DE102004051885A1 - Mechanically load-bearing actuator or bearing component made of mechanically hardened steel - Google Patents

Abstract

Mechanically resilient actuating or bearing component, consisting of an alloyed steel with an alloying fraction of at least 7% and a carbon content of 0.5-2.2%, with at least one functional surface mechanically loaded in use, at least in the region of a functional surface (4) a metastable austenite having a microstructural content of at least 80% is present, which is at least partially converted into martensite by a mechanical treatment of the functional surface (4).

Description

Territory of invention

The Invention relates to a mechanically loadable positioning or bearing component, consisting of an alloyed steel with an alloy content of at least 7% and a carbon content of 0.5 - 2.2%, with at least one mechanically loaded surface in use.

background the invention

Such Stell- or bearing components are known in different construction and are used in a wide variety of applications. When Stellelement are in particular engine elements such as drag or To call rocker arm, so mechanically actuated components, in turn put other components. As a bearing component is for example a roller bearing or its parts or a plain bearing and its parts like bearing bush, Bearing ring etc. to call. All these positioning or bearing components is common that at least one mechanically loaded in use Have functional surface over the For example, an actuating element in the form of a rocker arm on a Pestle or the like attacks, or in the case of a rolling bearing the rolling elements are running. The components are subject to high mechanical and tribological loads exposed, which is why it needed is to cure these components after mechanical processing. To the Dimensional and To achieve dimensional accuracy, finishing such as grinding or hard turning performed. The heat treatment itself takes place once, depending on the steel quality through hardening, e.g. at 100Cr6, or by case hardening, e.g. at 16MnCr5, or by various variants of nitriding treatments or coatings.

Of the The main disadvantage of most such treatments is the so-called hardening distortion and the resulting dimensional change. The component dimension thus varies as a result of the various particular thermal treatments between those originally present before treatment Shape or dimension and ultimately given after performing each treatment Parameter. The components are machined or chipless in the best possible microstructure and hardness conditions edited, then cured at high temperature and finally mechanically, so machined finished and, for example, by Shot blasting or rolling cold worked. Next to that in a row the thermal hardening treatment itself adjusting measure and hardness delay is the implementation the separate hardening step Furthermore also time consuming and expensive.

Summary the invention

Of the The invention is therefore based on the problem, an actuating or bearing element specify the type mentioned above, the simple and without the beginning produce dimensional and dimensional problems mentioned above is.

to solution This problem is with a mechanically strong Stell- or Bearing element consisting of the above-mentioned steel provided according to the invention, that at least in the area of a functional surface with a metastable austenite a structural component of at least 80% is present, through mechanical processing the functional area at least partially converted into martensite.

to Production of the actuator or bearing component according to the invention is a steel used, which forms a metastable austenite phase. This metastable Austenitic phase can be achieved by mechanical processing of the functional surface itself, So for example, the bearing surface of a towing or rocker arm or the tread a sliding bearing due to the mechanically induced energy locally be transformed into martensite. So there is a mechanically induced structural change and thus hardening directly in the area of the functional area.

These Properties become when using an alloyed steel with a Alloy content of at least 7% and a carbon content of 0,5 - 2,2% allows wherein the concrete steel used on the one hand a sufficiently high Has to have carbon in order to have a high martensitic hardness of more than 55 HRC, in particular from about 58 HRC. Furthermore, a corresponding "manganese nickel equivalent" (Cr-Ni) must be produced of metastable austenite at correspondingly high heat treatment temperatures be given, and finally must have a sufficient fine grain of the structure can 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% used. The fine grain and corresponding microstructural characteristics are to be ensured by the addition of, for example, molybdenum, aluminum, titanium or other alloying elements. It is also possible to use conventional tool steels such as X210Cr12 or X165CrMoV121, as used in particular for engine elements such as drag or rocker arms become.

A The second class of materials is the field of insert and tempering steels. These high-alloyed case-hardened steels such as. 14NiCrMo14 or even higher Alloy components with sums nickel-manganese-chromium greater than 7% and a Randkohlenstoffgehalt / Randstickstoffgehalt, produced by the usual case hardening or Carbonation, from 0,5 - 1,5% Carbon or 0.1-0.6% nitrogen also form a metastable austenite phase due to mechanical energy input locally converted into martensite. requirement is, that the alloying elements must be adjusted so that the martensite formation temperature after carburizing and / or nitriding during quenching not or only just below, so that an intermediate stage conversion or a Perlitzerfall falls short.

The These materials are therefore in principle capable of high Case hardening temperatures (direct or single hardening), e.g. above 1000 ° C and one fast quenching a quasi 80% or even higher austenite in the form carbon-rich edge zone, the aforementioned Carbon content is present at least in this peripheral zone, in the case Nitrous oxide should be the sum of nitrogen and carbon also lie in this area. The formed metastable austenite is therefore also available at room temperature, but is sufficient Energy input into martensite convertible, the conversion ability According to the invention of the mechanical processing depends.

The heat treatment for through hardening steels, in Frame which prefers already the transformation to the finished end component takes place, sees on the one hand the Hochtemperaturaustenitisierung and if necessary Carburizing at about 1000 - 1250 ° C and then a Quenching in salt bath until about 150 ° C or at room temperature before. Subsequently can be another cooling to room temperature in air, if still necessary. in the Result forms in the margins (if only there the sufficient high carbon content is present) or in the entire cross section an austenite portion of over 80%, preferably from above 90%, with optionally precipitated carbides and optionally Traces of martensite are present. Subsequently, the mechanical Finishing of the already formed but metastable austenite component by turning, milling or sleeping. Due to this type of structural stress on the functional surface arises in the corre sponding effective depths a mechanically induced martensitic Transformation of metastable austenite. Basically, the depth of the transformation zone depends on tool contact geometry (e.g., rake adjustment); To be generated contour, the duration and the amount of applied force and the prevailing temperature during mechanical processing.

All in all can in this way a very dimensionally stable component with a sufficient hardness be achieved in the relevant component area. The transformation of the used steel for component production is preferably carried out during the heat treatment for high-temperature austenitization. An additional high-temperature step for hardening of the material, as provided for in the prior art, is omitted after the hardening by martensitic transformation 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 a sufficiently high carbon content claimed in the invention Range is necessary is. The steel itself can, as described, have the metastable austenite be exhibiting melting alloy, but he can also by a separate nitration are generated, ie in the context of an electro-chemical Treatment.

Next the actuator or bearing component itself meets the invention itself a method for producing such a positioning or bearing component, which is characterized in that the component initially from a alloyed steel with an alloy content of at least 7% and a carbon content of 0.5 - 2.2% is formed during or after which the component is subjected to a temperature treatment, and then the component afterwards is quenched so that it is at least in the area of a functional surface of Component of a metastable austenite with a microstructural content of at least 80% forms, after which the functional area is mechanically processed, so that forms a border zone, the at least partially martensite has.

The Machining for martensite formation may be at elevated temperature preferably about 500 ° C, at room temperature or at reduced temperature to preferably a maximum of -200 ° C. In particular, the low temperature treatment is advantageous for martensite formation.

Provided the mechanical treatment at elevated temperature or at room temperature is done, it is appropriate to Improvement of the martensite formation to connect a deep-freeze treatment to preferably a maximum of -200 ° C. As a general rule can after a deep-freeze treatment a temperature treatment for starting the component up to a maximum 600 ° C done.

Also It is conceivable immediately after the component forming, ie before the mechanical treatment for martensite formation, a deep-freeze treatment up to preferably at most -200 ° C optionally after a tempering treatment up to 600 ° C interposed.

Of Furthermore, the functional surface can be used to further increase the strength also the other component surfaces after the mechanical treatment for martensite formation are post-treated mechanically, in particular by shot peening or rolling. Also a final Finishing such as grinding or honing can optionally be provided.

All in all offers the method according to the invention as well as the Stell- or Bearing component has the advantage that the hardening distortion due to the processing state is lifted once and not as in the usual process by soft machining and hard machining a double machining is required.

Short description the drawings

Further Advantages, features and details of the invention will become apparent the embodiment described below and with reference to the Drawing. This shows a schematic representation of a mechanical Control element 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 tilt lever 2 , on the front arm 3 a functional area 4 is provided, via which the rocker arm, for example, acts on a plunger. The rocker arm was made of a material which forms a metastable austenite phase during the subsequent quenching after the high-temperature austenitization, during which the temperature control of the rocker arm has been worked out.

To the functional area 4 hardening takes place now, unlike in the prior art, only a mechanical processing of the functional surface, for example by turning, milling or grinding, in the context of which processing, which is represented by the arrow B, is registered directly on the functional surface mechanical energy, the the Umklappvorgänge, ie the transformation of metastable austenite in martensite induced. It forms, as indicated by the dashed line, a region M in which a high content of martensite is present, while metastable austenite is present in the rest of the 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.

Of the Mechanical treatment for martensite formation can be as described connect a cryogenic treatment, in which the Component is cooled to, for example, -200 ° C, whereby the formation of the martensitic structure in the component edge zone M further promoted becomes. Alternatively, the processing can be carried out even at a reduced temperature done so that a separate freezing is not necessary. As part of a subsequent event, any tensions may be reduced become.

The in 1 shown rocker arms 2 represents only one embodiment. It is conceivable to harden other Stell- or bearing components by mechanically induced martensite. To call here are, for example, plain bearings, in which the running surfaces of the plain bearings, which are also formed of metastable austenite, are mechanically induced converted into martensite.

1

actuator

2

rocker arm

3

poor

4

functional surface

Claims (9)

Mechanically loadable actuator or bearing component, consisting 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 loaded functional surface in use, characterized in that at least in the region of a functional surface ( 4 ) is a metastable austenite having a microstructural content of at least 80%, which is obtained by a mechanical treatment of the functional surface ( 4 ) is at least partially converted to martensite. Stell 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. Stell or bearing component according to claim 1 or 2, characterized in that the steel is a metastable austenite having fusible alloy, or that the metastable austenite by a separate nitration is generated. Method for producing an actuator or bearing component according to one of the preceding claims, characterized that the component first of an alloyed steel with an alloying content of at least 7% and a carbon content of 0.5 - 2.2% is formed while or after which the component is subjected to a temperature treatment and then the component afterwards is quenched, so that at least in the area of a functional surface of Component of a metastable austenite with a microstructural content of at least 80% forms, after which the functional surface mechanically is processed so that forms a border zone, at least partially martensite. Method according to claim 4, characterized in that that the mechanical treatment at elevated temperature up to 500 ° C, at room temperature or at a reduced temperature to a maximum of -200 ° C. Method according to claim 5, characterized in that that after a mechanical treatment at elevated temperature or at room temperature a deep-freeze treatment to a maximum of -200 ° C takes place. Method according to claim 5 or 6, characterized that after a deep-freeze treatment a temperature treatment for starting the component up to a maximum 600 ° C takes place. Method according to one of claims 4 to 7, characterized that after the component forming a deep-freezing treatment to a maximum of -200 ° C, and optionally Thereafter, a temperature treatment for starting the component up to a maximum 600 ° C takes place. Method according to one of claims 4 to 8, characterized that the functional surface is mechanically aftertreated to further increase the strength is, in particular by shot peening or rolling.