EP0542951B1 - Process for tempering a rail vehicle wheel - Google Patents

Abstract

In a process for tempering at least parts of a wheel for rail vehicles, the tempering temperature is kept at least approximately constant or intermittently altered in the range of the temperature/time curves for the beginning and end of austenitic conversion. This provides a rail vehicle wheel with improved high-speed behaviour.

Description

The present invention relates to a process for isothermal tempering a wheel for rail vehicles with the on the points of the wheel surface that are subject to wear pearlitic structure is generated.

For speeds in excess of 160 km / h on rail vehicles normally full wheels are used. These are mainly made of unalloyed carbon steels manufactured and subjected to a heat treatment. Become state of the art Normal annealing and tread remuneration after UIC code 812-3 V. The tread remuneration consists of a continuous cooling of the Cooling ring by cooling with water and a subsequent tempering.

The strength and toughness of the rail wheels can also be increased by adding alloying elements. In this sense, the prior art includes AT-A-344 241, DE-A-24 57 719, DE-A-24 25 187 and DE-A-31 11 420 A1, as well as the publications Haverkamp K. -D., Forch K. and Werber K .: Influence of R _e / R _m and Strain Hardening on the Wear Behavior of Wheels, lecture collection for the International Wheels Congress Montreal 1988, Catot B. and Tourrade J.-C., Nouvelles nuances d 'acier pour roues monoblocs, Revue Générale des Chemins de Fer 105 (1986), pp. 169/180, and Forch K., 15 years of wheel / rail research program of the Federal Ministry for Research and Technology-Wheel Research, Thyssen Technical Reports, H2 (1985 ), Pp. 228/232.

Those with such additions of alloying elements provided raw materials for rail wheels subjected to a heat treatment and then quenched with oil. The resulting structure brings improved properties of these rail wheels.

Remuneration is based on a customary procedure from a continuous cooling process from the austenitizing temperature to temperatures below the formation of martensite without an intermediate stopping time and a subsequent starting process. The the resulting structure leads to a reduction in wear, however reacts in its wear characteristics overly sensitive to fluctuations in hardness in the tread area, which means continuous operation Deviations from the geometric roundness of the wheels occur. Especially under high speed conditions follow from this unacceptable Vibration exposure for vehicle and passenger.

DE-B-1 261 149 describes a method for tempering rail vehicle wheels known with which an independent of the wheel hardness Wear behavior achieved in the tread area becomes. Isothermal tempering creates a pearlitic structure generated, which leads to lower wear resistance, which, however, is approximately constant regardless of the hardness. This also applies to those arising from this type of remuneration Printing properties prevented. According to a variant, controlled cooling and subsequent tempering becomes one achieved higher wear resistance, but that of the Hardness is dependent.

It has been recognized that the procedural Fluctuations in hardness must be minimized and above In addition, the resulting structure is much smaller Wear sensitivity to remaining Must have residual fluctuations in hardness.

The present invention is therefore the Based on the task to create a procedure for the remuneration of wheels, as initially mentioned was defined. This is a heat treatment of the wheel material or at least to provide parts of the same, both for full rail vehicle wheels as well as for two-piece rail vehicle wheels. This treatment needs to be more common Rail wheel qualities an independent of the wheel hardness Wear behavior in the tread area guarantee. The material should be after the heat treatment have a uniform wear behavior with the highest possible hardness overall, in particular high tread hardness, so that the friction work lower in operation.

In terms of the task, heat treatment performed according to the characterizing part of claim 1.

The invention is then based on, for example explained by figures.

Fig. 1 bis 3

isotherme ZTU-Schaubilder für die Austenitumwandlung in einen Kohlenstoffstahl mit Perlit-Ferrit-Gefüge;

Fig. 4

eine schematische Darstellung eines Vollradvergütungsbades;

Fig. 5

eine Ansicht eines Partialtauchbades zur Vergütung des Radkranzes;

Fig. 6

ein Duschbad mit Duschring;

Fig. 7

eine weitere Vorrichtung zum Wärmebehandeln eines Schienenrades auf der Basis von Induktionsströmen;

Fig. 8 und 9

je eine Anordnung analog derjenigen gemäss Fig. 7 mit jeweils nebeneinander angeordnetem Dusch- und Induktions-Heizring.

Show it:

1 to 3

isothermal ZTU diagrams for the austenite transformation into a carbon steel with pearlite-ferrite structure;

Fig. 4

a schematic representation of a full-wheel compensation bath;

Fig. 5

a view of a partial immersion bath for remuneration of the wheel rim;

Fig. 6

a shower room with shower ring;

Fig. 7

another device for heat treating a rail wheel based on induction currents;

8 and 9

an arrangement analogous to that according to FIG. 7, each with a shower and induction heating ring arranged next to one another.

In these time / temperature conversion diagrams (ZTU diagrams), two curves C-shaped are drawn in between FIGS. 1 to 3 between temperatures A ₁ and M _s . A _{1 means} the highest transformation temperature at which the austenite transformation begins, while M _{s represents} the limit temperature below which martensite forms immediately, the amount of which increases as the cooling decreases.

The solid curves represent the course of the heat treatment of the rail wheel material parts.

1 to 3, the wheel material is first brought to at least the austenitizing temperature A ₃ and then quenched in such a way that the martensite forming temperature M _s according to line 1 is not reached. This quenching process is finished in point 2.

Now, in contrast to the previous procedure, no continuous cooling, but in the sense of 1 a quasi-isothermal treatment 5 inside the two dash-dotted, c-shaped Limit curves which indicate the start of austenite transformation and indicate the end of austenite transformation.

After completing the austenite transformation, at which if the temperature is above 300 ° C, this takes place slowed down cooling that the formation of residual stress is largely avoided.

The austenite transformation according to Fig. 1 is not completely isothermal, but quasi-isothermal. The temperature remains in the mean constant and above 300 ° C as this is the chosen one Line 5 shows. After the austenite transformation ends, there is a slow one Cool down, as is the curve part 6 of FIG. 1 reveals.

The desired effect of remuneration will be reached when inside the wheel rim cross section through intermittent cooling and subsequent Warming from the core area or, if necessary, the temperatures such as by external heat supply that vary as a result of structural change the desired hardness is achieved. It is m.a.W. a quasi-isothermal in the area of austenite transformation Intermittent treatment by cooling and heating evenly, in the sense of Fig. 3, curve 9, or increasing, in the sense of FIG. 2, curve 8, performed. This curve can basically also be falling.

As shown in Fig. 4, this will be at the austenitizing temperature heated wheel 10 completely in one Metal or salt bath 11 immersed in the conversion in the desired structural level. The temperature the bath is in a corresponding manner, for example by means of Heat removal through a heat exchanger 12, see hold isothermal long until austenite transformation completed in the corresponding bike areas and thus the isothermal coating of the wheel.

The remuneration takes place in the partial immersion bath according to FIG. 5 of the wheel rim even with only partial coverage the wheel through a bath 11, for example a metal, Oil, salt or water bath. By sufficient Rotational speed of the wheel is ensured that in the relevant areas of the wheel 10 sets a steady temperature condition. Also here there is a heat extraction corresponding to that according to Fig. 4.

5 with a shower ring or a segment-like shower element can be added, with which the heat treatment of the rotating wheel can be controlled such that from the cooling phase and self-starting from the still warm ones Zones out a constant in the mean Temperature during the austenite transformation phase is achieved.

The device according to FIG. 6 enables the temperature to be reduced sufficient for the isothermal process rotating rapidly around a holding device 13 Wheel body 14 when passing through the pliers-like Cooling segment 15, in the 16 the wheel rim is cooled with water. In the case insufficient self-heating is due to that located opposite inductive heating segment 17 with the inductive Grinding 18 a wheel heating possible. The Integration of both segments in a control loop enables an isothermal heat treatment with low temperature fluctuation range.

7 consists of an above lying induction ring completely surrounding the wheel 19 20 with the inductive loop 21 and the underlying one, also closed Shower ring 22. The wheel body 19 is vertical on one turntable that can be raised and lowered into the cooling or heating zone 23 fixed. The isothermal process is through corresponding movement of the turntable 23 completed.

Fig. 8 shows a further device, which from each one arranged side by side on one level Shower 24 and inductive heating ring 25 is constructed. One horizontally and vertically below the two rings sliding turntable 26 with fixed thereon Wheel body 27 takes over the necessary transport the same in the cooling and heating zone as required of the isothermal remuneration process.

An analog device is shown in FIG. 9, in which Heating 28 and cooling rings 29 are arranged. Here will however, the transport of the wheel body 30 by a appropriate handling machine 31 made so that, the requirements of thermal quality treatment accordingly, the wheel body from above is immersed in the heating 28 or cooling ring 29.

As can be seen in FIGS. 6 to 9, such Devices with additional heating devices, here, for example, with low-frequency induction loops or flame elements, for more precise Control of the isothermal process combined will.

The described quasi-isothermal coating of the wheel rim creates a structure in which material characteristics above the quality R8 shown in UIC 812-3 are achieved. Here, mostly the tread and the flange are quenched in their cross-section and over their entire circumference, for example by water cooled down to near freezing point, to a temperature that is optimally adapted to the structural condition and lies above M _s , and furthermore over a longer one, from the Depending on the composition of the wheel material, the temperature was kept constant at this temperature and cooled in air after the desired structural state had been set.

If this involves a heated rail vehicle wheel in one Quenching box rotates, can be from the combination of short quenching and reheating phases quasi-isothermal austenite transformation. Here is the quench intensity by a preferred arrangement of the wheel in the remuneration process and by the speed of rotation and the amount of water supplied adjustable.

The resulting material structure meets the requirements which on a rail vehicle wheel for pure disc-braked wheelsets are placed in its Opposed properties by making it an overall higher Coefficient of friction in the event of stress between Wheel and rail as well as one that is almost independent of its hardness Has wear behavior. Served for this the solution according to the invention becomes more austenite-stabilizing Alloy elements, especially one increased manganese, which is also improvement serves the isothermal remuneration.

With the exception of the content of an austenite stabilizing Alloying element should be according to UIC 812-3 given steel compositions are selected, with the lower C contents (e.g. R7) to be preferred are. The desired hardness values should refer to the upper limit values (e.g. for R9).

The heat treatment methods specified for solid wheels are on wheel tires using a holding device applicable accordingly.

A rail vehicle wheel treated in this way is largely free of residual stress, so that the tendency to axial faults caused by internal stresses, decrease even without starting the wheel becomes. This also makes a different location Wear on the wheel circumference avoided because operational hardening of the wheel tread no longer any influence on the wear behavior to take.

Finally, the wheel material is one according to the invention Rail vehicle wheel a carbonaceous Steel with manganese / silicon or manganese / vanadium additives. This allows for special needs the remuneration of a rail wheel as Part of a purely disc braked wheelset the optimal boundary conditions are guaranteed. With such additives, the tensile strength and Yield strength per se of soft steels by 100 N / mm2 each 1% Mn increased. The effect is with tempered steels even stronger. There is also a significant one Improve the impact strength. About that In addition, the manganese content lowers the critical cooling rate and increases the depth of hardening.

A rail vehicle wheel manufactured according to the invention is used for this purpose targeted to a purely disc braked Wheel set designed. It largely shows one resulting isothermal austenite transformation Material condition in the rim or tire on the under the most common wheel / rail stress conditions one much less hard here Dependency of wear behavior shows than others Structural states.

The explained quality treatment results in hardnesses of over 320 HB. At a holding temperature of 500 ° C that would have been Edge structure of R7 a final hardness of 305 HB.

Such a rail vehicle wheel can also a higher wheel / rail coefficient of friction and shows no tendency to discard the wheel disc.

Claims (4)

1. A process for isothermal hardening and tempering of parts of a wheel for a rail vehicle, by means of which a pearlitic structure is produced by heat-treatment at the points on the wheel surface which are subject to wear, characterised in that, in the austenitic conversion range, quenching is effected intermittently by cooling and heating to prevent internal compressive strain.
2. A process according to claim 1, characterised in that quenching is effected intermittently at short or long intervals.
3. A process according to either one of claims 1 or 2, characterised in that the intermittent treatment in the austenitic conversion range is effected quasiisothermally, or with a rising or falling trend.
4. A process according to any one of claims 1 to 3, characterised in that, after austenitic conversion, the temperature is raised again but remains below the austenitising temperature.

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