Bainite steel for frog with high wear resistance and impact resistance and preparation method of bainite steel

Abstract

The invention discloses bainite steel for frogs. The bainite steel is characterized by comprising the following alloy elements in percentage by mass: 0.2 to 0.35 percent of C, 0.6 to 1.1 percent of Al, 2.1 to 2.4 percent of Mn, 0.8 to 1.1 percent of Cr, 0.2 to 1.0 percent of Mo, 0.1 to 1.0 percent of Ni, 0.01 to 0.1 percent of Y and Slt. 0.01% and Plt; 0.005%, and the balance being Fe and inevitable impurities. The production process comprises the steps of electric furnace smelting, ladle vacuum refining, continuous casting, rolling, annealing, air cooling transformation and tempering. The bainite steel can improve the wear resistance and impact resistance of the frog, and the service life of the frog is remarkably prolonged by 40%.

Description

Technical Field

[0001] The present invention belongs to bainitic steel for railway switches, and more particularly to a bainitic steel for highly wear-resistant and impact-resistant switches. Background Art

[0002] As a plane crossing device that enables wheels to pass from one rail to another, railway switches are subject to the harshest service conditions, the most concentrated forces, and the shortest service life in railway lines. The materials used to manufacture railway switches mainly include cast high manganese steel and bainitic steel. Generally, bainitic steel assembled railway switches and welded high manganese steel railway switches are used for lines with a speed of 100 - 160 km / h, and pearlitic steel movable point switches are used for lines with a speed greater than 160 km / h. However, at present, the maximum speed of passenger lines in China can reach 350 km / h, and the axle load of heavy-haul trains is 21 t, which still has a significant gap compared with the 35.4 t or even 39 t axle loads in foreign countries.

[0003] Although high manganese steel switches have the advantages of good toughness, load hardening, and wear resistance, due to inevitable casting defects, they are prone to cracks and spalling, which become the main factors affecting their service life. Due to its comprehensive properties such as high strength, high toughness, and certain hardness, bainitic steel has been increasingly used in the production of rails and switches. For example, in the bainitic steel electroslag casting composite switch point rail with alloying elements of 0.15 - 0.4% C, 0.4 - 2.1% Si, 1.5 - 2.5% Cr, 1.0 - 2.0 Ni, 0.2 - 0.8 Mo, V < 0.1%, Nd < 0.1%, P < 0.035%, S < 0.01%, and the rest being iron, which is applied for the CN1416984A applied by the applicant, electroslag casting composite is adopted. Under the thermal action of high-temperature molten slag and the molten steel melted by the electrode, the local surface of the rail composite is melted, gradually solidified in the mold, and finally the rails are cast and combined together to form an integral switch point rail blank. It is also necessary to keep it at 820 - 950 °C for 1 - 4 hours for austenite transformation, and after cooling to room temperature, tempering treatment is carried out at 200 - 400 °C for 3 - 6 hours. The obtained tensile strength is 1320 MPa, the elongation rate is greater than 9%, and the room temperature impact toughness is greater than 75 J / cm 2, with a hardness of HRC 38 - 45 and a reduction of area of 50%. The heart rail material of the full bainitic steel frog and its manufacturing method disclosed in CN102936700A is made of high-purity 35MnCrSiAlNiMo bainitic steel, and its alloying elements are 0.34 - 0.36C, 1.5 - 1.7Mn, 1.4 - 1.6Cr, 1.2 - 1.4Si, 0.5 - 0.7Al, 0.5 - 0.8Ni, 0.3 - 0.4Mo, O < 0.0015, H < 0.0001, Ti < 0.01, B < 0.0005, V < 0.03, Nb < 0.01, S < 0.01, P < 0.01, and the rest are Fe and inevitable impurities. The heat treatment is austenitization at 900 - 950°C for 100 - 1800 min, followed by step quenching by quenching into salt baths at 550°C and 300 - 360°C. Keep it in the 550°C salt bath for 15 min and in the 300 - 360°C salt bath for 60 min, then air cool to room temperature, and then heat it to 320°C for 60 min for tempering treatment. Tensile strength is 1300 - 1600 MPa, yield strength is 1000 - 1300 MPa, elongation is ≥15%, and impact toughness at room temperature is 100 J / cm 2 , and impact toughness at low temperature is ≥70 J / cm 2(-40°C), with a hardness of HRC 42 - 50. The carbide-free bainitic frog steel disclosed in CN115948640A has alloying elements of 0.20 - 0.30% C, 1.5 - 2.1% Si, 1.10 - 2.00% Mn, 0.0 - 1.7% Cr, 0.10 - 0.60% Mo, 0.002 - 0.7% Ni, 0.01 - 0.15% V, 0.001 - 0.004% Al, 0.002 - 0.020% P, 0.002 - 0.020% S, and the rest is Fe. The heat treatment is to heat the rolled or forged steel at 10 - 15°C / min to 900 - 820°C, hold for 60 - 120 min, then cool from 700 - 820°C at a cooling rate of 5 - 15°C / s to 200 - 300°C, and finally temper to obtain a carbide-free bainite structure. The tensile strength is ≥1350 MPa, the elongation is ≥12%, the wear resistance is increased by more than 30%, and the service life cycle is 2 - 3 times that of ordinary high manganese steel. The bainitic steel for frog heart rail disclosed in CN109518080 has alloying elements of 0.25 - 0.32% C, 0.8 - 1.7% Si, 1.00 - 2.0% Mn, 0.5 - 1.5% Cr, 0.1 - 0.7% Mo, 0.1 - 0.6% Ni, 0 - 0.1% Cu, 0 - 0.3% V, 0 - 0.1% Al, 0 - 0.1% Ti, and the rest is Fe and inevitable impurities. The heat treatment is to heat the steel billet to 900 - 1000°C, hold for 100 - 150 min, then cool in the furnace to room temperature, then heat to 900 - 1000°C again, hold for 100 - 150 min, cool in flowing air to room temperature, then heat to 300 - 350°C and hold for 180 - 240 min and then air-cool to room temperature. The obtained bainitic steel has Rm > 1340 MPa, Rp 0.2 > 1011 MPa, A ≥ 13%, Z > 45%, AKu2 > 80 J, HRC 39 - 43.

[0004] However, compared with foreign products, there is still room for improvement in the strength, toughness, and hardness of the above bainitic steel frogs. Summary of the Invention

[0005] Aiming at the deficiencies in strength, toughness, and hardness of the existing steel for frogs, the purpose of the present invention is to provide a bainitic steel for high-wear-resistant and impact-resistant frogs and its preparation method.

[0006] The bainitic steel for frog provided by the present invention has alloying elements and mass component contents as follows: C 0.2-0.35%, Al 0.6-1.1%, Mn 2.1-2.4%, Cr 0.8-1.1%, Mo 0.2-1.0%, Ni 0.1-1.0%, Y 0.01-0.1%, S <0.01% and P <0.005%, and the rest is Fe and inevitable impurities.

[0007] Further, the alloying elements may also contain V 0.1-0.3%

[0008] Further, in a preferred embodiment, the alloying elements of the bainitic steel are C 0.3%, Al 0.8%, Mn 2.2%, Cr 1.0%, Mo 0.6%, Ni 0.6%, Y 0.06%, V 0.2%, and S <0.01%, P <0.005%, and the rest is Fe and inevitable impurities.

[0009] The production method of the bainitic steel for frog of the present invention is: electric furnace smelting - ladle vacuum refining - continuous casting - rolling - annealing - air cooling transformation - tempering.

[0010] Specifically:

[0011] (1) Electric furnace smelting: Smelt raw materials such as ferromanganese that meet the requirements in an electric furnace;

[0012] (2) Ladle refining: Refine the molten steel in a ladle in a vacuum atmosphere and adjust the components of Al and Y to make the components meet the requirements;

[0013] (3) Continuous casting: Perform continuous casting on a continuous caster to form a steel billet;

[0014] (4) Rolling: Heat the steel billet to 1100-1200 °C and roll it into shape on a rolling mill through rough rolling and finish rolling, and the final rolling temperature is 850-950 °C;

[0015] (5) Annealing: Heat the rolled steel billet to 900-1000 °C and hold it for 90-150 min;

[0016] (6) Air cooling: Cool the steel billet at a cooling rate of 2-10 °C / s to 200-350 °C, and then cool it to room temperature at a cooling rate of 0.01-0.5 °C / s.

[0017] (7) Tempering: Hold the steel billet at 250-320 °C for 300-600 min to stabilize the microstructure.

[0018] In the present invention, a reasonable carbon content is adopted to ensure the strength, hardness and wear resistance of the steel, and at the same time, its toughness and crack resistance are improved as much as possible.

[0019] Al can prevent the precipitation of carbides, reduce the hydrogen embrittlement sensitivity of bainitic steel, and improve the strength, toughness and wear resistance of the steel.

[0020] Y has the function of desulfurization and degassing, can inhibit the segregation of low-melting-point impurities at grain boundaries, refine grains, and improve the strength and toughness of the steel.

[0021] Mn has a solid-solution strengthening effect, improves the hardenability of bainitic steel, refines the structure, and improves the strength and toughness of bainitic steel.

[0022] Cr improves hardenability, refines the structure, and improves corrosion resistance.

[0023] Mo has a solid-solution strengthening effect, can improve strength and toughness, and also improve hardenability. Acting together with C, Si, and Mn, it shifts the bainite transformation line to the right.

[0024] Ni reduces the Bs point and improves strength and impact toughness.

[0025] The bainitic steel of the present invention controls phase transformation and microstructure through various strengthening means and heat treatment. Its tensile strength ≥ 1300 MPa, room-temperature impact toughness reaches ≥ 110 J / cm 2 、hardness 42 - 46 HRC, can improve the wear resistance and impact resistance of frog, and significantly increase the life by 40%. Specific embodiments

[0026] The following further describes the present invention in detail with reference to embodiments.

[0027] The following further illustrates the present invention with specific embodiments to help understand the content of the present invention.

[0028] I. Embodiments 1 - 4

[0029] The alloy element composition contents of Embodiments 1 - 6 are shown in Table 1

[0030] Table 1 Alloy element composition and its content of Embodiments 1 - 4

[0031] Component Example 1 Example 2 Example 3 Example 4 C 0.3％ 0.2％ 0.35％ 0.32％ Al 0.8％ 1.1％ 0.6％ 1.0％ Mn 2.2％ 2.1％ 2.4％ 2.3％ Cr 1.0％ 1.1％ 0.8％ 0.9％ Mo 0.6％ 0.2％ 1.0％ 0.8％ Ni 0.6％ 1.0％ 0.1％ 0.3％ Y 0.06％ 0.01％ 0.1％ 0.08％ V 0.2％ 0.3％ 0.1％ 0.2％ S 0.008 0.007％ 0.007％ 0.008％ P 0.003％ 0.003％ 0.002％ 0.003％ Fe Balance Balance Balance Balance

[0032] (1) Electric furnace smelting: Smelt raw materials such as ferromanganese that meet the requirements in an electric furnace;

[0033] (2) Ladle refining: Refine the molten steel in a ladle in a vacuum atmosphere and adjust the Al and Y components to make the composition meet the requirements;

[0034] (3) Continuous casting: Conduct continuous casting on a continuous caster to form steel billets;

[0035] (4) Rolling: The steel billet is heated to 1100 - 1200 °C and rolled into shape on a rolling mill through rough rolling and finish rolling, with the final rolling temperature being 850 - 950 °C;

[0036] (5) Annealing: The rolled steel billet is heated to 900 - 1000 °C and held for 90 - 150 min;

[0037] (6) Air cooling: The steel billet is forced to cool at a cooling rate of 2 - 10 °C / s to 200 - 350 °C, and then cooled to room temperature at a cooling rate of 0.01 - 0.5 °C / s.

[0038] (7) Tempering: The steel billet is held at 250 - 320 °C for 300 - 600 min to stabilize the microstructure.

[0039] II. Performance Testing

[0040] After testing, the mechanical properties of the alloy materials in Examples 1 - 4 are as follows:

[0041] Mechanical Properties of Examples 1 - 4

[0042] Mechanical properties Example 1 Example 2 Example 3 Example 4 Tensile strength (MPa) 1350 1320 1300 1330 Elongation rate (%) 15 13 14 14 <![CDATA[Impact toughness (J / cm 2 )]]> 120 111 114 115 Hardness (HRC) 46 44 45 46

[0043] Those of ordinary skill in the art can understand that the above - mentioned are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent substitution on some of the technical features. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A bainitic steel for frog, characterized in that The alloying elements and their mass component contents are as follows: C 0.2 - 0.35%, Al 0.6 - 1.1%, Mn 2.1 - 2.4%, Cr 0.8 - 1.1%, Mo 0.2 - 1.0%, Ni 0.1 - 1.0%, Y 0.01 - 0.1%, S < 0.01% and P < 0.005%, and the balance is Fe and inevitable impurities.

2. The bainitic steel for frog according to claim 1, characterized in that The alloying elements further contain V 0.1 - 0.3%.

3. The bainitic steel for frog according to claim 2, characterized in that Its alloying elements are C 0.3%, Al 0.8%, Mn 2.2%, Cr 1.0%, Mo 0.6%, Ni 0.6%, Y 0.06%, V 0.2%, as well as S < 0.01% and P < 0.005%, and the balance is Fe and inevitable impurities.

4. A production method of the bainitic steel for frog according to any one of claims 1 - 3, the process is: electric furnace smelting - ladle vacuum refining - continuous casting - rolling - annealing - air cooling transformation - tempering.

5. The production method according to claim 4, the specific process is: (1) Electric furnace smelting: Smelt the qualified raw materials in the electric furnace; (2) Ladle refining: Refine the molten steel in the ladle in a vacuum atmosphere and adjust the components of Al and Y to make the components meet the requirements; (3) Continuous casting: Carry out continuous casting on the continuous caster to form a steel billet; (4) Rolling: Heat the steel billet to 1100 - 1200 °C and roll it into shape through rough rolling and finish rolling on the rolling mill, and the final rolling temperature is 850 - 950 °C; (5) Annealing: Heat the rolled steel billet to 900 - 1000 °C and keep it warm for 90 - 150 min; (6) Air cooling: Cool the steel billet at a cooling rate of 2 - 10 °C / s to 200 - 350 °C, and then cool it to room temperature at a cooling rate of 0.01 - 0.5 °C / s. (7) Tempering: Keep the steel billet at 250 - 320 °C for 300 - 600 min to stabilize the microstructure.