Bearing component and its manufacturing method

Abstract

A bearing component and a method to form a bearing component. The bearing component comprises a first and a second metallic material wherein the first material presents a first carbon content and the second material presents a second carbon content, wherein the first material and the second material have been joined by a diffusion welding process. The diffusion welding process has resulted in a transition zone with a varying carbon content between the first material and the second material. The varying carbon content in the transition zone is essentially within an interval, wherein the interval end points are defined by the carbon content of the first material and the second material.

Claims

1. A method to form a bearing component, comprising: a first metallic material and a second metallic material, wherein the first metallic material presents a first carbon content and the second metallic material presents a second carbon content, wherein the first metallic material and the second metallic material have been joined by a diffusion welding process, wherein the diffusion welding process has resulted in a transition zone with a varying carbon content between the first metallic material and the second metallic material, and wherein the varying carbon content in the transition zone is essentially within an interval, and wherein the interval end points are defined by the carbon contents of the first metallic material and the second metallic material, the forming method comprising steps of: heating the first metallic material and the second metallic material and pressing them against each other under a specific pressure and for a period of time thereby allowing the materials to diffuse into each other at a joining temperature, wherein the first material having a first carbon activity that increases linearly as the first carbon content increases due to the step of heating, the second material having a second carbon activity that is constant during the step of heating as the second carbon content increases, the first metallic material presents a first carbon activity essentially similar to a second carbon activity of the second metallic material at the joining temperature such that there are no carbon gradients in the first material and no carbon gradients in the second material.

2. The method to form the bearing component according to claim 1, wherein the the carbon content changes at a depth of twenty millimeters from a surface of the bearing component.

3. The method to form the bearing component according to claim 1, wherein carbon has not formed cementites or iron carbides that are larger relative to a surrounding structure in the bearing component.

4. The method to form the bearing component according to claim 1, wherein the forming method is done by a hot isostatic pressing.

5. The method to form the bearing component according to claim 1, wherein the temperature is 1000-1300 degrees C.

6. The method to form the bearing component according to claim 1, wherein the temperature is 1100-1200 degrees C.

7. The method to form the bearing component according to claim 1, wherein the temperature is 1140-1160 degrees C.

8. The method to form the bearing component according to claim 1, wherein the pressure is 80-310 MPa.

9. The method to form the bearing component according to claim 1, wherein at least one of the first metallic material and the second metallic material is in powder form before heating.

10. The method to form the bearing component according to claim 1, wherein the bearing component is subsequently cut into at least two pieces creating at least two bearing components.

11. The method to form the bearing component according to claim 1, wherein the bearing component is one of: an inner ring of a bearing, or an outer ring of a bearing, or a roller of a roller bearing.

12. The method to form the bearing component according to claim 1, wherein the temperature is 1150 degrees C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Exemplifying embodiments will now be described more in detail with reference to accompanying drawings, as well as examples of undesirable features that the invention help to prevent, wherein

(2) FIG. 1a shows a cross section of a bearing ring made out of two materials according to the invention;

(3) FIG. 1b shows a cross section of a roller for a bearing made out of two materials according to the invention;

(4) FIG. 2 shows a graph illustrating two materials having the same carbon activity at a specific temperature. The carbon activity of the first material 2 is plotted while increasing its carbon content according to the invention;

(5) FIG. 3 shows a graph of a desirable sudden carbon content change according to the invention;

(6) FIG. 4 shows a graph of the transition zone 6 of FIG. 3 on a m level according to the invention;

(7) FIG. 5 shows a graph illustrating an undesirable carbon content change; and

(8) FIG. 6 shows a graph illustrating a phase fraction during the undesirable carbon content change from FIG. 5.

(9) The drawings present examples of the invention, and the undesirable features that the invention helps to prevent, in diagrams and graphs. These are exemplifying embodiments, thus they are not drawn to scale. Some details and features may even be exaggerated to better explain the invention. The invention is not limited to the embodiments and drawings described herein.

DETAILED DESCRIPTION OF DRAWINGS

(10) FIG. 1a shows a cross section of a bearing component 1 according to the invention, bearing component 1 being a ring. The bearing ring comprises a first 2 and a second 3 material wherein the diffusion welding process has resulted in a transition zone 6 between the first 2 and second 3 material. The figure shows a bearing ring, where the materials are aligned along the full width of the component, but it could also be so that one material is only applied on a selected portion of the component, such as for instance a raceway or a flange (not shown in figure).

(11) FIG. 1b shows a cross section of a bearing component 1 according to the invention, bearing component 1 being a roller. The roller comprises a first 2 and a second 3 material wherein the diffusion welding process has resulted in a transition zone 6 between the first 2 and second material 3. The figure shows a roller where the materials are aligned along the full width of the component, but it could also be so that one material is only applied on a selected portion of the component, such as for instance the main rolling surface or at the edges of the roller, etc.

(12) FIG. 2 shows a table illustrating two materials 2, 3 having the same carbon activity at a temperature of 1150 degrees Celsius (C). The carbon activity of the first material 2 is plotted while increasing its carbon content until the same carbon activity as the second material 3 is obtained. In this case the first material 2 needs to have a carbon content of 0.30-0.35 wt % to have the same carbon activity as the second material 3 of around 0.09 at the temperature of 1150 degrees C. Carbon activity can be affected both by changing the alloying content in the material, and by changing the temperature of the material. Both of these dimensions can be tampered with to adjust the carbon activity to optimize the bearing component 1 forming method. Hence an alternative way to optimize the carbon activity of the two materials if the carbon content of the materials to be joined is fixed, for instance if both materials are in solid form instead of one of them being in powder form, or if a specific alloy is needed, the temperature can be changed instead. The numbers of temperatures, carbon content and carbon activities given in this example can of course be different depending on the circumstances given with temperatures and materials to join etc.

(13) FIG. 3 shows a graph of a desirable sudden carbon content change according to the invention. Here it can be clearly seen that the carbon content changes suddenly at a depth if 20 mm from the surface of the bearing component, and it is clearly within the interval's 7 end points 40,50 defined by the carbon content 4,5 of the first 2 and second 3 material, in this case roughly 0.3 wt % and 0.8 wt %. The carbon content have not increased at any points, which indicates that the carbon has not formed cementites or other forms of complex metal or iron carbides that can be larger in comparison to the surrounding structure, for instance a martensitic structure, thus generally weaker than the surrounding materials. This is unacceptable in high performance mechanical components, such as high quality bearing components 1.

(14) FIG. 4 shows a graph of the desirable sudden carbon content change of FIG. 3 on a m*10-5 level according to the invention. This shows that even though the carbon content change in the transition zone 6 is essentially linear, meaning that the measured carbon content profile should not vary between a positive and negative derivative when looking at this plotted curve of the carbon content in the transition zone 6 when measured perpendicularly from the surface of the two materials to be joined, there may be measured variations to this. Small variations occur naturally in the material, but it could also be due to the equipment used when measuring and how delicate it is of course. With reservation for this, any un-linear change of carbon content in the transition zone 6 should be less than 50% of the carbon content interval (7 in FIG. 3) defined by the carbon content 4,5 of the of the two materials, in this case roughly 0.3 wt % and 0.8 wt %. Preferably any un-linear change of carbon content is less than 25% of the carbon content interval (7 in FIG. 3) It is also clear from the graph that more than 80% of the total change in carbon content interval (7 in FIG. 3) in the transition zone 6 takes place within a measured distance of 50 m in the radial distance of the bearing component's 1 cross section, even within a distance of 40 m.

(15) FIG. 5 shows a graph illustrating an undesirable peak 8 in carbon content. The carbon has clearly moved from one material to the other. The curve is un-linear and the carbon content clearly exceeds the interval 7 end points 40,50 defined by the carbon contents 4,5 of the materials, in this case roughly 1 wt % and 3.5 wt %. This happened at a depth of 20 mm from the surface of the bearing component.

(16) FIG. 6 shows a graph illustrating a phase fraction during the undesirable carbon content change from FIG. 5. It can be clearly seen that the carbon content increase that went beyond the interval (7 in FIG. 5) in an un-linear way, has resulted in a zone where the austenitic (fcc) microstructure has increased dramatically, simultaneously as larger fraction of weaker brittle microstructure phases such as cementite (cem) networks or more complex metal carbides has formed. Both microstructures went from being around 10% of the total microstructure to around 90% at a depth off 20 mm from the surface of the bearing component. This may significantly reduce the strength of any or both of the two joined materials. The cementite structure does not necessarily have to occur during the joining as such, but the higher level of carbon content could react and form a weak and brittle cementite phases during a subsequent heat treatment. At a depth off 21 mm from the surface of the bearing component we can see the normal face fractions of the materials again consisting of cementite and austenitic cast iron to a large extent.