CN111748730B - 900 MPa-grade high-toughness high-magnetism hot-rolled magnetic yoke steel and production method thereof - Google Patents

900 MPa-grade high-toughness high-magnetism hot-rolled magnetic yoke steel and production method thereof Download PDF

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CN111748730B
CN111748730B CN201910244024.4A CN201910244024A CN111748730B CN 111748730 B CN111748730 B CN 111748730B CN 201910244024 A CN201910244024 A CN 201910244024A CN 111748730 B CN111748730 B CN 111748730B
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胡晓萍
陆敏
王巍
宋凤明
温东辉
吴祖国
华骏山
郁锋
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Baoshan Iron and Steel Co Ltd
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Abstract

The 900 MPa-grade high-toughness high-magnetism hot-rolled magnetic yoke steel comprises the following components in percentage by weight: 0.15-0.30% of C, less than or equal to 0.50% of Si, 1.0-2.0% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, less than or equal to 0.06% of Ti, less than or equal to 0.05% of Nb, 0.20-0.80% of Mo, 0.20-0.80% of Cr, less than or equal to 0.60% of Ni, 0.02-0.15% of V, 0.0005-0.003% of B, 0.015-0.10% of Al, less than or equal to 0.010% of N, less than or equal to 0.0080% of O, and the balance of Fe and other unavoidable impurities; and, simultaneously: cr + Mo + Ni is more than or equal to 0.50 percent; the carbon equivalent CEV is more than or equal to 0.45 percent. The invention realizes that the yield strength of the steel plate reaches over 900MPa level through the tempered sorbite phase-change strengthening + V precipitation strengthening effect, and has higher low-temperature toughness. The invention forms a tempered sorbite structure in the steel through reasonable components and process design, and ensures that the structure stress in the steel is greatly reduced, thereby leading the product to have ultrahigh strength and high magnetic performance.

Description

900 MPa-grade high-toughness high-magnetism hot-rolled magnetic yoke steel and production method thereof
Technical Field
The invention relates to steel for a generator rotor yoke and a production method thereof, in particular to 900 MPa-grade high-toughness high-magnetism hot-rolled yoke steel and a production method thereof.
Background
The rotor magnetic yoke is a key part of the hydraulic generator, and the magnetic yoke of the large hydraulic generator is formed by stacking steel plate punching sheets. The reasonable selection of the magnetic yoke material and the manufacturing process have very important meanings for ensuring the installation quality and the operation performance of the hydraulic generator, effectively controlling the manufacturing cost of the hydraulic generator and the like. The performance requirements of the hydroelectric generator group on the yoke steel plate mainly include high tensile property: the magnetic yoke steel plate is subjected to huge centrifugal force and electromagnetic force, and the linear speed of the magnetic yoke can reach 130-170 m/s at the maximum runaway rotating speed; strict dimensional accuracy: the magnetic yoke steel plate has smooth and flat surface and uniform thickness so as to ensure that the high rotor magnetic yoke laminating coefficient and small waviness are obtained. High magnetic flux density: the magnetic yoke is a part of a magnetic circuit of the generator, and the design of the motor generally requires that the maximum working magnetic induction intensity Bm of a magnetic circuit material is not less than 1.58T.
The planning and construction of hydropower station projects such as Wudongde, white Crane beach, Yajiang and the like require large-scale hydroelectric generating sets with single-machine capacity of million kilowatts, which puts more strict requirements on the comprehensive performance of steel used for the rotor yoke part of the hydraulic generator. The Udongde and white crane beach hydropower station engineering currently selects ultrahigh-strength high-toughness magnet yoke steel with yield strength of 750MPa grade, which represents the highest level of commercial hot-rolled magnet yoke steel; and the requirements of hot-rolled magnetic yoke steel with yield strength up to 1000MPa level in hydropower engineering are provided.
At present, for example, Chinese patent application No. 200710051251.2 discloses a C-Mn-Ti-Nb series hot-rolled high-strength yoke steel, which comprises the following components in percentage by weight: c: 0.03-0.15%, Si is less than or equal to 0.15%, Mn: 1.00-1.80%, P is less than or equal to 0.025%, S is less than or equal to 0.015%, Ti: 0.08-0.18%, Nb:0.02-0.07%, Als: 0.02-0.10% and N less than or equal to 0.010%. The production process comprises the following steps: firstly, heating the cast plate blank to 1230-1280 ℃; then rough rolling is carried out, wherein the finish temperature of the rough rolling is more than or equal to 1100 ℃; then, finish rolling is carried out, wherein the finish rolling temperature is 850-930 ℃; and (3) after rolling, adopting laminar flow cooling and then coiling the steel plate, wherein the coiling temperature is 550-620 ℃, and obtaining the hot rolled plate coil. The yield strength is lower and is only 700MPa grade, and the magnetic induction property B50≥1.5T。
In addition, Chinese patent application number 201310412335.X discloses a high-strength magnetic yoke steel with yield strength more than or equal to 750MPa and a production method thereof, which comprises the following components in percentage by weight: c: 0.03-0.15%, Si is less than or equal to 0.15%, Mn: 1.10-1.90%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, and Ti: 0.08-0.18%, Nb: 0.075-0.120%, Als: 0.02-0.10%, N: less than or equal to 0.010 percent. The strength of the steel plate is further improved by improving the Nb content, and a controlled rolling and controlled cooling and heating continuous rolling process is adopted, wherein the heating temperature is 1280-1350 ℃, the rough rolling finishing temperature is not less than 1100 ℃, the finish rolling finishing temperature is 850-930 ℃, and the coiling temperature is 640-700 ℃. The yield strength is more than or equal to 750MPa, the tensile strength is more than or equal to 800MPa, the elongation is more than or equal to 11 percent, and the magnetic induction property B50≥1.5T。
Chinese patent application No. 201310412357.6 discloses a high-strength yoke steel with yield strength more than or equal to 800MPa and a production method thereof, and the steel disclosed by the invention is improved to 800MPa by further adding Mo (0.10-0.50%) on the basis of chemical components of steel of Chinese patent application No. 201310412332335. X. The production process comprises the following steps: heating the plate blank to 1280-1350 ℃; then rough rolling is carried out, wherein the finish temperature of the rough rolling is more than or equal to 1100 ℃; the finish rolling temperature is 850-930 ℃; and (3) after rolling, carrying out laminar cooling on the steel plate, and then coiling at the coiling temperature of 640-700 ℃ to obtain the hot rolled plate coil. The yield strength is more than or equal to 800MPa, the tensile strength is more than or equal to 850MPa, the elongation is more than or equal to 11 percent, and the magnetic induction property B50≥1.5T。
In order to further enhance the safety design of the motor, in the super-huge hydroelectric project, a large-scale hydraulic power plant with leading industry puts forward the requirement of increasing the high toughness of the yoke steel. Therefore, in order to meet the requirement of the low-temperature impact performance of the magnet yoke steel with the yield strength of more than or equal to 750MPa, ChinaPatent application No. 201510921787.X discloses a high-strength high-toughness magnet yoke steel with yield strength more than or equal to 750MPa and a production method thereof, and the high-strength high-toughness magnet yoke steel comprises the following components in percentage by weight: c: 0.015-0.030%, Si is less than or equal to 0.15%, Mn: 1.80-2.10%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Ti: 0.035-0.075%, Nb: 0.02-0.07%, Als: 0.02-0.10% and N is less than or equal to 0.005%. The low-temperature impact toughness of the steel plate is improved by reducing the content of C and increasing the content of Mn. The production process comprises the following steps: heating the cast plate blank to 1280-1350 ℃; then rough rolling is carried out, wherein the finish temperature of the rough rolling is more than or equal to 1100 ℃; then, fine rolling is carried out, wherein the final rolling temperature is 800-850 ℃; and (3) carrying out laminar cooling on the rolled steel plate, and then coiling, wherein the coiling temperature is 550-600 ℃. The yield strength is more than or equal to 750MPa, and the magnetic induction property B50Not less than 1.5T and impact energy KV at-40 deg.C2≥60J。
In addition, chinese patent application No. 201711087052.7 discloses "an ultra-high strength magnet yoke steel and a manufacturing method thereof", which comprises the following components by weight: c: 0.10-0.15%, Si is less than or equal to 0.15%, Mn: 1.85-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.010%, Ti: 0.20-0.30%, Nb: 0.05 to 0.07%, Mo: 0.35-0.55%, B: 0.001-0.003%, Als: 0.02-0.10 percent of Fe, less than or equal to 0.010 percent of N, and the balance of Fe and inevitable impurities. According to the steel, a bainite structure is obtained by adding a proper amount of bainite forming elements and matching with an ultra-fast cooling process, and the ultrahigh-strength magnetic yoke steel with the yield strength of 900MPa is obtained.
Disclosure of Invention
The invention aims to provide 900 MPa-level high-toughness high-magnetism hot-rolled magnetic yoke steel and a production method thereof, wherein the steel has ultrahigh strength (yield strength is more than or equal to 900MPa, tensile strength is more than or equal to 950MPa), 20 ℃ impact power KV and the production method thereof2Not less than 40J and magnetic induction property B50≥1.58T，B100≥1.73T，B200≥1.90T， B300Good comprehensive use performance of more than or equal to 1.93T and the like; the purposes of reducing tempered sorbite lattice distortion, reducing structural stress and the like are achieved, so that the magnetic performance of the steel plate is greatly improved, and the relevant requirements of the hydropower industry on rotor yoke steel are met;
in order to achieve the purpose, the technical scheme of the invention is as follows:
the invention realizes that the yield strength of the steel plate reaches over 900MPa level through tempering sorbite strengthening and V precipitation strengthening, and has higher low-temperature toughness. The invention forms a tempered sorbite structure in the steel through reasonable components and process design, and ensures that the structural stress in the steel is greatly reduced through the process, thereby leading the product to have ultrahigh strength and high magnetic performance.
Specifically, the 900 MPa-grade tempered sorbite hot-rolled magnetic yoke steel comprises the following components in percentage by weight: c: 0.15-0.30%, Si is less than or equal to 0.50%, Mn: 1.0-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Ti is less than or equal to 0.06%, Nb is less than or equal to 0.05%, Mo: 0.20-0.80%, Cr: 0.20-0.80%, Ni is less than or equal to 0.60%, V: 0.02-0.15%, B: 0.0005 to 0.003%, Al: 0.015-0.10% of Fe, less than or equal to 0.010% of N, less than or equal to 0.0080% of O, and the balance of Fe and other inevitable impurities; moreover, the above components should satisfy simultaneously:
Cr+Mo+Ni≥0.50％；
the carbon equivalent CEV is equal to or more than 0.45 percent of C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15.
The yield strength of the hot-rolled magnet yoke steel is more than or equal to 900MPa, the tensile strength is more than or equal to 950MPa, and the impact energy KV at the temperature of-20 DEG C2Not less than 40J and magnetic induction property B50≥1.58T，B100≥1.73T，B200≥1.90T， B300≥1.93T。
In the component design of the invention:
carbon (C) is one of important elements for strengthening the structure in steel, and plays a very important role in improving the strength of the phase change strengthened steel. In the invention, in order to obtain the yield strength reaching 900MPa level, the content of C is ensured to be more than 0.15 percent; meanwhile, the content of C cannot be too high, otherwise, the formed martensite structure has too large lattice distortion, and the low-temperature toughness and the magnetic property of the steel are deteriorated. In conclusion, the content of carbon should be controlled to be 0.15-0.30%.
Silicon (Si) is also one of the basic elements in steel. Si plays a part in deoxidation in the steel-making process. Si can also reduce the harm of other impurities in the steel, reduce the harmful influence on magnetism and obviously improve the magnetic induction performance of the steel; therefore, the content of Si in the present invention is designed to be 0.50% or less.
Manganese (Mn) is one of the basic elements in steel, is also an important element for expanding an austenite phase region, can reduce the critical quenching speed of the steel, stabilizes austenite, refines grains and improves the strength and toughness of the steel. Therefore, the Mn content is set to 1.0 to 2.0% in the present invention.
Phosphorus (P) is a harmful impurity element in steel. P is easy to be partially gathered on the grain boundary, and Fe is formed when the content of P in steel is higher2P is precipitated around the crystal grains to reduce the toughness and magnetic induction performance of the steel, so the lower the content of the P is, the better the P content is, and the P content is controlled to be less than or equal to 0.015 percent.
Sulfur (S) is a harmful impurity element in steel. The lower the S content in the steel, the better, the S content should be controlled within 0.005 percent.
Molybdenum (Mo) is one of the key elements in the present invention. Mo is an element for improving the hardenability of steel, and is beneficial to obtaining a martensite structure; meanwhile, Mo has good high-temperature tempering resistance, so that the strength of a tempered sorbite structure is improved, and 0.20-0.80% of Mo is contained in the invention;
nickel (Ni) is an effective element for improving the low-temperature toughness of steel and is beneficial to improving the low-temperature toughness of the steel plate, so that the Ni is less than or equal to 0.60 percent.
Since chromium (Cr) and boron (B) are elements for improving hardenability and are advantageous for obtaining martensite structure in the present invention, Cr is 0.20 to 0.80% and B is 0.0005 to 0.003%.
Niobium (Nb), vanadium (V) and titanium (Ti) are also important elements in the invention, and the main functions of adding a proper amount of Nb, V and Ti in the steel are to reduce the austenite grain size during quenching heat treatment, improve tempering resistance and improve the tensile property of the tempered sorbite. Therefore, the invention has Ti less than or equal to 0.06%, Nb less than or equal to 0.05%, V: 0.02-0.15%.
The basic role of aluminum (Al) in the present invention is mainly to deoxidize during steel making. Nitrogen (N) and oxygen (O) are impurity elements in the present invention.
The invention relates to a production method of 900 MPa-level tempered Soxhlet type hot-rolled magnet yoke steel, which comprises the following steps:
1) smelting and external refining
Smelting in a converter or an electric furnace, refining outside the furnace and casting into continuous casting billets or cast ingots;
2) reheating of billets or ingots
Heating temperature: keeping the temperature at 1150-1230 ℃ for more than or equal to 1 hour;
3) hot continuous rolling
Rough rolling, wherein the final rolling temperature is more than or equal to 1050 ℃, and the accumulated deformation is more than or equal to 50%;
performing multi-pass finish rolling, wherein the finish rolling temperature of the finish rolling is less than or equal to 950 ℃, the accumulated deformation is more than or equal to 70%, performing laminar cooling to 550-650 ℃, coiling, cooling to room temperature, and finishing and cutting the plate;
4) thermal treatment
Quenching and heat treating a steel plate, wherein the quenching and heat preservation temperature is 850-950 ℃, the heat preservation time t is more than or equal to 3 times of the plate thickness h, wherein t is unit min, h is unit mm, the water cooling speed is more than or equal to 20 ℃/s, and the water cooling termination temperature is less than or equal to 200 ℃;
and (3) tempering and heat treatment of the steel plate, wherein the tempering heat preservation temperature is 500-700 ℃, and the heat preservation time t is more than or equal to 4 times of the plate thickness h, wherein t is unit min, h is unit mm.
The invention reasonably solves the contradiction between the improvement of tensile strength and the improvement of magnetic performance, and obtains ultrahigh strength through structure strengthening on one hand and obtains better magnetic performance through realizing the great reduction of lattice distortion and residual stress in steel through a proper heat treatment process means by reasonably designing the Soxhlet type structure which is close to a balanced state. Through reasonable matching of components, heat treatment process and structure, the steel plate has good magnetic performance while the ultrahigh mechanical performance is ensured.
One of the key technologies of the invention is reasonable component design, so that the steel plate forms a sorbite structure with the characteristics of high strength, low lattice distortion, small residual stress and the like. Proper carbon content and alloy elements are added into the steel, so that the carbon equivalent CEV is more than or equal to 0.45 percent, thereby ensuring the hardenability of the steel plate and the ultrahigh tensile property of the steel plate; on the other hand, a proper amount of Cr, Mo and V elements are added into the steel, so that cementite, MoC, VC and other carbides are formed in the steel, and the steel plate still keeps ultrahigh tensile property in the process of reducing residual stress through heat treatment.
The second key technology of the invention is to design a reasonable heat treatment process, so that on one hand, carbon elements in the steel can basically and completely form carbide and do not exist in a solid solution state any more; meanwhile, through the heat treatment process, the quenching stress is reduced by more than 80 percent, and the steel plate with low residual stress or zero residual stress is obtained, so that higher magnetic performance is shown; through a reasonable heat treatment process, the magnetic property of the steel plate can be greatly improved, the requirement of rotor yoke steel is met, and meanwhile, the steel plate has excellent plate shape quality.
Based on the innovative components and process design thought, the invention can obtain the hot-rolled magnetic yoke steel with ultrahigh strength, high toughness and high magnetic induction performance, the yield strength is more than or equal to 900MPa, the tensile strength is more than or equal to 950MPa, the elongation is more than or equal to 10 percent, and the longitudinal impact energy KV at the temperature of minus 20 ℃ is higher than KV2Not less than 40J, magnetic induction property B50≥1.58T，B100≥1.73T， B200≥1.90T，B300The magnetic yoke has the advantages that the magnetic yoke is more than or equal to 1.93T, and the requirements of high strength and high magnetic induction performance for the rotor magnetic yoke of the super-huge type hydraulic generator with high single machine capacity can be met.
Drawings
FIG. 1 is a metallographic photograph of an example of the present invention.
Detailed Description
The invention is further illustrated by the following examples and figures.
Table 1 shows the composition of the steel of examples of the present invention, Table 2 shows the method of producing the steel of examples of the present invention, Table 3 shows the mechanical properties of the steel of examples of the present invention, and Table 4 shows the magnetic properties of the steel of examples of the present invention.
As can be seen from tables 3 and 4, examples 1 to 6 of the present invention all satisfied the yield strength of 900MPa or more, the tensile strength of 950MPa or more, the elongation of 14% or more, and the-20 ℃ longitudinal impact energy KV2Not less than 40J, magnetic induction property B50≥1.58T，B100≥1.73T，B200≥1.90T，B300≥1.93T。
Fig. 1 shows a typical metallographic photograph of the experimental steel of the examples. As can be seen from the metallographic photograph, the microstructure of the steel plate is a tempered sorbite, and the good tensile property, toughness and plasticity and magnetic property of the test steel are ensured.
Figure BDA0002010522180000071
Figure BDA0002010522180000081
Figure BDA0002010522180000091

Claims (3)

  1. The high-toughness high-magnetism hot-rolled magnetic yoke steel with the grade of 1.900MPa comprises the following components in percentage by weight: c: 0.20-0.30%, Si is less than or equal to 0.50%, Mn: 1.0-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Ti is less than or equal to 0.06%, Nb is less than or equal to 0.05%, Mo: 0.20-0.80%, Cr: 0.20-0.80%, Ni is less than or equal to 0.60%, V: 0.02-0.15%, B: 0.0005 to 0.003%, Al: 0.015-0.10% of Fe, less than or equal to 0.010% of N, less than or equal to 0.0080% of O, and the balance of Fe and other inevitable impurities; moreover, the above components should satisfy simultaneously:
    Cr+Mo+Ni≥0.50％；
    the carbon equivalent CEV is equal to or more than 0.45 percent of C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15;
    the microstructure of the hot-rolled magnetic yoke steel is tempered sorbite;
    the yield strength of the hot-rolled magnet yoke steel is more than or equal to 900MPa, the tensile strength is more than or equal to 950MPa, and the impact energy KV at the temperature of-20 DEG C2Not less than 40J and magnetic induction property B50≥1.58T，B100≥1.73T，B200≥1.90T，B300≥1.93T；
    The hot-rolled yoke steel is obtained by the following process, and comprises the following steps:
    1) smelting and refining outside the furnace;
    2) reheating a continuous casting blank or an ingot;
    3) hot continuous rolling
    Rough rolling, wherein the final rolling temperature is more than or equal to 1050 ℃, and the accumulated deformation is more than or equal to 50%;
    performing multi-pass finish rolling, wherein the finish rolling temperature of the finish rolling is less than or equal to 950 ℃, the accumulated deformation is more than or equal to 70%, performing laminar cooling to 550-650 ℃, coiling, cooling to room temperature, and finishing and cutting the plate;
    4) thermal treatment
    Quenching heat treatment of the steel plate, wherein the quenching heat preservation temperature is 850-950 ℃, the heat preservation time t is more than or equal to 3 times the thickness of the plate h, wherein t is unit min, h is unit mm, the water cooling speed is more than or equal to 20 ℃/s, and the water cooling termination temperature is less than or equal to 200 ℃;
    and (3) tempering and heat treatment of the steel plate, wherein the tempering heat preservation temperature is 500-700 ℃, and the heat preservation time t is more than or equal to 4 times of the plate thickness h, wherein t is unit min, h is unit mm.
  2. The production method of the 2.900 MPa-grade high-toughness high-magnetism hot-rolled magnetic yoke steel is characterized by comprising the following steps of:
    1) smelting and external refining
    Smelting in a converter or an electric furnace, refining outside the furnace, and casting into continuous casting billets or cast ingots; the weight percentage of the components is as follows: c: 0.20-0.30%, Si is less than or equal to 0.50%, Mn: 1.0-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Ti is less than or equal to 0.06%, Nb is less than or equal to 0.05%, Mo: 0.20-0.80%, Cr: 0.20-0.80%, Ni is less than or equal to 0.60%, V: 0.02-0.15%, B: 0.0005 to 0.003%, Al: 0.015-0.10% of Fe, less than or equal to 0.010% of N, less than or equal to 0.0080% of O, and the balance of Fe and other inevitable impurities; moreover, the above components should satisfy simultaneously:
    Cr+Mo+Ni≥0.50％；
    the carbon equivalent CEV is equal to C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15 and is more than or equal to 0.45 percent;
    2) reheating of billets or ingots
    Heating temperature: keeping the temperature at 1150-1230 ℃ for more than or equal to 1 hour;
    3) hot continuous rolling
    Rough rolling, wherein the final rolling temperature is more than or equal to 1050 ℃, and the accumulated deformation is more than or equal to 50%;
    performing multi-pass finish rolling, wherein the finish rolling temperature of the finish rolling is less than or equal to 950 ℃, the accumulated deformation is more than or equal to 70%, performing laminar cooling to 550-650 ℃, coiling, cooling to room temperature, and finishing and cutting the plate;
    4) thermal treatment
    Quenching heat treatment of the steel plate, wherein the quenching heat preservation temperature is 850-950 ℃, the heat preservation time t is more than or equal to 3 times the thickness of the plate h, wherein t is unit min, h is unit mm, the water cooling speed is more than or equal to 20 ℃/s, and the water cooling termination temperature is less than or equal to 200 ℃;
    tempering and heat treating the steel plate, wherein the tempering heat preservation temperature is 500-700 ℃, and the heat preservation time t is more than or equal to 4 times the plate thickness h, wherein t is unit min, h is unit mm;
    the microstructure of the obtained hot-rolled yoke steel is tempered sorbite.
  3. 3. The method for producing the 900 MPa-grade high-toughness high-magnetism hot-rolled magnetic yoke steel as claimed in claim 2, wherein the yield strength of the hot-rolled magnetic yoke steel is not less than 900MPa, the tensile strength is not less than 950MPa, and the impact energy KV at-20 ℃ is not less than2Not less than 40J and magnetic induction property B50≥1.58T，B100≥1.73T，B200≥1.90T，B300≥1.93T。
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