A heat treatment method capable of effectively improving the low temperature fracture toughness of rails

Abstract

The present invention discloses a heat treatment method that can effectively improve the low-temperature fracture toughness of rails, heating to 850°C±10°C at 0.8-1.2°C / s, keeping warm; cooling after taking out, entering the temperature of 760°C±10°C, using high-pressure gas for air cooling, the air pressure is 0.15-0.25MPa, and the corresponding average cooling rate is 4.5-5.5°C / s. When the sample temperature drops to 550°C±10°C, stop cooling, at which time the temperature will rise to 650°C±10°C again, and wait for 8-12s before quickly starting the water mist cooling method to quickly cool the rail head to room temperature; wherein the wind pressure continues to select 0.15-0.25MPa, the water cooling flow rate is 280-320L / h, and the average cooling rate is 8-12°C / s. Under the heat treatment thermal system of the present invention, the fracture toughness of the rails exceeds that of the heat treatment system, which can be applied to the production of rails.

Description

Technical Field

[0001] The invention relates to a heat treatment method capable of effectively improving the low-temperature fracture toughness of a rail. Background Art

[0002] The fracture toughness of rails is an important indicator of the rail's ability to resist unstable crack expansion. According to the requirements of Iron Standard 2344, rails must be K-tested before use. Ιc The determination of K is the critical value of the instability extension of the opening crack tip. This type of crack is the most dangerous in engineering components and is prone to cause low-stress brittle fracture. Ιc There are many factors, such as material organization, inclusion type and shape, sample size, loading speed, temperature, etc.

[0003] At present, this performance of rails is mainly based on the requirements of Iron Standard 2344. At -20℃, the single minimum value of rails made of materials other than U71MnH is The minimum average value is In actual production, rails are often unstable due to factors such as inclusion control level, rolling control, and cooling control. Usually, this value is distributed in This results in a decrease in the rail yield rate. Summary of the invention

[0004] In order to improve the yield rate of rails, the rails are controlled at -20°C. Ιc The stability of the value, the purpose of the present invention is to provide a heat treatment method that can effectively improve the low-temperature fracture toughness of rails. The present invention first conducts a heat treatment experiment on the experimental rails, samples the heat-treated samples according to GB / T4161 and conducts a fracture toughness experiment on an MTS810.23 testing machine to obtain the optimal controlled cooling system, and then applies the heat treatment system to the rail production line.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a heat treatment method capable of effectively improving the low temperature fracture toughness of rails. The specific heat treatment process is as follows:

[0007] Heat to 850℃±10℃ at 0.8-1.2℃ / s, and keep warm for 0.8-1.2min; start cooling after taking out, the entry temperature is 760℃±10℃, use high-pressure gas for air cooling, the air pressure is 0.15-0.25MPa, and the corresponding average cooling rate is 4.5-5.5℃ / s. When the sample temperature drops to 550℃±10℃, stop cooling. At this time, the temperature will rise to 650℃±10℃ again. This is due to the latent heat of phase change. After waiting for 8-12s, quickly start the water mist cooling method to quickly cool the rail head until it cools to room temperature; the wind pressure continues to be selected at 0.15-0.25MPa, the water cooling flow rate is 280-320L / h, and the comprehensive corresponding average cooling rate is 8-12℃ / s.

[0008] Further, the mixture was heated to 850°C at 1°C / s and kept at this temperature for 1 min.

[0009] Furthermore, the cooling entry temperature is 760°C.

[0010] Furthermore, the gas pressure is 0.2 MPa.

[0011] Furthermore, when the sample temperature drops to 550°C at an average cooling rate of 5°C / s, cooling is stopped and the temperature rises to 650°C again.

[0012] Furthermore, it is characterized in that after waiting for another 10 seconds, the water mist cooling mode is quickly started.

[0013] Furthermore, it is characterized in that the wind pressure is selected to be 0.2MPa and the water cooling flow rate is 300L / h.

[0014] Furthermore, the comprehensive corresponding average cooling rate is 10°C / s.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are:

[0016] Under the heat treatment system of the present invention, the fracture toughness of the rails exceeds This heat treatment system can be applied in the production of rails. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below in conjunction with the accompanying drawings.

[0018] Figure 1 Schematic diagram of the sampling location. DETAILED DESCRIPTION

[0019] A heat treatment method capable of effectively improving the low temperature fracture toughness of a rail comprises:

[0020] Take two 150cm long test rails, the chemical composition is shown in Table 1:

[0021] Table 1

[0022]

[0023] The heat treatment experiment was carried out in a small laboratory heating furnace according to the following experimental scheme:

[0024] Heat to 850℃ at 1℃ / s, keep warm for 1min, take out the sample and start cooling it in the pilot test machine. The sample temperature is 760℃ when entering the pilot test machine. Use high-pressure gas for air cooling with an air pressure of 0.2MPa, corresponding to an average cooling rate of about 5℃ / s. When the sample temperature drops to 550℃, stop cooling. At this time, the sample temperature will rise to about 650℃ again. This is due to the latent heat of phase change. After waiting for another 10s, quickly start the water mist cooling method to quickly cool the rail head until it cools to room temperature. The wind pressure continues to be selected at 0.2MPa, and the water cooling flow rate is 300L / h. The comprehensive corresponding average cooling rate is about 10℃ / s. The heat-treated rails are sampled and tested in accordance with GB / T4161. The experimental temperature is -20℃ and the sampling position is shown in the figure. Figure 1 ,The experimental results are shown in Table 2.

[0025] Table 2 Fracture toughness K Ιc Measurement results

[0026] Sample No. 1 2 3 4 5 average value Standard value 1# 35.6 35.8 35.9 33.9 37.0 35.64 29.0 2# 34.8 35.5 35.7 36.3 36.4 35.74 29.0

[0027] Experiments show that under this heat treatment system, the fracture toughness of the rails exceeds Finally, the heat treatment regime can be applied in the production of rails.

[0028] 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 heat treatment method capable of effectively improving the low temperature fracture toughness of rails, characterized in that: The specific heat treatment process is as follows: Heat to 850℃±10℃ at 0.8-1.2℃ / s, and keep warm for 0.8-1.2min; start cooling after taking out, the entry temperature is 760℃±10℃, use high-pressure gas for air cooling, the air pressure is 0.15-0.25MPa, and the corresponding average cooling rate is 4.5-5.5℃ / s. When the sample temperature drops to 550℃±10℃, stop cooling. At this time, the temperature will rise to 650℃±10℃ again. This is due to the latent heat of phase change. After waiting for 8-12s, quickly start the water mist cooling method to quickly cool the rail head until it cools to room temperature; the wind pressure continues to be selected at 0.15-0.25MPa, the water cooling flow rate is 280-320L / h, and the comprehensive corresponding average cooling rate is 8-12℃ / s.

2. The heat treatment method capable of effectively improving the low temperature fracture toughness of rail according to claim 1, characterized in that: Heat to 850°C at 1°C / s and keep warm for 1 min.

3. The heat treatment method capable of effectively improving the low temperature fracture toughness of rail according to claim 1, characterized in that: The entry temperature of the cooling is 760°C.

4. The heat treatment method capable of effectively improving the low temperature fracture toughness of rail according to claim 1, characterized in that: The air pressure is 0.2MPa.

5. The heat treatment method capable of effectively improving the low temperature fracture toughness of rail according to claim 1, characterized in that: The corresponding average cooling rate is 5℃ / s. When the sample temperature drops to 550℃, cooling is stopped and the temperature will rise to 650℃ again.

6. The heat treatment method capable of effectively improving the low temperature fracture toughness of rail according to claim 1, characterized in that: After waiting for another 10 seconds, quickly start the water mist cooling method.

7. The heat treatment method capable of effectively improving the low temperature fracture toughness of rail according to claim 1, characterized in that: The air pressure is selected as 0.2MPa and the water cooling flow rate is 300L / h.

8. The heat treatment method capable of effectively improving the low temperature fracture toughness of rail according to claim 1, characterized in that: The corresponding average cooling rate is 10℃ / s.

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