EP1805331A1

EP1805331A1 - Mechanically-stressed actuator or bearing component made from mechanically-hardened steel

Info

Publication number: EP1805331A1
Application number: EP05804438A
Authority: EP
Inventors: Ernst Strian; Werner Trojahn; Karl-Ludwig Grell
Original assignee: Schaeffler KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2004-10-26
Filing date: 2005-10-15
Publication date: 2007-07-11
Also published as: DE102004051885A1; WO2006045461A1

Abstract

The invention relates to a mechanically-stressed actuator or bearing component, made from steel alloy, with an alloy component of less than 7 % and a carbon content of 0.5 - 2.2 %, with at least one mechanically-stressed functional area in use, whereby at least in the region of a functional surface (4) a metastable austenite is present, having a structural content of at least 80 %, which is at least partly transformed into martensite by a mechanical processing of the functional surface (4).

Description

Name of the invention

Mechanically load-bearing actuator or bearing component made of mechanically hardened steel

Field of the invention

The invention relates to a mechanically load-bearing adjusting or bearing component, be¬ standing of an alloyed steel with an alloying content of at least 7% and a carbon content of 0.5 - 2.2%, with at least one mechanically charged in Ein¬ rate surface.

Background of the invention

Such actuator or bearing components are known in different designs and are used in a variety of applications. Engine elements such as towing or rocker arms, in particular mechanical actuated components which in turn provide other components, should be mentioned as the actuating element. As a bearing component, for example, a rolling bearing or its parts or a plain bearing and its parts such as bearing bush, bearing ring, etc. may be mentioned. All these actuating or bearing components have in common that they have at least one functionally mechanically loaded functional surface, via which, for example, an actuating element in the form of a rocker arm acts on a tappet or the like, or on which, in the case of a roller bearing, the rolling elements run , The components are exposed to high mechanical and tribological stresses, which is why it is necessary to harden these components after mechanical processing. To achieve dimensional and dimensional accuracy, finishing such as grinding or hard turning is performed. The heat treatment itself takes place once, depending on the steel quality, through hardening, for example at 100Cr6, or through case hardening, eg at 16MnCr5, or through various variants of nitriding treatments or Stratifications.

The main drawback of most such treatments is the so-called hardening distortion and the resulting dimensional change. The component dimension therefore varies as a result of the different, in particular thermal treatments, between the shape or dimensioning originally present before the treatment and the parameters finally given after the implementation of the respective treatments. In this case, the components are machined or chipless in the best possible microstructural and hardening state, subsequently hardened at high temperature and finally finished mechanically, ie by machining, and work-hardened, for example by shot blasting or rolling. In addition to the dimensional and hardness distortion occurring as a result of the thermal hardening treatment, the implementation of the separate hardening step is also time-consuming and cost-consuming.

Summary of the invention

The invention is therefore based on the problem to provide a control or bearing element of the type mentioned that is easy to make and without the problems mentioned in terms of dimensional and shape retention.

To solve this problem is provided according to the invention in a mechanically loadable actuator or bearing element consisting of the above-mentioned steel that at least in the region of a functional surface a metastable Austenite with a microstructure of at least 80% is present, which by machining the functional surface at least partly converted into martensite.

According to the invention, a steel which forms a metastable austenite phase is used to produce the positioning or bearing component. This metastable Austenitphase can by a mechanical treatment of the Fu surface itself, so for example, the bearing surface of a towing or rocker arm or the tread of a plain bearing due to the mechanically induced Energy can be converted locally into martensite. Thus, there is a mechanically induced structural change and thus hardening directly in the area of the functional surface.

These properties are made possible with the use of an alloyed steel with an alloying fraction of at least 7% and a carbon content of 0.5-2.2%, wherein the steel used on the one hand must have a sufficiently high carbon to produce a high martensitic one Hardness of over 55 HRC, in particular to achieve over 58 HRC. Furthermore, a corresponding "manganese nickel equivalent" (Cr-Ni) must be present for producing the metastable austenite at correspondingly high heat treatment temperatures, and finally a sufficient fine graininess of the structure must be able to be realized.

For this purpose, as described preferably steels with 0.5 to 2.2% carbon, an alloy content of chromium between 5 to 20%, a manganese content of 2 to 8% and a nickel content of not more than 6% are used. The fine granularity and corresponding microstructural characteristics are to be ensured by addition of, for example, molybdenum, aluminum, titanium or other alloying elements. Conventional tool steels such as e.g. X210Cr12 or X165CrMoVI 21, as used in particular in Motoren¬ elements such as towing or rocker arms.

A second class of materials is the field of charge and tempering steels. These high-alloyed case hardening steels such as 14NiCrMo14 or even higher alloying constituents with total values nickel-manganese chromium greater 7% and an edge carbon content / edge nitrogen content, produced by the usual case hardening or carbonization , of 0.5-1.5% of carbon or 0.1-0.6% of nitrogen also form a metastable austenite phase, which can be converted locally into mechanical stress by mechanical energy input. The prerequisite is that the alloying elements must be adjusted so that the martensite formation temperature after carburization and / or nitriding during quenching is not or only marginally is followed, so that an intermediate stage conversion or a Perlitzer case is omitted.

Said materials are thus in principle able to operate at high hardening curing temperatures (direct or Einfachhärtung), for example more than 1000 ⁰ C and a rapid quenching form a quasi of 80% or even higher austenite structure in the carbon-rich surface zone, wherein the aforementioned At least in this marginal zone, the carbon atom I is present; in the case of an attachment, the sum of nitrogen and carbon should likewise be in this range. The metastable austenite formed is therefore also present at room temperature, but can be converted into martensite with sufficient energy supply, the conversion capacity according to the invention depending on the mechanical processing.

The heat treatment in the case of through-hardening steels, within which be¬ preferably already the transformation takes place to finished final part, sees the one Hochtemperaturaustenitisierung and optionally carburizing at about 1000 - 1250 ° C and then quenching in a salt bath to about 150 ⁰ C or to room temperature. Subsequently, a further cooling to room temperature in air, if still necessary. As a result, an austenite content of more than 80%, preferably more than 90%, is formed in the edge zones (if only the sufficiently high carbon content is present there) or in the entire cross section, where appropriate carbides are precipitated and, if appropriate, traces of martensite are present. Subsequently, the mechanical finishing of the already formed, but me¬ unstable austenite component by turning, milling or slaving takes place. As a result of this type of structural stress on the functional surface, a mechanically induced martensitic transformation of the metastable austenite arises in the corresponding action depths. In principle, the depth of the transformation zone depends on the tool contact geometry (eg rake angle adjustment), the contour to be generated, the duration and the magnitude of the applied force and the prevailing temperature in the mechanical processing. Overall, a very dimensionally stable component with a sufficient hardness in the relevant component area can be achieved in this way. The forming of the steel used for component production preferably takes place during the heat treatment for high-temperature austenitization. An additional high-temperature step for hardening the material, as provided in the prior art, is omitted after curing by martensitic transformation takes place in the component according to the invention solely by the mechanically induced energy.

The functional surface should have a martensitic hardness of at least 55 HRC, in particular of at least 58 HRC, for which purpose a sufficiently high carbon content, which is in the range claimed according to the invention, is necessary. The steel itself may, as described, be a fusible alloy which exhibits the metastable austenite, but it may also be produced by a separate nitration, ie in the context of an electrochemical treatment.

In addition to the positioning or bearing component itself, the invention itself is a process for producing such a Stel I or bearing component, which is characterized in that the component first of an alloyed steel with an alloy content of at least 7% and a carbon content of 0 , 5-2.2%, during or after which the component is subjected to a temperature treatment, and then the component is subsequently quenched so that at least in the area of a functional surface of the component a metastable austenite with a microstructure proportion of at least 80 % forms, after which the functional surface is machined so that forms a marginal zone having at least partially martensite.

The mechanical processing for martensite formation temperature may preferably up to about 500 ⁰ C, at room temperature or at a reduced temperature of preferably up to a maximum at elevated Tempe¬ - 200 ° C carried out. In particular, the Tief¬ temperature treatment is advantageous for martensite formation. If the mechanical treatment takes place at elevated temperature or at room temperature, it is expedient to connect a deep-freeze treatment, preferably a maximum of -20 ° C., to improve the formation of martensite. In general, after a deep-freeze treatment, a temperature treatment for starting the component can take place up to a maximum of 600 ^° C.

It is also conceivable, immediately after the component shaping, before the mecha¬ African processing for martensite formation, a deep chill treatment to vor¬ preferably at most -200 ⁰ C, optionally followed by a Req assbehandlung up to 600 ⁰ C interpose.

Furthermore, for further increase in strength, the functional surface as well as the remaining component surfaces can be mechanically post-treated after the mechanical treatment for martensite formation, in particular by shot peening or rolling. A final finish such as grinding or honing can optionally also be provided.

Overall, the method according to the invention, as well as the adjusting or bearing component according to the invention, offers the advantage that the hardening distortion is canceled once by the processing state and a double machining is not required, as in the conventional method by soft machining and hard machining.

Brief description of the drawings

Further advantages, features and details of the invention will become apparent from the embodiment described below and from the drawing. This shows a schematic diagram of a mechanical Stellele¬ management in the form of a rocker arm. Detailed description of the drawing

The figure shows an inventive control element 1 in the form of a tiltable about its bearing eye rocker arm 2, on the front arm 3 onsfläche 4 funkti¬ is provided over which the rocker arm engages, for example on a plunger. The rocker arm was produced from a material which forms a metastable austenite phase after the high-temperature austenitization during which temperature treatment of the rocker arm was worked out during the subsequent ab initiation.

In order to harden the functional surface 4, a mechanical processing of the functional surface, for example by turning, milling or grinding, takes place in the context of which processing, which is represented by the arrow B, directly on the function, unlike in the prior art If mechanical energy is introduced, this induces the folding-over processes, ie the conversion of the metastable austenite into martensite. As is indicated by the dashed line, an area M is formed in which a high content of martensite is present, while metastable austenite is present in the remaining component body. As a result of the mechanically induced martensite formation so no further temperature treatment for curing of the component, which would adversely affect the dimensional and dimensional accuracy. Rather, the component retains the exact shape and dimensions given in the course of its original forming.

The mechanical treatment for the formation of martensite can be as beschrie¬ ben subzero treatment connect, under which the Bau¬ part, for example, -200 ⁰ C cooled, whereby the formation of the martensitic structure in the edge zone part M is further promoted. Alternatively, the processing can be carried out even at a reduced temperature, so that a separate freezing is not necessary. In the context of a subsequent start, any tensions can be reduced.

The rocker arm 2 shown in Fig. 1 is only a Ausführt! example. It is conceivable to harden other actuating or bearing components by mechanically induced martensite formation. Mention may be made here, for example, of sliding bearings in which the running surfaces of the sliding bearings, which are also formed of metastable austenite, are mechanically induced to be converted into martensite.

reference numerals

Actuator Rocker Arm Functional surface

Claims

claims

1. Mechanically resilient actuator or bearing component, consisting of an alloyed steel with an alloy content of at least 7% and ei¬ nem carbon content of 0.5 - 2.2%, with at least one mechanically loaded in use functional surface, characterized in that at least in the region of a functional surface (4), a metastable austenite with a microstructural proportion of at least 80% is present, which is at least partially converted into martensite by a mechanical treatment of the functional surface (4).

Second actuator or bearing component according to claim 1, characterized in that the functional surface (4) has a martensitic hardness of at least 55 HRC, in particular of at least 58 HRC.

3. actuator or bearing component according to claim 1 or 2, characterized gekennzeich¬ net, that the steel is a metastable austenite having fusible alloy, or that the metastable austenite is produced by a se¬ parate nitration.

4. A method for producing a control or bearing component according to one of the preceding claims, characterized gekennzeichi net that the Bau¬ part initially formed from an alloy steel with an alloy content of at least 7% and a carbon content of 0.5 - 2.2% is, during or after which the component is subjected to a temperature treatment and then the component is quenched, so that at least in the region of a functional surface of the Bau¬ part metastable austenite forms with a microstructure of at least 80%, after which the functional surface is machined, so

in that an edge zone is formed which at least partly has martensite.

5. The method according to claim 4, characterized in that the mecha¬ African processing at elevated temperature to 500 ⁰ C, at Raumtempe¬ carried temperature or at a reduced temperature up to -200 ⁰ C.

6. The method according to claim 5, characterized in that, after mechanical working at elevated ^"temperature or at a temperature Raumtem¬ deep chill treatment up to -200 ⁰ C.

7. The method according to claim 5 or 6, characterized in that after a deep-freezing treatment, a temperature treatment for tempering of the component to a maximum of 600 ⁰ C.

8. The method according to any one of claims 4 to 7, characterized in that after the component forming a deep-freezing treatment to a maximum of -200 ⁰ C, and optionally thereafter a> temperature treatment for tempering of the component to a maximum of 600 ° C.

9. The method according to any one of claims 4 to 8, characterized in that for further increase in strength, the functional surface is mechanically treated, in particular by shot peening or rolling.