900mpa grade magnetic yoke steel sheet and method for manufacturing the same

Abstract

The present application relates to a kind of 900MPa level magnetic yoke steel plate and its preparation method, wherein the preparation method includes rolling blank into steel strip, and the rolling temperature of final rolling is 820~900 ℃;Two-stage cooling process is used to cool the steel strip after final rolling, wherein, the first stage cooling is to cool the steel strip after final rolling to intermediate temperature 650~750 ℃ according to the cooling speed of 20~40 ℃ / S, the second stage cooling is to cool the steel strip to 250~350 ℃ according to the cooling speed of 90~110 ℃ / S;And the steel strip cooled to 250~350 ℃ is treated to obtain 900MPa level magnetic yoke steel plate.The microstructure of the magnetic yoke steel plate prepared by the present application is two-phase structure of ferrite and martensite, and the strength and toughness are better matched;The magnetic yoke steel plate prepared by the present application has good magnetism.

Description

Technical Field

[0001] This invention belongs to the field of smelting and rolling technology, specifically relating to a 900MPa grade magnetic yoke steel plate and its preparation method. Background Technology

[0002] The magnetic yoke is a key component used in the rotor of a hydro-generator. Specifically, the magnetic yoke is processed into yoke plates, which are stacked to form a large ring with a height of 2000-4000 mm and a diameter of over ten meters, and then connected to the rotor shaft of the hydro-generator. The magnetic yoke used in the hydro-generator rotor bears a huge moment of inertia; therefore, the magnetic pole steel must have high dimensional accuracy and sufficient strength to ensure the balance and stability of the unit during high-speed operation. At the same time, it must also have excellent magnetic flux density to reduce eddy current losses and improve operating efficiency.

[0003] With the continuous advancement of hydropower manufacturing technology, high-head, large-capacity impulse turbine generators are the future development direction. Due to the high head, large capacity, and high speed of these units, the requirements for the yield strength of the magnetic yoke steel plates have been significantly increased. For example, the yield strength of the magnetic yoke steel plates used in the Baihetan project has been increased from 750MPa to 900MPa. In addition, these units also place more stringent requirements on the strength-toughness matching, plate shape, and internal stress control of the steel plates.

[0004] Existing technology discloses "a 900MPa grade high-toughness, high-magnetic hot-rolled magnetic yoke steel and its production method," whose composition contains Mo: 0.20-0.80%, Cr: 0.20-0.80%, Ni≤0.60%, V: 0.02-0.15%, B: 0.0005-0.003%, and Cr+Mo+Ni≥0.50%. This magnetic yoke steel alloy has a high cost, and it does not propose a method for controlling the flatness, the most critical technical indicator for stacked 900MPa magnetic yoke steel; therefore, it cannot meet the high flatness requirements of high-head, large-capacity units for 900MPa magnetic yoke steel.

[0005] Existing technology also discloses "an ultra-high strength magnetic yoke steel and its manufacturing method", whose composition includes Ti: 0.20-0.30%, Nb: 0.05-0.07%, Mo: 0.35-0.55%, and B: 0.001-0.003%. This magnetic yoke steel has a high content of precious metals, and it also does not propose a method for controlling the flatness, the most critical technical indicator for stacked use of 900MPa magnetic yoke steel; therefore, it also cannot meet the high flatness requirements of high-head, large-capacity units for 900MPa magnetic yoke steel. Summary of the Invention

[0006] In order to solve all or some of the above problems, the present invention aims to provide a 900MPa-level magnetic yoke steel plate and its preparation method.

[0007] According to one aspect of the present invention, a method for preparing a 900MPa-level magnetic yoke steel plate is provided, comprising:

[0008] The billet is rolled into steel strip, and the final rolling temperature is 820-900℃;

[0009] A two-stage cooling process is used to cool the final rolled steel strip. The first stage cools the strip to an intermediate temperature of 650–750°C at a cooling rate of 20–40°C / s. The second stage cools the strip to 250–350°C at a cooling rate of 90–110°C / s.

[0010] The steel strip, cooled to 250–350°C, is processed to obtain a 900 MPa grade magnetic yoke steel plate.

[0011] Furthermore, by weight percentage, the billet comprises:

[0012] C: 0.10–0.20%, Si: 1.0–1.5%, Mn: 1.50–2.0%, P≤0.02%, S≤0.01%, Ti: 0.01–0.05%, Al: 0.30–0.70%, N≤0.008%, Ni: 0.10–0.40%, with the remainder being Fe and unavoidable impurities.

[0013] Furthermore, before rolling the billet into steel strip at a final rolling temperature of 820–900°C, the preparation method further includes:

[0014] The billet is continuously cast into slabs through converter smelting and ladle refining; and

[0015] The slab is heated to a target temperature of 1200-1300°C and held at that temperature for 70 minutes or more.

[0016] Furthermore, the rolling of the billet into steel strip, with a final rolling temperature of 820–900°C, specifically refers to:

[0017] The heat-insulated slab is rolled into a steel strip of the target thickness using a multi-stand hot continuous rolling mill, with a final rolling temperature of 820–900°C.

[0018] Furthermore, the process of treating the steel strip cooled to 250–350°C to obtain a 900 MPa grade magnetic yoke steel plate further includes:

[0019] The steel strip, cooled to 250–350°C, is processed to obtain a steel coil; and

[0020] The steel coil is flattened to control its elongation, and then the flattened steel coil is cross-cut to obtain a 900MPa grade magnetic yoke steel plate.

[0021] Furthermore, the process of treating the steel strip cooled to 250–350°C to obtain a steel coil specifically involves:

[0022] The steel strip cooled to 250–350°C is coiled; and the coiled steel coil is annealed in a bell-type furnace to obtain a steel coil, wherein the holding temperature is 400–500°C.

[0023] Furthermore, the process of controlling elongation involves flattening the steel coil and then cross-cutting the flattened coil to obtain a 900MPa grade magnetic yoke steel plate, specifically as follows:

[0024] The steel coil is flattened with an elongation of 1.0 to 2.0%, and the flattened steel coil is cross-cut to obtain a 900MPa grade magnetic yoke steel plate.

[0025] According to another aspect of the present invention, a 900MPa-level magnetic yoke steel plate is provided, which is prepared by any of the preparation methods described above.

[0026] Furthermore, the microstructure of the 900MPa grade magnetic yoke steel plate is a ferrite and martensite dual-phase microstructure, with a yield strength ReL≥900MPa, tensile strength Rm≥1000MPa, elongation A≥12%, impact energy at -20℃≥60J, B50≥1.56T, B100≥1.73T, B200≥1.90T, and B300≥1.95T.

[0027] Furthermore, the unevenness of the 900MPa grade magnetic yoke steel plate is ≤2mm / m, and the unevenness of the laser-cut magnetic yoke sheet is ≤2mm / m.

[0028] As can be seen from the above technical solution, the 900MPa-level magnetic yoke steel plate and its preparation method provided by the present invention have the following beneficial effects:

[0029] The magnetic yoke steel plate prepared by this invention has a two-phase structure of ferrite and martensite, achieving a better match between strength and toughness. The yield strength ReL≥900MPa, tensile strength Rm≥1000MPa, elongation A≥12%, and impact energy at -20℃≥60J.

[0030] The magnetic yoke steel plate prepared by this invention has good magnetic properties, with magnetic induction intensity B50≥1.56T, B100≥1.73T, B200≥1.90T, and B300≥1.95T.

[0031] The magnetic yoke steel plate of the present invention is prepared by hot rolling process, without relying on quenching and tempering heat treatment equipment, and without adding precious alloys such as Mo, Nb, and Cr, and has the characteristics of low cost, low energy consumption, and economic and environmental protection.

[0032] The magnetic yoke steel plate prepared by this invention has high flatness, with an unevenness ≤2mm / m; low internal stress, and the unevenness of the laser-cut magnetic yoke sheet is ≤2mm / m. It can well meet the requirements of high-head, large-capacity units for stacking 900MPa magnetic yoke steel. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating a method for preparing a 900MPa-level magnetic yoke steel plate according to an embodiment of the present invention. Detailed Implementation

[0034] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0035] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0036] like Figure 1 As shown, this invention illustrates a method for preparing a 900MPa-level magnetic yoke steel plate, comprising the following steps:

[0037] Step S001: Roll the billet into a steel strip, and the final rolling temperature is 820-900℃;

[0038] Step S002: A two-stage cooling process is used to cool the final rolled steel strip. The first stage of cooling involves cooling the final rolled steel strip to an intermediate temperature of 650–750°C at a cooling rate of 20–40°C / s. The second stage of cooling involves cooling the steel strip to 250–350°C at a cooling rate of 90–110°C / s.

[0039] Step S003: The steel strip cooled to 250-350°C is processed to obtain a 900MPa grade magnetic yoke steel plate.

[0040] This invention, through precise control of a two-stage cooling process, enables the rolled steel strip to undergo two phase transformations sequentially during laminar flow cooling, resulting in ferrite and martensite structures. The martensite structure ensures material strength, while the soft ferrite structure absorbs the martensitic phase transformation stress, improves the straightening plate shape, and achieves a good match between high strength and high toughness.

[0041] Traditional ferritic magnetic yoke steel cannot break through the 750MPa limit in yield strength. Therefore, in order to make the yield strength of magnetic yoke steel reach 900MPa, martensite structure must be introduced into the steel. However, the magnetic yoke steel plate in this embodiment has a "ferrite + martensite" dual-phase structure, which achieves a good match between high strength and high toughness.

[0042] In one embodiment, the billet comprises, by weight percentage:

[0043] C: 0.10–0.20%, Si: 1.0–1.5%, Mn: 1.50–2.0%, P≤0.02%, S≤0.01%, Ti: 0.01–0.05%, Al: 0.30–0.70%, N≤0.008%, Ni: 0.10–0.40%, with the remainder being Fe and unavoidable impurities.

[0044] The chemical composition system of the billet in this embodiment of the invention uses C, Si, Mn and Al as the main elements, without adding precious metals such as Nb, Mo and Cr, which has the advantage of low alloy cost.

[0045] Carbon (C) is the most economical and hardenable element in steel, playing a crucial role in improving the strength of martensitic steel. In this embodiment of the invention, to obtain magnetic yoke steel with a yield strength of 900 MPa, the C content must be above 0.10%. At the same time, the C content cannot be too high, otherwise the resulting martensite structure will be too dense, which will deteriorate the low-temperature toughness and magnetic properties of the steel. Based on this, the C content in this embodiment of the invention is 0.10–0.20%.

[0046] Silicon (Si) is a ferrite-forming element that can inhibit cementite formation, promote carbon enrichment in retained austenite, improve austenite stability, and accelerate the precipitation of polygonal ferrite. Si can also reduce the harmful effects of other impurities in steel, reduce the detrimental effects on magnetism, and significantly improve the magnetic induction properties of the invented steel. Moreover, in practical implementation, if the Si content is too low, the above effects cannot be achieved, while if the Si content is too high, the weldability and surface quality of the steel will deteriorate. Based on this, the Si content in the embodiments of the present invention is 1.0 to 1.5%.

[0047] Manganese (Mn) can play a solid solution strengthening role, improving the yield strength and tensile strength of steel. However, excessive Mn content can easily lead to central segregation, reducing the toughness and plasticity of steel. Based on this, the Mn content in the embodiments of the present invention is 1.5-2.0%.

[0048] Phosphorus (P) and sulfur (S) are harmful elements in steel, and the lower their content, the better; in this embodiment of the invention, the P content is ≤0.020% and the S content is ≤0.010%.

[0049] The Ti (titanium) content in the embodiments of the present invention is 0.01-0.05%, which is mainly used to refine the grains.

[0050] In this embodiment of the invention, the Al (aluminum) content is 0.3-0.7%. Al has a similar function to Si. Since excessive Si content will deteriorate the weldability and surface quality of steel, an appropriate amount of Al is added to replace Si.

[0051] In this embodiment of the invention, the Ni (nickel) content is 0.10-0.40%. Ni is an effective element for improving the low-temperature toughness of steel, which is beneficial for improving the low-temperature toughness of steel plates.

[0052] In one embodiment, before rolling the billet into a steel strip in step S001, and before the final rolling temperature is 820–900°C, the preparation method further includes:

[0053] The billets are continuously cast into slabs through converter smelting and ladle refining; and

[0054] Heat the slab to the target temperature of 1200-1300℃ and hold it at that temperature for 70 minutes or more.

[0055] In this step, by reasonably determining the heating temperature and holding time, it is necessary to ensure that the precipitates are fully dissolved while effectively avoiding excessively high temperatures that could lead to coarse grains after rolling. In this embodiment, the slab is heated to the target temperature of 1200–1300°C, and the holding time is ≥70 min.

[0056] In one embodiment, step S001, which involves rolling the billet into a steel strip, and the final rolling temperature being 820–900°C, specifically involves:

[0057] The heat-insulated slab is rolled into a steel strip of the target thickness using a multi-stand hot continuous rolling mill, with a final rolling temperature of 820-900℃ and a target thickness of 3-6 mm.

[0058] In this embodiment, a reasonable final rolling temperature not only ensures a good sheet shape, but also provides the necessary process conditions for subsequent process steps (two-stage cooling process).

[0059] In one embodiment, step S003, which processes the steel strip cooled to 250–350°C to obtain a 900 MPa-level magnetic yoke steel plate, further includes:

[0060] Steel strip cooled to 250–350°C is processed to obtain steel coils; and

[0061] The elongation rate is controlled by flattening the steel coil, and the flattened steel coil is then cross-cut to obtain a 900MPa grade magnetic yoke steel plate.

[0062] Because the shape and strength of different parts of the steel plate are somewhat uneven, it cannot be guaranteed that the shape of all parts will meet the requirements under a certain pressure. To address this, this embodiment develops an elongation control mode to control the elongation range of the steel plate during flattening, thereby ensuring the stable and controllable shape of the steel strip after flattening. The elongation control mode of this embodiment overcomes the shortcomings of existing technologies where, although martensitic steel has high strength, it is difficult to control the shape of thin-gauge plates, making it impossible to meet the high flatness requirements of magnetic yoke steel.

[0063] Specifically, the process of treating steel strip cooled to 250–350°C to obtain steel coils involves:

[0064] The steel strip cooled to 250–350°C is coiled; and the coiled steel coil is annealed in a bell-type furnace to obtain a steel coil, wherein the holding temperature is 400–500°C.

[0065] Specifically, during the annealing process, within the holding temperature range, the internal stress of the steel plate was effectively released while maintaining its strength. The coiled steel coils were annealed in a bell-type furnace at a holding temperature of 400–500℃.

[0066] Specifically, controlling the elongation rate involves flattening the steel coil and then cross-cutting the flattened coil to obtain a 900MPa grade magnetic yoke steel plate.

[0067] The steel coils are leveled with an elongation of 1.0 to 2.0%, and then cross-cut to obtain 900MPa grade magnetic yoke steel plates.

[0068] When leveling steel coils, due to the unevenness in shape and strength of different parts of the steel sheet, it is impossible to guarantee that the shape of all parts meets the requirements under certain pressure. To address this issue, this embodiment develops an elongation control mode, thereby ensuring the stable and controllable shape of the steel strip after leveling. In this embodiment, the elongation is controlled at 1.0% to 2.0% during the leveling process of the steel coil.

[0069] On the other hand, embodiments of the present invention provide a 900MPa-level magnetic yoke steel plate, which is prepared by any of the preparation methods of the above embodiments.

[0070] Among them, the microstructure of the 900MPa grade magnetic yoke steel plate is a ferrite and martensite dual-phase structure, with a yield strength ReL≥900MPa, tensile strength Rm≥1000MPa, elongation A≥12%, impact energy at -20℃≥60J, B50≥1.56T, B100≥1.73T, B200≥1.90T, and B300≥1.95T.

[0071] The unevenness of the 900MPa grade magnetic yoke steel plate is ≤2mm / m, and the unevenness of the laser-cut magnetic yoke sheet is ≤2mm / m, which can well meet the stacking requirements of 900MPa magnetic yoke steel for high-head and large-capacity units.

[0072] Compared with the prior art, the 900MPa grade hot-rolled magnetic yoke steel plate prepared in the embodiments of the present invention has the following advantages:

[0073] The magnetic yoke steel plate prepared in this embodiment of the invention has a two-phase structure of ferrite and martensite, achieving a better match between strength and toughness. The yield strength ReL≥900MPa, tensile strength Rm≥1000MPa, elongation A≥12%, and impact energy at -20℃≥60J.

[0074] The magnetic yoke steel plate prepared in this embodiment of the invention has good magnetic properties, with magnetic induction intensity B50≥1.56T, B100≥1.73T, B200≥1.90T, and B300≥1.95T.

[0075] The magnetic yoke steel plate of this invention is prepared by hot rolling process, without relying on quenching and tempering heat treatment equipment, and without adding precious alloys such as Mo, Nb, and Cr, which has the characteristics of low cost, low energy consumption, and economic and environmental protection.

[0076] The magnetic yoke steel plate prepared in this embodiment of the invention has high flatness, with an unevenness ≤2mm / m; low internal stress, and the unevenness of the laser-cut magnetic yoke sheet is ≤2mm / m. It can well meet the requirements of high-head, large-capacity units for stacking 900MPa magnetic yoke steel.

[0077] The specific embodiments of the present invention will be described in detail below with reference to specific examples, but the specific embodiments of the present invention are not limited to the following examples.

[0078] Example 1

[0079] This embodiment describes the preparation of a 900MPa grade hot-rolled magnetic pole steel plate. The steel plate is 3mm thick and 1300mm wide, and its chemical composition by mass percentage is as follows:

[0080] C: 0.14%, Si: 1.1%, Mn: 1.75%, P: 0.015%, S: 0.008%, Ti: 0.02%, Al: 0.45%, Ni: 0.2%, N: 0.006%, with the remainder being Fe and unavoidable impurities.

[0081] The preparation method of this embodiment includes the following sequential steps:

[0082] (1) Smelting: After being smelted in a converter and refined outside the furnace, it is continuously cast into slabs.

[0083] (2) Rolling: The slab is heated to 1270°C and rolled to the target thickness of 3mm using a multi-stand hot continuous rolling mill. The final rolling temperature is 850°C.

[0084] (3) Cooling: Two-stage cooling is adopted. The first stage cooling rate is 36℃ / S, the intermediate temperature is 680℃, and the second stage cooling rate is 108℃ / S. The steel strip is cooled to 280℃ and then coiled.

[0085] (4) Annealing: The steel coil is annealed in a bell furnace with a holding temperature of 450℃.

[0086] (5) Leveling: The annealed and cooled steel coil is leveled with a leveling elongation of 1.2%.

[0087] (6) Cross-cutting: After the steel strip passes through the coarse straightening machine and the fine straightening machine in sequence to eliminate internal stress, it is cross-cut into a steel plate with a length of 3500mm.

[0088] (7) Performance and flatness testing

[0089] Mechanical property test results: its yield strength ReL is 960MPa, tensile strength Rm is 1050MPa, and elongation is 14%. Magnetic induction intensity test results: B50 = 1.59T, B100 = 1.75T, B200 = 1.92T, B300 = 1.98T, impact energy at -20℃ is 92J. Steel plate unevenness: 1.5mm / m, unevenness of cut magnetic yoke: 1.2mm / m.

[0090] The chemical composition of the billets in Examples 2 to 6 is shown in Table 1 below. The process parameters in Examples 2 to 6 are shown in Table 2 below. The mechanical properties of the steel plates obtained in Examples 2 to 6 are shown in Table 3 below. The magnetic properties and roughness of the steel plates obtained in Examples 2 to 6 are shown in Table 4 below.

[0091] Table 1 shows the chemical composition (in %) of the billets used in Examples 2 to 6:

[0092] C Si Mn P S Ni Ti Al N Example 2 0.15 1.15 1.80 0.010 0.006 0.18 0.03 0.50 0.004 Example 3 0.16 1.20 1.60 0.008 0.004 0.25 0.04 0.40 0.005 Example 4 0.13 1.10 1.70 0.007 0.006 0.20 0.02 0.55 0.006 Example 5 0.14 1.25 1.85 0.009 0.003 0.19 0.04 0.45 0.007 Example 6 0.15 1.30 1.83 0.012 0.005 0.22 0.03 0.50 0.004

[0093] Table 2 shows the process parameters for Examples 2 to 6:

[0094]

[0095] Table 3 shows the mechanical properties of the steel plates obtained in Examples 2 to 6:

[0096]

[0097]

[0098] Table 4 shows the magnetic properties and unevenness results of the steel plates obtained in Examples 2 to 6:

[0099]

[0100] Specifically, Example 2:

[0101] This embodiment describes the preparation of a 900MPa grade hot-rolled magnetic pole steel plate. The steel plate is 3mm thick and 1300mm wide, and its chemical composition by mass percentage is as follows:

[0102] C: 0.15%, Si: 1.15%, Mn: 1.80%, P: 0.010%, S: 0.006%, Ti: 0.03%, Al: 0.50%, Ni: 0.18%, N: 0.004%, with the remainder being Fe and unavoidable impurities.

[0103] The preparation method of this embodiment includes the following sequential steps:

[0104] (1) Smelting: After being smelted in a converter and refined outside the furnace, it is continuously cast into slabs.

[0105] (2) Rolling: The slab is heated to 1280°C and rolled to the target thickness of 3mm using a multi-stand hot continuous rolling mill. The final rolling temperature is 860°C.

[0106] (3) Cooling: Two-stage cooling is adopted. The first stage cooling rate is 25℃ / S, the intermediate temperature is 720℃, and the second stage cooling rate is 97℃ / S. The steel strip is cooled to 290℃ and then coiled.

[0107] (4) Annealing: The steel coil is annealed in a bell furnace with a holding temperature of 470℃.

[0108] (5) Leveling: The annealed and cooled steel coil is leveled with a leveling elongation of 1.5%.

[0109] (6) Cross-cutting: After the steel strip passes through the coarse straightening machine and the fine straightening machine in sequence to eliminate internal stress, it is cross-cut into a steel plate with a length of 3500mm.

[0110] (7) Performance and flatness testing

[0111] Mechanical property test results: its yield strength ReL is 963MPa, tensile strength Rm is 1046MPa, and elongation is 15%. Magnetic induction intensity test results: B50 = 1.58T, B100 = 1.74T, B200 = 1.93T, B300 = 1.98T, impact energy at -20℃ is 106J. Steel plate unevenness: 1.5mm / m, unevenness of cut magnetic yoke: 1.3mm / m.

[0112] Example 3:

[0113] This embodiment describes the preparation of a 900MPa grade hot-rolled magnetic pole steel plate. The steel plate is 3mm thick and 1300mm wide, and its chemical composition by mass percentage is as follows:

[0114] C: 0.16%, Si: 1.20%, Mn: 1.60%, P: 0.008%, S: 0.004%, Ti: 0.04%, Al: 0.40%, Ni: 0.25%, N: 0.005%, with the remainder being Fe and unavoidable impurities.

[0115] The preparation method of this embodiment includes the following sequential steps:

[0116] (1) Smelting: After being smelted in a converter and refined outside the furnace, it is continuously cast into slabs.

[0117] (2) Rolling: The slab is heated to 1270°C and rolled to the target thickness of 3mm using a multi-stand hot continuous rolling mill. The final rolling temperature is 870°C.

[0118] (3) Cooling: Two-stage cooling is adopted. The first stage cooling rate is 30℃ / S, the intermediate temperature is 690℃, and the second stage cooling rate is 105℃ / S. The steel strip is cooled to 300℃ and then coiled.

[0119] (4) Annealing: The steel coil is annealed in a bell furnace with a holding temperature of 470℃.

[0120] (5) Leveling: The annealed and cooled steel coil is leveled with a leveling elongation of 1.3%.

[0121] (6) Cross-cutting: After the steel strip passes through the coarse straightening machine and the fine straightening machine in sequence to eliminate internal stress, it is cross-cut into a steel plate with a length of 3500mm.

[0122] (7) Performance and flatness testing

[0123] Mechanical property test results: its yield strength ReL is 952MPa, tensile strength Rm is 1055MPa, and elongation is 15%. Magnetic induction intensity test results: B50 = 1.59T, B100 = 1.75T, B200 = 1.94T, B300 = 2.01T, impact energy at -20℃ is 101J. Steel plate unevenness: 1.2mm / m, unevenness of cut magnetic yoke: 1.0mm / m.

[0124] Example 4:

[0125] This embodiment describes the preparation of a 900MPa grade hot-rolled magnetic pole steel plate. The steel plate is 3mm thick and 1300mm wide, and its chemical composition by mass percentage is as follows:

[0126] C: 0.13%, Si: 1.10%, Mn: 1.70%, P: 0.007%, S: 0.006%, Ti: 0.02%, Al: 0.55%, Ni: 0.20%, N: 0.006%, with the remainder being Fe and unavoidable impurities.

[0127] The preparation method of this embodiment includes the following sequential steps:

[0128] (1) Smelting: After being smelted in a converter and refined outside the furnace, it is continuously cast into slabs.

[0129] (2) Rolling: The slab is heated to 1280°C and rolled to the target thickness of 3mm using a multi-stand hot continuous rolling mill. The final rolling temperature is 870°C.

[0130] (3) Cooling: Two-stage cooling is adopted. The first stage cooling rate is 35℃ / S, the intermediate temperature is 690℃, and the second stage cooling rate is 98℃ / S. The steel strip is cooled to 310℃ and then coiled.

[0131] (4) Annealing: The steel coil is annealed in a bell furnace with a holding temperature of 460℃.

[0132] (5) Leveling: The annealed and cooled steel coil is leveled with a leveling elongation of 1.3%.

[0133] (6) Cross-cutting: After the steel strip passes through the coarse straightening machine and the fine straightening machine in sequence to eliminate internal stress, it is cross-cut into a steel plate with a length of 3500mm.

[0134] (7) Performance and flatness testing

[0135] Mechanical property test results: its yield strength ReL is 958MPa, tensile strength Rm is 1050MPa, and elongation is 16%. Magnetic induction intensity test results: B50 = 1.60T, B100 = 1.76T, B200 = 1.96T, B300 = 2.02T, impact energy at -20℃ is 96J. Steel plate unevenness: 1.0mm / m, unevenness of cut magnetic yoke: 0.9mm / m.

[0136] Example 5:

[0137] This embodiment describes the preparation of a 900MPa grade hot-rolled magnetic pole steel plate. The steel plate is 3mm thick and 1300mm wide, and its chemical composition by mass percentage is as follows:

[0138] C: 0.14%, Si: 1.25%, Mn: 1.85%, P: 0.009%, S: 0.003%, Ti: 0.04%, Al: 0.45%, Ni: 0.19%, N: 0.007%, with the remainder being Fe and unavoidable impurities.

[0139] The preparation method of this embodiment includes the following sequential steps:

[0140] (1) Smelting: After being smelted in a converter and refined outside the furnace, it is continuously cast into slabs.

[0141] (2) Rolling: The slab is heated to 1270°C and rolled to the target thickness of 3mm using a multi-stand hot continuous rolling mill. The final rolling temperature is 850°C.

[0142] (3) Cooling: Two-stage cooling is adopted. The first stage cooling rate is 38℃ / S, the intermediate temperature is 675℃, and the second stage cooling rate is 95℃ / S. The steel strip is cooled to 280℃ and then coiled.

[0143] (4) Annealing: The steel coil is annealed in a bell furnace with a holding temperature of 480℃.

[0144] (5) Leveling: The annealed and cooled steel coil is leveled with a leveling elongation of 1.6%.

[0145] (6) Cross-cutting: After the steel strip passes through the coarse straightening machine and the fine straightening machine in sequence to eliminate internal stress, it is cross-cut into a steel plate with a length of 3500mm.

[0146] (7) Performance and flatness testing

[0147] Mechanical property test results: its yield strength ReL is 980MPa, tensile strength Rm is 1067MPa, and elongation is 14%. Magnetic induction intensity test results: B50 = 1.57T, B100 = 1.73T, B200 = 1.92T, B300 = 1.97T, impact energy at -20℃ is 87J. Steel plate unevenness: 1.2mm / m, unevenness of the cut magnetic yoke: 0.8mm / m.

[0148] Example 6:

[0149] This embodiment describes the preparation of a 900MPa grade hot-rolled magnetic pole steel plate. The steel plate is 3mm thick and 1300mm wide, and its chemical composition by mass percentage is as follows:

[0150] C: 0.16%, Si: 1.30%, Mn: 1.83%, P: 0.012%, S: 0.005%, Ti: 0.03%, Al: 0.50%, Ni: 0.22%, N: 0.004%, with the remainder being Fe and unavoidable impurities.

[0151] The preparation method of this embodiment includes the following sequential steps:

[0152] (1) Smelting: After being smelted in a converter and refined outside the furnace, it is continuously cast into slabs.

[0153] (2) Rolling: The slab is heated to 1260°C and rolled to the target thickness of 3mm using a multi-stand hot continuous rolling mill. The final rolling temperature is 840°C.

[0154] (3) Cooling: Two-stage cooling is adopted. The first stage cooling rate is 28℃ / S, the intermediate temperature is 700℃, and the second stage cooling rate is 102℃ / S. The steel strip is cooled to 330℃ and then coiled.

[0155] (4) Annealing: The steel coil is annealed in a bell furnace with a holding temperature of 460℃.

[0156] (5) Leveling: The annealed and cooled steel coil is leveled with a leveling elongation of 1.4%.

[0157] (6) Cross-cutting: After the steel strip passes through the coarse straightening machine and the fine straightening machine in sequence to eliminate internal stress, it is cross-cut into a steel plate with a length of 3500mm.

[0158] (7) Performance and flatness testing

[0159] Mechanical property test results: its yield strength ReL is 975MPa, tensile strength Rm is 1065MPa, and elongation is 15%. Magnetic induction intensity test results: B50 = 1.59T, B100 = 1.75T, B200 = 1.93T, B300 = 2.00T, impact energy at -20℃ is 95J. Steel plate unevenness: 0.8mm / m, unevenness of cut magnetic yoke: 0.7mm / m.

[0160] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are merely illustrative of the invention and should not be construed as limiting its scope. It should be noted that any variations and substitutions equivalent to these embodiments should be considered to be covered within the scope of the claims. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a 900MPa-level magnetic yoke steel plate, characterized in that, include: The billet is rolled into steel strip, and the final rolling temperature is 820~900℃; A two-stage cooling process is used to cool the final rolled steel strip. The first stage cools the strip to an intermediate temperature of 650-750℃ at a cooling rate of 20-40℃ / s. The second stage cools the strip to 250-350℃ at a cooling rate of 90-110℃ / s. The steel strip cooled to 250~350°C is processed to obtain a 900MPa grade magnetic yoke steel plate; The billet, by weight percentage, comprises: C: 0.10~0.20%, Si: 1.0~1.5%, Mn: 1.50~2.0%, P≤0.02%, S≤0.01%, Ti: 0.01~0.05%, Al: 0.30~0.70%, N≤0.008%, Ni: 0.10~0.40%, with the remainder being Fe and unavoidable impurities; The process of processing the steel strip cooled to 250~350°C to obtain a 900MPa grade magnetic yoke steel plate further includes: processing the steel strip cooled to 250~350°C to obtain a steel coil; and controlling the elongation to perform a flattening process on the steel coil, and cross-cutting the flattened steel coil to obtain a 900MPa grade magnetic yoke steel plate. The process of processing the steel strip cooled to 250~350℃ to obtain a steel coil specifically involves: coiling the steel strip cooled to 250~350℃; and annealing the coiled steel coil in a bell-type furnace to obtain a steel coil, wherein the holding temperature is 400~500℃. The process of controlling the elongation rate to flatten the steel coil and then transversely cutting the flattened steel coil to obtain a 900MPa-level magnetic yoke steel plate specifically involves: controlling the elongation rate to 1.0~2.0% to flatten the steel coil and then transversely cutting the flattened steel coil to obtain a 900MPa-level magnetic yoke steel plate.

2. The method for preparing the 900MPa-level magnetic yoke steel plate according to claim 1, characterized in that, Before rolling the billet into steel strip at a final rolling temperature of 820~900℃, the preparation method further includes: The billet is continuously cast into slabs through converter smelting and ladle refining; and The slab is heated to a target temperature of 1200~1300℃ and held at that temperature for at least 70 minutes.

3. The method for preparing the 900MPa-level magnetic yoke steel plate according to claim 2, characterized in that, The process of rolling the billet into steel strip at a final rolling temperature of 820~900℃ specifically refers to: The heat-insulated slab is rolled into a steel strip of the target thickness using a multi-stand hot continuous rolling mill, and the final rolling temperature is 820~900℃.

4. A 900MPa grade magnetic yoke steel plate, characterized in that, It is prepared by the preparation method described in any one of claims 1-3.

5. A 900MPa-level magnetic yoke steel plate according to claim 4, characterized in that, The 900MPa grade magnetic yoke steel plate has a dual-phase microstructure of ferrite and martensite, with a yield strength ReL≥900MPa, tensile strength Rm≥1000MPa, elongation A≥12%, impact energy at -20℃≥60J, B50≥1.56T, B100≥1.73T, B200≥1.90T, and B300≥1.95T.

6. A 900MPa-level magnetic yoke steel plate according to claim 4, characterized in that, The unevenness of the 900MPa grade magnetic yoke steel plate is ≤2mm / m, and the unevenness of the laser-cut magnetic yoke sheet is ≤2mm / m.

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