WO2016184926A1

WO2016184926A1 - Method for the construction of bearings

Info

Publication number: WO2016184926A1
Application number: PCT/EP2016/061164
Authority: WO
Inventors: Valls Anglés ISAAC
Original assignee: Rovalma SA
Current assignee: Rovalma SA
Priority date: 2015-05-18
Filing date: 2016-05-18
Publication date: 2016-11-24
Anticipated expiration: 2017-11-18

Abstract

The present invention relates to a method to manufacture high performance bearings. The method plays special attention on the selection of the materials to construct the load bearing elements and in particular the runways. The resulting bearings can withstand high mechanical loads, high rotation speeds and/or high temperatures. The bearings of the present invention are also often easy to recycle.

Description

METHOD FOR THE CONSTRUCTION OF BEARINGS Field of the invention

The present invention relates to a method to manufacture cost effective high performance bearings having load bearing elements. Through the proper selection of the materials for the bearing components, and in particular for the runways, a bearing capable of sustaining higher loads is achieved. Moreover the bearings of the present invention are not difficult^to recycle. State of the art

There are several applications requiring bearings, and whose functionality is strongly limited by the achievable performance of the bearing. Often the limiting factors are the applicable load, the maximum speed or the temperature at which the bearing can work for^a prolonged time. If the loads in terms of applied mechanical load, temperature or rotation speed are too high the bearing will fail prematurely. Several failure mechanisms can appear, ranging from breakage or pitting to corrosion or wear or even creeping. When it comes to the load bearing elements (runways, they can also break due to excessive mechanical loading and even trough thermal shock) they often have fatigue due^ to the hertzian contact stress and obviously they are very often subjected to wear and even corrosion. In this document the denomination“rotating elements” will be used for the Rolling elements usually balls or cylinders, but could be any other kind of rollers. They are elements which are present in a number greater than 3 and as the name indicates rotate to^have a rolling contact instead of a purely sliding one. The denomination“runways” will be used for the races also named raceways or inner and outer rings which are the elements against whom the rotating elements roll. The term“load bearing elements” will be used when referring to both the“rotating elements” and the“runways”. So in principle one would wish to have a material with very high wear resistance, very^high mechanical resistance and very high fracture toughness to avoid the hertzian contact stress fatigue pitting, the breakage and the wear. If the bearing works in an aggressive environment also good resistance against the particular environment would be desirable. Obviously those properties are of interest in the whole temperature working range of the bearing.

^

The problem is that finding a material with such combination of properties is quite difficult. Especially the combination of high wear resistance and high mechanical resistance with high fracture toughness. The materials used for the load bearing elements of high performance bearings include steels, ceramics and metal matrix composites, mainly. Ceramics can present very high wear resistance and even mechanical strength (at least under compression) and this at elevated temperatures, but they have very low fracture toughness. On top ceramic runways are costly to manufacture^ and difficult to recycle. Steels on the contrary can present much higher fracture toughness, but they have much more limited wear resistance and even mechanical strength at high temperatures. Steels are often much more cost effective to manufacture and easy to recycle. Metal matrix composites can achieve a better compromise of the properties, but they are costly to produce and difficult to recycle. Mainly in high performance bearings, it is desirable to have as small and as light as possible bearings which can withstand high mechanical loads and which can withstand high rotational or translation (in case of linear displacement recirculation bearings) speeds. The problem is that the increase of temperature at the runaway/rotating element interface per unit of time with the increase of rotational speed is not a linear relation but rather an exponential one. And to make matters worse many runaway materials suffer a relevant property decay with temperature, especially in terms of wear resistance, mechanical strength and even resistance to the environment. In that scenario, ceràmics present the added advantage of suffering far less wear resistance and mechanical strength drop with increased temperature. But as mentioned they present very low fracture toughness and also they are quite expensive to manufacture. The problem of manufacturing a cost effective high performance bearing is not a trivial one. And even less if they should be environmentally friendly. For cost effectiveness and recyclability steel runways would be desirable which can also have quite high fracture^toughness, but unfortunately their wear resistance and even mechanical strength are quite strongly temperature dependant. The problem being that high performance bearings develop high temperatures in the runway/rotating element interface. Also some bearings work on an environment where high temperatures are not avoidable. High performance bearings are nowadays mostly constructed with steels, ceramics or metal matrix composites, specially the mechanical load bearing elements, namely the runways and the recirculating elements (balls, cylinders,…). In the case of steels, two main families are employed: the so called Cr steels like SAE 52100 when high temperatures are not a concern and AISI M-50 or the like otherwise. If the strategy tough^core– hard surface is employed case hardening steels are often employed with considerable lower %C content, like is the case in AISI 4320 and AISI 9310. In the case where corrosion resistance is required AISI 440C or similar materials are normally employed. For high end applications those materials are often produced in a very refined way often involving vacuum remelting. There are several patent applications related to diferent alloys for using in bearings as for example US 3,954,517 which describes an alloy for carburized bearing membres containing 0.1 to 0.3 % carbon, 0.2 to 1% manganese, 0.2 to 0.6% silicon, from an effective amount up to 1.2% chromium, 2.5 to 3.5% nickel, 4 to 6 % molybdenum and 0.25 to 0.85% vanadium. Another patent application, DE10336407B4 describes a bearing component, especially for use in a turbocharger sleeve manufactured by power metallurgy with a preferred particle size of the power of 0.5 to 40 ^m and a high cobalt content alloy. WO2014/131907A1 describes a heat treatment which plays a capital role to get the desired mechanical properties for known steels previously described in WO2012095532A1 and WO2010112319A1. These steels are heat treated to obtain a final microstructure consistinting on a pure or mainly or a lower bainite microestructure, which reduces the risk of crack for using in hot work tools steels. Several developments have been made from the design point of view, to increase the load capacity, to reduce friction and others. Usage of remelting practices for the purifying of beaing materials is a common practice. The probably better known technologies are VAR (Vacuum Arc Remelting) and ESR (Electro Slag Remelting). In both inclusion and/or detrimental gases are gradually taken out of the melt. The usage of powder metallurgy for the manufacturing of bearing steels is not known to the inventor. Detailed description of the invention

In an embodiment the present invention relates to a bearing and/or breaking disk, wherein at least a part of the load bearing elements of the bearing and/or at least part of the breaking disk contains an iron-based alloy of the following chemical composition, all percentages being indicated in weight percent:

%Ceq = 0.08– 1.9 % C = 0.08– 1.9 %N = 0 - 1.0 %B = 0– 1.0 %Cr < 3.0 %Ni = 0– 6 %Si = 0 - 1.4 %Mn = 0 - 3 %Al = 0 - 2.5 %Mo = 0 - 10 %W = 0 - 10 %Ti = 0 - 2 %Ta = 0 - 3 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0 - 4 %Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 6, %Ce = 0– 3 %La = 0– 3 the rest consisting of iron and trace elements wherein %Ceq = %C + 0.86 * %N + 1.2 * %B.

characterized in that

%Mo + ½ · %W > 2.0. In an embodiment of the invention the iron-based alloy, is used only in at least one of the runways, but not in the rotating elements. In an embodiment, the invention also involves the method of manufacture of the bearings and/or breaking disk comprising the step of constructing at least part of the load bearing elements of the bearing and/or breaking disk with an iron-based alloy of the following chemical composition, all percentages being indicated in weight percent: %Ceq = 0.08– 1.9 % C = 0.08– 1.9 %N = 0 - 1.0 %B = 0– 1.0 %Cr < 3.0 %Ni = 0– 6 %Si = 0 - 1.4 %Mn = 0 - 3 %Al = 0 - 2.5 %Mo = 0 - 10 %W = 0 - 10 %Ti = 0 - 2 %Ta = 0 - 3 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0 - 4 %Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 6, %Ce = 0– 3 %La = 0– 3

the rest consisting of iron and trace elements wherein %Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0. In another embodiment of the invention the method further comprises the step of applying a case hardening treatment. In another embodiment of the invention the method further comprises the step of applying compressive residual stresses at least locally to some of the active surfaces of the load bearing elements and/or breaking disk. In the context of the present invention the term“load bearing elements” is referred to both the“rotating elements” and the“runways”.^In the context of the present invention the term“rotating elements” is referred to the Rolling elements usually balls or cylinders, but could be any other kind of rollers. They are elements which are present in a number greater than 3 and as the name indicates rotate to have a rolling contact instead of a purely sliding one. In the context of the present invention the term “runways” is referred to the races also named raceways or inner and outer rings which are the elements against whom the rotating elements roll. It is well known that to resist temperature and provide good wear resistance in steels high alloying is desirable, but to have good resistance against herzian contact fatigue the lower the alloying the better, as long as the desired hardness is achieved. It also has to be taken into account that high performance bearings are often expected to have a shorter life when it comes to herzian contact fatigue, but the main challenge is to withstand the other failure mechanisms, like wear and mechanical property drop due to temperature. The inventor has seen that tendentially in most existing high performance bearing designs, the herzian contact fatigue solicitation is quite higher on the rotating elements than it is in the runways and thus a good strategy is to use higher alloying for the runways than for the rotating elements. The inventor has seen that an alternative way to approach the issue is by using a material for the runways which has good mechanical strength and wear resistance even when high rotation speeds and high loads are applied on the bearing. An additional alternative^ consists on lowering the temperature of the runway/rotating element interface for the same performance (namely mechanical load and rotating speed) by means of minimizing the generated heat and also by means of driving away the generated heat faster so that the temperature does not rise so much. Abundant research results are available on how to minimize friction in the rotating element/runway pair by means of controlling the surface^conditions and using different kind of lubricants. The lubricants can also be used to help in driving the heat away from the contact area. With the present invention this knowledge is combined with the selection of materials for the construction of the load bearing elements or at least the runways (it could even be just one of the runways for some special constructions) with recyclable iron based materials that to the eyes of the inventor^present the best compromise of wear resistance, fracture toughness, mechanical strength at high temperatures, thermal conductivity, softening resistance (both mechanical and thermal). Such iron based alloys are characterized by the following chemical composition,all percentages being indicated in weight percent: %Ceq = 0.08– 1.9 % C = 0.08– 1.9 %N = 0 - 1.0 %B = 0– 1.0 %Cr < 3.0 %Ni = 0– 6 %Si = 0 - 1.4 %Mn = 0 - 3 %Al = 0 - 2.5 %Mo = 0 - 10 %W = 0 - 10 %Ti = 0 - 2 %Ta = 0 - 3 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0 - 4 %Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 6, %Ce = 0– 3 %La = 0 - 3

^the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0. In the meaning of the present specification, trace elements refer to any element, otherwise indicated, in a quantity less than 2%. For some applications, trace elements ^ are preferible to be less than 1.4%, more preferable less than 0.9% and sometimes even more preferible to be less than 0.4%. Possible elements considered to be trace elements are H, He, Xe, Be, O, F, Ne, Na, Mg, P, S, Cl, Ar, K, Ca, Sc, Fe, Zn, Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Mt alone and/or in combination. For some applications, some trace elements or even trace elements in general can be quite detrimental for a particular relevant property (like it can be the case sometimes for thermal conductivity and toughness), for such applications it will be^desirable to keep trace elements below a 0.4 %, preferably below a 0.2%, more preferably below 0.14 % or even below 0.06%. In an embodiment of the invention all trace elements as a sum have a content bellow 2.0%, in other embodiment below 1.4%, in other embodiment below 0.8% and even in other embodiment below 0.2%. In an embodiment of the invention each individual trace element has a content bellow 2.0%, in other embodiment below 1.4%, in other embodiment below 0.8% and even in other embodiment below 0.2%. Furthermore, structurally, these iron based alloys are often, in the present invention, required to be characterized by at least one of the following:

- An at least partially martensitic and/or partially bainitic microstructure.

- A volume fraction of more than 2% of non-metallic nature particles (mostly carbides, borides, nitrides or compounds thereof).

- The presence of at least 1% (volume percent) of secondary carbides with a higher stability than cementite. (Higher stability in this context, means that they are thermodynamically more stable than cementite at a temperature of 540 ºC). - A low defect content microstructure characterized by a thermal diffusivity of more than 7.5 mm2/s. In an embodiment of the invention a partially martensític structure refers to a structure containing at least 10% martensite, in another embodiment at least 20% martensite, in another embodiment at least 30% martensite, in another embodiment at least 40% martensite, in another embodiment at least 50% martensite, in another embodiment at least 60% martensite,^ in another embodiment at least 70% martensite,^ in another embodiment at least 80% martensite, in another embodiment at least 90% martensite and even 100% martensitic structure. In an embodiment of the invention a partially bainitic structure refers to a structure containing at least 10% bainite, in another embodiment at least 20% bainite, in another embodiment at least 30% bainite, in another embodiment at least 40% bainite, in another embodiment at least 50% bainite, in another embodiment at least 60% bainite, in another embodiment at least 70% bainite, in another embodiment at least 80% bainite, in another embodiment at least 90% bainite and even 100% bainitic structure. In another embodiment of the present invention a combination of partially bainitic and partially martensític structure includes any possible combination of the preceding described partially bainític structure and partially martensític structure. In an embodiment of the invention a low defect content microstructure refers to a microstructure of the steel that allows obtaining a steel with a thermal diffusivity of more than 7.5 mm2/s using different cooling rates and heat treatments to obtain the desired properties such as a case hardening treatment. Since the load bearing elements of the bearings often suffer from the herzian contact fatigue where the maximum load promoting crack nucleation and propagation is subsuperficial, a strategy of selecting a softer material with a higher fracture toughness and^applying a superficial treatment to better withstand wear is not uncommon. For several applications the method of the present invention will require some sort of case hardening when the steel chosen for the load bearing elements has a low %Ceq. In those cases some sort of case hardening will need to be done when the %Ceq is lower than 0.39%, preferably when it is lower than 0.32%, more preferably when it is lower than 0.22%, or even when it is lower than 0.12%. Under“some sort of^case hardening” it is understood any method that can provide an increase of hardness to at least 0.1mm of the treated surface (case hardening, carburizing,….). For some applications it is better to control the %C. In those cases some sort of case hardening will need to be done when the %C is lower than 0.35%, preferably when it is lower than 0.28%, more preferably when it ^is lower than 0.16%, or even when it is lower than 0.09%. In an embodiment of the invention, the %Ceq is above 0.08%, in other embodiment above 0.2%, in other embodiment above 0.3%, in other embodiment above 0.4% and even above 0.5%. In another embodiment of the invention the %Ceq is normally less than 1.9%, in other embodiment less than 1.6%, in other embodiment less than 1.3%, in other embodiment less than 1.1%, in other embodiment less than 1% and even in other embodiment less than 0.9%. In an embodiment of the invention, the %Ceq is between 0.3 and 1.9%, in another embodiment between 0.35 and 1.9%, in another embodiment between 0.4 and 1.9%, in another embodiment between 0.5 and 1.9%, in another embodiment between 0.3 and 1.6%, in another embodiment between 0.35 and 1.6%, in another embodiment between 0.4 and 1.6%, in another embodiment between 0.5 and 1.6%, in another embodiment between 0.3 and 1.3%, in another embodiment between 0.35 and 1.3%, in another embodiment between 0.4 and 1.3%, in another embodiment between 0.5 and 1.3%, in another embodiment between 0.3 and 1.1%, in another embodiment between 0.35 and 1.1%, in another embodiment between 0.4 and 1.1%, in another embodiment between 0.5 and 1.1%, in another embodiment between 0.3 and 0.9%,^ in another embodiment between 0.35 and 0.9%, in another embodiment between 0.4 and 0.9%, in another embodiment between 0.5 and 0.9%. In an embodiment of the invention, the %C is above 0.08%, in other embodiment above 0.2%, in other embodiment above 0.3%, in other embodiment above 0.4% and even above 0.5%. In another embodiment of the invention the %C is less than 1.9%, in other embodiment less than 1.6%, in other embodiment less than 1.3%, in other embodiment less than 1.1%, in other embodiment less than 1%, in other embodiment less than 0.9% and even in other embodiment less than 0.5%. In an embodiment of the invention, the %C is between 0.3 and 1.9%, in another embodiment between 0.35 and 1.9%, in another embodiment between 0.4 and 1.9%, in another embodiment between 0.5 and 1.9%, in another embodiment between 0.3 and 1.6%, in another embodiment between 0.35 and 1.6%, in another embodiment between 0.4 and 1.6%, in another embodiment between 0.5 and 1.6%, in another embodiment between 0.3 and 1.3%, in another embodiment between 0.35 and 1.3%, in another embodiment between 0.4 and 1.3%, in another embodiment between 0.5 and 1.3%, in another embodiment between 0.3 and 1.1%, in another embodiment between 0.35 and 1.1% in another embodiment between 0.4 and 1.1%, in another embodiment between 0.5 and 1.1%, in another embodiment between 0.3 and 0.9%, in another embodiment between 0.35 and 0.9%, in another embodiment between 0.4 and 0.9%, in another embodiment between 0.5 and 0.9%. In this document the iron based alloys described in the last preceding paragraphs will be often described as steels, whether they fit the general description of steel or they don’t. The inventor has seen that for some applications the wear resistance of the bearing is significantly better when the material used for the runways and/or recirculating elements has been obtained with a very severe cooling. That is in the case of the alloy^ compositions of the present invention, a cooling rate of more than 10 ºC·s^-1, preferably more than 10² C·s^-1, more preferably more than 10⁴ ºC·s^-1, and even more than 10⁶ ºC·s- ¹ is encouraged for such group of applications. This cooling rate does not have to be sustained through all the manufacturing process, but at least somewhere in the range between Tm + 100 ºC and Tm– 400 ºC. Or at least the range between Tm + 50 ºC and Tm–^150 ºC. The inventors have seen that powder metallurgical way, can be very beneficial for the method of the present invention for some applications. Believed to be a way to be eluded due to the extra cost and specially due to the tendency of the technology to reduce the fracture toughness for a given composition, due to higher presence of inclusions specially^oxides and due to shorter mean lengths between carbides or other hard particles. But the inventor has seen that when special care is taken to avoid some large inclusions, it is a very advantageous way for some applications, especially those requiring extreme loads where lives below 10⁷ load cycles are expected, preferably when less than 4*10⁶ cycles are to be withhold, more preferably when less than 10⁶ cycles have to be withhold and even when less than 10⁵ cycles have to be withhold. What is to be understood under cycles to be withhold is the appearance of the first damage signs due to herzian contact fatigue when a NASA 5 ball fatigue test is performed with the nominal loading conditions. In an embodiment of the invention, the nominal life expectancy for the bearings and/or bearing elements constructed using the powder metallurgical way is up to 10⁷ cycles, in other embodiment up to 4*10⁶ , in other embodiment up to 10⁶ cycles, and even up to 10⁵ cycles. The bearings of the present invention and/or the breaking disk of the present invention can be manufactured using any existint technology, as for example powder metallurgical way. Powder metallurgical way includes any possible process for the obtaining of the powders regardless of the energy source used for the melting and or the process used for the generation of the powders, or whether no melting was required at all, since a chemical process was used instead or even a mechanical process. It should be noticed than powders of less than 10 mm in diameter are desirable and for many applications powders of 2000 microns or less, preferably 780 microns or less, more preferably 350 microns or less or even 180 microns or less. For some specific applications where the weight of the bearing^is important, departing from even smaller powders might result interesting, in such applications powders of 90 microns or less, preferably 64 microns or less more preferably 28 microns or less or even below the micrometer are desirable. When it comes to the mechanism employed to consolidate the powder, again different applications might benefit from different systems. The invention works regardless of which of these processes is employed. The consolidation can be made on a near-net shape basis or consolidation of a base geometry (even bars or blocks) that will after some shape modifications be configured into the desirable bearing element. Some examples of systems to consolidate powder on a near net shape basis include: any kind of sintering systems, any kind of additive manufacturing system, etc. Some examples of systems to consolidate powder on^a base geometry basis include: hot isostatic pressing (or substitutions thereof – substitution understood as a different system attaining similar properties), spray forming, etc. Reliability is crucial in high performance bearings, thus any method to reduce segregation, reduce inclusion level, improve micro-cleanliness, will be susceptible to be employable in the present invention if the associated cost allows. Some traditional examples of such systems include VIM (Vacuum Induction Melting), VAR (Vacuum Arc Remelting), ESR (Electro Slag Remelting), some special forging and annealing processing, some proper selection of refractories and ceramic powders, etc. There are many more and often some new systems are developed. In general it has been observed that increasing the alloying has a general tendency to increase the maximum allowable working temperature and the wear resistance of the load bearing elements of a bearing, but it affects negatively the fracture toughness and therefore the resistance to herzian contact fatigue. Good compromises are difficult and application dependant. For some applications with high heat generation, it has been seen that the %Moeq (%Mo + ½ · %W) levels should be rather higher, normally above 1.7%, often above 2.1%, preferably above 3.2% or even 4.5%. But high levels of %Moeq do tend to affect negatively the fracture toughness so for applications requiring high resistance to contact fatigue the levels of %Moeq should be rather low, normally below 4.8%, preferably below 3.7%, more preferably below 2.8% and even below 1.8%. In the context of the present invention % Moeq = %Mo+1/2%W. In an embodiment of the invention % Moeq is above 1.7%, in another embodiment is above 2.0%, in another embodiment is above 2.1%,^in another embodiment is above 3.2%, and even in another embodiment is above 4.5%. In an embodiment of the invention the %Mo content is above 2.0, in other embodiment above 2.5% and even in other embodiment above 3.0%. In another embodiment of the invention the %Mo content is between 1.5% and 8%, in another embodiment the %Mo content is between 1.5% and 5.5%, in another embodiment of the invention the %Mo is between 1.5 and 5.0%, even more in another embodiment of the invention the %Mo is between 1.5 and 4.5%. In another embodiment of the invention the %Mo content is between 2.5% and 8%, in another embodiment the %Mo content is between 2.5% and 5.5%, in another embodiment of the invention the %Mo is between 2.5 and 5.0%, even more in another embodiment of the invention the %Mo is between 2.5 and 4.5%.^ In another embodiment of the invention the %Mo content is between 3.5% and 8%, in another embodiment the %Mo content is between 3.5% and 5.5%, in another embodiment of the invention the %Mo is between 3.5 and 5.0% In another embodiment of the invention W is not absent in the iron based alloy and even more in another embodiment of the invention %W is above 0.1%, in other embodiment above 0.5% in other embodiment above 1.0%, in other embodiment above 1.5%. and even^in other embodiment above 2.0%. For several applications it could be interesting to have a %Mo content higher than %W. In a embodiment of the invention the %Mo content is 1.2 times higher than %W, in other embodiment the %Mo content is 1.5 times higher than %W, in other embodiment the %Mo content is 2.0 times higher than %W, in other embodiment^the %Mo content is 2.5 times higher^than %W, and even the %Mo content is 3 times higher^than %W. Also in applications with high levels of heat generated the inventor has seen that it is recommendable to use lower %Cr levels, normally less than 2.8% preferably less than 1.8%, and even less than 0.25%. A special attention has to be placed in elements that increase stacking fault energy. Very effective in this sense is %Ni and somewhat less %Mn. Thus for heavy sections it is often desirable to have a minimum %Ni content normally 0.5%, preferably 1.5% and even 3%. If %Mn is chosen for this goal higher amounts are required to attain the same effect. About double as much quantity is required^as is the case for %Ni. For applications where the working temperature is to attain temperatures in excess of 400 ºC during service it might be very interesting to have %Co present which tends to increase tempering resistance amongst others. Although for some compositions an amount of 0.8% might suffice, normally it is desirable to have a minimum of 1,0% preferably a 1,5% and for some applications even 2.7% (for some applications it is recommendable to use alternative elements to %Co since it affects fracture toughness negatively). Also for applications where wear resistance is important it is advantageous to use strong carbide formers, then %Zr+%Hf+%Nb+%Ta should be above 0.2%, preferably 0.8% and even 1.2%. Also %V is a good carbide former that tends to form quite fine colonies so for applications requiring high wear resistance at high ^temperatures but with moderate heat generation it can be interesting to have %V, it will generally be used with a content above 0.1%, preferably 0.3% and most preferably even more than 0.55%. For very high wear resistance applications it can be used with a content higher than 1.2% or even 2.2%. Other elements may be present, especially those with little effect on the objective of the present invention. In general it is expected to have less than 2% of other elements (elements not specifically cited), preferably 1%, more preferably 0.45% and even 0.2%. In an embodiment of the invention % Cr is less than 2.8%, in another embodiment is less than 2.0%, in another embodiment is less than 1.4%, in another embodiment is less than 0.8%, and even in another embodiment is less than 0.25%. In an embodiment of the invention the %Mn content is above 1.0%, in other embodiment above 2.0%, in other embodiment above 3.0%, and even in other embodiment above 6%. One traditional strategy in the conventional methods of manufacturing the load bearing elements of high performance bearings, is the usage of a tough material to better withstand contact fatigue, with a hard surface to better withstand wear. The traditional way is to use a lower %C steel (normally %C below 0.4%) to which a case hardening or another superficial treatment is applied. The inventor has seen that treatments involving diffusion will be preferred in the present invention (like carburation, nitriding, TD, CVD,….). The hard layer should not be too thick to avoid fragilizing^the area with the highest herzian contact fatigue loading. So it will normally be preferred to have a thickness of the material where the fracture toughness has been negatively affected by more than a 20% not exceeding 1mm, preferably not exceeding 0.4 mm, more preferably not exceeding 0.2 mm, and even not exceeding 0.1 mm. On the other hand if the layer is too thin it is not effective in helping withstanding wear, so for high wear applications a minimum thickness of 0.022 mm will be recommendable, preferably a thickness exceeding 0.06 mm, more preferably a thickness exceeding 0.22 mm, and even a thickness exceeding 0.42 mm. For some applications residual compressive stresses, either in the rotating elements and/or runways have been seen to be very beneficial on the durability of the bearing, when Herzian fatigue is the main failure mechanism. The way the compressive residual stresses have been obtained is of secondary importance. Cost efficiency might induce to use a particular way of obtaining the stresses for a certain application. The most common ways to induce the compressive stresses are trough the production of microscopic and/or^ macroscopic deformations and trough the transformation of the microstructure of the steel. Typical ways include: heat treatment, surface treatment, rolling, shot pening, diamond burnishing, severe grinding,…. The inventor has seen that this same way of proceeding can be employed for high performance breaking disks. Such disks are employed amongst others for airplanes, high speed trains and high performance automobiles. Whenever a high kinetic energy has to be transformed to heat at least partially trough the breaking system. As breaking disk is understood any element that has a relative movement with respect of another element (breaking pad) which applies a certain pressure against the breaking disk dissipating heat in the event of breaking, which results in a decrease of the relative speed of the breaking disk and elements attached to it with respect of the breaking pad. The breaking disk does not necessary have to have circular geometry. Although it will often be so, the moviment of the breaking disk does not necessary be of revolution nature. In an embodiment of the invention, all the iron based alloys described for the manufacture of the bearings of the invention can also be used in the breaking disk of the present invention described above. Examples EXAMPLE 1:

The bearings for high performance combustion motors and for turbines are often subjected to high temperatures often above 180 ºC. Given the strong drive for weight reduction in this kind of applications, high loads are quite common. Temperatures even ^ above 400 ºC are probable at the rotating element/runway interface.

^

For such applications following the method of the present invention a material with the following composition is chosen for the runways: %Ceq = 0.3– 1.5 %C = 0.3– 1.5 %N = 0– 0.4 %B = 0– 1.0

%Cr < 3.0 %Ni = 0– 3 %Si = 0– 0.8 %Mn = 0– 1.5

%Al = 0 - 1.5 %Mo = 1.5 - 8 %W = 0– 6 %Ti = 0 - 2

%Ta = 0– 1 %Zr = 0 - 3 %Hf = 0– 3 %V = 0– 2.5

%Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 4, %Ce = 0– 1

%La = 0 - 1

the rest consisting of iron and trace elements wherein, %Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0. Trace elements being any element of the following list in a quantity less than 1% (preferably less than 0,4%, needless to say any of the elements can be absent): He, Xe, Be, F, Ne, Na, Mg, Cl, Ar, K, Ca, Sc, Fe, Zn, Ga, Ge, Se, Br, Kr, Rb, Sr, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Te, I, Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Mt alone and/or in combination. The material being remelted trough ESR, VAR or equivalent process. Special attention ^ being played in minimizing the content of certain elements, which should be kept as low as possible for this application: %P < 0.005%; %S < 0.001%; %H < 1 ppm; %O < 10 ppm. In addition, some microstructural characteristics were taken into account:

- A volume fraction of more than 2% of non-metallic nature particles (mostly carbides, ^borides, nitrides or compounds thereof).

- The presence of at least 1% (volume percent) of secondary carbides with a higher stability than cementite. (Higher stability in this context, means that they are thermodynamically more stable than cementite at a temperature of 540 C). - A low defect content microstructure characterized by a thermal diffusivity of more than 7.5 mm²/s.

Moreover, a material with the following composition is chosen for the rotating elements:

%Ceq = 0.3– 1.2 % C = 0.3– 1.2 %N = 0– 0.4 %B = 0– 0.4

%Cr < 3.0 %Ni = 0– 3 %Si = 0– 0.8 %Mn = 0– 1.5

%Al = 0 - 1.5 %Mo = 1.5 - 5 %W = 0– 3 %Ti = 0 - 2

%Ta = 0– 1 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0– 2.5

%Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 4, %Ce = 0– 1 %La = 0– 1

the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0. Trace elements being any element of the following list in a quantity less than 1% (preferably less than 0,4%, needless to say any of the elements can be absent): He, Xe, ^ Be, F, Ne, Na, Mg, Cl, Ar, K, Ca, Sc, Fe, Zn, Ga, Ge, Se, Br, Kr, Rb, Sr, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Te, I, Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Mt alone and/or in combination. The material being remelted trough ESR, VAR or equivalent process. Special attention ^ being played in minimizing the content of certain elements, which should be kept as low as possible for this application: %P < 0.005%; %S < 0.001%; %H < 1 ppm; %O < 10 ppm. In addition, some microstructural characteristics were taken into account:

- An at least partially martensitic and/or partially bainitic microstructure.

- The presence of at least 1% (volume percent) of secondary carbides with a higher stability than cementite. (Higher stability in this context, means that they are thermodynamically more stable than cementite at a temperature of 540 C). EXAMPLE 2:

The bearings for landing gears are subjected to punctual very high loads. On top catastrophic failure is not acceptable, so special care has to be taken to make sure the load bearing elements do not break suddenly. For such applications following the method of the present invention a material with the following composition is chosen: %Ceq = 0.08– 0.4 % C = 0.08– 0.4 %N = 0– 0.1 %B = 0– 0.1

%Cr < 3.0 %Ni = 0– 3 %Si = 0– 0.8 %Mn = 0– 1.5 %Al = 0 - 1.5 %Mo = 1.5 - 8 %W = 0– 6 %Ti = 0 - 2

%Ta = 0– 1 %Zr = 0 - 3 %Hf = 0– 3 %V = 0– 2.5

%Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 4, %Ce = 0– 1

%La = 0– 1

the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0. Trace elements being any element of the following list in a quantity less than 1%^ (preferably less than 0,4%, needless to say any of the elements can be absent): He, Xe, Be, F, Ne, Na, Mg, Cl, Ar, K, Ca, Sc, Fe, Zn, Ga, Ge, Se, Br, Kr, Rb, Sr, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Te, I, Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Mt alone and/or in combination. The material being melted by means of vacuum induction melting (VIM or VCAP) remelted trough ESR, VAR or equivalent process. Special attention being played in minimizing the content of certain elements, which should be kept as low as possible for this application: %P < 0.007%; %S < 0.002%; %H < 1 ppm; %O < 10 ppm. ^In addition, some additional steps were to be applied to the load bearing elements:

- Case hardening with a depth of more than 0.2mm and a superficial hardness of more than 58 HRc.

^

Claims

Claims 1. A bearing having load bearing elements wherein at least a part of the load bearing elements contains an iron-based alloy of the following chemical composition, all percentages being indicated in weight percent:

%Ceq = 0.08– 1.9 % C = 0.08– 1.9 %N = 0 - 1.0 %B = 0– 1.0

%Cr < 3.0 %Ni = 0– 6 %Si = 0 - 1.4 %Mn = 0 - 3

%Al = 0 - 2.5 %Mo = 0 - 10 %W = 0 - 10 %Ti = 0 - 2

%Ta = 0 - 3 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0 - 4

%Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 6, %Ce = 0– 3

%La = 0– 3,

the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0.

^

2. A bearing according to claim 1 wherein the iron-based alloy is characterized by having a partially martensitic and/or partially bainitic microstructure.

3. A bearing according to claim 1 wherein the iron-based alloy is characterized by having a volume fraction higher than 2% of non-metallic particles.

4. A bearing according to claim 1 wherein the iron-based alloy is characterized by having the presence of at least 1% volume of secondary carbides that are thermodynamically more stable than cementite at the temperature of 540 ºC. 5. A bearing according to claim 1 wherein the iron-based alloy is characterized by having a low defect microstructure characterized by a thermal diffusivity higher than 7.

5 m²/s.

6. A bearing according to at least two of claims 2 to 5.

7. A bearing according to any one of claims 1 to 6 wherein:

%Ceq = 0.35– 1.9; % C = 0.35– 1.9; %N = 0 - 1.0; %B = 0– 1.0

8. A bearing according to any one of claims 1 to 7 wherein %Cr < 1.4.

9. A bearing according to any one of claims 1 to 8 wherein %Mo > 2.5.

10. A bearing according to any one of claims 1 to 9 wherein W is not absent.

11. A method for the manufacturing of a high performance bearing comprising the step of constructing at least a part of the load bearing elements of the bearing with an iron- based alloy of the following chemical composition, all percentages being indicated^ in weight percent:

%Ceq = 0.08– 1.9 % C = 0.08– 1.9 %N = 0 - 1.0 %B = 0– 1.0

%Cr < 3.0 %Ni = 0– 6 %Si = 0 - 1.4 %Mn = 0 - 3

%Al = 0 - 2.5 %Mo = 0 - 10 %W = 0 - 10 %Ti = 0 - 2

%Ta = 0 - 3 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0 - 4

%Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 6, %Ce = 0– 3

%La = 0– 3,

the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0.

12. A method for the manufacturing of a bearing comprising the step of constructing at least a part of the load bearing elements of the bearing with an iron-based alloy of the following chemical composition, all percentages being indicated^in weight percent: %Ceq = 0.08– 1.9 % C = 0.08– 1.9 %N = 0 - 1.0 %B = 0– 1.0

%Cr < 3.0 %Ni = 0– 6 %Si = 0 - 1.4 %Mn = 0 - 3

%Al = 0 - 2.5 %Mo = 0 - 10 %W = 0 - 10 %Ti = 0 - 2

%Ta = 0 - 3 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0 - 4

%Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 6, %Ce = 0– 3

%La = 0– 3,

the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that %Mo + ½ · %W > 2.0.

13. A method according to any one of claims 11 to 12 where:

%Ceq = 0.28– 1.9 % C = 0.28– 1.9 %N = 0 - 1.0 %B = 0– 1.0

^

14. A method according to any one of claims 11 to 12 where the alloy has the following composition:

%Ceq = 0.08– 0.35 % C = 0.08– 0.35 %N = 0 - 0.2 %B = 0– 0.2

and the method further comprises the step of applying a case hardening treatment.

15. A method according to any one of claims 11 to 14 where the iron-based alloy is characterized by having at least one of the following features:

- an at least partially martensitic and/or partially bainitic microstructure;

- a volume fraction higher than 2% of non-metallic particles.

- the presence of at least 1% volume of secondary carbides that are thermodynamically more stable than cementite at the temperature of 540 ºC. - a low defect microstructure characterized by a thermal diffusivity higher than

16. A method according to any one of claims 11 to 14 where the iron-based alloy is characterized by at least two of the following features:

- an at least partially martensitic and/or partially bainitic microstructure;

- a volume fraction higher than 2% of non-metallic particles.

- the presence of at least 1% volume of secondary carbides that are thermodynamically more stable than cementite at the temperature of 540 ºC. - a low defect microstructure characterized by a thermal diffusivity of higher than 7.5 mm2/s.

17. A method according to any one of claims 11 to 16 where the method further comprises the^step of applying compressive residual stresses at least locally to some of the active surfaces of the load bearing elements.

18. A method according to any one of claims 11 to 17 where the iron-based alloy of the present invention is used only in at least one of the runways, but not in the rotating elements.

^

19. A method for the manufacturing of a high performance breaking disk comprising the step of constructing at least a part of the breaking disk with an iron-based alloy of the following chemical composition, all percentages being indicated in weight percent: %Ceq = 0.08– 1.9 % C = 0.08– 1.9 %N = 0 - 1.0 %B = 0– 1.0 %Cr < 3.0 %Ni = 0– 6 %Si = 0 - 1.4 %Mn = 0 - 3 %Al = 0 - 2.5 %Mo = 0 - 10 %W = 0 - 10 %Ti = 0 - 2 %Ta = 0 - 3 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0 - 4 %Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 6, %Ce = 0– 3 %La = 0 - 3

the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0.

20. A method for the manufacturing of a breaking disk comprising the step of constructing at least a part of the breaking disk with an iron-based alloy of the following chemical composition, all percentages being indicated in weight percent:

%Ceq = 0.08– 1.9 % C = 0.08– 1.9 %N = 0 - 1.0 %B = 0– 1.0 %Cr < 3.0 %Ni = 0– 6 %Si = 0 - 1.4 %Mn = 0 - 3 %Al = 0 - 2.5 %Mo = 0 - 10 %W = 0 - 10 %Ti = 0 - 2 %Ta = 0 - 3 %Zr = 0 - 3 %Hf = 0 - 3 %V = 0 - 4 %Nb = 0 - 1.5 %Cu = 0 - 2 %Co = 0– 6, %Ce = 0– 3 %La = 0 - 3

the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0.

21. A method according to any one of claims 11 to 20 where the alloy has the following composition: Cr < 1.4

22. A method to any one of claims 11 to 21 where the alloy has the following composition: %Cr < 0.8

23. A method according to any one of claims 11 to 22 where the alloy has the following composition:%Cr < 0.25

24. A method according to any one of claims 11 to 23 where at least some of the elements are constructed starting from powder, including the case where the element is constructed^ through machining or forming starting from an already consolidated powder, like for example a spray formed or HIP with or without thermos-conformation billet. Moreover the nominal life expectancy for the elements constructed using the powder metallurgical way is 10⁷ or less cycles.

25. A method according according to any one of claims 11 to 24 where all trace elements as a sum have a content below 0.8 %.

26. A method according according to any one of claims 11 to 24 wherein each trace element individually has a content below 0.8 %.

27. A method according to any one of claims 11 to 24 where all trace elements as a sum have a content below 0.2 %.

28. A method according to any one of claims 11 to 24 wherein each trace element individually has a content below 0.2 %.

^

29. A method according to any one of claims 11 to 28 where %Mo > 2.5

30. A breaking disk wherein at least a part of the breaking disk contains an iron-based alloy of the following chemical composition, all percentages being indicated in weight percent:

the rest consisting of iron and trace elements wherein,

%Ceq = %C + 0.86 * %N + 1.2 * %B,

characterized in that

%Mo + ½ · %W > 2.0.

31. A breaking disk according to claim 30 wherein the iron-based alloy is characterized by having at least one of the following features:

- a partially martensitic and/or partially bainitic microstructure;

- a volume fraction higher than 2% of non-metallic particles.

32. A breaking disk according to claim 30 where the iron-based alloy is characterized by at least two of the following features:

- a partially martensitic and/or partially bainitic microstructure;

- a volume fraction higher than 2% of non-metallic particles.

- the presence of at least 1% volume of secondary carbides that are thermodynamically more stable than cementite at the temperature of 540 ºC. - a low defect microstructure characterized by a thermal diffusivity higher than 7.5 mm²/s.

33. A breaking disk according to any one of claims 30 to 32 wherein:

%Ceq = 0.35– 1.9; % C = 0.35– 1.9; %N = 0 - 1.0; %B = 0– 1.0 34. A breaking disk according to any one of claims 30 to 33 wherein %Cr < 1.4. 35. A breaking disk according to any one of claims 30 to 34 wherein %Mo > 2.5. 36. A breaking disk according to any one of claims 30 to 35 wherein W is not absent.