RU2058998C1 - Rail heat treatment method - Google Patents

Abstract

FIELD: ferrous metallurgy, namely heat treatment of rails. SUBSTANCE: method comprises steps of additional bulk heating of a rail necking portion up to 300-400 C after the rail had been subjected to bulk heating and oil cooling; performing an tempering of the rail, had been heated, upon condition of temperature difference of a sole and a head of the rail, being equal to 100-200 C at an initial period of the tempering. EFFECT: enhanced non-lenarity of rails. 1 cl, 1 tbl

Description

 The invention relates to ferrous metallurgy, in particular to heat treatment of rails.

Known is a method of heat treatment of rails, comprising a bulk quenching, tempering and additional leave soles and neck rail at a temperature above 500 ^C. forcibly-bent state sole outwards [1]
The disadvantage of this method is the need for additional operations to achieve straightness.

Closest to the proposed is a method of heat treatment of rails, including volumetric heating of the rail, cooling in oil and tempering [2]
In implementing this method, the temperature of the rail at the time the problem in quenching car 780-850 ^C. rails are in the oil for at least 5 min. The oil temperature of 40-100 ° ^C issued from the quenching car track with temperature not exceeding 100 ^{° C} and formed into a packet set in a multisection tempering furnace. Tempering time of 2 hours. Heating up to the tempering temperature of 470 ^{° C} is carried out gradually.

The disadvantage of this method is that after heat treatment is not achieved the required level of straightness of the rails. This is due to the fact that the rails are bent during hardening and tempering treatment does not reduce their misalignment, so as leave the rails begin at a temperature not exceeding 100 ^{° C,} when the rail has a high elasticity in the initial tempering period is not deformed plastically. During further heating, the ductility of the rails increases, however, the temperature over the entire cross-section of the rail profile increases uniformly, as a result of which it does not deform, and the straightness does not decrease.

 The purpose of the invention to increase the straightness of the rails due to the implementation of their plastic deformation in the initial period of vacation.

The object is achieved by the fact that in the known method comprising volumetric heating, cooling oil and leave, after the start of additional rails volumetric heating to 300-400 ^{° C} and is carried out under the condition of the sole difference of temperatures and head rails heated in the range of 100-200 ^C. during the first 12-24 minutes of vacation.

 These distinctive features provide plastic deformation of the rail by concavity on the head and compressive stresses are formed in it. The value of compressive stresses characterizes the degree of plastic deformation of the rails, namely, the higher the level of compressive stresses, the higher the degree of plastic deformation.

It was established experimentally that the desired effect is achieved only when the temperature of the rail, and hence the neck of 300-400 ^{° C} before a holiday, and the sole difference of the head temperature and 100-200 ^{° C} within the first 12-24 minutes tempering.

When the heating temperature of the bulk of the rail at least 300 ^{° C} is no sufficient plastic deformation of the rail, since the elasticity of the metal is still quite high, and hence the level of compressive stress in the head is reduced. As a result, the initial straightness of the rails is not eliminated.

At a temperature of volumetric heating rail above 400 ^{° C} during subsequent tempering is an additional curvature of the rail in the tempering furnace, whereby misalignment of the rails may even increase.

The difference between the sole and the head temperature less than ^{100 °} C is ensured effectively plastic deformation of the rails, as the level of compressive stress is small. When the difference is higher than 200 ^° C, the degree of plastic deformation of the rails increases so much that there are areas of local directness formed in the tempering furnace, and as a result, the straightness of the rails is higher than with optimal heat treatment parameters.

While maintaining the temperature difference of the sole and head rails 100-200 ^{° C} for a time less than 12 minutes does not provide sufficient plastic deformation of the rails (level of compressive residual stress is small). If the indicated temperature difference between the sole and the head persists for more than 24 minutes, then there is even a danger of additional curvature of the rails due to the appearance of sections of local directness.

A comparative analysis of the proposed technical solution with the prototype shows that the inventive method of heat treatment of rails is different from the prototype. If the rental rails prototype process started at a temperature not higher than the rail 100 ^{° C,} the proposed method at 300-400 ^C by additional heating surround the rails. In the prototype method, the temperature of all elements of the rail profile in the initial period of tempering (12-24 min) is the same, and in the proposed method between the temperatures of the sole and head provide a difference of 100-200 ^about C. These distinctive features provide the implementation of plastic deformation of the rails in the initial period of tempering and reduce their directness.

PRI me R. Processing according to the proposed method was subjected to rails of type P65 from steel M 76 of the following composition, wt. carbon 0.74; manganese 0.92; silicon 0.28; phosphorus 0.03; sulfur 0.027. Temperature for hardening rails 840 ^{° C,} the holding time in the tempering furnace 55 minutes. The hardening of the rails was made in oil. Additional volumetric heating rails performed before tempering to temperatures of 250-430 ^C (see table), tempering rails produced at ⁴⁸⁰ ° C for 2 hours. At the initial tempering period (12-24 min) provided the difference in temperatures of the sole and head ^about 50-230 C by moving the rails in the zone with a temperature of 500-550 ° ^C.

The rails were also processed in the manner described in the prior art, namely the volumetric heating to 850 ^{° C,} cooling rails in oil and tempering for 2 hours at 470 ° ^C.

 To assess the degree of plastic deformation of the rails in the tempering furnace, residual stresses were determined using strain gauges. The directness was measured after cold dressing using a control line 1 m long and a set of probes (± 0.05 mm) along the rail deflection arrow.

The results are presented in the table. Their analysis showed that at the additional heating rails by volume up to 300-400 ^{° C} and the temperature difference between the sole and head ^about 100-200 C. holiday period (12-24 minutes) intensive plastic deformation occurs in the tempering furnace. Compressive residual stresses on the rolling surface of the rail head are in the range of 50-80 MPa.

 Rail straightness The smallest maximum deflection boom does not exceed 0.35 mm.

When the heating temperature of the additional volume of at least 300 ^{° C} temperature difference between the sole and the head more than 200 ^{° C} and maintaining a difference of more than 24 min misalignment of the rails increases (the maximum deflection is increased to 0.50 mm) due to the increased plastic deformation.

At a temperature of the additional bulk heating over 400 ^{° C,} a temperature difference of less than 100 ^{° C} and saves this difference is less than 12 minutes, the maximum deflection is also increased and is 0.45 mm.

 Thus, the smallest straightness of the rails is achieved with the claimed parameters.

 The proposed method allows to reduce the straightness of the rail, and, therefore, to increase their operational stability. Particularly promising is the use of the method in the manufacture of rails for high-speed highways, where high demands are placed on the straightness of rails.

 The proposed method can be implemented in the conditions of industrial production of rails on existing technological equipment.

Claims (1)

METHOD FOR THERMAL PROCESSING OF RAILS, including volumetric heating, cooling in oil and tempering, characterized in that before tempering an additional volumetric heating of the rails is carried out up to 300 400 ^o С in the neck, and tempering of the heated rail is carried out under the condition of a temperature difference of sole and head of 100 200 ^o С within 12 24 minutes of vacation.

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