A process for tempering a 100-meter bainite rail

Abstract

The application discloses a kind of hundred meters bainite rail tempering processes, belong to the field of rail heat treatment.The application controls the heating temperature, heating speed, holding time, cooling speed, final cooling temperature, cooling mode and rail charging mode of different positions of hundred meters bainite rail heat treatment, so that bainite rail is fully tempered, and the purpose of reducing residual stress of hundred meters bainite rail, stabilizing organization, improving hundred meters rail length performance uniformity and stability is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel rail heat treatment, in particular to a hundred-meter bainite steel rail tempering process. BACKGROUND

[0002] The rapid development of heavy haul railway steel rails puts forward more stringent requirements on the strength, toughness, wear resistance and fatigue resistance of steel rails. The pearlitic steel rails commonly used at present have basically reached the limit of their strength and toughness due to their composition and organizational structure characteristics, and their impact toughness and fracture toughness are also relatively low, which cannot fully meet the service requirements of heavy haul railways. Bainite steel rails have good strength, plasticity, toughness, wear resistance and rolling contact fatigue performance, and are very suitable for service application in heavy haul railways and harsh sections.

[0003] Bainite steel rails are more sensitive to heat treatment processes. Compared with pearlitic steel rails, bainite steel rails contain residual austenite in the structure, and the TRIP effect of the residual austenite during straightening and tempering can greatly improve the strength, toughness and comprehensive performance of the steel. The unstable residual austenite in bainite steel rails is prone to stress-induced martensitic transformation, which can cause deterioration of the toughness and plasticity of bainite steel rails and generate large residual stress inside, seriously affecting the comprehensive mechanical properties and use of the steel rails. Therefore, appropriate tempering treatment is needed for bainite steel rails to improve the content and stability of residual austenite in the steel.

[0004] At the same time, a reasonable tempering process can reduce or inhibit the temper brittleness caused by other elements, has obvious delaying effect on temper brittleness, and improves the strength and toughness of the steel rail. The tempering temperature is a crucial heat treatment parameter in the processing of bainite steel rails. Too low tempering temperature may result in little change after processing, and too high tempering temperature may cause temper brittleness, thereby damaging the strength and toughness of the steel. Therefore, the tempering process of bainite steel rails has an important influence on the strength and toughness, temper brittleness and residual stress of the steel rail after tempering.

[0005] The patent with application number 202210868014.X provides a high-strength and high-toughness bainite steel rail heat treatment process. The rail head is cooled by water mist + air cooling to room temperature, and then the steel rail is subjected to two tempering treatments at 300-350℃ for 5-10h, and the obtained steel rail has a tensile strength of about 1364MPa, an elongation of about 18%, and an impact of about 170J. The patent based on online heat treatment technology for performance control does not specify the performance indicators of the hundred-meter steel rail, and also does not specify the residual stress indicators that affect the service performance of the steel rail.

[0006] The patent with the application number 201510919742.9 provides an alloy system and a heat treatment method of a bainite rail and the bainite rail, and the heat treatment method comprises: normalizing treatment by heating at 900-940 DEG C for 8h; after austenitizing by heating again at AC3+50-70 DEG C, holding for 7h, water cooling to 320-350 DEG C above the MS point, and then stacking the rail into a holding pit at 320-350 DEG C for 5h treatment; and finally tempering treatment by heating to 320-370 DEG C for 9h. The patent adopts the heat treatment process route of normalizing + quenching + tempering, needs to treat the rail by heating for three times, does not adopt the online waste heat treatment process, increases the energy consumption which is too high, is not conducive to energy saving and emission reduction, and more than 5h isothermal phase change treatment, and the domestic and foreign hundred-meter rail production plants do not have the equipment for isothermal treatment immediately after quenching, so the heat treatment process cannot be used for hundred-meter rail production and application, and seriously restricts the application of the hundred-meter rail on the main line.

[0007] The patent with the application number 202110517476.2 provides a heat treatment process of a high-strength and high-toughness bainite rail, and the patent forms a lower bainite and low-carbon martensite complex organization by controlling the cooling speed and final cooling temperature at different temperature stages in the online heat treatment process of the rail, improves the organization segregation, and thus improves the strength, toughness, wear resistance and contact fatigue performance of the rail. The patent is heated to 250 DEG C-330 DEG C for 10-30h for tempering treatment, and finally the residual stress of the rail is less than or equal to 280 MPa. The patent is based on the performance regulation of the online heat treatment technology, does not explain the indexes of the hundred-meter rail performance, and the residual stress of the rail is relatively high, which is 280 MPa. In the actual line application service process, the residual stress is too high to cause rail core damage. SUMMARY

[0008] The purpose of the present application is to provide a hundred-meter bainite rail tempering treatment process, so that the bainite rail is fully tempered, and the purpose of reducing the residual stress of the hundred-meter bainite rail, stabilizing the organization, improving the uniformity and stability of the hundred-meter rail performance is achieved.

[0009] To solve the above technical problems, the present application adopts the following technical scheme:

[0010] The present application provides a hundred-meter bainite rail tempering treatment process, which comprises:

[0011] 1) The weight percentage of the chemical composition of the rail is C: 0.20-0.40%, Si: 0.90-1.50%, Mn: 2.00-2.60%, Cr: 0.80-1.40%, Ni: 0.20-0.80%, Mo: 0.15-0.60%, P≤0.022%, S≤0.015%, Al:≤0.010%, and the rest is Fe and inevitable impurities.

[0012] 4) The production process of the 100-meter bainite rail after tempering treatment is: rail specification and quantity checking, 100-meter rail loading into the furnace, ignition heating, stepwise temperature rising, holding, slow cooling treatment, 100-meter rail unloading from the furnace, and rail air cooling.

[0013] 5) The heating of the 100-meter bainite rail after tempering treatment adopts the principle of separate control of different zones, that is, 10 heating zones are adopted for the 100-meter bainite rail, and the heating process of each zone is as follows: zone 1 and zone 10, the heating speed is controlled to be 75-85 ℃ / h; zone 2, zone 3, zone 8 and zone 9, the heating speed is controlled to be 65-75 ℃ / h; zone 4, zone 5, zone 6 and zone 7, the heating speed is controlled to be 55-65 ℃ / h; and the heating temperature and the heating speed of the 10 different zones are controlled, so that the purpose of uniform temperature in the 100-meter furnace is achieved.

[0014] 6) The heating process of the 100-meter bainite rail after tempering treatment is: the rail is heated from room temperature to 150-200 ℃, and held for 1-3 h; the rail is continuously heated to 250-300 ℃, and held for 10-20 h; and the rail is continuously heated to 350-400 ℃, and held for 2-5 h.

[0015] 7) The cooling process of the 100-meter bainite rail after tempering treatment is: when the heating of the 100-meter rail reaches the target temperature and the holding time, the 100-meter rail is subjected to slow cooling treatment with the furnace, and the cooling speed is controlled to be 5-10 ℃ / h; the final cooling temperature of the rail is controlled to be below 200 ℃; and when the target final cooling temperature is reached, the rail is unloaded for air cooling treatment.

[0016] Further, the microstructure of the bainite rail is a complex phase structure of low-carbon martensite + lower bainite + residual austenite, wherein the proportion of martensite is 50-60%, the proportion of bainite is 30-40%, and the proportion of residual austenite is 5-15%.

[0017] Further, the specification section of the bainite rail after tempering treatment is 60 kg / m or 75 kg / m, and the length is a fixed-size 100-meter rail.

[0018] Further, the heating process of each zone is as follows: zone 1 and zone 10, the heating speed is controlled to be 80 ℃ / h; zone 2, zone 3, zone 8 and zone 9, the heating speed is controlled to be 70 ℃ / h; and zone 4, zone 5, zone 6 and zone 7, the heating speed is controlled to be 60 ℃ / h; and the heating temperature and the heating speed of the 10 different zones are controlled, so that the purpose of uniform temperature in the 100-meter furnace is achieved.

[0019] Further, the loading method of the 100-meter bainite rail after tempering treatment is: the stacking layer number is ≤5, the layer spacing is ≥50 mm, and the interval between the rails in the layer is ≥80 mm.

[0020] Compared with the prior art, the beneficial technical effects of the present application are:

[0021] The present application controls the heating temperature, heating speed, holding time, cooling speed, final cooling temperature, cooling mode and rail loading mode of the tempering heat treatment of the bainite rail of 100 meters, so that the bainite rail is fully tempered, and the purposes of reducing the residual stress of the bainite rail of 100 meters, stabilizing the structure, improving the uniformity and stability of the performance of the bainite rail of 100 meters are achieved.

[0022] The bainite rail of 100 meters obtained based on the present application has the following properties: the residual stress is ≤200 MPa, the residual stress fluctuation range of the bainite rail of 100 meters is ≤15 MPa; the tensile strength is between 1306-1321 MPa, the tensile strength fluctuation range of the bainite rail of 100 meters is ≤15 MPa; the tread hardness is between 411-415 HBW, and the tread hardness fluctuation range of the bainite rail of 100 meters is ≤4 HBW. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a planar schematic diagram of the rail loading method for the bainite rail of 100 meters.

[0024] Figure 2 It is a three-dimensional schematic diagram of the rail loading method for the bainite rail of 100 meters. DETAILED DESCRIPTION

[0025] The present application is a tempering treatment process and rail loading method for the bainite rail of 100 meters, and the specific implementation method comprises the following steps:

[0026] 1) The production flow of the tempering treatment of the bainite rail of 100 meters is as follows: rail specification and quantity checking → bainite rail of 100 meters loading → ignition and heating → stepwise heating → holding → slow cooling treatment → bainite rail of 100 meters unloading → rail air cooling.

[0027] 2) The weight percentage of the chemical composition of the bainite rail of 100 meters is as follows: C: 0.20-0.40%, Si: 0.90-1.50%, Mn: 2.00-2.60%, Cr: 0.80-1.40%, Ni: 0.20-0.80%, Mo: 0.15-0.60%, P≤0.022%, S≤0.015%, Al: ≤0.010%, and the rest is Fe and inevitable impurities.

[0028] 3) The specification section of the bainite rail for tempering treatment is 60 kg / m or 75 kg / m, and the length is the bainite rail of 100 meters of fixed size.

[0029] 4) The microstructure of the bainite rail is a complex structure of low-carbon martensite + lower bainite + residual austenite, wherein the proportion of martensite is 50-60%, the proportion of bainite is 30-40%, and the proportion of residual austenite is 5-15%.

[0030] 5) The rail loading method for the bainite rail of 100 meters is shown in the schematic diagram Figure 1and schematic Figure 2 Wherein, the number of layers of the 100-meter rail stack is less than or equal to 5, the spacing between the layers of the rail is greater than or equal to 50 mm, and the spacing between the rails in the layers is greater than or equal to 80 mm, as shown in the schematic Figure 1 , the schematic Figure 2 .

[0031] 6) The 100-meter bainite rail tempering treatment heating adopts the principle of separate control in different zones, that is, 10 heating zones are used for the 100-meter bainite rail.

[0032] 7) The heating process for each zone of the 100-meter tempering furnace is as follows: Zone 1 and Zone 10: the heating speed is controlled at about 80℃ / h; Zone 2, Zone 3, Zone 8 and Zone 9: the heating speed is controlled at about 70℃ / h; Zone 4, Zone 5, Zone 6 and Zone 7: the heating speed is controlled at about 60℃ / h.

[0033] 8) The heating process for the 100-meter bainite rail tempering treatment is as follows: the rail is heated from room temperature to 150-200℃, and the temperature is maintained for 1-3h; the rail is continuously heated to 250-300℃, and the temperature is maintained for 10-20h; the rail is continuously heated to 350-400℃, and the temperature is maintained for 2-5h.

[0034] 9) The cooling process for the 100-meter bainite rail tempering treatment is as follows: after the heating of the 100-meter rail reaches the target temperature and the holding time, the rail is subjected to furnace cooling treatment, the cooling speed is controlled between 5-10℃ / h, and the final cooling temperature of the rail is controlled below 200℃, and when the target final cooling temperature is reached, the rail is taken out of the furnace and air-cooled to room temperature.

[0035] Table 1 Comparison of different heat treatment processes of each example

[0036]

[0037] Table 2 Mechanical properties of the rails corresponding to each example

[0038]

[0039] From Table 1 and Table 2, it can be seen that the tensile strength of the rail of Example 1 is between 1419-1449MPa, the fluctuation of the tensile strength along the length is 30MPa; the tread hardness is between 439-450HBW, the fluctuation of the tread hardness along the length is 11HBW; the residual stress is between 330-395MPa, and the fluctuation of the residual stress along the length is 65MPa.

[0040] The tensile strength of the rail of Example 2 is between 1373-1397MPa, the fluctuation of the tensile strength along the length is 24MPa; the tread hardness is between 425-435HBW, the fluctuation of the tread hardness along the length is 10HBW; the residual stress is between 293-332MPa, and the fluctuation of the residual stress along the length is 39MPa.

[0041] The tensile strength of the steel rail of the example 3 is between 1330-1347 MPa, the fluctuation of the tensile strength along the length of the steel rail is 17 MPa; the tread hardness is between 417-423 HBW, the fluctuation of the tread hardness along the length of the steel rail is 6 HBW; the residual stress is between 241-268 MPa, the fluctuation of the residual stress along the length of the steel rail is 27 MPa.

[0042] The tensile strength of the steel rail of the example 4 is between 1306-1321 MPa, the fluctuation of the tensile strength along the length of the steel rail is 15 MPa; the tread hardness is between 411-415 HBW, the fluctuation of the tread hardness along the length of the steel rail is 4 HBW; the residual stress is between 181-196 MPa, the fluctuation of the residual stress along the length of the steel rail is 15 MPa.

[0043] Compared with the example 1, the example 2 and the example 3, the example 4 has smaller fluctuation of the tensile strength along the length of the steel rail, the fluctuation of the tread hardness along the length of the steel rail and the fluctuation of the residual stress along the length of the steel rail. The example 4 has excellent stability and uniformity of the performance along the length of the steel rail, which is more beneficial to the service of the steel rail in the seamless line and can reduce the damage caused by the fluctuation of the strength and the hardness.

[0044] The above-described examples are only used to describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by the ordinary skilled in the art shall fall within the protection scope of the present application determined by the claims.

Claims

1. A process for tempering a 100-metre bainite rail, characterised in that: Comprise: 1) the weight percentage of the chemical composition of the steel rail is C: 0.20-0.40%, Si: 0.90-1.50%, Mn: 2.00-2.60%, Cr: 0.80-1.40%, Ni: 0.20-0.80%, Mo: 0.15-0.60%, P≤0.022%, S≤0.015%, Al: ≤0.010%, and the rest is Fe and its inevitable impurities; 2) the production process of the 100-meter bainite steel rail tempering treatment is: steel rail specification and quantity checking→100-meter steel rail loading→ignition heating→stepwise temperature rising→holding→slow cooling treatment→100-meter steel rail unloading→steel rail air cooling; 3) the heating of the 100-meter bainite steel rail tempering treatment adopts the principle of separate control of different zones, that is, 10 heating zones are adopted for the 100-meter bainite steel rail, and the heating process of each zone is: zone 1 and zone 10: the heating speed is controlled at 75-85℃ / h; zone 2, zone 3, zone 8 and zone 9: the heating speed is controlled at 65-75℃ / h; zone 4, zone 5, zone 6 and zone 7: the heating speed is controlled at 55-65℃ / h; by controlling the heating temperature and heating speed of the 10 different zones, the purpose of uniform temperature in the 100-meter furnace is achieved; 4) the heating process of the 100-meter bainite steel rail tempering treatment is: the steel rail is heated from room temperature to 150-200℃, and held for 1-3h; the steel rail is continuously heated to 250-300℃, and held for 10-20h; the steel rail is continuously heated to 350-400℃, and held for 2-5h; 5) the cooling process of the 100-meter bainite steel rail tempering treatment is: after the heating of the 100-meter steel rail reaches the target temperature and the holding time, the 100-meter steel rail is subjected to slow cooling treatment with the furnace, and the cooling speed is controlled at 5-10℃ / h, and the final cooling temperature of the steel rail is controlled below 200℃, and when the target final cooling temperature is reached, the steel rail is unloaded for air cooling treatment; The specification section of the bainite steel rail after tempering treatment is 60kg / m or 75kg / m, and the length is the 100-meter steel rail of fixed size; the loading method of the 100-meter bainite steel rail tempering treatment is: the stacking layer number is ≤5, the layer spacing is ≥50mm, and the interval between the steel rails in the layer is ≥80mm.

2. The process for tempering a 100-metre bainite steel rail according to claim 1, characterized in that: The microstructure of the bainite steel rail is a complex phase structure of low-carbon martensite + lower bainite + residual austenite, wherein the proportion of martensite is 50-60%, the proportion of bainite is 30-40%, and the proportion of residual austenite is 5-15%.

3. The process for tempering a 100-metre bainite steel rail according to claim 1, characterized in that: The heating process of each zone is: zone 1 and zone 10: the heating speed is controlled at 80℃ / h; zone 2, zone 3, zone 8 and zone 9: the heating speed is controlled at 70℃ / h; zone 4, zone 5, zone 6 and zone 7: the heating speed is controlled at 60℃ / h; by controlling the heating temperature and heating speed of the 10 different zones, the purpose of uniform temperature in the 100-meter furnace is achieved.

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