A bainite frog with excellent toughness and plasticity and its preparation method

Abstract

The present invention relates to a bainite frog with excellent toughness and plasticity, and its chemical composition by weight percentage includes: C 0.25 - 0.35%, Si 1.0 - 2.0%, Mn 1.50 - 2.00%, P 0.002 - 0.015%, S 0.002 - 0.010%, Cr 0.80 - 1.50%, Mo 0.30 - 0.80%, Ni 0.30 - 0.80%, V 0.03 - 0.10%, Al 0.001 - 0.004%, and the balance is Fe. In addition, the present invention also relates to a preparation method of the above bainite frog with excellent toughness and plasticity. Through the above technical solution of the present invention, the strength and toughness of the bainite frog are improved, and the running safety of the frog is enhanced.

Description

Technical Field

[0001] The present invention relates to a bainite frog with excellent toughness and plasticity and a preparation method thereof. More specifically, it relates to a steel for bainite frog and a preparation method thereof, which use a large flow of air to perform normalizing treatment to refine the structure, and at the same time perform isothermal treatment above the martensite transformation temperature to obtain bainite and retained austenite tissues with a content of more than 95%, reduce the content of martensite tissue, and improve the toughness and plasticity of the bainite frog. Background Art

[0002] With the development of railways in various countries towards high speed and heavy haul, higher requirements are correspondingly put forward for the performance of the frog heart rail. The frog is an important component of the railway track structure and is a special device that withstands high-intensity impact and rolling when the wheels of locomotives and rolling stocks transfer from one track to another. The contact force between the locomotive and rolling stock and the rail is transmitted through the contact spots between the wheels and the rail. When the wheels just pass through the frog, the contact surface between the tip of the frog and the wheels suddenly becomes very small, and the contact stress between the two becomes very high, often resulting in the main damage of the frog being concentrated in the tip area. Moreover, the frog plays a role in guiding the turn, causing the wheels to be guided and turned, and the wheels will be affected by multiple forces together, resulting in creep on the surface of the frog and surface damage. Therefore, extremely strict requirements are imposed on the performance of the materials for the frog. This frog component requires sufficient strength, good stability, wear resistance, and a long service life.

[0003] However, the strength, toughness, and wear resistance of the existing prepared bainite frogs are generally poor, especially the toughness and plasticity of the materials cannot meet the requirements, and there are often damages such as cracks and spalling during service.

[0004] Therefore, the present invention proposes a bainite frog with excellent toughness and plasticity and a preparation method thereof to meet the requirements of frogs for heavy-haul railways or frogs for turnout railways. Summary of the Invention

[0005] The purpose of the present invention is to ensure the strength and toughness of the existing on-line heat-treated bainite frog, while reducing the content of martensite tissue in the frog, increasing and refining the content of bainite and retained austenite, improving the toughness and plasticity of the frog, ensuring the safety of train operation, and meeting the requirements of frogs for heavy-haul railways or frogs for turnout railways.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] According to one aspect of the present invention, there is provided a bainitic frog with excellent toughness and plasticity, and its chemical composition by weight percentage includes: C 0.25 - 0.35%, Si 1.0 - 2.0%, Mn 1.50 - 2.00%, P 0.002 - 0.015%, S 0.002 - 0.010%, Cr 0.80 - 1.50%, Mo 0.30 - 0.80%, Ni 0.30 - 0.80%, V 0.03 - 0.10%, Al 0.001 - 0.004%, and the rest is Fe.

[0008] In one embodiment of the present invention, the length of the bainitic frog is ≤ 50 m.

[0009] In one embodiment of the present invention, the structure of the bainitic frog is a bainite + martensite + retained austenite complex structure.

[0010] In one embodiment of the present invention, the content of bainite + retained austenite tissue in the bainite + martensite + retained austenite complex structure is ≥ 95%.

[0011] In one embodiment of the present invention, the tensile strength of the bainitic frog is ≥ 1380 MPa, the elongation is ≥ 20%, the normal temperature impact is ≥ 80 J, and the low temperature impact at - 40 °C is ≥ 50 J.

[0012] According to another aspect of the present invention, there is provided a preparation method of the bainitic frog with excellent toughness and plasticity as described above, including the following steps:

[0013] 1) Smelt and cast a steel billet with the chemical composition by weight percentage as follows: C 0.25 - 0.35%, Si 1.0 - 2.0%, Mn 1.50 - 2.00%, P 0.002 - 0.015%, S 0.002 - 0.010%, Cr 0.80 - 1.50%, Mo 0.30 - 0.80%, Ni 0.30 - 0.80%, V 0.03 - 0.10%, Al 0.001 - 0.004%, and the rest is Fe;

[0014] 2) Heat and roll the obtained steel billet, the final rolling temperature is 950 - 1000 °C, and when air - cooled to 800 - 850 °C, send it into a constant - temperature blast furnace for heat treatment. The constant - temperature blast furnace adopts top - bottom air convection cooling, and both sides of the furnace chamber are heated and insulated;

[0015] 3) Rapidly cool the steel billet in the constant - temperature blast furnace from 800 - 850 °C to 350 - 450 °C at a rate of 2 - 5 °C, and keep it at a constant temperature of 350 - 450 °C for 30 - 100 h;

[0016] 4) Cool and straighten the steel billet treated in the constant - temperature blast furnace to prepare a bainitic frog with excellent toughness and plasticity.

[0017] In one embodiment of the present invention, the top and bottom of the constant temperature blast furnace are cooled by air convection through the installed fans, and the two sides of the furnace chamber are heated and insulated by the installed resistance wires.

[0018] In one embodiment of the present invention, when the top and bottom of the constant temperature blast furnace are cooled by air convection, the air flow rate is 10000 - 12500 m 3 / h, and the distance between the fans installed at the top and bottom and the billets is 1 - 1.5 m.

[0019] In one embodiment of the present invention, 1 - 10 layers are processed at a time in the constant temperature blast furnace, with 1 - 15 billets in each layer, and the number of billets heat-treated at a time in the constant temperature blast furnace is ≤ 150.

[0020] In one embodiment of the present invention, protective casting is carried out throughout the smelting and casting process, and protective casting is carried out in a manner of low sulfur control of 0.002 - 0.010%.

[0021] By adopting the above technical solutions, the present invention has the following advantages compared with the prior art:

[0022] The present invention improves the strength and toughness of the bainite frog and enhances the running safety of the frog. Detailed Description of the Invention

[0023] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments of the present invention are described in detail, those skilled in the art can easily appreciate that various modifications are feasible without substantially departing from the teachings of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, parameters, etc. of the following exemplary embodiments.

[0024] In order to improve the strength, toughness, and wear resistance of the bainite frog, domestic and foreign research has adopted medium carbon and low alloy compositions to form a bainite-martensite duplex structure, and then tempering is used to reduce the adverse effects brought by martensite. According to the material characteristics, alloy + rapid cooling + isothermal treatment can reduce the martensite content in the steel and improve the ductility and plasticity of the material.

[0025] Therefore, based on the above principle, the present invention designs a low alloy composition system of 0.25 - 0.35%. By rapidly cooling to above the martensite transformation temperature (Ms) point after rolling and holding for a long time, the bainite tissue content can be increased and the martensite content can be reduced. This method is the core of the present invention.

[0026] After the bainite frog is rolled, the finishing rolling temperature is between 950 - 1000 °C, and the phase transformation start temperature is relatively high. It needs to be air-cooled to 800 - 850 °C and then put into the furnace for cooling. To increase the high-temperature cooling rate and maintain the low-temperature temperature change, the coordinated control of top-bottom air cooling and furnace sidewall heating and heat preservation is adopted to realize the production of steel for bainite frog with optimized toughness and plasticity.

[0027] The present invention relates to a bainite frog with excellent toughness and plasticity and a preparation method thereof. The bainite frog with excellent toughness and plasticity provided by the present invention, its chemical composition by weight percentage includes: C 0.25 - 0.35%, Si 1.0 - 2.0%, Mn 1.50 - 2.00%, P 0.002 - 0.015%, S 0.002 - 0.010%, Cr 0.80 - 1.50%, Mo 0.30 - 0.80%, Ni 0.30 - 0.80%, V 0.03 - 0.10%, Al 0.001 - 0.004%, and the rest is Fe. The preparation method of the bainite frog with excellent toughness and plasticity of the present invention mainly adopts the carbon content of 0.25 - 0.35% and the Cr-Mo-V microalloy composition design. After smelting and rolling, it is directly charged into a 50-meter-long constant-temperature blast furnace at 350 - 450 °C by using the rolling waste heat. The charging temperature is 800 - 850 °C. The top-bottom air convection cooling is adopted in the furnace, and the air flow rate is 10000 - 12500 m 3 / h, the distance between the top-bottom fan and the specimen is 1 - 1.5 m, and the two sides of the furnace chamber are heated by resistance wires to ensure that the bainite frog after rolling is rapidly cooled to 350 - 450 °C at 2 - 5 °C / s and kept at this temperature for 30 - 100 h. The bainite frog produced by this method has a tensile strength ≥ 1380 MPa, an elongation rate ≥ 20%, a normal temperature impact ≥ 80 J, a -40 °C low-temperature impact ≥ 50 J, and a bainite + retained austenite structure ≥ 95%, and is especially suitable for frogs for heavy-haul railways or steel for turnouts in railway tracks.

[0028] The above technical solutions of the present invention will be described in detail below through specific embodiments.

[0029] A preparation method of a bainite frog with excellent toughness and plasticity provided by an embodiment of the present invention includes the following steps:

[0030] (1) Smelt and cast a steel billet according to the chemical composition by weight percentage as follows: C 0.25 - 0.35%, Si 1.0 - 2.0%, Mn 1.50 - 2.00%, P 0.002 - 0.015%, S 0.002 - 0.010%, Cr 0.80 - 1.50%, Mo 0.30 - 0.80%, Ni 0.30 - 0.80%, V 0.03 - 0.10%, Al 0.001 - 0.004%, and the rest is Fe;

[0031] (2) Heat and roll the obtained billets, with the finish rolling temperature being 950 - 1000 °C. When air-cooled to 800 - 850 °C, send them into a constant-temperature blast furnace for heat treatment. The constant-temperature blast furnace is equipped with top and bottom fans for air convection cooling, with an air flow rate of 10000 - 12500 m 3 / h. The distance between the top and bottom fans and the billets is 1 - 1.5 m. Both sides of the furnace chamber are heated and insulated by the installed resistance wires;

[0032] (3) Rapidly cool the billets in the constant-temperature blast furnace from 800 - 850 °C to 350 - 450 °C at a rate of 2 - 5 °C, and keep them at a constant temperature of 350 - 450 °C for 30 - 100 h;

[0033] (4) Cool and straighten the billets processed in the constant-temperature blast furnace to prepare bainite frog with excellent toughness and plasticity.

[0034] For the above method, the present invention lists the parameters adopted in the processes of Examples 1 - 5 and Comparative Examples 1 - 4. The specific parameters are shown in Tables 1 - 2 below. Table 1 shows the chemical compositions of the billets used in Examples 1 - 5 and Comparative Examples 1 - 4 of the present invention, and Table 2 shows the parameters of the heat treatment processes used in Examples 1 - 5 and Comparative Examples 1 - 4 of the present invention.

[0035] The frogs of Examples 1 - 5 and Comparative Examples 1 - 4 of the present invention are subjected to full-process protected casting, and preferably adopt a low sulfur control of 0.002 - 0.010%, and their chemical compositions are shown in Table 1.

[0036] Table 1 Chemical Compositions of Frogs in Examples 1 - 5 and Comparative Examples 1 - 4 / %

[0037]

[0038] The same heating process and rolling process are adopted in Examples 1 - 5 and Comparative Examples 1 - 4, and different heat treatment processes are adopted, as shown in Table 2.

[0039] Table 2 Heat Treatment Processes of Examples 1 - 5 and Comparative Examples 1 - 4

[0040]

[0041]

[0042] After the frogs of the above Examples 1 - 5 and Comparative Examples 1 - 4 are cooled and straightened, according to the requirements of TBT 3467 - 2016 "Alloy Steel Composite Frog", the microstructure and properties are inspected. The data statistics are shown in Table 3.

[0043] Table 3 Performance Data of Frogs in Examples 1 - 5 and Comparative Examples 1 - 4

[0044]

[0045] As can be seen from Table 3 above, the tensile strength of the bainite frog prepared by the present invention is ≥1380 MPa, the elongation is ≥20%, the impact at normal temperature is ≥80 J, the low-temperature impact at -40 °C is ≥50 J, and the bainite + retained austenite structure is ≥95%. It is particularly suitable for the steel used for the frog or turnout of heavy-haul railways. The present invention improves the strength and toughness of the bainite frog and enhances the operation safety of the frog.

[0046] The above is only the preferred embodiment of the present invention and is not intended to limit the scope of implementation of the present invention; any modification or equivalent replacement of the present invention without departing from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A bainite frog with excellent ductility and plasticity, characterized in that Its chemical composition by weight percentage includes: C 0.25 - 0.35%, Si 1.0 - 2.0%, Mn 1.50 - 2.00%, P 0.002 - 0.015%, S 0.002 - 0.010%, Cr 0.80 - 1.50%, Mo 0.30 - 0.80%, Ni 0.30 - 0.80%, V 0.03 - 0.10%, Al 0.001 - 0.004%, and the rest is Fe; the structure of the bainite frog is bainite + martensite + retained austenite complex structure; the content of bainite + retained austenite tissue in the bainite + martensite + retained austenite complex structure is ≥95%; the tensile strength of the bainite frog is ≥1455 MPa, the elongation is ≥20%, the impact energy at room temperature is ≥95 J, and the impact energy at -40 °C is ≥55 J.

2. The bainite frog with excellent toughness and plasticity according to claim 1, characterized in that, The length of the bainite frog is ≤50 m.

3. A preparation method of a bainite frog with excellent toughness and plasticity as described in any one of claims 1-2, characterized in that, It includes the following steps: 1) Smelt and cast a steel billet with the chemical composition by weight percentage as follows: C 0.25 - 0.35%, Si 1.0 - 2.0%, Mn 1.50 - 2.00%, P 0.002 - 0.015%, S 0.002 - 0.010%, Cr 0.80 - 1.50%, Mo 0.30 - 0.80%, Ni 0.30 - 0.80%, V 0.03 - 0.10%, Al 0.001 - 0.004%, and the rest is Fe; 2) Heat and roll the obtained steel billet, the final rolling temperature is 950 - 1000 °C, and when air-cooled to 800 - 850 °C, send it into a constant-temperature blast furnace for heat treatment. The constant-temperature blast furnace uses top-bottom air convection cooling, and both sides of the furnace chamber are heated and insulated; 3) Rapidly cool the steel billet in the constant-temperature blast furnace from 800 - 850 °C to 350 - 450 °C at a rate of 2 - 5 °C, and keep it at a constant temperature of 350 - 450 °C for 30 - 100 h; 4) Cool and straighten the steel billet processed in the constant-temperature blast furnace to prepare a bainite frog with excellent toughness and plasticity.

4. The preparation method according to claim 3, wherein The top and bottom of the constant-temperature blast furnace achieve air convection cooling through the installed fans, and both sides of the furnace chamber are heated and insulated through the installed resistance wires.

5. The preparation method according to claim 4, wherein When the top and bottom of the constant-temperature blast furnace conduct air convection cooling, the air flow rate is 10000 - 12500 m3 / h, and the distance between the fans installed at the top and bottom and the steel billet is 1 - 1.5 m.

6. The preparation method according to claim 3, wherein, The constant-temperature blast furnace processes 1 - 10 layers at a time, each layer has 1 - 15 steel billets, and the number of steel billets heat-treated in the constant-temperature blast furnace at a time is ≤150.

7. The preparation method according to claim 3, wherein During the whole process of smelting and casting, protective casting is carried out, and protective casting is carried out in a way of low sulfur control of 0.002 - 0.010%.

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