Method for obtaining a heat treatment process for effectively reducing the crack propagation rate of bainite composite steel rails

Abstract

The present invention discloses a method for obtaining a heat treatment process that effectively reduces the crack propagation rate of bainite-martensite dual-phase steel rails. A 100-meter steel rail is divided into four equal parts, with each 25 m as a section, which are respectively marked as sections A, B, C, and D along the rolling direction of the steel rail. To ensure the representativeness of sampling, a group of samples is taken at the 10 m position of each section, with 2 specimens in each group, and the length of each specimen is 50 cm, for a total of four groups. After sampling, a heat treatment experiment plan is formulated and experiments are carried out in a small heat treatment furnace. Finally, specimens are prepared and crack propagation experiments are carried out on an MTS testing machine, and the experimental results are statistically analyzed to obtain the optimal heat treatment plan. The purpose of the present invention is to provide a method for obtaining a heat treatment process that effectively reduces the crack propagation rate of bainite-martensite dual-phase steel rails, so as to effectively reduce the crack propagation rate of on-line quenched bainite-martensite dual-phase steel rails during service and improve the safety of the steel rails during service.

Description

Technical Field

[0001] The present invention relates to the technical field of heat treatment processes, and in particular to a method for obtaining a heat treatment process for effectively reducing a crack growth rate of a Bema complex phase rail. Background Art

[0002] Online quenched Bema complex phase rails are widely used in heavy-duty railways due to their high strength, high toughness and high wear resistance. When in service, due to the alternating load at the wheel-rail contact point and the friction parallel to the running direction, coupled with the residual stress inside the rails, they are extremely sensitive to the microcracks generated during the production process. The rapid expansion of microcracks may cause brittle fracture of the rails and lead to accidents. Therefore, effectively controlling the crack growth rate is of great research significance to improving the safety of heavy-duty rails in service.

[0003] At present, the standard used in my country to evaluate the crack growth rate of rails is GB / T6398, which uses three-point bending, single-side notch, and crack growth test on MTS testing machine. The specific sampling position and sample size (see Figure 1 , Figure 2 ).

[0004] In order to effectively improve the crack growth rate of rails during service and control their development into macro cracks or core damage, thereby improving the safety of heavy-load trains, researchers have achieved good results by optimizing alloy element distribution, controlling rolling, cooling and other means. Summary of the invention

[0005] The purpose of the present invention is to provide a method for obtaining a heat treatment process that effectively reduces the crack growth rate of a Bema duplex rail, so as to effectively reduce the crack growth rate of an online quenched Bema duplex rail during service and improve the safety of the rail in service.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The invention discloses a method for obtaining a heat treatment process for effectively reducing the crack growth rate of a Bema complex phase rail. The method comprises the following steps: dividing a 100-meter rail into four equal parts, each 25 meters being a section, and marking the sections A, B, C, and D along the rolling direction of the rail. To ensure that the sampling is representative, a group of samples is taken from 10 meters of each section, each group of which has two samples, and the sample length is 50 cm, and a total of four groups are taken. After sampling, a heat treatment experimental plan is formulated, and the experiment is carried out in a small heat treatment furnace. Finally, the sample is prepared, and a crack growth experiment is carried out on an MTS testing machine. The experimental results are statistically analyzed, and an optimal heat treatment plan is obtained.

[0008] Further, the specific steps include:

[0009] 1). Sampling: Divide the 100-meter rail into four equal parts, with each section of 25 meters, and mark them as A, B, C, and D along the rolling direction of the rail. To ensure the representativeness of the sampling, take a group of samples from 10 meters of each section. The sample length is 50 cm, and there are 2 samples in each group, marked as 1#~8#, for a total of four groups;

[0010] 2) Heat treatment experimental plan: Four groups of samples were placed in a small heat treatment furnace for orthogonal experiments. The experimental plan is as follows:

[0011] Solution 1: Heat samples 1#, 3#, 5#, and 7# to 250°C and keep them warm for 4 hours, then cool them down in the furnace. After cooling to room temperature, heat them to 150°C and keep them warm for 1 hour, then cool them down in the furnace to room temperature.

[0012] Solution 2: Heat samples 2#, 4#, 6#, and 8# to 450°C and keep them warm for 4 hours, then cool them to room temperature in the furnace, then heat them to 150°C and keep them warm for 1 hour, then cool them to room temperature in the furnace;

[0013] 3) Processing crack growth rate test specimens: Process 1# to 8# specimens into crack growth specimens respectively;

[0014] 4) Crack extension test: The test was carried out on an MTS-810 testing machine with a loading frequency of f = 15 Hz and a maximum load of P max =12kN, stress ratio R=0.5;

[0015] 5) Data analysis: combined with the Paris formula Where c = 3.8078 × 10 -11 , m = 2.8005 is the experimental constant, when When the fatigue crack growth rate in scheme 1 is Fatigue crack growth rate in Scheme 2 when When Option 2

[0016] It can be seen that, given the same range of stress factors, the crack growth rate of Scheme 1 is smaller, which is suitable for use in the later heat treatment process of quenched Bema duplex rail.

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

[0018] The method invented this year can obtain the best heat treatment process, thereby effectively reducing the crack growth rate of online quenched Bema duplex rails, curbing the formation of late "core damage" and macro cracks, increasing the service life of the rails, reducing the "core damage" defects of a certain depth on the rail head tread, increasing the yield rate of the rails, and improving the service stability and service life of the rails. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the accompanying drawings.

[0020] Figure 1 Sampling location for crack propagation test specimens;

[0021] Figure 2 is the size of the crack propagation test specimen;

[0022] Figure 3 Sampling location for heat treatment test specimens. DETAILED DESCRIPTION

[0023] A method for obtaining a heat treatment process for effectively reducing the crack growth rate of a Bema complex phase rail comprises the following steps:

[0024] 1) Sampling: Divide the 100-meter rail into four equal parts, with each section of 25 meters, and mark them as A, B, C, and D along the rolling direction of the rail. To ensure the representativeness of the sampling, take a group of samples from 10 meters of each section. The sample length is 50 cm, and there are 2 samples in each group, marked as 1# to 8#, for a total of four groups;

[0025] 2) Heat treatment experimental plan: Four groups of samples were placed in a small heat treatment furnace for orthogonal experiments. The experimental plan is as follows:

[0026] Solution 1: Heat samples 1#, 3#, 5#, and 7# to 250°C and keep them warm for 4 hours, then cool them down in the furnace. After cooling to room temperature, heat them to 150°C and keep them warm for 1 hour, then cool them down in the furnace to room temperature.

[0027] Solution 2: Heat samples 2#, 4#, 6#, and 8# to 450°C and keep them warm for 4 hours, then cool them to room temperature in the furnace, then heat them to 150°C and keep them warm for 1 hour, then cool them to room temperature in the furnace;

[0028] 3) Processing crack growth rate test specimen: according to Figure 2 According to the requirements, 1#~8# specimens are processed into crack expansion specimens respectively;

[0029] 4) Crack extension test: The test was carried out on an MTS-810 testing machine with a loading frequency of f = 15 Hz and a maximum load of P max =12kN, stress ratio R=0.5;

[0030] 5) Data analysis: combined with the Paris formula Where c = 3.8018 × 10 -11 , m = 2.8005 is the experimental constant, when When the fatigue crack growth rate in scheme 1 is Fatigue crack growth rate in Scheme 2 when When Option 2 It can be seen that, given the same range of stress factors, the crack growth rate of Scheme 1 is smaller, and it is recommended for use in the later heat treatment process of quenched Bema duplex rail.

[0031] The embodiments described above are only descriptions of the preferred embodiments 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 method for obtaining a heat treatment process that effectively reduces the crack propagation rate of bainite composite steel rails, characterized in that, it specifically includes the following steps: 1). Sampling: Divide the 100-meter steel rail into four equal parts, with each 25m as a section, and mark them as sections A, B, C, and D along the rolling direction of the steel rail. To ensure the representativeness of the sampling, take a group of samples at the 10m position of each section. The length of the specimen is 50cm, and there are 2 specimens in each group, which are respectively marked as 1# to 8#. A total of four groups are taken; 2) Heat treatment experiment plan: Place the four groups of specimens in a small heat treatment furnace for orthogonal experiments respectively. The experimental plan is as follows: Plan 1: Heat the 1#, 3#, 5#, and 7# specimens to 250°C, keep them warm for 4h, then cool them in the furnace, and after cooling to room temperature, heat them to 150°C again, keep them warm for 1h, and then cool them in the furnace to room temperature; Plan 2: Heat the 2#, 4#, 6#, and 8# specimens to 450°C, keep them warm for 4h, then cool them in the furnace to room temperature, and after cooling to room temperature, heat them to 150°C again, keep them warm for 1h, and then cool them in the furnace to room temperature; 3) Process the crack propagation rate experiment specimens: Process the 1# to 8# specimens into crack propagation specimens respectively; 4) Crack propagation experiment: Conduct the experiment on an MTS-810 type testing machine, with a loading frequency of f = 15Hz, a maximum load of Pmax = 12kN, and a stress ratio of R = 0.5; 5) Data analysis: combined with the Paris formula where c = 3.8018×10 -11 , m = 2.8005 are experimental constants. When , the fatigue crack growth rate in Plan 1 the fatigue crack growth rate in Plan 2 When in Solution 1 in Solution 2 It can be seen that when given the same stress factor range, the crack growth rate of Solution 1 is smaller, making it suitable for use in the heat treatment process of quenched bainite-martensite composite steel rails in the later stage.

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