Method for producing a rolling element bearing component, rolling element bearing component, and rolling element bearing

Abstract

The invention relates to a method for producing a rolling element bearing component (1), wherein: the rolling element bearing component (1) is formed from a rolling element bearing steel of the type 100CrMnSi6-4 or 100Cr6; the rolling element bearing component (1) is heated to form an austenitic microstructure and subsequently quenched in a hot salt bath to a first temperature of between 170°C and 200°C, such that a pearlitic and / or ferritic microstructure is present at least in a core region (8) of the rolling element bearing component (1); thereafter, the rolling element bearing component (1) is heated to at least a second temperature in the temperature range from 220°C to 280°C and held for at least 7 hours, forming a predominantly bainitic microstructure at a surface (7) of the rolling element bearing component (1). The invention also relates to a rolling bearing component (1) and to 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 of type 100CrMnSi6-4 or 100Cr6. Furthermore, this invention relates to rolling bearing components and rolling bearings. Background Technology

[0002] DE 10 2006 052 834A1 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% by weight and a total chromium, nickel, and molybdenum content between 1.4% and 3.0% by weight. 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] WO 00 / 63 455A1 describes a steel from the SAE 52100 series, which has 0.9% to 1.0% carbon by weight, 0.15% to 0.40% silicon by weight, 0.25% to 0.80% manganese by weight, 1.30% to 1.95% chromium by weight, a maximum of 0.25% nickel by weight, and 0.05% to 0.35% molybdenum by weight, and has an ultrafine bainitic microstructure for use in rolling bearing components. In this case, starting from an austenitic microstructure, cooling is performed to 250°C above the martensitic initiation temperature, and this temperature is typically held for 180 minutes to produce ultrafine bainite.

[0004] DE 10 2006 059 050A1 discloses a method for heat-treating rolling bearing components made of penetration-hardened bainitic rolling bearing steel. The method is performed in two steps, wherein cooling is initiated from the austenitizing temperature in a salt bath at a temperature ranging from 180°C to 210°C until temperature equilibrium is reached, followed by a transfer to a second bath lasting approximately one hour. The temperature of the second bath is approximately 220°C to 240°C. This produces a uniform bainitic microstructure throughout the component.

[0005] US2010 / 0 296 764A1 describes a rolling bearing element made of bearing steel with a through-hardened bainitic and / or martensitic microstructure. Compressive stress is generated on the surface through induction hardening.

[0006] EP 0 908 257A2 describes a method for producing small gears as sintered components having a bainitic microstructure. An edge layer comprising a martensitic microstructure is formed by surface hardening. Summary of the Invention

[0007] The object of this invention is to further develop a method for producing rolling bearing components, rolling bearing components, and rolling bearings.

[0008] This objective is achieved by the following: a method for producing a rolling bearing component having the features of claim 1, a rolling bearing component having the features of claim 3, and a rolling bearing having the features of claim 6. Preferred or advantageous embodiments of the invention are derived from the dependent claims, the following description, and the accompanying drawings.

[0009] In the method according to the invention for producing rolling bearing components made of rolling bearing steel of the type 100CrMnSi6-4 or 100Cr6, the rolling bearing component is heated to form an austenitic microstructure, and then quenched in a hot salt bath to a first temperature between 170°C and 200°C, such that a pearlitic and / or ferrite microstructure is present at least in the core region of the rolling bearing component, wherein the rolling bearing component is then immediately heated to at least a second temperature in the temperature range between 220°C and 280°C and held for at least 7 hours, wherein a predominantly bainitic microstructure is formed on the surface of the rolling bearing component.

[0010] First, the rolling bearing components are formed from rolling bearing steel of type 100CrMnSi6-4 or 100Cr6 through a suitable manufacturing process. The most suitable rolling bearing steel is 100CrMnSi6-4, which is relatively inexpensive and still exhibits the desired properties after heat treatment. Alternatively, 100Cr6 is also suitable because this material is also inexpensive and suitable for shell hardening. At the start of heat treatment, the rolling bearing components are heated to the austenitizing temperature and then quenched to a first temperature between 170°C and 200°C, wherein the quenching rate is selected to prevent cracking in the surface of the rolling bearing components while simultaneously producing a technically optimal and excessively rolling-resistant shell on the lateral surfaces of the rolling bearing components with the lowest possible deformation. In particular, the quenching rate is selected such that quenching in the upper temperature range occurs faster than the formation of pearlite morphology. Furthermore, the quenching rate is selected based on the geometry of the rolling bearing components and the quenching medium, i.e., a hot salt bath, particularly the heat capacity of the hot salt bath. The calculation of the optimal quenching rate can be performed using software in a known manner. In addition, the quenching rate can be measured during quenching using an introduced thermocouple.

[0011] In this regard, it has proven particularly effective to cool the core region of the rolling bearing component at a quenching rate of up to 2 K / s. This enables the formation of a pearlitic and / or ferrite microstructure in the core region of the rolling bearing component.

[0012] The term "core region" is understood to refer to the area located inside a rolling bearing component and at a certain distance from the surface of the rolling bearing component. In the case of a component, such as a solid rolling element, this region extends from the center of the component beyond at least 75% of the diameter of the rolling element. In the case of annular rolling bearing components, the core region is also understood to refer to the area located inside the rolling bearing component and at a certain distance from the surface of the rolling bearing component, this region being defined by the inner and outer diameters and extending from the center of the wall thickness formed by the inner and outer diameters beyond at least 75% of the wall thickness.

[0013] During quenching in a hot salt bath, a phase transformation occurs in the microstructure of the rolling bearing component, wherein a predominantly pearlitic and / or predominantly ferrite microstructure is formed on the surface, in a region near the surface, and in the core region, or in a region away from the surface of the rolling bearing component. The resulting microstructure depends essentially on the necessary solid solution state in the microstructure and the alloy composition and geometry of the rolling bearing component.

[0014] A relatively mild quenching effect can be achieved through a hot salt bath, and this quenching effect can be adjusted by the temperature and water content of the hot salt bath.

[0015] Here, the preferred water content is at least 0.3% by volume. Suitable salt baths are available on the market under the name AS140 from the manufacturer Durferrit GmbH, Mannheim.

[0016] A related advantage is the reduction in crack formation due to thermal stress. Furthermore, lower residual stress can be achieved in rolling bearing components with variable dimensions, sizes, and weights. The rolling bearing component is quenched in a hot salt bath until a pearlitic and / or ferrite microstructure is achieved, at least in the core region. In this respect, the entire rolling bearing component may have already reached the temperature of the hot salt bath. However, it is also conceivable that only a portion of the rolling bearing component has reached the temperature of the hot salt bath, while another portion, particularly a portion closer to the core of the rolling bearing component, still has a temperature higher than the initial temperature. Quenching or quenching in a hot salt bath is performed in a time-controlled manner.

[0017] Ferrite is a single-phase composition of iron, consisting of the ferrite phase. Ferrite forms a polyhedral, non-twinned microstructure, is softer than martensite, and is relatively easy to form. In particular, the alloying elements chromium and silicon promote ferrite formation. A microstructure comprising ferrite means that the microstructure, particularly in the core region of rolling bearing components, consists essentially or primarily of ferrite. Therefore, the microstructure comprises ferrite even if it is not entirely and solely composed of ferrite. Thus, even slight deviations from a fully ferrite microstructure, particularly up to 5% by volume—where other microstructures may also be present—are still understood to be ferrite-containing microstructures within the meaning of this invention.

[0018] On the other hand, pearlite is a layered eutectoid component of steel, i.e., a mixture of ferrite and cementite phases, which occurs due to the coupled crystallization in iron-carbon alloys with carbon content between 0.02% and 6.67%. Pearlite is softer than martensite. A microstructure including pearlite means that the microstructure, particularly in the core region of rolling bearing components, consists essentially or primarily of pearlite. Therefore, the microstructure includes pearlite, even if it is not entirely and solely formed by pearlite. Thus, even slight deviations from a completely pearlite microstructure, particularly up to 5% by volume—where other microstructures may also be present—are still understood to be pearlite-containing microstructures within the meaning of this invention.

[0019] A mixture of pearlite and ferrite can also exist in the core region of rolling bearing components.

[0020] After quenching, the rolling bearing component is removed from the hot salt bath and subsequently reheated to at least a second temperature within a temperature range of 220°C to 280°C. The second temperature is selected based on the alloy composition and dimensions of the rolling bearing component. The phrase "at least a second temperature within a temperature range of 220°C to 280°C" is understood to mean that the rolling bearing component is held within this temperature range for a certain period of time, wherein the temperature can be varied within this range according to a heat treatment strategy, and in particular, can be adjusted incrementally in a targeted manner. It is conceivable that the rolling bearing component is reheated to only a single second temperature throughout the entire treatment time. Alternatively, it is conceivable that multiple temperatures are incrementally set within the temperature range of 220°C to 280°C to establish a desired microstructure on or near the surface of the rolling bearing component. The holding time at at least a second temperature within the temperature range of 220°C to 280°C also depends on the heat treatment strategy selected in each case. In any case, the holding time exceeds 7 hours. In other words, the rolling bearing component is held at a temperature between 220°C and 280°C for at least 7 hours, regardless of the temperature approaching or remaining within that range during said time. The second temperature is maintained until a bainitic microstructure forms on or near the surface of the rolling bearing component.

[0021] In the context of this invention, the phrase "immediately thereafter" will be understood to mean that the rolling bearing component is not cooled below 170°C after it has been quenched from the austenitizing temperature to the first temperature. Instead, the rolling bearing component is reheated to one or more temperatures between 220°C and 280°C for at least 7 hours after quenching, such that after heat treatment, a predominantly pearlitic and / or ferrite microstructure is present in the core region, and a bainitic microstructure or predominantly bainitic microstructure is present on or near the surface. In other words, the rolling bearing component is directly reheated after quenching.

[0022] Bainite is a microstructure formed by isothermal and continuous cooling of both at temperatures below the pearlite morphology and above the martensite morphology. Upper bainite comprises bundles of acicular ferrite. Between the individual ferrite needles are more or fewer 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 microstructure including bainite refers to a microstructure in the surface or near-surface region of a rolling bearing component that is substantially or primarily composed of bainite. Therefore, this microstructure includes upper bainite, even if the microstructure is not entirely upper bainite or only upper bainite. Therefore, even slight deviations from a fully bainitic microstructure—where other microstructures may also exist—are still understood to be within the meaning of this invention as a microstructure including upper bainite. In particular, it is preferred that the bainite in the region near the surface contains no more than 5% pearlite by volume. Preferably, pearlite is not present at all on the surface of the rolling bearing component.

[0023] Rolling bearing components can be formed as component blanks close to their final geometry, wherein further processing, particularly machining, can be performed after the component is cooled from a temperature range between 220°C and 280°C to bring the rolling bearing component to its final geometry. Alternatively, the component may already exist in its final geometry before heat treatment. Rolling bearing components can be designed as, for example, inner rings, outer rings, or rolling elements of a rolling bearing, wherein the production and heat treatment of the rolling bearing components described herein are particularly suitable for components with large dimensions, particularly diameters or thicknesses greater than 85 mm. In other words, rolling bearing components preferably with a diameter of at least 85 mm, particularly 200 mm, are heated to form an austenitic microstructure and subsequently quenched in a hot salt bath to a first temperature such that a pearlitic and / or ferritic microstructure is present at least in the core region of the rolling bearing component, wherein, immediately thereafter, the rolling bearing component is heated to at least one second temperature between 220°C and 280°C and held in this temperature range for at least 7 hours to form a bainitic microstructure on the surface of the rolling bearing component.

[0024] 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, which is considered advantageous here, hardenability can also be modified by changing the carbon content and the content of dissolved alloying elements such as chromium through the austenitizing temperature. The solution state and quenching effect required for the geometry of the rolling bearing component to be treated or the corresponding application can be determined in advance by means of software and / or experiments.

[0025] The processing of rolling bearing components results in the formation of residual compressive stress on their surfaces. This residual compressive stress occurs during the transformation of the microstructure to a bainitic microstructure, and this happens on or near the surface of the rolling bearing component. This residual compressive stress is a negative residual stress within the component's microstructure, which leads to increased fatigue strength at the surface of the rolling bearing component. Additionally, it prevents crack formation and improves the corrosion resistance of the rolling bearing component.

[0026] Furthermore, the rolling bearing component is preferably treated to have a surface hardness of at least 58 HRC. A hardness of 58 HRC (Rockwell hardness) corresponds to a Vickers hardness of approximately 655 HV. Therefore, the rolling bearing component according to the invention has a hardness of 58 HRC and a bainitic microstructure on its surface. The so-called hardening depth—at which the hardness of the rolling bearing component is 550 HV1 or 52.3 HRC—is preferably at a depth perpendicular to the surface of the rolling bearing component, approximately 5.2% of the thickness or diameter of the rolling bearing component. According to DIN 50190-1, the surface hardening depth is a vertical distance from the surface of the corresponding component at which the hardness has decreased to a value of 550 HV1. The change in hardness from the surface to the core is determined by hardness measurement. The unit HRC consists of HR (hardness, Rockwell), which is the name of the test method, followed by another letter, here C, where C indicates scale and therefore the 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 for scale C is 1372.931 N.

[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 foregoing components can be designed as a rolling bearing component having a pearlitic and / or ferritic microstructure in the core region of the rolling bearing component and a large amount of bainitic microstructure on the surface of the rolling bearing component.

[0028] Specifically, the rolling bearing components are designed as rolling elements, which are designed as solid or hollow rollers.

[0029] 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

[0030] Further improvements to the present 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:

[0031] Figure 1 A schematic block diagram of a method for producing rolling bearing components according to the present invention is shown.

[0032] Figure 2 A schematic cross-sectional view of the height of a rolling bearing according to a preferred embodiment of the present invention is shown.

[0033] Figure 3 It was shown as a basis Figure 2 A schematic cross-section of the rolling element in a rolling bearing component.

[0034] Figure 4 A diagram is shown for 100CrMnSi6-4, a rolling bearing steel that exhibits a minimum cooling rate based on different austenitizing temperatures during the austenitizing time, in order to prevent pearlite from exceeding 5% by volume in the edge regions.

[0035] Figure 5 A graph showing the austenitizing temperature of 100CrMnSi6-4 for rolling bearing steel at 855°C indicates the critical distance from the surface of the rolling element to the surface of the rolling element for 5% pearlite morphology by volume in the edge region, based on the austenitizing time and therefore the degree of austenitization and the diameter of the rolling element. Detailed Implementation

[0036] 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. In this context, the rolling element 5 of the rolling bearing 2 will be understood as the rolling bearing component 1. This rolling element 5 can be mounted according to... Figure 2 In the rolling bearing 2, that is, spatially mounted between the outer ring 3 and the inner ring 4, the rolling elements 5 are arranged and guided at intervals in the circumferential direction by a cage 6. To better understand, in Figure 3 The rolling element 5 is shown again in cross-section.

[0037] In the first method step 100, the corresponding rolling element 5 is formed of rolling bearing steel 100CrMnSi6-4, and the rolling element is based on... Figure 2 and Figure 3 It is designed as a cylindrical roller with a diameter D of at least 85 mm. This can be achieved, for example, through machining. According to... Figure 2The outer ring 3 and / or inner ring 4 can also be formed from 100CrMnSi6-4 and produced by the same method according to the invention. This production involves heat treatment of the rolling bearing component 1, which is explained below.

[0038] In the second method step 101, the rolling element 5 is heated to a hardening temperature or austenitizing temperature to form an austenitic microstructure, and held at this temperature until complete austenitization of the microstructure has occurred, particularly until the necessary solution treatment is achieved. Subsequently, in the third method step 102, the rolling element 5 is introduced into a hot salt bath and quenched from the austenitizing temperature to a first temperature. Depending on the properties and mixing ratio of the hot salt bath, the material properties of the rolling bearing component 1, and the austenitizing temperature, the hot salt bath currently has a temperature between 170°C and 200°C. The hot salt bath is used to cool the rolling element 5 at a controlled rate (see reference). Figure 4 The rolling element 5 is cooled by a relatively mild quenching effect, during which a phase transformation of the microstructure occurs. In this process, the austenitic microstructure of the rolling element 5 transforms into a pearlitic and / or ferrite microstructure during quenching. Therefore, a microstructure comprising pearlite and / or ferrite is formed at least in the core region 8 of the rolling bearing component 1.

[0039] After the rolling element 5 has been quenched, in the fourth method step 103, the rolling element is directly reheated. Specifically, immediately after quenching, the rolling bearing component 1 is heated to at least a second temperature within a temperature range of 220°C to 280°C, wherein the at least second temperature is held for at least 7 hours. In other words, the rolling element 5 can be held for 7 hours at a single second temperature. Alternatively, the rolling element 5 can be gradually heated to multiple different temperatures within the temperature range of 220°C to 280°C and held at those temperatures, wherein the total holding time between 220°C and 280°C is at least 7 hours. By holding at least a second temperature within the temperature range of 220°C to 280°C for more than 7 hours, a microstructure transformation occurs, wherein a bainitic microstructure is formed on the surface 7 and in the edge region 9 near the surface of the rolling bearing component 1. This heat treatment allows for the more economical production of rolling bearing components 1 with larger-sized, hardened housing designs, because even with materials of lower alloy content, this heat treatment creates excessive rolling resistance surfaces—in the case of rolling element 5, excessive rolling resistance lateral surfaces or raceways—and prevents cracking in the rolling bearing component 1. Furthermore, the heat treatment on surface 7, where the associated microstructure transforms into a bainitic microstructure, sets residual compressive stress, which also prevents cracking in the rolling element 5. After heat treatment, the rolling element 5 has a surface hardness of at least 58 HRC or 655 HV. At a hardening depth A corresponding to approximately 5.2% of the diameter D of the rolling element 5, i.e., approximately 4.4 mm in this case, the rolling element 5 has a hardness of at least 550 HV1. It is conceivable to perform another heat treatment step, such as tempering, to reduce thermally induced stress within the rolling element 5. Additionally, mechanical post-treatment can be performed to bring the rolling element 5 to its final geometry.

[0040] Figure 4 A diagram is shown for 100CrMnSi6-4, a rolling bearing steel, which has a minimum cooling rate in Kelvin per second based on different austenitizing temperatures of 855°C, 865°C, and 875°C within an austenitizing time measured in minutes. This time must be maintained to prevent the formation of more than 5% pearlite by volume in this type of rolling bearing steel. It can thus be seen that a higher minimum cooling rate must be set according to the degree of austenitization and increases with the degree of austenitization.

[0041] Figure 5Also shown are graphs for rolling elements of different diameters made of rolling bearing steel 100CrMnSi6-4, and in each case, austenitizing at an austenitizing temperature of 855°C according to austenitizing times of 45 minutes, 90 minutes, and 150 minutes. As the degree of austenitization increases, and as the diameter of the rolling element or roller (in millimeters) increases, the critical distance to the surface of the rolling element decreases. This critical distance corresponds to the hardening depth A between the core region 8 and the surface 7 of the rolling element 5 (see reference). Figure 3 The bainite edge region 9 is located within this hardening depth, and no pearlite morphology exceeding 5% by volume appears within this hardening depth. Therefore, for the same degree of austenitization of the rolling element 5, the hardening depth A and thus the thickness of the bainite edge region 9 decrease with increasing diameter D of the roller or rolling element 5.

[0042] List of reference numerals

[0043] 1 Rolling bearing components

[0044] 2 Rolling bearings

[0045] 3 Outer Ring

[0046] 4 Inner Ring

[0047] 5. Rolling elements

[0048] 6. Cage

[0049] 7 Surface

[0050] 8 core area

[0051] 9. Edge Area

[0052] 100 First Method Steps

[0053] 101 Second Method Steps

[0054] 102 Third Method Steps

[0055] 103 Fourth Method Steps

[0056] A Hardening Depth

[0057] D diameter

Claims

1. A method for producing a rolling bearing component (1), wherein, The rolling bearing component (1) is formed of a rolling bearing steel of the type 100CrMnSi6-4 or 100Cr6, wherein the rolling bearing component (1) is heated to form an austenitic microstructure and is subsequently quenched in a hot salt bath to a first temperature of between 170°C and 200°C, such that a pearlitic and / or ferritic microstructure is present at least in a core region (8) of the rolling bearing component (1), wherein the rolling bearing component (1) is thereafter immediately heated to at least a second temperature in a temperature range of between 220°C and 280°C and held for a holding time of at least 7 hours, wherein a predominantly bainitic microstructure is formed on a surface (7) of the rolling bearing component (1) and a residual compressive stress is generated.

2. The method according to claim 1, characterized in that The core region (8) of the rolling bearing component (1) is cooled with a quenching rate of at most 2 K / s.

3. The method according to any one of the preceding claims, characterized in that The rolling bearing component (1) is transferred to a further bath having a temperature in the range from 220°C to 280°C for heating to the second temperature.

4. The method according to claim 1 or 2, characterized in that The second temperature is incrementally increased towards 280°C during the holding time.

5. A rolling bearing component (1) produced by the method according to any one of claims 1 to 4, characterized in that The rolling bearing component (1) has a bainitic microstructure on the surface (7) and a pearlitic and / or ferritic microstructure in the core region (8).

6. The rolling bearing component (1) according to claim 5, characterized in that The rolling bearing component (1) has a surface hardness of at least 58 HRC.

7. The rolling bearing component (1) according to claim 5 or 6, characterized in that The rolling bearing component (1) has a diameter (D) of at least 85 mm.

8. 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 on the inner ring (4), wherein, The outer ring (3) and / or the inner ring (4) and / or the respective rolling element (5) is a rolling bearing component (1) according to any one of claims 5 to 7.

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