CN116987974A

CN116987974A - High-strength high-toughness low-permeability medium manganese steel and manufacturing method thereof

Info

Publication number: CN116987974A
Application number: CN202311017807.1A
Authority: CN
Inventors: 黄红乾; 杜林秀; 吴红艳; 高秀华; 高彩茹; 陶振; 刘洋
Original assignee: 东北大学
Priority date: 2023-08-14
Filing date: 2023-08-14
Publication date: 2023-11-03
Anticipated expiration: 2043-08-14
Also published as: CN116987974B

Abstract

A high-strength high-toughness low-permeability medium manganese steel and a manufacturing method thereof belong to the field of high-strength steel production technology and electric power transmission and electric power machinery interdisciplinary subjects. The components are as follows: c:0.05-0.2%, si:0.1-0.5%, mn:5-8%, P less than or equal to 0.02%, S less than or equal to 0.01%, als 0.01-0.05%, cr+Ni+Mo+V+Cu+Co+Re+Ti less than or equal to 1.5%, and the balance of Fe and unavoidable impurities. The comprehensive mechanical properties of the medium manganese steel are as follows: rp (Rp) _0.2 And the microstructure of the finished product is a lath-shaped tempered martensite structure, a lath-shaped reversed austenite structure and a small amount of carbide, wherein the lath-shaped tempered martensite structure and the reversed austenite structure are alternately distributed. In a weak alternating magnetic field with the magnetic field strength less than or equal to 3000A/m, the alternating current relative magnetic permeability is between 18 and 300, and the magnetic permeability, hysteresis and eddy current loss are obviously reduced compared with the traditional structural steel.

Description

High-strength high-toughness low-permeability medium manganese steel and manufacturing method thereof

Technical Field

The invention belongs to the field of high-strength steel production technology, power transmission and electric machinery intersection subjects, and particularly relates to high-strength high-toughness low-permeability medium manganese steel and a manufacturing method thereof.

Background

Along with the rapid development of the modern power industry, conventional ferromagnetic materials such as low-carbon structural steel, number steel, chromium-molybdenum alloy steel and the like are widely applied to the fields of power mechanical equipment, transformers, flywheel energy storage, rail transit, national defense and military industry and the like. The conventional steels are soft magnetic materials with stronger magnetism, and under the excitation of alternating current, pulse current and multiple harmonic currents, the ferromagnetic materials are easy to generate hysteresis and eddy current loss, so that the system heating problem is caused, the energy conversion efficiency is reduced and the like. The current solution is to use low-magnetic steel or non-magnetic steel for manufacturing. Generally, steel having a static magnetic permeability of less than 1.5 is referred to as low magnetic steel, and steel having a static relative magnetic permeability of less than 1.01 is referred to as nonmagnetic steel. The application of nonmagnetic steel or low-magnetic steel as a functional material is attracting attention, and in electric machinery, it is used as an end ring, wedge, rotor strap, shield for ribbon ac cable of ac rotor, external frame member of large-scale transformer, electric power fitting for electric occasion, gyroscope, etc., where eddy current must be avoided, and magnetic field location due to permanent magnet and current needs to be disturbed, etc.

In the industries of power transmission, electric power fittings, large transformers, high-power electric furnaces and the like, a great deal of demands are also made on non-magnetic steel and low-magnetic steel. The electric power fitting is various devices for connecting and combining an electric power system in a line, plays roles in transmitting mechanical load, electric load and protection, is a metal part for assisting power transmission in an electric power overhead line, and can be generally divided into three main types of line fittings, power transformation fittings and power plant fittings, wherein the line fittings are the most various. The electric power transmission (such as steel core of steel-cored aluminum stranded wire), electric power fittings, high-power electric furnaces and electromagnetic ovens often have higher alternating current, alternating magnetic fields can be generated around the alternating current, traditional structural steel has higher magnetic permeability, the alternating magnetic fields are easy to magnetize, hysteresis and eddy current loss can be generated in the repeated magnetization process, and a series of problems such as heating and power loss are caused. The alternating current transmission process causes the problems of alternating current transmission resistance caused by alternating current inductance in the iron core steel stranded wire and surrounding iron components (such as a transformer shell and the like) and the like, and the transmission process generates heat and the like, so that huge transmission loss is caused. The statistical data shows that the loss caused by the increment of the alternating current resistance relative to the direct current resistance of the alternating current transmission line accounts for 2% -5% of the transmission loss, and the influence on the transmission efficiency of the power grid, energy conservation and emission reduction is huge.

In order to solve the problems of hysteresis and eddy current loss of ferrous materials around alternating current and power and heat caused by the hysteresis and eddy current loss, the non-magnetic induction type electromagnetic induction motor can be manufactured by adopting non-magnetic copper, aluminum alloy or non-magnetic steel in theory, or the distance between an electric wire and a metal component is increased, and the electromagnetic induction strength is reduced. The nonmagnetic copper, aluminum alloy and nonmagnetic steel have higher alloy cost and lower alloy strength, and are difficult to popularize in large scale practically. The high-manganese non-magnetic steel has lower cost, and has higher difficulty in industrial production and processing due to higher alloy content, thereby influencing popularization and application.

The magnetic field and the electric field have similar properties, and the magnetic field always propagates along the minimum loss path, i.e. the magneto-resistive minimum path. Steel is generally a good magnetic conductor, and the metal components around the alternating magnetic field are good magnetic conductors, with the magnetic field preferentially propagating in the metal structure. In the process of the alternating magnetic field propagating in the steel, the electron spin magnetic field in the steel can be excited to continuously change, and hysteresis loss and eddy current loss are caused. The magnitude of the magnetic resistance is inversely proportional to the magnitude of the relative magnetic permeability of the magnetic material, the larger the magnetic permeability, the smaller the magnetic resistance, the lower the magnetic permeability, and the larger the magnetic resistance. Silicon steel has higher magnetic permeability, is a path for preferentially transmitting magnetic fields, and is generally used as electrical steel. The total magnetic flux in the magnetic circuit is conserved, the most ideal electromagnetic field design is that the larger and the better the magnetic permeability in the magnetic circuit is, and the materials in the magnetic field outside the magnetic circuit are all material mediums with the relative magnetic permeability close to 1. However, there are often a large number of metal structures around the electromagnetic field actually used, and these metal structures generally have high magnetic permeability and low magnetic resistance, so that when the magnetic field propagates preferentially along the metal structures, ac inductance and resistance are caused, and hysteresis and eddy current loss are generated. The magnetic permeability of the metal member is reduced, the magnetic resistance is increased, the passing magnetic flux of the metal member is reduced, and eddy current and hysteresis loss of the metal member caused by an alternating magnetic field are reduced.

The alternating current is surrounded by an iron core material which is an inductive element, and the iron loss of the inductive element is generally composed of hysteresis loss and eddy current loss. The magnitude of the hysteresis loss of the inductance element depends on the material property of the iron core, the frequency of the power supply and the area of the hysteresis loop of the iron core material, and the hysteresis loss is proportional to the frequency of the power supply and is the maximum magnetic induction intensity B _m Is proportional to the square of (2). The eddy current loss of the inductance element is the loss caused by the eddy current induced by the alternating magnetic flux in the iron core, the magnitude of the eddy current loss is also dependent on the material property of the iron core, the frequency of the power supply and the area of the hysteresis loop of the iron core material, and the eddy current loss is directly proportional to the frequency of the power supply and is equal to the maximum magnetic induction intensity B _m Proportional to the ratio. In general, the total loss Ps of the inductance element is hysteresis loss P _h And eddy current loss P _e The total loss is calculated as follows:

P _s ＝P _h +P _e ＝α _h fB _m ² V+β _e fB _m ² V

wherein alpha is _h ，β _e All are coefficients related to the properties of iron core (iron) materials, f is the working frequency of an alternating magnetic field, the industrial working frequency is 50Hz, B _m And V is the volume of the iron core material. From the above formula, the hysteresis loss is linearly proportional to the frequency and the volume of the metal member, and is related to the maximum magnetic induction B _m The square of the magnetic field strength is proportional. Ac maximum magnetic induction B of iron core material _m And maximum magnetic field strength H _m The following relationship exists:

B _m ＝μH _m

wherein mu and H _m Respectively alternating current magnetic permeability and maximum magnetic field strength, at magnetic field strength H _m Under certain conditions, the maximum magnetic induction Bm is in direct proportion to the alternating current magnetic permeability mu, and the magnetic induction B can be effectively reduced by reducing the alternating current magnetic permeability mu _m . The ac permeability mu is generally a very small value, generally 10 ^-3 -10 ^-5 H/m(N/A ² ) For convenience of comparison in production practice, the relative permeability mu is adopted _r To characterize the magnetic permeability, the calculation formula is as follows:

μ ₀ ＝4π×10 ^-7 H/m

wherein mu is ₀ Is vacuum magnetic permeability and is a fixed constant. Relative permeability mu _r The magnitude of (a) is consistent with the magnitude of the alternating current magnetic permeability mu, and the magnetic permeability is generally referred to as alternating current relative magnetic permeability mu _r . It can be seen from the above that by reducing the ac relative permeability mu _r Reducing the maximum magnetic induction intensity B _m Hysteresis loss can be reduced, eddy current loss can be reduced, and total loss can be effectively reduced. Relative permeability mu _r The smaller the hysteresis and eddy current losses in the metal component.

In the metal structural member around the AC magnetic field, the total loss and relative permeability mu of the core material _r Closely related, these losses are manifested as heating inside the metal. In general, the relative permeability μ of copper, aluminum and nonmagnetic steel _r Less than 1.1. Therefore, in order to reduce hysteresis loss and eddy current loss in the metal sink around the alternating current, it is generally preferable to use the relative permeability μ _r Lower copper, aluminum, non-magnetic steel to reduce hysteresis loss and eddy current loss. However, copper, aluminum and nonmagnetic steel generally have higher alloy cost and lower strength, and limit the application of the alloy to electric machinery and other parts.

Ac relative permeability mu _r The magnetic permeability is a function which is a dynamic magnetic permeability and not a fixed value, and the magnetic permeability is closely related to parameters such as frequency f, microstructure, composition, grain size, stress size and the like. The ac permeability generally decreases progressively with increasing frequency fLow, but generally remains relatively stable in the low frequency range (1 kHZ). The alternating current relative permeability is changed along with the intensity of the induction magnetic field, and the initial permeability mu is general _i Minimum, with the increase of the magnetic field intensity H, the magnetic permeability is gradually increased to reach a certain magnetic field intensity H _μ When the relative magnetic permeability reaches the maximum value mu _m The relative permeability field strength is then increased stepwise.

In general, the difference in relative magnetic permeabilities between ferritic steel and austenitic steel is large, and the difference in relative magnetic permeabilities between ferritic structure (α -phase), bainitic, martensitic steel (α' -phase), cementite (Fe ₃ C) All have ferromagnetic properties with a relative permeability of between about 50 and 800, while steels with austenitic structure (gamma phase) are paramagnetic with a relative permeability close to 1. The coarse ferrite structure has a relative initial permeability of more than 200, and the martensite, bainite, tempered martensite, carbide and other structures have relative initial permeability of 50-150. Common steels are ferrite structures with ferromagnetic body-centered cubic (bcc) structures and have high magnetic permeability. Ac relative permeability μ of structural steel having ferrite+pearlite structure in general _r Fluctuating between 200-8000. For example, the relative initial permeability of the conventional low carbon structural steel Q235B is about 270-300, and the maximum relative permeability reaches 1000-3000. The change of magnetic permeability between different steel grades with ferrite structure is little, and generally the smaller the crystal grains are, the higher the tensile strength and hardness are, and the lower the initial magnetic permeability and the maximum magnetic permeability are. At present, conventional low-magnetic steel or non-magnetic steel is generally limited to steel with a stable austenitic structure, a large amount of expensive alloy elements are required to be added to obtain the austenitic structure so as to ensure the stability of the austenitic structure, and the high-alloy cost is realized, so that the large-scale popularization and application of the non-magnetic steel are influenced.

The theoretical relative permeability of steel with complete austenitic structure (100%) is 1, but the austenitic steel produced in actual industry is separated out due to microcomponent segregation in solidification process, ferromagnetic phase (delta phase, alpha phase and carbide), mechanical deformation in cold working process induces phase transformation, improper welding process and other factors, a certain amount of non-austenitic structures such as ferrite, martensite, bainite and carbide are easy to generate, the drastic increase of alternating current relative permeability is generally caused, the actually produced relative alternating current permeability generally fluctuates between 1.01-15.0, and the actually produced low-magnetic steel is not completely 'nonmagnetic'.

Patent CN 101445890a discloses a novel high-strength low-magnetic steel, and the components and mass percentages of the high-strength low-magnetic steel are: 0.24-0.38% C, 14.5-16.5% Mn, 3.0-4.0% Ni, 1.3-1.9% Mo, 0.6-1.6% V, 0.2-0.4% Nb,<0.03％S、<0.03% P, and the balance being Fe. The high-strength low-magnetic steel has higher strength and good comprehensive mechanical properties: rm (Rm)>830MPa、Rp _0.2 >640MPa、A>18％、Z>35, the relative magnetic permeability is less than 1.01. The steel still contains more than 13% of Mn, 3-4% of Ni and 1.3-1.9% of Mo, and the alloy cost is still relatively high.

The patent CN 109097679A discloses a marine low-magnetic steel and a preparation method thereof, wherein the low-magnetic steel comprises, by mass, 1.22-1.53% of C, 0.17-0.28% of Si, 8.9-9.8% of Mn, less than or equal to 0.005% of P, less than or equal to 0.002% of S and less than or equal to Ni:0.11-0.34%, co 0.01-0.18%, and Fe and unavoidable impurities in balance; the low magnetic steel has higher C content, and the weldability is affected.

Patent CN89104759.X discloses an iron-manganese-aluminum-carbon austenitic nonmagnetic steel and low temperature steel, wherein the steel contains 19-21% of Mn, 2.3-3.2% of Al, 0.25-0.33% of C, less than or equal to 0.7% of Si, less than or equal to 0.05% of S, less than or equal to 0.04% of P and the balance of Fe. Mn and C stabilize austenite structure, al inhibits gamma- & gtepsilon martensitic transformation, so that the new steel has extremely low magnetic permeability and high toughness at 77K and above. The austenitic nonmagnetic steel has higher Mn and Al contents, and the industrial production faces certain difficulties.

Patent CN100345994C discloses an austenite non-magnetic steel and a preparation method thereof, wherein the non-magnetic steel comprises, by weight, 20% -26% of manganese, 2% -10% of chromium, 1% -4% of aluminum, 0.18% -0.24% of carbon, 0.10% -0.20% of rare earth elements, less than or equal to 0.04% of sulfur, less than or equal to 0.04% of phosphorus, and the balance of iron, wherein the relative magnetic permeability mu of the prepared steel plate is less than or equal to 1.5.

From the above patent, the conventional austenitic structure of non-magnetic steel or low-magnetic steel is two types, one type is Cr-Ni austenitic stainless steel, and elements more than or equal to 13% Cr and more than or equal to 8% Ni are generally required to be added, so that the cost is high, and the material strength is generally lower. The other type is high Mn series non-magnetic steel, in order to ensure the stability of an austenite structure, more than or equal to 13 percent of Mn element and higher content of C element are generally needed to be added (the low C content is needed to be increased, so that the stability of the austenite is ensured), the higher C content seriously influences the weldability of the material, and when the manganese content is higher, the volatilization of manganese in the metallurgical process is serious, and the production and the manufacture are also difficult. In general, the strength of steel grades with austenitic structures is generally low (yield strength is lower than 600 MPa), the strength of materials is improved through solid solution and precipitation strengthening, the alloy cost is high, the steelmaking and continuous casting processes have higher production difficulty, and the high cost prevents the application of industrial production. The great market demand and the expensive material cost of the non-magnetic steel cause great difficulty in popularization and application of the non-magnetic steel, and the material research and development are also in urgent need of reducing the material manufacturing cost of the non-magnetic steel and improving the mechanical strength and the weldability of various non-magnetic steels.

In general, most of the application occasions of non-magnetic steel metal structural parts are to reduce hysteresis loss and eddy current loss of steel structural parts around an alternating magnetic field, and the magnitude of relative magnetic permeability of steel is reduced, so that the hysteresis loss and the eddy current loss can be greatly reduced. Steel metal components around alternating magnetic fields have been designed to avoid environments with high excitation currents or strong magnetic fields, typically in environments with weaker magnetic fields. The steel with lower relative magnetic permeability is selected, the range of a Rayleigh (Rayleigh) elastic region (reversible magnetization) of the steel is increased, the Rayleigh constant is reduced, the magnetization difficulty is increased, and therefore, hysteresis and eddy current loss are reduced, and the method is feasible in the production technology.

The magnitude of the relative permeability of steel is closely related to the parameters of the microstructure type, proportion, and density distribution of domain walls of the material. According to Globus et al magnetic domain wall theory, the magnetic permeability is in direct proportion to the size of the magnetic domain wall, and the microstructure structures such as crystal boundary, nonmagnetic phase, carbide and the like can be used as the magnetic domain wall, and generally, the smaller the crystal grain is, the higher the strength is, and the lower the magnetic permeability is; the larger the grain size, the lower the strength, and instead the larger the permeability. Silicon steel used in industry often has coarse grains and relatively high relative permeability. The higher the strength of the low carbon steel, the lower the magnetic permeability, and the magnetic permeability is reduced along with the increase of the C content in the steel, but the low carbon steel with ferrite structure is mainly provided with a certain limit for reducing the magnetic permeability, the relative magnetic permeability of common ferrite steel is generally between 50 and 800, and the number, proportion, direction, distribution and other parameters of main magnetic domain walls are related.

In general, the magnetic properties of a ferrite structure having a body-centered cubic (bcc) structure and an austenite structure having a face-centered cubic (fcc) structure are completely different. Ferrite structure is easy magnetization phase, and relative initial magnetic permeability is generally above 200; the austenitic structure is a nonmagnetic phase and the theoretical relative permeability is equal to 1. The difference between the relative magnetic permeability of ferrite structure and austenite structure is huge, and the development of dual-phase steel with ferrite structure and austenite structure can effectively reduce the relative magnetic permeability of steel. In general, the magnitude of the relative permeability of a dual phase steel having an austenitic and ferritic structure decreases as the austenitic structure ratio increases, but the magnitude of the relative permeability is not only a function of the austenitic structure ratio but also a closely related microstructure distribution. According to the related data, it is shown that the duplex stainless steel (2507) having ferrite and austenite structures with grain sizes (> 10 μm) has tensile strength of generally 700-900MPa, austenite structure ratio of 40-60%, maximum relative permeability of 400-800, whereas the 0Cr16Ni6 high strength duplex stainless steel forms lath-shaped ferrite and austenite structures after special heat treatment, the tensile strength of generally 1100-1300MPa, austenite structure ratio of 40-60%, maximum relative permeability of only 60-80, which is related to microstructure size distribution and number of magnetic domain walls of 0Cr16Ni6 high strength duplex stainless steel and 2507 duplex stainless steel. Although the 0Cr16Ni6 duplex martensitic stainless steel has lower relative permeability, the alloy elements which are higher and expensive are required to be added, and the production cost is higher.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide low-cost high-strength high-toughness low-permeability medium manganese steel and a manufacturing method thereof, and the low-permeability steel with excellent weldability is obtained by combining the optimal design of steel plate alloy elements and a special heat treatment process, and has better comprehensive mechanical properties, excellent strength, low-temperature toughness and toughness matching.

The low-permeability medium manganese steel with high strength and high toughness comprises the following chemical components in percentage by mass: c:0.05-0.20%, si:0.10-0.50%, mn:5.0 to 8.0 percent, P is less than or equal to 0.020 percent, S is less than or equal to 0.010 percent, als is 0.010 to 0.050 percent, cr+Ni+Mo+Ti+V+Cu+Co+Re is less than or equal to 1.5 percent, and the balance is Fe and unavoidable impurities.

A manufacturing method of high-strength high-toughness low-permeability medium manganese steel comprises the following steps:

1) After raw materials are prepared according to components and proportions, smelting by adopting a vacuum induction furnace;

2) Molding and pouring into a blank;

3) Homogenizing and heating the die casting blank;

4) Carrying out high-temperature hot rolling;

5) And (5) performing critical tempering heat treatment.

Wherein, in the step 2), the die is a cast iron die, and the casting temperature is 1580+/-20 ℃;

In the step 3), the heating temperature of the cast die casting blank is 1200+/-25 ℃, the heating time is 1-3h, the heat is preserved for 2-4h at the temperature, and the total heating and heat preserving time is 4-6h;

in the step 4), rolling is controlled to be at 1100-1200 ℃, the rolling temperature is controlled to be at 800-950 ℃, hot rolling is carried out after tapping, and then air cooling is carried out to room temperature, wherein the cooling rate is more than 0.1 ℃/s;

in step 5), the heat treatment steps are as follows: homogenizing and preserving heat for 1-4h at 400-450 ℃ after hot rolling, then rapidly heating to 600-700 ℃, and preserving heat for 0.5-6h; the total tempering time is 1-8h.

The high-strength high-toughness low-permeability medium manganese steel has comprehensive mechanical properties: rp (Rp) _0.2 More than or equal to 650MPa, rm more than or equal to 850MPa, A more than or equal to 20%, and magnetismIn a weak alternating magnetic field with the field strength less than or equal to 3000A/m, the alternating current relative magnetic permeability is between 18 and 300, and the magnetic permeability, hysteresis and eddy current loss are obviously reduced compared with the traditional structural steel.

The high-strength high-toughness low-permeability medium manganese steel is characterized in that a finished product microstructure subjected to special heat treatment is a tempered martensite structure in which laths of 20-300nm are alternately distributed, a double-phase structure of a reversed austenite structure and a small amount of nano carbide, wherein the content of the reversed austenite structure is 15-50%, the content of the nano carbide is less than 5%, the rest is the tempered martensite structure, and the content of the reversed austenite structure is adjusted according to tempering temperature and time.

The high-strength high-toughness low-permeability medium manganese steel has the saturation magnetic induction intensity B under the condition of 50-1000Hz alternating magnetic field _s Between 0.50 and 1.70T, corresponding to the saturation magnetic field strength H _s More than 20000A/m, and coercive force H under the condition of saturated magnetic induction magnetic field _c A remanence ratio B of 1500-4800A/m _r /B _s The initial relative magnetic permeability is between 0.50 and 0.90, the initial relative magnetic permeability is between 18 and 100, the maximum magnetic permeability is between 50 and 300, the peak magnetic permeability is between 2500 and 7000A/m for the magnetic field intensity, the fluctuation range of the relative magnetic permeability is smaller, the Barkhausen noise is smaller, the Barkhausen irreversible jump is smaller, the magnetization process mainly rotates magnetic domain walls, the irreversible displacement of the magnetic domain walls is smaller, and the hysteresis loss is smaller.

The invention relates to a saturation induction intensity B of high-intensity high-toughness low-permeability medium manganese steel _s Initial relative permeability mu _r And maximum magnetic permeability mu _m According to the actual needs, the reversed austenite structure with different proportions can be obtained by adjusting chemical components and a heat treatment process, so that the saturation magnetic induction intensity and the relative magnetic permeability with different values can be obtained.

The hysteresis loss and the eddy current loss of the high-strength high-toughness low-permeability medium manganese steel in an alternating magnetic field are obviously reduced compared with those of the traditional structural steel. The total loss of the steel in a 50Hz alternating magnetic field, namely hysteresis loss and eddy current loss, is tested by adopting a measuring silicon steel sheet B-H analyzer, and the total loss is reduced by more than 90 percent compared with the traditional ferrite structural steel in a weak magnetic field below 3000A/m. At saturation field strength, the total loss is reduced by more than 30% compared with the traditional ferrite structure.

The high-strength high-toughness medium manganese steel provided by the invention has the advantages of smaller relative magnetic conductivity, smaller magnetic induction intensity and smaller hysteresis and eddy current loss under the condition of low magnetic field intensity, and is very suitable for being used as low magnetic steel in an adjacent low-magnetic environment. Under the low magnetic field intensity below 1000A/m, the saturation magnetic induction intensity is lower than 50mT, the remanence ratio is lower than 0.10, the relative magnetic permeability is lower than 50, the total loss is lower than 0.2W/kg, and compared with the total loss of 3-5W/kg of the traditional low-carbon ferrite structural steel, the total loss is reduced by more than 95%.

The high-strength high-toughness medium manganese steel has coercive force H under the condition of high magnetic field strength and saturated magnetic field strength _c The magnetic alloy belongs to semi-hard magnetic alloy, has obvious hysteresis alloy characteristic at 1500-5000A/m, and can be used as occasions such as high-strength hysteresis motor rotating shafts in future.

The high-strength high-toughness low-permeability medium manganese steel adopts an alternating current magnetic permeameter (also called as a B-H analyzer) to measure alternating current magnetic characteristics within the range of 50-1000 Hz. The total loss adopts the same test method as the silicon steel sheet, the total loss of the medium manganese steel, namely hysteresis loss and eddy current loss, is tested, and is compared with the magnetic property of the high-strength low-alloy structural steel Q690D, and all the data of the test show that the medium manganese steel has extremely small hysteresis loop area at low magnetic field strength, and the hysteresis loss and the eddy current loss are reduced by more than 95 percent compared with the traditional high-strength low-alloy steel, so that the method is very suitable for the situation of alternating weak magnetism in the near electricity.

Compared with the prior art, the invention has the following obvious advantages:

mn content is far lower than that of high-Mn austenitic steel, alloy cost is far lower than that of austenitic stainless steel and high-Mn austenitic steel, the serious problem of Mn volatilization in industrial smelting production of high-Mn steel is avoided, production process flow is simple, and production difficulty and cost are far lower than those of high-Mn steel.

2. Under the condition of weak magnetic field strength, the magnetic permeability, hysteresis and eddy current loss are low. Dynamic AC magnetic test shows that in weak magnetic field below 3000A/m, initial relative magnetic conductivity is 19-40, maximum magnetic conductivity is 50-300, rayleigh constant is only 0.3-1, and the AC loss curve of 50Hz is 0.1-0.3% of low-carbon structural steel Q235 Rayleigh Li Changshu (-210), so that the total loss of manganese steel in low magnetic conductivity is reduced by more than 95% compared with that of traditional ferrite and pearlitic high-strength structural steel, and the low magnetic conductivity has excellent magnetic property.

3. The medium manganese steel has more excellent mechanical properties, and a series of excellent properties of high strength, high toughness, high elongation, good low-temperature toughness, higher fatigue resistance, lower C content and good weldability. The medium manganese steel has a nano-scale composite dual-phase structure, lath-shaped tempered martensite with the length of 20-300nm and dual-phase structures of inverted austenite are alternately distributed, the proportion of the austenite structures is 15-50%, the tempered martensite is a ferromagnetic phase, the inverted austenite phase is a paramagnetic phase, the inverted austenite paramagnetic phase separates the tempered martensite ferromagnetic phases to form magnetic domain walls, the magnetization of the ferromagnetism is hindered, meanwhile, the interaction magnetization influence among the ferromagnetic phases is reduced, the alternating magnetic permeability is greatly reduced, and the hysteresis loss and the eddy current loss are reduced under the condition of lower austenite content.

4. The medium manganese steel has higher resistivity and is beneficial to reducing eddy current loss. The resistivity of the steel is generally most closely related to the alloy component content of the steel, the Mn element has the effect of obviously improving the resistivity of the steel, the high Mn content improves the resistivity of the steel, the eddy current loss is reduced, and the alloy has wide application in electric power fittings and machines. JMatPro theory calculation shows that the resistivity of the steel is as follows

4.5×10 ^-7 Omega.m, is the resistivity of conventional structural steel Q345B 2.0X10 ^-7 The increase of the resistivity of the steel is beneficial to reducing the eddy current loss and the skin depth in the alternating magnetic field environment, reducing the internal consumption in the power generation process and being beneficial to energy conservation and emission reduction.

5. The steel realizes excellent magnetic properties by adopting lower alloy cost, and the relative magnetic permeability is far lower than that of the known common steel types. The magnetic properties of the steel can be adjusted in a larger range by adjusting chemical components and a heat treatment process, and the steel has a larger optimization space. Tables 1 and 2 show the ac magnetic characteristic parameters of common steel grades and experimentally measured low-carbon medium-manganese steel and low-alloy high-strength steel. As can be seen from the table, after the medium manganese steel is subjected to critical heat treatment, the initial magnetic permeability and the maximum magnetic permeability are obviously reduced, and after the 6Mn steel is subjected to heat treatment, the initial magnetic permeability is only 19, and the maximum magnetic permeability is only 50.

6. The medium manganese steel has the characteristics of low magnetic permeability, low coercive force and low loss under the condition of low magnetic field intensity, namely magnetic field intensity less than 3000A/m, can be used as low magnetic steel, has higher hysteresis characteristic under the condition of high magnetic field intensity, namely magnetic field intensity more than or equal to 15000A/m, belongs to semi-hard magnetic alloy, has coercive force as high as 4820A/m under the saturated magnetic field intensity, has excellent hysteresis characteristic, can be used as hysteresis alloy, and has far lower price than the traditional Fe-Co-Ni hysteresis alloy.

The invention provides low-cost high-strength high-toughness low-permeability medium manganese steel produced by adopting a traditional continuous casting process on the basis of a large number of alternating-current hysteresis loss tests, which has a ferrite and austenite dual-phase structure with nano-scale distribution of laths, and the austenite phase isolates ferrite phases, can be used as magnetic domain walls, blocks or reduces the interaction influence of the magnetization process of ferromagnetic phases (alpha phases), and reduces the mutual magnetic exchange energy among ferrite phases. The alternating current relative magnetic permeability of the medium manganese steel is between 18 and 300, the total loss is reduced by more than 90 percent compared with the common steel structural steel under the low magnetic field intensity below 3000A/m, and the alloy cost is reduced by 60 to 80 percent compared with austenitic stainless steel and high manganese non-magnetic steel. Under the condition of weak magnetic field or low exciting current, the magnetic iron has the outstanding performances of high strength, high toughness, low magnetic conductivity, difficult magnetization, high resistance, low coercivity and the like, and reduces hysteresis loss and eddy current loss caused by exciting current, so the magnetic iron is very suitable for being used as 'low magnetic steel'. The strong magnetic field below 20000A/m also shows higher coercive force, has better hysteresis property, realizes the compromise of low magnetism, high strength and low cost, accelerates the popularization and application of the low magnetic steel in industrial production, and has wide application prospect in the future.

TABLE 1 AC magnetic characteristic parameters of common Steel grades

Table 2 experimental measurement of ac magnetic characteristic parameters of low carbon medium manganese steel and conventional low alloy high strength steel

Drawings

FIG. 1 shows tensile stress-strain curves of medium manganese steel under different process conditions in an embodiment of the invention;

FIG. 2 is a SEM microstructure of a manganese steel sheet after quenching and heat treatment in accordance with an embodiment of the present invention;

FIG. 3 shows the 50Hz AC hysteresis loop of the medium manganese steel 6MnT2 sample in the embodiment of the invention under different magnetic field intensities;

FIG. 4 shows the 50Hz AC basic magnetization curve and magnetic permeability data of a medium manganese steel 6MnT2 sample in the embodiment of the invention;

FIG. 5 shows a 50Hz AC total loss curve of a sample of medium manganese steel 6MnT2 in an embodiment of the invention, wherein the total loss is the sum of hysteresis loss and eddy current loss;

FIG. 6 shows B-H hysteresis loops measured at high magnetic field strengths of 30000A/m and 10000A/m for samples of medium manganese steel under different process conditions in the examples of the invention, and compared with hysteresis loops of a comparative steel grade;

FIG. 7 shows B-H hysteresis loops of samples of medium manganese steel in different process states under a weak magnetic field of 3000A/m, and is compared with the hysteresis loops of a comparison steel type, and the area surrounded by the hysteresis loops represents the hysteresis loss of one cycle;

FIG. 8 shows B-H hysteresis loops of samples of different components and process states of medium manganese steel in the embodiment of the invention under the weak magnetic field of 1000A/m, compared with the hysteresis loops of the comparison steel, the area surrounded by the hysteresis loops represents the hysteresis loss of one cycle;

FIG. 9 is a graph showing the comparison of a 50Hz AC basic magnetization curve of a sample and a comparison steel grade with respect to the comparison steel grade in the process state of a medium manganese 6Mn steel in the embodiment of the present invention;

FIG. 10 is a graph showing the relative permeability of the 50Hz alternating current amplitude of the test sample and the comparative steel grade under different process conditions of the medium manganese steel in the embodiment of the invention; wherein the graph (a) is a 50Hz alternating current relative amplitude permeability comparison graph of the medium manganese steel plate and the 6.5Si steel under different compositions and process states; FIG. (b) is a graph showing the comparison of 50Hz AC relative amplitude permeability of a medium manganese steel plate and Q690D steel under different components and process conditions;

FIG. 11 is a graph showing a 50Hz total loss curve of 6Mn steel and a comparative steel grade under different process conditions in the example of the present invention; wherein the graph (a) is a comparison graph of the total AC loss curve of the 6Mn steel and the comparison steel grade under different process states under the condition of saturation magnetization; FIG. b is a graph showing the total AC loss curve of 6Mn steel and comparative steel under different process conditions at a low magnetic field strength of 5000A/m or less;

FIG. 12 is a graph showing the comparison of the real and imaginary magnetic permeability of 50Hz and the relative magnetic permeability of 50Hz and 1000Hz of 6MnT of the present invention; wherein the graph (a) is a 50Hz alternating current real and imaginary relative magnetic permeability comparison graph of medium manganese steel 6 MnT; FIG. (b) is a graph showing the relative permeability of medium manganese steel 6MnT2 at high frequency 1000Hz and low frequency;

FIG. 13 is a graph of the AC relative permeability of a medium manganese 6MnT steel versus a low alloy structural Q690D steel in an embodiment of the present invention;

FIG. 14 is a graph comparing the total loss of the medium manganese 6MnT steel and the low alloy Q690D steel in the example of the present invention;

FIG. 15 is a graph showing the comparison of total loss curves of alternating current and the ratio of total loss of the medium manganese steel 6MnT and the high-strength low-alloy Q690D steel with the low magnetic field strength below 5000A/m, wherein the graph (a) is a graph showing the comparison of total loss curves of the Q690D steel and the medium manganese low-magnetic 6MnT2 steel with the total loss of the magnetic field strength below 5000A/m, and the graph (b) is the proportional relation of the total loss of the 6MnT steel and the Q690D steel;

FIG. 16 is a graph showing the coercivity of 6Mn steel under different heat treatment process conditions compared with the coercivity of a comparative steel grade under a low magnetic field strength of 5000A/m or less.

Detailed Description

The present invention will be described in further detail with reference to examples, which are not intended to limit the scope of the invention. The present invention will be described in detail below:

the medium manganese steel is smelted by adopting a vacuum induction furnace, and smelting components of a practical final embodiment are shown in table 3.

Table 3 Spectrum analysis Components (%)

Wherein, the steel types with the compositions of 5Mn and 6Mn are materials adopted in the embodiment of the invention, and Q690D steel (also called VN steel) and 6.5Si are the existing materials, which are used as comparative examples.

The steel ingot cast by the low-permeability medium manganese steel is heated at 1200+/-20 ℃ for 4-6 hours, hot rolled into a steel plate with the thickness of 4-5mm after being discharged, and air cooled to room temperature at 850-950 ℃. Because of the excellent hardenability of medium manganese steel, air-cooling can be done, and the air-cooled sample is also regarded as a quenched sample, and the steel denoted by Q, for example, 6MnQ represents a steel sheet of 6Mn steel hot-rolled and air-cooled to room temperature.

The heat treatment process of the low-permeability medium manganese steel with different components comprises the following steps: the steel plate is preheated and homogenized at 400-450 ℃ after hot rolling, then is quickly heated to 600-700 ℃, and is preserved for 0.5-4 hours, the specific preservation time is determined according to the thickness of the steel plate and the preservation temperature, and the higher the preservation temperature is, the shorter the preservation time is, the lower the preservation temperature is, and the longer the preservation time is. Under different heat preservation temperatures and heat preservation time, the material has distinct mechanical properties and magnetic properties. The preferable heat preservation temperature is 650 ℃, and the heat preservation time is 10-20min/mm. The heat preservation temperature is 700 ℃, the heat preservation time is 5-10min/mm, and the magnetic property and the mechanical property are better under the process conditions.

Example 1

The high-strength high-toughness low-permeability medium manganese steel comprises the following chemical components in percentage by mass: 0.06%, mn:5.12%, si:0.17%, ti:0.017%, cr:0.43%, ni:0.27%, mo:0.20%, cu:0.18%, P:0.015%, S:0.005%, the balance being Fe and unavoidable impurities. In this example, the steel prepared from the above components is marked as 5Mn, and the specific preparation method includes the following steps:

1) The industrial high-quality low-carbon scrap steel is used as a raw material, wherein the components comprise less than or equal to 0.15% of C, less than or equal to 0.50% of Si, less than or equal to 1.50% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, and the balance of Fe and unavoidable impurities, wherein the balance of alloy elements are prepared by adopting corresponding pure metals according to a proportion, and then are smelted by adopting a vacuum induction furnace;

2) After molten steel is completely melted, pouring the molten steel into a cast iron mold at the temperature of 1600 ℃ to obtain 25kg of cylindrical cast ingot with the diameter of 150 mm;

3) Heating the prepared cast ingot to 1200 ℃ in a resistance furnace for 2 hours, and preserving heat for 3 hours;

4) Rolling, wherein the initial rolling temperature is controlled to be 1100 ℃, the final rolling temperature is controlled to be 920 ℃, the steel plate with the thickness of 5mm is hot rolled after being discharged from a furnace, air cooling is carried out to room temperature after rolling, and the steel plate obtained by direct rolling is recorded as 5MnQ.

And (3) preparing a tensile sample according to the standard, then carrying out mechanical property test, preparing a magnetic sheet sample with the thickness of 30mm and 100mm and 1mm by adopting linear cutting, and removing a heat affected zone and a surface oxide layer by adopting sand paper for magnetic property test.

Example 2

The smelting process and the chemical composition of the final smelting cast ingot of the high-strength high-toughness low-permeability medium manganese steel are completely the same as those of the embodiment 1, the rolling process is also the same as that of the embodiment 1, and the heat treatment process is as follows: the rolled steel plate is preheated and homogenized at 400 ℃ for heat preservation for 1h, then heated to 650 ℃ at 3-10 ℃/min, heat preserved for 1h, and then air cooled to room temperature, and the prepared steel plate is marked as 5MnT1.

And (3) preparing a tensile sample according to the standard, then carrying out mechanical property test, cutting a magnetic sheet sample with the thickness of 30mm and 100mm and 1mm by adopting linear cutting, and removing a heat affected zone and a surface oxide layer by adopting sand paper for magnetic property test.

Example 3

The smelting process and the chemical composition of the final smelting cast ingot of the high-strength high-toughness low-permeability medium manganese steel are the same as those of the example 1, the rolling process is the same as that of the example 1, and the heat treatment process is as follows: the rolled steel plate is preheated and homogenized at 400 ℃ for heat preservation for 1h, then heated to 650 ℃ at 3-10 ℃/min, heat preservation for 2h, and then air-cooled to room temperature, and the prepared steel plate is denoted as 5MnT2.

Example 4

The high-strength high-toughness low-permeability medium manganese steel comprises the following chemical components in percentage by mass: 0.16%, mn:6.17%, si:0.16%, ti:0.006%, cr:0.43%, ni:0.21%, mo:0.22%, cu:0.22%, V:0.194%, P:0.015%, S:0.005%, the balance being Fe and unavoidable impurities. In this example, the steel prepared from the above components is labeled 6Mn, and the specific preparation method comprises the following steps:

2) After the molten steel is completely melted, pouring the molten steel into a cast iron mold at the temperature of 1580 ℃ to obtain 25kg of cylindrical cast ingot with the diameter of 150 mm;

4) Hot rolling is carried out, the initial rolling temperature is 1100 ℃, the final rolling temperature is controlled to be 900 ℃, the steel plate with the thickness of 5mm is hot rolled after being discharged from a furnace, air cooling is carried out to room temperature after rolling, and the steel plate obtained by direct rolling is recorded as 6MnQ.

Example 5

The smelting process and the chemical composition of the final smelting cast ingot of the high-strength high-toughness low-permeability medium manganese steel are the same as those of the example 4, the rolling process is also the same as that of the example 4, and the specific heat treatment process is as follows:

the rolled steel plate is preheated, homogenized and insulated for 2 hours at 400 ℃, then quickly heated to 620 ℃, insulated for 2 hours, and then air-cooled to room temperature, and the prepared steel plate is denoted as 6MnT1. And (3) preparing a tensile sample according to the standard, then carrying out mechanical property test, cutting a magnetic sheet sample with the thickness of 30mm and 100mm and 1mm by adopting linear cutting, and removing a heat affected zone and a surface oxide layer by adopting sand paper for magnetic property test.

Example 6

the rolled steel plate is preheated, homogenized and insulated for 2 hours at 400 ℃, then quickly heated to 650 ℃, insulated for 4 hours, and then air-cooled to room temperature, and the prepared steel plate is recorded as 6MnT2.

Example 7

the rolled steel plate is preheated and homogenized at 400 ℃ for heat preservation for 1h, then is quickly heated to 700 ℃, is heat preserved for 1h, is then air-cooled to room temperature, and the prepared steel plate is recorded as 6MnT-700.

Preparing a tensile sample and an impact sample from the steel plate prepared by the steps according to the standard, and performing mechanical property test; meanwhile, a magnetic sheet sample with the thickness of 30mm and 100mm and 1mm is cut by linear cutting, and a heat affected zone and a surface oxide layer are removed by sanding for magnetic property testing.

The medium-manganese high-strength steel with different components and process states is prepared through the above examples 1-7, and then a tensile sample is prepared according to the standard for mechanical property test; meanwhile, preparing a magnetic sheet sample, and testing magnetic characteristics under a corresponding state; metallographic and VSM magnetometer samples in different technological states are prepared simultaneously.

The magnetic property of the low-permeability high-strength medium manganese steel disclosed by the invention adopts the international electrotechnical commission standard IEC404-2:1996 method for measuring magnetic properties of Electrical sheet (tape) by Epstein square coil, which relates to measurement by a single-sheet permeameter customized by the rule of measuring device, the exciting coil and the test coil are 700 turns, the maximum alternating current magnetic field strength is 30000A/m, and the size of the test sample is '0.5-1 mm multiplied by 30mm multiplied by 100 mm'. The medium manganese steel is also a low-quality soft magnetic material, and the monolithic permeameter for measuring the high-permeability silicon steel sheet has enough precision to measure various magnetic properties of the medium manganese steel.

In order to meet the requirements of an alternating current magnetometer on a sample, a plurality of alternating current magnetometer samples with the sizes of 30mm x 100mm x 1mm and 30mm x 100mm x 0.5mm are cut from medium manganese steel plates under different components and process states by adopting a wire cutting method, and are hereinafter referred to as magnetic sheets for short. And (3) polishing the wire-cut sample step by using 80-2000 meshes of sand paper, and removing the wire-cut heat affected zone and the surface oxide layer.

In order to illustrate and explain the excellent mechanical and magnetic properties of the medium manganese steel, the traditional low alloy high strength steel Q690D prepared in the laboratory is adopted as a comparison steel type, the steel has a microstructure of ferrite and bainite, is a microstructure common to the traditional high strength steel, and the mechanical properties of the comparison steel type are shown in table 4.

The medium manganese steel prepared by the invention has excellent mechanical properties, and the mechanical properties under different heat treatment process states are shown in table 4. Fig. 1 shows the tensile stress strain curves of medium manganese steel under different process conditions. As can be seen from Table 4 and FIG. 1, after the medium manganese steel is subjected to critical reversal annealing treatment, the yield strength and the tensile strength are reduced, but the elongation is greatly improved, the elongation is far higher than that of the traditional low alloy high strength steel Q690D, and the comprehensive performance is obviously improved. The product of strength and elongation of the prepared medium manganese steel is 23.5-32.2GPa, and the medium manganese steel has better toughness, and the low-temperature impact energy at minus 20 ℃ is also more than 150J, and has better low-temperature toughness.

Table 4 shows a comparison of the mechanical properties of manganese steel and conventional high strength structural steel

Fig. 2 shows an SEM morphology microstructure of a 5MnT steel plate after quenching and critical tempering, wherein the microstructure mainly comprises tempered martensite and inverted austenite double-phase structures which are distributed in a submicron-level lath shape and a small amount of dispersed nano-scale carbides, so that a lath-shaped mixed double-phase structure matched with a large-angle grain boundary is formed, and the inverted austenite content is 15-50%.

In order to illustrate and explain the excellent magnetic properties of the medium manganese steel, the traditional low alloy high strength structural steel Q690D with the yield strength of 690MPa prepared in a laboratory and the high silicon steel 6.5Si are used as comparison steel types to respectively represent the traditional ferrite high strength steel and the electrical steel, and the traditional ferrite high strength structural steel and the electrical steel are subjected to static and alternating current magnetic property test under the same detection equipment condition with the medium manganese steel to compare the alternating current magnetic property data. Q690D is a low alloy high strength structural steel reinforced by microalloy elements VN (also referred to as VN in the figure), has a dual phase structure of ferrite and bainite, and has higher strength and toughness. The high silicon steel 6.5Si is electrical steel, has higher magnetic permeability and higher resistivity, and is beneficial to reducing hysteresis and eddy current loss. The actual chemical compositions of the Q690D and 6.5Si steels are shown in Table 3.

Samples of different shapes and thicknesses have different demagnetizing factors and magnetic property testing requires standardized samples. In fig. 12 (b), the alternating current magnetization curves of the samples with different thicknesses of 5MnT1 are compared, and the detection result shows that the magnetization curves and the loss curves of the samples with the magnetic force sheets with the thickness of 1mm and 0.5mm are basically consistent with each other at the alternating current weak magnetic field intensity, namely, the magnetic field intensity is less than 5000A/m, and the samples with the magnetic force sheets with the thickness of 0.5mm are easier to magnetize than the samples with the magnetic force sheets with the thickness of 1mm at the strong magnetic field intensity, so that the total loss is less under the high magnetic field intensity, which is mainly less eddy current loss. Considering the processing difficulty of the 0.5mm magnetic sheet sample, the alternating-current magnetic test results are all the detection results of the 30mm x 100mm x 1mm sample without special description. The silicon steel sheet is a 0.35mm silicon steel sheet, and the rest are 1mm samples.

The alternating-current magnetic characteristic test adopts a customized single-chip permeameter tested by a silicon steel sheet, and the magnetizing coil and the detecting coil are both 700 turns for testing. The common low-carbon low-alloy structural steel is also a soft magnetic material, is more difficult to magnetize than silicon steel, generally needs higher magnetizing current for magnetization, has the maximum magnetizing current of 30000A/m, and can meet the alternating current magnetic characteristic test requirement of the common structural steel. Adopts METALS-2010S alternating current magnetic permeameter to test different medium manganese steel magnetic force sheet samples in different magnetic field intensity H _m The hysteresis loops under the test are measured one by one, and a dynamic alternating current magnetization curve is drawn.

The magnetic field intensity of the medium manganese steel is below 400A/m of 50Hz, and the magnetic induction intensity B _m Extremely low, low induced voltage, and fixed magnetic field strength H _m In general, initial permeability is not detected by the method of (a) and the magnetic induction B is fixed _m The method of (2) makes a measurement item by item, both being equivalent in effect. In general, the initial permeability of steel is approximate at low frequencies below 1000Hz, so that the initial permeability is corrected and evaluated by using alternating current with the frequency of 1000Hz in a weak magnetic field below 400A/m. It is clear from test comparison that under the condition of alternating current magnetization with the frequency of 1000Hz and 50Hz, the numerical difference of the relative magnetic permeability between the two is smaller than 2, and the relative magnetic permeability under the condition of the frequency of 1000Hz is slightly lower than the relative magnetic permeability of the frequency of 50 Hz.

FIGS. 3, 4 and 5 show hysteresis loops, AC magnetization curves and amplitude relative permeability mu of medium manganese steel 6MnT under different magnetic field strengths _a 50Hz ac total loss curve. As can be seen from the figure, the medium manganese steel 6MnT has a maximum magnetic induction B at a magnetic field strength of 30000A/m _m Only 0.82T, the hysteresis loop area is larger, the magnetic induction intensity is only 0.3T under the magnetic field intensity of 5000A/m, and the magnetic induction intensity B _m With the intensity of the magnetic field H _m The increase is slow. Magnetic induction intensity B under 540A/m magnetic field intensity _m A magnetic field strength of 0.014T, a relative permeability of 20.7, 540A/m or less, a magnetic induction strength B _m Comparatively low and difficult to measure. By fixing the magnetic induction intensity B _m By measurement, 50. 50hHz ac dynamic initial relative permeability of 19.5 and maximum relative permeability of 52 at field strength 6500A/m can be determined. The result of the total loss curve of alternating current at the frequency of 50Hz shows that the total loss curve is rapidly increased under the magnetic field intensity of less than 3000A/m and less than 3W/kg and more than 3000A/m.

FIG. 6 shows the hysteresis loops of 50Hz alternating current B-H of medium manganese steel of different compositions and states measured by a B-H analyzer at a high magnetic field strength of 25000A/m, and compared with the hysteresis loops of comparative steels Q690D and 6.5 Si; as can be seen from the graph, when the alternating magnetic field intensity is 5600A/m, the Si steel reaches the alternating saturation magnetic induction intensity B _s 1.76T. When the alternating-current external magnetic field intensity is 20000A/m, the Q690D steel and the 5MnQ reach the alternating-current saturation magnetic induction intensity B _s 1.98T and 1.81T, respectively. Maximum magnetic induction B of 6MnQ, 5MnT1, 5MnT2, 6MnT1 and 6MnT2 when the alternating applied magnetic field strength is 25000-30000A/m _m 1.81T, 1.43T, 0.93T, 1.11T and 0.81T, respectively. After tempering heat treatment, the magnetic induction intensity of the medium manganese steel is greatly reduced, and a reversed austenite structure is formed in the structure in the tempering treatment process, so that the medium manganese steel gradually loses magnetism. The longer the heat treatment time, the more austenite structure content, and the maximum magnetic induction B _m The more obvious the drop, the shorter the hysteresis loop becomes _m And becomes more slow as the magnetic field strength increases. Under the same heat treatment process conditions, the magnetic induction intensity of the 6Mn steelThe degree is less than 5Mn steel, which means that 6Mn steel contains more austenite structure.

FIGS. 7 and 8 show the 50Hz AC B-H hysteresis loop of medium manganese steel plates of different compositions and states measured by a B-H analyzer at magnetic field strengths of 3000A/m and 1000A/m, respectively, and compared with comparative steel grades Q690D and 6.5Si steel. The size of the area enclosed by the hysteresis loop represents the size of the total hysteresis loss in one magnetization period. It can be seen from the figure that the hysteresis loop area of the Q690D steel is far greater than that of the medium manganese steel at the same magnetic field strengths of 3000A/m and 1000A/m. The heat-treated 5Mn and 6Mn medium manganese steel is smaller than the quenched medium manganese steel, and the longer the heat treatment time is, the smaller the hysteresis loop area is. The hysteresis loop area of the 6Mn steel is smaller than that of the 5Mn steel. This shows that after heat treatment, the medium manganese steel has lower hysteresis loss under the condition of low magnetic field intensity.

FIG. 9 shows the 50Hz AC basic magnetization curve comparison of medium manganese steel plates and comparison steel types under different compositions and process conditions. As can be seen from the graph, the silicon steel is relatively easy to magnetize, and the magnetic induction intensity of 1T can be achieved under the alternating magnetic field intensity of 150A/m. Under the alternating magnetization current of 1200A/m, the Q690D steel can achieve the magnetic induction intensity of 1T, is relatively easy to magnetize, and most structural steels with ferrite structures need the alternating magnetic field intensity to be between the Q690D steel and the Si steel to achieve the magnetic induction intensity of 1T. The medium manganese steel has lower magnetic permeability, is generally difficult to magnetize, the rapid rising area of the magnetic induction intensity is far lagged behind the conventional steel grade, the saturated magnetic induction intensity is lower than that of the conventional steel grade, and the magnetic induction intensity of the medium manganese steel reaching 1T needs more than 4000A/m. Under the same magnetic field intensity, different steel grades reach magnetic induction intensity B _m The gap is huge.

The Si steel can reach the maximum magnetic induction intensity B under the magnetic field intensity of 3000A/m _m The magnetic induction of the steel was 1.62T, Q690D was 1.45T,6MnQ, 6MnT1 and 6MnT2 was only 0.85T, 0.78T and 0.35T, respectively. Under the weak magnetic field intensity of 1000A/m, the Si steel can reach the maximum magnetic induction intensity B _m The magnetic induction of the steel was 1.4T, Q690D was 0.6T,6MnQ, 6MnT1 and 6MnT2 were only 0.15T, 0.08T and 0.04T, respectively. Hysteresis lossThe eddy current loss is equal to the maximum magnetic induction intensity B _m The magnetic induction intensity is reduced in proportion, so that hysteresis loss can be effectively reduced.

Fig. 10 (a) and (b) show the 50Hz ac relative amplitude permeability contrast of medium manganese steel sheet with common steel grade at different compositions and process conditions. From the graph, the difference of magnetic permeability of different steel types is huge, 6.5Si steel has higher relative magnetic permeability, the maximum amplitude magnetic permeability can reach 3600, and Q690D relative magnetic permeability is between 100 and 650, which is consistent with the magnetic permeability range of most low-carbon structural steel between 100 and 800. The magnetic permeability of the medium manganese steel is far lower than that of Q690D high-strength structural steel, the relative magnetic permeability is between 20 and 250, wherein the initial magnetic permeability of 6MnT steel is only 19, the maximum magnetic permeability is only 52, and the magnetic permeability is far lower than that of conventional structural steel.

FIGS. 11 (a) and (b) show graphs comparing the total AC loss curve for 6Mn steel versus comparative steel grade at various process conditions. As is clear from FIG. (a), in the case of saturation magnetization, si steel was used as electric steel, the total AC loss curve was the lowest, the total AC loss Ps was less than 5W/kg under the ordinary 50Hz AC magnetic field, the total AC loss was the largest for the 6MnQ steel, and the total AC loss was not large for the Q690D and 6MnT1 steels. For conventional steel grades, the higher the strength, the greater the total ac loss under saturated magnetization. However, the saturation hysteresis loss of the 6MnT steel is only 60% of that of the Q690D high-strength steel. FIG. 11 (b) shows the total AC loss comparison of medium manganese steel with the comparison steel grade at a low magnetic field strength below 5000A/m. As can be seen from the graph, the total loss of the heat-treated 6MnT steel below 3000A/m is obviously lower than that of the Si steel, the Q690D steel and the 6MnQ steel, and the main reason is that the relative magnetic permeability of the 6Mn steel is obviously reduced after the heat treatment, and the hysteresis loss and the eddy current loss are also greatly reduced.

Fig. 12 (a) and (b) show the comparison of the real and imaginary relative permeability of 50Hz and the high frequency 1000Hz and the low frequency relative permeability of medium manganese steel 6MnT 2. In the graph (a), the ac real relative permeability μ' and the imaginary relative permeability μ″ are respectively the elastic permeability and the loss permeability of the magnetic material, the elastic permeability representing the permeability of the stored energy in the magnetic material, the loss permeability being related to the loss of one magnetization cycle of the magnetic material. The ac relative permeability is not specifically described, and is generally referred to as amplitude permeability, and the amplitude permeability μ has the following relationship between real and imaginary relative permeability:

as can be seen from the graph (b) of FIG. 12, the initial permeability of the elastic relative permeability of the medium manganese steel is only 19.5, the maximum permeability is only 45.6, the initial value of the loss permeability is 0, and the maximum loss permeability is only 15. The hysteresis and eddy current loss of alternating current are all closely related in frequency, and the higher the frequency is, the larger the various losses are. In FIG. 12 (b), it can be seen that the permeability at a high frequency of 1000Hz is consistent with the present pair permeability at a low frequency of 50 Hz. This also shows that medium manganese steel has a good effect of reducing hysteresis and eddy current loss at high frequency.

Fig. 13 and 14 show graphs comparing the ac relative permeability and total loss curves of the medium manganese low magnetic 6MnT steel and the high strength low alloy structural steel Q690D. The high-strength low-alloy structural steel Q690D is a microalloyed reinforced ferrite+pearlite structure steel, has a yield strength of greater than 550MPa, and is consistent with the microstructure type of conventional structural steel. The initial permeability of Q690D is 100, the maximum permeability is 650, and the average permeability is 350; the initial magnetic permeability of 6MnT2 is 19, the maximum magnetic permeability is only 45, the average magnetic permeability is 35, and the alternating current relative maximum magnetic permeability of 6MnT2 steel is reduced by more than 90 percent compared with the high-strength low-alloy structural steel.

Fig. 14 compares the total loss curve of Q690D with that of medium manganese low magnetic 6MnT steel. It can be seen from the figure that at any magnetic field strength, the total loss curve of 6MnT2 steel is always lower than Q690D, and more pronounced at weak magnetic fields below 3000A/m. Q690D is a rapid increase in hysteresis loss at magnetic field strengths above 1000A/m, and the total loss curve can reach a maximum at magnetic field strengths above 5000A/m, which means that low carbon structural steels can generally only be used at magnetic field strengths below 1000A/m, ordinary structural steels such as Q235 steel grades are lower in strength, and initial permeability and maximum permeability are higher and can only be used at lower magnetic field strengths. The hysteresis loss of the medium manganese steel is slowly increased, the loss is less than 5W/kg under the magnetic field intensity of 3000A/m, and the total loss curve can reach the maximum value under the large magnetic field intensity of more than 20000A/m.

FIGS. 15 (a) and (b) are graphs comparing the total loss curve of Q690D and the total loss curve of the medium-manganese low-magnetic 6MnT steel under 5000A/m. It is clear from fig. 15 (a) that the total loss detail of the 6MnT steel is lower than Q690D. Fig. 15 (b) shows the total loss of 6MnT2 steel in proportion to Q690D. Under the magnetic field intensity below 3000A/m, the total loss of 6MnT2 steel is only below 10% of Q690D, under the magnetic field intensity below 1000A/m, the total loss of 6MnT steel is only below 5% of Q690D, under the strong magnetic field intensity, the total loss of medium manganese steel 6MnT2 is also rapidly increased, the proportion between the two is rapidly reduced, and under the saturated magnetic field intensity, the total loss of medium manganese steel 6MnT2 is only 70% of high-strength low-alloy structural steel Q690D. In the conventional electromagnetic design, the magnetic field intensity of the metal structural member is generally smaller than 3000A/m, and if the medium manganese 6MnT steel is adopted as the metal structural member, the total loss of the 6MnT steel is reduced by more than 90% compared with the total loss of the general structural steel under the same mass condition, so that the method has great popularization significance in electric machinery.

FIG. 16 is a graph showing the coercivity of 6Mn steel versus magnetic field strength for different heat treatment process conditions. As can be seen from the graph, when the 6Mn steel is subjected to heat treatment at the temperature below 650 ℃, the maximum coercivity is 2600-3100A/m under the saturation magnetic induction intensity, and when the steel is subjected to heat treatment at the temperature of 700 ℃, the coercivity under the saturation magnetic field intensity can reach 4800A/m, and the steel has higher hysteresis property. The coercive force of the 6MnT steel is lower than that of the high-strength low-alloy structural steel Q690D under the magnetic field strength of 3000A/m or less; the coercive force of the medium manganese steel 6MnT2 is lower than that of the 6.5Si steel under the low magnetic field strength of 1000A/m or less. The smaller the coercive force is, the smaller the hysteresis loss is, so that the hysteresis loss of 6MnT steel is lower than that of Q690D steel under the magnetic field strength below 3000A/m, and the hysteresis loss of medium manganese steel 6MnT2 is lower than that of 6.5Si steel under the low magnetic field strength below 1000A/m.

The medium manganese can be clearly seen from the comparative graph of the magnetic characteristic data of the plurality of examplesSpecial magnetic properties of steel. After heat treatment, the medium manganese steel has lower alternating current relative magnetic permeability in the whole magnetic field intensity interval. Has lower magnetic induction intensity B under low magnetic field intensity _m Lower real, imaginary permeability, loss angle and coercivity, lower hysteresis and eddy current losses. At a weak magnetic field strength of 3000A/m, the total AC loss of 50Hz is reduced by more than 90 percent compared with Q690D high-strength structural steel with ferrite structure. Under the strong magnetic field intensity, the magnetic field has higher coercive force, hysteresis and eddy current loss.

The medium manganese steel can obtain a large amount of reversed austenite structures which exist stably at room temperature under the condition of only adding 5-8% of Mn content, thereby greatly reducing the alternating current magnetic induction intensity B _m And ac permeability, thereby greatly reducing hysteresis and eddy current loss. In the magnetic field range of 30000A/m, the maximum magnetic induction intensity of the quenched 6MnQ is 1.81T, and after a special heat treatment process, the maximum magnetic induction intensity of the 6MnT2 steel is changed into 0.82T, and the maximum magnetic induction intensity B _m The magnetic conductivity is reduced by more than 50 percent and is far lower than that of the conventional high-strength steel with a ferrite structure. The medium manganese steel can greatly reduce hysteresis and eddy current loss of metal components around an alternating magnetic field with lower alloy cost, and has wide application space in the near-electricity environment in the future.

After critical annealing treatment, the medium manganese steel provided by the invention has excellent mechanical properties, excellent magnetic properties and lower magnetic permeability, is favorable for reducing hysteresis and eddy current loss in structural steel, and is very suitable for being used in the critical electromagnetic environments of metal parts around an electromagnetic field, electric machinery and the like. The method is mainly characterized in that after the medium manganese steel is subjected to critical annealing treatment, nano-scale composite lath martensite and inverted austenite dual-phase structure in the microstructure of the steel are nonmagnetic, and the austenite structure is used as a magnetic domain wall to effectively prevent magnetization, so that alternating-current magnetic permeability is reduced. Meanwhile, the nanoscale austenitic structure also isolates the connection between ferromagnetic phases, so that the exchange energy between the ferromagnetic phases is reduced, the magnetization intensity is reduced, and the magnetic permeability is further reduced. The high manganese component also increases the resistivity of the steel, which is 3-4 times that of the common structural steel, and reduces eddy current loss. The alternating-current hysteresis loss experiment shows that after the medium manganese steel is subjected to critical tempering heat treatment, the magnetic permeability and the total loss are reduced by more than 90 percent compared with the conventional high-strength structural steel, and the hysteresis and the eddy-current loss can be effectively reduced.

The production processes such as vacuum smelting and die casting defined in the embodiment of the invention do not limit the production scope of the invention, and the same effect can be obtained by adopting the industrial production modes such as converter, continuous casting and the like to produce the low-permeability medium manganese steel, which is also the protection scope defined by the invention.

Claims

1. The low-permeability medium manganese steel with high strength and high toughness is characterized by comprising the following chemical components in percentage by mass: c:0.05-0.20%, si:0.10-0.50%, mn:5.0 to 8.0 percent, P is less than or equal to 0.020 percent, S is less than or equal to 0.010 percent, als is 0.010 to 0.050 percent, cr+Ni+Mo+Ti+V+Cu+Co+Re is less than or equal to 1.5 percent, and the balance is Fe and unavoidable impurities.

2. The high-strength high-toughness low-permeability medium manganese steel according to claim 1, wherein the obtained low-permeability medium manganese steel has the following comprehensive mechanical properties: rp0.2 is more than or equal to 650MPa, rm is more than or equal to 850MPa, A is more than or equal to 20%, and the alternating current relative magnetic permeability is between 18 and 300 in a weak alternating magnetic field with magnetic field strength of less than or equal to 3000A/m.

3. The high strength high toughness low permeability medium manganese steel according to claim 1, wherein the microstructure of the finished product is a tempered martensite structure in which laths of 20-300nm are alternately distributed, a duplex structure of a reversed austenite structure, and a small amount of nano carbides, wherein the reversed austenite structure content is 15-50%, the nano carbides content is less than 5%, the rest is the tempered martensite structure, and the reversed austenite structure content is adjusted according to tempering temperature and time.

4. The high-strength high-toughness low-permeability medium manganese steel according to claim 1, wherein the low-permeability medium manganese steel has an alternating magnetic field of 50-1000Hz Under the piece, saturation induction intensity B _s Between 0.50 and 1.70T, corresponding to the saturation magnetic field strength H _s More than 20000A/m; coercive force H under saturated magnetic induction magnetic field condition _c A remanence ratio B of 1500-4800A/m _r /B _s Between 0.50 and 0.90, the initial relative permeability is between 18 and 100, the maximum permeability is between 50 and 300, and the peak permeability is between 2500 and 7000A/m for the magnetic field strength.

5. The high strength high toughness low permeability medium manganese steel according to claim 1, wherein the low permeability medium manganese steel has a saturation induction less than 50mT, a remanence ratio less than 0.10, a relative permeability less than 50, and a total loss less than 0.2W/kg at low magnetic field strengths of 1000A/m or less.

6. The method for manufacturing a high-strength high-toughness low-permeability medium manganese steel according to any one of claims 1 to 5, comprising the steps of:

2) Molding and pouring into a blank;

3) Homogenizing and heating the die casting blank;

4) Carrying out high-temperature hot rolling;

5) And (5) performing critical tempering heat treatment.

7. The method for producing a high strength and toughness low permeability medium manganese steel according to claim 6, wherein in step (2), the mold is a cast iron mold, and the casting temperature is 1580±20 ℃.

8. The method for producing a high strength and high toughness low permeability medium manganese steel according to claim 6, wherein in step (3), the casting die blank is heated to 1200.+ -. 25 ℃ for 1-3 hours, and is kept at that temperature for 2-4 hours, and the total heating and keeping time is 4-6 hours.

9. The method for producing a high strength and high toughness low magnetic permeability medium manganese steel according to claim 6, wherein in step (4), the rolling is controlled to a rolling start temperature of 1100 to 1200 ℃ and a rolling finish temperature of 800 to 950 ℃, and the steel sheet is hot rolled after tapping and then air-cooled to room temperature.

10. The method for producing a high strength and toughness low magnetic permeability medium manganese steel according to claim 6, wherein in step (5), the heat treatment step is as follows: homogenizing and preserving heat for 1-4h at 400-450 ℃ after hot rolling, then rapidly heating to 600-700 ℃, and preserving heat for 0.5-6h; the total tempering time is 1-8h.