the wear caused by friction. However, when the friction coefficient is too low, the friction force generated by the contact surface of the two objects is small, and slipping is easy to occur, which will also affect the use effect of the workpiece during application. The hardened layer of the present invention has a moderate friction coefficient, improves friction and wear performance and does not significantly affect other properties of the substrate.

[0065] An embodiment of the second aspect of the present invention provides a method for preparing the metal material according to the first aspect of the present invention, comprising the following steps:

[0066] Providing a metal substrate, and performing nitrocarburizing on at least a portion of the surface of the metal substrate to form a hardened layer on at least a portion of the surface;

[0067] The surface hardness of the hardened layer is 550 to 700 Vickers hardness and the depth is 20 to 50 μm;

[0068] The hardness of the hardened layer decreases from the outside to the inside; the inside refers to the direction toward the metal substrate.

[0069] The preparation method of the metal material of the present invention actually includes a surface chemical heat treatment method of a metal substrate. This surface treatment does not form a coating on the surface of the metal substrate by means of outward growth or coating, but by utilizing a nitrocarburizing process to penetrate elements such as carbon and nitrogen into a certain depth on the surface of the metal substrate, that is, to grow inward on the surface of the metal substrate to form a hardened layer. The hardened layer formed on the surface of the metal substrate by this method includes nitrides and carbides. Both compounds are hard particle points. They are dispersed in the surface structure of the metal substrate, so that the formed hardened layer has a certain surface hardness. Generally speaking, there will be a certain concentration gradient of nitrogen and nitrogen elements within a certain distance from the surface of the substrate. The element concentration is the highest at the surface, and the element concentration gradually decreases as it moves inward. Correspondingly, the hardness of the surface of the obtained metal material is also the highest, and the hardness gradually decreases inward, that is, the hardness of the hardened layer shows a distribution that decreases from the outside to the inside, and this distribution is also conducive to improving the surface hardness of the metal material while reducing the impact on the flexibility of the metal material itself.

[0070] It can be seen that the preparation method of the present invention forms a hardened layer on the surface of the metal substrate by nitrocarburizing. The formation of this hardened layer improves the hardness of the metal material surface, and the improvement of hardness also affects the friction coefficient and wear rate, achieving the effect of reducing the friction coefficient and wear rate, and improving the friction and wear performance of the metal material. When the metal is used as a specific workpiece, such as a flexible wheel part, in production, the improvement of friction and wear performance can improve its durability and precision degradation rate. In order to better improve the performance of the metal material, the control of the surface hardness and depth of the hardened layer formed is crucial. The change in the surface hardness of the hardened layer will affect the friction coefficient and wear rate, and at the product level it is related to the service life and precision retention rate of the workpiece. When the surface hardness of the hardened layer is low, the wear resistance is poor, the wear rate increases, and the friction coefficient will also increase. After long-term friction and wear accumulation, the precision degradation rate is large and the service life of the product is short; when the surface hardness of the hardened layer is high, the high surface hardness is large The gap between the hardness of the core of the substrate is large. When the material is deformed during use, the contradiction caused by the hardness gap between the inside and the surface of the substrate is easy to cause damage to the material, affecting the durability. As for the depth of the hardened layer, the control of the depth of the hardened layer is not only to ensure that the hardened layer can exert its ideal effect, but also to avoid excessive impact on the flexibility of the metal material itself.

[0071] Compared with traditional coatings, the hardened layer formed on the surface of the metal substrate by this preparation method can effectively further improve the durability. This is because a new coating is formed on the surface of the metal substrate. In essence, the coating and the substrate are two materials, and there is a problem of bonding between the two. No matter how high the original bonding is, after long-term operation, friction and wear, the bonding will inevitably fail, causing the coating to fall off and lose the strengthening effect. The hardened layer formed by the preparation method of the present invention is actually integrated with the metal substrate, and is an improvement on a part of the metal material itself. There is a metallurgical bond between the metal substrate and the hardened layer, and there is no problem of bonding, which has a better effect in improving the durability.

[0072] It should be understood that the at least partial surface includes any surface of the metal substrate. For example, when the metal substrate is a hollow body, it may include an inner surface, an outer surface, or a portion of at least one of the inner surface and the outer surface.

[0073] In some embodiments of the present invention, the at least partial surface is at least one surface of the metal substrate.

[0074] Furthermore, the metal substrate is essentially a metal material. After being processed by the preparation method of the second embodiment of the present invention, the metal substrate with a hardened layer on the surface in the first embodiment of the present invention is obtained to form a metal material. Therefore, in the preparation method, the metal substrate and the hardened layer are metallurgically bonded. It should be understood that nitrocarburizing generally forms a metallurgical bond.

[0075] In some embodiments of the present invention, during the nitrocarburizing process, the treatment temperature is 380-470°C.

[0076] In some embodiments of the present invention, during the nitrocarburizing process, the treatment time is 4 to 8 hours.

[0077] In the process of nitrocarburizing a metal substrate to prepare a metal material, controlling deformation is a key to the surface chemical heat treatment of nitrocarburizing. Due to the thermal expansion and contraction of the metal substrate, irreversible deformation often occurs when the metal substrate is treated at a high temperature and then cooled. Therefore, the present invention further adjusts the treatment temperature during the nitrocarburizing process to avoid significant deformation of the metal substrate, which affects its subsequent application.

[0078] According to the preparation method in some specific examples of the present invention, during the nitrocarburizing process, the change in the treatment temperature will affect the penetration of nitrogen and carbon elements, thereby affecting the ratio of carbides and nitrides in the hardened layer on the surface of the metal substrate, that is, the content of carbides and nitrides in the hardened layer, and the penetration of nitrogen and carbon elements is the key to improving the hardness of the hardened layer. When the treatment temperature rises during the nitrocarburizing process, the source gas of nitrogen and carbon elements decomposes more fully, the concentration of nitrogen and carbon elements is higher, and they are better focused on the surface of the substrate, achieving a better nitrocarburizing effect, thereby improving the hardness. However, too high a treatment temperature is also proportional, that is, as mentioned above, it will cause the metal substrate to deform and affect its use.

[0079] The processing time during the nitrocarburizing process will affect the depth of the hardened layer. As the processing time increases, the deeper the penetration of carbon and nitrogen elements, the deeper the hardened layer. However, when the depth of the hardened layer is too deep and occupies a high proportion of the thickness of the metal substrate, it will affect the flexibility of the metal substrate itself. Therefore, the processing time also needs to be reasonably controlled.

[0080] It is understood that the treatment temperature may be 380° C., 400° C., 420° C., 430° C., 450° C. or 470° C. In some embodiments of the present invention, the treatment temperature is 400-450° C. In some specific embodiments of the present invention, the treatment temperature is 420-430° C.

[0081] Furthermore, the treatment time may be 4 hours, 5 hours, 6 hours, 7 hours or 8 hours. In some embodiments of the present invention, the treatment time is 4 to 6 hours.

[0082] In some embodiments of the present invention, the nitrocarburizing process is performed in an atmosphere of ammonia, nitrogen and carbon dioxide.

[0083] In nitrocarburizing, ammonia decomposes into nitrogen at heat treatment temperature and is the main source of nitrogen, while carbon dioxide decomposes to produce carbon, which is the main source of carbon. The main function of nitrogen is to help further increase the hardness of the hardened layer, improve wear resistance, and promote the formation of the hardened layer. The nitrogen content can be adjusted by affecting the nitrogen potential in the atmosphere.

[0084] In some embodiments of the present invention, during the process of introducing gas, the ventilation rate of ammonia is 160-200 L / min; the ventilation rate of nitrogen is 60-100 L / min; and the ventilation rate of carbon dioxide is 2-3 L / min.

[0085] In the process of forming a hardened layer by nitrocarburizing, the gas ventilation volume has an impact on the concentration of nitrogen and carbon elements and the formation of the hardened layer. For example, with the increase of ammonia flow rate, the nitrogen content in the environment increases, and in the hardened layer, the nitride content in the hardened layer will also increase, while increasing the carbon dioxide flow rate will affect the carbon content in the environment, that is, the carbide content in the hardened layer increases, and the content of nitrogen and carbon elements will affect the density of the hardened layer. In addition, since the ventilation volume affects the amount of nitrogen and carbon elements in the environment, and the nitrogen ventilation volume also affects the nitrogen potential in the environment, the adjustment of the ventilation volume is conducive to promoting the formation of the hardened layer, further adjusting the surface hardness of the hardened layer, and improving the friction and wear performance.

[0086] According to the ventilation amounts of ammonia, nitrogen and carbon dioxide described above, it can be seen that in the process of nitrocarburizing of the present invention, nitriding treatment is mainly performed.

[0087] It should be understood that in some specific embodiments, within the ventilation volume range of the present invention, the ammonia ventilation volume is 160 to 200 L / min, the nitrogen ventilation volume is 60 to 100 L / min, and the carbon dioxide ventilation volume is 2 to 3 L / min, any ventilation volume value can be selected to form a hardened layer on the surface of the substrate.

[0088] Specifically, the ventilation volume of ammonia can be 160L / min, 170L / min, 180L / min, 190L / min or 200L / min; the ventilation volume of nitrogen can be 60L / min, 70L / min, 80L / min, 90L / min or 100L / min; the ventilation volume of carbon dioxide can be 2L / min, 2.5L / min or 3L / min.

[0089] In some embodiments of the present invention, the ventilation volume of ammonia can be 170-190 L / min; the ventilation volume of nitrogen can be 70-80 L / min; and the ventilation volume of carbon dioxide can be 2.3-2.7 L / min.

[0090] In some embodiments of the present invention, the metal substrate further includes a preheating step before the nitrocarburizing.

[0091] In some embodiments of the present invention, the preheating temperature is 200-300° C. In some specific embodiments of the present invention, the preheating temperature is 230-280° C.

[0092] In some embodiments of the present invention, the preheating time is 10 to 30 minutes.

[0093] Before nitrocarburizing the metal substrate, it is preheated first. The preheating temperature is generally lower than the temperature during nitrocarburizing, so that the metal substrate has a certain temperature first to avoid direct contact with the high temperature environment during the nitrocarburizing process. The temperature rise rate is too fast, causing deformation of the metal substrate.

[0094] In some embodiments of the present invention, a cooling step is further included after the nitrocarburizing; the cooling is inert gas cooling.

[0095] After the nitrocarburizing heat treatment, an inert gas is introduced during the cooling stage. The inert gas will not chemically react with the metal substrate and can protect the surface of the metal substrate to prevent oxidation or other forms of corrosion of the workpiece during the cooling process.

[0096] Furthermore, the inert gas introduced during the cooling process may be any inert gas, for example, the inert gas includes nitrogen.

[0097] In order to better protect the surface of the metal substrate during the gas cooling process, the ventilation rate of the inert gas can be controlled. In some embodiments of the present invention, the ventilation rate of the inert gas is 200-300 L / min.

[0098] It is understood that, in the gas cooling process, it is generally not necessary to cool to room temperature by gas cooling, because the metal substrate can remain stable at a certain temperature. In some embodiments of the present invention, the gas cooling process cools to an ambient temperature below 120°C.

[0099] In the entire preparation method, in order to remove oil or impurities on the surface of the metal substrate so that the surface of the substrate is clean during the surface chemical heat treatment of nitrocarburizing, thereby better forming a hardened layer and achieving metallurgical bonding, it is generally possible to choose to clean the metal substrate first.

[0100] In some embodiments of the present invention, the cleaning treatment includes cleaning with a cleaning liquid. Optionally, the cleaning liquid may be acetone or anhydrous ethanol; and the cleaning may be ultrasonic cleaning. In some embodiments of the present invention, the cleaning treatment time is 10 to 30 minutes. It should be understood that the cleaning time and cleaning method are not limited to 10 to 30 minutes of ultrasonic cleaning, and the cleaning of the substrate can be achieved.

[0101] An embodiment of a third aspect of the present invention provides a flexible spline, comprising the metal material described in the first aspect of the present invention.

[0102] For general rigid mechanical parts, they will not deform or deform very little during their service, when they are in operation or rub against other parts. Therefore, improving the friction and wear performance of these rigid mechanical parts can achieve significant results simply by coating their surfaces with a high-hardness coating. However, this method is not feasible for flexible parts such as flexible splines. Taking the flexible spline as an example, the tooth surface part of the barrel wall area is the main source of wear, and the thinnest part of this area is only about 0.2mm. The flexible spline is a flexible part that has been undergoing cyclic deformation during its service. It is difficult to withstand such a long period of reciprocating deformation by directly coating the surface of the flexible spline with a high-hardness coating. The coating is easy to fall off, resulting in failure. For the flexible spline, the strengthening effect is lost, the friction and wear performance decreases rapidly, and the durability of the flexible spline is significantly reduced. The metal material provided by the present invention has a metallurgically bonded hardened layer on its surface, and the hardened layer has a specific hardness and depth range, which can improve the surface hardness while ensuring the flexibility of the material itself. When it is used to prepare a flexible wheel, the obtained flexible wheel has the same effect, so it can effectively improve the friction and wear performance of the flexible wheel and will not fail due to cyclic deformation.

[0103] At the same time, the preparation method of the metal material of the present invention is to perform surface chemical heat treatment on the metal substrate, namely, nitrocarburizing. This method is simpler and does not require the introduction of a new coating. It can not only form a hardened layer with high surface hardness on the surface of the flexible wheel without destroying the flexibility of the flexible wheel, but also avoid significant deformation of the flexible wheel during the treatment process through adjustment of the atmosphere or control of the temperature, thereby affecting its use.

[0104] In some embodiments of the present invention, at least one side of the flexible wheel is provided with a hardened layer; the depth of the hardened layer is 10-25% of the minimum wall thickness of the flexible wheel. It should be understood that when the depth of the hardened layer is within the range of 10-25%, it will not have a significant impact on the flexibility of the flexible wheel itself, and thus will not affect the durability after reciprocating deformation. For example, the depth of the hardened layer can be selected to be 10%, 15%, 20% or 25%.

[0105] In some embodiments of the present invention, the minimum wall thickness of the flexspline is 200 μm±2%.

[0106] In some embodiments of the present invention, the hardened layer may be provided on two surfaces of the flexible wheel, including an inner surface and an outer surface.

[0107] It should be understood that when the hardened layer is provided on two surfaces of the flexspline, the total depth of the hardened layer is 20-50% of the minimum wall thickness of the flexspline.

[0108] An embodiment of a fourth aspect of the present invention provides a harmonic reducer, comprising the metal material described in the first aspect of the present invention, or the flexible spline described in the third aspect of the present invention.

[0109] The harmonic reducer contains parts made of metal materials, such as flexible splines. The metal material has a hardened layer on the surface of the metal substrate, which has excellent friction and wear properties, a low friction coefficient, and a low wear rate. The hardened layer and the metal substrate are metallurgically bonded, and there is no problem of bonding failure. Therefore, it can not only effectively reduce the wear rate of the flexible spline parts and reduce the accuracy degradation rate after durability, but also improve the durability life, so that the harmonic reducer has the characteristics of long life, low wear, and high precision retention.

[0110] An embodiment of the fifth aspect of the present invention provides an industrial robot joint component, comprising the metal material described in the first aspect of the present invention, or the flexible spline described in the third aspect of the present invention, or the harmonic reducer described in the fourth aspect of the present invention.

[0111] The harmonic reducer is the core component of the industrial robot and directly determines the performance of the robot joint. The performance of the harmonic reducer mainly includes two aspects: one is the durability life, that is, how long it can operate normally in the robot system. This indicator is related to wear. If the wear continues to accumulate, it will exceed the critical point that can be used, and the product will fail; the other is the accuracy degradation rate, which is the relative percentage of the difference in accuracy performance before and after durability, which affects the main role of the harmonic reducer in the robot, which is the positioning accuracy. Generally speaking, as the use time of the harmonic reducer increases, wear occurs between the parts of the harmonic reducer, thereby affecting the positioning accuracy of the robot. The metal material of the present invention contains a hardened layer on the surface of the metal substrate, that is, the metal material surface contains a hardened layer, which has excellent friction and wear performance, and there is no problem of failure of bonding force, and the surface of the flexible wheel containing the metal material of the present invention also contains a hardened layer, which also has a hardened layer that can improve friction and wear performance. This advantage can improve the service life, that is, the durability life, and reduce the accuracy degradation rate after durability. From the perspective of industrial robots, it is beneficial to improve its service life and positioning accuracy.

[0112] The present invention is further described in detail below by specific examples. Unless otherwise specified, the raw materials, reagents or devices used below can be obtained from conventional commercial sources. Unless otherwise specified, the experiments or test methods are conventional methods in the art.

[0113] Unless otherwise specified, the raw materials used in the following examples / comparative examples are commercially available products and are used directly without further treatment.

[0114] The flexible splines used in the embodiments and comparative examples are made of the same material and process, and are all prepared by existing conventional processes. The material is SNCM439 material, and the thickness of the thin wall of the flexible spline is 200μm±2%; the metal substrate material used in the embodiment is the same as that of the flexible spline, which is SNCM439 material, and the core hardness is equivalent.

[0115] The metal substrates of Examples 1 to 5 are round-shaped SNCM439 materials; the metal substrates of Examples 6 to 10 are flexible wheels.

[0116] Example 1

[0117] Embodiment 1 provides a metal material, including a metal substrate, a hardened layer is provided on the surface of the metal substrate; the surface hardness of the hardened layer is 550 HV; the depth of the hardened layer is 35 μm;

[0118] The measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500;

[0119] The metal substrate is a disc-shaped material with a diameter of 50 mm and a thickness of 10 mm, and the core hardness is 420 HV.

[0120] The metal material can be obtained by the following preparation method, which specifically comprises the following steps:

[0121] S1. Cleaning: The metal substrate is ultrasonically cleaned with acetone or anhydrous ethanol for 20 minutes to remove surface oil and impurities;

[0122] S2. Preheating: Place the cleaned metal substrate into a furnace for preheating at a temperature of 250°C for 20 minutes;

[0123] S3. Atmosphere control: Ammonia, nitrogen and carbon dioxide are introduced into the heat treatment furnace, and the ventilation volumes are controlled at 180 L / min, 80 L / min and 2.5 L / min respectively;

[0124] S4. Nitrocarburizing: heat treating the metal substrate in a heat treatment furnace at a temperature of 400°C for 6 hours;

[0125] S5. Cooling: The heat-treated metal material is gas-cooled with the ventilation volume controlled at 200-300 L / min until the temperature in the furnace is lower than 120°C, and then the metal material is taken out.

[0126] Example 2

[0127] Embodiment 2 provides a metal material, including a metal substrate, a hardened layer is provided on the surface of the metal substrate; the surface hardness of the hardened layer is 700 HV; the depth of the hardened layer is 35 μm;

[0128] The measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500;

[0129] The metal substrate is a disc-shaped material with a diameter of 50 mm and a thickness of 10 mm, and the core hardness is 420 HV.

[0130] The metal material can be obtained by the following preparation method, which specifically comprises the following steps:

[0131] S1. Cleaning: The metal substrate is ultrasonically cleaned with acetone or anhydrous ethanol for 20 minutes to remove surface oil and impurities;

[0132] S2. Preheating: Place the cleaned metal substrate into a furnace for preheating at a temperature of 250°C for 20 minutes;

[0133] S3. Atmosphere control: Ammonia, nitrogen and carbon dioxide are introduced into the heat treatment furnace, and the ventilation volumes are controlled at 180 L / min, 80 L / min and 2.5 L / min respectively;

[0134] S4. Nitrocarburizing: heat treating the metal substrate in a heat treatment furnace at a temperature of 450°C for 6 hours;

[0135] S5. Cooling: The heat-treated metal material is gas-cooled with the ventilation volume controlled at 200-300 L / min until the temperature in the furnace is lower than 120°C, and then the metal material is taken out.

[0136] Example 3

[0137] Embodiment 3 provides a metal material, including a metal substrate, a hardened layer is provided on the surface of the metal substrate; the surface hardness of the hardened layer is 625 HV; the depth of the hardened layer is 20 μm;

[0138] The measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500;

[0139] The metal substrate is a disc-shaped material with a diameter of 50 mm and a thickness of 10 mm, and the core hardness is 420 HV.

[0140] The metal material can be obtained by the following preparation method, which specifically comprises the following steps:

[0141] S1. Cleaning: The metal substrate is ultrasonically cleaned with acetone or anhydrous ethanol for 20 minutes to remove surface oil and impurities;

[0142] S2. Preheating: Place the cleaned metal substrate into a furnace for preheating at a temperature of 250°C for 20 minutes;

[0143] S3. Atmosphere control: Ammonia, nitrogen and carbon dioxide are introduced into the heat treatment furnace, and the ventilation volumes are controlled at 180 L / min, 80 L / min and 2.5 L / min respectively;

[0144] S4. Nitrocarburizing: heat treating the metal substrate in a heat treatment furnace at a temperature of 425°C for 4 hours;

[0145] S5. Cooling: The heat-treated metal material is gas-cooled with the ventilation volume controlled at 200-300 L / min until the temperature in the furnace is lower than 120°C, and then the metal material is taken out.

[0146] Example 4

[0147] Embodiment 4 provides a metal material, including a metal substrate, a hardened layer is provided on the surface of the metal substrate; the surface hardness of the hardened layer is 625 HV; the depth of the hardened layer is 50 μm;

[0148] The measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500;

[0149] The metal substrate is a disc-shaped material with a diameter of 50 mm and a thickness of 10 mm, and the core hardness is 420 HV.

[0150] The metal material can be obtained by the following preparation method, which specifically comprises the following steps:

[0151] S1. Cleaning: The metal substrate is ultrasonically cleaned with acetone or anhydrous ethanol for 20 minutes to remove surface oil and impurities;

[0152] S2. Preheating: Place the cleaned metal substrate into a furnace for preheating at a temperature of 250°C for 20 minutes;

[0153] S3. Atmosphere control: Ammonia, nitrogen and carbon dioxide are introduced into the heat treatment furnace, and the ventilation volumes are controlled at 180 L / min, 80 L / min and 2.5 L / min respectively;

[0154] S4. Nitrocarburizing: heat treating the metal substrate in a heat treatment furnace at a temperature of 425°C for 8 hours;

[0155] S5. Cooling: The heat-treated metal material is gas-cooled with the ventilation volume controlled at 200-300 L / min until the temperature in the furnace is lower than 120°C, and then the metal material is taken out.

[0156] Example 5

[0157] Embodiment 5 provides a metal material, including a metal substrate, a hardened layer is provided on the surface of the metal substrate; the surface hardness of the hardened layer is 625 HV; the depth of the hardened layer is 35 μm;

[0158] The measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500;

[0159] The metal substrate is a disc-shaped material with a diameter of 50 mm and a thickness of 10 mm, and the core hardness is 420 HV.

[0160] The metal material can be obtained by the following preparation method, which specifically comprises the following steps:

[0161] S1. Cleaning: The metal substrate is ultrasonically cleaned with acetone or anhydrous ethanol for 20 minutes to remove surface oil and impurities;

[0162] S2. Preheating: Place the cleaned metal substrate into a furnace for preheating at a temperature of 250°C for 20 minutes;

[0163] S3. Atmosphere control: Ammonia, nitrogen and carbon dioxide are introduced into the heat treatment furnace, and the ventilation volumes are controlled at 180 L / min, 80 L / min and 2.5 L / min respectively;

[0164] S4. Nitrocarburizing: heat treating the metal substrate in a heat treatment furnace at a temperature of 425°C for 6 hours;

[0165] S5. Cooling: The heat-treated metal material is gas-cooled with the ventilation volume controlled at 200-300 L / min until the temperature in the furnace is lower than 120°C, and then the metal material is taken out.

[0166] Example 6

[0167] In Example 6, the same preparation method as in Example 1 is used, the metal substrate is a flexible plywood, and the flexible plywood is surface treated to form a hardened layer on the surface of the flexible plywood. The surface hardness of the hardened layer is 550 HV; the depth of the hardened layer is 35 μm; and the measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500.

[0168] Example 7

[0169] In Example 6, the same preparation method as in Example 2 is used, the metal substrate is a flexible plywood, and the flexible plywood is surface treated to form a hardened layer on the surface of the flexible plywood. The surface hardness of the hardened layer is 700 HV; the depth of the hardened layer is 35 μm; and the measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500.

[0170] Example 8

[0171] In Example 6, the same preparation method as in Example 3 is used, the metal substrate is a flexible wheel, and the flexible wheel is surface treated to form a hardened layer on the surface of the flexible wheel. The surface hardness of the hardened layer is 625 HV; the depth of the hardened layer is 20 μm; and the measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500.

[0172] Example 9

[0173] In Example 6, the same preparation method as in Example 4 is used, the metal substrate is a flexible plywood, and the flexible plywood is surface treated to form a hardened layer on the surface of the flexible plywood. The surface hardness of the hardened layer is 625 HV; the depth of the hardened layer is 50 μm; and the measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500.

[0174] Example 10

[0175] In Example 6, the same preparation method as in Example 5 is used, and the metal substrate is a flexible plywood. The flexible plywood is surface treated to form a hardened layer on the surface of the flexible plywood. The surface hardness of the hardened layer is 625 HV. The depth of the hardened layer is 35 μm. The measurement range of the depth of the hardened layer is the range of the hardness of the hardened layer HV ≥ 500.

[0176] Comparative Example 1

[0177] Comparative Example 1 provides a metal material, the material and specification of which are exactly the same as those of Example 1, but no surface treatment is performed, that is, there is no hardened layer on the surface.

[0178] Comparative Example 2

[0179] Comparative Example 2 provides a flexible wheel, which is prepared by a conventional process and is not subjected to surface treatment to form a hardened layer.

[0180] The parameters of the preparation methods of the metal materials in the above-mentioned Examples 1 to 5 are summarized in Table 1 below.

[0181] Table 1 Treatment temperature and time of nitrocarburizing in Examples 1 to 5

[0182] Processing temperature / ℃ Processing time / h Example 1 400 6 Example 2 450 6 Example 3 425 4 Example 4 425 8 Example 5 425 6

[0183] The performance tests of the products of the above-mentioned embodiments 1 to 10 and comparative examples 1 to 2 are carried out below. Among them, for the tests of the embodiments, the surface hardness, core hardness and depth of the hardened layer are tested on the metal materials of embodiments 1 to 5, and the tests of the friction coefficient and wear rate are also carried out on the metal materials of embodiments 1 to 5; the endurance life and the accuracy degradation rate after endurance are tested on the flexible wheels of embodiments 6 to 10 as samples.

[0184] It should be understood that since the metal material of Examples 1 to 5 is the same as the material of the flexible splines of Examples 6 to 10, the core hardness is equivalent, and the preparation method is the same, that is, the corresponding nitrocarburizing surface chemical heat treatment with the same processing parameters is respectively performed, and the friction or wear surface is a hardened layer on the surface, therefore, for the flexible spline, the hardness, hardened layer depth, friction coefficient and wear rate of its surface hardened layer should be equivalent to its corresponding metal material.

[0185] The specific test method is as follows:

[0186] 1. Surface hardness and depth of hardened layer, core hardness of substrate

[0187] For the metal materials of the above-mentioned embodiments 1 to 5 and the metal material of comparative example 1, the surface hardness, core hardness and hardened layer depth were measured with reference to the test method in GBT 9450-2005 Determination and verification of carburizing and quenching hardened layer depth of steel parts.

[0188] The test results are shown in Table 2 below.

[0189] Table 2 Hardness parameters in Examples 1 to 5 and Comparative Example 1

[0190]

[0191]

[0192] In Table 2, the surface hardness of the hardened layer of Examples 1 to 5 is within the range of 550 to 700 HV, and the depth of the hardened layer is 20 to 50 μm, which meets the requirements of the present invention for the surface hardened layer of the metal substrate.

[0193] In the embodiments, the hardness of the hardened layer on the surface of the metal substrate is distributed decreasing from the outside to the inside (towards the metal substrate).

[0194] 2. Friction coefficient and wear rate

[0195] The metal materials of Examples 1 to 5 (round cakes with a diameter of 50 mm and a thickness of about 10 mm, made of SNCM439) or the metal materials of Comparative Example 1 are clamped on a standard friction and wear tester for testing. The friction pair is a steel ball made of GCr15 material and a diameter of 12.7 mm. The friction pair motion form is reciprocating motion. The lubrication condition is to add grease for harmonic reducer products, the load is 30N, the speed is 20mm / s, the reciprocating frequency is 3.2Hz, the reciprocating stroke is 3mm, the temperature is room temperature, and the time is 10min. During the test, the instrument will automatically record the corresponding friction coefficient. After the test, the sample is observed under a laser confocal microscope, and the wear volume is obtained by contour scanning, and then the corresponding wear rate can be calculated. The specific calculation formula is as follows:

[0196] Wear rate = wear volume / (normal load × sliding distance); K represents the wear rate, V represents the wear volume, F represents the normal load, and s represents the sliding distance, then the formula is K = V / (F × s).

[0197] The test results of the friction coefficient and wear rate of Examples 1 to 5 and Comparative Example 1 are shown in Table 3 below.

[0198] Table 3 Friction coefficient and wear rate of Examples 1 to 5 and Comparative Example 1

[0199] Friction coefficient <![CDATA[Wear rate (mm 3 / Nm)]]> Example 1 0.115 <![CDATA[3×10 -7 ]]> Example 2 0.105 <![CDATA[1×10 -7 ]]> Example 3 0.11 <![CDATA[2×10 -7 ]]> Example 4 0.11 <![CDATA[2×10 -7 ]]> Example 5 0.11 <![CDATA[2×10 -7 ]]> Comparative Example 1 0.15 <![CDATA[2×10 -6 ]]>

[0200] In Table 3, the metal substrate surfaces in Examples 1 to 5 contain a hardened layer, that is, the metal material surfaces contain a hardened layer. During the test, the surface hardened layer is rubbed and worn. Compared with the metal material in Comparative Example 1 that is not subjected to any surface treatment, the friction coefficient and wear rate of Examples 1 to 5 are significantly lower. The wear rate is at least one order of magnitude lower than that of Comparative Example 1, and the friction coefficient is reduced by at least 23%.

[0201] 3. Durable life of flexible pulley

[0202] The flexible wheels of Examples 6 to 10 and Comparative Example 2 were assembled into harmonic reducer products to verify the bench life of the whole product. The entire experimental process was an accelerated durability test. The specific conditions were: temperature 25°C, humidity controlled at less than 35%, and conducted on a customized durability bench for harmonic reducers. The final result was the equivalent durability time of the harmonic reducer product, in h.

[0203] The following provides the test results of the flexspline durability life of Examples 6 to 10 and Comparative Example 2, as shown in Table 4.

[0204] Table 4 Durability of flexible pulleys in Examples 6 to 10 and Comparative Example 2

[0205] Example 6 Example 7 Example 8 Example 9 Example 10 Comparative Example 2 Durable life / h ＞15000 ＞11000 ＞13000 ＞10000 ＞12000 ＞4000

[0206] It can be seen from Table 4 that the flexible splines in Examples 6 to 10 having a hardened layer on their surfaces obtained by surface chemical heat treatment have a durability life of at least 2.5 times that of Comparative Example 1, and a durability life of not less than 10,000 hours, while the untreated flexible spline in Comparative Example 2 has a durability life of only 4,000 hours, which is a general level.

[0207] 4. Precision degradation rate of flexible wheel after durability

[0208] The flexible wheels of Examples 6 to 10 and Comparative Example 2 are assembled into harmonic reducer products. The accuracy performance of the harmonic reducer products before durability is first tested. If the value is a, the unit is arc*sec. Then, the product is subjected to a whole machine bench life verification under the same conditions as the third durability life test. After the life test is completed, the accuracy performance of the product after durability is retested. If the value is b, the unit is arc*sec, then 100×(ab) / a is the accuracy degradation rate of the product after durability, in %.

[0209] The accuracy degradation rates of the flexible plies of Examples 6 to 10 and Comparative Example 2 after durability are shown in Table 5 below.

[0210] Table 5 Accuracy degradation rate of Examples 6 to 10 and Comparative Example 2

[0211] Example 6 Example 7 Example 8 Example 9 Example 10 Comparative Example 2 Accuracy degradation rate / % ＜50 ＜30 ＜50 ＜30 ＜40 ＞50

[0212] In Table 5, the accuracy degradation rate of the harmonic reducer using the flexible spline of Comparative Example 2 after durability is more than 50%, while the accuracy degradation rate of Examples 6 to 10 does not exceed 50%, which has excellent accuracy retention compared to the flexible spline without any treatment.

[0213] Combined with the test results in Tables 2 to 5 above, the test results of Examples 1 to 5, Examples 6 to 10 and Comparative Example 2 are further analyzed as follows:

[0214] By comparing the test results of Examples 1 to 10 and Comparative Examples 1 to 2, it can be seen that in Examples 1 to 10 of the present invention, the test results of metal materials and flexible wheels are better than those of Comparative Examples 1 to 2, and have obvious advantages over Comparative Examples 1 to 2 in terms of friction coefficient, wear rate, durability life and precision degradation rate.

[0215] By comparing Examples 1 to 5 with Examples 6 to 10, it can be seen that there are differences in the test results between different Examples.

[0216] Combined with the metal substrates of Example 1, Example 2 and Example 5, and the corresponding flexible splines of Example 6, Example 7 and Example 10, the following analysis is performed:

[0217] Comparing Example 1, Example 2 and Example 5, it can be seen that the surface hardness and depth of the hardened layer are affected by the treatment temperature and treatment time of nitrocarburizing. When the nitrocarburizing treatment time is the same, as the treatment temperature increases, the surface hardness of the hardened layer gradually increases, but the depth of the hardened layer remains basically unchanged. This is because as the temperature increases, the atmosphere in the heat treatment furnace decomposes more fully, and the nitrogen and carbon elements are more likely to focus on the surface of the substrate, so that the concentration of nitrogen and carbon elements on the surface is higher, and then the ratio of carbides and nitrides in the hardened layer is higher, and the surface hardness is higher. The treatment time mainly affects the depth of the hardened layer. As time goes on, the nitrogen and carbon elements on the surface of the substrate continuously penetrate into the interior. The longer the time, the deeper the penetration, and the higher the depth of the hardened layer, until equilibrium is reached. Therefore, the treatment temperature mainly affects the surface hardness, and the treatment time mainly affects the depth of the hardened layer.

[0218] Compared with Example 5, the surface hardness of the hardened layer of Example 1 is lower, and the depth of the hardened layer is the same. For friction and wear performance, the surface hardness has a greater impact. If the surface hardness is lower, the friction coefficient is slightly reduced, and the wear rate is also reduced. This change corresponds to Example 10 and Example 6 at the product level. Since the surface hardness of the hardened layer is lower, it means that the difference with the hardness of the base material itself is smaller, which is more conducive to the durability, so the durability is longer; and since the surface hardness of the hardened layer is lower, the wear resistance is poor, so the precision degradation rate is higher, that is, the precision retention is worse.

[0219] Compared with Example 5 (Example 10) and Example 2 (Example 7), the surface hardness of the hardened layer of Example 2 is higher, the depth of the hardened layer is the same, and the influence trend is opposite to the previous paragraph.

[0220] Combined with the metal materials of Example 3, Example 4 and Example 5, and the corresponding flexible splines of Example 8, Example 9 and Example 10, the following analysis is performed:

[0221] In Examples 3 to 5 and Examples 8 to 10, the main difference is the treatment time of nitrocarburizing, which affects the depth of the hardened layer but hardly affects the surface hardness.

[0222] Since the friction coefficient and wear rate in the experiment are short-term tests and are mainly related to the surface hardness of the substrate, that is, the surface hardness of the hardened layer, the friction coefficient and wear rate of Examples 3 to 5 are basically consistent.

[0223] From the product performance analysis in Examples 8 to 10, compared with Example 10, the hardened layer depth of Example 8 is lower, only 20 μm, and the proportion of the minimum wall thickness of the entire flexible wheel (about 200 μm) is also relatively low. The total depth of the hardened layer on both sides is 40 μm, and the total proportion is 20%. It can be understood that based on the wall thickness of the flexible wheel, most of the flexible wheel is still a matrix material with higher flexibility, which is more conducive to reciprocating deformation and is more conducive to durability than Example 10. Therefore, Example 8 has a longer durability life; however, due to the reduction in the depth of the hardened layer, the volume of the hardened layer that has not been worn after the same durability is smaller, so the accuracy retention is poor.

[0224] Compared with Example 10, the hardened layer depth of Example 9 is higher, reaching 50μm, and the thickness ratio of the entire flexible wheel thin wall is 50%. It can be understood that from the perspective of the flexible wheel wall thickness, the general wall thickness of the flexible wheel is made of a material with a higher hardness. Therefore, when the flexible wheel is constantly deformed reciprocatingly during actual working, it is not conducive to the durability and the durability is reduced. However, with the increase in the depth of the hardened layer, the volume of the hardened layer that has not been worn after durability is larger, so the accuracy retention is better.

[0225] To sum up, the surface of the metal material of the present invention is provided with a hardened layer metallurgically bonded to the metal substrate, which has a certain surface hardness and depth, can effectively improve the friction and wear performance of the metal material, and the metallurgical bonding method avoids the problem of bonding force failure and improves the life of the hardened layer during wear. At the product level, it improves the durability and precision degradation rate.

[0226] At the same time, the preparation method of the metal material provided by the present invention performs nitrocarburizing surface chemical heat treatment on the metal substrate without causing significant deformation of the metal substrate, is easy to operate, and is suitable for surface treatment of workpieces, such as flexible splines, to prepare flexible splines with a surface hardened layer.

[0227] Using the flexible wheel or metal material of the present invention in a harmonic reducer can effectively improve the service life and precision retention of the harmonic reducer, so that the harmonic reducer product has the advantages of long life, low wear, high precision retention, etc.

[0228] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A metal material, characterized in that: It comprises a metal substrate, wherein a hardened layer is arranged on the surface of the metal substrate; the surface hardness of the hardened layer is 550 to 700 Vickers hardness and the depth is 20 to 50 μm; The hardness of the hardened layer is distributed decreasing from the outside to the inside; the inside refers to the direction toward the metal substrate; The metal substrate and the hardened layer are metallurgically bonded.

2. The metal material according to claim 1, characterized in that: The measurement range of the depth of the hardened layer is a range in which the Vickers hardness of the hardened layer is greater than or equal to 500.

3. The metal material according to claim 1, characterized in that: The core hardness of the metal substrate is 400-450 in Vickers hardness.

4. The metal material according to claim 1, characterized in that: The metal substrate includes an alloy.

5. The metal material according to claim 1, characterized in that: The friction coefficient of the hardened layer is 0.08 to 0.

13.

6. A method for preparing the metal material according to any one of claims 1 to 5, characterized in that: The following steps are involved: Providing a metal substrate, and performing nitrocarburizing on at least a portion of the surface of the metal substrate to form a hardened layer on at least a portion of the surface; The surface hardness of the hardened layer is 550 to 700 Vickers hardness and the depth is 20 to 50 μm; The hardness of the hardened layer decreases from the outside to the inside; the inside refers to the direction toward the metal substrate.

7. The preparation method according to claim 6, characterized in that: During the nitrocarburizing process, the treatment temperature is 380-470°C; And / or, the processing time is 4 to 8 hours.

8. The preparation method according to claim 6 or 7, characterized in that: The nitrocarburizing process is carried out in an atmosphere of ammonia, nitrogen and carbon dioxide.

9. The preparation method according to claim 8, characterized in that: During the process of introducing the gas, the ventilation rate of the ammonia is 160-200 L / min; the ventilation rate of the nitrogen is 60-100 L / min; and the ventilation rate of the carbon dioxide is 2-3 L / min.

10. The preparation method according to claim 6, characterized in that: The metal substrate further includes a preheating step before the nitrocarburizing; and / or the preheating temperature is 200-300°C.

11. The preparation method according to claim 6, characterized in that: The method further includes a cooling step after the nitrocarburizing; the cooling step is inert gas cooling.

12. A flexible wheel, characterized in that: The metal material comprises the metal material according to any one of claims 1 to 5.

13. The flexible wheel according to claim 12, characterized in that: At least one side of the flexible wheel is a hardened layer; the depth of the hardened layer is 10-25% of the minimum wall thickness of the flexible wheel.

14. A harmonic reducer, characterized in that: The invention comprises the metal material as claimed in any one of claims 1 to 5, or the flexible spline as claimed in any one of claims 12 to 13.

15. An industrial robot joint component, characterized in that: It comprises the metal material as described in any one of claims 1 to 5, or the flexible wheel as described in any one of claims 12 to 13, or the harmonic reducer as described in claim 14.

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