A straightening process capable of reducing residual stress in bainite rails

Abstract

The invention discloses a straightening process capable of reducing the residual stress of a bainite rail, and reasonably optimizes the pressing amount and straightening speed of 2#, 4#, 6# and 8# straightening rollers that affect the residual stress of the bainite rail after straightening: the roller entry speed of the bainite rail before straightening is set to 2.4-2.6 m / s, the straightening rate is set to 0.7-0.9 m / s, the pressing amount of the 2# straightening roller is 25-27 mm, the pressing amount of the 4# straightening roller is 8.5-8.7 mm, the pressing amount of the 6# straightening roller is 6.1-6.3 mm, and the pressing amount of the 8# straightening roller is 1.7-1.9 mm, so that the straightened bainite rail can meet the requirements of the iron standard 2344 for straightness. The purpose of the invention is to provide a straightening process capable of reducing the residual stress of a bainite rail, so as to effectively control the magnitude of the residual stress of the bainite rail after straightening.

Description

Technical Field

[0001] The invention relates to a straightening process capable of reducing the residual stress of a bainite rail. Background Art

[0002] Bainite rails have the characteristics of high strength and high toughness, and are ideal products for today's heavy-duty railways. However, as their strength increases, the residual stress of bainite rails also increases. The residual stress of bainite rails is 1.5 times that of ordinary rails. The increase in residual stress will bring many negative effects. For example, bainite rails must be tempered in time after quenching, otherwise, the rails may have "uncovering" defects on the cooling bed (see Figure 1 ), especially the increase of residual stress in the rail head is the main cause of the "core damage" defect 1mm-5mm below the rail head tread when the rail is in service. Therefore, effectively reducing the residual stress of bainitic rails is not only related to the yield rate and service life of the product, but also has important significance for the safety of train operation. At present, the residual stress is mainly reduced by reasonable pre-bending and straightening processes of the rails at home and abroad. However, when the rails are straightened, the magnitude of the straightening force is related to the original curvature and yield strength of the rails. In addition, due to the particularity of the internal microstructure of bainitic rails, bainitic rails are also significantly different from other pearlite rails in straightening technology. In view of the particularity of bainitic rails, a matching straightening process should be explored to achieve a method of ensuring the outer dimensions of the rails while also obtaining a smaller residual stress. Summary of the invention

[0003] The purpose of the present invention is to provide a straightening process capable of reducing the residual stress of a bainite rail, so as to effectively control the magnitude of the residual stress of the bainite rail after straightening.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a straightening process capable of reducing the residual stress of a bainite rail. During the straightening process, the pressing amount and the straightening speed of the 2#, 4#, 6# and 8# straightening rollers that affect the residual stress of the bainite rail after straightening are reasonably optimized:

[0006] The roller speed of the bainitic rail before straightening is set to 2.4-2.6m / s, the straightening rate is set to 0.7-0.9m / s, the reduction of the 2# straightening roller is 25-27mm, the reduction of the 4# straightening roller is 8.5-8.7mm, the reduction of the 6# straightening roller is 6.1-6.3mm, and the reduction of the 8# straightening roller is 1.7-1.9mm. The straightened bainitic rail can meet the straightness requirements of the Iron Standard 2344.

[0007] Furthermore, the straightening process controls the residual stress within +250 MPa, and the straightened bainite rail has no "lidding" defect on the cooling bed.

[0008] Furthermore, the roller speed of the bainitic rail before straightening is set to 2.5m / s, the straightening rate is set to 0.8m / s, the reduction of the 2# straightening roller is 26mm, the reduction of the 4# straightening roller is 8.6mm, the reduction of the 6# straightening roller is 6.2mm, and the reduction of the 8# straightening roller is 1.8mm. The straightened bainitic rail can meet the straightness requirements of the Iron Standard 2344.

[0009] Compared with the prior art, the beneficial technical effects of the present invention are:

[0010] The straightened bainite rail obtained by the straightening process of the present invention can meet the straightness requirement of Iron Standard 2344, and the residual stress is controlled within +250MPa. The straightened bainite rail has no "lidding" defect on the cooling bed. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will be further described below in conjunction with the accompanying drawings.

[0012] Figure 1 The diagram is a schematic diagram of the straightening process of the present invention that can reduce the residual stress of a bainite rail. DETAILED DESCRIPTION

[0013] A straightening process that can reduce the residual stress of bainite rails is proposed. Different straightening processes are adopted for bainite rails with a specification of 60kg / m and a straightness of 2m and 2.4mm after residual heat quenching at an ambient temperature of 15°C. Through multiple groups of experiments, the reduction amount and straightening speed of 2#, 4#, 6#, and 8# straightening rollers that affect the residual stress of the bainite rails after straightening are reasonably optimized during the straightening process:

[0014] The roller speed of the bainitic rail before straightening is set to 2.4-2.6m / s, the straightening rate is set to 0.7-0.9m / s, the reduction of the 2# straightening roller is 25-27mm, the reduction of the 4# straightening roller is 8.5-8.7mm, the reduction of the 6# straightening roller is 6.1-6.3mm, and the reduction of the 8# straightening roller is 1.7-1.9mm. The straightened bainitic rail can meet the straightness requirements of the Iron Standard 2344.

[0015] Example

[0016] like Figure 1 As shown, a straightening process capable of reducing residual stress of bainite rail comprises:

[0017] (1) Send the pre-bent rails to the straightening machine, and the straightness of the rails must meet relevant requirements;

[0018] (2) Set the straightening machine program 1: the roller speed is set to 2.5 m / s, the pressure reduction of the 2# straightening roller is set to 26 mm, the pressure reduction of the 4# straightening roller is set to 8.6 mm, the pressure reduction of the 6# straightening roller is set to 6.2 mm, and the pressure reduction of the 8# straightening roller is set to 1.8 mm.

[0019] (3) Setting procedure 2: After the front end of the rail enters the straightening machine, reduce the roller speed to 0.8 m / s and straighten the rail.

[0020] The specific experimental schemes and experimental results of different processes are shown in Table 1.

[0021] Table 1

[0022]

[0023]

[0024] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A straightening process capable of reducing residual stress in bainitic rails, It is characterized in that The reduction amount and straightening speed of 2#, 4#, 6# and 8# straightening rollers, which affect the residual stress of bainite rail after straightening, were reasonably optimized: The roller speed of the bainitic rail before straightening is set to 2.4-2.6m / s, the straightening rate is set to 0.7-0.9m / s, the reduction of the 2# straightening roller is 25-27mm, the reduction of the 4# straightening roller is 8.5-8.7mm, the reduction of the 6# straightening roller is 6.1-6.3mm, and the reduction of the 8# straightening roller is 1.7-1.9mm. The straightened bainitic rail can meet the straightness requirements of the Iron Standard 2344.

2. The straightening process for reducing residual stress of bainite rail according to claim 1, It is characterized in that The straightening process controls the residual stress within +250MPa, and the straightened bainite rail has no "lidding" defect on the cooling bed.

3. The straightening process for reducing residual stress of bainite rail according to claim 1, It is characterized in that The roller speed of the bainitic rail before straightening is set to 2.5m / s, the straightening rate is set to 0.8m / s, the reduction of the 2# straightening roller is 26mm, the reduction of the 4# straightening roller is 8.6mm, the reduction of the 6# straightening roller is 6.2mm, and the reduction of the 8# straightening roller is 1.8mm. The straightened bainitic rail can meet the straightness requirements of the Iron Standard 2344.

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