DE102013220840B4 - Bearing element for a rolling or sliding bearing - Google Patents

Abstract

Bearing element (1) for a sliding or rolling bearing (2), which bearing element (1) at least partially from a powder metallurgical composite material containing a steel-based metallic phase and a hard material phase is formed, or at least partially comprises such a composite material, characterized in that the steel contains 0.2-0.6% by weight of carbon, 0.1-0.3% by weight of nitrogen, 0.5-2% by weight of molybdenum and 13-15% by weight of chromium wherein the composite material comprises a total of 1-1.5% by weight of carbon, 0.1-2% by weight of nitrogen, 0.5-4% by weight of molybdenum and 14-15.75% by weight of chromium, wherein the carbon-nitrogen ratio is 0.5-4, and the hard material phase contains less than 4 wt% vanadium and / or less than 3 wt% nickel.

Description

Field of the invention

The invention relates to a bearing element for a rolling or sliding bearing, which bearing element at least partially from a powder metallurgical composite material containing a steel-based metallic phase and a hard material phase, is formed or at least partially comprises such a composite material.

Background of the invention

Bearing elements for rolling or sliding bearings, in particular in the form of bearing rings, are well known and are usually formed from mechanically as well as corrosive particularly durable materials. In addition to classical bearing steels, these include powder metallurgical composite materials which comprise a metallic phase and a hard material phase.

The DE 42 12 966 A1 describes a heat-resistant, corrosion-resistant martensitic chromium steel with mass fractions of 0.005 to 0.5 percent carbon, 0.2 to 1 percent nitrogen, 0.5 to 3 percent molybdenum and 14 to 18 percent chromium.

The DE 11 2004 001 371 T5 describes a sintered sliding member having a back metal and an iron-containing sintered body joined thereto having a martensite phase having a concentration of carbon dissolved in the solid state of 0.15 to 0.5% by weight and carbide having a content of 5 to 50% by volume contains.

The DE 10 2008 024 055 A1 describes a bearing ring with a carrier element and a functional element which consists at least in the region of the bearing raceway of a different material than the carrier element, wherein one or both of the elements consists of segments joined together.

However, there is still a need for development of mechanically as well as highly corrosive materials which the use of corresponding bearing elements in non-conventionally lubricated operating situations, especially in corrosive acting (thin) liquid, especially aqueous media in which corresponding bearing elements permanently outsourced and of which the bearing elements be flushed through, allow. Such, in particular due to a not effectively realizable lubrication of the bearing elements, mechanically as well as corrosive demanding operating situations are particularly in applications in hydraulic structures, such. As marine power plants, floodgates, or in salt or fresh water turbines, or in Bohrkopf-, compressor or pump bearings. In these applications, there is also the danger of cavitation of corresponding bearing elements.

Summary of the invention

The invention has for its object to provide a, especially against mechanical and also corrosive stresses, highly durable bearing element.

The object is achieved by a bearing element according to claim 1.

According to the invention, a bearing element is proposed, which is formed at least in sections from a steel-based metallic phase and a powder metallurgical composite material containing a hard material phase, respectively, or at least partially comprises such a powder metallurgical composite material. The special feature of the bearing element according to the invention consists in the (chemical) composition of the metallic phase, d. H. of the steel on which the metallic phase is based. This steel comprises as essential alloying elements carbon in a proportion of 0.2-0.6 wt.%, Nitrogen in an amount of 0.1-0.3 wt.%, Molybdenum in an amount of 0.5-2 Wt .-% and chromium in a proportion of 13-15 wt .-%.

The abovementioned alloying elements are in each case elementary, ie in pure form, in the abovementioned proportions. The stated proportions by weight therefore do not refer to the carbon or nitrogen contained in carbon or nitrogen compounds or the molybdenum or chromium contained in molybdenum or chromium compounds, but to the elemental, ie in pure form, in the metallic phase present carbon or nitrogen respectively the elemental, ie in pure form, present in the metallic phase molybdenum or chromium.

Of course, the steel forming the metallic phase contains, as usual, iron, impurities and, if appropriate, further alloying elements, so that a total composition of 100% by weight results.

The effective amount of the steel forming the metallic phase is typically greater than 30. The sum of the effect is determined according to the following PREN formula, which gives a measure of the corrosion resistance of the steel to pitting or crevice corrosion: 1 × chromium% by weight + 3 , 3 × content of molybdenum in% by weight + 16 × content of nitrogen in% by weight.

The steel forming the metallic phase is therefore a high-alloyed tool steel. The weight proportions, d. H. the concentrations of the alloying elements require a mechanically highly stressable and a highly corrosion resistant material. The mechanical properties are determined by the alloying elements carbon, molybdenum and nitrogen, the high corrosion resistance of the powder metallurgical composite material results from the relatively high proportion of chromium.

Specifically, the powder metallurgical composite material is characterized by high strength, toughness, hardness, rollover and wear resistance and high corrosion resistance.

The particular chemical as well as proportionate composition of the metallic phase forming steel is thus the basis for the special property profile of the powder metallurgical composite material, which also without conventional lubrication of the bearing element or a receiving this bearing member, for use in both mechanical and corrosive predestined for highly demanding applications. Corresponding applications can z. B. in corrosive environments, d. H. z. B. in aqueous, corrosive chlorine-containing environments such. As in the field of marine power plants, generally hydraulic structures, or other marine applications, such. As ships lie.

The bearing element according to the invention or the composite material forming this is by powder metallurgy process, d. H. based on a powdery starting material or a powdery starting material mixture, prepared. The use of powder metallurgical methods is particularly advantageous because it allows the formation of microstructures with (nearly) isotropic properties. Likewise, the use of powder metallurgical methods allows near-net-shape production or primary shaping of the bearing element, which largely reduces the need for mechanical post-processing steps and is therefore efficient in terms of production technology and thus also economically.

A powder metallurgical process for producing the bearing element is, for example, hot isostatic pressing, HIP for short; Consequently, a powder metallurgical production engineering principle from the field of primary forming, according to which a powdered starting material or a powdered starting material mixture is compacted or pressed and sintered under the influence of pressure and temperature.

Another conceivable powder metallurgical method for producing a bearing element according to the invention or the composite material forming this is the Sprühkompaktierverfahren, which is also a powder metallurgy manufacturing principle from the field of primary shaping, according to which a powdered starting material or a powdered starting material mixture sprayed onto a substrate and a component is "built up" by a layer-wise application on the carrier material. An advantage of the spray-compacting process over hot-isostatic pressing is that it is not absolutely necessary to compact the powdery starting materials. A further advantage of the spray-compacting process is the possible realization of a "tailor-made" material composition of the composite material, which can accordingly be produced with spatially distributed substance or concentration gradients. Thus, it is possible, for example, a composite material with an outer, d. H. near the surface or edge layer, highly alloyed and inner, d. H. Off-surface or edge layer removal, low alloy steel composition form.

In the context of powder metallurgical production of the composite material, it is conceivable that the powdery material or material mixture forming the metallic phase with a hard material phase forming to combine powdered material or material mixture in the context of a powder metallurgical process. Alternatively, it is conceivable first to produce the metallic phase by a powder metallurgical process and to form the hard material phase in the metallic phase by a subsequent formation of precipitates, for example in the course of the primary shaping of the composite material or a heat treatment.

The volume fraction of the hard material phase in the composite material is in particular in a range between 8 and 30% by volume, preferably in a range between 15 and 25% by volume. It is important to ensure that the volume fraction of the hard material phase does not fall below 8% by volume in order to ensure a high hardness of the composite material and, consequently, of the bearing element. Of course, the volume fraction of the hard material phase in exceptional cases, of course, below 8 vol .-% or above 30 vol .-%.

In addition to the volumetric proportion of the hard material phase, the shape, size and distribution of the hard material particles or hard material grains forming the hard material phase in the metallic phase serving as the matrix are decisive for the property profile of the composite material. The hard materials or hard grains are preferably round or roundish shape. The size of coherent hard materials or hard material grains is in a range between 1 and 100 microns, preferably in a range between 3 and 10 microns. It is important to ensure the most coherent possible distribution of the hard material phase forming hard particles or hard grains in the serving as a matrix metallic phase.

A characteristic for the shape, size and distribution of the hard material phase forming hard particles or hard grains represents the surface quality of the bearing element in a finished state. Here, it is desirable that roughness Ra for bearing elements with an outer diameter above 500 mm after finish machining below 0 , 5 microns and bearing elements with an outer diameter below 500 mm below 0.3 microns. Roughness investigations showed that roughness values Ra in the range of 0.15-0.2 μm can be achieved for bearing elements according to the invention with outside diameters above 500 mm, which points to a particularly coherent microstructure, ie. H. a particularly coherent distribution of the hard particles or hard grains in the metallic phase can conclude.

In an expedient development of the invention, the steel forming the metallic phase of the powder metallurgical composite material additionally contains 0.1-2% by weight of manganese, 0.1-1% by weight of silicon and a nickel content of less than 1% by weight. The alloying of manganese, silicon and nickel requires a further improvement of the mechanical properties, in particular the yield strength and tensile strength, as well as the wear resistance of the composite material. In exceptional cases, the weight proportions of the additional alloying elements manganese, silicon and nickel can also be above or below the aforementioned value ranges.

The hard material phase associated with the powder metallurgical composite material can be formed from at least one of the following hard material compounds or comprise at least one of the following hard material compounds: borides, carbides, namely vanadium carbide and / or niobium carbide, nitrides, namely vanadium nitride and / or niobium nitride, silicides. Of course, mixtures (chemically) of different hard material compounds are conceivable.

A preferred embodiment of the bearing element according to the invention provides that the powder metallurgical composite material a total of 1-1.5 wt .-% carbon, 0.1-2 wt .-% nitrogen, 0.5-4 wt .-% molybdenum and 14-15 Contains 75 wt .-% chromium, wherein the carbon-nitrogen ratio is 0.5-4, and the hard material phase contains less than 4 wt .-% vanadium and / or less than 3 wt .-% nickel. Part of the carbon, nitrogen, molybdenum and chromium are elemental, and another part of the carbon, nitrogen, molybdenum and chromium are in carbon, nitrogen, molybdenum or chromium compounds. Investigations showed that by this composition a powder metallurgical composite material with both mechanical properties, i. H. in particular strength, toughness, hardness, rollover and wear resistance, as well as in view of the corrosion resistance particularly advantageous properties is realized.

The hardness of the bearing element is in a range of 55 to 70 HRC (hardness Rockwell), preferably above 59 HRC, at least in the region of its surface or edge layer or in near-surface edge layer regions. The surface or boundary layer of the bearing element may have a certain structural area, which differs from further inward structural areas in its properties, in particular the hardness, and thus can be distinguished from areas located further inside. Typical surface or edge layer areas are z. B. bearing element side provided raceway surfaces for sliding or rolling elements. Of course, the bearing element also overall a consistent hardness exhibit. In exceptional cases, the hardness of the bearing element may of course be below 55 HRC or above 70 HRC.

In order to further increase the corrosion resistance of the bearing element, the bearing element can at least partially with a protective layer, such as. As a protective coating based on a polymer to be coated against corrosive media. Alternatively or additionally, the bearing element may comprise at least one metallic protective body forming a sacrificial anode, or may be connected to an electrically conductive one. Both variants provide protection against corrosive stresses of the bearing element, wherein the coating of the bearing element with a corresponding protective layer, a passive corrosion protection and by the protective anode forming a sacrificial anode active corrosion protection is realized. In the latter case, the bearing element is usually electrically conductive with the protective body, which consists of a compared to the bearing element forming composite material more noble metal such. B. a metal based on aluminum, magnesium or zinc, is formed. The protective body forming the sacrificial anode can be embedded at least in sections in a receiving body formed from an electrically conductive material, in particular a metal. In this case, the receiving body is suitably connected to the bearing element.

A further advantageous embodiment of the bearing element according to the invention provides that the bearing element is at least partially provided with an electrically insulating coating. The electrically insulating coating may, for. Example, be formed of a ceramic material or a plastic material and allows electrical insulation of the bearing element against electrically conductive third objects.

In the bearing element according to the invention, it may be, for. B. to a bearing ring, d. H. an outer or an inner ring, a sliding or rolling bearing act. The bearing element may also be a sliding or rolling element.

The invention further relates to a sliding or rolling bearing which comprises at least one bearing element according to the invention as described above. As mentioned, the bearing element (s) may be bearing rings and / or sliding or rolling elements. With regard to the plain or rolling bearing according to the invention, all statements relating to the bearing element according to the invention apply analogously.

Short description of the drawing

An embodiment of the invention is illustrated in the drawing and will be described in more detail below. It shows:

1 a schematic diagram of a rolling bearing, comprising a bearing element according to an embodiment of the invention, and

2 a diagram illustrating the corrosion resistance of bearing elements according to two embodiments of the invention.

Detailed description of the drawing

1 shows a schematic diagram of a bearing element 1 according to an embodiment of the invention. The bearing element 1 is part of a rolling bearing 2 , At the bearing element 1 it is the outer ring 3 of the rolling bearing 2 , The inner ring 4 of the rolling bearing 2 could equally as a corresponding bearing element 1 be formed according to an embodiment of the invention. The same applies to the between the outer ring 3 and the inner ring 4 rolling rolling elements 5 which is in a cage 6 are stored.

The bearing element 1 is formed from a powder metallurgical, ie produced by powder metallurgy, composite material. The powder metallurgical composite material comprises a metallic phase formed on a steel and a hard material phase formed from a hard material.

The hard material phase is formed from a bonding, carbide, nitride or silicide compound or a mixture of at least two of the stated hard material compounds. In particular, the hard material phase is a niobium carbide or a vanadium carbide compound or a niobium nitride or a vanadium nitride compound. The volume fraction of the hard material phase in the composite material is above 5 vol. %, in particular in a range between 10 and 30% by volume. The hard material phase is present in the metallic phase serving as matrix in the form of finely distributed round or spherical grains. The size of coherent hard grains is in particular in a range between 3 and 10 microns.

The structural properties of the composite material are largely isotropic. The structure fineness is very high (ASTM KG> 7-8). Micro-unit grade (K-value) investigations revealed K4 = 0 and K1 <4.

The steel forming the metallic phase of the composite material contains 0.2-0.6% by weight of carbon, 0.1-0.3% by weight of nitrogen, 0.5-2% by weight of molybdenum and 13-15% by weight .-% chromium. In addition, the steel additionally contains manganese, silicon and nickel as well as iron and common impurities.

A preferred variant of the steel forming the metallic phase of the composite material contains the alloying elements shown in the following table: element C N Not a word Cr Mn Si Ni of weight% 0.20 0.10 0.50 13,00 0.10 0.10 0.99 to% by weight 0.60 0.30 2.00 15.00 2.00 1.00 0

The overall composition of the bearing element 1 preferably comprises 1-1.5% by weight of carbon, 0.1-2% by weight of nitrogen, 0.5-4% by weight of molybdenum and 14-15.75% by weight of chromium, wherein the carbon-nitrogen ratio is 0.5-4, and the hard material phase contains less than 4 wt% vanadium and / or less than 3 wt% nickel.

The roughness value Ra of the bearing element 1 is in a range between 0.15 and 0.2 microns, which provides a high surface quality of the bearing element 1 conditionally.

The hardness of the bearing element 1 is above 58 HRC, especially above 61 HRC. In particular, corresponding hardness values for the surface layers or raceway surfaces of the bearing element are 1 given. Experiments showed that the high hardness of the bearing element 1 the formation of cavitations, in applications in which the bearing element 1 operated partially or completely filled with an aqueous medium, significantly reduced. The experiments showed that the cavitation removal rate of a bearing element formed from the composite material according to the invention 1 approximately 30% below the Kavitationsabtragsrate of bearing elements of conventional bearing steel.

That the bearing element 1 forming composite material is characterized by a high strength, toughness, hardness, rollover and wear resistance and high corrosion resistance. The yield strength of the composite material is typically above 1500 MPa, the maximum tensile stress is typically above 1800 MPa.

The outer ring 3 and the inner ring 4 of the rolling bearing 2 each with a protective layer 7 coated or coated against corrosive media. The protective layer 7 represents a passive corrosion protection and is formed for example from a paint based on a plastic material.

On the outer ring 3 or the inner ring 4 of the rolling bearing 2 is also a disc 8th attached, in which electrodes for sacrificial anodes forming metallic protective body 9 are embedded. The sacrificial anodes forming metallic protective body 9 are z. As aluminum or zinc, generally of a less noble metal than the composite material formed and on the outer ring 3 or the inner ring 4 of the rolling bearing 2 appropriate. The protective body 9 thus provide active corrosion protection of the bearing element 1 or the rolling bearing 2 Depending on whether the disc 8th from an electrically conductive, ie, for example, a metallic material, or electrically insulating, ie, for example, of a plastic material, formed material, the electrodes may be electrically conductive or electrically isolated.

The rolling bearing 2 is outside circumference, ie in particular in the region of the outer circumference of the outer ring 3 , and on the inner peripheral side, ie in particular in the region of the inner circumference of the inner ring 4 , also with an electrically insulating coating 10 Mistake. The electrically insulating coating 10 is made of an electrically insulating material, such. As a ceramic material, and is used for electrical insulation of the bearing rings.

2 shows a diagram for illustrating the corrosion resistance of two inventive bearing elements 1 different chemical composition. Based on 2 can be compared to a improved from a conventional bearing steel corrosion resistance of the bearing elements of the invention 1 set forth composite composite material.

In the in 2 As shown in the diagram, the electrical current (y-axis) is plotted against the electrical potential (x-axis). Shown are experimental results from investigations of the pitting corrosion potential or the repassivation potential (Ag / AgCl, 3.5% NaCl, 20 ° C). The curves 11 represent the measurement results for a bearing element according to the invention 1 a first chemical composition, the curves 12 represent the measurement results for a bearing element according to the invention 1 a second chemical composition, the curves 13 represent the measurement results for a non-inventive bearing element from a conventional bearing steel.

Visible begins by the rise of the curves 11 . 12 . 13 indexed material dissolution in the bearing elements according to the invention 1 much later than the non-inventive bearing element. The repassivation potential, ie the potential at which the curves hit the x-axis again after the increase, lies with the bearing elements according to the invention 1 significantly higher compared to the non-inventive bearing element. The investigations prove the good corrosion resistance of the bearing elements according to the invention 1 ,

LIST OF REFERENCE NUMBERS

1

bearing element

2

roller bearing

3

outer ring

4

inner ring

5

rolling elements

6

Cage

7

protective layer

8th

disc

9

protective body

10

electrically insulating coating

11

Curve

12

Curve

13

Curve

Claims (8)

Bearing element ( 1 ) for a sliding or rolling bearing ( 2 ), which bearing element ( 1 ) is formed at least in sections from a powder metallurgical composite material containing a steel-based metallic phase and a hard material phase, or at least partially comprises such a composite material, characterized in that the steel 0.2-0.6 wt .-% carbon, 0 Containing 1-0.3% by weight of nitrogen, 0.5-2% by weight of molybdenum and 13-15% by weight of chromium, wherein the composite material contains a total of 1-1.5% by weight of carbon, 0, 1-2 wt .-% nitrogen, 0.5-4 wt .-% molybdenum and 14-15.75 wt .-% chromium, wherein the carbon-nitrogen ratio is 0.5-4, and the hard material phase less as 4 wt .-% vanadium and / or less than 3 wt .-% nickel. Bearing element according to claim 1, characterized in that the steel additionally contains 0.1-2 wt .-% manganese, 0.1-1 wt .-% silicon and a nickel content less than 1 wt .-%. Bearing element according to one of the preceding claims, characterized in that the hard material phase is formed from at least one of the following hard material compounds or comprises at least one of the following hard material compounds: borides, carbides, namely vanadium carbide and / or niobium carbide, nitrides, namely vanadium nitride and / or niobium nitride, silicides , Bearing element according to one of the preceding claims, characterized in that the hard material phase in the composite material has a proportion in a range between 8 and 30 vol .-%, namely 15-25 vol .-%. Bearing element according to one of the preceding claims, characterized in that the hardness is at least in the region of the surface in a range of 55 to 70 HRC, while above 59 HRC. Bearing element according to one of the preceding claims, characterized in that it at least partially with a protective layer ( 7 ) is coated with respect to corrosive media and / or that it comprises at least one metallic protective body forming a sacrificial anode ( 9 ). Bearing element according to one of the preceding claims, characterized in that it has a bearing ring ( 3 . 4 ) or a sliding or rolling element ( 5 ). Sliding or rolling bearings ( 2 ) comprising at least one bearing element ( 1 ) according to one of the preceding claims.

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