GUIDE AND SUPPORT ELEMENT FOR RAILWAY VEHICLE

Description

[0001] The present invention relates to the field of guide elements and rolling support for railway vehicles and the welding of these elements together and more particularly to the field of track switches and the welding of these to rails.

[0002] In the railway sector, crossing frogs and other track components must withstand repeated passage of rolling stock. It is therefore essential that these components achieve sufficient hardness levels to resist the repeated pressures exerted by moving railway vehicles. Publication WO 2015 / 182743 provides an example of a composition for optimizing hardness on the top surface of a rail.

[0003] A common solution for ensuring a minimum level of hardness is the use of cast steel with a manganese composition, which gives it an austenitic structure. This manganese steel, also known as Hadfield steel, has a hardness of 220 HB. After an explosion hardening process, this steel can achieve a hardness of 320 HB.

[0004] However, implementing this solution results in track components whose repeated vehicle traffic leads to deformation of the track surfaces. This deformation necessitates on-site intervention involving the reprofiling of the track components to prevent deterioration and the premature appearance of cracks. Furthermore, during the casting process, casting defects can occur, leading to damage to the track components when a vehicle, even a light one, travels near the casting defect.

[0005] Furthermore, while this steel meets the hardness requirements for track switch components, it has the drawback of not allowing for the production of parts that can be directly welded to each other or to associated rails. Indeed, welding a Hadfield steel track switch component to a rail requires the addition of a stainless steel insert to overcome the slow cooling imposed by the rail steel. The welding time for such a connection between a switch and a rail is therefore twice as long due to the essential presence of this insert.

[0006] To overcome the drawbacks associated with manganese steel, an alternative solution is the use of hardened, rolled, martensitic steel. This steel has the advantage of allowing the production of parts with a hardness between 380 HB and 400 HB.

[0007] However, the martensitic structure of this steel changes at temperatures as low as 250°C, which, during preheating and welding, leads to a rapid degradation of the steel's original hardness. Therefore, welding a track switch component made of this steel compromises its quality and results in premature wear of the part in service. Furthermore, this steel exhibits low ductility and toughness, which contributes to the rapid propagation of cracks.

[0008] The present invention aims to overcome this drawback by proposing a steel railway vehicle bearing guide and support element whose composition allows it to meet the hardness requirements imposed by the function of this bearing support piece, while allowing direct weldability without insert piece of the crossing core with a second element without excessive alteration of its hardness properties.

[0009] To this end, the invention relates to a guide and bearing support element for a railway vehicle, characterized in that at least a portion positioned in the upper part of the element and forming the running surface is made of steel whose composition includes, in addition to Fe: 0 , 15 ≤ C ≤ 0,3 % , 1 ≤ Mn ≤ 2 % , 0 , 2 % ≤ Ni ≤ 1 % , 0 , 5 ≤ Cr ≤ 2 % , steel exhibiting a mixed structure of tempered martensite and bainite and residual austenite after being heat-treated with quenching and controlled speed and duration.

[0010] The invention also relates to a method for assembling at least one element according to the invention with a complementary part by direct spark welding, comprising in particular: a first step carried out by a first sparking phase intended to increase the temperature of the surfaces to be welded in a homogeneous manner, the duration of this first step being between 15 s and 40 s, a second step carried out by a preheating phase by Joule effect of the parts to be welded, the duration of this second step being between 45 s and 55 s with a heating intensity between 55 kA and 70 kA, a third step carried out by a second sparking phase to deoxidize the faces to be welded while avoiding their re-oxidation, the duration of this third step being between 12 s and 22 s, with a sparking intensity between 16 kA and 19 kA and a travel speed at the end of sparking between 2mm / s and 3mm / s, a step of bringing the surfaces to be welded into contact.

[0011] A direct weld of at least one element according to the invention, made entirely of steel of the aforementioned composition, with at least one rail obtained by an assembly process according to the invention, is characterized in that the breaking force F, expressed in kN, of the weld in bending according to EN14587-3 is greater than the product of the modulus of inertia W at the level of the pad, expressed in cm³, by 4.261 according to the formula: F ≥ 4 , 261 x W patin

[0012] The invention will be better understood from the following description, which relates to at least one preferred embodiment, given by way of non-limiting example, and explained with reference to the accompanying schematic drawings, in which: there figure 1 is a schematic representation of an example of the construction of an element of the invention made from a single steel of the claimed composition, the figure 2is a schematic representation of an example of the construction of an element of the invention made by superimposing two different types of steel.

[0013] It should be noted that, in this document, the expression "rail vehicle guidance and rolling support element" refers to track and rail equipment and, more particularly, to the various components of this track equipment, including crossing frogs, crossing frogs, frog points, switches, check switches and half switches.

[0014] The invention relates to a guide and bearing support element 2 for a railway vehicle, characterized in that at least a portion positioned in the upper part of the element 2 and forming the running surface is made of a steel 1 whose composition includes, in addition to Fe: 0 , 15 ≤ C ≤ 0,3 % , 1 ≤ Mn ≤ 2 % , 0 , 2 % ≤ Ni ≤ 1 % , 0 , 5 ≤ Cr ≤ 2 % , steel 1 exhibiting a mixed structure of tempered martensite and bainite and residual austenite after being heat-treated with quenching and controlled speed and duration.

[0015] According to a particular construction, the guiding and supporting element 2 consists of a superposition of at least two different types of steel 1, 1bis in the form of a "sandwich", so that the upper portion of the element is formed of a steel 1 of the aforementioned composition.

[0016] According to a particular preferred alternative construction, element 2 of the invention is characterized in that the whole of element 2 is made with a steel 1 of the aforementioned composition.

[0017] For this second construction feature, the construction of an element 2 made entirely of steel 1 of this composition and with such a structure allows us to take advantage of the high mechanical strength properties of steel 1 to meet the recurring wear and impact stresses borne by the track switch, while ensuring optimal weldability. This optimization of weldability is characterized in particular by various tests detailed in standard EN14587-3, specifically specified in paragraphs §10.4.9 and §10.4.10.

[0018] It is therefore possible to characterize the resistance of the guide and bearing support element 2 of the invention thanks to certain properties of the steel 1, which are in particular: an elastic limit at 0.2% strain (Rp 0.2%) which is greater than 1050 MPa, a limit at break (Rm) which is greater than 1400 MPa, an elongation at break (A%) which is greater than 11%.

[0019] Thanks to the low carbon concentration compared to manganese steel and the heat treatment of the steel 1 in component 2 of the invention, the weldability of the component is optimized. A carbon concentration in steel 1 between 0.15% and 0.3% makes it possible to obtain, on the one hand, a sufficiently high hardness of steel 1 and, on the other hand, good weldability. Combining these two properties is difficult to achieve because carbon concentrations favoring these properties are incompatible.

[0020] According to a particular property, element 2 of the invention, constructed with such steel 1, is characterized in that its surface hardness exceeds 440 HB. This initial surface hardness has the advantage of being further improved by work hardening, for example in service, to increase it to a hardness exceeding 540 HB. Such hardness thus slows the wear rate of the track switch in use. Constructing a crossing frog with such steel 1 also eliminates the risk of deformation of the track surfaces by limiting, or even eliminating, the need for on-site reprofiling.

[0021] The metallurgical structure composed of tempered martensite, bainite and residual austenite obtained through chemical composition in combination with a controlled cooling quenching heat treatment and tempering allows the realization of a wear-resistant cross core whose material surface is capable of working hardening in service.

[0022] According to a particular construction feature, element 2 according to the invention is characterized in that the quantity of nickel is less than 0.8%. Preferably, the quantity of nickel is on the order of 0.4%.

[0023] According to another construction feature, element 2 according to the invention is characterized in that the amount of carbon is greater than 0.2%.

[0024] According to another construction feature, element 2 according to the invention is characterized in that the quantity of manganese is less than 1.5%.

[0025] According to another construction feature, element 2 according to the invention is characterized in that the amount of chromium is less than 1.5%.

[0026] According to a particular construction feature, element 2 of the invention has a height ranging from 80 mm to 200 mm. The steel 1 used in element 2 of the invention allows for the production of a part with a thickness of approximately 200 mm without altering its strength and hardness properties. This property thus permits the construction of elements 2 with significant variability in thickness, while maintaining homogeneity of hardness and direct weldability.

[0027] The invention also relates to a method for assembling at least one element 2 according to the invention with a complementary part 4 by direct spark welding, comprising in particular: a first step carried out by a first sparking phase intended to increase the temperature of the surfaces to be welded in a homogeneous manner, the duration of this first step being between 15 s and 40 s, a second step carried out by a preheating phase by Joule effect of the parts to be welded, the duration of this second step being between 45 s and 55 s with a heating intensity between 55 kA and 70 kA, a third step carried out by a second sparking phase to deoxidize the faces to be welded while avoiding their re-oxidation, the duration of this third step being between 12 s and 22 s, with a sparking intensity between 16 kA and 19 kA, a step of bringing the surfaces to be welded into contact.

[0028] According to a particular implementation of the process of the invention, the first sparking phase is preferably carried out for a duration greater than 30 s. Such a duration makes it possible to guarantee a uniformity and homogeneity of temperature on the section of the element 2 of the invention to be welded.

[0029] According to another complementary feature of the implementation of the invention, the preheating phase is carried out with an intensity of approximately 60 kA so that the characteristics of steel 1 are not excessively affected. Thus, although the hardness of element 2 varies in the heat-affected zone during this preheating, it should be noted that in this zone, the average hardness is approximately 370 HB.

[0030] According to another implementation feature, the assembly process according to the invention is characterized in that, at the end of the second sparking phase, the feed rate is between 2 mm / s and 3 mm / s.

[0031] According to a specific feature of this additional implementation of the process of the invention, the advance speed of the second sparking phase remains sufficiently slow to avoid any short circuit, preferably being between 2 mm / s and 2.8 mm / s.

[0032] It should be understood that in the context of an on-site installation, the supplementary part 4 is generally made up of a section of rail intended to be positioned in line with a track switch.

[0033] A direct weld 3 of an element 2 is made entirely with steel 1 of the aforementioned composition with at least one rail 4, obtained by an assembly process according to the invention. This direct weld 3, i.e. without an insert, obtained by the process of the invention, is characterized in that the breaking strength F, expressed in kN, of the weld 3 in bending according to EN14587-3 is greater than the product of the modulus of inertia W at the level of the pad, expressed in cm³, by 4.261 according to the formula: F ≥ 4 , 261 x W patin

[0034] This breaking strength in bending is measured in the context of a test carried out according to the standard EN14587-3, detailed in paragraph §10.4.7 and in its annex B, after welding an element 2 of the invention with a rail 4.

[0035] According to a particular feature of this direct weld 3, the breaking strength is greater than 1,600 kN for a rail section 4 with a 60E1 profile whose inertia modulus W in the foot is equal to 375.5 cm³. By comparison, welding an identical rail to a conventionally produced austenitic manganese steel crossing frog only guarantees a bending breaking strength of around 850 kN for the same rail profile.

[0036] Furthermore, it should be noted that the resistance obtained by a direct weld 3 of the invention between an element 2 according to the invention made entirely of steel of the aforementioned composition and a rail 4 corresponds to the resistances classically obtained in the context of a weld between two rails 4 of a standard track.

[0037] According to an additional feature of this direct weld 3, the fatigue resistance using the "all or nothing" method without failure is at least 5 million cycles with a stress of 21 to 210 MPa. This fatigue resistance is measured in a test carried out according to standard EN14587-3, detailed in section §10.4.8 and in its Annex D. For comparison, a conventional single-core weld in austenitic manganese steel exhibits a resistance without failure of 5 million cycles with a stress of only 14 to 144 MPa.

[0038] Of course, the invention is not limited to the embodiment described and shown in the accompanying drawings. Modifications remain possible, particularly with regard to the composition of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention as defined by the claims.

Claims

1. Rolling support and guide element (2) for a railway vehicle, characterized in that at least a portion positioned in the upper part of the element and forming the rolling surface is produced with a steel (1), the composition of which comprises, in addition to Fe: - 0.15 ≤ C ≤ 0.3 % , - 1 ≤ Mn ≤ 2 % , - 0.2 % ≤ Ni ≤ 1 % , - 0.5 ≤ Cr ≤ 2 % , the steel (1) having a mixed structure of tempered martensite and residual austenite and bainite after having been heat treated with quenching and at controlled rate and duration.

2. Element (2) according to Claim 1, characterized in that the whole of the element is made with a steel (1) of the composition according to Claim 1.

3. Element (2) according to either of Claims 1 and 2, characterized in that the quantity of nickel in the composition of the steel is of the order of 0.4%.

4. Element (2) according to one of the preceding claims, characterized in that the surface hardness is greater than 440 HB.

5. Element (2) according to one of Claims 1 to 4, characterized in that the element has a height of between 80 mm and 200 mm.

6. Method for assembling at least one element (2) according to one of Claims 1 to 5 with a complementary piece (4) by direct flash welding, comprising in particular: - a first step carried out by a first flashing phase intended to increase the temperature of the surfaces to be welded in a homogeneous manner, the duration of this first step being between 15 s and 40 s, - a second step carried out by a phase of preheating by Joule effect of the parts to be welded, the duration of this second step being between 45 s and 55 s with a heating current of between 55 kA and 70 kA, - a third step carried out by a second flashing phase to deoxidize the faces to be welded while avoiding their re-oxidation, the duration of this third step being between 12 s and 22 s and with a flashing current of between 16 kA and 19 kA, - a step of bringing the surfaces to be welded into contact.

7. Assembly method according to Claim 6, characterized in that, at the end of the second flashing phase, the speed of advance is between 2 mm / s and 3 mm / s.

8. Assembly, characterized in that the assembly is formed by at least one element (2) according to one of Claims 2 to 5 assembled to a rail (4).