UA34469C2 - Method for heat-treating profiled rolled metal, device for realisation the same and profiled rolled metal - Google Patents

Abstract

The invention concerns to a method for thermal treatment of profiled rolled metal, in particular, of railway rails.

Description

The invention relates to a method of thermal treatment of profiled rolled steel, in particular railway rails, with increased heat removal from parts of the profile surface when cooled from the gamma region of the iron-based material, and in the desired (desired) cross-sectional zone(s), in particular, in the zone of the head of the rails, the transformation into a fine-grained pearlite structure with increased strength, in particular, with increased resistance to abrasion and increased hardness, is carried out, and under certain conditions, deformation or bending of the rolled product is reduced, preferably mostly eliminated, in particular rail caused by warping as a result of heat treatment, perpendicular to the longitudinal axis when cooled to room temperature, in particular, after the transformation of the structure in the strongly cooled (cooled) zone (zones) of the cross section, and increased stiffness and strength are achieved when bending the rolled with alternating sign cycle.

In addition, the invention relates to a device for heat treatment of profiled rolled steel, in particular railway rails, consisting mainly of at least one zone for preparing the rolled steel on a roller conveyor with a device for positioning the rolled steel, a cooling treatment zone with devices for portioned heat removal with a high intensively from the rolled surface and with a zone for the final cooling of the rolled product to room temperature, as well as with the means (mechanisms) of laying, transverse transportation, retention and manipulation.

Finally, the invention concerns a profiled roll, in particular a railway rail, consisting of a rail head with at least a partially pearlite structure, a sole! rail and necks between the head and the sole of the rail.

Profiled rolling, in particular, railway rails, manufactured or manufactured! in most cases, it is made of iron-based alloys with a content of, wt.9o: carbon (C) 0.4-1.0; silicon (51) 0.1-1.2; manganese (Mp) 0.5-3.5; if chromium is required up to 1.5, as well as other alloying elements with a concentration of less than 195, the rest is iron and due to technological (technological) impurities.

Due to the commonly used sizes, for example, weighing from 30 kg/m to 100 kg/m, and the resulting ratio of the cross section to the perimeter of the rails when cooled after form-forming heating in still air, for example, in rolling mill refrigerators and the like, as a result of slow cooling, the structure is transformed from austenitic to a granular coarse pearlite structure, which in this case has ferrite inclusions. At the same time, the material mentioned at the beginning! with the above-mentioned structure have Brinell hardness in the range from 250 NV to 350 NV.

The growth of the expected volume of transportation and higher axial loads, as well as the desire to increase the practical use of railway rails for the service life, led to a large number of proposals for increasing the hardness and wear resistance of the material. At the same time, more favorable or improved properties of a material with a Brinell hardness of 400 HB and higher can be achieved by heat treatment and/or by means of alloying techniques.

However, the rail! in the field, among other things, in order to create seamless operating lengths or multi-line sections, we must weld well, so that the measure of alloying techniques with the aim of increasing the hardness or strength and viscosity of the material due to welding problems in most cases can be performed! only in a small amount, they can be purposefully implemented with the help of heat treatment adapted to the composition of the steel (0OE-C-3446794, 1986; EP-B-0187904, 1986; EP-B-0186373, 1986). Tayuke for economic reasons of this kind of method! they did not justify themselves on a wider scale.

In order to improve the operational quality of rails and turnout parts from the above-mentioned materials, it is possible, as is known to a specialist, to obtain a fine-grained pearlite structure by heat treatment (thermal improvement)! material At the same time, it is important to set conditions or standards during cooling! cooling, corresponding to the temperature of austenization. In the document EP-B-0293002 (1990) for that reason, for example, it is proposed that, after the initial high cooling intensity, an isothermal structural transformation of the material is practically carried out at approximately 530°C. From the application of the Federal Republic of Germany Mo 2820784 (1978), moreover, white it is known to quench rails of a certain composition in boiling water and achieve them due to additives, as well as a measure of moving the desired intensity of cooling in order to obtain a fine-grained pearlite state of the structures!.

In accordance with the Austrian patent Mo 323224 (1992), it was already proposed to manufacture rails with a homogeneous fine pearlite structure when alloyed with the help of certain cooling parameters, for example, cooling rates from 10"C/s to 20"C/s to temperatures a maximum of 550°C. However, for the above-mentioned measures, a common disadvantage is that the same intensity of cooling of the surface depending on the mass of the rolled profile can lead to different cooling rates and different structural formations in nearby surface zones, and that it is often necessary to take expensive measures in order to to avoid undesirable local structural formations or properties of the material, in particular, excessive hardness and fragility in the parts of the rail that are loaded mainly on the bend.

It was also repeatedly proposed to purposefully establish a heterogeneous microstructure in the cross section of the rail, namely in accordance with the corresponding loads. From the application of FRG Mo 3006695 (1985), for example, a method is known, according to which a hot-rolled rail is transformed over the entire cross section by cooling, after which the rail head, in particular with the help of inductive heating, is reaustenized and then hardened.

In addition, in accordance with UUO 94/02652 (1994), which describes the closest analogue of the claimed method, it was proposed to cool the profiled roll from temperatures! austenization in certain zones of the cross section, in particular, the surface of the rail head, with the same intensity in the longitudinal direction and obtaining a fine-grained pearlite structure! with increased hardness and resistance to abrasion, and cooling with different intensity in the cross-section along the periphery, which ensures straightness of the rolling stock, and the head of the rail is cooled to temperatures! on the surface from 4507C to 550"C in a cooling medium with a specially set cooling intensity, and thanks to this, a fine-grained structure is created in the head of the rail.

For this type of processing, a device for suspended hardening of rails in accordance with publication OE-4003363-C1 (1991), which is a prototype of the claimed device, is suitable, containing at least one zone of preliminary preparation of rolled steel in the form of a roller conveyor with a device for positioning rolled steel, a cooling zone in the form of a tank with a liquid for extracting heat from the rolled surface with greater intensity in the longitudinal direction, in particular the rail head, with a device for fixing the rail, a final cooling zone in the air to room temperature, a device for transverse transportation of the rolled product, a device for manipulation, allowing to transport or cool rails in a suspended position, preferably with the head down, on the refrigerator of the rolling mill, and, however, the purposeful formation of a heterogeneous structure! on the cross section is hardly possible.

As a result of applying the above-mentioned methods and devices, a rolled product such as a railway rail consisting of a rail head with at least a partially fine-grained pearlite structure, a rail sole and a neck between the rail head and the rail sole, described in the mentioned publications, is obtained.

The general shortcoming of all the methods and devices known so far is that, although when producing profiled rolled products, these solutions lead to the achievement of the goal in limited areas or in relatively separate technological operations, however, they cannot show a satisfactory overcoming of the general problem when economically producing high-quality long rails with special quality characteristics.

In this case, the invention wants to help and sets itself the goal of indicating, while eliminating the shortcomings of known types of production, a new method that can be used to produce a rolled product with especially favorable operational properties. In addition, the task of the invention is to create a device, in particular, for the implementation of the method, and to perform rolling, in particular, a rail, for maximum loads.

This is achieved by the fact that rolled steel, in particular, a rail, with an average temperature of a maximum of 1100C, preferably a maximum of 900"C, but at least 750"C, at which it is straightened in the straight longitudinal direction when plastically shaped, in the straightened position it is transferred to the transverse direction and withstand, in the course of the first cooling operation of the rolled steel or rail, the last or last one is cooled to temperatures below 860"С, preferably to temperatures! about 820"С, in particular from 57С to 120"С higher than the Agz temperature! of an alloy with the same local with the intensity of cooling, preferably mainly by radiation in still (open) air, after which, during the second cooling operation, heat is removed from the roll in a longitudinal direction, mostly with the same local, if viewed in a cross section along the periphery, different intensity, and at least in one zone along the periphery of the profiled roll, an increased cooling intensity is created, including m zone(s) with a large ratio of the cross-section to the perimeter or with a high fraction of the volume related to the surface, or with a high mass concentration and/or with a local high temperature of the rolled product corresponds to the greater (greater) intensity(s) of cooling , in particular, the rail, and the zone (zones) with such an increased cooling rate are brought to temperatures! transformation, during which, under these cooling conditions, a martensite-free fine-grained pearlite structure is formed, after which, during the subsequent operation, cooling to room temperature is carried out! with the same (uniform) local intensity of cooling, for example, in still (open) air.

It is important that straightening is carried out along the straight line during plastic molding and that it is carried out in the temperature range from 7507C to 1100"C. As it was found, temperatures below 750"C can lead to partially elastic bending with deviations from leveling along the straight line and subsequently to the inhomogeneous (uneven) intensity of cooling in the longitudinal direction of the rail. The temperature! rolled higher than 11007С in most cases promote the growth of austenite grains or the formation of large grains, which in the end can negatively affect the properties of the material.

On the basis of the rolled steel aligned in a straight line for the formation of a fine-grained pearlite zone of cross-section, uniformly established in the longitudinal direction, it turned out to be important that the rolled steel is held and during the first cooling operation evenly (equally) cooled to temperatures below 860"С with the same local intensity of cooling. However, on the one hand, there may be a leveled local inhomogeneity of the temperature distribution in the longitudinal direction, which is caused under these conditions by the adjacency of places to the device of transverse transportation, on the other hand, they establish an axisymmetric or centrally symmetrical distribution of temperatures in the cross-section of the profiled roll and thanks to this stabilizes the straightness of the latter. It is especially preferable to carry out uniform (equalizing) cooling to a temperature from 5"C to 120"C above the temperature of the alloy, so that! create favorable conditions for a partial pr formation of the structure into a fine-grained pearlite structural form in parts of the cross section. At the same time, the Agz temperature is the temperature at which the transformation of the gamma lattice into the alpha lattice of the alloy begins at a cooling rate of 3C/min.

The cooling of rolled steel is mainly directed with the same longitudinal direction, with different along the perimeter, if you look at the cross section, the intensity of heat removal is known by itself. However, it is important for the zone with increased intensity of surface cooling that corresponds to the mass concentration of the rolled product. In combination with straight alignment, uniform (equalizing) cooling and installation of symmetrical temperature distribution! and by bringing it into line with the cooling zones, it is possible to keep the cooling rate, which is different in the cross-sectional zones, essentially the same in the longitudinal direction of the roll. At the same time, it is important to establish the value of the cooling rate, with which the provided rolled zone is brought to the temperature! transformations. As in fig. 3, which shows the time-temperature transformation diagram of an alloy with a certain composition known to a specialist, at higher cooling values, different from Az-temperatures, for example, curve "c" and "a", martensitic particles are formed in the structure , as a result of which the material, although it acquires a higher hardness, nevertheless significantly loses elasticity and has an increased tendency to destruction, and its intended use is no longer possible. Low values of cooling, for example, curve "p", contribute to the formation of a coarse-grained pearlite soft structure. Thus, it is important to set the local cooling rates so high that the formation of martensite was excluded when transformed in any case, but so that a fine-grained pearlite structure was formed in the zone of increased cooling intensity.

After the complete transformation of the structure, in order to reduce or basically prevent warping of the rolled sheet, the latter is brought to room temperature with the same local intensity of cooling.

It is especially preferable when heat treatment after hot deformation of a rolled product with a degree of deformation from 1.8 to 895, preferably from 2 to 595, is carried out in the last transition at a temperature of at least 750"7C and a maximum of 10507C with heat from hot plastic molding (hot final deformation with a degree of deformation or reduction of the cross-sectional area from 1.895 to 895 leads to the grinding of austenite grains, if plastic deformation is carried out in the temperature range from 770"C to 105070. As it turned out, degrees of deformation below 1.895 lead to the formation of especially large grains in places or grain growth; on the contrary, deformations greater than 895 cause a strong increase in temperature in the central or internal zones, obviously due to the energy released during plastic deformation, as a result of which local inhomogeneities of structures and defects from the point of view of quality may appear.

Taking into account the fact that, after cooling to room temperature, the rolled product is generally aligned in a straight line or coaxially, and, in particular, has an increased stiffness and bending strength during the alternating cycle, a great advantage is that during the second cooling operation create an increased intensity of cooling in two or more zones along the perimeter of the profiled roll. Thanks to this, in several zones of the cross-sectional area close to the surface, it is possible to achieve higher hardness and higher strength of the material due to a finer pearlite structure. When the roll is loaded on a bend, in which the most distant location from the neutral fibers or the zero line of the cross-section zone has the highest stress, it is possible to create at least two of these peripheral zones with increased strength. At the same time, as it was discovered, the viscosity of the material in the area of the soles can also be hung from the rail! a rail that prevents rupture due to the formation of cracks.

Preferably, the rolled part that has the highest mass concentration, for example, the rail head, is cooled by the method of immersion or immersion in a cooling liquid, at the same time from the second (other), provided for in the future for enhanced cooling of the part (parts) ) rolled with a lower mass concentration, for example, the sole! rail, the heat is removed with the help of a means with a lower cooling intensity, for example, with the help of compressed air or by spraying a mixture of air and water. With the help of this type of action, it is possible to prevent the formation of a high internal stress state and thermal warping of the rolled product.

In order to avoid the harmful formation of martensite and obtain a fine-grained pearlite structure in the iron-based alloys mentioned above, it is an advantage that the value of the cooling intensity, in particular, the composition of the cooling liquid for immersion cooling is set in such a way that in the temperature range from From 800°C to 4507°C, the zones close to the surface, mainly the submerged part, are cooled at a rate of 1.67°C/s to 2.4°C/s, preferably around 2.0°C. This cooling rate is it is also preferable for economic reasons, because when the desired rolled quality is achieved, a short-term cooling is required during the second technological operation, and thus higher productivity can be achieved.

To reduce curvatures! It turned out to be preferable that in the case of a profiled roll with a T-shaped cross-sectional area, as, for example, it occurs on the sole of a railway rail, the area or surface opposite to the rail neck is cooled with increased intensity, preferably with the help of compressed air or by spraying a mixture of air and water. However, in order to improve durability characteristics, it turned out to be especially favorable when the surface zone opposite the rail neck with increased cooling intensity is formed basically symmetrically relative to the axis of the rail neck and limited in the longitudinal direction.

In addition, when the increased intensity of cooling of the peripheral relative to the mass concentration or the mouth of the rail neck of the cross-section zones of the profiled roll is excluded and/or the zones are protected from increased heat removal or at least heated for a short time, then it is possible to obtain a structure with the same or smaller strength of the material. Thanks to this, the danger of destruction is unexpectedly reduced, in particular, in case of shock and/or changing long-term load of the rolled product.

Special stability of forms! can be achieved when the intensity of cooling on the surface of the profiled roll, in particular the rail, is set in such a way that the zones in which the transformation of gamma structures takes place! when cooled, they form mostly parallel symmetrically and/or parallel to the neutral plane, preferably concentrically relative to the center of gravity or the center of gravity of the cross-sectional area.

So! to achieve basically the same local intensity of cooling in the longitudinal direction and to maintain a more stable transfer of heat to the cooled medium, in accordance with the invention, it is possible to provide that the rolling stock, the part of which is related to the cross section, is immersed in the cooling liquid in the tank for immersion, while cooling in this cooling liquid is carried out by moving in a longitudinal direction relative to the tank for cooling liquid or the tank for immersion and/or at least during the time during which the rolled part is immersed in the cooling liquid , the latter is loaded with vibrations or given oscillatory motion. As it was found out, you died! significantly improve the homogeneity of the achieved quality.

A device of the above-mentioned type for a complete solution to problems! when manufactured with special properties of the profiled roll in accordance with the invention, it is distinguished by the fact that the roller conveyor has in the preparation zone a device known in itself for the positioning of the roll and means for leveling along the straight line or the axis of the profiled roll when the latter is plastically shaped, the transverse transportation device has a means for direct or of the coaxial translation of the roll, mainly perpendicular to the axis of the axes! preparation in the zone of cooling treatment, in this zone of dispositions! a well-known device for hardening rolled steel, in particular the rail head, with the help of coolant in a tank for immersion with a fixing and controlling device and an adjustable additional cooling device for intensifying the cooling of at least the second zone! rolled, in particular the sole! rail, and the zone of final cooling has a place of storage for rolled steel with the purpose of cooling it to room temperature!.

It is known that the most important thing is the alignment along the straight line or the axis, the main way to improve the properties of the profiled roll, which is carried out relative to the cross section or partial zones. Due to the prevention of bending along the entire length or in partial zones, it is possible to maintain the same pre-determined cooling conditions or cooling intensity of the rolled product, if viewed in an axial direction, so that differences in strength or hardness along the forming profiles are excluded. Studies have shown that different distances relative to the wall of the coolant reservoir and/or the axis of jet cooling can cause disproportionate deviations in hardness and hardness values.

In addition, when leveling, it is important that the rolled product is subjected to plastic shaping with the help of appropriate devices, so that! prevent elastic return under certain conditions! in a partially curved shape. Coaxial transportation of the profiled roll to the cooling zone by straight-line transverse transportation is of great importance for the exclusion of additional correct devices. In addition to that, a control device is provided in the cooling zone, with the help of which reception and retention, immersion in a tank with cooling liquid or hardening of partial zones of the rolled product can be carried out, as well as transfer to the final cooling zone. At the same time, at least one device for additional cooling may be provided for intensive cooling of the second zones of the cross-section.

In the improved version of the device, the advantage is that the additional cooling device can be installed on the rolling stock and have an adjustable cooling intensity, and thus further local heat removal can be provided according to the method.

There is also a preferred embodiment in which the additional cooling device has details for creating a local flow of the cooling medium, limited in the longitudinal or axial direction of rolling, essentially continuous in the transverse direction, and, if necessary, means to prevent enhanced heat removal from the surface (surfaces) adjacent to the cooled surface. Thanks to this, it is possible to create a sharp limitation of the cooling zone and exclude intensive heat removal in adjacent zones or create a lower material stiffness in those zones, and in accordance with the second embodiment, the additional cooling device is implemented in the form of pneumatic cooling or spray cooling .

It is possible to increase the homogeneity of hardness and hardness values in the longitudinal direction of the profiled roll if the roll is moved in the cooling liquid in the longitudinal direction relative to the immersion tank and/or relative to the additional cooling device and/or if on the immersion tank and/or or in the coolant itself! devices, with the help of which the cooling liquid can move turbulently and/or be driven into oscillating motion.

It was found that relative movements, as well as oscillatory movements or shock waves between the cooling medium and the product, create conditions comparable to the local intensity of cooling and favorable conditions for improving properties.

The rail in accordance with the invention, manufactured, in particular, in accordance with the above instructions, if necessary, manufactured in the device described above, differs in that in the cross section of the rail, the latter has high strength indicators in the upper zone of the head and solid enough material, there are indicators in the lower zone of the head, in the neck and in the peripheral parts of the soles! lower, and in the central zone on the base surface of the sole, compared to the peripheral parts and the neck, there is an increase in values! hardness of the material, and especially uniform quality features are achieved when installed symmetrically with respect to the main axis of the cross-section profile or symmetrically with respect to the perpendicular axis of the cross-section of the rail! basically the same value of hardness of the material. This kind of rail even under complicated loads, such as, for example, with high axial forces, and/or high frequency of use, and/or small radii of curvatures! the section of the track has improved operational properties.

In fig. 1 shows the course of heat treatment of rails; in fig. 2 -- cross section of the rail; in fig. 3 -- a diagram of the transformation of the rail material in time-temperature coordinates.

As schematically presented in fig. 1, in zone A of the preparation on the roller conveyor 1, profiled rolled products, such as a rail, are positioned by means of an accumulator (preparations) fed to a given point (not shown). Then, with the help of the correct means 2 and Z, the rail 4 is leveled along a straight line, and the centering form of the correct means is preferred, which also corrects the bend in the vertical plane. After straightening, the roll is transported transversely through the storage area to the cooling zone B and installed in the control device with the help of retaining means 5, and support during delivery is provided in such a way that bending does not occur across the longitudinal axis. In a known manner, the roll or rail 4 is partially immersed in the cooling liquid 6, which is located in the tank 7 for immersion, with the help of retaining means 5. At the same time, it is important that the distance of the surface of the rail 4 from the walls of the tank for immersion along the length from all sides is the same and significant in size, and also with the purpose of increasing the effectiveness and, in particular, with the purpose of equalizing the intensity of cooling of the rolled surface, it is preferable in particular, the rolling stock 4 can be installed with the possibility of movement in the longitudinal direction in the tank 7 for immersion or in the cooling medium 6 within the limits, for example, from 0.5 m to 5 m.

Appropriately, it is also possible to use the arrangement in the cooling medium 6 or on the tank for submersion of the generator! oscillating, which brings the cooling medium into an oscillating motion with a frequency, for example, from 100 oscillating to 800 oscillating per minute, which affects the intensity of cooling.

On the flat part of the rolled surface, in this case, on the sole 8 of the rail 4, additional cooling 9 can be placed or installed. A similar device for additional cooling can have a device for supplying water 10 or air 11 and can create parts of the rolled surface or the sole of the rail directional jet flow 12. To establish in the peripheral parts 13 a lower intensity of cooling and to create a rolled surface or sole only in the central zone 14! rail zone with increased hardness of the material, it is preferable to provide for the release of the cooling medium, for example, with the help of a suction device.

After cooling the rolled part, in particular rail 4, immersed in the cooling medium and the opposite, loaded with the jet stream 12, at the material transformation temperature with an intensity conducive to the formation of a fine-grained pearlite structure, for example, in accordance with fig. 3, approximately to temperatures! 5007C with cooling rate according to curve "1", rail in the zone

After final cooling, it can be transferred to the place of 15 storage for cooling to room temperature!

As shown in fig. 2, rail 4 in accordance with the invention has three zones with different structure or hardness, and transitional formations! continuously In the head 16 of the rail, there is a fine-grained pearlite zone 17 with hardness values from 340 to 390 according to Brinell, if necessary, up to 425 units of hardness according to Brinell, which passes down into zone 18 with lower hardness, for example, with a hardness according to Brinell from 300 to 340. In the connecting neck 19, which in practical use must have a high viscosity, the values of Brinell hardness are set from 280 to 320. In the sole of the rail 8 in the peripheral zones 13, as well as in the neck 19 of the rail, a pearlite coarse-grained structure is indicated or lamellar formation with a Brinell hardness of 280 to 320. Thanks to this formation, the structure and properties of the material with reduced hardness values largely exclude the initiation of cracks and fractures. On the contrary, in the center on the side of the base on the sole 8 of the rail, a zone 14 with increased material hardness and Brinell hardness values from 300 to 350 and higher is formed. As it was discovered, this kind of distribution of the mechanical properties of the material along the cross section of the rail contributes to high stability and, most importantly, durability, in particular, under complicated operating conditions.

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