Continuous casting round billet and preparation method and application thereof

Abstract

The invention provides a continuous casting round billet as well as a preparation method and application thereof. The continuous casting round billet comprises the following components: 0.17 to 0.19 weight percent of C, 0.62 to 0.68 weight percent of Mn, 1.62 to 1.70 weight percent of Cr, 0.29 to 0.31 weight percent of Mo, 1.52 to 1.60 weight percent of Ni, 0.017 to 0.025 weight percent of Nb, 0.020 to 0.030 weight percent of Al, 0.0075 to 0.0110 weight percent of N, 0.20 to 0.28 weight percent of Si, less than or equal to 0.010 weight percent of P, less than or equal to 0.005 weight percent of S and the balance of Fe. The tensile strength of the obtained continuous casting round billet is preferably as high as 1520 MPa or above, the yield strength is preferably as high as 1130 MPa or above, the impact energy at-40 DEG C (KV2) is preferably as high as 50 J or above, and the carbon segregation range of the cross section is preferably as low as 0.033% or below.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy materials, and relates to a continuous casting round billet and a preparation method and application thereof, and in particular to a continuous casting round billet for offshore wind power gearbox gears and a preparation method thereof. Background Art

[0002] The wind turbine gearbox is the core component of the wind turbine. Its main function is to transfer the kinetic energy generated by the wind rotor to the generator under the action of wind. It is the key link in the conversion from high torque and low speed to low torque and high speed. The wind turbine gearbox is mainly composed of sun gear, planetary gear, etc., and mainly uses 18CrNiMo7-6 steel. In view of the complexity of the working environment of wind turbine gears, the units are installed in high mountains, wilderness, beaches, islands and other wind outlets. They are subject to irregular wind force of changing direction and load and the impact of strong gusts. They are affected by extreme heat and cold and extreme temperature differences all year round. In addition, the natural environment is inconvenient for transportation. Once a fault occurs, it is very difficult to repair. Therefore, its reliability and service life are much higher than those of general machinery. It has high requirements for gear raw materials. Therefore, it is particularly important to strengthen the research on steel for wind turbine gearboxes.

[0003] At present, due to the restrictions of composition and internal composition segregation of the continuous casting round billets used for wind power gearbox gears on land, after forging and heat treatment, the tensile strength is basically controlled at 1200-1400MPa, the yield strength is basically controlled at 900-1000MPa, and the average impact energy at -40℃ (KV2) is basically controlled at 20~35J. The overall performance of the cross section of the forging varies greatly, which restricts the application prospects of wind power gearboxes.

[0004] CN107201482A discloses a gear steel for wind power and a preparation method thereof, wherein the main components include C: 0.12-0.20%, Mn: 2.6-3.8%, Si: 0.26-0.35%, Ni: 0.44-0.56%, Mo: 1.4-2.5%, Cr: 1.2-2.0%, Ti: 0.005-0.010%, W: 0.33-0.46%, Hf: 0.15-0.23%, P≤0.030%, S≤0.030%, and the balance is Fe and unavoidable impurities; the tensile strength is only 1150MPa and the yield strength is only 918MPa, and there is still a lot of room for improvement, and it still cannot meet the operating requirements of offshore wind power gearboxes in harsh environments; and the amount of metal elements added is relatively high, and the production cost is relatively high.

[0005] CN116695022A discloses a high-strength and tough gear round steel for wind power and a preparation method thereof, wherein the main components include: C: 0.15-0.21%, Si: 0.17-0.40%, Mn: 0.50-0.90%, P≤0.025%, S≤0.025%, Cr: 1.50-1.80%, Ni: 1.40-1.70%, Mo: 0.25-0.35%, Al ≤0.030%, Cu≤0.015%, O≤0.002%, N≤0.01%, H≤0.00015%, (La+Ce): 0.015~0.03% and the balance is Fe. The tensile strength of the gear round steel is 1130~1170MPa, and the yield strength is 900~940MPa. There is still a lot of room for improvement and it cannot meet the operating requirements of wind power gearboxes in harsh environments.

[0006] Therefore, people are in urgent need of developing a high-strength and high-toughness continuous casting round billet and its preparation method, which can refine the grain structure in the steel, significantly improve the cross-sectional component segregation phenomenon, meet the requirements of gearbox gears for offshore wind turbines, and have important research significance for the field of wind power generation. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a continuous casting round billet and a preparation method and application thereof. By optimizing the element composition and content ratio of the continuous casting round billet, the tensile strength is as high as 1450-1550MPa, the yield strength is as high as 1050-1150MPa, and the impact energy at -40°C (KV2) is as high as 45-55J. At the same time, the cross-sectional component segregation phenomenon is improved, and the cross-sectional carbon segregation extreme value is ≤0.040%; and the preparation process is simple and controllable; the continuous casting round billet can meet the requirements of gearbox gears for offshore wind turbines.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a continuous casting round billet, which comprises the following components: C: 0.17-0.19wt%, Mn: 0.62-0.68wt%, Cr: 1.62-1.70wt%, Mo: 0.29-0.31wt%, Ni: 1.52-1.60wt%, Nb: 0.017-0.025wt%, Al: 0.020-0.030wt%, N: 0.0075-0.0110wt%, Si: 0.20-0.28wt%, P≤0.010wt%, S≤0.005wt% and the balance Fe.

[0010] The content of each element can be selected as follows: C: 0.17-0.19wt%, for example, 0.17wt%, 0.175wt%, 0.18wt%, 0.185wt% or 0.19wt%; Mn: 0.62-0.68wt%, for example, 0.62wt%, 0.63wt%, 0.64wt%, 0.65wt%, 0.66wt%, 0.67wt% or 0.68wt%; Cr: 1.62-1.70wt%, for example, 1.62wt%, 1.63wt%, 1.64wt%, 1.65wt%, 1.66 wt%, 1.67wt%, 1.68wt%, 1.69wt% or 1.70wt%; Mo: 0.29-0.31wt%, for example, 0.29wt%, 0.295wt%, 0.30wt%, 0.305wt% or 0.31wt%; Ni: 1.52-1.60wt%, for example, 1.52wt%, 1.53wt%, 1.54wt%, 1.55wt%, 1.56wt%, 1.57wt%, 1.58wt%, 1.59wt% or 1.60wt%; Nb: 0.017-0.025wt%, for example, 0. 0.017wt%, 0.018wt%, 0.019wt%, 0.020wt%, 0.021wt%, 0.022wt% or 0.023wt%, 0.024wt% or 0.025wt%; Al: 0.020-0.030wt%, for example, 0.020wt%, 0.022wt%, 0.024wt%, 0.026wt%, 0.028wt% or 0.030wt%; N: 0.0075-0.0110wt%, for example, 0.0075wt%, 0.0080wt%, 0.0085wt%, 0.0090wt% t%, 0.0100wt%, 0.0105wt% or 0.0110wt%; Si: 0.20~0.28wt%, for example, it can be 0.20wt%, 0.22wt%, 0.24wt%, 0.26wt% or 0.28wt%; P≤0.010wt%, for example, it can be 0.010wt%, 0.009wt%, 0.008wt%, 0.007wt% or 0.006wt%, etc.; S≤0.005wt%, for example, it can be 0.005wt%, 0.004wt%, 0.003wt%, 0.002wt% or 0.001wt%.

[0011] The present invention optimizes the design of the elements C, Mn, Cr, Mo and Ni in the chemical composition of the continuous casting round billet, adds specific contents of Nb, Al and N elements, and adjusts the ratio of Al and N elements. The composite elements work together to refine the grain structure of the continuous casting round billet and improve the internal component segregation of the continuous casting round billet; at the same time, the tensile strength, yield strength and impact work of the continuous casting round billet at -40°C (KV2) are improved, meeting the requirements of gearbox gears for offshore wind turbines.

[0012] Preferably, the C content in the continuous casting round billet is 0.175-0.190wt%.

[0013] Preferably, the Mn content in the continuous casting round billet is 0.63-0.65wt%.

[0014] Preferably, the Cr content in the continuous casting round billet is 1.64-1.66wt%.

[0015] Preferably, the content of Mo in the continuous casting round billet is 0.29-0.30wt%.

[0016] Preferably, the Ni content in the continuous casting round billet is 1.54-1.57wt%.

[0017] Preferably, the Nb content in the continuous casting round billet is 0.020-0.023wt%.

[0018] Preferably, the Al content in the continuous casting round billet is 0.022-0.027wt%.

[0019] Preferably, the N content in the continuous casting round billet is 0.0085-0.0095wt%.

[0020] Preferably, the sum of the contents of C and Mn in the continuous casting round billet is 0.805-0.840wt%, for example, it may be 0.805wt%, 0.815wt%, 0.82wt%, 0.825wt%, 0.83wt%, 0.835wt% and 0.840wt%.

[0021] The present invention further preferably has a sum of the contents of C and Mn in the continuous casting round billet of 0.805-0.840wt%, which is beneficial to improving the strength and hardness of the product while stabilizing the plasticity and toughness of the product; if the sum of the contents of C and Mn is too low, the strength and hardness of the product may be reduced, deformation may occur after long-term use, and the service life may be affected; if the sum of the contents of C and Mn is too high, the product may become more brittle, have lower toughness, be easy to break, and have poor performance.

[0022] Preferably, the sum of the contents of Cr and Mo in the continuous casting round billet is 1.93-1.95wt%, for example, 1.93wt%, 1.935wt%, 1.94wt%, 1.945wt% or 1.95wt%.

[0023] The present invention further preferably has a sum of Cr and Mo contents in the continuous casting round billet of 1.93-1.95wt%, which is beneficial to improving the strength, hardness, wear resistance and corrosion resistance of the product while maintaining good plasticity and toughness; if the sum of Cr and Mo contents is too low, the wear resistance and corrosion resistance of the product will be reduced, affecting the service life; if the sum of Cr and Mo contents is too high, the brittleness of the product will increase, the toughness will decrease, affecting the performance.

[0024] Preferably, the mass ratio of Al to N in the continuous casting round billet is (2-4):1, for example, it can be 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1 or 4:1; preferably, it is (2.4-3.0):1.

[0025] The present invention further states that the mass ratio of Al to N in the continuous casting round billet is (2-4):1, which can significantly improve the tensile strength, yield strength and low-temperature impact of the product by affecting the pinning effect of the austenite grain boundary, thereby affecting the growth unevenness and grain size of the austenite grains, thereby improving the overall performance of the material; if the mass ratio of Al to N is too high, carburization and nitridation will occur on the surface of the continuous casting round billet, thereby reducing the strength and corrosion resistance of the continuous casting round billet and affecting the overall performance of the product; if the mass ratio of Al to N is too low, the strength and plasticity of the product will be reduced, making it easy to deform and break when subjected to force.

[0026] In a second aspect, the present invention provides a method for preparing the continuously cast round billet as described in the first aspect, the preparation method comprising: continuously casting and cooling molten steel in sequence to obtain the continuously cast round billet.

[0027] The continuous casting round billet of the present invention can be obtained by directly continuous casting molten steel and then cooling it. By regulating the element composition of the molten steel and the parameters of the continuous casting process, a high-strength and tough continuous casting round billet is successfully prepared, and at the same time, the grain structure is refined and the cross-sectional component segregation phenomenon is improved. The preparation process is simple and controllable, and the cost is low.

[0028] The method for preparing the molten steel comprises: selecting a steel ingot raw material according to the composition of the continuous casting round billet described in the first aspect, and sequentially subjecting the steel ingot raw material to KR desulfurization, converter smelting, ladle refining and vacuum refining to obtain the molten steel.

[0029] Preferably, the continuous casting is carried out in a continuous casting machine.

[0030] Preferably, the pulling speed during continuous casting is 0.20-0.33 m / min, for example, it can be 0.20 m / min, 0.22 m / min, 0.24 m / min, 0.26 m / min, 0.28 m / min, 0.30 m / min, 0.32 m / min or 0.33 m / min, preferably 0.24-0.32 m / min.

[0031] Preferably, the superheat during continuous casting is 15-25°C, for example, it can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C or 25°C.

[0032] It is worth mentioning that superheat refers to the difference between the pouring temperature of molten steel during the process and the liquidus temperature.

[0033] The present invention further preferably sets the pulling speed during continuous casting to 0.20-0.33 m / min and the superheat to 15-25°C, which is beneficial to the uniform growth of the entire shell of the continuous casting round billet during solidification and the floating of inclusions, improves the surface and core quality of the continuous casting round billet, thereby improving the cross-sectional segregation phenomenon, and a reasonable superheat has the effect of refining the grains, thereby improving the strength and hardness of the product; if the superheat during continuous casting is too low, it leads to uneven growth of the shell during the relative solidification and crystallization process of the molten steel, which is not conducive to the floating of inclusions, and the low pulling speed leads to surface stress cracks during the solidification process, resulting in a significant decrease in the strength and toughness of the continuous casting round billet; if the superheat during continuous casting is too high, it leads to poor surface fluidity of the continuous casting billet and uneven growth of the shell, and ultimately causes a large number of shrinkage holes and other quality defects in the continuous casting round billet during the solidification process; the pulling speed is too high, resulting in uneven growth of the shell, which is easy to cause cracks in the casting billet, and in severe cases, steel leakage accidents occur.

[0034] Preferably, the current of electromagnetic stirring of the crystallizer in the continuous casting machine is 160-230A, for example, it can be 160A, 170A, 180A, 190A, 200A, 210A, 220A or 230A.

[0035] Preferably, the frequency of the electromagnetic stirring of the crystallizer is 1.5-2 Hz, for example, 1.5 Hz, 1.6 Hz, 1.7 Hz, 1.8 Hz, 1.9 Hz or 2 Hz.

[0036] The present invention further preferably sets the current of the electromagnetic stirring of the crystallizer in the continuous casting machine to 160-230A and the frequency to 1.5-2Hz; this is beneficial to strengthening the convection, heat transfer and mass transfer processes of the molten steel, controlling the solidification process of the continuously cast round billet, reducing the superheat and inclusion content in the molten steel, and improving the quality of the cast billet; if the current or frequency of the electromagnetic stirring of the crystallizer is too low, the quality of the continuously cast round billet will be reduced, including the quality grade of subcutaneous bubbles, non-metallic inclusions, center segregation, shrinkage cavities and corner cracks; if the current or frequency of the electromagnetic stirring of the crystallizer is too high, it will lead to enhanced fluctuations in the steel liquid level in the crystallizer, and slag rolling may occur, thereby affecting the quality of the continuously cast round billet.

[0037] Preferably, the current of the terminal electromagnetic stirring in the continuous casting machine is 800-850A, for example, it can be 800A, 810A, 820A, 830A, 840A or 850A, etc., preferably 810-830A.

[0038] Preferably, the frequency of the terminal electromagnetic stirring is 6 to 9 Hz, for example, 6 Hz, 6.5 Hz, 7 Hz, 7.5 Hz, 8 Hz, 8.5 Hz or 9 Hz.

[0039] The present invention further preferably sets the current of the terminal electromagnetic stirring in the continuous casting machine to 800-850A and the frequency to 6-9Hz; this is beneficial to improving the center segregation, porosity and shrinkage problems of the continuously cast round billet; if the current or frequency of the terminal electromagnetic stirring is too low, the quality of the continuously cast round billet will be reduced, and the level of center carbon segregation, center porosity and shrinkage will increase, thereby affecting the quality and performance of the final product; if the current or frequency of the terminal electromagnetic stirring is too high, a white bright band phenomenon will occur in the continuously cast round billet, affecting the performance of the product.

[0040] Preferably, the cooling method includes annealing.

[0041] Preferably, the annealing includes entering the furnace, heating up, keeping the temperature, cooling down and exiting the furnace in sequence.

[0042] Preferably, the annealing comprises: entering the furnace at ≥450°C, first heating to 650-700°C and keeping the temperature for 20-24h, then cooling to ≤250°C before exiting the furnace.

[0043] The temperature entering the furnace is ≥450°C, for example, 450°C, 480°C or 500°C; the temperature is raised to 650-700°C, for example, 650°C, 680°C or 700°C; the insulation time is 20-24h, for example, 20h, 22h or 24h; the temperature is lowered to ≤250°C, for example, 250°C, 220°C or 200°C.

[0044] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0045] The molten steel is continuously cast in a continuous casting machine, wherein the pulling speed during continuous casting is 0.20-0.33 m / min, the superheat is 15-25°C, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 160-230A, the frequency is 1.5-2Hz, the current of the terminal electromagnetic stirring in the continuous casting machine is 800-850A, and the frequency is 6-9Hz; then annealing is adopted for cooling, and the annealing comprises: putting into the furnace at ≥450°C, first heating to 650-700°C and keeping warm for 20-24h, then cooling to ≤250°C and then taking out of the furnace, and finally obtaining the continuously cast round billet.

[0046] In a third aspect, the present invention provides an application of the continuously cast round billet described in the first aspect, wherein the continuously cast round billet is used to prepare gears, preferably gears for offshore wind power gearboxes.

[0047] The continuously cast round billet provided by the present invention can be used to prepare gears for offshore wind power gearboxes. The strength and toughness of the round billet can meet the requirements for the operation of offshore wind power gearboxes and the round billet has a long service life.

[0048] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The continuous casting round billet provided by the present invention optimizes the content ratio of C, Mn, Cr, Mo and Ni elements, and uses the composite strengthening principle of Nb, Al and N elements to add specific contents of Nb, Al and N, and adjust the ratio of Al and N. The composite elements work together to enhance the strength and toughness of the obtained continuous casting round billet, refine the grain structure and improve the cross-sectional segregation phenomenon. The tensile strength is preferably as high as 1520MPa or more, the yield strength is preferably as high as 1130MPa or more, and the impact energy at -40°C (KV2) is preferably as high as 50J or more. At the same time, the cross-sectional component segregation phenomenon is improved, and the cross-sectional carbon segregation extreme value is preferably as low as 0.033% or less.

[0051] (2) The present invention provides a method for preparing a continuously cast round billet. The method controls the pulling speed, superheat, current and frequency of electromagnetic stirring of the crystallizer, and current and frequency of electromagnetic stirring of the end during continuous casting, so that the prepared continuously cast round billet has high strength and high toughness, and can meet the requirements of the use environment and life of offshore wind power gearbox gears. In addition, the method has simple procedures, easy-to-control conditions and low cost.

[0052] (3) Application of the continuous casting round billet provided by the present invention. The continuous casting round billet can be used to prepare gears for offshore wind power gearboxes, which can meet the requirements of being used in a low temperature environment of -40°C, have high strength and toughness, and a long service life. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0054] The specific implementation method of the present invention provides a continuous casting round billet and a preparation method and application thereof, wherein the continuous casting round billet comprises the following components:

[0055] C: 0.17~0.19wt%, Mn: 0.62~0.68wt%, Cr: 1.62~1.70wt%, Mo: 0.29~0.31wt%, Ni: 1.52~1.60wt%, Nb: 0.017~ 0.025wt%, Al: 0.020~0.030wt%, N: 0.0075~0.0110wt%, Si: 0.20~0.28wt%, P≤0.010wt%, S≤0.005wt% and the balance Fe.

[0056] 1. Implementation

[0057] Example 1

[0058] The present embodiment provides a continuous casting round billet and a preparation method thereof, wherein the continuous casting round billet comprises the following components: C: 0.180wt%, Mn: 0.64wt%, Cr: 1.65wt%, Mo: 0.295wt%, Ni: 1.56wt%, Nb: 0.021wt%, Al: 0.0240wt%, N: 0.0087wt%, Si: 0.24wt%, P: 0.009wt%, S: 0.004wt% and the balance Fe.

[0059] The preparation method comprises the following steps:

[0060] The molten steel is continuously cast in a continuous casting machine, the pulling speed during continuous casting is 0.26 m / min, the superheat is 20°C, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 200A, the frequency is 1.75 Hz, the current of the terminal electromagnetic stirring in the continuous casting machine is 820A, and the frequency is 8 Hz; then annealing is used for cooling, and the annealing includes: entering the furnace at 450°C, first heating to 680°C and keeping warm for 24 hours, and then cooling to 250°C before taking out of the furnace, and finally obtaining the continuously cast round billet.

[0061] Example 2

[0062] The present embodiment provides a continuous casting round billet and a preparation method thereof, wherein the continuous casting round billet comprises the following components: C: 0.175wt%, Mn: 0.638wt%, Cr: 1.64wt%, Mo: 0.29wt%, Ni: 1.54wt%, Nb: 0.020wt%, Al: 0.022wt%, N: 0.0085wt%, Si: 0.20wt%, P: 0.008wt%, S: 0.003wt% and the balance Fe.

[0063] The preparation method comprises the following steps:

[0064] The molten steel is continuously cast in a continuous casting machine, the pulling speed during continuous casting is 0.24m / min, the superheat is 15°C, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 180A, the frequency is 1.5Hz, the current of the terminal electromagnetic stirring in the continuous casting machine is 810A, and the frequency is 6Hz; then it is cooled by annealing, and the annealing includes: entering the furnace at 500°C, first heating to 650°C and keeping warm for 20h, and then cooling to 220°C before taking out of the furnace, and finally obtaining the continuously cast round billet.

[0065] Example 3

[0066] The present embodiment provides a continuous casting round billet and a preparation method thereof, wherein the continuous casting round billet comprises the following components: C: 0.18wt%, Mn: 0.65wt%, Cr: 1.66wt%, Mo: 0.29wt%, Ni: 1.57wt%, Nb: 0.023wt%, Al: 0.027wt%, N: 0.0090wt%, Si: 0.28wt%, P: 0.010wt%, S: 0.005wt% and the balance Fe.

[0067] The preparation method comprises the following steps:

[0068] The molten steel is continuously cast in a continuous casting machine, the pulling speed during continuous casting is 0.32m / min, the superheat is 25°C, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 210A, the frequency is 2Hz, the current of the terminal electromagnetic stirring in the continuous casting machine is 830A, and the frequency is 9Hz; then it is cooled by slow cooling in the pit, and the annealing includes: entering the furnace at 480°C, first heating to 660°C and keeping warm for 22h, and then cooling to 200°C before taking out of the furnace, and finally obtaining the continuously cast round billet.

[0069] Example 4

[0070] This embodiment provides a continuous casting round billet and a preparation method thereof. The preparation method of the continuous casting round billet is the same as that of Embodiment 1 except that the drawing speed during the continuous casting is 0.20 m / min.

[0071] Example 5

[0072] This embodiment provides a continuous casting round billet and a preparation method thereof. The current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 160A, and the rest is the same as that in Embodiment 1.

[0073] Example 6

[0074] This embodiment provides a continuous casting round billet and a preparation method thereof. Except that the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 230A, the rest is the same as that of Embodiment 1.

[0075] Embodiments 7 to 14

[0076] Examples 7 to 14 adjust the elemental composition and content ratio on the basis of Example 1, and the rest are the same as Example 1. The elemental composition and content ratio are shown in Examples 7 to 14 in Table 1. The content of the unadjusted components is the same as that of Example 1, and the content of the adjusted components corresponds to the adjustment of the Fe content.

[0077] 2. Comparison

[0078] Comparative Examples 1 to 8 adjust the elemental composition and content ratio on the basis of Example 1, and the rest are the same as Example 1. The elemental composition and content ratio are shown in Comparative Examples 1 to 8 in Table 1. The content of the unadjusted component is the same as that of Example 1, and the content of the adjusted component corresponds to the Fe content.

[0079] Table 1

[0080] project C (wt%) Mn (wt%) Cr(wt%) Mo (wt%) Ni(wt%) Nb(wt%) Al(wt%) N (wt%) Example 1 0.180 0.64 1.65 0.295 1.56 0.021 0.0240 0.0087 Example 7 0.170 0.64 1.65 0.295 1.56 0.021 0.0240 0.0087 Example 8 0.180 0.66 1.65 0.295 1.56 0.021 0.0240 0.0087 Example 9 0.180 0.64 1.68 0.295 1.56 0.021 0.0240 0.0087 Example 10 0.180 0.64 1.65 0.270 1.56 0.021 0.0240 0.0087 Embodiment 11 0.180 0.64 1.65 0.295 1.40 0.021 0.0240 0.0087 Example 12 0.180 0.64 1.65 0.295 1.56 0.017 0.0240 0.0087 Embodiment 13 0.180 0.64 1.65 0.295 1.56 0.021 0.0200 0.0087 Embodiment 14 0.180 0.64 1.65 0.295 1.56 0.021 0.0240 0.0075 Comparative Example 1 0.165 0.64 1.65 0.295 1.56 0.021 0.0240 0.0087 Comparative Example 2 0.180 0.70 1.65 0.295 1.56 0.021 0.0240 0.0087 Comparative Example 3 0.180 0.64 1.80 0.295 1.56 0.021 0.0240 0.0087 Comparative Example 4 0.180 0.64 1.65 0.26 1.56 0.021 0.0240 0.0087 Comparative Example 5 0.180 0.64 1.65 0.295 1.45 0.021 0.0240 0.0087 Comparative Example 6 0.180 0.64 1.65 0.295 1.56 0.015 0.0240 0.0087 Comparative Example 7 0.180 0.64 1.65 0.295 1.56 0.021 0.015 0.0087 Comparative Example 8 0.180 0.64 1.65 0.295 1.56 0.021 0.0240 0.0060

[0081] 3. Test and its results

[0082] The tensile strength, yield strength, impact energy (-40°C) and extreme value of carbon segregation in cross section (taking Φ500mm specification as an example) of the continuous casting round billet provided in the above embodiments and comparative examples were tested and calculated, and the results are shown in Table 2.

[0083] Table 2

[0084]

[0085] From Table 2, we can see that:

[0086] (1) It can be seen from Examples 1 to 3 that the present invention optimizes the content of elements such as C, Mn, Cr, Mo and Ni in the continuous casting round billet by adjusting and controlling the content of elements such as C, Mn, Cr, Mo and Ni, and combines them with specific contents of Nb, Al and N elements. The elements work together to improve the impact toughness of the continuous casting round billet, the tensile strength is increased to more than 1520 MPa, the yield strength is increased to more than 1130 MPa, and the impact energy is as high as more than 50 J at -40°C. The carbon content segregation extreme of the cross section of the obtained continuous casting round billet is as low as less than 0.033% (Φ500 mm specification).

[0087] (2) It can be seen from Example 1 and Examples 4 to 6 that the present invention further improves the strength and toughness of the continuously cast round billet by further optimizing the parameters of the continuous casting process, including the pulling speed, the current and frequency of the electromagnetic stirring of the crystallizer within a specific range, and effectively improves the degree of component segregation in the cross section of the continuously cast round billet; at the same time, the impact energy at -40°C is also improved.

[0088] (3) Based on Example 1 and Examples 7 to 11, it can be seen that the present invention further optimizes the contents of C, Mn, Cr, Mo and Ni. The combination of these elements works together to improve the strength and toughness of the resulting continuous casting round billet, while improving the component segregation phenomenon in its cross section.

[0089] (4) Based on Example 1 and Examples 12 to 14, it can be seen that the present invention further preferably adds specific contents of Nb, Al and N elements, and controls the ratio of Al and N elements within the range of (2.4 to 3):1, utilizes their joint strengthening principle, maximizes the synergistic effect, and improves the overall performance of the resulting continuous casting round billet.

[0090] (5) Combining Example 1 with Comparative Examples 1 to 8, it can be seen that the tensile strength of the continuously cast round billets in Comparative Examples 1 to 8 drops to below 1465 MPa, the yield strength drops to below 1065 MPa, and the impact energy at -40°C is greatly reduced to below 43 J; the extreme difference in carbon content segregation in the cross section increases to above 0.036%. It can be seen that the present invention greatly improves the strength and toughness of the continuously cast round billets by optimizing the elemental components and their content ratios, and can meet the requirements of the use environment and service life of steel for offshore wind power gears.

[0091] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A continuous casting round billet, characterized in that: The continuous casting round billet comprises the following components: C: 0.17-0.19wt%, Mn: 0.62-0.68wt%, Cr: 1.62-1.70wt%, Mo: 0.29-0.31wt%, Ni: 1.52-1.60wt%, Nb: 0.017-0.025wt%, Al: 0.020-0.030wt%, N: 0.0075-0.0110wt%, Si: 0.20-0.28wt%, P≤0.010wt%, S≤0.005wt% and the balance Fe.

2. The continuous casting round billet according to claim 1, characterized in that: The C content in the continuous casting round billet is 0.175-0.190wt%; Preferably, the content of Mn in the continuous casting round billet is 0.63-0.65wt%; Preferably, the Cr content in the continuous casting round billet is 1.64-1.66wt%; Preferably, the content of Mo in the continuous casting round billet is 0.29-0.30wt%; Preferably, the content of Ni in the continuous casting round billet is 1.54-1.57wt%; Preferably, the Nb content in the continuous casting round billet is 0.020-0.023wt%; Preferably, the Al content in the continuous casting round billet is 0.022-0.027wt%; Preferably, the N content in the continuous casting round billet is 0.0085-0.0095wt%.

3. The continuous casting round billet according to claim 1 or 2, characterized in that: The sum of the contents of C and Mn in the continuous casting round billet is 0.805-0.840wt%; Preferably, the sum of the contents of Cr and Mo in the continuous casting round billet is 1.93-1.95wt%; Preferably, the mass ratio of Al to N in the continuous casting round billet is (2-4):1, preferably (2.4-3.0):

1.

4. A method for preparing a continuous casting round billet according to any one of claims 1 to 3, characterized in that: The preparation method comprises: The molten steel is continuously cast and cooled in sequence to obtain the continuously cast round billet.

5. The preparation method according to claim 4, characterized in that: The continuous casting is carried out in a continuous casting machine; Preferably, the pulling speed during continuous casting is 0.20 to 0.33 m / min, preferably 0.24 to 0.32 m / min; Preferably, the superheat degree during continuous casting is 15-25°C.

6. The preparation method according to claim 5, characterized in that: The current of electromagnetic stirring of the crystallizer in the continuous casting machine is 160-230A, preferably 180-210A; Preferably, the frequency of the electromagnetic stirring of the crystallizer is 1.5-2 Hz.

7. The preparation method according to claim 5 or 6, characterized in that: The current of the terminal electromagnetic stirring in the continuous casting machine is 800-850A, preferably 810-830A; Preferably, the frequency of the terminal electromagnetic stirring is 6 to 9 Hz.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The cooling method includes annealing; Preferably, the annealing includes, in sequence, entering the furnace, heating up, keeping the temperature, cooling down and exiting the furnace; Preferably, the annealing comprises: entering the furnace at ≥450°C, first heating to 650-700°C and keeping the temperature for 20-24h, then cooling to ≤250°C before exiting the furnace.

9. The preparation method according to any one of claims 4 to 8, characterized in that: The preparation method comprises the following steps: The molten steel is continuously cast in a continuous casting machine, wherein the pulling speed during continuous casting is 0.20-0.33 m / min, the superheat is 15-25°C, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 160-230A, the frequency is 1.5-2Hz, the current of the terminal electromagnetic stirring in the continuous casting machine is 800-850A, and the frequency is 6-9Hz; then annealing is adopted for cooling, and the annealing comprises: putting into the furnace at ≥450°C, first heating to 650-700°C and keeping warm for 20-24h, then cooling to ≤250°C and then taking out of the furnace, and finally obtaining the continuously cast round billet.

10. An application of the continuous casting round billet according to any one of claims 1 to 4, characterized in that: The continuously cast round billet is used for preparing gears, preferably gears for offshore wind power gearboxes.

Images