Production method of new high-strength wear-resistant bainite frog steel

Abstract

The invention discloses a production method of a novel high-strength wear-resistant bainite steel for frogs, wherein the steel for frogs contains 0.26-0.35% C by mass percentage. The method comprises the following steps: S1, heating the steel billet obtained after smelting and casting to 1250-1300°C; S2, rolling or forging the heated steel billet; S3, heat treating the steel for frogs obtained after rolling or forging, wherein the final cooling temperature of the heat treatment is 100-200°C; S4, heat-insulating the steel for frogs cooled to the final cooling temperature by heat treatment, wherein the heat-insulating treatment time is 3-5h; S5, tempering the steel for frogs after the heat-insulating treatment. The method of the invention can control the organization through heat treatment, while ensuring the strength and toughness of the existing online heat-treated bainite rails, improve the safety of rail operation, and meet the requirements of steel for frogs for heavy-duty railways.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a production method of a novel high-strength and wear-resistant bainite frog steel. Background Art

[0002] During the service, the frog is subjected to complex alternating loads from the wheels, and the working conditions of the frog are very harsh. The frog is the most severely stressed and damaged component in the railway line.

[0003] The as-cast structure of traditional high manganese steel frogs is a mixed structure of austenite, pearlite and carbide. In order to obtain a single-phase austenite structure, high manganese steel is usually treated with water toughening at home and abroad. The high manganese steel frog is heated to the austenitizing temperature, kept warm for a certain period of time, and then quickly cooled to room temperature. After water toughening, the strength and plastic toughness of the high manganese steel frog are significantly improved. The high manganese steel frog has good processability. Under the interaction of impact load and contact stress, the dislocation density increases, the dislocations are crossed and piled up, and the solute atoms interact with the dislocations, so that the high manganese steel frog is strengthened. After strengthening, the hardness of the high manganese steel frog increases sharply, and high-density dislocations and twins are generated on the surface, which improves the wear resistance of the surface and maintains good toughness in the core. The high manganese steel frog must be fully hardened under huge impact loads or pressure. The method of explosive hardening is usually used to increase the hardness of the surface of the high manganese steel frog. After explosive hardening, the service life of the high manganese steel frog is significantly improved. However, there are certain defects such as shrinkage cavities and looseness after casting, and cracks or collapses will appear on the surface, resulting in reduced wear resistance of high manganese steel frogs.

[0004] Therefore, the comprehensive performance of bainite frog still has room for further improvement. Summary of the invention

[0005] The main purpose of the present invention is to provide a new production method of high-strength and wear-resistant bainite frog steel, which controls the structure through heat treatment, improves the running safety of the rail while ensuring the strength and toughness of the existing online heat-treated bainite rail, and meets the requirements of heavy-duty railway frog steel.

[0006] In order to solve at least one of the above technical problems, the present invention adopts the following technical solution:

[0007] According to the present invention, a production method of a novel high-strength wear-resistant bainite frog steel is provided, wherein the frog steel contains 0.26-0.35% C by mass percentage, and the method comprises the following steps: S1, heating a steel billet obtained after smelting and casting to 1250-1300° C.; S2, rolling or forging the heated steel billet; S3, heat-treating the frog steel obtained after rolling or forging, wherein the final cooling temperature of the heat treatment is 100-200° C.; S4, heat-insulating the frog steel cooled to the final cooling temperature after the heat treatment, wherein the heat-insulating treatment time is 3-5 hours; and S5, tempering the frog steel after the heat-insulating treatment.

[0008] According to one embodiment of the present invention, the composition of the frog steel is, by mass percentage, 0.30-0.35% C, 1.20-2.1% Si, 1.50-2.50% Mn, 0.002-0.020% P, 0.002-0.020% S, 1.0-1.50% Cr, 0.40-0.80% Mo, 0.30-0.70% Ni, 0.01-0.08% V, 0.001-0.004% Al, and the rest is Fe and unavoidable impurity elements.

[0009] According to one embodiment of the present invention, in step S1, the heating time is controlled within a range of 200 to 500 minutes.

[0010] According to one embodiment of the present invention, in step S2, the final cooling temperature of rolling or forging is 950-1000°C, and the rolling compression ratio or forging ratio is ≥4:1.

[0011] According to one embodiment of the present invention, in step S3, the cooling start temperature of the heat treatment is 740-820°C, and the cooling rate is 10-15°C / s.

[0012] According to one embodiment of the present invention, in step S5, the frog steel after the insulation treatment is heated to 250-350° C. at a rate of 30-50° C. / s and then tempered and kept for 6-120 hours.

[0013] According to one embodiment of the present invention, in step S5, the tempered frog steel is slowly cooled to room temperature in the furnace.

[0014] According to one embodiment of the present invention, protective casting is performed throughout the entire casting process.

[0015] In the production method of the new high-strength wear-resistant bainite steel for frogs according to the embodiment of the present invention, the microstructure is controlled by heat treatment, while ensuring the strength and toughness of the existing online heat-treated bainite rails, the rail operation safety is improved to meet the requirements of heavy-duty railway frog steel. The new high-strength wear-resistant bainite steel for frogs produced by this method has a tensile strength of ≥1500MPa, an elongation of ≥15%, and a cross-sectional shrinkage of ≥50%. The wear resistance is improved by 30%, which is particularly suitable for railway frogs with axle weights greater than 25 tons and annual transportation volume greater than 300 million tons. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A flow chart showing a method for producing a novel high-strength and wear-resistant bainite frog steel according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0019] Bainitic frog steel refers to a steel type that is heated to austenitization and then air-cooled or heat-treated to form a bainitic structure. Bainitic frog steel has high strength and toughness. Bainitic frog steel is based on air-cooled bainitic steel, supplemented by the addition of alloying elements such as Si, Cr, and Ni to obtain bainitic structure under air-cooling conditions; and after austenitization, the bainite is cooled rapidly to achieve the purpose of bainitic frog steel structure and performance by isothermal treatment, air cooling, controlled cooling, etc.

[0020] Martensite has different morphological characteristics with different carbon content. After quenching, there is film or blocky retained austenite distributed between martensite, with a content of 6-15%. Influenced by factors such as heat treatment process and material composition, in addition to martensite and retained austenite, other organizations also appear in the microstructure of bainitic frog steel.

[0021] Figure 1 A flow chart showing a method for producing a novel high-strength wear-resistant bainite frog steel according to an embodiment of the present invention, wherein the frog steel contains 0.26-0.35% C by mass, and generally comprises the following steps:

[0022] S1, heating the steel billet obtained after smelting and casting to 1250-1300°C;

[0023] S2, rolling or forging the heated steel billet;

[0024] S3, heat treating the frog steel obtained after rolling or forging, wherein the final cooling temperature of the heat treatment is 100-200° C.;

[0025] S4, performing heat preservation treatment on the frog steel that has been heat-treated and cooled to the final cooling temperature, wherein the heat preservation treatment time is 3 to 5 hours;

[0026] S5, tempering the frog steel after the insulation treatment.

[0027] The present invention uses 0.24-0.35% C to diffuse fully from the supersaturated martensite to the untransformed austenite after high quenching temperature treatment, stabilizes the untransformed austenite, and then retains it when finally cooled to room temperature. In the production method of the novel high-strength wear-resistant bainite frog steel according to the embodiment of the present invention, the composition of the frog steel is preferably: 0.30-0.35% C, 1.20-2.1% Si, 1.50-2.50% Mn, 0.002-0.020% P, 0.002-0.020% S, 1.0-1.50% Cr, 0.40-0.80% Mo, 0.30-0.70% Ni, 0.01-0.08% V, 0.001-0.004% Al, and the rest is Fe and inevitable impurity elements.

[0028] In some embodiments, the following parameters may be used in steps S1 to S2: After smelting and casting, the steel billet is heated to 1250-1300°C for 200-500 minutes. After dephosphorization, the steel billet is rolled or forged, wherein the final cooling temperature of the rolling or forging is 950-1000°C, and the rolling compression ratio or forging ratio is ≥4:1.

[0029] When the frog steel is cooled to the final cooling temperature after heat treatment, the frog steel is subjected to heat preservation treatment in step S4. The bainitic frog steel is heated to the austenitizing temperature and kept for a period of time, then quenched to a certain temperature within the martensite phase transformation range, and then kept at this temperature or higher to diffuse the carbon in the supersaturated martensite into the untransformed austenite, and finally quenched to room temperature to obtain a mixed structure composed of martensite and carbon-rich stable residual austenite with high strength and good plastic toughness.

[0030] In some embodiments, in step S4, the heat preservation treatment of the frog steel is heated to 250-350°C at 30-50°C / s and then tempered for 6-120h. The bainitic frog steel is quenched to a martensitic phase transformation temperature range of 100-200°C, kept warm for a certain period of time, and then quickly heated to the tempering and holding temperature, which will produce more residual austenite, which has a significant impact on the performance of the steel. That is, stable residual austenite will increase the plasticity of the steel. Among them, the tempering time is mainly related to the heating medium, furnace temperature, chemical composition of the steel, structure, sample size and shape, furnace loading method and furnace loading, and the sample size, shape and structure have the most obvious influence on the tempering time. The cross-sectional thickness of the frog steel can usually reach 116mm. According to the commonly used empirical formula for tempering (1):

[0031] T=a×K×D (1)

[0032] In the formula, T is the heating time (min); a is the heating coefficient (min / mm), which is related to the workpiece size, heating medium, and chemical composition of the steel; K is the furnace loading correction coefficient (take 1.5-2.0); D is the effective thickness of the part (mm)

[0033] The minimum calculated tempering time is 300 minutes, i.e. 5 hours.

[0034] At the same time, in the embodiment of the present invention, the structure of the frog steel is a composite structure of bainite + martensite + paratenite, the content of martensite and paratenite in the structure is small, and the transformation during the tempering process is affected by the extrusion of the bainite structure, the transformation rate is extremely low, and the required tempering time is long. Experimental research shows that the longest tempering time is 120h, and the longest time for international bainite material is more than 30 days.

[0035] In some embodiments, protective casting is performed throughout the casting process to control the nitrogen, hydrogen, and oxygen contents of the frog steel.

[0036] The following is a description based on specific embodiments.

[0037] The frog steels of the embodiments and comparative examples of the present invention are cast through full-process protection, wherein the main chemical components of embodiments 1 to 5 are shown in Table 1 in terms of mass percentage, and the components of comparative examples 1 to 4 are the same as those of embodiments 1 to 4.

[0038] Table 1 Chemical composition of frog steel in the embodiments and comparative examples (%)

[0039]

[0040] The embodiment and the comparative example adopt the same heating process, the heating temperature is 1250-1300°C, and the heating time is controlled at 200-500min. The same rolling or forging parameters are adopted, the starting temperature of rolling or forging is 950-1000°C, and the rolling compression ratio or forging ratio is ≥4:1. Different heat treatment processes are adopted, as shown in Table 2.

[0041] Table 2 Heat treatment process of examples and comparative examples

[0042]

[0043] In the embodiment and comparative example, according to the requirements of TB / T 2344 "Technical Conditions for Ordering 43kg / m to 75kg / m Rails", tensile specimens were processed and inspected according to the tensile specimen sampling position. At the same time, metallographic structure inspection was carried out according to the metallographic specimen inspection position. The tensile and metallographic data statistics are shown in Table 3.

[0044] Table 3 Tensile properties of rails in embodiments and comparative examples

[0045]

[0046] Combining Tables 1 and 2, the relevant parameters of the composition design, heating process, and rolling process of the comparative example are not within the predetermined range. As shown in Table 3, the new high-strength wear-resistant bainite frog steel produced by this method has a tensile strength of ≥1500MPa, an elongation of ≥15%, and a cross-sectional shrinkage of ≥50%. The wear resistance is improved by 30%, and it is particularly suitable for railway frogs with axle weights of >25 tons and annual transportation volume of >300 million tons.

[0047] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for producing a novel high-strength and wear-resistant bainite frog steel, characterized in that: The frog steel comprises, by mass percentage, 0.30-0.35% C, 1.20-2.1% Si, 1.50-2.50% Mn, 0.002-0.020% P, 0.002-0.020% S, 1.0-1.50% Cr, 0.40-0.80% Mo, 0.30-0.70% Ni, 0.01-0.08% V, 0.001-0.004% Al, and the rest is Fe and unavoidable impurity elements. The method comprises the following steps: S1, heating the steel billet obtained after smelting and casting to 1250-1300°C; S2, rolling or forging the heated steel billet; S3, heat treating the frog steel obtained after rolling or forging, wherein the heat treatment has a cooling start temperature of 740-820°C, a cooling rate of 10-15°C / s, and a final cooling temperature of 100-200°C; S4, performing heat preservation treatment on the frog steel that has been heat-treated and cooled to the final cooling temperature, wherein the heat preservation treatment time is 3 to 5 hours; S5, tempering the frog steel after the insulation treatment.

2. The method according to claim 1, characterized in that: In step S1, the heating time is controlled within a range of 200 to 500 minutes.

3. The method according to claim 1, characterized in that: In step S2, the final cooling temperature of rolling or forging is 950-1000°C, and the rolling compression ratio or forging ratio is ≥4:

1.

4. The method according to claim 1, characterized in that: In step S5, the frog steel after the insulation treatment is heated to 250-350° C. at a rate of 30-50° C. / s and then tempered and kept for 6-120 hours.

5. The method according to claim 4, characterized in that In step S5, the tempered frog steel is slowly cooled to room temperature in the furnace.

6. The method according to claim 1, characterized in that Protective casting is carried out throughout the casting process.

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