RU2755713C1 - Apparatus and method for heat treatment of a long-length product with an l-shaped profile with a sole, neck, head - Google Patents

Abstract

FIELD: heat treatment.

SUBSTANCE: invention relates to apparatuses for heat treatment of a long-length product with an L-shaped profile with a sole, neck and head, and to methods for heat treatment of said product. The apparatus comprises a conveyor for continuous movement of the product at a preset constant speed, a high-frequency current source, an inductor for heating the contact surface area of the head of the product, configured to be installed parallel to the contact surface of the head of the product, and electrically connected with the high-frequency current source, a tubular element with holes for water-air spray cooling of the heated area of the contact surface of the product, and a heat-resistant screen. The inductor is made with a length of no less than 3.5 N and a width of no less than (H-5), wherein H is the height of the contact surface of the head, mm, the tubular element comprises tubes with holes, wherein the tubular element is located directly behind the inductor, fastened rigidly at the same level with the inductor and separated therefrom by the heat-resistant screen. The method involves continuous movement of the product on the conveyor at a speed of 400 to 800 mm/min with the product passing through a local induction heating area, wherein the local induction heating area is made with a length of no less than 3.5 N and a width of no less than N-5, wherein H is the height of the contact surface of the head, mm, an alternating electromagnetic field with a frequency of 100 to 300 Hz for heating the product to a temperature of (Ac₃+45°C)-(Ac₃+75°C) with the heating rate of (32-68) °C /s, wherein the subsequent water-air sprayer cooling is executed at the rate of (10-15) °C /s, forming a hardness gradient from the surface into the base of the product to the depth of 12 to 15 mm.

EFFECT: increased wear resistance of the contact surface of the head of the L-shaped profile.

11 cl, 17 dwg

Description

The invention relates to the field of metallurgy, to devices and methods for heat treatment of long steel products of L-shaped profile having a sole, a neck and a head, in particular to the technological process of thermal hardening of the contact surface of the head, counter rail angle, counter rail and brake tire of a car retarder to increase their durability.

Known technical solution, which is aimed at reducing the intensity of wear of the working edge of the corner of the counter rail, reducing its rigidity and ensuring a more favorable passage of wheelsets of the rolling stock. The specified technical result is achieved by the fact that the counter-rail corner contains the sole, the neck and the head, while the height of the counter-rail corner in the cross-section is made variable and the following ratios are fulfilled for it 4.6 ^≤ a / b ^≤ 5.0 and 0.75 ^≤ c / d ^≤ 0.6, where a is the width of the head in the cross-section of the counter-rail corner, b is the width of the head part with the maximum height in the cross-section of the counter-rail corner, c is the range of head height variation across its width in the cross-section of the counter-rail corner, d is the maximum height head in the cross section of the counter rail corner. (Patent for utility model RU No. 108760, on application 2011123082 dated 06/08/2011, IPC Е01В 5/18). The disadvantage of this technical solution is the inconsistency of the overall, installation, connecting and profile dimensions with the design requirements according to GOST R 55497-2013, an insufficient decrease in the wear rate of the working edge of the corner, which leads to a decrease in the performance of the counter rail corner.

Known brake tires used on all types of car retarders made of L-shaped steel profile (Sagaitis V.S, Sokolov V.N. M: Transport, 1988.132-133 s). Brake tires are made of rolled section hot-rolled steel 50HG according to TU14-1-3188-81 of a certain profile with a carbon content of 0.47-0.49%, chromium 0.97-1.01%, nickel 0.10-0.14%. The brake tire, according to its functional purpose, can be conditionally divided into two parts, this is a wearing part and a sole for fastening, in the form of a solid groove, which has mounting holes for bus bolts and placement of bus bolt heads. The disadvantage of this brake tire is the insufficient reduction in the intensity of wear of the worn working part and, as a consequence, the short service life of the tire.

Known technical solution for the induction heating of the rail head to hardening temperatures. The electromagnetic field acting on the rail head is created by inducing high-frequency currents in a linear conductor connected by means of plates to an inductive conductor, and the linear conductor has a larger diameter than the inductive conductor. The distance between the inductive conductor and the rail head is fixed and the heating is carried out continuously - sequentially. (Patent for invention RU No. 2008363 on application 4940763 dated January 20, 1991, IPC C21D 9/04). The disadvantage of this device is the absence of specific parameters of the inductive conductor (inductor), the inductor is linear and is located perpendicular to the rail line, which does not allow creating the necessary temperature gradient in the counter-rail angle head for heating it to a depth of more than 12 mm and subsequent hardening.

Known is a rail heating device at the weld seam containing a power source electrically connected to a coil (inductor) for heating the heat-affected zone of the weld of a rail foot part, and means for cooling, while the inductor for heating is installed on the side of the lower surface of the rail foot part and has the length of the outer region in the direction of the length of the rail 1.2Lh or more, and in the direction of the width of the rail equal to 1.1W or more, where Lh is the length of the heat-affected zone of the weld "HAZ" of the rail foot part in the direction of the length of the rail, mm, W - rail foot width, mm. (Patent for invention RU No. 2661199 on application 2016138553 dated 09/06/2015, IPC C21D 9/04). The disadvantage of the device lies in the fact that the parameters of the inductor for heating are determined depending on the parameters of the heat-affected zone, which are unacceptable for use when heating long steel products of the L-shaped profile with a base, a neck and a head, high-frequency currents, so that to obtain the necessary warming up the hardening head to a depth of at least 12 mm.

The objective of the proposed technical solution is to increase the wear resistance of long steel products with an L-shaped profile with a sole, a neck and a head.

In the process of solving the problem, the technical result is achieved, which consists in increasing the wear resistance of the contact surface of the L-shaped profile head by creating a hardened, wear-resistant layer with a hardness gradient from the surface to the depth of the base to 12-15 mm.

The specified technical result is achieved by a device for heat treatment of a long product with an L-shaped profile having a sole, a neck and a head, which contains a conveyor for continuous movement of the product at a given constant speed, a high frequency current source (HFC), an inductor for heating the contact surface area of the product head , installed parallel to the contact surface of the product head and electrically connected to the HDTV source, a tubular element with holes for water-air spray cooling of the heated area of the contact surface of the product, while the inductor is made with a length of at least 3.5 N and a width of at least (H-5) , where H is the height of the contact surface of the head, mm, the tubular element is made of tubes with holes and is located directly behind the inductor, fixed motionlessly at the same level with the inductor, separated from it by a heat-resistant screen. In addition, the heat-resistant screen is made of quartz glass, the tubular element contains 1-5 tubes, tubes with holes located perpendicular to the length of the contact surface of the product head, the product has an L-shaped profile of the counter-rail angle of the SP850 type according to GOST R 55497-2013, the product has a G- the shaped profile of the counter-rail of the RK type according to GOST R 55497-2013, the product has an L-shaped profile of the brake tire of the carriage retarder according to TU 14-1-3188-81.

The linear dimensions of the inductor have two limiting dimensions, the length of the outer region is not less than 3.5N, and the width is not less than (H-5), i.e. less than the width of the contact surface of the head of the product by at least 5.0 mm. The width of the inductor affects the formation of a rapid heating region of the head close to the edges of the contact surface. A decrease in this size leads to rapid heating and cooling of the edges, this significantly increases the hardness of the edges, compared to the hardness in the central part of the contact surface of the head, as well as to the appearance of significant tensile stresses due to the formation of a martensite structure during cooling. In the future, during the operation of the product, the appearance of brittle fractures is possible. Compliance with this size leads to heating, in large part, in the central part of the contact surface of the head of the product, and the edges are heated by the heat from this area. Most of the supplied energy is concentrated in the central part, which further has a beneficial effect on the properties of the corner edges of the contact surface.

The linear dimensions of the inductor not less than 3.5N in the longitudinal direction determine the area of the heating depth of the contact surface of the head of the article, at a given constant speed of passage of the article in the region of induction heating. With an increase in the length of 3.5N, the head can warm up to the entire thickness, since the heating time increases, which will lead to heating of the material throughout the entire volume of the product, with overheating of the contact surface, and, as a consequence, obtaining a material structure with lower performance properties. When the length is reduced to less than 3.5N, the contact surface of the head may be underheated to an unnecessary depth, which will lead to a decrease in the thickness of the hardened layer, less than 12 mm, and as a consequence, a decrease in the wear resistance of the product. This size was determined experimentally. A tubular element with holes for water-air spray cooling of the heated contact zone containing 1-5 tubes with holes located perpendicular to the length of the contact surface of the product head, allows for cooling at the required speed, as well as, if necessary, use the heat from the volume of the head for heating the surface and reusing it cool, obtaining a more uniform structure of the hardened layer over the entire depth of the glued layer and the required hardness gradient. The presence of a heat-resistant screen made of quartz glass and fixed in close proximity to the inductor, between the inductor and the tubular element for water-air spray cooling of the heated zone, will allow the necessary hardening of the product and increase the safety in operation.

FIG. 1 shows a device for heat treatment of long products with an L-shaped profile, and section A-A in FIG. 1.

A device for heat treatment of a long product with an L-shaped profile having a base 1.1, a neck 1.2 and a head 1.3. consists of a conveyor (not shown in the figure) for continuous movement of the product, an HDTV source (not shown in the figure), electrically connected to the inductor 2 for heating the zone 2.1 of the contact surface of the head 1.3 and a tubular element 3 for water-air spray cooling of the heated zone 2.1 , made in the form of tubes 3.1, 3.2, 3.3, 3.4 with holes located perpendicular to the length of the contact surface of the head of the product, and executions of quartz glass heat-resistant screen 4 installed between inductor 2 and element 3. Inductor 2 has a length of at least 3.5H, and a width less than the width of the head of the product by at least 5.0 mm. A copper tube cooled by running water is used as an inductor. The cross-sectional shape of the tube can be round, elliptical, rectangular, etc. The device for cooling the inductor 2 and the device for cooling the heated zone 2.1 of the contact surface of the head 1.3 have separate water supply.

The device works as follows. The inductor 2 is installed parallel to the contact surface of the head 1.3 with a gap to the surface of 1.5 to 3.5 mm, the zone 2.1 of the contact surface of the head 1.3 is heated, and the product begins to move relative to the inductor 2 and the tubular element 3 at a given constant speed. The power of the induction heating source is up to 100 kW. Rapid cooling of the heated zone 2.1 of the contact surface of the head 1.3 of the product makes it possible to obtain a hardened layer 5 with a depth of up to 12 mm and a hardness gradient of 20- (190-210) HB. At the final stages of heat treatment, the product is tempered and the product temperature is brought to ambient temperature. The product is moved to the next technological section of production for straightening machining.

The proposed device for heat treatment of a long product with an L-shaped profile having a sole, a neck, a head, provides low heat energy consumption for heating, high productivity and the possibility of obtaining products with high wear resistance.

There is a method of heat treatment of welded joints of rails, including heating the entire section of the rail in the zone of the welded joint and hardening the head by forced cooling with simultaneous cooling of the neck and base in air, while heating the entire section of the rail in the zone of the welded joint to the temperature of the beginning of phase transformations in the metal is carried out with the distribution of the temperature field in a shape close to trapezoidal, the upper base of which is the heating zone of the rail head, equal in width to the heat-affected zone of welding, and the lower base is the heating zone of the rail base, which is at least 2 3 times, between the end of the heating process and the start of quenching of the rail head, a time delay is carried out, which ensures the temperature equalization over the section and the formation of a homogeneous structure in the entire heated volume, the quenching of the head is performed by forced cooling with compressed air to the completion temperature. uctural transformations. Patent for invention RU No. 2309185 on application 2006105596 dated 22.02. 2006 IPC C21D 9/04).

The overlapping essential features of the proposed method and this analogue are: sequential along the length of the profile induction heating of the head for hardening, cooling and self-tempering.

The disadvantage of this technical solution is the lack of specific heating parameters, and the lack of movement of the rail relative to the heating elements.

A known method of heat treatment of rails to reduce the hardness of the metal in the surface layer of the rail and eliminate thermal stresses and deformation of the rail, including the simultaneous induction heating of the head and foot of the rail. Induction heating of the rail head is carried out to a temperature of 500-700 ° C, induction heating of the rail foot is carried out to a temperature of 150-350 ° C at a rail travel speed of 1.2-3.5 m / min. Induction heating of the rail head is carried out at a current strength of 80-140 A and a voltage of 250-400 V in the inductor. The induction heating of the rail foot is carried out at a current strength of 50-100 A and a voltage of 100-250 V in the inductor. (Patent for invention RU No. 2418077 on application No. 2010113540 dated 07.04.2010, IPC C21D 9/04).

The overlapping essential features of the proposed method and this analogue are: induction heating of the head when moving the product.

The disadvantage of this method is insufficient heating temperature, lack of inductor parameters.

There is a known method of heat treatment of shaped profiles of points of turnouts, including elastic bending of the profile with a convexity on the head, induction heating of the head for hardening, cooling and self-tempering, sequential along the length of the profile, characterized in that when induction heating of the head for hardening is sequential along the length of the profile, the power of induction heating is sequential increase with an increase in the cross-sectional area of the heated head or successively decrease with a decrease in the cross-sectional area of the heated head, maintaining the same temperature of the head for hardening along the profile length, while the power of induction heating of the head for hardening is regulated in accordance with the formula

where N _i is the power of induction heating of the head for hardening in a given place;

N _max is the power of induction heating of the head for hardening in the place with the maximum cross-sectional area of the head;

F _i is the cross-sectional area of the head at a given place where the head is heated for hardening;

F _max is the maximum cross-sectional area of the head when it is heated for hardening. In addition, induction heating of the side faces of the head for hardening, before heating the head for hardening, it is heated to the scaling temperature, the head is heated by induction heating with medium frequency currents, the head is heated by flame heating, the head is cooled with compressed air with a temperature ranging from - 10 to + 10 ° C, the cooling of the head is carried out with a water-air mixture in a ratio of 1: 3 to 3: 1. (Patent for invention RU No. 2340685 on application No. 2006136864 dated 17.10.2006, IPC C21D9 / 04).

The overlapping essential features of the proposed method and this analogue are: installation of the inductor symmetrically to the profile with a gap to the surface of 2 to 5 mm, heating the surface layer of the head to a temperature above Ac ₃ (920 ° C), sequential movement of the product relative to the inductor at a speed of about 300 mm / min, Cooling with pressure nozzles.

The disadvantage of this method is that the declared parameters of the heat treatment of the switch point can not be used for heat treatment of the counter rail angle due to the fact that the geometric parameters of the cross section of the switch point and the section of the counter rail angle head differ significantly. There are no specific dimensions for the inductor.

There is a known method of hardening long metal products, including heating the product and subsequent low-temperature tempering, while the long product is continuously moved on the conveyor at a speed of 3-10 mm / s with the passage of the product through a local heating zone by an alternating electromagnetic field with a frequency of 8-20 kHz, providing heating products in the local zone to a temperature of 800-1000 ° C, and the subsequent tempering is carried out to a temperature of 300-200 ° C to ensure the formation of a martensitic metal structure by local intensive cooling with a jet of compressed air, after which the product temperature is brought to ambient temperature. In addition, the jet of cooling compressed air is directed mainly to the areas of the metal product intended for mechanical contact with external media. (Patent for invention RU No. 2437943 on application No. 2010140118 dated September 30, 2010, IPC C21D 1/42). This technical solution was adopted as a prototype.

The coinciding essential features of the proposed method and this prototype are: they are continuously moved on a conveyor at a speed of 10 mm / s with the passage of the product through the local heating zone, ensuring the heating of the product in the local zone to a temperature above 800 ° C, and the subsequent tempering is carried out to a temperature of 300- 200 ° C to ensure the formation of the martensitic structure of the metal by local intensive cooling, after which the temperature of the product is brought to ambient temperature. the jet of the cooling medium is directed mainly to the areas of the metal product intended for mechanical contact with external media.

The disadvantage of this method is that the declared heat treatment parameters cannot be used for an L-shaped product containing a sole, a neck and a head, due to the fact that high heating temperature parameters are set, there are no spacer cooling parameters, and the design dimensions of the inductor are absent.

The objective of the proposed technical solution is to increase the reliability in the operation of long steel products with an L-shaped profile with a sole, a neck and a head.

In the process of solving the problem, the technical result is achieved, which consists in increasing the wear resistance of the L-shaped profile head by creating a hardened, wear-resistant layer having a hardness gradient from the surface deep into the base up to 12 mm with a hardness gradient of (190-210) HB.

The technical result is achieved by the method of heat treatment of a long steel product with an L-shaped profile, containing a base, a neck and a head, including induction heating of the head for hardening, cooling and self-tempering, sequential along the length of the profile, while the long product is continuously moved on a conveyor at a speed of (400-800 ) mm / min, with the passage of the product through a local zone of induction heating, a length of at least 3.5H, and a width of at least (H-5), where H is the height of the contact surface of the head, mm by an alternating electromagnetic field with a frequency of 100-300 Hz, ensuring heating the product to a temperature of (A ₃ s + 45) ° C- (A ₃ s + 75) ° C, at a heating rate of (32-68) ° C / s, and subsequent water-air spray cooling at a rate of (10-15 ) ° С / s, with the formation of a hardness gradient from the surface to the depth of the base by 12-15 mm. heat treatment is carried out on the corner of the brake tire made of steel 50HG containing the mass. %: С - (0.46-0.54), Si - (0.17-0.37), Mn - (0.7-1.0), Ni - up to 0.25, S - up to 0.035, Р - up to 0.035, Cr - (0.9-1.2) , Cu - up to 0.2, Fe -, base, or counter-rail angle made of steel E68 containing mass. %: С - (0.60 0.73), Si - (0.13-0.28), Mn - (0.7-0.8), S - up to 0.03, Р - up to 0.03, V - (0.03-0.07), Al - up to 0.02, Fe - base, or counter-rail angle made of steel E55X containing, mass. %: С - (0.55-0.60), Si - (0.13-0.28), Mn - (0.7-0.8), S - up to 0.035, Р - up to 0.02, Cr - (0.35-0.45), V - (0.03-0.07), Al - up to 0.02, Fe - base. In addition, water-spray cooling is carried out from the side of the contact surface of the head of the product, and the first line cools the surface immediately behind the inductor, the following lines at intervals, allowing the surface to warm up due to internal heat, heat treatment is carried out by the brake tire of the car retarder made of steel 50HG GOST 14959 -79, the heat treatment is carried out on the counter-rail angle of the SP850 type made of steel E68 GOST R 55497-13, the heat treatment is carried out on the counter-rail angle of the SP850 type made of steel E55X GOST R 55497-13.

Studies carried out by the authors of the designs of products used on the railway have shown that there is a number of long products with an L-shaped profile with a sole, a neck and a head, close and close in geometric parameters to the wearing part of the head, and similar loading conditions of the contact surfaces. Such products are the counter rail and the brake tire. The proposed method of heat treatment of long steel products with an L-shaped profile with a sole, a neck and a head is aimed at increasing the wear resistance of these products by creating a hardened, wear-resistant layer along the cross section of the head with a hardness gradient from the surface to the depth of the base up to 12 mm with a gradient (190- 210) HB, maintaining the original structure and mechanical properties of the hardness of the neck and sole material.

Investigations of the mechanism of wear of the contact surfaces "corner of the counter rail-rim of the railway wheel" "corner of the brake tire-rim of the railway wheel", carried out by the authors of the proposed technical solution, showed that the mechanisms of wear have much in common. This is due to similar conditions of mechanical loading of contact surfaces and a slight difference in the elemental composition and structure of steels used in the manufacture of these products, which made it possible to apply the developed method of heat treatment using induction heating and subsequent hardening to these products.

The wear mechanisms of the contact surfaces in the system "railroad wheel rim - counter-rail angle head" and "railroad wheel rim - brake tire" are caused by high impact effects and sliding of contact surfaces relative to each other. Investigations of the wear of contact surfaces made it possible to reveal that in the surface layer of all samples cut from the head of the counter-rail angle and the head of the brake tire, there are zones of plastic deformation, the boundaries between which are clearly visible. Superficial, "white" zone, in which the grain boundaries do not appear at significant magnification. Below the surface zone there is a transition zone, in which strongly deformed grains are visible, the degree of grain deformation (the ratio of the grain size measured in two mutually perpendicular directions) reaches a fivefold value. The thicknesses of the zones of plastic deformation, in different parts of the contact surface, have different values within the limits in the white zone - 86-304 µm, the transition zone in the range of 48-87 µm.

Numerous cracks, probably of fatigue nature, are found in the surface layer. They originate at surface defects and penetrate deep into the material as the number of contact load cycles increases. As a rule, cracks make an angle with the contact surface in the range of 0-35 ° (Fig. 2 and Fig. 3). The length of the described cracks can reach 200-3000 microns, and in some cases even more.

The method of scanning microscopy in the surface layer of the samples revealed hairs (Fig. 4), causing delamination of the material, leading, together with surface cracks, to its destruction. The formation of hairs is associated with the accumulation of defects at the interfaces between the layers of the material subjected to impacts, as well as permanent shear deformations. The merging of hairs, which become stress concentrators, and microcracks lead to delamination of the subsurface layer of the material. As a result of material delamination, numerous metal chips occur on the side surface of the wheel rim (Fig. 4 and Fig. 5). During the movement of the car, the contact of the corner of the counter-rail and the corner of the brake tire occurs with the side surfaces (rims) of successively running wheels, in which, according to GOST 9036-59 and 4835-59, the inner surfaces of the rims are processed according to the 3rd class of cleanliness, and the outer surfaces are mechanically refined. not exposed at all, have a rough rough surface. The contact interaction of the car wheel with such a surface can occur at high speeds, the forces of the wheel on the bell-head cannot reach 30 Kn, and the pressure at the point of contact, on the outer surface, is 4.0-6.0 MPa. During operation, a roll up to 5 mm in height is formed on the outer side surface of railway wheels, which has a high hardness (HB 300 and higher), which accelerates the process of wear of the contact surfaces of the corner of the counter-rail and brake tires. Wear at a constantly changing sliding speed, constantly changing contact surfaces on the side of the car wheel, high pressure concentration in the contact spots, contributes to the adhesive interaction of the materials in contact, the formation of microcracks and wear particles. Also, several near-surface layers of various thicknesses are formed, the properties of which differ from those of the base material, this is due to the processes of plastic deformation of the surface layer with different contact pressure and its subsequent destruction. The study of the change in the microhardness of the head material from the surface into the volume showed that the microhardness in the surface contact zone reaches values (Нμ 775), decreases in the near-surface layers, the microhardness decreases to a depth of 2.5 mm (Нμ 233). As a result of cyclic mechanical loads during metal sliding on metal, crystal lattice defects accumulate not at the surface, but at a certain depth. Over time, this leads to the appearance of voids and cracks parallel to the surface. (Fig. 6 and Fig. 7). When the cracks reach a critical value, the surface layer of the metal is sheared off in the form of a sheet-like wear particle. Then, the same thing happens with the exposed underlying layers of material. This process, the grasping and tearing of particles, occurs continuously. Since the process of running-in in rubbing pairs goes on constantly, and there is no period of "steady wear" when the wear of rubbing surfaces is minimal, then in the absence of this period, wear of the contact surface occurs more intensively, compared to the processes of "steady wear".

With this mechanism of contact surface wear, the main direction to reduce fracture is the creation of metal structures in the material with increased wear resistance, while such a structure should extend to a considerable depth. The most suitable way to create structures with increased wear resistance in a material, for long steel products, is HFC hardening to the depth of the wear part of the product, in this case, up to 12-15 mm, with the creation of a martensite structure with increased hardness and wear resistance.

The proposed method of heat treatment was implemented on steels that are included in the list of materials recommended for the manufacture of a 50KhG brake tire and an E68, E50Kh counter rail angle, having an L-shaped profile containing a sole, a neck, a head, the chemical composition of which is shown in Table 1, Fig. 8 and Table 2, FIG. nine.

The composition of steels includes carbon, which affects changes in the strength of steel during heat treatment, and reduces its ductility. Silicon binds excess oxygen and increases its strength, but reduces its ductility. Manganese increases strength by combining with sulfur and reduces its harmful effects. Copper slightly increases the strength of steel and increases its resistance to corrosion. Chromium increases the strength of steel without reducing ductility and improves its corrosion resistance.

Induction heating is characterized by three parameters: specific power, heating duration and current frequency. Specific power is the power converted into heat per 1 cm ^{2 of the} surface of the heated metal (kW / cm ² ). The rate of heating of the product depends on the value of the specific power: the higher it is, the faster the heating is carried out. The heating duration determines the total amount of heat energy transferred, and therefore the reached heating temperature. The current frequency determines the thickness of the heated layer. To obtain deep hardening, the current frequency should be as low as possible. The cooling rate of the material is also important, since the structure of the hardened layer depends on it, and, as a result, the operational properties of the product. By varying the value of the specific power, the duration of heating and the frequency of the current, the heating temperature, the cooling rate of the heated volume, we achieved the required metal structure and the hardness gradient from the surface layer deep into the base. The features of induction heating during HFC hardening to a given depth were taken into account. Heating is carried out to a higher temperature than with conventional surface hardening. At a high heating rate, above the temperature of the critical points at which the transition of pearlite to austenite occurs, the transition temperature rises, while most of the transformation of pearlite should be completed in a very short heating and holding time.

Obtaining the required metal structure and hardness gradient along the height of the product head was carried out in a specific sequence.

Investigations of mechanical properties, investigation of the structure were carried out on samples cut from the corners of the counter rail or brake tire. Temperature control during heating and cooling is carried out by a pyrometer at each stage of induction heating and subsequent cooling with a temperature measurement accuracy of 0.1 ° C.

The following parameters of the method were used:

H is the width of the head of the product, mm.

Ni is the width of the inductor, mm.

Li is the length of the inductor, mm.

tн - heating time of the product surface, sec.

Тн - surface heating temperature ° С,

Vi is the speed of movement of the product, mm / sec, (mm / min),

Vнt is the heating rate of the product surface, ° С / sec.

Vot - speed of spacer cooling, sec.

to - spacer cooling time, sec.

The temperature of Ac3 was taken Ac3 = 775 ° C,

Example 1

Determination of the maximum width of the inductor for hardening the brake tire from 50HG in accordance with GOST 14959-79. The width of the inductor was considered acceptable provided that there were no microcracks on the edges of the corner, and unacceptable in the presence of microcracks.

The inductor was heated on a VCG 100-66 unit.

A loop-type inductor was manufactured, rectangular, with a side equal to Ni = 0.8H, and a length equal to Li = 5H

The spray cooling device had three lines of cooling holes at a distance from each other.

The heated sample was mounted on a conveyor.

The inductor and the water-air spray cooling device were fixed at a height of 2.0 mm above the plane of the corner of the product.

After heat treatment, the hardness and microhardness were determined, the structure of the alloy was investigated, and the presence of microcracks was monitored.

Determination of the maximum width of the inductor was determined at a constant speed of movement of the product. The rest of the parameters were determined by the formulas.

The surface heating temperature was set above the Ac3 melting point by 60 ° C, equal to 775 ° C. The heating time was determined by the formula tn = Li / Vi.

The heating rate Vнt was determined by the formula: Vнt = Тн / tн.

The speed of the spacer cooling was taken in the range (10-15) ° C / sec.

The spacer cooling time to was determined by the formula: to = Tn / Vot.

The width of the brake bar is 50 mm. The width of the inductor is Ni = 35 mm.

The length of the inductor Li = 3.5H = 3.5 × 50 = 175 mm.

Product speed Vi = 600 mm / min = 10 mm / sec.

Surface heating temperature 775 + 60 = 835 ° С.

Heating time L / Vi = 175/10 = 17.5 sec.

Heating rate 835 / 17.5 = 47.7 ° C / sec.

Spray cooling time 835 ° C / 12 ° C sec. = 70 sec.

The inductor on the working plane was installed as follows: the edge of the inductor, in width, was installed parallel to the edge of the corner at a distance from 0 mm from the edge, this edge was considered as right. The distance of the inductor from the left edge was 15.0 mm, this edge was considered to be left.

Experimental results: there were microcracks on the right edge, and no microcracks on the left edge. The structure of the steel is martensite. The results are shown in Table 3, FIG. ten.

Example 2

The inductor and heat treatment modes were similar to example 1.

The inductor was installed with an offset relative to the right edge by 1.0 mm. The distance of the inductor from the left edge was 14.0 mm.

Results: there were microcracks on the right edge, no microcracks on the left edge. The structure of the steel is martensite. The results are shown in Table 3, FIG. ten.

Example 3

The inductor and heat treatment modes were similar to example 1.

The inductor was adjusted with an offset relative to the right edge by 2.0 mm. The distance of the inductor from the left edge was 13 mm.

Results: there were microcracks on the right edge, no microcracks on the left edge. The structure of the steel is martensite. The results are shown in Table 3, FIG. ten.

Example 4

The inductor and heat treatment modes were similar to example 1. The inductor was installed with an offset relative to the right edge by 2.5 mm. The distance of the inductor from the left edge was 12.5 mm.

Results: there were microcracks on the right edge, no microcracks on the left edge. The structure of the steel is martensite. The results are shown in Table 3, FIG. ten.

From the results obtained (examples 1-4) it follows that the maximum distance of the inductor from the edge, when there is no formation of microcracks on the edge of the corner during heat treatment of the HFC brake tire made of steel 50HG GOST 14959-79 is 2.5 mm. The maximum width of the inductor for heat treatment of the brake tire corner, with a symmetrical arrangement of the inductor along the width of the brake tire corner equal to 50 mm, is 45 mm or 5.0 mm less than the width of the corner.

Examples 5-8

According to the scheme and in the modes of similar examples (examples 1-4), the maximum size of the inductor in width for heat treatment of steel E68 GOST 55497-13 of the counter-rail angle was determined. The results of studies to determine the maximum width of the inductor in width for heat treatment of the counter rail head from steel E68 GOST 55497-2013 are presented in Table 3, examples 5-8, Fig. ten.

When the width of the angle head is 40 mm, microcracks do not form on the edges if the edge of the inductor is at least 2.5 mm away from the edge of the head. The maximum width of the inductor for heat treatment of the counter rail corner, with a symmetrical arrangement of the inductor along the width of the counter rail corner equal to 40 mm, is 35 mm or 5.0 mm less than the width of the corner.

Examples 9-12

According to the scheme (examples 1-4) and in modes similar to example 1, the maximum size of the inductor in width for heat treatment of steel E55X GOST 55497-2013 counter rail angle was determined. The results of studies to determine the permissible maximum width of the inductor in width, for heat treatment of the head of the counter rail angle made of steel E68 GOST 55497-13 are presented in table No. 3, examples 9-12, fig. ten.

When the width of the angle head is 40 mm, microcracks do not form on the edges if the edge of the inductor is at least 2.5 mm away from the edge of the head. Consequently, the maximum width of the inductor for heat treatment of the counter rail corner, with a symmetrical arrangement of the inductor along the counter rail corner width equal to 40 mm, is 35 mm or 5.0 mm less than the width of the corner.

From the results obtained, examples (1-12), table No. 3, fig. 10 it follows that during heat treatment of an L-shaped product containing a sole, a neck and a head, when a head with a width of (40-50) mm is heated by high-frequency currents, the inductor must have a width less than the width of the angle head at least 5, 0 mm, that is, have a size equal to H-5.

Example 13

Determination of the minimum surface heating rate for hardening a 50HG brake tire in accordance with GOST 14959-79. The minimum heating rate was considered acceptable when obtaining the martensitic microstructure of the material and the gradient in hardness from the surface to the depth of the base up to 12 mm, by an amount in the range (190-210) HB. Determination of hardness was carried out at three levels: on the surface, at a depth of 7-8 mm and at a distance of up to 12 mm.

A loop-type inductor was manufactured, rectangular in shape, with a side equal to Ni = 0.8H, and a length equal to Li = 3.6H, the width of the brake tire angle is 50 mm. The inductor was placed symmetrically to the relative centerline of the angle. The heating rate was determined by the time of movement of the product relative to the inductor when the surface was heated to a temperature of (Ac3 + 60) ° C = 775 + 60 = 835 ° C. The initial speed of movement was taken equal to 10 m / s. In the following examples, the travel speed was reduced. When obtaining material properties that do not correspond to the accepted conditions, the heating rate of the previous example was taken as the minimum heating rate.

Heat treatment modes

Inductor width H = 35 mm.

The length of the inductor is L = 3.6H = 3.6 × 50 = 180 mm.

Product speed Vi = 600 mm / min = 10 mm / sec.

Surface heating temperature Тн = 775 + 60 = 835.

Heating time t = L / Vi = 180/10 = 18 sec.

Heating rate 835 ° C / 18.0 ° C sec = 46.3 ° C / sec.

Spray cooling time 835 ° C / 12 ° C / sec. = 70 sec.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is within the permissible values. The results are shown in Table 4, FIG. eleven.

Example 14

The speed of movement of the product is taken 400 mm / min, or 6.67 mm / sec.

Surface heating temperature 775 + 60 = 835 ° С.

Heating time 180 / 6.67 = 26.98 sec.

Heating rate 835 ° C / 26.98 ° C sec = 30.95 ° C / sec.

Spray cooling time 835 ° C / 12 ° C sec. = 70 sec.

The rest of the heat treatment modes are similar to example 13.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is within the permissible values. The results are shown in Table 4, FIG. eleven.

Example 15

The speed of movement of the product is taken as 6.34 mm / sec.

Surface heating temperature 775 + 60 = 835 ° С.

Heating time 180 / 6.34 = 28.40 sec.

Heating rate 835 ° C / 28.40 ° C sec = 29.4 ° C / sec.

Spray cooling time 835 ° C / 12 ° C sec. = 70 sec.

The rest of the heat treatment modes were similar to example 13.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is below the permissible values. The results are shown in Table 4, FIG. eleven.

From the results obtained for determining the minimum heating rate for steel 50HG GOST 14959-79 brake tire, presented in table No. 4, Fig. 11. (examples 13-15) it follows that during heat treatment of an L-shaped product containing a sole, a neck and a head 50 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the minimum heating rate is 31 ° C / sec.

Examples 16-18

According to the scheme and in the modes similar to example 13-15, the minimum heating rate for heat treatment of the counter-rail angle made of steel E68 GOST 55497-13 was determined. From the results obtained to determine the minimum heating rate for the heat treatment of the counter rail angle head made of steel E68 GOST 55497-13 counter rail angle presented in Table 4, Fig. 11. (examples 16-18) it follows that during heat treatment of an L-shaped product containing a base, a neck and a head 40 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the minimum heating rate is 31 ° C / sec.

Examples 19-21

According to the scheme and in the modes of similar examples 13-15, the minimum heating rate was determined during heat treatment of the counter-rail angle made of steel E55HG GOST 55497-13. From the results obtained to determine the minimum heating rate for heat treatment of the counter rail angle head FOR steel E55HG GOST 55497-13 counter rail angle presented in Table 4, Fig. 11. (examples 19-21) it follows that during heat treatment of an L-shaped product containing a base, a neck and a head 40 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the minimum heating rate is 31 ° C / sec.

From the results obtained, examples (13-21), table No. 4, fig. 11. it follows that during heat treatment of an L-shaped product containing a sole, a neck and a head, when a head with a width of (40-50) mm is heated by high-frequency currents, the minimum heating rate of the corner surface is 31, ° C / sec. With a decrease in speed, the gradient of hardness in height decreases, less than 190НВ. (Examples 15, 18, 21).

Example 22

Determination of the maximum surface heating rate for hardening a brake tire made of 50HG steel in accordance with GOST 14959-79. The maximum heating rate was considered acceptable when obtaining the martensitic microstructure of the material and the gradient in hardness from the surface deep into the base up to 12 mm, by an amount in the range (190-210) HB. Determination of hardness was carried out at three levels: on the surface, at a depth of 7-8 mm and at a distance of up to 12 mm. A loop-type inductor was manufactured, rectangular in shape, with a side equal to Ni = 0.8H, and a length equal to Li = 3.6H, the width of the brake tire angle is 50 mm. The inductor was placed symmetrically to the relative centerline of the angle. The heating rate was determined by the time of movement of the product relative to the inductor when the surface was heated to a temperature of (Ac3 + 60) ° C = 775 + 60 = 835 ° C.

The initial speed of movement was taken equal to 11.67 mm / sec. (700 mm / min). In the following examples, the travel speed was increased. When obtaining material properties that did not correspond to the accepted conditions, the heating rate of the previous example was taken as the maximum.

Heat treatment modes

Inductor width Ni = 35 mm.

The length of the inductor is Li = 3.6H = 3.6 × 50 = 180 mm.

Surface heating temperature Тн = 775 + 60 = 835 ° С.

The travel speed is 11.67 mm / s.

Heating time t = L / Vi = 180 / 11.67 = 15.42 sec.

Heating rate 835 ° C / 15.42 = 54.15 ° C / sec.

Spray cooling time 835 ° C / 12 ° C / sec. = 70 sec.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is within the permissible values. The results are shown in Table 5, FIG. 12.

Example 23

The speed of movement of the product is taken as 800 mm / min, or 13.33 mm / sec.

Surface heating temperature 775 + 60 = 835 ° С.

Heating time 180 / 13.33 = 13.5 sec.

Heating rate 835 ° C / 13.3 ° C sec = 61.85 ° C / sec.

Spray cooling time 835 ° C / 12 ° C sec. = 70 sec.

The rest of the heat treatment modes were similar to example 13.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is in the limit of permissible values. The results are shown in FIG. 12, in table 5,

Example 24

The speed of movement of the product is taken (820 mm / min) 13.66 mm / sec.

Surface heating temperature 775 + 60 = 835 ° С.

Heating time 3.5 × 50 / 13.66 = 13.18 sec.

Heating rate 835 ° C / 13.18 ° C sec = 63.35 ° C / sec.

Spray cooling time 835 ° C / 12 ° C sec. = 70 sec.

The rest of the heat treatment modes were similar to example 13.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is higher than the permissible values. The results are shown in FIG. 12 in table 5.

From the results obtained for determining the maximum heating rate for steel 50HG GOST 14959-79 of the brake tire, presented in Table 5, Fig. 12. (examples 22-24) it follows that during heat treatment of an L-shaped product containing a sole, a neck and a head 50 mm wide, high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, by an amount in the range (190-210) HB, the maximum heating rate is 62 ° C / sec.

Example 25-27

According to the scheme and in the modes of similar examples 22-24, the maximum heating rate was determined for heat treatment of the counter-rail angle made of steel E68 GOST 55497-13. From the results obtained to determine the minimum heating rate for the heat treatment of the counter rail angle head made of steel E68 GOST 55497-13 counter rail angle presented in Table 4, Fig. 12. (examples 25-27) it follows that during heat treatment of an L-shaped product containing a base, a neck and a head 40 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the maximum heating rate is 62 ° C / sec.

Example 28-30

According to the scheme and in the modes similar to example 22-24, the maximum heating rate was determined for heat treatment of the counter-rail angle made of steel E55HG GOST 55497-13. From the results obtained to determine the minimum heating rate for the heat treatment of the counter rail angle head made of steel E55HG GOST 55497-13 counter rail angle presented in Table 5, Fig. 12. (examples 28-30) it follows that during heat treatment of an L-shaped product containing a base, a neck and a head 40 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the maximum heating rate is 62 ° C / sec.

From the data obtained, examples (22-30) table No. 5, Fig. 12. it follows that during heat treatment of an L-shaped product containing a sole, a neck and a head, when a head with a width of (40-50) mm is heated by high-frequency currents, the maximum heating rate of the contact surface is 62.0 ° C / sec. With an increase in the heating rate, the gradient of hardness along the height increases, above 210HB. (Examples 24, 27, 30).

Example 31

Determination of the maximum surface heating temperature for hardening a brake tire made of 50HG steel in accordance with GOST 14959-79.

The maximum heating temperature was considered acceptable when obtaining the martensitic microstructure of the material and the gradient in hardness from the surface to the depth of the base up to 12 mm, by an amount in the range (190-210) HB. Determination of hardness was carried out at three levels: on the surface, at a depth of 7-8 mm and at a distance of up to 12 mm. A loop-type inductor was manufactured, rectangular in shape, with a side equal to Ni = 0.8H, and a length equal to Li = 3.6H, the width of the brake tire angle is 50 mm. The inductor was placed symmetrically to the relative centerline of the angle. The maximum heating temperature was determined when the surface was heated from the temperature (Ac3 + 60) ° С = 775 + 60 = 835 ° С. In subsequent experiments, it increased. The movement speed was taken equal to 11.67 mm / sec. (700 mm / min). In the following examples, the travel speed was maintained. When obtaining material properties that did not correspond to the accepted conditions, the heating temperature of the previous example was taken as the maximum.

Modes:

Inductor width Ni = 35 mm.

The length of the inductor is Li = 3.6H = 3.6 × 50 = 180 mm.

Surface heating temperature Тн = 775 + 65 = 835 ° С.

The travel speed is 11.67 mm / s.

Heating time t = L / Vi = 180 / 11.67 = 15.42 sec.

Heating rate 835 ° C / 15.42 = 54.15 ° C / sec.

Spray cooling time 835 ° C / 12 ° C / sec. = 70 sec.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is in the limit of permissible values. The results are shown in Table 6, FIG. 13.

Example 32

Heating temperature (А ₃ s + 70) ° С = 775 + 70 = 850 ° С.

The travel speed is 11.67 mm / s.

Inductor width H = 35 mm.

The length of the inductor is L = 4.5H = 4.5 × 40 = 180 mm.

Heating time t = L / Vi = 180 / 11.67 = 15.42 sec.

Heating rate 850 ° C / 15.42 = 55.12 ° C / sec.

Spray cooling time 850 ° C / 12 ° C / sec. = 71 sec.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is in the limit of permissible values. The results are shown in Table 6, FIG. 13.

Example 33

Surface heating temperature (А ₃ s + 75) ° С = 775 + 80 = 855 ° С.

The speed of movement of the product is 11.67 mm / sec.

Heating time t = L / Vi = 180 / 11.67 = 15.42 sec.

Heating rate 855 ° C / 15.42 ° C sec = 55.45 ° C / sec.

Spray cooling time 855 ° C / 12 ° C sec. = 72 sec.

Results:

The structure of the steel is martensite. The gradient of hardness along the height of the corner is higher than the permissible values. The results are shown in Table 6, FIG. 13.

From the results obtained for determining the maximum heating temperature for steel 50HG GOST 14959-79 brake tire, presented in table 6, Fig. 13. (examples 31-33) it follows that during heat treatment of a product with an L-shaped profile containing a sole, a neck and a head 50 mm wide, high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface to the depth of the base up to 12 mm, by an amount in the range (190-210) HB, the maximum heating temperature is 850 ° C / sec.

Examples 34-36

According to the scheme and in the modes of similar examples 31-33, the maximum heating temperature for heat treatment of the counter-rail angle made of steel E68 GOST 55497-13 was determined.

From the results obtained for determining the maximum heating rate for the heat treatment of the counter rail angle head made of steel E68 GOST 55497-13 of the counter rail angle presented in Table 6, Fig. 13. (examples 34-37) it follows that during heat treatment of an L-shaped product containing a base, a neck and a head 40 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the maximum heating temperature is 850 ° C.

Examples 37-39

According to the scheme and in the modes of similar examples 31-33, the maximum heating temperature for heat treatment of the counter-rail angle made of steel E55HG GOST 55497-13 was determined. From the results obtained to determine the maximum heating rate for the heat treatment of the counter rail angle head made of steel E55HG GOST 55497-13 counter rail angle presented in Table 6, Fig. 13. (examples 37-39) it follows that during heat treatment of an L-shaped product containing a base, a neck and a head 40 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the maximum heating temperature is 850 ° C.

From the data obtained, examples (31-39) table no. 6, fig. 13. it follows that during heat treatment of an L-shaped article containing a sole, a neck and a head, when the head is heated within the range of (40-50) mm with high-frequency currents, the maximum heating temperature of the contact surface is 850 ° C. With an increase in the heating temperature, the gradient of hardness along the height increases, above 210HB. (Examples 33, 36, 39).

Example 40

Determination of the minimum heating temperature for a brake tire made of steel 50HG in accordance with GOST 14959-79.

The minimum heating temperature was considered acceptable when obtaining the martensitic microstructure of the material and the gradient in hardness from the surface to the depth of the base up to 12 mm, by an amount in the range (190-210) HB. A loop-type inductor was manufactured, rectangular in shape, with a side equal to 0.925N, and a length equal to 4.5N, the width of the brake tire angle is 50 mm. The minimum heating temperature was determined when the surface was heated from the temperature (Ac3 + 50) ° С = 775 + 50 = 825 ° С; in the following examples, the heating temperature decreased.

The movement speed was taken equal to 6.67 mm / sec. (400 mm / min) In the following examples, the travel speed was maintained. When obtaining material properties that did not correspond to the accepted conditions, the heating temperature of the previous example was taken as the minimum

Modes:

Inductor width Ni = 35 mm.

The length of the inductor is Li = 4.5N = 4.5 × 40 = 180 mm.

Surface heating temperature Тн = 775 + 50 = 825 ° С.

The travel speed is 6.67 mm / s.

Heating time t = L / Vi = 180 / 6.67 = 26.98 sec.

Heating rate 825 ° C / 26.98 ° C sec = 31.44 ° C / sec.

Spray cooling time 825 ° C / 12 ° C / sec. = 68.75 sec.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is in the limit of permissible values. The results are shown in Table 7, FIG. fourteen.

Example 41

The speed of movement of the product is 6.67 mm / sec.

The surface heating temperature is 775 + 45 = 820 ° C.

Heating time 3.5 × 50 / 6.67 = 26.24 sec.

Heating rate 820 ° C / 26.24 ° C sec = 31.25 ° C / sec.

Spray cooling time 820 ° C / 12 ° C sec. = 68.34 sec.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is in the limit of permissible values. The results are shown in Table 7, FIG. fourteen.

Example 42

The speed of movement of the product is taken as 6.67 mm / sec.

Surface heating temperature 775 + 40 = 815 ° С.

Heating time 3.5 × 50 / 6.67 = 26.24 sec.

Heating rate 815 ° C / 26.24 ° C sec = 31.06 ° C / sec.

Spray cooling time 815 ° C / 12 ° C sec. = 67.92 sec.

Results: Steel structure - martensite. The gradient of hardness along the height of the corner is less than the permissible values. The results are shown in Table 7, FIG. fourteen.

The results of determining the minimum heating rate of the brake tire corner are presented in Table 7, FIG. fourteen.

From the results obtained for determining the minimum heating temperature for steel 50HG GOST 14959-79 of the brake tire, presented in Table 7, Fig. 14. (examples 40-42) it follows that during heat treatment of a product with an L-shaped profile containing a sole, a neck and a head 50 mm wide, high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface to the depth of the base up to 12 mm, by an amount in the range (190-210) HB, the minimum heating temperature is 820 ° C.

Examples 43-45

According to the scheme and in the modes of similar examples 40-42, the minimum heating temperature was determined for heat treatment of the counter-rail angle made of steel E68 GOST 55497-13.

From the results obtained for determining the minimum heating temperature for the heat treatment of the counter rail angle head made of steel E68 GOST 55497-13 counter rail angle presented in Table 7, Fig. 14. (examples 43-45) it follows that during heat treatment of a product of an L-shaped profile containing a base, a neck and a head 40 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the minimum heating temperature is 820 ° C.

Examples 46-48

According to the scheme and in the modes of similar examples 40-42, the minimum heating temperature was determined for heat treatment of the counter-rail angle made of steel E55HG GOST 55497-13.

From the results obtained for determining the minimum heating temperature for heat treatment of the counter rail head from steel E55HG GOST 55497-13 of the counter rail, shown in Table 7, Fig. 14. (examples 46-48) it follows that during heat treatment of a product with an L-shaped profile containing a base, a neck and a head 40 mm wide by high-frequency currents, to obtain a martensitic microstructure of the material and a gradient in hardness from the surface deep into the base up to 12 mm, on value in the range (190-210) HB, the minimum heating temperature is 820 ° C.

From the obtained data of example 40-48, it follows that the minimum heating temperature of the contact surface, at which, with a symmetric arrangement of the inductor along the width of the corner, with a hardened layer depth of at least 12 mm, is (A ₃ s + 45) ° C = 820 ° C ... At this temperature, the required gradient in hardness and structure (martensite) is created. With a decrease in the heating temperature of the contact surface below the minimum gradient in hardness decreases, less than 190 HB. Examples 42, 45, 48.

Determination of the minimum length of the inductor The determination of the minimum values of the length of the inductor was carried out by calculation using previously obtained data. Heating temperatures of the contact surface to a temperature of (А ₃ s + 45) ° С and (А ₃ s + 75) ° С, at a heating rate of the contact surface within (32-64) ° С / sec, the speed of movement of the product relative to the inductor within (400-800) mm / min.

Of the possible options, the minimum length of the inductor was determined at the maximum heating temperature of the contact surface (А ₃ s + 75) ° С, the minimum heating rate is Vнt = 32 ° С / sec, the minimum speed of movement of the product relative to the inductor is Vi = 400 mm / min. The length of the loop-type inductor, rectangular in length for heating the head of width H, must be at least 3.5 N.

The larger value of the length of the inductor is determined from the design conditions and heat treatment performance and was not the subject of the proposed technical solution.

FIG. 15 and 16 show typical dependences of changes in microhardness from the surface deep into the base of hardened steel 50KhG, example 21 and steel E68, example 34. FIG. 17 shows a typical structure of martensite of 55KhG steel, example 21.

The implementation of the proposed method is illustrated by a drawing (Fig. 1), which shows a functional diagram of a device with which a method of hardening long (extended) metal products, for example, a brake tire corner or a counter rail corner, is carried out. The proposed method is carried out in the following way. A long product is placed on a conveyor and continuously moved at a speed of (400-800) mm / min. When moving, the product passes through the induction heating zone created by high-frequency currents with a frequency of (150-200) Hz. The frequency range is determined automatically by the inverter of the HDTV installation, where the surface of the product is heated in the temperature range of 820-850 ° C (the temperature of the product on the surface). After heating, the product is cooled to a temperature of 300-200 ° with a water-air jet and subsequent self-tempering. A stream of water-air mixture is directed to the contact surface of the product. The proposed method makes it possible to quench products with a hardened layer up to 12 mm and a hardness gradient up to (190-210) HB. The wear resistance of products increases up to 3 times. The proposed method is used in the technological process for thermal hardening of the brake tire and the counter rail angle.

Claims (11)

1. A device for heat treatment of a long product with an L-shaped profile having a sole, a neck and a head, containing a conveyor for continuous movement of the product at a given constant speed, a high-frequency current source, an inductor for heating the area of the contact surface of the product head, configured to be installed in parallel the contact surface of the product head and electrically connected to a high-frequency current source, a tubular element with holes for water-air spray cooling of the heated area of the product contact surface and a heat-resistant screen, while the inductor is made with a length of at least 3.5 N and a width of at least (H-5 ), where H is the height of the contact surface of the head, mm, the tubular element contains tubes with holes, while the tubular element is located directly behind the inductor, fixed motionlessly at the same level with the inductor and separated from it by a heat-resistant screen. 2. The device according to claim 1, characterized in that the tubular element contains from 2 to 5 tubes configured to be arranged perpendicular to the length of the contact surface of the head of the article. 3. The device according to claim 1, characterized in that the product of the L-shaped profile is made in the form of a counter-rail angle of the SP850 type. 4. The device according to claim 1, characterized in that the product of the L-shaped profile is made in the form of a counter rail. 5. The device according to claim 1, characterized in that the product of the L-shaped profile is made in the form of a brake tire of a car retarder. 6. A method of heat treatment of a long product with an L-shaped profile having a sole, a neck and a head, by means of a device according to claim 1, including induction heating of the head for hardening, water-air spray cooling and self-tempering, sequential along the length of the product profile, characterized in that the product is continuously moved on a conveyor at a speed of 400-800 mm / min with the passage of the product through a local zone of induction heating, while the local zone of induction heating is created with a length of at least 3.5N and a width of at least H-5, where H is the height of the contact surface of the head , mm, by an alternating electromagnetic field with a frequency of 100-300 Hz for heating the product to a temperature of (Ac ₃ + 45 ° C) - (Ac ₃ + 75 ° C) at a heating rate (32-68) ° C / s, while the subsequent water-air spray cooling is carried out at a rate of (10-15) ° C / s with the formation of a hardness gradient from the surface to the depth of the product base by 12-15 mm. 7. The method according to claim 6, characterized in that the water-air cooling is carried out from the side of the contact surface of the product head, and the surface is cooled immediately after induction heating by means of the first line of holes made in the tubes of the tubular element, and subsequent cooling is carried out by means of the following lines of holes , made in the tubes of the tubular element, at intervals of time, providing heating of the contact surface of the head of the product due to the internal heat of the product. 8. The method according to claim 7, characterized in that heat treatment of the product is carried out in the form of a brake tire of a carriage retarder made of 50KhG steel. 9. The method according to claim 7, characterized in that heat treatment of the product is carried out in the form of a counter-rail angle made of E68 steel. 10. The method according to claim 7, characterized in that heat treatment of the product is carried out in the form of a counter-rail angle of the SP850 type made of steel E68. 11. The method according to claim 7, characterized in that heat treatment of the product is carried out in the form of a counter-rail angle of the SP850 type made of E55X steel.

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