A method for straightening a bainite rail with low additional residual stress by on-line heat treatment

Abstract

The application discloses a low-additional-residual-stress on-line heat treatment bainite rail straightening method, and is aimed at optimizing the on-line heat treatment state bainite rail straightening process, and focuses on the horizontal straightening roller which influences the residual stress and flatness of the rail, so that the additional residual stress of the rail after straightening is further reduced under the premise of meeting the flatness requirement of the rail.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel rail metallurgical rolling, in particular to a low-addition residual stress online heat treatment bainite rail straightening method. BACKGROUND

[0002] As the most important component in heavy rail structure, the size and distribution of internal residual stress and fatigue performance of high-strength heat-treated steel rail will directly affect the service performance of the rail. Studies have shown that if there is excessive residual stress and an unfavorable distribution in the internal, it is easy to cause early fatigue and sudden brittle fracture of the rail, causing train derailment and overturning accidents, which poses a great potential threat to railway safety. Bainite rail has high strength and high impact toughness, and is considered the best choice to replace pearlite rail and improve the wear resistance and safety of the line.

[0003] However, compared with traditional pearlite rail, bainite rail has higher residual stress, about 1-2 times higher than pearlite rail. Excessive residual tensile stress in the rail head and rail bottom of the online heat-treated bainite rail will lead to the risk of rail head core damage, rail waist cracking and rail bottom fracture during rail service on the line, seriously affecting the safety of line service and the service performance of the rail. There are many factors that affect the residual stress of the rail, including material properties, heat treatment process parameters, geometry, processing technology, environmental factors, etc. The residual stress of the online heat-treated bainite rail is mainly composed of organizational stress, thermal stress and straightening stress, and the additional residual stress during straightening is high. The organizational stress and thermal stress of the rail are fixed characteristics of the material and cannot be changed, so in order to meet the low residual stress requirements of the rail in service, the additional residual stress during rail straightening should be controlled.

[0004] Patent No. 202310229575.X discloses a straightening process that can reduce the residual stress of bainite rail, with an entry speed of 2.4-2.6 m / s, a straightening rate of 0.7-0.9 m / s, and a 2# straightening roll reduction of 25-27 mm. This patent is a straightening process for hot-rolled bainite rail, and the entry speed and straightening speed do not meet the actual production situation, and the 2# roll reduction is obviously too large, which cannot guarantee low residual stress after straightening. Patent No. 202310229570.7 discloses a pre-bending process that can improve the straightness of bainite rail before straightening. This patent is a pre-bending process for hot-rolled bainite rail, including chord height control, pre-bending trolley operation, etc. The travel and operation of 1-40# pre-bending trolleys according to the chord height of 1.5-1.9 m is not suitable for rails produced by online heat treatment. SUMMARY

[0005] The application aims to provide a low-additional residual stress online heat treatment bainite rail straightening method, which is optimized for the online heat treatment state bainite rail straightening process, and focuses on the horizontal straightening roller which influences the residual stress and flatness of the rail.

[0006] To solve the above technical problems, the application adopts the following technical scheme:

[0007] The low-additional residual stress online heat treatment bainite rail straightening method is used for straightening the online heat treatment bainite rail by using a flat-stand combined straightening machine, and the straightening process follows the premise of meeting the rail flatness requirement and adopts the straightening idea of minimum reduction, wherein the reduction of the 2# horizontal roller is controlled between 16-18 mm, the reduction of the 4# horizontal roller is controlled between 12-14 mm, the reduction of the 6# horizontal roller is controlled between 8-10 mm, the reduction of the 8# horizontal roller is controlled between 1-3 mm, and the reduction of the 9# horizontal roller is controlled between -2-1 mm.

[0008] The rail straightening bite-in speed is between 0.5-1.0 m / s, the penetration speed is between 1.0-1.5 m / s, the straightening speed is between 1.5-2.0 m / s, and the rail straightening temperature is ≤60℃.

[0009] Further, the production process of the online heat treatment state bainite rail comprises: hot metal pretreatment, combined blowing converter smelting, LF refining, VD vacuum degassing, large billet continuous casting, billet slow cooling, billet heating, 100-meter rail rolling, 100-meter online heat treatment, combined straightening, and flaw detection, wherein the bainite rail heating temperature is between 1200-1250℃, the rolling start temperature is between 1080-1150℃, the final rolling temperature is between 930-950℃, the controlled cooling start temperature is between 650-700℃, the controlled cooling final cooling degree is between 100-150℃, and the reheat temperature is between 230-280℃.

[0010] Further, the rail comprises the following chemical components in percentage by mass: C: 0.16-0.30%, Si: 0.60-1.10%, Mn: 1.50-2.40%, Cr: 0.60-1.20%, Ni: ≤0.70%, Mo: 0.10-0.40%, Nb: ≤0.06%, V: ≤0.09%, P: ≤0.022%, S: ≤0.015%, Al: ≤0.010%, and the rest is Fe and inevitable impurities.

[0011] Further, only one straightening is allowed, and the straightened rail should be flat and straight without wave bending, hard bending and obvious distortion.

[0012] Further, under the premise of meeting the rail straightness requirement, the rail straightening additional residual stress meets ≤100MPa.

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

[0014] Under the premise of the existing process route, by adopting specific heat treatment process and straightening process, the residual stress and straightening additional residual stress of the on-line heat treated bainite rail are effectively reduced, the service performance of the rail is effectively improved, and under the premise of meeting the rail straightness requirement, the rail straightening additional residual stress is ≤100MPa. BRIEF DESCRIPTION OF DRAWINGS

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

[0016] Figure 1 For the rail straightness of the 100-meter rail in Example 1;

[0017] Figure 2 For the rail straightness of the 100-meter rail in Example 2;

[0018] Figure 3 For the rail straightness of the 100-meter rail in Example 3;

[0019] Figure 4 For the rail straightness of the 100-meter rail in Example 4;

[0020] Figure 5 For another display picture of the rail straightness of the 100-meter rail in Example 4 after straightening. DETAILED DESCRIPTION

[0021] A low-additional-residual-stress on-line heat treated bainite rail straightening method, comprising:

[0022] 1) The on-line heat treated bainite rail targeted by the present application comprises the following chemical components in percentage by mass: C: 0.16-0.30%, Si: 0.60-1.10%, Mn: 1.50-2.40%, Cr: 0.60-1.20%, Ni: ≤0.70%, Mo: 0.10-0.40%, Nb: ≤0.06%, V: ≤0.09%, P ≤0.022%, S ≤0.015%, Al: ≤0.010%, and the rest is Fe and inevitable impurities.

[0023] 2) The production process of the on-line heat treated bainite rail of the present application comprises: hot metal pretreatment → combined blown converter smelting → LF refining → VD vacuum degassing → large square billet continuous casting → billet slow cooling → billet heating → 100-meter rail rolling → 100-meter on-line heat treatment → composite straightening → flaw detection.

[0024] 3) The on-line heat treatment bainite rail steel billet heating temperature is between 1200-1250℃, the rolling temperature is between 1080-1150℃, the final rolling temperature is between 930-950℃, the controlled cooling starting temperature is between 650-700℃, the controlled cooling final cooling degree is between 100-150℃, and the re-heating temperature is between 230-280℃.

[0025] 4) After the on-line heat treatment bainite rail is smelted, rolled and on-line heat treated, when the rail temperature is ≤60℃, the rail can be straightened. The on-line heat treatment bainite rail should be straightened by using a horizontal-vertical combined straightening machine. The straightening process follows the straightening idea of using the minimum reduction under the premise of meeting the rail straightness requirement.

[0026] 5) The horizontal-vertical combined straightening machine parameter setting: the 2# horizontal roller reduction is controlled between 16-18mm, the 4# horizontal roller reduction is controlled between 12-14mm, the 6# horizontal roller reduction is controlled between 8-10mm, the 8# horizontal roller reduction is controlled between 1-3mm, and the 9# horizontal roller reduction is controlled between -2-1mm.

[0027] 6) The rail straightening bite-in speed is between 0.5-1.0m / s, the penetration speed is between 1.0-1.5m / s, and the straightening speed is between 1.5-2.0m / s. The rail is only allowed to be straightened once. The straightened rail should be straight, without wave bending, hard bending and obvious distortion.

[0028] Table 1 Comparison of different straightening processes and residual stresses in the implementation process

[0029]

[0030] Table 2 Hundred-meter rail straightness under different examples

[0031]

[0032] From Table 1, Table 2 and Figures 1-5 It can be seen that the on-line heat treatment bainite rail produced under the straightening process of Example 4 has a residual stress ≤287MPa after straightening, and an additional straightening residual stress ≤100MPa, which is the lowest macro residual stress and straightening additional residual stress in each example. At the same time, the hundred-meter rail straightness is also the best, meeting the standard requirement for hundred-meter rail straightness. Under the premise of meeting the hundred-meter rail straightness requirement, the on-line heat treatment bainite rail realizes the goals of low straightening reduction, low straightening additional residual stress and low macro residual stress, thereby reducing the risk of rail head core damage, rail waist cracking and rail bottom cracking during the rail on-line service process, and further improving the line operation safety and rail service performance.

[0033] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A method of on-line heat treatment of bainitic rail with low additional residual stresses, characterised in that: The on-line heat treated bainite rail should be straightened by using a flat-stand compound straightening machine, and the straightening process follows the straightening idea of using the minimum reduction under the premise of meeting the rail straightness requirement, wherein the reduction of the 2# horizontal roller is controlled between 16-18 mm, the reduction of the 4# horizontal roller is controlled between 12-14 mm, the reduction of the 6# horizontal roller is controlled between 8-10 mm, the reduction of the 8# horizontal roller is controlled between 1-3 mm, and the reduction of the 9# horizontal roller is controlled between -2-1 mm; The rail straightening bite-in speed is between 0.5-1.0 m / s, the penetration speed is between 1.0-1.5 m / s, the straightening speed is between 1.5-2.0 m / s, and the rail straightening temperature is ≤60℃.

2. The low-additive residual stress on-line heat treated bainite rail straightening method according to claim 1, characterized in that: The production process of the on-line heat treated bainite rail comprises: hot metal pretreatment → complex blowing converter smelting → LF refining → VD vacuum degassing → large bloom continuous casting → billet slow cooling → billet heating → 100-meter rail rolling → 100-meter on-line heat treatment → compound straightening → flaw detection; wherein the bainite rail heating temperature is between 1200-1250℃, the rolling start temperature is between 1080-1150℃, the final rolling temperature is between 930-950℃, the controlled cooling start temperature is between 650-700℃, the controlled cooling final cooling degree is between 100-150℃, and the reheat temperature is between 230-280℃.

3. The low-additive residual stress on-line heat treated bainite rail straightening method of claim 1 wherein: The rail comprises the following chemical components in mass percentage: C: 0.16-0.30%, Si: 0.60-1.10%, Mn: 1.50-2.40%, Cr: 0.60-1.20%, Ni: ≤0.70%, Mo: 0.10-0.40%, Nb: ≤0.06%, V: ≤0.09%, P: ≤0.022%, S: ≤0.015%, Al: ≤0.010%, and the rest is Fe and inevitable impurities.

4. The low-additive residual stress online heat treated bainite rail straightening method of claim 1, wherein: Only one straightening is allowed, and the straightened rail should be straight, without wave bending, hard bending and obvious distortion.

5. The low-additive residual stress online heat treated bainite rail straightening method of claim 1 wherein: Under the premise of meeting the rail straightness requirement, the rail straightening additional residual stress meets ≤100 MPa.

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