A method for producing a low alloy steel rail for foreign subways

Abstract

The application discloses a production method of low-alloy steel rail for foreign subway, and the rail comprises the following elements in percentage by mass: C: 0.78-0.82%, Si: 0.50-0.85%, Mn: 1.13-1.25%, Cr: 0.60-0.70%, P: 0.02% or less, and S: 0.02% or less. The balance is iron and inevitable impurities. The specific production process of the rail is as follows: (1) heating of the billet; (2) rolling: the billet is rolled into the rail by a universal rolling mill, the opening rolling temperature is 1132 DEG C, and the final rolling temperature is 933 DEG C; (3) straightening; and (4) ultrasonic flaw detection. The application aims to provide a production method of low-alloy steel rail for foreign subway, and high-hardness hot-rolled rails are obtained by process optimization under the premise of adding less alloy types, so that the performance requirements of foreign users on the low-alloy rail in the American standard are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metallurgical materials, in particular to a production method of low alloy steel rail for foreign subway. BACKGROUND

[0002] The AREMA standard is one of the internationally recommended rail standards for customers to purchase rails, and most of the American countries adopt this standard to purchase rails from China. Therefore, there is a considerable market demand. In addition, other ore resource countries are also building heavy haul railways, and the market of low alloy rails will also expand. By developing low alloy medium strength rails with rail head tread hardness above 325HB, Rp0.2≥80.0ksi (550MPa), Rm≥147ksi (1010MPa), and elongation not less than 8%, the market competitiveness of Baotou Steel products can be improved, the blank of rail varieties can be filled, the economic benefits can be increased, and the demand for exporting rails to America can be met. SUMMARY

[0003] The purpose of the present application is to provide a production method of low alloy steel rail for foreign subway, which obtains high hardness level hot-rolled rail through process optimization under the premise of adding less alloy types, and meets the performance requirements of foreign users for low alloy medium rails.

[0004] To solve the above technical problems, the present application adopts the following technical scheme:

[0005] The production method of low alloy steel rail for foreign subway provided by the present application comprises the following elements in percentage by mass: C: 0.78-0.82%, Si: 0.50-0.85%, Mn: 1.13-1.25%, Cr: 0.60-0.70%, P≤0.02%, S≤0.02%. The balance is iron and inevitable impurities.

[0006] The specific production process of the rail is as follows:

[0007] (1) Steel billet heating: the steel billet is rolled in the 2# line of the rail beam factory, and the heating time and temperature of the rail are as follows:

[0008] The preheating section or heating I section is 639±10℃, the heating II section is 839±10℃, the heating III section is 1232±10℃, the soaking section is 1209±10℃, and the total heating time is 237±10min.

[0009] (2) Rolling: the steel billet is rolled into a rail by a universal mill, and the opening rolling temperature is 1132±10℃ and the finish rolling temperature is 933±10℃.

[0010] The rail rolling process is tracked and temperature is measured, according to the temperature drop curve analysis, the IH rail is mainly divided into three stages in the cooling process, the first stage is the high temperature austenite cooling interval, 950-680℃, the rail is moved to the upper cooling bed after finishing rolling, which shows that the temperature drops faster, the time is 180s, and the cooling speed is 0.89℃ / s; the second stage is 680-630℃, the rail carries out pearlite transformation, and the latent heat of phase transition is released, which shows that the platform appears on the temperature, the austenite is transformed into pearlite in this period of time, the time is 540s, and the cooling speed is 0.07℃ / s; the third stage is 586-498℃, which is the cooling speed of the rail on the cooling bed after the pearlite transformation is completed, and no phase change occurs, and the cooling speed is 0.24℃ / s;

[0011] (3) straightening: the rail is cooled on the cooling bed, and then is straightened in a straightening machine, the straightened rail is subjected to surface inspection and flatness inspection, no damage is found on the surface, the flatness inspection meets the standard requirements, the straightening temperature of the rail should not be higher than 60℃, the straightened rail should be straight, and no wave bending, hard bending and obvious distortion are allowed, and the rail is allowed to be rolled once only;

[0012] (4) ultrasonic flaw detection: the rail is subjected to ultrasonic flaw detection, and the head, rail waist, rail bottom and rail bottom corner are detected, and no internal defects exceeding the standard are found in the whole length of the rail.

[0013] Further, the low alloy steel rail for foreign subway is a pearlitic rail steel.

[0014] Further, the average interlamellar spacing of the nanoscale pearlite microstructure of the prepared pearlitic rail is 0.19μm.

[0015] Further, the prepared pearlitic rail meets the following requirements: the hardness value is 325-340HBW.

[0016] Further, the prepared pearlitic rail meets the following requirements: the yield strength is 651-672MPa, the tensile strength is 1120-1159MPa, and the elongation is 8-11%.

[0017] Compared with the prior art, the beneficial technical effects of the present application are:

[0018] The average interlamellar spacing of the nanoscale pearlite microstructure of the prepared pearlitic rail is 0.21μm, the hardness value is 325-340HBW, the yield strength is 590-672MPa, the tensile strength is 1120-1159MPa, and the elongation is 8-11%. BRIEF DESCRIPTION OF DRAWINGS

[0019] The present application will be further described below in combination with the drawings.

[0020] Figure 1 It is a schematic view of rail cross section hardness test.

[0021] Figure 2 Figure 1 is a low-magnification photograph of a steel rail;

[0022] Figure 3 Figure 2 is a photograph of the microstructure of a test steel;

[0023] Figure 4 Figure 3 is a photograph of the interlamellar spacing of the pearlite of a rail head. DETAILED DESCRIPTION

[0024] A production method of a low-alloy steel rail for a foreign subway, comprising the following steps:

[0025] The pearlitic rail steel comprises the following components in percentage by mass: C: 0.78-0.82%, Si: 0.50-0.85%, Mn: 1.13-1.25%, Cr: 0.60-0.70%, P≤0.02%, S≤0.02%. The balance is iron and inevitable impurities.

[0026] The specific production process of the steel rail is as follows:

[0027] (1) Steel billet heating: the steel billet is rolled in the 2# line of the rail beam factory, and the heating time and temperature of the steel rail are shown in Table 1.

[0028] Table 1 Steel rail heating process

[0029]

[0030] Rolling: the steel billet is rolled into a steel rail by a universal rolling mill, and the opening rolling temperature is 1132℃ and the final rolling temperature is 933℃.

[0031] Table 2 Temperature change of IH steel rail after rolling

[0032]

[0033] The temperature of the steel rail rolling process is tracked, and according to the temperature drop curve analysis, the IH rail is mainly divided into three stages in the cooling process. The first stage is the high-temperature austenite cooling interval (about 950-680℃), and the steel rail is moved to the upper cooling bed after finishing rolling, which shows a rapid temperature drop, and the time is about 180s, and the cooling speed is 0.89℃ / S; the second stage (about 680-630℃) is the pearlite transformation of the steel rail, and the latent heat of phase transition is released, which shows a platform in temperature, and the austenite is transformed into pearlite in this period, and the time is about 540s, and the cooling speed is 0.07℃ / S; the third stage (586-498℃) is the cooling speed of the steel rail on the cooling bed after the end of the pearlite transformation, and no phase change occurs, and the cooling speed is 0.24℃ / S.

[0034] (3) Straightening: the steel rail is cooled on the cooling bed and then enters the straightening machine for straightening, the straightened steel rail is subjected to surface inspection and flatness inspection, no damage is found on the surface, the flatness inspection meets the standard requirements, the straightening temperature of the steel rail should not exceed 60 DEG C, the straightened steel rail should be straight, no wave bending, hard bending and obvious distortion are allowed, and the steel rail is allowed to be rolled once. A reasonable straightening process is formulated for the steel rail.

[0035] (4) Ultrasonic flaw detection: the steel rail is subjected to ultrasonic full-length flaw detection, and the head, rail waist, rail bottom and rail bottom corner are detected, and no internal defects exceeding the standard are found in the full length of the steel rail.

[0036] The present application also provides a pearlitic steel rail obtained by the preparation method.

[0037] The rail tread hardness and tensile property of the front, middle and rear sections of the debugging steel rail are detected, and the specific test results are shown in Table 3.

[0038] Table 3 Steel rail test results

[0039]

[0040] The cross-section hardness of the 103# sample is tested in the technical center laboratory, and the test results are shown in the following Figure 1 .

[0041] Table 4 Steel rail cross-section test results

[0042]

[0043] IH hot-rolled steel rail 103# takes one sample for steel rail macroscopic inspection, and the test results do not find white spots, excessive shrinkage and segregation, internal cracks, skin peeling, delamination, visible inclusions and other defects, and all are qualified, and the macroscopic photos are shown in Figure 2 . The steel rail ultrasonic flaw detection is qualified, and no internal defects are found.

[0044] IH steel rail 103# and 203# metallographic structure are tested, and the test results show that the metallographic structure is pearlite structure, and the maximum value of the steel rail decarburization layer depth is 0.35mm, as shown in Figure 3 .

[0045] The inclusions of the steel rail 103# are detected, and the specific test results are shown in Table 5.

[0046] Table 5 Steel rail inclusion test results

[0047]

[0048] The pearlite interlamellar spacing of the IH rail head was measured by SEM, and the measured result was 0.19 μm. The photograph of the interlamellar spacing is shown in Figure 4 .

[0049] Table 6 IH rail interlamellar spacing test results

[0050]

[0051] The above-described embodiments are only to describe the preferred modes of the present application, and are not intended to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for producing a low alloy steel rail for foreign subways, characterized by: The steel rail comprises the following element components in percentage by mass: C: 0.78-0.82%, Si: 0.50-0.85%, Mn: 1.13-1.25%, Cr: 0.60-0.70%, P≤0.02%, S≤0.02%; the balance is iron and inevitable impurities; The specific production process of the steel rail is as follows: (1) Steel billet heating: the steel billet is rolled in the 2# line of the rail beam factory, and the heating time and temperature of the steel rail are as follows: Preheating section or heating I section 639±10℃, heating II section 839±10℃, heating III section 1232±10℃, Soaking section 1209±10℃, total heating time 237±10min; (2) Rolling: the steel billet is rolled into a steel rail by a universal mill, and the opening rolling temperature is 1132±10℃ and the final rolling temperature is 933±10℃; The temperature of the steel rail rolling process is tracked, and according to the temperature drop curve analysis, the IH rail is mainly divided into three stages in the cooling process, the first stage is the high temperature austenite cooling interval, 950-680℃, the steel rail is moved to the upper cooling bed after final rolling, which shows a rapid temperature drop, the time is 180s, and the cooling speed is 0.89℃ / s; the second stage is 680-630℃, the steel rail performs pearlite transformation, and releases latent heat of phase transition, which shows a platform in temperature, this period of time the austenite is transformed into pearlite, the time is 540s, and the cooling speed is 0.07℃ / s; the third stage is 586-498℃, which is the cooling speed of the steel rail on the cooling bed after the end of the pearlite transformation, and no phase change occurs, and the cooling speed is 0.24℃ / s; (3) Straightening: the steel rail is cooled on the cooling bed and then enters the straightening machine for straightening, the surface of the straightened steel rail is inspected and the flatness is tested, no damage is found on the surface, the flatness test meets the standard requirements, the straightening temperature of the steel rail should not exceed 60℃, the straightened steel rail should be straight, without wave bending, hard bending and obvious distortion, and only one roll straightening is allowed; (4) Ultrasonic flaw detection: the steel rail is subjected to ultrasonic flaw detection, and the head, rail waist, rail bottom and rail bottom corner are detected, and no internal defects exceeding the standard are found in the whole length of the steel rail.

2. The production method of low alloy steel rail for foreign subway according to claim 1, characterized in that: The low alloy steel rail for foreign subway is a pearlitic steel rail.

3. The production method of low alloy steel rail for foreign subway according to claim 1, characterized in that: The prepared pearlitic steel rail meets the hardness value of 325-340HBW.

4. The production method of low alloy steel rail for foreign subway according to claim 1, characterized in that: The prepared pearlitic steel rail meets the yield strength of 651-672MPa, the tensile strength of 1120-1159MPa, and the elongation of 8-11%.

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