RU2456352C1 - Procedure and device for thermal treatment of rails - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: rails are cooled at cooling speeds in the range of 2÷20°C/sec with a smooth change in the speed of cooling during heat treatment, which allows to obtain a uniform finely dispersed structure of sorbite hardening to a depth of 22 mm from the surface and to obtain hardness on the roll surface to the HB401. Adjustment of cooling capacity of the gaseous medium is performed by a programed mode by means of a pulsed quasi-continuous and/or continuous injection of water into the air stream. Depending on the chemical composition of rail steel and the rail initial temperature being not lower than austenitisation temperature flow of the gaseous medium is controlled from 20 to 60 m³/min per one running metre of a rail, whereby the flow of injected water is up to 12 l/min per one running metre of rail. In addition, the water content in the gas medium is up to 0.2 litre of water per 1 cubic metre of air. The gaseous medium pressure is controlled in the range from 0.005 to 0.1 MPa.

EFFECT: versatility of the method and the device that allow for thermal treatment of rails of both carbon non-alloy steels and of alloy steel.

12 cl, 5 tbl, 4 dwg

Description

The invention relates to the field of ferrous metallurgy, in particular to methods for heat treatment of rails, including railway rails.

A known method of cooling a rail (patent RU 2266966 C21D 9/04, C21D 11/00, C21D 1/02), comprising passing a heated rail through a cooling section with inlet and outlet regions and cooling to convert the rail microstructure into a pearlite or ferrite-pearlite microstructure, characterized in that the rail is passed through a cooling section, consisting of separate, independent, sequentially located along the length of the cooling section cooling modules with independently adjustable cooling parameters and with intermediate regions, Proposition between the cooling modules for removing the structural stresses, with means for determining the actual temperature of the rail head. Depending on the corresponding value of the actual temperature of the part in the intermediate region, the cooling intensity parameters of at least the next cooling module are adjusted to provide a predetermined temperature of the rail head during the entire passage of the cooling section, exceeding the critical temperature of formation of the bainitic structure.

The disadvantage of this method can be attributed to the limited range of adjustment of cooling rates during the cooling mode. In addition, the temperature drop on the surface of the head during the first 4-5 s of the cooling regime reaches 350 ° C - 450 ° C, which can lead to the formation of bainitic structures in the microstructure of the surface layers of the rail. Thus, the main disadvantage of this method is the high temperature fluctuations on the surface of the rail head (from 350 ° C to 100 ° C), which can lead to heterogeneity of the macrostructure.

Another disadvantage is the heterogeneity of the heat treatment along the length of the rail, since in the continuous heat treatment mode with regulation of the cooling intensity in separate independent modules, different sections of the rail go through different cooling modes.

A known method and device of differentiated hardening with cooling of the rail head and sole of the rail using compressed air through a system of collectors with holes (nozzles) (US patent 4913747, IPC C21D 9/04). This patent is selected as a prototype rail heat treatment device.

The device consists of:

mechanisms for loading, unloading, positioning and fixing the rail in a head up (on the sole) position, a turbocharger, a duct system and manifolds with openings (nozzles) for supplying a cooling medium to a rail, positioning mechanisms of the upper, lower, and side manifolds with a part of the supply ducts, the system air supply regulation and temperature control system.

This method and device allows heat treatment of rails only from alloyed and high carbon (hypereutectoid with a carbon content of 0.9 ÷ 1.2 wt.%) Steels.

The main disadvantage of the method and device is the narrow range of regulation of cooling rates, providing heat treatment of rails with speeds up to 4.5 ° C / s, since the cooling medium is air, which does not allow heat treatment of rails made of carbon unalloyed steel, since this requires speed cooling significantly higher (10 ° C / s or more).

Another disadvantage of the device is the use of powerful drives and complex metal structures, since for the heat treatment of each rail it is necessary to raise and lower the design of the upper and side rail cooling collectors with part of the supply ducts.

There is another method of heat treatment of rails (patent RU 2280700 C21B 9/04), including continuous cooling of the head, followed by controlled cooling of the rail profile elements, characterized in that the rail from rolling heating is cooled to a temperature of 820-870 ° C and cooled in two environments: initially compressed air from the surface of the head for 20-30 s at an air flow rate of 3000-4000 m ³ / h, at an air temperature of 10-25 ° C and a pressure of 0.55 MPa, then the head is cooled with a water-air mixture at a water flow rate of 25-30 l / min, water temperature 1 0-30 ° C and a pressure of 0.3-0.4 MPa, while cooling the rail head, the sole is cooled with a water-air mixture at a water temperature of 10-30 ° C, a flow rate of 6-7 l / min and a pressure of 0.08-0, 09 MPa.

This method is applicable for the heat treatment of rails from unalloyed carbon (hypereutectoid) steels, but is limited for the heat treatment of hypereutectoid and alloy steels, which is its significant drawback.

Other disadvantages of this method include: a sharp change in the cooling rate of the rail after the air-water mixture is supplied with a water flow rate of 25-30 l / min to the rail profile, which violates the principle of uniform cooling and can lead to the formation of heterogeneity of macro- and microstructure. And also the use of air with a high pressure of 0.55 MPa, at its indicated costs, entails the need for high-power compressors and high-volume receivers, which will lead to the complication of the device and high energy consumption.

The objectives of the proposed method and device are: regulation of the cooling ability of the gas cooling medium both impulse quasi-continuously and continuously, expanding the range and smoothness of regulation of cooling rates, reducing the time of heat treatment of rails, the possibility of heat treatment of rails from unalloyed and alloyed steels, obtaining high hardness on the rolling surface , increasing the plastic and strength properties of heat-treated steel, simplifying the device and reducing energy consumption.

The technical result is the creation of a method and device that allows:

- to regulate the cooling ability of the gas cooling medium as a pulse quasicontinuously, or continuously according to the programmed mode;

- carry out the heat treatment of rails from carbon unalloyed (hypereutectoid and hypereutectoid) and alloy steels;

- produce cooling of rails with cooling rates in the range of 2-20 ° C / s;

- quasi-continuously smoothly or abruptly change the cooling rate during the heat treatment at various stages of cooling;

- reduce the pressure in the gas cooling medium supply system;

- to obtain a homogeneous finely dispersed pearlite structure (sorbitol quenching) to a depth of more than 22 mm from the surface due to the intensification of the cooling ability of the gaseous medium during cooling;

- to obtain hardness on the rolling surface to HB401, to increase the plastic and strength properties of heat-treated steel by reducing the dispersion of perlite;

- reduce the total heat treatment time of the rail, simplify the device and reduce energy consumption.

The technical result is achieved by a method of heat treatment of rails, including continuous cooling from rolling and / or reheating from a temperature not lower than the austenization temperature of the head and sole of the rail at the same time, according to the invention, the rail is cooled by air with regulation of the degree of air humidity and its pressure during heat treatment, when this regulation of the cooling ability of the medium is carried out by pulsed quasi-continuous and / or continuous injection of water into the air stream through rogrammno preset mode. In addition, the gas flow is regulated, depending on the chemical composition of the rail steel, with a flow rate of 10 ÷ 60 m ³ / min per meter of running rail, while the flow rate of injected water is changed to 12 l / min per one running meter of rail.

In addition, the flow of the gas medium is regulated depending on the initial rail temperature, the values of humidity and the temperature of the source air and the temperature of the water.

In addition, the water content in the gas medium is up to 0.2 liters of water per cubic meter of air.

In addition, the pressure of the gas medium is regulated within the range of 0.005 ÷ 0.1 MPa.

In addition, the cooling rate is regulated in the range of 2 ÷ 20 ° C / s.

The technical result of the method of heat treatment of rails is carried out on a device for heat treatment of rails, which includes mechanisms for loading, unloading, positioning and fixing the rail, a turbocharger, a duct system and manifolds with nozzle openings for supplying a cooling medium simultaneously to the rail head and sole, duct positioning mechanisms and collectors with nozzle openings, a cooling medium control system, a temperature control system, characterized in that it has a system of pulsed quasi-continuous and / or continuous injection of water into a gas stream containing a water tank, a system of water pipelines, flow regulators and pressure regulators, controlled valves, controlled control valves, pulse injectors with a control system that allows water injection in a pulsed quasi-continuous and / or continuous mode in software defined mode.

In addition, to regulate the flow and pressure of the gaseous medium in accordance with the programmed mode, the system has pressure reducing and control valves. In addition, the control system allows you to determine the temperature of the rail, the temperature and humidity of the source gas medium, the temperature of the water and adjust the cooling mode based on the data obtained.

In addition, the device is equipped with mechanisms for moving rails and / or collectors relative to the vertical and / or horizontal axis.

In addition, the device allows cooling of rails of various profiles by changing the distance from the surface of the rail profile elements to the nozzle openings.

In addition, the control system allows you to control the pressure and flow rate of the gas medium and set the mode of operation of the turbocharger.

The implementation of the claimed invention is explained in the following figures.

Figure 1 is an example of a control diagram of the injector.

Figure 2 is a schematic diagram of a heat treatment device.

Figure 3 is a schematic diagram of a heat treatment device indicating controlled process parameters.

4 is an example of a device for heat treatment of rails. General form.

The implementation of the invention

In the process of heat treatment of the rail, in the initial cooling period, the surface temperature of the rail head is gradually reduced to the temperature of minimum austenite stability during pearlitic transformation for 1 ÷ 90 s, not exceeding the incubation period. Then, at the second stage, the cooling rate necessary for the formation of the finely dispersed pearlite structure in the surface layer is set, then the cooling rate is set to ensure the formation of the finely dispersed pearlite structure as the pearlite transformation moves deeper into the head.

Cooling is carried out with a gaseous medium with adjustable cooling ability in the heat treatment process. By injecting water into the air stream and changing the pressure of the gaseous medium, the cooling ability of the gaseous medium is controlled, thereby obtaining a predetermined rail cooling rate. Water injection is carried out in a pulsed, quasi-continuous mode with a change in the pulse duration from 20 to 10,000 ms or more, as well as a duty cycle of pulses from 1 to 10,000.

Reliability is the ratio of the sum of the duration of the pause between pulses and the duration of the pulse to the pulse duration.

Q = (T _pauses + T _imp ) / T _imp , where

T _pauses - pause between pulses;

T _imp - pulse duration.

In the case when, during a pulsed quasi-continuous injection of water into the air stream, the pause between pulses approaches zero (T _pauses ≈0), there is a continuous injection of water into the air stream, and the pulse duration is approximately equal to the duration of the cooling mode (T _imp ≈ T _{cooling mode} ) .

An example of an injector control diagram is shown in FIG.

The pulsed water supply and the fast air outflow in the device create a homogeneous cooling gas medium with an adjustable cooling capacity that allows changing the rail cooling rate within 2-20 ° C / s. The temperature of the injected water can vary between 10-45 ° C.

The temperature of the source air can vary from minus 30 ° C to plus 50 ° C, and humidity - in the range of 40-100%. With a minimum moisture content of 10 g / m ³ per 1 pulse of 50 ms, 0.008 g / m ^{3 of} water will be added, i.e. less than 0.1%. With a maximum moisture content of 200 g / m ³ for 1 pulse of 1000 ms, 3.33 g of water will be added, i.e. less than 1.7%. For one pulse of water injection, 0.008-3.33 g / m ³ is supplied into the air stream, which leads to a smooth, quasi-continuous change in the moisture content in the air (less than 1.7%), i.e. achieve a smooth change in cooling rate.

Table 1 presents the experimentally obtained data on the dependence of the cooling rate of the rail head on the pressure of the gas medium.

Table 1 Data on the dependence of the cooling rate of the rail head on the pressure of the gas medium Coolant / manifold pressure Gas medium Pressure 0.005 MPa Pressure 0.015 MPa Pressure 0.025 MPa Pressure 0.04 MPa Pressure 0.05 MPa Pressure 0.1 MPa Initial cooling rate, ° C / s 2.0 4.34 4,55 4.82 4.91 4.99

The pressure of the gas cooling medium is determined in accordance with the chemical composition of the rail steel in the range of 0.005-0.1 MPa.

With an increase in air pressure above 0.1 MPa, the cooling rate increases slightly, a further increase is not economically feasible.

The lower cooling rate range of 2 ° C / s is achieved by supplying a gaseous medium at a pressure of 0.005 MPa without water injection.

Table 2 presents the experimentally obtained data on the dependence of the cooling speed of the rail head on air flow and the amount of injected water.

table 2 Dependences of the cooling rate on the pressure of the gaseous medium and the amount of injected water Gas pressure, MPa 0.005 0.015 0,025 0.04 0.05 0.1 Gas flow rate, m ³ / min per 1 m.p. rail 8 20,0 35.0 45.0 50,0 60.0 Water consumption, l / min per 1 m.p. rail - 0.2-4.0 0.35-7.0 0.45-9.0 0.5-10.0 0.6-12.0 Cooling rates, C / s 2 4,5-10,0 4.7-15.0 4.9-17.0 5.6-18.0 6.0-20.0

Rails from rolling and / or reheating to austenitization temperature are cooled by differentially supplying a gaseous medium to various elements of the rail profile: to the head rolling surface, side surfaces of the head and the bottom of the rail.

Heat treatment modes are set programmatically, based on experimental data, in accordance with the chemical composition of rail steel, the required physical and mechanical properties, the initial temperature of the rail before cooling, and the temperature and humidity of the initial gas medium and the temperature of the water.

To ensure minimal curvature of the rail, the necessary cooling mode of the sole is selected, depending on the mode of cooling of the head.

Cooling is carried out to a temperature of 150 ÷ 500 ° C depending on the chemical composition of rail steel.

This method of heat treatment of rails is carried out on a device, a schematic diagram of which is shown in figure 2, which shows:

1. Rail.

2. The lower collector, which is a container with nozzle holes for cooling the surface of the head.

3. Side collectors, which are a container with nozzle holes for cooling the side surfaces of the rail head.

4. The upper collector, which is a container with nozzle holes for cooling the bottom of the rail.

5. Turbocharger.

6. A regulator, for example a pressure reducing valve to maintain a given pressure of a gas medium or water.

7. Pressure sensors.

8. A regulator, for example control valves, for regulating the flow of water or a gas medium.

9. Injector.

10. Water supply device.

11. A container of water.

12. Management system.

13. The mechanism of positioning and fixing.

14. Air preparation system.

15. Filter system.

16. The water pipeline.

17. The pipeline gas environment.

I - The cooling zone of the rolling surface of the rail head (PCG).

II - The cooling zone of the side surfaces of the rail head.

III - Zone of cooling the bottom surface of the rail.

Figure 3 presents a schematic diagram of a heat treatment device indicating controlled technological parameters, where:

18 - Pressure of the gaseous medium.

19 - Water pressure.

20 - Gas flow rate.

21 - Water consumption.

22 - The temperature of the gas medium.

23 - Water temperature.

24 - Rail temperature.

25 - Humidity of the gas environment.

Figure 4 shows an example of a device for heat treatment of rails - General view, where:

26 - Tilter.

27 - The loading mechanism.

28 - Unloading mechanism.

13 - Mechanism for positioning and fixing the rail.

29 - Positioning mechanism of the upper manifold.

30 - Positioning mechanism of the lower and side collectors.

31 - Roller rail receiving rail.

32 - Roller rail issuing rail.

This method is carried out in the described device as follows.

Received in a position on the side of the rolling or reheating of the rail rail tilter 26 (figure 4) turns over to the receiving roller 31 (figure 4.). The loading mechanism 27 transfers the rail to the positioning and fixing mechanism 13, while the positioning mechanism of the upper collector 29 raises the upper collector. After fixing the rail head down, the upper collector is lowered and the rail is cooled.

When changing to different types of rails, the positioning mechanism of the lower and side collectors 30 controls the distance from the surface of the rail head to the collectors.

The air entering the injection system of the gas medium passes through a filter system 15 (Fig.2), an air preparation system 14 to prevent the influence of seasonal fluctuations in the temperature of the source air.

Further, the air from the turbocharger 5 (Fig.2) through the pressure reducing valve 6 and control valves 8 is supplied to the manifolds 2, 3, 4. Moreover, the control system 12 by means of valves 6 and 8 controls the pressure and flow rate of the gas medium.

Water from the tank 11 or any other source by the water supply device 10, through the control valves 8, is supplied to the injectors 9. Due to the injection of water by the injectors 9 into the gas flow, the cooling ability of the gas medium is changed.

Then the gas medium is fed into the collectors 2, 3, 4 and sent to the cooling zone of the rail surface I, II, III. Moreover, the control system 12 automatically sets the operation mode of the valves 8 so that the injectors 9 operate in a quasi-continuous and / or continuous pulse mode, due to which the cooling ability of the gas medium changes smoothly.

The control system 12 (Fig. 2), according to the programmed mode, controls the heat treatment of the rail with the correction of the mode according to the controlled parameters 18-25 (Fig. 3).

At the end of the cooling mode, the positioning mechanism of the upper collectors 29 (Fig.6) raises to the upper position, the unloading mechanism 28 moves the rail to the roller conveyor 32.

The experiments were carried out on the cooling device shown in figure 2, figure 3 and figure 4, on full-profile samples of the rail P65 1200 mm long. Samples taken from steels with chemical compositions shown in table 3.

Table 3 Chemical composition of rail steel samples No. p.p C Mn Si P S Al V Cr Ni Cu Ti Mo N one 0.78 0.97 0.37 0.010 0.009 0.004 0.056 0.277 0.115 0.009 less than 0,0050 2 0.76 0.95 0.37 0.012 0.005 0.005 0,052 0,037 0.107 0.013 0.0034 less than 0,0050 0.0086

According to the results of the experiments, each hardened sample was subjected to laboratory tests. The hardness, microstructure, and physicomechanical properties of the rail were investigated.

Table 1 shows the experimental data of the dependence of the rail cooling rate on the pressure of the gas medium.

Table 2 shows the experimental data of the dependence of the rail cooling rate on the pressure of the gas medium and the amount of injected water.

From table 1 and table 2, the technological parameters and intervals of cooling rates were selected for rail samples made of chromium alloyed steel of chemical composition No. 1 and carbon steel No. 2 from table 3.

Data on the technological parameters of heat treatment of samples of R65 rails from steel of chemical composition No. 1 and No. 2 from table 3 and the results of physical and mechanical tests and studies of the microstructure are shown in table 4 and table 5.

Thus, the proposed method allows the heat treatment of rails of both alloyed and unalloyed (carbon hypereutectoid and hypereutectoid) steels with various preset cooling modes.

The method and device for heat treatment of rails allows to obtain the structure of fine-grained hardening sorbitol to a greater depth, to increase the physical and mechanical properties of steel and thereby increase the operational stability of rails.

Claims (12)

1. A method of heat treatment of rails, including continuous cooling of simultaneously the rail head and sole from rolling and / or reheating from a temperature not lower than the austenization temperature, characterized in that the rail is cooled by air with regulation of changes in the degree of air humidity and its pressure during heat treatment by pulsed quasi-continuous and / or continuous injection of water into the air flow with the provision of changing the cooling ability of the medium. 2. The method according to claim 1, characterized in that the air flow is regulated depending on the chemical composition of rail steel with a flow rate of 10 ÷ 60 m ³ / min per meter of running rail, while the flow rate of injected water is changed to 12 l / min per one meter running rail. 3. The method according to claim 1, characterized in that the flow of air is regulated depending on the initial temperature of the rail, the values of humidity and temperature of the source air and water temperature. 4. The method according to claim 1, characterized in that the water content in the air is maintained within 0.2 l of water per cubic meter of air. 5. The method according to claim 1, characterized in that the air pressure is regulated within the range of 0.005 ÷ 0.1 MPa. 6. The method according to claim 1 or 2, characterized in that the cooling rate of the rail is controlled in the range of 2 ÷ 20 ° C / s. 7. A device for heat treatment of a rail, comprising mechanisms for loading, unloading, positioning and fixing the rail, a turbocharger, a duct system and manifolds with nozzle openings for supplying a cooling medium to the rail head and sole at the same time, positioning mechanisms for ducts and manifolds with nozzle openings, a control system coolant supply, temperature control system, characterized in that it has a system of pulsed quasi-continuous and / or continuous injection of water into the air a stream containing a water tank, a system of water pipelines, water flow and pressure regulators in the form of controlled valves and controlled control valves, pulse injectors with a control system for injecting water in a pulsed quasi-continuous and / or continuous mode into an air stream with a controlled change in the degree humidity and its pressure to ensure changes in the cooling ability of the medium, while the mechanisms of loading, unloading, positioning and fixing the rail are made with the possibility the location of the rail during processing with the head down. 8. The device according to claim 7, characterized in that it has a flow rate and air pressure regulator in the form of controlled valves and controlled control valves in accordance with a program-defined mode. 9. The device according to claim 7, characterized in that the control system is configured to determine the temperature and humidity of the source air environment, water temperature and based on the obtained correction data of the cooling mode. 10. The device according to claim 7, characterized in that it is equipped with mechanisms for moving rails and / or collectors relative to the vertical and / or horizontal axis. 11. The device according to claim 7, characterized in that it is configured to change the distance of nozzle openings to the surface of rail profile elements when cooling rails of various profiles. 12. The device according to claim 7, characterized in that the control system has the ability to control the pressure and flow rate of the air and set the mode of operation of the turbocharger.

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