WO2013087379A1

WO2013087379A1 - Roller bearing component

Info

Publication number: WO2013087379A1
Application number: PCT/EP2012/073179
Authority: WO
Inventors: Jürgen Gegner; Tristan Kaiser
Original assignee: Aktiebolaget Skf
Priority date: 2011-12-12
Filing date: 2012-11-21
Publication date: 2013-06-20
Also published as: EP2791379A1; DE102011088234A1

Abstract

An embodiment of a component (100) comprises at least one section (110) which comprises a steel where the section (110) extends from a surface (120) of the component (100) into an interior of the component (100), and an outer zone (130) in the section (110) which directly adjoins the surface (120) of the component (100) and in which a proportion of a chemical element changes in a measurable way in the steel. The steel in the outer zone (130) has, at least in sections, a microstructure having grains having an index of 5 or above in accordance with ASTM‑E 112 (2010 edition), where the steel has a proportion of chromium which is not more than 7% by weight and the steel additionally comprises tantalum in a proportion by weight of more than 0.4% by weight, niobium in a proportion by weight of more than 0.1% by weight, titanium in a proportion by weight of more than 0.12% by weight or vanadium in a proportion by weight of more than 0.05% by weight. Such a component (100) can thus have a smaller grain size after a heat treatment in the course of its production.

Description

WÄLZ BEARING COMPONENTS Embodiments relate to a component, for example a rolling bearing component, for example a rolling bearing component of a large machine, such as a wind turbine or an industrial gearbox.

In many machines and systems, high mechanical loads occur in different shapes and forms. Often, but by no means exclusively, components are here concerned that perform relative movements to each other, so for example, translational or rotational movements. In addition to continuous loads, short-term and / or local loads may occur, which can lead to material shortage or a static overstressing of the relevant components.

It is precisely for such components (eg machine parts) that steel is used on account of its far-reaching manufacturability, its strength, its deformability, its weldability and many other properties. Among the important technological features is that steel can be completely or partially hardened or surface treated by other processes. For example, if only a surface hardening or surface hardening is performed, so the corresponding treated edge layer or surface harder and therefore mechanically and tribo logically resistant, while deeper areas of the component have a lower hardness and therefore a greater toughness, whereby the component as a whole cyclically and statically higher becomes more resilient. Dynamic loads are often introduced into the surface of the components in this, so have a strong impact on the typically cured areas. These stresses can cause dislocation movements in the material, which can ultimately lead to plastic deformation in the interior of the component. The associated stress of the range of grain boundaries in the structure of steel can lead to an inter-crystalline fracture before reaching the strength in volume under susceptible material condition.

To counteract grain boundary failure, preference is given to using steels which have a large number of grain boundaries, ie have small crystals in the microstructure, since in this way the mechanical stresses and segregation with weakening elements (eg phosphorus, sulfur) or even compounds (For example, carbides) are distributed over a larger number and thus area of grain boundaries and decreases the stress of the individual grain boundaries.

The hardening of the steel is typically thermal, with the steel of the component being at least partially heated accordingly. Examples of methods used here include martensitic or bainitic through hardening and induction hardening.

Among the thermochemical methods by which the surface layer of the steel can be chemically modified include methods that can be used to improve the structural stability of the steel. For this purpose, for example, in the context of carbonitriding or carbon-nitrogen case-hardening of a steel carbon and nitrogen can be introduced into this, wherein the steel is also exposed to elevated temperatures in the context of this method. Here, the z. As unalloyed or low-alloyed steel, z. As a case steel, typically a carbon content by 0.05 to 0.3 wt .-%. The treatment of a through hardening steel in a carbon and nitrogen donating atmosphere, typically having a carbon content of about 1 weight percent (wt% or%), such as 100 Cr6, its derivatives and similar steels, is often referred to as carbonitriding , Carbonitriding thus includes both the nitrogen enrichment of the edge layer of through hardening steels and a variant of case hardening, the so-called carbon-nitrogen case hardening, based on Conventional case-hardenable steels typically employing steels having a carbon content of between about 0.05 and 0.3 percent by weight.

These processes are thermal processes, so that there is a risk that above the austenitic temperature of the steel to an undesirable heating and thus overheating of the structure can occur. As a result, an increased grain growth, so a coarse grain formation occur. This can lead to a reduced strength in the subsequent insert structure due to a weakening of the grain boundaries (eg due to segregation, ie attachment of harmful elements), with a tendency to intergranular fracture.

So far, conventional steels, for example conventional case-hardened steels or through-hardening bearing steels, have been used here. During process control, an attempt is then made to carry out the curing process in such a way that excessive grain growth is avoided.

Proceeding from this, therefore, the object of the present invention is to provide a component having a smaller grain size after a heat treatment in the context of its production.

This object is achieved by a component according to claim 1.

A component according to an exemplary embodiment comprises at least one section that comprises a steel, wherein the section extends from a surface of the component to an interior of the component, and a boundary zone in the section that directly adjoins the surface of the component, and in which a proportion of a chemical element in the steel changes measurably. The steel in the edge zone hereby has, at least in sections, a structure with grains having a ratio of 5 or more in accordance with ASTM-E 112 (2010 edition) (ASTM = American Society for Testing Materials), the steel having a chromium content (Cr). which is at most 7% by weight. The steel further comprises tantalum (Ta) at more than 0.4 weight percent by weight, niobium (Nb) at more than 0.1 weight percent, titanium (Ti) at more than 0.12 weight percent, or vanadium (V) at a weight fraction of more than 0.05 percent by weight. Embodiments of a component is based on the finding that a smaller particle size after a heat treatment in the production of the component can be achieved by adding to the steel of the component an alloying element which inhibits grain growth but at least inhibits it. Tantalum, niobium, titanium and vanadium have been found to be effective in this regard, but due to their differential suitability for inhibiting grain growth, they have different proportions by weight in the steel. The chromium content of the steel should be at most 7 percent by weight in order to reduce competition with the abovementioned alloying elements with respect to the carbon also contained in the steel. Thus, there is a presumption that the formation of corresponding precipitates, such as carbides, nitrides or carbonitrides, based on the corresponding alloying elements and corresponding mixed crystals, at least partially causes the inhibiting effect on the grain growth by stabilizing the grain boundaries.

Thus, by means of a case hardening process or a carburizing process, it is possible to provide components in which the steel in the edge zone has, at least in sections, a microstructure with grains having a coefficient of 5 or more according to ASTM. The heat treatment causes a measurable change of a chemical element of the steel in the edge zone. The material of the component according to an embodiment is thus less susceptible to grain growth and coarse grain formation during carburization or carbonitriding and optionally subsequent hardening by alloying or microalloying with said alloying elements. This may be, for example, a change in the carbon content or a change in the nitrogen content. For example, in the context of the case hardening process or as part of the carbomtring process, carbon and / or nitrogen can be released or exchanged with the component on the basis of a medium acting on the component from the surface. In the case of a component according to one exemplary embodiment, the proportion of the chemical element in the edge zone can thus change by at least 0.1 percent by weight. In other embodiments of a component, however, even smaller changes in the proportion of the chemical element to the steel may be measurable. Thus, for nitrogen, changes in the content are typically from about 10 ppm (Parts Per Million, parts of a million), for Carbon in the range from about 0.01 percent by weight detectable and measurable. In untreated steel, for example, the nitrogen content is in the range of a few 10 to a few 100 ppm. In the case of a component according to an embodiment, it may be possible for the steel in the edge zone to have substantially completely a structure with grains having a characteristic value of 5 or more according to ASTM. The edge zone here comprises the zone in which, starting from the surface of the component, a change in the chemical composition of the steel results from the manufacturing process of the component. This typically extends at least 0.1 millimeters into the component, preferably at least 1 mm or up to more than 10 mm. For example, in the context of case hardening in the edge zone, the carbon content of the steel changes measurably and for the material properties of the steel to a considerable extent. In the case of carbonitriding, the nitrogen content also changes in the edge zone, it being possible, depending on the initial composition of the steel, to form locally an increase, a maximum or even an at least partial reduction of the carbon content. Thus, in principle, for example in the case of very thin components, the edge zone and the section of the component which comprises or consists of the steel can be identical. If they are not identical, in a part of the non-peripheral part of the component, the steel will be essentially in its original chemical composition prior to case hardening or carbonitriding.

A component according to an embodiment thus builds on a (micro) alloyed, grain-stable steel for a heat treatment process, which may be, for example, a case hardening or carbonitriding. A component according to one embodiment therefore often represents a case-hardened or carbonitrided component or a component produced by case-hardening or carbonitriding.

In a component according to an embodiment, the proportion by weight of tantalum, of niobium, of titanium or of vanadium may amount to at most 2 percent by weight. Thus, while the proportion of one of the alloying elements tantalum, niobium, titanium or vanadium on the steel tends to increase the inhibiting effect with respect to grain growth, a proportion exceeding about 2 percent by weight may lead to less favorable competing reactions. Because of the engagement For example, the alloying elements tantalum, niobium, titanium or vanadium can be used to increase the accessible process temperatures to more than 1000.degree. C., for example up to 1150.degree. C., which can often only be achieved with conventional steels at the expense of increased coarse grain formation.

In embodiments of a component on the other hand, in the corresponding steel with a niobium content (Nb), the proportion of tantalum (Ta) at least 1 times, at least 5 times, at least 10 times, at least 20 times, at least 50th times or at least 100 times the amount of niobium (Nb). In these proportions of the niobium (Nb) and tantalum (Ta) masses, it is found that niobium very frequently occurs as a contamination or additional element of tantalum. In other words, in a component according to one embodiment, the steel may optionally have tantalum with a (weight) proportion greater than 1, 5, 10, 20, 50 or more 100 times (by weight) of niobium.

In a component according to one embodiment, the chromium content may amount to at most 5 percent by weight. This may make it possible to reduce competition reactions of the alloying elements tantalum, niobium, titanium or vanadium with the carbon of the steel, optionally with nitrogen or other chemical elements or compounds which may compete with these alloying elements and their stabilizing effect on grain size. However, chromium can help or improve the hardenability of the steel within the limits mentioned.

In a component according to an embodiment, the steel may further comprise an alloying element with a weight fraction between 0.1 and 5 weight percent, wherein the alloying element is molybdenum (Mo), nickel (Ni), silicon (Si), manganese ( Mn) or chromium (Cr). The use of these elements as (additional) alloying element can lead to a further improvement in the grain stability, static strength and / or hardenability in the heat treatment of the steel, so that a component according to an embodiment, starting from the surface in the edge zone to a case hardening depth of at least 5 mm may have a hardness of at least 52.5 HRC, without causing an increased coarse grain formation occurs. It may thus be improved if necessary, a fatigue resistance and / or a static strength of the material. If necessary, this can be done by increasing the share these (additional) alloying elements can be further increased. It may therefore be useful for a component according to one embodiment to increase the weight fraction of the (additional) alloying element to values between 1 and 5 percent by weight. Additionally or alternatively, the manganese content of the deoxidizing and / or the molybdenum content can improve the tempering resistance.

The case hardening depth should be understood as the vertical distance from the surface during case hardening until reaching an ultimate hardness of 550 HV1 or 52.5 HRC. For the purposes of the present description, nominal weight percentages are used with respect to the individual components. In the case of steels, deviations from the nominal proportions may occur due to the production-related processes of steel production. The proportion of an alloying element or another component (eg carbon) of a steel of a concrete exemplary embodiment may therefore be below or exceeding the nominal values within the scope of the usual manufacturing and manufacturing tolerances.

In the case of a component according to an exemplary embodiment, the steel may thus have hardness or hardenability with at least one hardness value at least one distance value from the surface, at least in sections in the edge zone, optionally also substantially completely in the edge zone and / or in the section of the component. wherein the at least one hardness value is in an interval given by an HRCmax value and an HRCmin value, wherein the HRCmax and HRCmin values exceed the HRCmax and HRCmin values given in Table 2 by up to 1, 2 or 3 HRC may be exceeded or exceeded.

In a component according to an embodiment, the steel in the edge zone may have a carburizing depth of at least 5 mm and / or a carbonitriding depth of at least 0.1 mm, the carburizing depth being a distance from the surface of the component at which a carbon content of the steel is below a predetermined amount of carbon, for example 0.35% by weight, and wherein the carbonitriding depth is a distance from the surface of the component at which a nitrogen content of the steel falls below a predetermined nitrogen content, for example 0.05% by weight. In principle, the values of the predetermined carbon content and the predetermined nitrogen content can be set as desired. In the area of carbon is the above Down to 0.35 weight percent widely used. Other values are used for the predetermined nitrogen content. For example, the predetermined proportion of nitrogen may be 0.5% by weight, 0.35% by weight, 0.25% by weight, 0.2% by weight, 0.15% by weight or 0.1% by weight. In other embodiments, the carbonitriding depth may also be at least 0.4 mm, at least 0.5 mm, or at least 0.75 mm.

In other embodiments, the carburizing depth and / or the carbonitriding depth may also be values of less than 5 mm or less than 0.1 mm. However, these depths can also take on larger values.

Thus, in one embodiment, the component in the edge zone at least in sections, but optionally also continuously, have a carbon content of at least 0.35 weight percent and a hardness value of at least 52.5 HRC.

In a component according to one embodiment, the steel may have non-metallic inclusions in accordance with ASTM E45 (2011 Edition) and ISO 4967 (1998-10 release date) which are at most equal to the values defined in Table 3. Alternatively or additionally, the steel may also have non-metallic inclusions in accordance with DIN 50602: 1985, which correspond at most to the values defined in Table 4.

A component according to an exemplary embodiment may be a rolling bearing component, for example a rolling bearing component of a large-scale machine, for example a wind power plant, a tidal power plant, a generator, a construction machine, a transporter, a train, a rolling mill, a marine propulsion, a paper machine or an aircraft.

The use of such a steel in a component according to an exemplary embodiment can thus optionally enable improved hardenability and / or improved grain stability and / or static strength, so that curing with a greater case hardening depth of, for example, 100.degree. B. at least 5 mm can be achieved without this uses a reinforced coarse grain formation. Of course, in other embodiments, lower case hardening depths can be achieved. Embodiments of the present invention will be explained below with reference to the accompanying drawings.

Fig. 1 shows a cross section through a component according to an embodiment;

Fig. 2 shows a cross section through a tapered roller bearing with components according to embodiments;

FIG. 3 illustrates a profile of a hardness and a carbon content along a line perpendicular to a surface of a component according to an embodiment produced by a case hardening process; FIG. and

4 illustrates a graph of a hardness, a carbon content, and a nitrogen content along a line perpendicular to a surface of a component according to an embodiment prepared by a carbonitriding process based on a thermosetting steel.

In the context of the present description, summary reference characters for objects, structures, and other components are used when describing the component in question itself or several corresponding components within one embodiment or within several embodiments. Passages of the description which refer to one component are therefore also transferable to other components in other embodiments, unless this is explicitly excluded or if this results from the context. If individual components are designated, individual reference symbols based on the corresponding summarizing reference symbols are used. In the following description of embodiments, therefore, the same reference numerals designate the same or similar components. Components which occur multiple times in one exemplary embodiment or in different exemplary embodiments may in this case be embodied identically and / or differently with respect to some of their technical parameters or implemented. It is thus possible, for example, that several components within an embodiment may be identical with respect to one parameter, but different with respect to another parameter.

1 shows a cross-sectional view through a component 100 according to an exemplary embodiment. The component 100 can be, for example, a rolling bearing component, that is to say, for example, a roller bearing ring (inter alia outer or inner ring) or else a rolling body (inter alia a cylindrical roller, ball and tapered roller). The component 100 in this case has a portion 110 which extends from a surface 120 of the component into an interior of the component 100. The section 110 in this case has a steel, which is described in more detail below.

By a manufacturing method, which can include, for example, case hardening or carbonitriding, the section 110 further comprises a in Fig. 1 only schematically drawn edge zone 130, extending from the surface 120 of the component 100, starting in the interior of the component 100 extends into it. In the peripheral zone, a proportion of a chemical element of the steel measurably changes from its initial value, for example by at least 0.1 percent by weight.

In the component shown in FIG. 1, the edge zone in the sectional plane shown there extends along three sides into the interior of the component 100. Thus, the component 100 also has a further section 140 into which the edge zone 130 does not extend. The exact course of the edge zone 130 may of course deviate from the course drawn in FIG. 1 in this case. If, for example, the further section 140 is likewise made of steel, ie if the component 100 is embodied in one piece or in one piece, the further section 140 may not have been exposed during case hardening or carbonitriding to the mostly gaseous medium used in this case. Especially in such a case, deviations in the contour of the edge zone 130 from the version shown in Fig. 1 can occur.

Likewise, the component 100 may be made of a multi-cell or multi-piece. In such a case, the further portion 140 may optionally already be connected to the portion 110 during case hardening or carbonitriding. The sections For example, 110 and 140 may differ from one another in terms of their composition in such a way that the material of the further section 140 can not be changed by one of the aforementioned processes, but both sections 110, 140 are connected to one another in a material-locking manner, that is to say at the molecular level. If necessary, however, the two sections can also be used with the help of other z. B. positive and / or non-positive connection techniques (eg., Screwing, jamming, shrinking, etc.) to be interconnected.

In many applications, strong mechanical stresses occur, which lead to material fatigue of the relevant component. Frequently, these loads are short-term, intermittent or periodic dynamic loads that often act only on small areas of the component, so for example via a point or line contact. To design the corresponding components more resistant to fatigue, therefore, hardened steels are often used. In particular, steels are preferred here which have small particle sizes in order to distribute occurring mechanical stresses to a large number of grains and weakening segregation or precipitation deposits to reduce the coverage (areal density) to a large number and thus the area of grain boundaries.

In case hardening as well as during carbonitriding, the component 100 to be machined is exposed at elevated temperature to a medium which releases carbon (C) and optionally nitrogen (N) to the component 100 or the steel enclosed in it. In principle, both solid, liquid and gaseous media can be used as the medium, with gaseous media generally being used in today's technology. For example, carbon monoxide gas (CO gas) is often used in case hardening, with the carbonitriding medium often comprising a hydrocarbon mixture (CH _x gas) and ammonia (NH ₃ ). The temperatures used here are in the range between about 750 ° C and 1100 ° C and 1200 ° C.

Both the delivery and replacement of the carbon with the component and the delivery of the nitrogen to the component 100 during its manufacture is a thermally activated process. This means that the process is increasing Temperature and more effective with a longer process duration. The same applies to the transformation of the microstructure of the steel associated with the hardening, as well as the migration or diffusion of the alloying elements and the other elements mentioned (in particular carbon and nitrogen).

However, this can easily lead to overheating of the structure, which in turn can lead to the coarse grain formation and thus often associated material-weakening grain boundary segregations and thus to a reduction in the fatigue resistance and static strength of the material and component.

By using a steel having a chromium content of not more than 7% by weight and further containing one of the alloying elements tantalum (Ta) in a proportion by weight of more than 0.4% by weight, niobium (Nb) by weight more than 0, 1 percent by weight, titanium (Ti) having a weight fraction of more than 0.12 percent by weight or vanadium (V) having a percent by weight of more than 0.05 percent by weight, the process temperatures compared to conventional steels can be significantly increased. By using such a steel, it is possible to raise the process temperatures in the range of more than 1000 ° C or 1100 ° C in order to achieve sufficient curing in a shorter time and still not let the grains of the structure grow too much , Thus, it may be possible, at least in sections, to achieve in the edge zone 130 a structure with grains having a characteristic value of 5 or more according to ASTM, as will be described in more detail below.

For example, starting from a steel having a carbon content of between 0.15 and 0.2 weight percent and a chromium content of less than 7 weight percent, and optionally less than 5 weight percent, tantalum at 0.5 weight percent may be added to the steel as another alloying element The temperatures used in case hardening or carbonitriding may be shifted to significantly higher values. With regard to the chromium content (Cr), it is presently assumed that this may lead to undesired competition reactions with the other alloying elements and formation of precipitates, in particular in the form of carbides, nitrides or carbonitrides, and / or mixed crystals for stabilizing the grain boundaries by reducing the grain boundaries Grain boundary mobility complicates. This applies both to case-hardening or carbonitriding, as well as an optional supplementary curing step. Case hardening and carbonitriding process times typically vary between a few tens of seconds to several days, for example between 1 to 4 hours or even up to 70 hours and above. The exact process parameters can be determined numerically, for example. For example, the software "SimCarb" can be used for this, as described in the publications HTM J. Heat Treatm. Mat. 64 (2009), 53, HTM J. Heat Treatm. Mat. 64 (2009), 115 and HTM J. Heat Treatm., Mat. 64 (2009), 186. By using this steel as a material, it may, for example, also be possible to achieve carburizing or case-hardening depths of more than 5 mm, thereby rendering the structure more grain-stable during carburizing and hardening Depending on the specific composition of a steel according to an exemplary embodiment of the present invention, case hardening depths of 10 mm and optionally above this can be achieved.

However, embodiments are not limited to such components having a case hardening depth of at least 5 mm. It is also possible, according to embodiments of the present invention, to realize components having lower or greater case hardening depths, for example of at least 100 μm, at least 1 mm or at least one of the further possible case hardening depths mentioned here within the scope of the present description. Likewise, however, through-hardened components 100 can also be produced according to an exemplary embodiment.

Of course, by adjusting parameters such as the exact process conditions or the composition of the steel, other parameters can be positively influenced. Thus, for example, by adjusting the pressure of the gaseous medium, the temperatures used and / or an initial carbon content, an improvement in the inductive solderability of the steel can be achieved.

Thus, embodiments of the present invention make it possible to increase the temperatures used in a heat treatment and thus to reduce the aforementioned risk of coarse grain formation. By using steels in accordance with the Thus, for example, in accordance with examples of the present invention, the temperature desired for conventional carbon case hardening or carbon-nitrogen case hardening may be increased to within the range above 1000 ° C. Depending on the amount of added alloying material is called an alloy or a micro-alloy. In the field of so-called microalloying, the proportion of alloy material (often an alloying metal) is in a range that is typically unspecified. Regardless of this, however, in the context of the present description, the term alloying is understood to mean both that of microalloying and of alloying.

In a component 100, the steel may further comprise, as an additional alloying element, a proportion by weight of between 0.1 and 5 percent by weight of molybdenum (Mo), nickel (Ni), silicon (Si), manganese (Mn) or chromium (Cr). As a result, it seems possible to expose the component 100 to higher temperatures. Thus, for example, by adding about 1% by weight of molybdenum to a sample and a sample without such a molybdenum additive, a finer microstructure could be achieved with otherwise identical process parameters. In embodiments of the present invention, the weight fraction for this alloying element is often in the range between 0.8% and 1.5% by weight. For example, steel according to an embodiment of the present invention may be produced based on 50CrMo4 or 43CrMo4 as a base alloy. Further examples are steels according to embodiments of the present invention based on 50CrV4. As some of these base alloys also show, in the case of embodiments, a plurality of the aforementioned alloying elements can also be used.

In the case of steels with niobium content (Nb), the proportion by weight of tantalum (Ta) is frequently at least 1 times, at least 5 times, at least 10 times, at least 20 times, at least 50 times, or at least 100 times. times the weight fraction of niobium (Nb). In these proportions of the niobium (Nb) and tantalum (Ta) masses, it is found that niobium very often occurs as a tantalum contaminant. Especially with regard to the possibility of improved hardenability and the possible positive effects on the steel and the components comprising it. Studies suggest that tantalum (Ta) may lead to better hardenability of the steel than niobium (Nb). Although niobium does not appear to have any seriously negative effects, the studies indicate that tantalum niobium could lead to better hardenability compared to niobium.

In this context, the possibility is discussed whether this could possibly be due to the formation of tantalum carbide (TaC) in the microstructure. Thus, there is an initial desire to limit the niobium content in comparison to the tantalum content. In the case of particularly high-quality applications, therefore, a proportion of tantalum of at least 120 times, at least 150 times or at least 200 times the proportion of niobium can also correspond, these ratios already being close to the limit of the technical separation possibility of the two elements. Due to the apparently not very detrimental effect of niobium (Nb), it may therefore be more suitable for economic and procurement reasons, and for reasons of actual steel production, to tolerate a certain amount of niobium to simplify the process of steel production and / or more technically stable to keep.

With regard to chromium (Cr) it may be advisable, in embodiments, to limit the chromium content to a maximum of 5% by weight, to a maximum of 3.8% by weight or to a maximum of 2.1% by weight. Thus, if appropriate, a competitive situation in the formation of carbides or other carbon-containing compounds, complexes or deposits between tantalum and chromium can be prevented. It may also be advisable to add molybdenum (Mo) by weight up to 0.6% by weight.

For the sake of completeness, it is useful to point out that a steel is a material whose mass fraction of iron (Fe) is greater than that of any other element whose carbon content is generally less than 2% by weight. is and can contain other elements.

A steel, as it can be used in a component 100 according to an embodiment, can be designed as a bearing steel, as defined for example in ISO 683-17: 1999. Such a steel based on a 43CrMo4-based alloy according to one exemplary embodiment can achieve, for example, one or more hardness values. chen, as listed in Table 1 reproduced below. Table 1 compares a minimum HRC value (HRCmin) for a typical steel alloy and a maximum HRC value (HRCmax) for a typical steel alloy as a function of a distance d from a quenched face in mm. The hardenability can be measured by Jominy forehead quenching tests at different face distances.

Table 1 :

(1 [mm] HRCmax HRCmin

1.5 61 53

3 61 53

5 61 52

7 60 51

9 60 49

11 59 43

13 59 40

15 58 37

20 56 34

25 53 32

30 51 31

35 48 30

40 47 30

45 46 29

50 45 29 The hardness values are given here according to Rockwell according to the HRC scale. Depending on the exact alloy composition, deviating HRC values may also be achievable. Thus, based on the abovementioned base alloy 43CrMo4, HRC values which are above or below the stated minimum and / or maximum HRC values HRCmax and HRCmin, respectively, may also be achievable.

Depending on the steel used according to embodiments of the present invention, hardnesses starting at about 40 HRC in the case of a carbon steel content of 0.25 wt .-% to almost 70 HRC in a steel having a carbon content of 0.6 wt .-% or higher can be achieved.

Thus, in the case of a steel according to one exemplary embodiment-for example based on a 50CrMo4 base alloy-one or more hardness values can be determined according to the following minimum and maximum HRC values HRCmin and HRCmax given in Table 2 as a function of the distance d from the quenched end face in mm be achievable.

Table 2:

(1 [mm] HRCmax HRCmin

1.5 65 60

3 65 60

5 64 59

7 64 58

9 63 57

11 63 56

13 63 55

15 62 53

20 61 50

25 60 47

30 58 45

35 57 44

40 55 43

45 54 42

50 54 42

Here too, depending on the precise alloy composition and also, if appropriate, based on other base alloys, corresponding minimum and maximum HRC values HRCmin or HRCmax values can be achievable which have 1, 2 or 3 HRC levels or values above or below in Table 2. The hardenability can also be measured here by Jominy forehead quenching tests at different end face distances. As previously discussed, steels used in embodiments of the present invention exhibit reduced grain growth in the heat treatment and thus (generally) small grain size. According to ASTM standard E 112 (2010 edition) (ASTM = American Society for Testing Materials), they have microstructures with grains having a ratio of 5, 6, 7 or more. After the preparation of a cut, a photo is compared at a magnification of 100: 1 with different standard images. Class 5 corresponds here to grains with an average diameter of about 60 μm, those of class 6 those with an average diameter of about 45 μm, those of class 7 those with a mean diameter of about 35 μm and those of class 8 such with a mean diameter of about

22 μιη. In the case of steels, the size or grain boundaries of, optionally former, austenite grains are referred to as grain size and grain boundaries.

With regard to the microstructure of non-metallic inclusions, exemplary embodiments of steels can be quantified using, for example, the measurement methods defined in the standards ASTM E45 (Edition 2011) and ISO 4967 (Issuing date 1998-10) and DIN 50602: 1985. Even with these methods, cuts are made and compared in a 100: 1 magnification with standard images. Embodiments may be provided according to the following microstructural classes or better. Table 3 shows nonmetallic inclusions according to ASTM E45 (2011 edition) and ISO 4967 (1998-10 edition), which can achieve exemplary embodiments.

Table 3:

Jernkontret

default chart

A (fine or thin) 2.5

A (thick) 1.5

B (fine or thin) 2.0

B (thick) 1.0

C (fine or thin) 0.5

C (thick) 0.5

D (fine or thin) 1.0

D (thick) 1.0 Accordingly, Table 4 shows non-metallic inclusions according to DIN 50602: 1985, which can achieve embodiments. In this case, bar diameter d in mm is compared with characteristic cumulative K values. Table 4:

d [mm] K factor

200 <d K4 <20

140 <d <200 K4 <18

100 <d <140 K4 <16

70 <d <100 K4 <14

35 <d <70 K4 <12

17 <d <35 K3 <15

8 <d <17 K3 <10

d <8 K2 <12

These steels can be produced, for example, in a process comprising two steps which can be carried out simultaneously or sequentially. Here, in a first step, a base alloy of the steel is provided, which is then alloyed in a second step with the first and the second alloying element.

In principle, they can be produced by all processes, even if due to economic and / or process-related characteristics, individual processes tend to be used in peripheral areas. Thus, it is possible to carry out both method steps, for example in the case of only small tonnages to be produced in the context of the crucible steel process or the electrical steel process, wherein the alloying elements in chemically pure form (eg metallic form), for example as powder or as granules (pieces), is added as a chemical compound or as an alloy.

However, the process steps can also be carried out sequentially. For example, the step of providing the base alloy may include providing pig iron in a blast furnace route, but also by other methods. The pig iron can then be processed to steel in the course of a blowing process (eg LD process or Linz-Donawitz process) or a fresh-hearth process (eg Siemens-Martin process). be. As an optional further step, the provision of the base alloy may further comprise refining resulting in an adjustment (generally a decrease) in the content of elements such as silicon (Si), manganese (Mn), sulfur (S), or even phosphorus (P) , Also, by adding further elements, the properties of the base alloy produced in this way can optionally be further changed. Examples include aluminum, (Al), vanadium (V), chromium (Cr), calcium (Ca), silicon (Si), niobium (Nb), titanium (Ti), nickel (Ni), and molybdenum (Mo). For example, deoxidation can be achieved by adding aluminum (AI), silicon (Si), calcium (Ca) or calcium compounds.

In the second step of alloying with the alloying elements, they can then be added to the base alloy in metallic or chemically bonded form. The step of alloying with the alloying elements in this case is a typical step of secondary metallurgy, which can be performed, for example, in a Pfannenofenver after refining. In this case, optionally further alloying elements can be added, as far as this is still necessary or desired. For example, chromium, tantalum and molybdenum can have a corrosion-inhibiting effect. The step of alloying with the alloying elements takes place here at a temperature of less than 1600 ° C, where appropriate, the temperature can be limited to values of below 1550 ° C or below 1500 ° C.

In the context of secondary metallurgy, further process steps may be included, such as degassing by vacuum degassing or by other methods. This can optionally be followed by further mechanical, thermal or other further processing steps, such as rolling of the steel.

Fig. 2 shows a cross section through a tapered roller bearing 200 for a large-scale plant, such as a wind turbine, a tidal power plant, rolling mill or a construction machine. The tapered roller bearing 200 comprises an outer ring 210 and an inner ring 220, which are shown in Fig. 2 with respect to a line of symmetry 230, wherein the line of symmetry 230 coincides with the axis of the tapered roller bearing 200. Between the inner ring 220 and the outer ring 210, a plurality of frusto-conical rolling elements 240 are arranged, which are guided by an optional cage 250. By a relative movement of the inner ring 220 to the outer ring 210, the rolling elements 240 roll on a running surface 260 of the inner ring 220 and a running surface 270 of the outer ring 210. For lateral guidance of the rolling elements 240, the tapered roller bearing 200 has guide rims. The inner ring thus comprises a first board 280 and a second board 290, while the outer ring shown here has no lateral guide rims.

The outer ring 210 and the inner ring 220 both each represent components according to embodiments of the present invention, as it has already been shown as a component 100 in FIG. 1. They are in this case made entirely of steel, thus differing from the component 100 shown in FIG. 1, for example, in that the component shown there at least only in sections has a corresponding steel. In other words, the component 100-1, that is to say the outer ring 210, and the component 100-2, that is to say the inner ring 220, respectively coincide with their corresponding sections 110-1 and 110-2 of the components 100.

The outer ring 210 and the inner ring 220 accordingly each have an edge zone 130-1 or 130-2, which respectively lie directly below the surfaces 120-1 and 120-2 of the two components 110. In these changes - as described in connection with FIG. 1 - the proportion of a chemical element measurable, so for example by at least 0.1 wt .-%. If, for example, the two components 100 are subjected to case hardening as part of their production, the proportion of the carbon (C) changes in the edge zones 130-1 and 130-2, as will be described in more detail in connection with FIGS. 3 and 4. This also results in a hardening of the steel up to a case hardening depth, which is often referred to by the formula character CHD (Case Hardening Depth) or Eht ("case hardening depth") and based on an ultimate hardness of 550 HV1 or 52.5 HRC.

The case hardening depth may here be at least 5 mm, for example. Depending on requirements, a lower hardening range of 10 mm or more can be produced, which counteracts premature fatigue, especially in the case of heavily loaded components, such as the rolling bearing rings of large machines, and also for higher machining allowances for large rolling bearing rings (eg due to distortion ). But also in the field of rolling elements and other construction or machine parts are curing areas with Case hardening depths in the extent described often very desirable for various reasons.

Steels that are used in embodiments of the present invention are so curable that they can be made high-strength at least in sections in the edge zone 130. They are therefore suitable as steels for rolling bearings and for other applications in which the components made from them are subjected to strong dynamic and / or static loads. Rolling bearings are typically cyclic and / or static compressive, with the improved hardenability and grain stability counteracting fatigue, spontaneous failure and wear. The lack of critical tensile stresses and the high hydrostatic pressure in Hertzian contact cause the hardened steel to flow microplastically and lead to a fatigue life which is orders of magnitude greater than that of comparable cyclic tensile, compressive or circumferential bending stress (rolling fatigue fatigue).

Conventional carbon case hardening, often called simply case hardening, relies on the controlled diffusion of carbon, mostly from controllable hydrocarbon atmospheres, into the edge zone 130 of a component 100 and subsequent hardening. Component reliability, resource conservation and production cost efficiency make for high levels

Accuracy of the process objectives advisable. However, these stringent requirements are often not met in practice. A promising process optimization of case hardening can thus be improved with the help of a powerful computer simulation tool.

Case hardening typically includes the sub-steps of carburizing, quenching and tempering. The products are characterized by high hardness, strength

(Yield strength) and tear-resistant residual compressive stresses in the claimed surface layer as well as good core toughness and thus increased security against splitting fracture and impact load. Treated conventionally unalloyed or low-alloyed steels with carbon contents of about 0.05 to 0.30 wt .-%, which corresponds to basic hardness in the range between 30 HRC and 50 HRC. The method is particularly used for mechanical, by material fatigue or wear, heavily stressed components that need to absorb additional shock loads. These include tools, gears and Gears, bearings, drive, cam and crankshaft shafts, spindles, spindles, pistons, bolts, screws and steel cages. Under certain load or operating conditions, a higher residual austenite content in the edge zone 130 can have a favorable effect on the service life.

The thermochemical carbon enrichment of the near-surface edge zone 130 is effected by diffusion, which is introduced industrially predominantly from the gas phase. The inert gas-controllable, oxygen-containing hydrocarbon mixtures are often called fast because of the achievable carburization rates (carbon numbers). The process temperatures are conventionally between 850 ° C and 980 ° C, but may also be significantly higher for steels, as used in the context of components 100 according to embodiments.

The components 100 are in this case first, z. B. in a protective atmosphere, heated. Although today's furnace technology permits largely any process control, conventional isothermal normal pressure gas carburizing consists of only two process steps: the saturation and the equalization stage. Typically, industrial plants provide comparable carbon numbers in both phases. The respective shares in the total duration of treatment are roughly 80% and 20%. In the saturation or carbonation stage, carbon levels of 0.8 to 1.3 wt% are used for the carbon. This value is as close as possible to the carbide or soot limit of the steel or plant used. The carbon uptake in the edge zone 130 is thereby maximally accelerated.

The subsequent compensation or diffusion phase of such a two-stage process for smoothing the steep, near-surface concentration gradient takes place at a reduced carbon level between 0.55 and 0.95% by weight. The desired marginal carbon content is often between 0.6 and 0.85 wt .-%>. Surface hardnesses of about 58 to 65 HRC should be achieved.

Suitable quenchers with different intensity and cooling rate are water, which often causes a strong distortion and increased risk of cracking, or surfactant mixtures, hardness emulsions, oils, molten salts or cooling gases, for example helium (He), which is injected under high pressure with up to 40 bar.

Industrial direct hardening, which can be carried out particularly economically from carburizing heat, is often applied with hardening temperatures of about 800 ° C. with intermediate cooling and double hardening, which results in particularly high core toughness.

Firing is typically carried out at 150 to 200 ° C for 2 to 4 hours. The most important process targets for carburizing and hardening are the carburizing and case hardening depths, which are usually between 0.05 mm for precision engineering and 10 mm and above, for example. B. for large gears or bearings and heavy machinery. Technically, values between 0.5 and 4 mm are usually required. In addition, the marginal carbon content and the surface hardness are sometimes important parameters. In addition, application-related setpoint limits can be defined or specific profile shapes required, for example, in the outer workpiece area.

For the process control, the mathematical prediction of the carbon and hardening depth profile in real time for constant manipulated variable control is advisable. The resulting residual austenite distribution is also becoming more important.

Components 100 according to one exemplary embodiment can be produced, for example, with nitrogen-diluted methanol cracking gas as the carrier gas, with a comparatively low overpressure of 6 mbar also being used for safety reasons. Added natural gas can then serve as carbon donor, with a C-current probe can be used to monitor the process parameters.

3 shows a schematically simplified representation of a profile of the carbon fraction 300 (c (C)) and a hardness curve 310 (H = hardness) as a function of a depth (d = depth) of the surface 120 of the component 100, which is part of a Case hardening process was prepared. Starting from the surface 120 of the component (d = 0), the carbon content has essentially a first constant value before it decreases and strives for a second value c ₀ (C) inside the workpiece. The first value of the carbon content c (C) is above the second value c ₀ (C), which in the considerably corresponds to the carbon content of the steel before case hardening. FIG. 3 further shows a dotted line 320 separating the edge zone 130 of the component 100 from the remainder of the component 100 and the portion 110 (not shown in FIG. 3) upon reaching the core composition of the steel.

The hardness curve 310 shows a similar behavior as the curve 300 of the carbon content c (C). Again, starting from the surface 120, the latter, too, essentially has a constant value, which in a transition region falls to a second value H0 which corresponds to the hardness in the interior of the component 100. The hardness curve 310 in this case essentially follows that of the carbon fraction 300. Between the two, as is also shown in FIG. 3, certain deviations frequently occur in reality, which may be due, for example, to a lack of hardenability of the steel.

The hardness can be specified, for example, according to Rockwell according to the HRC scale, possibly after revaluation. Depending on the steel used in accordance with embodiments of the present invention, hardnesses starting from about 40 HRC in the case of a steel having a carbon content of 0.25 wt .-% up to almost 70 HRC in a steel with a carbon content of 0.6 wt. -% or above. The hardenability can be determined by Jominy forehead quenching tests at different face distances.

The resulting hardness is determined predominantly by the carbon content. The other alloying metals improve the hardenability (hardening acceptance) and prevent excessive grain growth, whereby even a small, above-mentioned proportion of the alloying element acts grain-stabilizing. This also applies to higher shares.

Also, by a suitable optional alloying with other alloying elements, for example with molybdenum (Mo), nickel (Ni), silicon (Si), manganese (Mn) or chromium (Cr), the grain growth in the heat treatment (further) is hindered. Typical contents of these alloying elements are between 0.1 and 5 wt .-%.

It is believed that embedded carbides impede grain growth as they act as barriers to grain boundary motion and austenite transformation as seeds, thus helping to grain formation. Therefore, these steels are with Increasing alloying addition overheating insensitive than unalloyed steels with the same carbon content. The stored carbides prevent excessive grain growth. Especially tantalum carbide (TaC) is particularly advantageous here, since this does not seem to dissolve so quickly compared to other carbides.

The Auikohlungstiefe can according to DIN EN 10052: and defined in the usual manner as a vertical surface distance for a concentration of 0.35 wt .-% of carbon (C) are denoted by Ato, 3 ₅ 1994-01 (terms of the heat treatment of ferrous materials). The choice of said carbon content is based on the assumption that completely martensitic microstructure at this point has a limit of 550 HV 1, corresponding to about 52.5 HRC, the case hardening depth CHD (Case Hardening Depth, in German-language literature often Eht) according to DIN EN ISO 2639: 2003-04 (Steel - Determination and testing of case hardening depth). However, other predetermined carbon levels can be used to define a depth of carbonization. These can be distinguished by appropriately modified subscripts in the symbol (eg At _0i32 ).

For example, courses 300, 310 as shown in FIG. 3 may be after a 70 hour carburization, a cool in a salt bath at 320 ° C., an anneal for 20 hours to reduce hydrogen in the steel, and then austenitize under shielding gas at 805 ° C for 70 minutes, at which the change in the carbon distribution is often negligible (simple hardening). As a quenching agent can be used heated to 100 ° C hardness oil. The component 100 may thereafter, for example, cool for several minutes in air.

For example, to a depth of about 3.5 mm, the carbon content may be above 0.6 wt%. Hardness values above 60 HRC are possible with these concentrations. Similarly, case hardening depths CHD of, for example, 6.4 to more than 10 mm can be achieved.

FIG. 4 shows a schematically simplified representation of a profile of the carbon fraction 300 (c (C)), a hardness curve 310 (H = hardness) and a profile of a nitrogen fraction 330 (c (N)) as a function of a depth (d = depth) of the surface 120 of the component 100 made in the context of a carbonitriding with an optional curing has been. The course of the nitrogen component 330 has an at least similar course to the course of the carbon component 300 from FIG. 3, although the change from a first value present on the surface 120 of the component 100 to a second value c ₀ (N) in the interior of the component takes place at a significantly shorter distance. Typical nitrogen contents can thus at the surface in the region of a few tenths to a few percent by weight, often of several tenths of a weight percent, are as ₀ (N) is located in the interior of the component, the value c more in the range of some 10 to some 100 ppm.

As a result of the increased varying nitrogen content occurring in the area of the surface 120 of the component 100, in FIG. 4 the carbon content 300 (c (C)) has a slightly reduced value compared to a maximum value. Thus, the nitrogen at the surface 120 causes, due to diffusion processes, a change in the carbon content at the surface compared to a carburizing without a simultaneous nitrogen enrichment, and thus a varying nitrogen content in the surface layer. Likewise, due to the process temperatures used in carbonitriding, carbon leakage occurs through diffusion from the surface 120 of the component, which, however, is compensated by at least partial uptake from the carbon emitting medium. The medium thus acts as an "effusion barrier" with respect to the carbon, in that carbon emanating from the surface 120 due to the process temperatures can be replaced by carbon from the medium.

Because of the nitrogen-changed activity-concentration relationship of carbon, the carbon content 300 (c (C)) has a local maximum in about a range where the nitrogen content 330 has fallen to a value at which the influence of diffusion processes has become less important , Depending on the specific course of the involved shares 300, 330, this can take place, for example, in the region of the largest change in the nitrogen content 330.

As is also shown by the profile 300 of the carbon component c (C), which already has a value in the area of the surface 120, that is to say at d = 0, which is approximately in the region of the value c ₀ (C) in the interior of the component in the steel used here, a hardening steel with a carbon content of about 1 wt .-%, for example based on the steel 100Cr6. Since, despite the described change in the carbon content c (C) in the region of the edge zone 130, this typically is not below a value of about 0.8% by weight, however, this change in the carbon content c (C) scarcely results in a change in the hardness history 300 (H). This is therefore essentially constant. The carbon-releasing medium in carbonitriding can be chosen so that the uniform starting carbon content of a hardening steel used is changed as little as possible.

On the basis of a definition of the carbonitriding depth CNtyy which is similar to the carburization depth At _xx , where xx and yy respectively represent predetermined limit values of the carbon or nitrogen fractions, the local maximum of the carbon fraction 300 (c (FIG. C)) approximately at the Carbonitriertiefe. Compared to carbon-nitrogen case hardening based on a case hardening steel with a carbon content of typically less than 0.6% by weight, the change in nitrogen content c (N) here occurs at a much smaller length scale than the typical carburizing depth At _xx on. As a result, the point of maximum change in the profile of the nitrogen content 330 substantially coincides with the carbonitride depth. The change in the nitrogen content c (N), as shown in FIG. 4, occurs so frequently in one embodiment of a component on a length scale which amounts to several 100 .mu.m, ie, for example, comprises 500 .mu.m. The use of microalloyed grain-stable steels according to the invention makes it possible to increase the time and / or increase the temperature of the carbonitriding, so that even deeper zones of influence CNt _{yy can be achieved} by 1 mm or more with suitable insertion of the material.

While the hardness curve 310, starting from the surface 120 (d = 0), essentially has its value in the interior of the component (H (d) = H ₀ ), the course of the carbon component 300 on the surface 120 of the component 100 has a first value which is smaller than a second value in the region of the local maximum. As already described in connection with FIG. 3, the profile 300 then again approaches a third value Co (C) in the interior of the component 100. The third value Co (C) corresponds approximately to the profile 300 shown in FIG first value at the surface 120 (d = 0). In the edge zone 130, therefore, both the carbon content c (C) and the nitrogen content c (N) change in this exemplary embodiment, while a change in the hardness curve 310 present after curing essentially does not take place. In the case of a carbon-nitrogen case hardening of a non-hardening steel, so for example a case steel, it comes through the absorption of carbon from the donating medium also to a measurable change in the carbon content in the region of the surface 120 and thus the edge zone 130. So In this carbonitriding process, which counts for case hardening, carbon is taken up from the medium in the steel, that is to say in the component 100, whereby the carbon content increases in such a way that an increase in the hardness in the boundary layer also accompanies this after the (insert) hardening. However, here as well, the carbon content typically has a local maximum due to diffusion processes, which does not lie on the surface 120 of the component 100. Thus, the carbon content on the surface 120 has a first value that increases to a higher second value, namely, the value of the local maximum, and then drops to a third value that is inside the component 100 and approximately equal to the original carbon concentration. At the same time, the medium also serves as a source of nitrogen. It is therefore also in such a process in the peripheral zone 130 to a change in the nitrogen content c (N) and also to a measurable change in the carbon content c (C).

A non-hardening steel is typically such a steel, which has a carbon content of at most 0.6 wt .-% before the case hardening and / or the carbon-nitrogen case hardening, usually at most 0.3 wt .-%, while a through-hardening Steel is one in which, typically before carbonitriding, the carbon content is at least 0.6% by weight. Apart from the component shown in FIG. 1, the inner ring 210 shown in FIG. 2 and the outer ring 220 of a single-row tapered roller bearing 200 have hitherto been described. Embodiments of the present invention are, however, by no means limited thereto. In addition to multi-row (eg double-row) roller bearing rings, rolling elements (inter alia, a cylindrical roller, ball and tapered roller) and other components to be hardened Wälzlager- components include the embodiments also other types of

Rolling bearings, such as cylindrical roller bearings, roller bearings, ball bearings, four-point bearings and needle bearings as well as plain bearings, intermediate rings and other construction and machine parts of the rotary and linear bearing technology. Also components of other disciplines of vehicle and mechanical engineering can be implemented as embodiments of the present invention become. In principle, this includes all components which have at least one region which is subjected to an increased load.

As has already been explained above, components according to embodiments can be made completely or partially, that is, in sections, from steel. In other words, embodiments in this regard are not limited to a complete embodiment of a material. Examples of these are composite components which have a correspondingly shaped section in which steel according to an embodiment of the present invention is implanted together with a corresponding edge hardening region. Other areas of the component in question can be made, for example, from another metal, another alloy or another steel. A connection can be made in these cases, for example, cohesively in the form of a soldered or welded connection. However, other connection methods are also conceivable here, for example a non-positive or positive connection or also an adhesive as another form of the integral connection. These methods can be used, for example, when soldering or welding is out of the question, ie if the substances involved are not solderable or weldable. Examples of this may be plastics or glass fiber reinforced materials. In embodiments, which are not completely made of a steel according to an embodiment, but at least have a section, this may extend from the surface along a straight line such that the straight line runs completely in the steel until it reaches a (further) Surface section emerges from the component.

In embodiments, the component or its section comprising the steel may optionally comprise further materials. Thus, such a component can also be made entirely or in a corresponding section of a material which comprises the steel. Such a material may comprise, for example, a fiber reinforced steel or other hybrid material combination using steel according to one embodiment.

A steel, as it can be used in the context of an embodiment, may be a bearing steel. Among the possible fields of application of exemplary embodiments of the present invention are, first of all, all large plants in which individual components are subjected to a corresponding mechanical load which makes surface hardening advisable. These include wind and tidal power plants as well as generators, construction machinery, cranes, excavators, vans, trains, marine propulsion, aircraft, rolling mills and other machinery. In principle, it may also be advisable to use embodiments in smaller systems and their components, since even in such systems, for example, by sudden shock loads high stresses may occur. Micro-alloyed grain stable steels for case hardening or carbonitriding according to embodiments of the present invention, as well as corresponding components, are therefore applicable in a wide field of applications.

The features disclosed in the above description, the claims and the drawings may be of importance both individually and in any combination for the realization of embodiments in their various embodiments and - unless otherwise stated in the description - arbitrarily combined with each other become.

A component 100 according to an exemplary embodiment can thus have a smaller grain size after a heat treatment during its production.

Claims

Patented component

A component (100) comprising: at least a portion (110) comprising a steel, the portion (110) extending from a surface (120) of the component (100) into an interior of the component (100); and an edge zone (130) in the portion (110) immediately adjacent to the surface (120) of the component (100) and in which a proportion of a chemical element in the steel changes measurably; the steel in the edge zone (130) having, at least in sections, a structure with grains having a ratio of 5 or more according to ASTM-E 112 (2010 edition); wherein the steel has a chromium content of at most 7 percent by weight; and wherein the steel further comprises tantalum at greater than 0.4 weight percent by weight, niobium at greater than 0.1 weight percent, titanium at greater than 0.12 weight percent, or weight at weight greater than 0, Has 05 weight percent.

2. Component (100) according to claim 1, wherein the chemical element is carbon or nitrogen.

3. A component (100) according to any one of the preceding claims, wherein the proportion of the chemical element changes by at least 0.1 percent by weight.

4. Component (100) according to one of the preceding claims, in which the proportion by weight of tantalum, of niobium, of titanium or of vanadium is at most 2 percent by weight.

5. Component (100) according to any one of the preceding claims, wherein the chromium content is at most 5 percent by weight.

6. The component (100) according to any one of the preceding claims, wherein the steel further comprises an alloying element in a weight proportion between 0.1 and 5 weight percent, wherein the alloying element is molybdenum, nickel, silicon, manganese or chromium.

7. The component (100) according to one of the preceding claims, wherein the steel in the edge zone has a carburizing depth of at least 5 mm and / or a carbonitriding depth of at least 0.1 mm, the carburizing depth being at a distance from the surface of the component in which a carbon content of the steel falls below a predetermined carbon content, for example 0.35 weight percent, and wherein the carbonitriding depth is a distance from the surface of the component at which a nitrogen content of the steel is below a predetermined nitrogen level, for example 0.05 weight percent , falls.

8. component (100) according to any one of the preceding claims, which has a hardness of at least 52.5 HRC, starting from the surface in the edge zone to a case hardening depth of at least 5 mm.

A component (100) according to any one of the preceding claims, wherein the non-metallic inclusions are in accordance with ASTM E45 (2011 edition) and ISO 4967 (1998-10 release date) which corresponds at most to the values defined in Table 3, or of non-metallic inclusions in accordance with DIN 50602: 1985, which corresponds at most to the values defined in Table 4.

Component (100) according to one of the preceding claims, wherein the component (100) is a rolling bearing component, for example a rolling bearing component of a large machine, such as a wind turbine, a tidal power plant, a generator, a construction machine, a van, a train, a rolling mill, a marine propulsion , a paper machine or an airplane.