DE102021132703A1 - Process for manufacturing a rolling bearing component - Google Patents

Abstract

The invention relates to a method for producing a rolling bearing component (1), the rolling bearing component (1) being made from a rolling bearing steel and having a wall thickness or a diameter of at least 85 mm at at least one point, the rolling bearing component (1) being used to form an austenitic Structure is heated and then cooled in a warm salt bath below the martensite start temperature of the rolling bearing steel, in such a way that the rolling bearing component (1) is formed with a martensitic structure in a surface layer area of the rolling bearing component (1) and with a structure made of perlite and in the core area of the rolling bearing component (1). /or upper bainite structure is formed. The invention also relates to a rolling bearing component (1) and a rolling bearing (2).

Description

The invention relates to a method for producing a rolling bearing component, the rolling bearing component being formed from a rolling bearing steel. Furthermore, the invention relates to a rolling bearing component and a rolling bearing.

From the DE 10 2006 052 834 A1 describes a process for manufacturing a roller bearing ring, in which a bearing ring made of low-alloy, through-hardenable steel with a carbon content of more than 0.5% by weight and a total content of chromium, nickel and molybdenum of between 1.4% by weight -% to 3.0% by weight is produced. The bearing ring undergoes a hardening treatment in which the bearing ring is heated to an external temperature between 800°C and 880°C and then quenched until it reaches a temperature below 150°C.

the DE 10 2006 059 050 A1 describes a process for the heat treatment of rolling bearing components made of through-hardened bainitic rolling bearing steel with residual compressive stresses in the edge area and a maximum martensite content of 5% and a maximum residual austenite content of 3%. For this purpose, a two-stage heat treatment is carried out in which the component is cooled from the austenitizing temperature in a salt bath with a temperature in the range of 180 to 210 °C slightly below the martensite start temperature and is held until the temperature has equalized. The component is then heated in another bath to a temperature slightly above the martensite start temperature. The result is a bainitic structure in the entire component.

In the case of large rolling bearings with a diameter of around one meter or more, the rolling elements are dimensioned accordingly. The components often have cross sections or wall thicknesses of 85 mm or more. So that such components can be heat treated in a technically flawless manner, high-alloy steels are used, which incur corresponding costs. In the case of bearing rings, larger cross-sections are also made from through-hardening steel in a shell-hardened design. This possibility does not exist for large-format rolling elements, since such high tensile stresses occur at the edges (= transition from lateral surface to front side) in the event of abrupt quenching that there is a high probability that cracks will form.

The object of the present invention is to further develop a method for producing a roller bearing component from a roller bearing steel which has a wall thickness or a diameter of at least 85 mm at at least one point and to specify a roller bearing component produced by means of the method and a roller bearing.

This object is achieved by a method for producing a rolling bearing component having the features of claim 1, by a rolling bearing component having the features of claim 6 and by a rolling bearing having the features of claim 10. Preferred or advantageous embodiments of the invention result from the subclaims of the following description and the attached figures.

In a method according to the invention for producing a rolling bearing component, the rolling bearing component is made of a rolling bearing steel and is formed at least in one place with a wall thickness or a diameter of at least 85 mm, the rolling bearing component being heated to form an austenitic structure and then in a hot salt bath below the martensite start temperature of the rolling bearing steel is cooled, such that the rolling bearing component is formed with a martensitic structure in a surface layer region of the rolling bearing component and is formed with a structure consisting of pearlite and/or upper bainite in a core region of the rolling bearing component.

In other words, the roller bearing component is first formed from a roller bearing steel. 100CrMo7-3 or 100CrMnSi6-4 is advantageously suitable as the roller bearing steel from which the roller bearing component is formed. At the beginning of the heat treatment, the rolling bearing component is heated to the austenitization temperature and then quenched, with the quenching speed being selected in such a way that cracking in the surface of the rolling bearing component is prevented, but at the same time a technically optimal and roll-resistant shell on the lateral surface of the rolling bearing component with as little as possible delay arises. The quenching speed is selected in particular depending on the geometry of the rolling bearing component and the quenching medium, ie the hot salt bath, in particular its heat capacity.

In the hot salt bath, the roller bearing component is in particular cooled to a temperature T in the range from 20 to 70° C., in particular 50 to 70° C., below the martensite start temperature of the roller bearing steel.

The temperature T is preferably kept constant over a period of 10 to 20 minutes.

During quenching in the warm salt bath, a phase transformation takes place in the microstructure Rolling bearing component, wherein a substantially martensitic microstructure is formed on the surface or in the area near the surface. Consequently, a martensitic surface layer hardening takes place as a result of the quenching. Furthermore, due to the slower cooling in areas of the rolling bearing component that are far from the surface, in particular in the core or in the core area of the rolling bearing component, a substantially pearlitic and/or a substantially bainitic microstructure is formed. When considering the continuous time-temperature diagram, i.e. the graphical representation of the transformation processes in the structure of an alloy as a function of temperature and time, the pearlite field and/or the bainite field is passed through during quenching for areas of the rolling bearing component that are far from the surface, with the corresponding structure changing adjusts Which microstructure is established essentially depends on the alloy composition and the geometry of the rolling bearing component.

A martensite or a martensitic microstructure is to be understood as meaning a metastable microstructure which is formed from the austenitic starting microstructure without diffusion, in particular by rapid quenching of the steel starting from the hardening or austenitizing temperature. The increase in hardness during the transformation occurs because the carbon atoms dissolved in the austenite lattice can no longer leave their lattice positions due to the short time span of the transformation, with the austenite folding over into martensite without diffusion and the enclosed carbon atoms thus straining the crystal lattice. Martensite is hard, high strength but also very brittle, which is why such steels are usually tempered after quenching to avoid any cracks.

Pearlite, on the other hand, is a lamellar, eutectoid structural component of steel, i.e. a phase mixture of ferrite and cementite that occurs as a result of coupled crystallization in iron-carbon alloys with carbon contents between 0.02% and 6.67%. Pearlite is softer than martensite. A structure consisting of pearlite is to be understood as meaning that the structure in the core area of the rolling bearing component essentially consists of pearlite. Thus, the structure consists of pearlite even if it does not have a pearlitic structure completely and exclusively. Even a slight deviation from a completely pearlitic microstructure, in which other microstructures can also be present, is therefore still to be understood as a microstructure consisting of pearlite within the meaning of this invention.

Bainite is a structure that is formed at temperatures below pearlite formation up to martensite formation, both isothermally and with continuous cooling. Upper bainite consists of acicular ferrite arranged in packets. Between the individual ferrite needles there are more or less continuous films of carbides parallel to the needle axis. A distinction must be made between upper bainite and lower bainite, which, on the other hand, consists of ferrite plates, within which the carbides form at an angle of 60° to the needle axis. Bainite is also softer than martensite but harder than pearlite. A structure consisting of upper bainite is to be understood as meaning that the structure in the core area of the rolling bearing component essentially consists of upper bainite. Thus the structure consists of upper bainite even if it is not entirely and exclusively upper bainite. Even a slight deviation from a completely bainitic microstructure, in which other microstructures can also be present, is therefore still to be understood as a microstructure consisting of upper bainite within the meaning of this invention.

The roller bearing component formed using the method according to the invention can be formed as a component blank which is formed close to the final geometry, with further treatment, in particular mechanical processing, taking place after the component has cooled in order to bring the roller bearing component into the final geometry. Alternatively, the component can already be in its final geometry before the heat treatment.

The rolling bearing component is designed, for example, as an inner ring, an outer ring or as a rolling element of a rolling bearing.

The hardenability of the steel in question is determined by the choice of alloy composition. In the case of through-hardenable steels, such as 100CrMnSi6-4, the hardenability can also be changed by changing the carbon content and the content of dissolved alloying elements, such as chromium, via the level of the austenitization temperature. The required state of solution for the geometry of the rolling bearing component to be treated and the quenching effect can be determined in advance using software or tests.

The warm salt bath preferably has a temperature between 150°C and 210°C. In particular, the hot salt bath has a temperature of between 160°C and 200°C, depending on the material. The composition of the hot salt bath is selected with regard to the requirements for the quenching parameters, whereby a quenching speed can be set at which the martensitic structure on the surface of the rolling bearing component and remote from the surface, especially in the core of the Rolling bearing component, forms a structure consisting of pearlite and / or upper bainite. In particular, the salt warm bath has a water content of 0.5 to 1%.

Furthermore, the cooling process is adjusted and, if necessary, extended by the warm salt bath in such a way that the temperatures of the edge and core of the rolling bearing component can equalize. The associated advantages are reduced crack formation as a result of thermal stress. Furthermore, lower residual stresses can be achieved in rolling bearing components with variable dimensions, size and weight.

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

The roller bearing component is preferably cooled to room temperature after the temperature of the hot salt bath has been reached. As soon as the temperature of the rolling bearing component has equalized the temperature of the hot salt bath, the rolling bearing component is removed from the bath so that the rolling bearing component can continue to cool down to room temperature. Room temperature means a temperature between 18°C and 25°C, in particular between 20°C and 25°C.

The rolling bearing component according to the invention has a wall thickness or a diameter of at least 85 mm, in particular at least 200 mm. In the case of a roller bearing ring, the wall thickness is considered here, and in the case of a rolling element, its diameter is considered.

The rolling bearing component formed using the method according to the invention consists of martensite in a surface layer region up to at least a depth below a surface of the rolling bearing component of 10 mm and has a hardness in the range from 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. Consequently, a rolling bearing component according to the invention has a hardness of between 60 HRC and 65 HRC and a martensitic microstructure up to at least a first surface distance of 10 mm.

The HRC unit is made up of HR (Rockwell hardness) as a designation of the test method, followed by another letter, here C, which indicates the scale and thus the test forces and bodies. A diamond cone with a 120° point angle and a test preload of 98.0665 N is used for scale C (C stands for “cone”). The additional test force for scale C is 1372.931 N.

Furthermore, the roller bearing component according to the invention has a hardness in the range from 30 HRC to 35 HRC in its core area. A hardness of 30 HRC corresponds to a Vickers hardness of about 300 HV and a hardness of 35 HRC corresponds to a Vickers hardness of about 345 HV. Consequently, the roller bearing component according to the invention has a hardness in the range from 30 HRC to 35 HRC and a pearlitic and/or bainitic microstructure in its core area.

This means that the rolling bearing component consists of martensite in a surface layer area and pearlite and/or upper bainite in the core area.

In the case of rolling bearing components with wall thicknesses or cross sections of at least 200 mm, the pearlitic and/or bainitic microstructure that forms the core region is preferably present from a depth of 70 mm below the surface of the component.

A roller bearing according to the invention comprises an outer ring and/or an inner ring and a multiplicity of roller bodies that roll on the outer ring and/or on the inner ring, the outer ring and/or the inner ring and/or the respective roller body being a roller bearing component in accordance with the previous statements. In other words, either only the outer ring, only the inner ring, only the rolling elements or any combination of the components mentioned can be designed as a rolling bearing component according to the invention, which has an essentially martensitic microstructure on the surface and an essentially pearlitic and/or upper bainite microstructure.

The above statements on the method apply equally to the rolling bearing component according to the invention and to the rolling bearing according to the invention, and vice versa.

• 1 eine stark schematische Schnittdarstellung eines erfindungsgemäßen Wälzlagers nach einer bevorzugten Ausführungsform,
• 2 ein schematischer Querschnitt eines erfindungsgemäßen Wälzlagerbauteils des Wälzlagers gemäß 1, und
• 3 ein schematisches Blockschaltbild eines erfindungsgemäßen Verfahrens zur Herstellung des Wälzlagerbauteils nach 2.

Further measures improving the invention are presented in more detail below together with the description of preferred exemplary embodiments of the invention with reference to the figures. Identical or similar elements are provided with the same reference symbols in the figures. Here shows

• 1 a highly schematic sectional view of a roller bearing according to the invention according to a preferred embodiment,
• 2 a schematic cross section of a rolling bearing component of the rolling bearing according to the invention 1 , and
• 3 a schematic block diagram of a method according to the invention for producing the rolling bearing component 2 .

According to 1 is a method according to the invention for the production of a rolling element designed as a rolling element 5 1, which is in the 2 and 3 is shown, visualized according to a block diagram. In other words, the rolling body 5 is to be understood as a rolling bearing component 1 in the present case. An example rolling element 5 is in 2 installed in a roller bearing 2, with the rolling element 5 in 3 is shown in cross section.

In 1 is in a first step 100 of the rolling elements 5, according to the 2 and 3 is in each case designed as a cylindrical roller with a diameter D of at least 85 mm, in this case 200 mm, made of the material 100CrMo7-3. A variety of rolling elements 5 produced in this way are in accordance with 2 trained and mounted rolling bearing 2 spatially spaced between an outer ring 3 and an inner ring 4 and in the circumferential direction by a cage 6 to each other. The outer ring 3 and/or the inner ring 4 can also be made of 100CrMo7-3 and have the same heat treatment. The heat treatment is explained below. Alternatively, the rolling elements 5, the inner ring 4 and/or the outer ring 3 can be made of 100CrMnSi6-4.

In a second method step 101, the rolling body 5 is heated to a hardening or austenitization temperature to form an austenitic structure and is kept at this temperature until the structure has been completely austenitized. Then, in a third method step 102, the rolling body 5 is fed to a hot salt bath and cooled. The hot salt bath has a temperature between 150° C. and 210° C. depending on the properties and the mixing ratio of the hot salt bath, the material properties of the roller bearing component 1 and the austenitization temperature. By means of the hot salt bath, the rolling body 5 is cooled at a controlled cooling rate, in particular in a range from 5 to 10 K/s, with a phase transformation of the structure taking place. The austenitic microstructure on the surface of the rolling body 5 converts to a martensitic microstructure due to the comparatively rapid cooling. In other words, after cooling, the rolling body 5 has on the surface, in particular in a surface layer region, up to at least a depth A1 below the surface of the rolling body 5 of 10 mm, cf. 3 , a martensitic structure. The greater the distance from the surface of the rolling body 5, the slower the cooling of the rolling body 5 proceeds, so that a structure consisting of pearlite and/or upper bainite is formed in the core region of the rolling bearing component 1. In other words, the roller bearing component 1 has in the core area, with cross sections of at least 200 mm, in particular at a depth A2 below the surface of the rolling body 5 of 70 mm, cf. 3 , a structure consisting essentially of perlite. Depending on the geometry and dimensions of the rolling body 5, a structure consisting essentially of upper bainite can also form. Both upper bainite and pearlite are softer than martensite, so that a comparatively hard shell with a hardness in the range from 60 HRC to 65 HRC forms on the rolling element 5 in the surface layer area. In contrast, the pearlitic or bainitic structure of the rolling body 5 has a hardness in the range of 30 HRC to 35 HRC in the core area.

In a fourth method step 103, the rolling body 5 is removed from the salt bath after reaching the temperature of the salt bath, i.e. when the rolling body 5 has a temperature that corresponds to the temperature of the salt bath or is in the range of the temperature of the salt bath and is brought to room temperature. i.e. to about 20 °C. With such a heat treatment, rolling bearing components with larger dimensions can be produced more cost-effectively, since a roll-resistant surface, in the case of the rolling element a roll-resistant outer surface or raceway, is created even with materials with a lower alloy content by such an adapted heat treatment, and the rolling bearing component does not tear during quenching.

It is conceivable that further heat treatment steps, for example tempering, are carried out in order to reduce the thermally induced stresses within the rolling body 5 . Furthermore, a mechanical post-treatment can be carried out in order to bring the rolling body 5 into its final geometry.

Reference List

1

rolling bearing component

2

roller bearing

3

outer ring

4

inner ring

5

rolling elements

6

Cage

100

First step of the process

101

Second step

102

Third step in the process

103

Fourth step

A1

Depth below a surface of the rolling bearing component

A2

Depth below a surface of the rolling bearing component

D

diameter

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102006052834 A1 [0002]
• DE 102006059050 A1 [0003]

Claims (10)

Method for producing a rolling bearing component (1), the rolling bearing component (1) being made from a rolling bearing steel and having a wall thickness or a diameter of at least 85 mm at at least one point, the rolling bearing component (1) being heated to form an austenitic structure and then being heated is cooled in a hot 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 a surface layer region of the rolling bearing component (1) and with a structure made of pearlite and/or in a core region of the rolling bearing component (1). upper bainite existing structure is formed. procedure after claim 1 , characterized in that cooling to a temperature T in the range from 20 to 70 °C below the martensite start temperature of the roller bearing steel takes place in the hot salt bath. procedure after claim 2 , characterized in that the temperature T is kept constant over a period of 10 to 20 minutes. Procedure according to one of Claims 1 until 3 , characterized in that the salt warm bath has a temperature between 150°C and 210°C. Procedure according to one of Claims 1 until 4 , characterized in that the roller bearing component (1) is cooled to room temperature after reaching the temperature of the salt bath. Rolling bearing component (1) made of rolling bearing steel with a wall thickness or a diameter of at least 85 mm, produced by the method according to one of Claims 1 until 5 , characterized in that the rolling bearing component (1) consists of martensite in a surface layer region up to at least a depth (A1) below a surface of the rolling bearing component (1) of 10 mm and has a hardness in the range from 60 HRC to 65 HRC and in a The core area of the rolling bearing component (1) consists of pearlite and/or upper bainite and has a hardness in the range from 30 HRC to 35 HRC. Rolling bearing component (1) according to claim 6 , characterized in that the roller bearing component (1) has a wall thickness or a diameter (D) of at least 200 mm. Rolling bearing component (1) according to claim 7 , characterized in that the roller bearing component (1) has a wall thickness or a diameter (D) of at least 200 mm and at a depth (A2) below the surface of the roller bearing component (1) of 70 mm consists of perlite and/or upper bainite. Rolling bearing component (1) according to one of Claims 6 until 8th , characterized in that the roller bearing component (1) consists of steel with the composition 100CrMo7-3 or 100CrMnSi6-4. Rolling bearing (2), comprising an outer ring (3) and/or an inner ring (4) and a multiplicity of rolling bodies (5) which roll on the outer ring (3) and/or on the inner ring (4), the outer ring (3) and/or the inner ring (4) and/or the respective rolling body (5) as a rolling bearing component (1) according to one of Claims 6 until 9 is trained.

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