Straightening and tempering process for reducing residual stress of rail web of exit steel rail

Abstract

The invention discloses a straightening and tempering process for reducing the residual stress of the rail web of an outlet steel rail, which reasonably optimizes the rolling reduction and straightening speed of 2 #, 4 #, 6 # and 8 # straightening rollers which influence the residual stress of the outlet steel rail after straightening in the straightening process: setting the roller entering speed of the outlet steel rail before straightening to be 2.0-2.5 m / s, and setting the straightening speed to be 0.8-0.1.2 m / s; the rolling reduction of the 2 # straightening roll is 16-20 mm, the rolling reduction of the 4 # straightening roll is 12-15 mm, the rolling reduction of the 6 # straightening roll is 7-9 mm, and the rolling reduction of the 8 # straightening roll is 0.1-1.0 mm; the tempering temperature is 300-400 DEG C, heat preservation is conducted for 4-12 h, and after heat preservation is finished, the steel rail is taken out of the furnace and air-cooled to the room temperature. The invention aims to effectively control the magnitude of the rail web residual stress after the outlet steel rail is straightened.

Description

Technical Field

[0001] The present invention belongs to the technical field of rail manufacturing, and particularly relates to a straightening and tempering process for reducing the residual stress in the rail web of export rails. Background Art

[0002] Residual stress is an important index for evaluating the performance of rails. In the Technical Conditions for Ordering Rails of 43 kg / m to 75 kg / m in TB / T 2344-2012, only the longitudinal residual stress at the center point of the rail base is required, and the longitudinal residual tensile stress at the center of the rail base is required to be ≤ 250 MPa. However, during the service of the rail, due to rust, character defects, and cold damage, etc., fatigue crack sources are likely to form in the rail web. If the residual tensile stress in the rail height direction is too large at this time, combined with the bending stress during train operation, it is extremely easy to cause longitudinal cracking in the rail web. The length of such cracking can reach more than 1 m, which is likely to cause derailment of the train and pose a great safety hazard. Therefore, there is an urgent need for a rail manufacturing method to reduce the residual stress in the rail web along the rail height direction.

[0003] Currently, there is no research and invention on the control of flatness, straightening additional stress, and residual stress during the production process for export rails, and all research and inventions do not explain the residual stress in the rail web. In the actual service process of the rail, the residual stress and service state of the rail are the key points. Therefore, a reasonable straightening process and tempering process can further reduce the residual stress of the rail, especially the residual stress in the rail web, thereby effectively improving the service performance of the rail. Summary of the Invention

[0004] The purpose of the present invention is to provide a straightening and tempering process for reducing the residual stress in the rail web of export rails, so as to effectively control the magnitude of the residual stress in the rail web after straightening of export rails.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A straightening and tempering process for reducing the residual stress in the rail web of export rails according to the present invention reasonably optimizes the reduction amount and straightening speed of the 2#, 4#, 6#, and 8# straightening rolls that affect the residual stress of the export rails after straightening: the entry roll speed before straightening the export rails is set to 2.0 - 2.5 m / s, the straightening rate is set to 0.8 - 1.2 m / s, the reduction amount of the 2# straightening roll is 16 - 20 mm, the reduction amount of the 4# straightening roll is 12 - 15 mm, the reduction amount of the 6# straightening roll is 7 - 9 mm, and the reduction amount of the 8# straightening roll is 0.1 - 1.0 mm; the whole rail after straightening is subjected to tempering treatment, wherein the tempering temperature is 300 - 400 °C, the heat preservation time is 4 - 12 h, and after the heat preservation is completed, it is taken out of the furnace and air-cooled to room temperature.

[0007] Further, the tempering temperature is 350 - 400 °C, and the heat preservation time is 4 - 8 h.

[0008] Further, the tempering temperature is 400°C and the holding time is 4 hours.

[0009] Further, the tempering temperature is 400°C and the holding time is 6 hours.

[0010] Further, the tempering temperature is 350°C and the holding time is 8 hours.

[0011] Further, the tempering temperature is 300°C and the holding time is 4 hours.

[0012] Further, the reduction of the 2# straightening roll is 18 mm, the reduction of the 4# straightening roll is 13 mm, the reduction of the 6# straightening roll is 8 mm, and the reduction of the 8# straightening roll is 0.6 mm; the straightening speed is 0.9 m / s.

[0013] Compared with the prior art, the beneficial technical effects of the present invention are:

[0014] The exit rail obtained by the straightening and tempering process of the present invention can meet the requirements of the European standard for flatness and microstructure, and also control the residual stress in the web within 50 MPa. Description of the Drawings

[0015] The present invention will be further described below in conjunction with the description of the drawings.

[0016] Figure 1 It is the microstructure morphology corresponding to different tempering processes. Detailed Embodiments

[0017] A straightening and tempering process for reducing the residual stress in the web of the exit rail. Through multiple experiments on the rail after heat treatment with a specification section of 136RE and an ambient temperature of 15°C for the exit rail, different straightening processes are adopted, and the reductions of the 2#, 4#, 6#, and 8# straightening rolls and the straightening speed that affect the residual stress of the straightened exit rail during the straightening process are reasonably optimized and combined with relevant tempering processes:

[0018] The entry speed of the exit rail before straightening is set to 2.0 - 2.5 m / s, the straightening speed is set to 0.8 - 0.12 m / s, the reduction of the 2# straightening roll is 16 - 20 mm, the reduction of the 4# straightening roll is 12 - 15 mm, the reduction of the 6# straightening roll is 7 - 9 mm, and the reduction of the 8# straightening roll is 0.1 - 1.0 mm.

[0019] The straightened exit rail is promptly subjected to tempering treatment. The heating temperature of the tempering process is between 300 and 400°C, the holding time is 4 - 12 hours, and after the holding is completed, it is taken out of the furnace and air-cooled to room temperature:

[0020] Table 1 Comparison of Different Straightening and Tempering Processes in Each Embodiment

[0021]

[0022] As can be seen from Table 1, for the rails used in Examples 1-5 and Comparative Example 1, without special instructions, other steps for preparing the rails, such as furnace charge smelting, LF refining, vacuum treatment, casting, cooling, heating furnace heating, rolling, heat treatment, processing, etc. are all conventional operations in the art. The flatness and residual stress in the rail web were compared under different straightening and tempering processes with the same composition.

[0023] For Example 1, the straightening process parameters were set at the upper limit and were combined with a relatively high tempering temperature. For Examples 2, 3, and 4, the straightening process was set at the middle limit and was combined with different tempering temperatures to match the response time. All of these three examples obtained good flatness. Except for Example 5 which adopted a lower tempering process and the residual stress in the rail web was not lower than 50 MPa, the other two examples both met the requirement of being lower than 50 MPa. For Example 5, both the straightening process parameters and the tempering process were controlled at the lower limit, resulting in poor flatness of the obtained rail and the residual stress in the rail web being greater than 50 MPa.

[0024] Comparative Example 1 shows the flatness and residual stress in the rail web after the straightening process was set at the middle limit and without the tempering process. Compared with Examples 2 and 3, the residual stress in the rail web of the rail after tempering decreased from 84 to 35 and 22 MPa, and the effect of reducing the residual stress was significant.

[0025] During the process of the embodiments of the present invention, compared with Examples 1-4, the microstructure of the rail did not deteriorate, and it was all pearlite plus a small amount of ferrite microstructure.

[0026] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A straightening and tempering process for reducing the residual stress in the web of export rails, characterized in that, The reduction and straightening speed of the 2#, 4#, 6#, and 8# straightening rolls that affect the residual stress of the rail after straightening during the straightening process were reasonably optimized: the entry speed of the rail before straightening was set to 2.0 - 2.5 m / s, the straightening rate was set to 0.8 - 1.2 m / s, the reduction of the 2# straightening roll was 16 - 20 mm, the reduction of the 4# straightening roll was 12 - 15 mm, the reduction of the 6# straightening roll was 7 - 9 mm, and the reduction of the 8# straightening roll was 0.1 - 1.0 mm; the whole straightened rail was subjected to tempering treatment, where the tempering temperature was 300 - 400 °C, the heat preservation time was 4 - 12 h, and after the heat preservation was completed, it was taken out of the furnace and air-cooled to room temperature.

2. The straightening and tempering process for reducing the residual stress in the web of the exported rail according to claim 1, wherein The tempering temperature is 350 - 400 °C, and the heat preservation time is 4 - 8 h.

3. The straightening and tempering process for reducing the residual stress in the web of the exported rail according to claim 2, characterized in that, The tempering temperature is 400 °C, and the heat preservation time is 4 h.

4. The straightening and tempering process for reducing the residual stress in the web of the exported rail according to claim 3, characterized in that, The tempering temperature is 400 °C, and the heat preservation time is 6 h.

5. The straightening and tempering process for reducing the residual stress in the web of the exit rail according to claim 4, characterized in that, The tempering temperature is 350 °C, and the heat preservation time is 8 h.

6. The straightening and tempering process for reducing the residual stress in the web of the exported rail according to claim 1, characterized in that, The tempering temperature is 300 °C, and the heat preservation time is 4 h.

7. The straightening and tempering process for reducing the residual stress in the web of the exported rail according to claim 5, characterized in that, The reduction of the 2# straightening roll is 18 mm, the reduction of the 4# straightening roll is 13 mm, the reduction of the 6# straightening roll is 8 mm, and the reduction of the 8# straightening roll is 0.6 mm; the straightening rate is 0.9 m / s.

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