EP0884396B1 - Method for manufacturing a railway wheel and railway wheel so obtained - Google Patents

Abstract

A railway wheel, comprising a rim connected to a hub by a flange which is less thick in the axial direction than the rim, is made of steel containing less than 0.35% carbon and less than 5% in total of alloying elements has an Ms point above 270 degrees C. During manufacture it is tempered and then heated at over 550 degrees C, so that at least the outer surface of the rim has mechanical properties as follows: Rm=860-960 MPa, Rp 0.2 at least 700 MPa, K1c at least 80 MPa per square m. Also claimed is a wheel of this sort, made of steel containing by weight 0.2-0.24% carbon, 0.9-1.1% manganese, 0.9-1.1% silicon, 1-1.2% chromium and 0.2-0.25% molybdenum, the rest being iron and impurities. The wheel has the mechanical properties listed above which are not affected by braking equivalent to 540 degrees C maintained for one hour.

Description

The invention relates to a steel railway wheel and its manufacturing process.

A railway wheel has a rim, the peripheral part of which constitutes the running surface and a hub which is used to mount it on an axle. In general, the rim and the hub are connected by a connecting veil which can have various forms.

When mounted on an axle, itself mounted on a bogie, the wheel is accompanied by a braking device which can be disc or shoe.

A disc brake device consists of one or more discs mounted on the axle and brake shoes that can be tightened on the discs. Such a device has the advantage of separating the rolling and braking functions, therefore allow to optimize separately the characteristics of the discs and the running surface. On the other hand, it has the disadvantage of being bulky and, therefore, to be ill-suited to small diameter wheels, for example of diameter less than six hundred and fifty millimeters. It also has the disadvantage of being too costly to be economically usable for freight wagons commodity.

A shoe braking device generally comprises two shoes and means for applying these shoes against the running surface. This device has the advantage of being less bulky than the previous one, but it makes the two fill rolling and braking functions by the same surface, which presents disadvantages. In particular, it is not possible to optimize the characteristics of the running surface since the requirements of each function are not not the same. In addition, the braking which is done by friction on the surface of bearing accelerates wheel wear.

To remedy this drawback, it has been proposed to produce a brake wheel which combines the advantages of the disc braked wheel and the disc braked wheel hoofs. This wheel essentially comprises a rim sufficiently massive to that the lateral flanks can serve as a bearing surface for the hooves which come grip the wheel as the brake shoes do for the locking devices disc braking. With this type of wheel, which generally does not have a web, friction braking on the lateral flanks generates overheating. This overheating, by transmitting to the hub, can deteriorate the setting of the wheel on the axle, or even cause an unacceptable heating of the grease of the bearing boxes. Also, in order to avoid these drawbacks, it has been proposed, in the French patent application FR 2 708 891, to produce a brake wheel comprising a constriction between the rim and the hub, forming a kind of veil, intended to provide a thermal barrier function between the rim and the hub.

Railway wheels, whether of the conventional type or of the wheel type brake, are made of steels defined in standard UIC 812-3 (UIC: Union International Railways). These are either carbon steels containing 0.48% to 0.70% carbon, less than 0.5% silicon, less than 0.9% manganese, less than 0.3% chromium, less than 0.3% copper, less than 0.08% molybdenum, less than 0.3% nickel, and less than 0.05% vanadium. The wheels are either standardized to obtain a ferrite-perlite type structure having a tensile strength of between 600 and 940 MPa, either hardened and returned to obtain a structure also of the ferrite-perlite type, but having a tensile strength of between 780 and 1050 Mpa. In general, quenching is limited to the running surface. But, for certain wheels, the hardening is performed in bulk.

It has also been proposed to produce steel wheels of the 25CMSD4 type. quenched and tempered to obtain a tensile strength of between 1100 and 1200 MPa. This steel contains between 0.26% and 0.29% carbon, approximately 1% of manganese, about 1% silicon, about 1.1% chromium and between 0.26% and 0.29% molybdenum. With this steel, the structure is sometimes bainitic in the hardened areas.

Regardless of the grade of steel used, when the wheels are hardened and tempering, tempering is carried out at a temperature less than or equal to 510 ° C., maximum tempering temperature that can be achieved while satisfying the conditions imposed by standard UIC 812-3, intended to guarantee satisfactory service.

All of these metallurgical solutions have drawbacks, either because that the running surfaces resist poor loads, either because the wheels wear the rails too much, either because the braking causes cracks friction surfaces of the brake shoes, or, finally, because cracks are gradually form in the connection area of the rim and the web. These wheel damage, which is not mutually exclusive, and which is generated by operation, reduce the service life of the wheel and must be combated.

Furthermore, the mechanical characteristics of the wheels thus treated are deteriorated by heavy braking, in particular by holding braking when crossing passes in mountainous regions. This results in disadvantages for certain uses, such as transporting goods in some regions.

The aim of the present invention is to propose a metallurgical solution for the manufacture of a railway wheel, more particularly a rail wheel braked by a shoe, and in particular a brake wheel, which significantly improves the service life of this wheel, in particular by reducing its sensitivity to braking.

To this end, the subject of the invention is a method of manufacturing a railroad wheel of the type comprising a hub, a rim comprising a rolling surface and lateral flanks, and a connecting web between the hub and the rim, the thickness of the connecting veil being substantially reduced compared to the thickness of the rim measured between the lateral flanks, this railway wheel being made of a low alloy steel whose sum of the contents of elements of alloy is less than 5%, and whose chemical composition is such that, in% by weight: 0.2% ≤ C ≤ 0.24% 0.9% ≤ Mn ≤ 1.1% 0.9% ≤ If ≤ 1.1% 1% ≤ Cr ≤ 1.2% 0.2% ≤ Mo ≤ 0.25% Ni ≤ 0.3% Cu ≤ 0.3% Sn ≤ 0.04% P ≤ 0.035% S ≤ 0.035%, the remainder being iron and impurities resulting from the production, and whose Ms point is greater than 270 ° C. According to this process, hardening is carried out on the wheel and then tempering at a temperature greater than or equal to 550 ° C. in order to obtain, at least in the vicinity of the rolling surface and the lateral flanks of the rim, the following mechanical characteristics : 860 Mpa ≤ Rm ≤ 960 Mpa rp 0.2 ≥ 700 MPa K1c ≥ 80 MPa.m 1/2 , and a structure of ferrito-pearlitic steel.

Preferably, the quenching is limited to the rolling surface and the lateral sides of the rim.

The railway wheel can be, in particular, of the brake wheel type, say, a wheel in which the lateral flanks of the rim directly realize bearing surfaces for brake linings.

Finally, the invention relates to a railway wheel according to claim 4. In particular, such a wheel is made of steel, the sum of the contents of alloying elements of which is less than 5%, and the chemical composition of which comprises , in weight : 0.2% ≤ C ≤ 0.24% 0.9% ≤ Mn ≤ 1.1% 0.9% ≤ If ≤ 1.1% 1% ≤ Cr ≤ 1.2% 0.2% ≤ Mo ≤ 0.25% Ni ≤ 0.3% Cu ≤ 0.3% Sn ≤ 0.04% P ≤ 0.035% S ≤ 0.035% the remainder being iron and impurities resulting from production, the mechanical characteristics being, at least in the vicinity of the rolling surface and of the lateral sides of the rim: 860 Mpa ≤ Rm ≤ 960 MPa rp 0.2 ≥ 700 MPa K1c ≥ 80 MPa.m 1/2 These characteristics are not affected by braking equivalent to maintaining at 540 ° C for 1 hour.

The invention will now be described in more detail, but not restrictive, opposite the single appended figure which represents, in section, a half radial section of a brake wheel.

The wheel, of revolution around the axis 1, comprises a hub 2 pierced with a hole axial 3 intended to receive an axis not shown, a rim 4 and a web 5 for connection between the rim 4 and the hub 2. The thickness of the web 5 is substantially more smaller than the thickness of the rim 4, these two thicknesses being measured parallel to the axis 1. The rim 4 has on the one hand a rolling surface 6 bordered on one side by a flange 7, and on the other hand two lateral flanks 8a and 8b which each have a friction surface 9a and 9b on which one can apply two brake pads 10a and 10b. The friction surfaces 9a and 9b are each separated from the most peripheral part 11 of the rim 4, by two grooves annulars 12a and 12b.

When the wheel is operated, the rolling surface 6 is in contact with a rail not shown, and supports all the load. As a result, it is subject to rolling fatigue. The rotation can be done with a certain slip, it is particularly the case during braking, and this sliding causes wear. The running surface must resist as best as possible the forces resulting from these phenomena which also generate similar phenomena on the rail, and the rail must resist it. So that the running surface resists fatigue well bearing, the yield strength of the steel in the vicinity of the bearing surface, i.e. over a certain depth under the running surface, must be greater than 700 MPa, and preferably greater than 800 MPa, and so that it good resistance to wear, hardness or tensile strength of steel must greater than 860 MPa. However, if the hardness of the running surface is too large, the rail wears out very quickly. Also, the tensile strength of the steel must remain less than 960 MPa, and preferably less than 940 MPa.

During braking by tightening the pads 10a and 10b against the surfaces 9a and 9b of the lateral flanks 8a and 8b of the rim, the friction generates a very significant local heating and complex phenomena which result in wear, possibly formation small, fragile, hardened areas, and by initiating cracks. Completely comparable phenomena can be generated on the running surface by the friction of the wheel on the rail, for example in the event of inadvertent locking of the wheel, or, quite simply, in the event of braking in the case of braked wheels. by shoes coming to be applied on the running surface. To avoid too rapid deterioration of these surfaces 9a and 9b, and more generally of the surfaces on which the brake pads or brake shoes rub, the steel must have a point Martensitic transformation start point greater than 270 ° C., and preferably above 285 ° C. To avoid rapid propagation of cracks, in the vicinity of these friction surfaces, the steel must have sufficient toughness so that the K1c is greater than 80 Mpa.m ^1/2 . More precisely, when performing a plurality of tests to measure K1c, all the individual values must be greater than 70 Mpa.m ^1/2 , and the average must be greater than 80 Mpa.m ^1/2 .

The inventors have also found that, during braking, the temperature of the rim could exceed 500 ° C, and that the corresponding temperature rise was equivalent to maintaining at 540 ° C for 1 hour. Also, the structure of the steel in this part of the wheel must be such that the mechanical characteristics do not are not affected by such overheating.

Finally, the connection area between the rim and the web is subjected to forces which can cause cracks. To limit the risk of cracking in these areas, it is very desirable that these areas have constraints compression residuals.

To obtain these characteristics, a low-alloy steel as defined in the claims is used, and whose chemical composition contains, by weight, at most 5% of alloying elements, and less than 0.24% carbon. The carbon content is limited to 0.24% in order to avoid the formation of cracks on the surface during braking. Carbon content and the contents of alloying elements must be chosen to allow obtaining by quenching, a ferrito-pearlitic structure which, after tempering at a temperature higher than 550 ° C, allows to obtain the characteristics defined above. Of preferably, the hardenability of the steel should not be too great to allow obtain residual compression stresses in the connection area between the rim and the veil. Indeed, these residual constraints cannot be obtained only by a partial hardening of the rim which does not affect the web.

• de 0,2 % à 0,24 %, et, de préférence, de 0,205 % à 0,235 % de carbone afin d'obtenir une limite d'élasticité suffisante, une résistance pas trop importante et un point Ms suffisamment haut ;
• de 0,9 % à 1,1 %, et, de préférence, de 0,95 % à 1,03 % de manganèse pour obtenir une trempabilité suffisante sans qu'elle soit trop importante,
• de 0,9 % à 1,1 %, et, de préférence, de 0,95 % à 1,03 % de silicium, car cet élément améliore la résistance à l'usure, cependant, en trop grande quantité, il fragilise l'acier ; de 1 % à 1,2 %, et, de préférence, de 1,05 % à 1,13 % de chrome pour améliorer la trempabilité et obtenir un rapport Re/Rm satisfaisant ;
• de 0,2 % à 0,25 %, et, de préférence, de 0,22 % à 0,25 % de molybdène, pour permettre d'effectuer un revenu à une température supérieure à 550 °C sans que la trempabilité soit trop augmentée, en particulier pour éviter la formation de bainite dans les zones trempées ;

le reste étant du fer et des impuretés ou résiduels résultant de l'élaboration.The chemical composition of steel includes, by weight:

• from 0.2% to 0.24%, and preferably from 0.205% to 0.235% of carbon in order to obtain a sufficient elastic limit, not too high a resistance and a sufficiently high Ms point;
• from 0.9% to 1.1%, and preferably from 0.95% to 1.03% of manganese to obtain sufficient quenchability without being too great,
• from 0.9% to 1.1%, and preferably from 0.95% to 1.03% silicon, since this element improves wear resistance, however, in too large a quantity, it weakens the 'steel; from 1% to 1.2%, and preferably from 1.05% to 1.13% chromium to improve the hardenability and obtain a satisfactory Re / Rm ratio;
• from 0.2% to 0.25%, and preferably from 0.22% to 0.25% molybdenum, to allow tempering to be carried out at a temperature above 550 ° C. without the quenchability being too increased, in particular to avoid the formation of bainite in hardened areas;

the remainder being iron and impurities or residues resulting from the production.

Residuals are, in particular, nickel and copper, the contents of which must, preferably, remain less than 0.3%, and better still, less than 0.2%.

The impurities are, in particular, tin, the content of which must preferably be remain below 0.04%, and better still, below 0.025%, the phosphorus of which the content should preferably remain less than 0.035%, and better still, less at 0.02%, and the sulfur, the content of which must preferably remain below 0.035%, and better still, less than 0.02%.

The wheel is produced by hot forging of a piece of steel in accordance with prior art, then it is subjected to a heat treatment of quenching and tempering.

The quenching treatment is carried out after heating the wheel above the AC point ₃ of the steel, by rapid cooling, for example, with water. Water cooling can affect the entire wheel, but it is preferable to cool only the peripheral parts of the rim with water, that is to say, the running surface and the sidewalls. . In fact, it is by performing a partial hardening that residual compression stresses can be generated in the connection area of the rim and the web. After the partial hardening, the wheel is allowed to cool down in the air. Partial hardening can advantageously be carried out on the wheel arranged vertically and rotating on its axis, the coolant being concentrated on the part of the rim located at the bottom. Partial hardening can lead to a bainitic structure being obtained in the vicinity of the running surface and the lateral flanks, in an area corresponding, for example, to the hatched part of FIG. 1. The presence of bainite is avoided by suitably adjusting the composition chemical, and in particular by limiting the molybdenum content to a maximum of 0.25%.

After quenching, tempering is carried out at a higher temperature at 550 ° C. for a time comprised, preferably, between 0.5 and 3 hours, but preferably the tempering temperature should remain below 600 ° C. Income at such a high temperature provides properties mechanical insensitive to overheating caused by braking.

Claims (5)

1. A method of manufacturing a railway wheel of the type comprising a hub, a rim having a tread and lateral flanks, and a web connecting the hub and the rim, the web being significantly thinner than the rim between its lateral flanks, and made of a low-alloy steel in which the total content of alloying elements is less than 5% and whose chemical composition includes, by weight: 0.2% ≤ C ≤ 0.24% 0.9% ≤ Mn ≤ 1.1% 0.9% ≤ Si ≤ 1.1% 1% ≤ Cr ≤ 1.2% 0.2% ≤ Mo ≤ 0.25% Ni ≤ 0.3% Cu ≤ 0.3% Sn ≤ 0.04% P ≤ 0.035% S ≤ 0.035%, the remainder being iron and manufacturing impurities, and whose Ms point is greater than 270°C, in which method the wheel is at least partly quenched and annealed at a temperature greater than 550°C so that after quenching and annealing, at least in the vicinity of the exterior surfaces of the rim, the mechanical characteristics of the steel are as follows: 860 MPa ≤ Rm ≤ 960 MPa Rp0.2 ≥ 700 MPa K1c ≥ 80 MPa.m1/2, and the structure of the steel is a ferrite-perlite structure.
2. A method according to claim 1, characterised in that quenching is restricted to the tread and to the lateral flanks of the rim.
3. A method according to claim 2, characterised in that the quenching is applied to the wheel when it is disposed vertically and rotating about a horizontal axis.
4. A railway wheel of the type comprising a hub, a rim having a tread and lateral flanks, and a web connecting the hub and the rim, the web being significantly thinner than the rim between its lateral flanks, and made of a low-alloy steel in which the total content of alloying elements is less than 5%, whose Ms point is greater than 270°C and whose chemical composition includes, by weight: 0.2% ≤ C ≤ 0.24% 0.9% ≤ Mn ≤ 1.1% 0.9% ≤ Si ≤ 1.1% 1% ≤ Cr ≤ 1.2% 0.2% ≤ Mo ≤ 0.25% Ni ≤ 0.3% Cu ≤ 0.3% Sn ≤ 0.04% P ≤ 0.035% S ≤ 0.035%, the remainder being iron and manufacturing impurities, and in that, at least in the vicinity of the exterior surfaces of the rim, the structure of the steel is a ferrite-perlite structure and the mechanical characteristics of the steel are as follows: 860 MPa ≤ Rm ≤ 960 MPa Rp0.2 ≥ 700 MPa K1c ≥ 80 MPa.m1/2, the above mechanical characteristics not being affected by braking equivalent to maintaining a temperature of 540°C for one hour.
5. A railway wheel according to claim 4, characterised in that it is a brake wheel and the lateral flanks of the rim provide bearing surfaces for brake linings.

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