Method for producing a rolling bearing component

Abstract

The invention relates to a method for producing a rolling bearing component (1), wherein the rolling bearing component (1) is formed from a rolling bearing steel and has a wall thickness or a diameter of at least 85 mm at at least one point, wherein the rolling bearing component (1) is heated to form an austenitic structure and is then cooled in a warm salt bath below the martensite start temperature of the rolling bearing steel, such that the rolling bearing component (1) is formed with a martensitic structure in the edge layer region of the rolling bearing component (1) and with a structure comprising pearlite and / or upper bainite in the core region of the rolling bearing component (1). The invention also relates to a rolling bearing component (1) and a rolling bearing (2).

Description

Technical Field

[0001] This invention relates to a method for producing rolling bearing components, wherein the rolling bearing components are formed from rolling bearing steel. Furthermore, this invention relates to rolling bearing components and rolling bearings. Background Technology

[0002] DE 10 2006 052 834 A1 discloses a method for producing rolling bearing rings, wherein the bearing rings are produced from low-alloy penetrable hardening steel with a carbon content greater than 0.5 wt% and a total chromium, nickel, and molybdenum content between 1.4 wt% and 3.0 wt%. The bearing rings undergo a hardening treatment in which they are heated to an external temperature between 800°C and 880°C and then quenched until the bearing rings reach a temperature below 150°C.

[0003] DE 10 2006 059 050 A1 describes a method for heat-treating a rolling bearing component made of penetration-hardening bainitic rolling bearing steel, the component having residual compressive stress in the edge region and a maximum martensite content of 5% and a maximum retained austenite content of 3%. For this purpose, a two-stage heat treatment is performed, wherein the component is cooled in a salt bath at a temperature ranging from 180°C to 210°C from the austenitizing temperature to slightly below the martensitic initiation temperature, and held until temperature equilibrium is achieved. The component is then heated in another bath to a temperature slightly above the martensitic initiation temperature. As a result, a bainitic structure is obtained throughout the component.

[0004] In the case of large rolling bearings with diameters of approximately one meter or more, the rolling elements are sized accordingly. These components typically have a cross-section or wall thickness of 85 mm or greater. High-alloy steel is used so that these components can be heat-treated in a technically feasible manner, which incurs a corresponding cost. In the case of bearing rings, even larger cross-sections are formed using a hardened outer shell design made of penetrable hardening steel. This possibility does not exist for large rolling elements because, in the case of sudden quenching, high tensile stress occurs at the edges (i.e., the transition from the lateral surface to the front side), making crack formation highly probable.

[0005] The object of this invention is to further develop a method for producing rolling bearing components from rolling bearing steel, the rolling bearing components having a wall thickness or diameter of at least 85 mm at at least one point, and the object of this invention is to provide rolling bearing components and rolling bearings produced by said method. Summary of the Invention

[0006] This objective is achieved by the following: a method for producing a rolling bearing component, a rolling bearing component, and a rolling bearing.

[0007] In the method for producing a rolling bearing component according to the invention, the rolling bearing component is formed of rolling bearing steel and has a wall thickness or diameter of at least 85 mm at at least one point, wherein the rolling bearing component is heated to form an austenitic structure and then cooled in a warm salt bath to a temperature below the martensitic initiation temperature of the rolling bearing steel, such that the rolling bearing component is formed to have a martensitic structure in the edge layer region of the rolling bearing component and a structure including pearlite and / or upper bainite in the core region of the rolling bearing component.

[0008] In other words, the rolling bearing components are first formed from rolling bearing steel. 100CrMo7-3 or 100CrMnSi6-4 are advantageously suitable as rolling bearing steels for forming the rolling bearing components. At the beginning of heat treatment, the rolling bearing components are heated to the austenitizing temperature and then quenched, wherein the quenching rate is selected such that cracking occurs on the surface of the rolling bearing components, while forming a technically optimal and anti-rolling shell on the lateral surfaces of the rolling bearing components with as little delay as possible. The quenching rate is selected in particular based on the geometry of the rolling bearing components and the quenching medium, i.e., a hot salt bath, especially the heat capacity of the hot salt bath.

[0009] In a warm salt bath, the rolling bearing components are specifically cooled to a temperature T that is 20°C to 70°C lower than the martensitic initiation temperature of the rolling bearing steel, and particularly 50°C to 70°C lower.

[0010] The temperature T is preferably kept constant for a period of 10 to 20 minutes.

[0011] During quenching in a warm salt bath, a phase transformation occurs in the microstructure of the rolling bearing component, where a predominantly martensitic microstructure forms on or near the surface. Thus, a martensitic surface layer hardens due to quenching. Furthermore, due to slower cooling in regions of the rolling bearing component away from the surface, particularly in or near the core, a predominantly pearlitic and / or predominantly bainitic microstructure forms. When considering a continuous time-temperature diagram, i.e., a graphical representation of the transformation process in the alloy structure according to temperature and time, for regions of the rolling bearing component away from the surface, pearlitic and / or bainitic regions are experienced during quenching, where the corresponding structures are adjusted. The type of microstructure formed depends essentially on the alloy composition and geometry of the rolling bearing component.

[0012] Martensite, or martensitic microstructure, is understood to mean a metastable microstructure formed from an austenitic initiation microstructure without diffusion, particularly through rapid quenching of steel starting from the hardening or austenitizing temperature. An increase in hardness is achieved during the transformation because the carbon atoms dissolved in the austenitic lattice cannot leave their lattice positions due to the short transformation time. The austenite folds into martensite without diffusion, and the enclosed carbon atoms thus strain the lattice. Martensite is hard and has high strength, but it is also brittle, which is why this type of steel is typically tempered after quenching to prevent any cracking.

[0013] On the other hand, pearlite is a layered eutectoid structural component of steel, i.e., a mixture of ferrite and cementite phases, obtained through coupled crystallization in iron-carbon alloys with carbon content between 0.02% and 6.67%. Pearlite is softer than martensite. A structure including pearlite is understood to mean that the structure in the core region of a rolling bearing component is substantially composed of pearlite. Therefore, the structure includes pearlite, even if it is not a completely pearlitic structure or a pure pearlitic structure. Thus, even slight deviations from a completely pearlitic microstructure, where other microstructures may exist, are still understood to be pearlitic microstructures within the meaning of this invention.

[0014] Bainite is a structure formed by isothermal and continuous cooling of both at temperatures below the pearlite morphology and above the martensite morphology. Upper bainite comprises bundled acicular ferrite. Between the individual ferrite needles are more or less continuous carbide films parallel to the axis of the needles. A distinction must be made between upper bainite and lower bainite, which, on the other hand, comprises ferrite plates in which the carbides are formed at a 60° angle to the axis of the needles. Bainite is softer than martensite but harder than pearlite. A structure including upper bainite is understood to mean that the structure in the core region of a rolling bearing component substantially includes upper bainite. Therefore, the structure includes upper bainite, even if the structure is not entirely upper bainite and purely upper bainite. Therefore, even slight deviations from the microstructure of complete bainite, where other microstructures may exist, are still understood to be microstructures including upper bainite within the meaning of this invention.

[0015] The rolling bearing component formed using the method according to the invention can be formed as a component blank close to its final geometry, wherein further processing, particularly machining, is performed after the component has cooled to bring the rolling bearing component to its final geometry. Alternatively, the component may already be in its final geometry before heat treatment. The rolling bearing component is designed, for example, as an inner ring, outer ring, or rolling element of a rolling bearing.

[0016] The hardenability of the corresponding steel is determined by the selection of the alloy composition. In the case of penetration-hardening steels, such as 100CrMnSi6-4, hardenability can also be modified by changing the carbon content and the content of dissolved alloying elements, such as chromium, using the level of the austenitizing temperature. The required solution state and quenching effect for the geometry of the rolling bearing component to be treated can be determined in advance using software or experiments.

[0017] The warm salt bath preferably has a temperature between 150°C and 210°C. More specifically, the warm salt bath has a temperature between 160°C and 200°C, depending on the material. The composition of the warm salt bath is selected according to the requirements of the quenching parameters, thereby setting a quenching rate at which martensitic structures are formed on the surface of the rolling bearing component, and structures including pearlite and / or upper bainite are formed away from the surface, particularly in the core of the rolling bearing component. Specifically, the warm salt bath has a water content of 0.5% to 1%.

[0018] Furthermore, the cooling process is adjusted using a warm salt bath and extended if necessary, allowing for a more uniform temperature distribution between the edges and core of the rolling bearing component. A related advantage is a reduction in crack formation due to thermal stress. Additionally, lower residual stress can be achieved in rolling bearing components with variable dimensions, sizes, and weights.

[0019] The preferred cooling rate between the austenitizing temperature and the salt bath temperature is in the range of 5 K / s to 10 K / s, depending on the wall thickness or cross-section of the rolling bearing component.

[0020] The rolling bearing components are preferably cooled to room temperature after reaching the temperature of the warm salt bath. Once the temperature of the rolling bearing components has equalized with the temperature of the warm salt bath, the rolling bearing components are removed from the bath so that they can continue to cool to room temperature. Room temperature is defined as a temperature between 18°C ​​and 25°C, particularly between 20°C and 25°C.

[0021] The rolling bearing component according to the invention has a wall thickness or diameter of at least 85 mm, particularly at least 200 mm. Here, the wall thickness is considered in the case of the rolling bearing ring, while the diameter is considered in the case of the rolling element.

[0022] The rolling bearing component formed using the method according to the invention comprises martensite in the edge layer region of the rolling bearing component up to a depth of at least 10 mm below the surface of the rolling bearing component and has a hardness in the range of 60 HRC to 65 HRC. A hardness of 60 HRC (Rockwell hardness) corresponds to a Vickers hardness of about 700 HV, and a hardness of 65 HRC corresponds to a Vickers hardness of about 830 HV. Therefore, the rolling bearing component according to the invention has a hardness and martensitic microstructure between 60 HRC and 65 HRC up to a first surface distance of at least 10 mm.

[0023] The HRC unit is composed of HR (Rockwell hardness), which is the name of the test method, followed by another letter, here C, where C stands for scale and therefore for test force and object. A diamond cone with a 120° apex angle and an initial test force of 98.0665 N is used for scale C (C stands for "cone"). The additional test force used for scale C is 1372.931 N.

[0024] Furthermore, the rolling bearing component according to the invention has a hardness in its core region ranging from 30 HRC to 35 HRC. A hardness of 30 HRC corresponds to a Vickers hardness of approximately 300 HV, and a hardness of 35 HRC corresponds to a Vickers hardness of approximately 345 HV. Therefore, the rolling bearing component according to the invention has a hardness in its core region ranging from 30 HRC to 35 HRC and has a pearlitic and / or bainitic microstructure.

[0025] This means that the rolling bearing components include martensite in the edge layer region and pearlite and / or upper bainite in the core region.

[0026] In rolling bearing components with a wall thickness or cross-section of at least 200 mm, a pearlitic and / or bainitic microstructure forming the core region is preferably included starting at a depth of 70 mm below the surface of the component.

[0027] The rolling bearing according to the invention comprises an outer ring and / or an inner ring and a plurality of rolling elements rolling on the outer ring and / or the inner ring, wherein the outer ring and / or the inner ring and / or the corresponding rolling elements are rolling bearing components according to the foregoing embodiments. In other words, only the outer ring, only the inner ring, only the rolling elements, or any combination of the aforementioned components can be designed as a rolling bearing component according to the invention, which has a generally martensitic microstructure on its surface and a generally pearlitic and / or upper bainitic microstructure.

[0028] The foregoing statements regarding the method are equally applicable to the rolling bearing components according to the invention and the rolling bearing according to the invention, and vice versa. Attached Figure Description

[0029] Other improvements to the invention will now be described using the accompanying drawings and a description of preferred exemplary embodiments. In the drawings, the same or similar elements are given the same reference numerals. In the drawings:

[0030] Figure 1 A schematic cross-sectional view of the height of a rolling bearing according to a preferred embodiment of the present invention is shown.

[0031] Figure 2 The invention is shown according to the following: Figure 1 A schematic cross-section of the rolling bearing components of the rolling bearing, and

[0032] Figure 3 The invention illustrates the use of [the invention] for production according to [the invention]. Figure 2 A schematic block diagram of a method for manufacturing rolling bearing components. Detailed Implementation

[0033] according to Figure 1 The method for producing a rolling bearing component 1 designed as a rolling element 5 according to the present invention is visualized according to the block diagram, wherein the rolling bearing component 1 is in Figure 2 and Figure 3 As shown in the diagram. In other words, the rolling element 5 is understood in this case as the rolling bearing component 1. Figure 2 In the example, the rolling element 5 is shown as being mounted in the rolling bearing 2, wherein the rolling element 5 is in Figure 3 The cross-section is shown in the middle.

[0034] exist Figure 1 In the first method step 100, a rolling element 5 is made of material 100CrMo7-3, which is based on... Figure 2 and Figure 3 The design uses cylindrical rollers with a diameter D of at least 85 mm, and in this case 200 mm. A large number of rolling elements 5, produced in this manner, are arranged in the space between the outer ring 3 and the inner ring 4, and in the circumferential direction by a cage 6, according to... Figure 2 The rolling bearing 2 was designed and assembled.

[0035] The outer ring 3 and / or the inner ring 4 can also be made of 100CrMo7-3 and undergo the same heat treatment. The heat treatment is explained below. Alternatively, the rolling element 5, the inner ring 4 and / or the outer ring 3 can be made of 100CrMnSi6-4.

[0036] In the second method step 101, the rolling element 5 is heated to a hardening or austenitizing temperature to form an austenitic structure and held at that temperature until the structure is fully austenitized. Then, in the third method step 102, the rolling element 5 is fed into a warm salt bath and cooled. The warm salt bath has a temperature between 150°C and 210°C, depending on the properties and mixing ratio of the warm salt bath, the material properties of the rolling bearing component 1, and the austenitizing temperature. Using the warm salt bath, the rolling element 5 is cooled at a controlled cooling rate, particularly in the range of 5 K / s to 10 K / s, during which a phase transformation of the structure occurs. The austenitic microstructure on the surface of the rolling element 5 transforms into a martensitic microstructure due to the relatively rapid cooling. In other words, after cooling, the rolling element 5 has a martensitic structure on its surface, particularly in the range from the edge layer region of the rolling element 5 downwards to a depth A1 at least 10 mm below the surface of the rolling element, see [reference needed]. Figure 3 The greater the distance from the surface of the rolling element 5, the slower the cooling of the rolling element 5, resulting in the formation of a structure including pearlite and / or upper bainite in the core region of the rolling bearing component 1. In other words, see... Figure 3 In the core region with a cross-section of at least 200 mm, particularly at a depth A2 of 70 mm below the surface of the rolling element 5, the rolling bearing component 1 has a structure substantially composed of pearlite. Depending on the geometry and dimensions of the rolling element 5, a structure substantially composed of upper bainite may also be formed. Both upper bainite and pearlite are softer than martensite, resulting in a relatively hard shell with a hardness in the edge layer region of the rolling element 5, ranging from 60 HRC to 65 HRC. In contrast, the pearlite or bainite structure of the rolling element 5 has a hardness in the core region ranging from 30 HRC to 35 HRC.

[0037] In step 103 of the fourth method, after reaching the temperature of the warm salt bath, i.e., when the rolling element 5 has a temperature corresponding to or within the temperature range of the warm salt bath, the rolling element 5 is removed from the warm salt bath and brought to room temperature, i.e., approximately 20°C. This heat treatment allows for the more economical production of rolling bearing components with larger dimensions because, through this suitable heat treatment, even with materials having low alloy content, a rolling resistance surface, or in the case of the rolling element, a rolling resistance lateral surface or raceway, can be produced, and the rolling bearing component does not crack during quenching.

[0038] It is conceivable that further heat treatment steps, such as tempering, can be performed to reduce the thermally induced stress within the rolling element 5. Furthermore, mechanical post-processing can be performed to bring the rolling element 5 to its final geometry.

[0039] List of reference numerals

[0040] 1 Rolling bearing components

[0041] 2 rolling bearings

[0042] 3 Outer Ring

[0043] 4 Inner Ring

[0044] 5 rolling elements

[0045] 6 cages

[0046] 100 First Method Steps

[0047] 101 Second Method Steps

[0048] 102 Third Method Steps

[0049] 103 Fourth Method Steps

[0050] Depth below the surface of the A1 rolling bearing component

[0051] Depth below the surface of the A2 rolling bearing component

[0052] D is the diameter.

Claims

1. A method for producing a rolling bearing component (1), wherein, The rolling bearing component (1) is formed of rolling bearing steel and has a wall thickness or diameter of at least 85 mm at at least one point, wherein the rolling bearing component (1) is heated to form an austenitic structure and then cooled in a warm salt bath to a temperature below the martensitic initiation temperature of the rolling bearing steel, such that the rolling bearing component (1) is formed to have a martensitic structure in the edge layer region of the rolling bearing component (1) and a structure including pearlite and / or upper bainite in the core region of the rolling bearing component (1).

2. The method according to claim 1, Its features are, In the warm salt bath, the rolling bearing component is cooled to a temperature T ranging from 20°C to 70°C lower than the martensitic initiation temperature of the rolling bearing steel.

3. The method according to claim 2, Its features are, The temperature T remains constant over a period of 10 to 20 minutes.

4. The method according to any one of claims 1 to 3, Its features are, The warm salt bath has a temperature between 150°C and 210°C.

5. The method according to any one of claims 1 to 3, Its features are, The rolling bearing component (1) is cooled to room temperature after reaching the temperature of the warm salt bath.

6. A rolling bearing component (1), said rolling bearing component being made of rolling bearing steel with a wall thickness or diameter of at least 85 mm, said rolling bearing component being manufactured by the method according to any one of claims 1 to 5, Its features are, The rolling bearing component (1) comprises martensite in the edge layer region of the rolling bearing component (1) up to a depth of at least 10 mm below the surface of the rolling bearing component and has a hardness in the range of 60 HRC to 65 HRC, and the rolling bearing component comprises pearlite and / or upper bainite in the core region of the rolling bearing component (1) and has a hardness in the range of 30 HRC to 35 HRC.

7. The rolling bearing component (1) according to claim 6. Its features are, The rolling bearing component (1) has a wall thickness or diameter of at least 200 mm.

8. The rolling bearing component (1) according to claim 6. Its features are, The rolling bearing component (1) has a wall thickness or diameter of at least 200 mm and comprises pearlite and / or upper bainite at a depth of 70 mm below the surface of the rolling bearing component (1).

9. The rolling bearing component (1) according to any one of claims 6 to 8. Its features are, The rolling bearing component (1) comprises steel having a composition of 100CrMo7-3 or 100CrMnSi6-4.

10. A rolling bearing (2) comprising an outer ring (3) and / or an inner ring (4) and a plurality of rolling elements (5) rolling on the outer ring (3) and / or the inner ring (4), wherein, The outer ring (3) and / or the inner ring (4) and / or the corresponding rolling element (5) are designed as rolling bearing components (1) according to any one of claims 6 to 9.

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