WO2013127566A1

WO2013127566A1 - Process for producing a bearing component

Info

Publication number: WO2013127566A1
Application number: PCT/EP2013/051125
Authority: WO
Inventors: Werner Trojahn
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2012-02-29
Filing date: 2013-01-22
Publication date: 2013-09-06
Also published as: DE102012203110A1

Abstract

Process for producing a bearing component (9) having a carbon gradient present at least in the region of the marginal layer (8) thereof, wherein molten metal is sprayed onto a carrier (7) in a spraying process and the carbon content of the metal to be sprayed on is varied during the spraying operation, wherein at least two separate spraying devices (2a, 2b) are used to spray at least two molten masses (S₁, S₂), wherein the first molten mass (S₁) has a relatively low carbon content and the second molten mass (S₂) has a carbon content which is higher compared thereto, wherein the spray cones (6a, 6b) overlap and the quantities discharged by the spraying devices (2a, 2b) are varied during the spraying operation, characterized in that the second molten mass (S₂) has a Cr content of at least 13%.

Description

Name of the invention

Method of manufacturing a bearing component Description

Field of the invention

The invention relates to a method for producing a bearing component with a carbon gradient given at least in the region of its boundary layer, wherein molten metal is sprayed onto a substrate in a spraying process and the carbon content of the metal to be sprayed is varied during the spraying process, using at least two separate spraying devices two melts are sprayed, of which the first melt has a lower carbon content and the second melt has a higher carbon content, wherein the spray cones overlap and the discharge quantities of the sprayers are varied during the spraying process. Background of the invention

Bearing components are known in various forms and are used to build various types of bearings such as roller bearings, spherical plain bearings or linear bearings. Rolling, for example, are known to consist of at least two components, namely one or more rings, between which the rolling elements, such as rollers run. Since bearing components are usually considerably loaded during operation, it is known to harden them defined edge. To generate a defined hardness in the region of the edge layer, a gradient structure is set by a carburization treatment, within which carbon is enriched in the surface layer by a heat treatment process. Optionally, a carbonitriding, so an additional nitrogen enrichment in the region of the surface layer done. This boundary layer becomes after the carburizing treatment as a result of at least For example, for rolling bearing rings, the hardness is usually 58 HRC or more, for example, in the case of rolling bearing rings. The non-enriched core remains softer according to the original composition, depending on the starting material used, the hardness is between 20-45 HRC. Thus, for example, the ring produced contains a tough core and a hard, everywhere solid outer layer.

Due to the stresses of such a rolling bearing component, however, large hardening depths of more than 2 mm are required, for example, during case hardening, which require a heat treatment time of several hours, depending on the particular material selected. This is associated with this treatment step a considerable amount of time. A contrast improved, initially described method for producing a bearing component is known from DE 10 2006 023 690 A1. There, a spray layer is formed by spray compaction, which has a carbon gradient. For this purpose, a molten metal is sprayed onto a support in a spraying process, the carbon content of the metal to be sprayed being varied during the spraying process. This is done by using two separate sprayers that spray two different melts. The first melt has a lower carbon content while the second melt has a higher carbon content. The spray cones overlap, so depending on how much melt is released by one or the other sprayer, the carbon content of the sprayed metal can be adjusted accordingly. In such a Sprühkompaktier process, the respective melt is atomized in a gas atomizer in a protective gas stream into spherical droplets. The gas rapidly cools the melt droplets to a temperature between the liquidus and solidus temperatures, often even slightly below the solidus temperature. These cooled droplets are sprayed onto the carrier surface at high speed. Due to the high kinetic energy they compact, it forms a high-density composite material, which has a homogeneous structure and has a high density. Consequently, by using the two different melts and, as a result, the variation of the carbon content, an arbitrary carbon gradient can be set. Consequently, after the boundary layer is sprayed successively in layers, a content which changes depending on the variation of the carbon content is also produced within the finished surface layer. A long-lasting carburizing is not required, nevertheless, the bearing component can be cured, the required hardness values can be easily achieved.

As described bearing components are claimed differently depending on the application. They are subject to Hertz ^'rule pressing, they can be affected by other high forces in different directions, as they can also be claimed corrosive. To design such a bearing component corrosion resistant usually a corresponding starting steel is used to form the metal bearing component. That is, the starting component, which is then typically thermally treated to carburize or embroider it, has a uniform steel composition over its component cross-section. Known steel compositions are, for example, X102CrMo17, X20CM3 or X30CrMoN15-1. The steel as such is corrosion resistant. The corrosion resistance is ultimately only on the surface that is claimed, but not needed in the core of the workpiece. There the alloy content of Cr, which provides the corrosion resistance, is superfluous.

Summary of the invention

The invention is therefore based on the problem of specifying a method for the production of a bearing component which, where corrosion resistance is required, exhibits this property, combined with a rollover strength in this claimed range, but which requires the use of a special, the component as such does not require over the component cross-sectional steel composition with corrosion-resistant property.

To solve this problem, it is provided according to the invention in a method of the aforementioned type that the second melt has a content of Cr of at least 13%.

The inventive method provides for the production of a bearing component by spray compacting, wherein at least the edge layer of the bearing component is produced by spray compacting. Two different melts are used, which differ on the one hand in the carbon content. The first melt has a low carbon content. By contrast, the second melt has a higher carbon content, with which the outer edge layer or the edge layer section is formed. In other words, the carbon gradient can be adjusted in the edge layer area by corresponding spraying or mixing of these two melts, so that the corresponding hardness and also roll-over strength can be achieved on the edge layer side. The second melt, in addition to the higher carbon content, is further characterized by containing a chromium content of at least 13%, preferably more. In other words, a sufficiently high chromium content is produced in the outer edge layer via the second melt, which gives this sprayed-on edge layer section the required corrosion resistance. By using the method according to the invention in conjunction with the use of the second melt with the additional high chromium content, on the one hand the required carbon gradient can be produced in order to be able to roll over the edge layer and to lay it out with sufficient hardness, but on the other hand, the corrosion resistance required on the surface layer side is also imparted.

The cross-section of the bearing component may consequently consist of a steel composition which is not designed as before, the bearing component Overall, to give the corrosion resistance. Rather, a steel can be used that is free from corresponding alloying components that provide corrosion resistance. In this connection, it is conceivable to use as support a metal carrier, for example a tube, which consists of the "simple" steel composition, which therefore has no special properties, in particular with regard to corrosion resistance Alternatively, it is also conceivable to form the bearing component itself via this spray-compacting method, in which case the component core is formed by the first melt which does not contain chromium In this connection, it is conceivable to form such an edge layer both on the inside and on the outside, ie that first the second melt is sprayed at the beginning of the spraying process, after which the first melt is admixed and then to the formation of the Component body completely the first melt is sprayed, after which is changed to form the outer edge layer again on a spraying of the second melt. The method according to the invention thus permits the formation of a corrosion-resistant and roll-over-resistant surface, specifically and only where these properties are required. Another advantage is that it also allows mechanical properties to be generated in the surface layer, which are advantageous.

The content of Cr in the second melt should be at least 13% and at most 25%.

The carbon content of the first layer should be <35%, it is preferably in the range of about 0.2%. The carbon content of the second melt should be> 0.45%, but should not exceed about 0.75%. The second melt should also have a nitrogen content of 0.05 to 5% in a further development of the invention. In other words, the surface layer formed via the second melt is not only carburized but also embroidered, ie it is enriched both with carbon and with nitrogen. This nitrogen feed may, if appropriate, be introduced by melting the melt before spraying under a nitrogen atmosphere, and / or by using nitrogen or a nitrogen-enriched gas as the carrier gas for spraying. However, the melting under nitrogen atmosphere and / or the use of such a carrier gas also applies with respect to the first melt, which consequently can likewise have a certain nitrogen content.

In a development of the invention, it can be provided that the second melt contains one or more hard materials or one or more hard materials in powder form are injected into the spray cone. Such hard materials are wear-resistant and are in the form of the finest particles with a particle size of 1 nm - 200 μιτι either introduced directly melt side, or blown into the spray cone. Carbides, nitrides or borides, if appropriate also mixed, can be added as hard materials.

As already described, a prefabricated component, in particular a tube, which becomes an integral component of the manufactured rolling bearing component can be used as the carrier. D. h., On this tube, the melt compound is sprayed, after which the individual components are cut from the tube. Alternatively, the carrier can be a carrier to be reused, in particular a ceramic tube, onto which the metal is sprayed to form the entire rolling bearing component to be produced. In this case, as described, the component base body is also formed by spray-compacting from the first melt.

In addition to the method, the invention further relates to a bearing component, in particular a roller bearing component, primarily in the form of a ring or a roller, wherein at least one boundary layer by spraying two in the carbon holding different fusions is formed, within which edge layer at least partially varies the carbon content, which bearing component is characterized in that within the boundary layer, a zone is formed with a chromium content of at least 13%. This zone is as described on the outside and / or inside, it forms the immediately loaded layer. Such a bearing component can be produced in particular in the manner described above.

The bearing component may further comprise a metallic prefabricated carrier on which the edge layer is formed. Alternatively, it may be a spray-compacted component made entirely by spraying.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention is shown in the drawing and will be described in more detail below. Show it:

Figure 1 is a schematic diagram of a spray device for explaining the method according to the invention;

Figure 2 is a partial view of a rolling bearing component according to the invention showing the carbon and the chromium gradient; and

FIG. 3 shows a partial view of a second rolling bearing component according to the invention, showing the gradient of carbon and chromium.

Detailed description of the drawing

Figure 1 shows in the form of a schematic diagram of a spray device 1 for carrying out the method according to the invention. This comprises two separately operable spraying devices 2a, 2b, to each of which separate melt reservoirs 3a, 3b are assigned. In the melt reservoir 3a, there is a low-carbon melt Si. The carbon retention of this melt is preferably below 0.35%, preferably in the range of about 0.2%. Optionally, other alloying elements such as Cr (maximum about 1%), Mo (maximum about 2%), Ni and / or Mn (each about 4% maximum) and Si (maximum about 1, 5%) and other steel companion be included in addition to the usual iron.

A melt S ₂ having a high carbon content is accommodated in the melt reservoir 3b. This melt has a carbon content of at least 0.45%, the carbon content should not be more than 0.75%. Furthermore, this melt has a chromium content of at least 13% to a maximum of 25%. Other alloying elements such as Mo (maximum approx. 2%), Ni and / or Mn (maximum approx. 4%) as well as Si (max. Approx. 1, 5%) as well as other steel companions may be included, but not necessarily. The list of the respective alloying elements is by no means exhaustive. It is only decisive that this second melt S _{2 has} a higher carbon content compared to the first melt Si and the said chromium content of at least 13%.

The two sprayers 2a, 2b are supplied in the example shown via a common carrier gas supply 4, but it is also conceivable, of course, that each spraying device 2a, 2b has its own carrier gas supply 4. The carrier gas used in the example shown is nitrogen. Alternatively, it is also conceivable to use a nitrogen-containing carrier gas. The respectively sprayed melt, which is sprayed in the form of minute metal droplets 5a with respect to the melt Si or 5b with respect to the melt S ₂ , can be additionally enriched with nitrogen via this added nitrogen.

The sprayers 2a, 2b spray the melt drips 5a, 5b in the form of a respective spray cone 6a, 6b. As shown in FIG. 1, the spray cones 6a, 6b in the example shown overlap in the vicinity of the carrier 7, which is sprayed, completely. The carrier 7 is, for example, a tube made of a hardenable metal which becomes part of the bearing component to be produced, it forms the component main body. Alternatively, the carrier 7 can also be a reusable carrier, for example in the form of a ceramic tube, which is sprayed on, with the spray-compacted component then being removed from the carrier.

FIG. 2 shows in the form of a schematic diagram a detail of a bearing component 9 produced according to the invention. It is assumed that the carrier 7 is a metal tube which forms the component main body and onto which an edge layer 8 is sprayed by spraying the two melts Si and S. _{2 was} applied. For this purpose, the carrier 7 rotates, see FIG. 1. The spraying devices 2a, 2b are now activated in such a way that a corresponding carbon gradient and chromium gra- dient are formed in the layered layer 8 deposited in layers. On the still unsprayed carrier 7 only melt Si is sprayed on first, ie, that at the beginning of the process, only the spraying device 2a is operated. Hereby, a first boundary layer zone 8a consisting of melt-compacted metal of the melt Si is formed, see FIG. 2. When a sufficient thickness of the boundary layer zone 8a is reached, the discharge quantity of the spray device 2a is reduced, synchronously the spray device 2b is switched on and the melt S _{2 is} sprayed. The reduction of the delivery via the spraying device 2a and the increase in the delivery via the spraying device 2b takes place synchronously and uniformly so that essentially the same amount of melt is always sprayed on. The variation takes place in such a way that the spraying device 2 is switched off completely shortly after the start of the switching process, and consequently the melt Si is no longer sprayed out, but only melt S ₂ via the now fully operating spraying device 2b. Over this, the boundary layer zone 8b is formed, which forms the actual loaded edge zone. In her must be given to the component parameters, ie, it must have the sufficient mechanical strength or be hardened accordingly, so that it is roll-over, as they must have the desired corrosive properties. FIG. 2 shows a diagram which shows the carbon content and the chromium content via the surface layer 8. Evidently, the carbon content according to the curve I increases from the inside to the outside via the boundary layer 8, which results from the fact that the melt Si has the low carbon content, while the melt S _{2 has} the high carbon content. Since the melt Si forms the boundary layer zone 8a, a lower carbon content is present in this area, while the boundary layer zone 8b has a high carbon content, since it is formed by the melt S ₂ .

Correspondingly, it behaves with the chromium content according to the curve II. The melt S ₂ contains no chromium in the example shown, which is why no chromium is present in the boundary layer zone 8b. The design of such an edge layer makes it possible, on the one hand, to harden it, in particular in the region of the edge layer zone 8b, in such a way that the desired hardness values are achieved. In addition, the surface layer 8b is also corrosion-resistant, since it contains the high chromium content. The component base body formed by the support 7 as well as the boundary layer zone 8a need not possess this corrosion-resistant property since they are not subject to corrosive stress.

Figure 3 shows an embodiment in which a reusable carrier 7, so for example a ceramic tube was used, on which the bearing member 9, which is shown as such in Figure 3 in a partial sectional view, sprayed on the sprayers 2a, 2b completely has been. This is, for example, a ring with an inner and an outer, a carbon gradient having surface layer. At the beginning 2b melt S ₂ is sprayed first on the spraying device so that a first boundary layer zone is formed, which consists exclusively of the high carbon content and the high chromium content having melt _S2. After reaching a minimum layer thickness, the spraying power of the spraying device 2b is lowered continuously and the spraying device 2a is closed. switched and continuously increased their spray performance. The reduction and the increase in the respective power is preferably synchronous, so that at any time a total spray power of 100% is given. To form the essential structure, 100% of the melt Si is sprayed, ie, the rolling body component in the core consists only of material of the melt Si, as shown in FIG. In order to form the outer surface layer, the process is then reversed again, ie, the spraying power of the spraying device 2a is continuously reduced again, while the power of the spraying device 2b is continuously increased. It forms an outer edge layer 8, consisting only of melt S ₂ , wherein in the boundary layer 8 in Ü transition region between the melt Si and the melt S ₂ , again as well as in the region of the inner surface layer, the carbon gradient and the Chromium gradient forms. This results in a ring or a tube with a curable hole (since the inner surface is formed solely by the melt S ₂ ) and a less curable core (since only consisting of the melt Si) and a higher curable outer outer layer (which in turn only formed from melt S ₂ ).

On the right is a carbon-chromium diagram. Evidently, the carbon content, represented by the curve I, decreases from a high content on the inside, it forms a gradient. In the region of the component core, the carbon content is low, since this is formed only by the melt Si. He then climbs back to the outer edge. This corresponds to the fact that the two edge layers are formed over the melt S ₂ .

Similarly, the behavior of the chromium content behaves according to curve II. Also, the chromium content is high at the two edges, since only melt S ₂ with the chromium content is present there. It decreases in the transition region to the core, and decreases to 0, assuming that the melt Si contains no chromium. He inevitably rises again to the edge area. Overall, the inventive method allows easy generation of a carbon gradient structure in the region of inner and / or outer surface layers, a special carburizing step is therefore no longer necessary. In addition, according to the invention, a corrosion-resistant property can only be imparted there, where this is necessary because one of the sprayed melts has a high chromium content.

LIST OF REFERENCE NUMBERS

I spraying device

2a spraying device

2b spraying device

3a melt reservoir

3b melt reservoir

4 carrier gas supply

5a melt droplets

5b melt droplets

6a spray cone

6b spray cone

7 carriers

8 edge layer

9 bearing component

5 ₁ melt

5 ₂ melt

I curve

II curve

Claims

claims

Method for producing a bearing component (9) with a carbon gradient given at least in the region of its boundary layer (8), wherein molten metal is sprayed onto a carrier (7) in a spraying process and the carbon content of the metal to be sprayed is varied during the spraying process, using at least two separate spraying devices (2a, 2b) are sprayed with at least two melts (Si, S ₂ ), wherein the first melt (Si) has a lower carbon content and the second melt (S ₂ ) has a higher carbon content, whereby the spray cones ( 6a, 6b) and the discharge quantities of the spray devices (2a, 2b) are varied during the spraying process, characterized in that the second melt (S ₂ ) has a Cr content of at least 13%.

A method according to claim 1, characterized in that the content of Cr is at most 25%.

A method according to claim 1 or 2, characterized in that the carbon content of the first melt (Si) <0.35% and the carbon content of the second melts (S ₂ )> 0.45%.

Method according to one of the preceding claims, characterized in that the second melt (S ₂ ) has a nitrogen content of 0.05 to 5%.

Method according to one of the preceding claims, characterized in that the second melt (S ₂ ) contains one or more hard materials or one or more hard materials in powder form are injected into the spray cone (6b). Method according to one of the preceding claims, characterized in that the melts (Si, S ₂ ) are melted before spraying under a nitrogen atmosphere, and / or that is used as the carrier gas for spraying nitrogen or a nitrogen-enriched gas.

Method according to one of the preceding claims, characterized in that as carrier (7) a prefabricated component, in particular a tube is used, which is an integral part of the manufactured bearing component (9), or that the carrier (7) is a reusable carrier, in particular a Pipe is sprayed onto the metal to be produced to form the entire bearing component (9).

Bearing component (9), in particular rolling bearing component, in particular in the form of a ring or a roll, wherein at least one edge layer (8) by spraying two in the carbon content different melts (Si, S ₂ ) is formed, within which edge layer (8) at least partially the carbon content varies, characterized in that within the boundary layer (8) a zone (8b) is formed with a chromium content of at least 13%, in particular produced by a method according to one of claims 1 to 7.

Bearing component according to claim 8, characterized in that it comprises a metallic prefabricated carrier (7) on which the edge layer (8) is formed, or that it is a spray-compacted component produced entirely by a spraying process.