CN110218853B - Process method for preparing low-temperature high-magnetic-induction oriented silicon steel - Google Patents

Process method for preparing low-temperature high-magnetic-induction oriented silicon steel Download PDF

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CN110218853B
CN110218853B CN201910563069.8A CN201910563069A CN110218853B CN 110218853 B CN110218853 B CN 110218853B CN 201910563069 A CN201910563069 A CN 201910563069A CN 110218853 B CN110218853 B CN 110218853B
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nitriding
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steel strip
oriented silicon
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CN110218853A (en
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高洋
郭小龙
王雄奎
孙亮
骆新根
申明辉
程祥威
丁哲
程迪夫
夏乘峰
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Wuhan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • C21D3/02—Extraction of non-metals
    • C21D3/04—Decarburising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
    • C21D8/1255—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest with diffusion of elements, e.g. decarburising, nitriding
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces

Abstract

The invention discloses a process method for preparing low-temperature high-magnetic-induction oriented silicon steel, and belongs to the technical field of steelmaking. The process method is different from the traditional nitriding technology after the decarburization annealing of the cold-rolled sheet, the nitriding is carried out within the temperature range of the initial primary recrystallization in the initial stage of the decarburization annealing of the cold-rolled sheet, and the escape of nitrogen is reduced by controlling the nitrogen content of different sheet thicknesses and forming an internal oxidation layer in the decarburization process, so that a stable nitride precipitation phase is formed. The method controls the surface layer of primary recrystallized grains after nitriding and decarbonizing to be smaller and the size ratio of the primary recrystallized grains to the central layer grain to be in a proper range, increases the number of Gaussian crystal nuclei, reduces the size of finished product grains to achieve the aim of reducing iron loss, and achieves the double aims of improving the iron loss of products and ensuring the stable performance. The beneficial effects of improving the iron loss of the product, improving the magnetic stability, saving energy and reducing consumption are obtained.

Description

Process method for preparing low-temperature high-magnetic-induction oriented silicon steel
Technical Field
The invention relates to process control of high-magnetic-induction oriented silicon steel, belongs to the technical field of steelmaking, and particularly relates to a process method for preparing low-temperature high-magnetic-induction oriented silicon steel.
Background
The silicon steel has low loss and low magnetostrictionThe magnetic material has excellent magnetic properties such as expansion and contraction, and is the most important magnetic material in the power and electronic industries. Silicon steels are generally classified into oriented silicon steels and non-oriented silicon steels. Wherein, the oriented silicon steel utilizes the abnormal growth of secondary recrystallization of crystal grains to ensure that the finished product tissue presents Gaussian texture {111}<001>Preferred orientation of (a). Of internal crystal lattice, due to the oriented nature of the finished grains<001>The shaft is as parallel as possible to the rolling direction, and this material has good magnetic permeability in the rolling direction and can obtain high magnetic strength, and therefore it is widely used in the manufacture of transformer cores. As a main electromagnetic conversion carrier component, the design and manufacture of the iron core are one of the most important links in the transformer manufacturing process. If the iron core is selected too large, the volume of the transformer is increased, the cost is increased, and if the iron core is selected to be smaller, the magnetic induction of the silicon steel sheet must be provided with a guarantee value to limit. Generally, the magnetic induction intensity B of silicon steel sheets under the condition of 800A/m and 50Hz alternating magnetic field is used in the transformer industry800The magnetic induction of the silicon steel sheet is 1.7T under the condition of 50Hz alternating magnetic field, and the iron loss P is used as reference data under the working condition of the iron core17/50The parameter is rated for its loss. B is800At least 1.89T, and B800Higher, higher iron loss P17/50The lower the product grade, the higher the product grade, and the more the requirement for manufacturing the miniaturized low-cost and high-energy-efficiency transformer can be met. The additional value of the prepared high-grade oriented silicon steel product brought to production enterprises and the power industry is correspondingly improved.
The current production methods for manufacturing high magnetic induction oriented silicon steel mainly comprise three production methods, namely a high-temperature slab heating preparation method for heating a hot-rolled slab to above 1300 ℃, a medium-temperature slab heating preparation method for heating the slab to between 1200 ℃ and 1300 ℃, and a low-temperature slab heating preparation method for heating the slab to below 1200 ℃ (called low-temperature high magnetic induction oriented silicon steel). Because a series of metallurgical problems of low yield, large equipment loss, high fuel consumption, many product surface defects and the like are caused by the overhigh heating temperature of the hot rolled slab, the production of high magnetic induction oriented silicon steel by adopting a low-temperature slab method is a main development trend. The reason why the hot rolled slabs used in the different methods have different heating temperatures is due to the different types of inhibitors used. The medium-temperature and high-temperature slab method adopts MnS, CuS and the like with higher solid solution temperature as the innate inhibitor, and the MnS, the CuS and the like are added in the alloying process of steel making and formed in the hot rolling process, so the heating temperature is higher; the low-temperature plate blank method adopts the method of obtaining the inhibitor by the post-procedure of silicon steel, reduces the dependence on the inherent inhibitor, redesigns the components and reduces the requirement on the solid solution temperature, thereby successfully reducing the heating temperature by more than 100 ℃, and more meeting the green and environment-friendly requirement of the urban manufacturing factory in the future.
The acquisition of the acquired inhibitor is a very key technical link in the manufacturing technology of the low-temperature high-magnetic-induction oriented silicon steel, and the importance and the difficulty of the acquired inhibitor are reflected in two aspects: firstly, controlling the influence of the acquired inhibitor on the secondary recrystallization growth; secondly, a stable method for inhibiting the formation of the compound. In the first aspect, the effect of the conventional congenital inhibitors on the secondary recrystallization starts already in the primary recrystallization process of the oriented silicon steel, so that the primary recrystallization of the high-temperature slab process product is smaller. And because the low-temperature high-magnetic-induction oriented silicon steel has less congenital inhibitor and the acquired inhibitor is formed after decarburization annealing, the primary crystal grain is larger and difficult to control, and better product performance is not easy to obtain. In a second aspect, the latter inhibitor is sufficiently nitrided in the surface layer of the silicon steel by nitriding treatment after decarburization annealing, and then is converted into nitride precipitation. The formation of nitride is related to the design of steel grade components, nitriding temperature and high temperature annealing process control.
With the development of the low-temperature high-magnetic induction oriented silicon steel manufacturing technology, the defects of the existing manufacturing method are found: nitriding is carried out after primary recrystallization is formed as described above, the inhibition effect of nitride precipitation relative to primary grains is limited, a certain amount of inherent inhibitor is provided by adding alloy solute elements in the steelmaking alloying process, and the influence performance of inclusions in steel is easily increased. ② nitriding is carried out after primary recrystallization, but primary grain size is too large in decarburization annealing process, and primary recrystallization size is difficult to control. The decarburization needs longer annealing time, and coarse primary grains are easily caused to influence the performance of a final product, namely a 'control window' of a low-temperature steel process is narrower. Thirdly, a mixture oxide layer consisting of silicon dioxide and ferric oxide is formed on the surface layer of the silicon steel after decarburization, so that nitrogen is prevented from diffusing to an iron matrix; and the grain boundary of the primary crystal grain growth after decarburization is reduced, and the diffusion rate of nitrogen is also influenced. Both of which cause a decrease in nitriding efficiency and medium usage.
In this regard, technological improvements and innovations directed to the acquired inhibitor acquisition method are continuously being proposed.
Research shows that the nitriding efficiency is inversely proportional to the nitriding temperature, because the ammonia decomposition rate is increased along with the increase of the nitriding temperature, the content of active nitrogen atoms is reduced, the nitriding amount is reduced, the existing nitriding process is mostly implemented in a range of more than 700 ℃, and the nitriding temperature can also cause different precipitated phases of the obtained nitrides. Japanese patent laid-open publication Nos. Hei 2-247331, Hei 7-118746 and the like in the nineties of the last ninety years disclose a method of manufacturing oriented silicon steel by heating a slab at a temperature lower than 1200 ℃ and forming (Al, Si) N compensating for the innate inhibitor by nitriding in a wide range of 700 ℃ to 1000 ℃ after decarburization, which requires strict control of the primary recrystallization diameter in conjunction with a high temperature annealing process and still has a problem that the primary grain coarsening is difficult to control before. European patent EP0950120B1 discloses a high temperature nitriding method at 850 ℃ -1050 ℃, and because the nitride formed at higher temperature is more stable, and nitrogen elements at the later stage are not easy to escape, stable AlN inhibitor can be obtained at the decarburization annealing stage so as to stabilize the magnetic performance of the product, but the nitriding efficiency is low due to higher nitriding temperature.
In order to solve the problem of nitriding efficiency, the Chinese patent application (application publication No. CN101294268A, application publication date: 2008-10-29) proposes that plasma low-temperature nitriding is adopted, so that the nitriding temperature can be effectively reduced, the nitriding efficiency is improved, and the product performance and the stability are also improved. This technique is relatively demanding and costly.
On the other hand, the nitriding efficiency can also be improved by solving the blocking effect of the internal oxidation layer on the nitriding. The Chinese invention patent application (application publication No. CN101748259A, application publication date: 2010-06-23) proposes that a decarburized plate is deformed by a small reduction rate of 1.5-3% before nitriding to damage an internal oxidation layer so as to achieve better nitriding efficiency, but the method adds a cold rolling procedure in continuous decarburization and nitriding annealing, and the rolling process without lubrication has higher requirements on a roller, so that the product cost is increased.
There is also an innovative method for improving nitriding efficiency without the influence of gas nitriding on the surface and properties, and japanese patent laid-open No. 62-40315 discloses earlier a method for nitriding an oriented silicon steel in a high-temperature annealing process by coating MgO containing MnN or ferromanganese nitride as a spacer after decarburization, which, although excellent magnetic properties can be obtained, is affected by the MgO coating process and the magnetic properties are difficult to be uniform in the process environment of high-temperature annealing coils.
Further, in order to avoid the influence of nitriding after decarburization, a technique of nitriding before completion of the decarburization process has started to appear:
the Chinese invention patent application (application publication No. CN102041440A, application publication date: 2011-05-04) proposes that nitriding treatment is carried out by a normalizing process before decarburization annealing to obtain nitride precipitation as inhibitor reinforcement, so that good magnetic performance is obtained. However, in actual production, since the precipitated phase of the nitride is unstable after low-temperature nitriding, escape of nitrogen in the later process and early nitriding affect the primary crystal grains, and the performance is easily unstable.
Japanese patent laid-open No. 2-294428 discloses a method for producing high magnetic induction oriented silicon steel by simultaneous decarburization and nitriding annealing, which can improve nitriding efficiency and production efficiency, but does not consider the change of primary crystal grains caused by the change of nitriding process, and the product performance is liable to be unstable.
Therefore, although the improved process method can effectively improve the nitriding efficiency, the technical defect exists in the stable control of the primary crystal grains after decarburization, so that the product performance cannot be improved on the basis of reducing the production energy consumption and improving the production efficiency.
Disclosure of Invention
In order to solve the technical problems, the invention provides a process method for preparing low-temperature high-magnetic-induction oriented silicon steel. The process method not only starts nitriding within the range of the initial recrystallization starting temperature, but also reduces the escape of nitrogen by controlling the nitrogen content in different plate thicknesses and forming an internal oxidation layer in the decarburization process, and is favorable for forming a stable nitride precipitated phase. And the surface layer of the primary recrystallized grains after nitriding and decarbonizing is controlled to be smaller, and the ratio of the surface layer to the size of the grains of the central layer is controlled to be within a proper range, so that the number of Gaussian crystal nuclei is increased, and the size of the grains of a finished product is reduced to achieve the purpose of reducing iron loss. Thereby realizing the dual purposes of improving the iron loss of the product and ensuring the stable performance.
In order to achieve the aim, the invention discloses a process method for preparing low-temperature high-magnetic induction oriented silicon steel, which comprises the steps of continuous casting blank forming, casting blank heating, hot rolling, normalizing annealing, cold rolling, continuous nitriding and decarburization annealing, surface coating, coiling, high-temperature annealing, stretching, flattening, insulating layer coating and drying, curing and annealing;
the continuous nitriding and decarburization annealing process specifically comprises the following steps:
1) heating the cold-rolled sheet to 500-670 ℃ and soaking and nitriding, wherein the nitriding atmosphere is NH3+N2+H2The mixed gas of (3);
2) controlling the steel strip nitriding increment delta N after the nitriding-decarburization annealing is finished according to the soaking nitriding treatment time, wherein the steel strip nitriding increment delta N satisfies the following mathematical relation formula I:
Figure BDA0002108790550000041
wherein, the Delta N, the nitriding increment of the steel strip, unit and ppm;
t, nitriding treatment time, unit, s;
d, steel strip thickness, unit, mm;
3) soaking the steel strip at 820-860 ℃ and carrying out decarburization annealing treatment, wherein the decarburization annealing time is 120-360 s, detecting the carbon content and the nitriding increment delta N of the steel strip after decarburization is finished, controlling the carbon content in the decarburized steel strip to be lower than 5ppm, and controlling the nitriding increment delta N of the steel strip to meet the following formula II mathematical relation:
(185) -155 XD- Δ N-198-91 XD formula II;
4) after the nitriding and decarburization annealing processes are finished, the grain distribution on the rolled section of the steel strip is characterized in that the ratio n of the average size of grains from the upper surface and the lower surface of the steel strip to the 1/4 thickness intervals of the steel strip to the average size of grains from the upper surface and the lower surface of the steel strip to the 1/4 thickness intervals of the rolled section of the steel strip is less than or equal to 0.76; and the ratio n satisfies the following formula III mathematical relation:
Figure BDA0002108790550000051
wherein n is2The number of crystal grains in the thickness interval of 1/4 above and below the central line of the rolling direction section;
n1the number of crystal grains in the interval from the upper surface to the lower surface of the steel strip to 1/4 thickness distances from the upper surface to the lower surface.
Further, in step 1), the NH3The volume percentage content A satisfies the following formula IV mathematical relation:
A＝0.165×10-6×T2-0.962×10-4x T +0.055 formula IV;
wherein T is nitriding temperature in DEG C.
Further, in step 1), the N is2And H2Is 1: 3.
Further, in the step 3), the decarburization annealing atmosphere is wet N2+H2Mixed gas, wherein the partial pressure ratio p of water vapor is pSteam of water/pHydrogen gas0.27 to 0.35.
Further, the high-magnetic-induction oriented silicon steel comprises the following components in percentage by mass;
0.035-0.060% of C, 2.55-3.55% of Si, 0.0100-0.0350% of Als, 0.03-0.2% of Mn, 0.0020-0.0100% of S, 0.0040-0.0100% of N, less than 0.07% of Cu, 0.03-0.2% of Cr and the balance of Fe and inevitable impurities.
Further, the high-magnetic-induction oriented silicon steel comprises the following components in percentage by mass;
0.035-0.060% of C, 3.0-3.3% of Si, 0.0100-0.0350% of Als, 0.085-0.095% of Mn, 0.0020-0.0100% of S, 0.0062-0.0086% of N, less than 0.04% of Cu, 0.03-0.16% of Cr and the balance of Fe and inevitable impurities.
Further, the casting blank heating process comprises the step of controlling the heating temperature to be 1100-1250 ℃.
Further, the hot rolling process comprises the step of conventionally hot rolling the steel plate into a hot rolled coil with the thickness of 1.5-3.8 mm.
Further, the cold rolling process comprises the step of cold rolling to a finished product with the thickness of not more than 0.30mm according to the reduction ratio of 87-92%.
Further, the high-temperature annealing comprises the step of controlling the purification temperature to be 1150-1250 ℃, and the content of nitrogen and the content of sulfur in the steel strip after the annealing are not higher than 10 ppm.
Preferably, the surface coating is a coating of MgO release agent.
The principle of the process method of the invention is as follows: the method has the advantages that the traditional nitriding treatment is carried out from the low-temperature section of the heating stage of decarburization annealing in advance after the decarburization annealing, the defects that in other technologies, a normalized nitriding layer is difficult to keep through acid washing, the traditional nitriding treatment is low in efficiency at a high temperature, primary recrystallization is difficult to control, an internal oxidation layer is formed and then is influenced by the nitriding treatment are overcome, and the method is high in nitriding efficiency, small in energy medium loss, good in finished product surface quality, excellent in magnetic performance and the like. The principle of the specific process parameters is as follows:
(1) the lower nitriding temperature range is 500-670 ℃, because the temperature region is the temperature at which the primary recrystallization of the Fe + 3% Si alloy oriented silicon steel starts to occur, fine and uniform primary grains are quickly formed under the temperature condition, the maximum number of primary recrystallized grains and grain boundaries is provided, the nitriding efficiency is improved, and meanwhile, the early intervention of nitriding treatment well inhibits the primary recrystallization growth of the surface layer.
(2) The invention proposes that the consumption of the nitriding medium ammonia gas required under different nitriding temperatures accounts for the volume percentage of the nitriding mixture gas, because the decomposition rate of the ammonia gas is higher along with the increase of the nitriding temperature in the nitriding process within the range of 500-1100 ℃, the active nitrogen atoms adsorbed by a steel strip are less, and the nitriding efficiency is reducedA large number of test results show that the nonlinear relation A of the ammonia consumption and the nitriding temperature in the nitriding process is 0.165 multiplied by 10-6×T2-0.962×10-4×T+0.055；
(3) According to the invention, the magnetic performance of the final product is ensured according to the nitrogen increasing quantity delta N required by products with different thicknesses after nitriding and decarbonizing, and a linear relation between the optimal control range of delta N and the thickness of a cold-rolled coil is found through tests, so that a method for ensuring the proper nitrogen permeability of products with different thicknesses is provided;
(4) the invention provides that the partial pressure ratio p of water vapor is pSteam of water/pHydrogen gasThe range of 0.27-0.35 is that a proper internal oxidation layer can be generated in the decarburization atmosphere, so that the escape of early-stage low-temperature nitriding in the process of annealing is reduced, and the nitriding increment delta N is ensured to be within the target control range after the nitriding-decarburization annealing is finished.
(5) The invention provides that the ratio n of the average size of the crystal grains of the nitriding-decarburization annealing surface layer and the central layer is less than or equal to 0.76, because the technology can effectively ensure the depth of the nitriding layer, successfully inhibit the growth of primary crystal grains of the surface layer before primary recrystallization growth and coarsening, and ensure that the size of the crystal grains of the surface layer is less than that of the central layer and is within a proper ratio value n after decarburization annealing is finished. The analysis is based on the principle of electrical steel materials because the Gaussian crystal nucleus is mainly formed in the primary crystal grain of the surface layer, and the reduction of the size of the crystal grain of the surface layer is favorable for obtaining fine and more Gaussian crystal nuclei as secondary recrystallization crystal nuclei, so that the size of the finished product crystal grain is reduced, and the iron loss of the low-temperature high-magnetic-induction oriented silicon steel is reduced. And the average grain size ratio n in the different zones was calculated according to formula III because the area from the top and bottom surfaces of the strip to the thickness range of 1/4 a from the top and bottom surfaces was equal to the area from the top and bottom of 1/4 a from the center line of the rolled cross-section (as shown in fig. 1, S1＝S2) Observing the number n of crystal grains in two regions1And n2Then, due to the average radius
Figure BDA0002108790550000071
Equation III can be deduced.
Therefore, compared with the prior art, the method overcomes the defects of the nitriding treatment in the traditional process, effectively inhibits primary recrystallization by nitriding in advance at a low-temperature section, reduces the dependence of low-temperature high-magnetic induction oriented silicon steel on inherent inhibitors such as MnS and AlN, widens the smelting control window of oriented silicon steel alloy, and has the advantages of wider content of elements formed by the inherent inhibitors such as Mn and quicker content requirement range of elements formed by the inherent inhibitors such as Als, thereby having better performance stability in actual production. And the nitriding efficiency is improved, and the consumption of nitriding media is reduced. Meanwhile, the oxide layer is prevented from being damaged by nitriding treatment after decarburization, and the surface quality of the product is improved. The magnetic induction of the final product is not lower than 1.914T, the adhesion is not lower than B-level, and the iron loss value of the product with the same specification is reduced by at least more than 4.8 percent compared with the traditional process.
The beneficial effects of the invention are mainly embodied in the following aspects:
1. the invention solves the problems of low nitriding efficiency and high cost in the prior art, and is different from the traditional nitriding technology before decarburization after cold rolling, nitriding is started within the range of initial recrystallization starting temperature, and nitrogen escape is reduced by controlling nitrogen content in different plate thicknesses and forming an internal oxidation layer in the decarburization process, so that a stable nitride precipitated phase is formed. The method controls the primary recrystallized grains after nitriding and decarbonizing to have smaller surface layer and the grain size ratio of the primary recrystallized grains to the central layer within a proper range, increases the number of Gaussian crystal nuclei, and reduces the grain size of finished products so as to achieve the purpose of reducing iron loss; the dual purposes of improving the iron loss of the product and ensuring the stable performance are achieved.
2. According to the method, the low-temperature high-magnetic-induction oriented silicon steel product produced by the embodiment is subjected to nitriding treatment at a lower temperature, and the consumption of nitriding media is reduced by at least 5.7%; in the final product with the same specification, the average value of the magnetic property B800 of the process of the embodiment is more than 1.914T, and the iron loss P17/50 is reduced by more than 4.8 percent compared with the comparative example; and the adhesiveness rating of the product in the invention reaches B level and above.
Drawings
FIG. 1 is a schematic illustration of the statistics of the grains of a cross section of a steel strip according to the present invention;
wherein, S in FIG. 11Representing the division of the steel strip between the upper and lower surfaces and the 1/4 thickness intervals therefrom, S2Representing the 1/4 thickness interval above and below the center line of the rolling section.
Detailed Description
In order to better explain the invention, the following further illustrate the main content of the invention in connection with specific examples, but the content of the invention is not limited to the following examples.
The invention discloses a process method for preparing low-temperature high-magnetic-induction oriented silicon steel, which comprises the following process flows of:
(1) comprises the following components in percentage by weight: 0.035 to 0.060 percent of C, 2.55 to 3.55 percent of Si, 0.0100 to 0.0350 percent of Als, 0.03 to 0.2 percent of Mn, 0.0020 to 0.0100 percent of S, 0.0040 to 0.0100 percent of N, less than 0.07 percent of Cu, 0.03 to 0.2 percent of Cr, and the balance of Fe and inevitable impurities for smelting;
(2) heating the casting blank after continuous casting and forming, wherein the heating temperature is controlled to be 1100-1250 ℃;
(3) conventionally hot rolling into a hot rolled coil with the thickness of 1.5-3.8 mm, and performing normalized annealing;
(4) cold rolling to a finished product thickness of no more than 0.30mm according to a reduction ratio of 87-92%;
(5) the cold-rolled sheet is subjected to continuous nitriding-decarburization annealing after conventional alkali washing:
5.1) soaking at 500-670 ℃ to carry out nitriding treatment in NH atmosphere3+N2+H2Mixed gas of (wherein N)2:H21:3) and the volume percentage a of ammonia gas used satisfies the following formula IV, depending on the nitriding treatment temperature:
A＝0.165×10-6×T2-0.962×10-4x T +0.055 formula IV;
wherein T is nitriding temperature in DEG C.
5.2) controlling the steel strip nitriding increment after the nitriding-decarburization annealing is finished according to the soaking nitriding treatment time, wherein the method for controlling the steel strip nitriding increment delta N after the nitriding-decarburization annealing is finished according to the soaking nitriding treatment time is that the steel strip nitriding increment delta N is in accordance with the following formula I:
Figure BDA0002108790550000081
wherein, the Delta N, the nitriding increment of the steel strip, unit and ppm;
t, nitriding treatment time, unit, s;
d, steel strip thickness, unit, mm.
5.3) heating to 820-860 ℃ for soaking and carrying out decarburization annealing treatment, wherein the decarburization annealing atmosphere is wet N2+H2Mixed gas, wherein the partial pressure ratio p of water vapor is pSteam of water/pHydrogen gas0.27 to 0.35, and the decarburization annealing time is 120 to 360 seconds. After the decarburization is finished, detecting the carbon content and the nitriding increment delta N of the steel strip, controlling the carbon content in the steel strip after the decarburization to be lower than 5ppm, and controlling the nitriding increment of the steel strip to accord with a formula II; (185) -155 XD- Δ N-198-91 XD formula II;
5.4) after the nitriding-decarburizing annealing is completed according to the steps, the grain distribution on the rolled section of the steel strip is characterized in that the ratio n of the average size of grains from the upper surface to the lower surface of the steel strip to the thickness range of 1/4 mm to the average size of grains in the rest range (from the thickness range of 1/4 mm from the central line of the rolled section of the steel strip) is less than or equal to 0.76; and n is calculated according to formula III below:
Figure BDA0002108790550000091
wherein n is2The number of crystal grains in the thickness interval of 1/4 above and below the central line of the rolling direction section;
n1the number of crystal grains in the interval from the upper surface to the lower surface of the steel strip to 1/4 thickness distances from the upper surface to the lower surface.
(6) Coating a high-temperature annealing separant on the surface of the steel strip after decarburization and annealing, and then coiling;
(7) carrying out conventional high-temperature annealing, wherein the high-temperature annealing purification temperature is 1150-1250 ℃, and the nitrogen content and the sulfur content in the steel strip after the annealing are not higher than 10 ppm;
(8) carrying out conventional stretching, flattening, insulating layer coating, drying, curing and annealing; and (5) standby.
Preparing the low-temperature high-magnetic-induction oriented silicon steel according to the alloy element composition, the technological process and the parameters to obtain tables 1, 2 and 3, wherein the nitriding method of the embodiment 1-11 is low-temperature-section soaking nitriding treatment in the heating process of decarburization annealing; the nitriding method of the comparative examples 1 to 11 is the conventional nitriding treatment after decarburization annealing;
TABLE 1 elemental composition of examples and comparative examples
Figure BDA0002108790550000092
Figure BDA0002108790550000101
TABLE 2 tabulation of the process parameters for each example and comparative example
Figure BDA0002108790550000102
Figure BDA0002108790550000111
TABLE 3 Material parameters and product magnetic Properties for examples and comparative examples
Figure BDA0002108790550000112
Figure BDA0002108790550000121
As can be seen from the above tables 1, 2 and 3, compared with the conventional decarburization and nitridation process, the heating zone low-temperature nitridation process of the invention has the advantages that the same nitrogen increment delta N can be achieved by adopting the same nitridation time, the gas amount of the nitridation medium can be saved by 5.7-64.5%, and the surface adhesion of the product can reach grade B or above. The magnetic induction of the product is not less than 1.914TIron loss P compared to the comparative product17/50At least reduced by more than 4.8 percent.
Low-temperature high-magnetic-induction grain-oriented silicon steels were prepared according to the alloy element compositions and the processes and parameters described above to obtain tables 4, 5, and 6, in which examples 12 to 17 were prepared according to the gold element compositions and the processes and parameters described above, and comparative examples 12 to 17 were prepared not within the above ranges.
TABLE 4 elemental composition of examples and comparative examples
Figure BDA0002108790550000122
Figure BDA0002108790550000131
TABLE 5 tabulation of the process parameters for each example and comparative example
Figure BDA0002108790550000132
TABLE 6 Material parameters and product magnetic Properties of examples and comparative examples
Figure BDA0002108790550000133
Figure BDA0002108790550000141
The adhesion grade standard in the above table is determined in accordance with GB/T2522-2007.
As can be seen from the above tables 4, 5 and 6, the magnetic properties of the product are better only when the nitriding process and the decarburization process are within the ranges required by the present application, and beyond the scope of the present application, the magnetic properties or the surface adhesion quality of the product are affected even when the nitriding-decarburization process is employed.
The above examples are merely preferred examples and are not intended to limit the embodiments of the present invention. In addition to the above embodiments, the present invention has other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.

Claims (10)

1. A process method for preparing low-temperature high-magnetic induction oriented silicon steel comprises the steps of continuous casting blank forming, casting blank heating, hot rolling, normalizing annealing, cold rolling, continuous nitriding and decarburization annealing, surface coating, coiling, high-temperature annealing, drawing, leveling, insulating layer coating and drying, curing and annealing;
the continuous nitriding and decarburization annealing process specifically comprises the following steps:
1) heating the cold-rolled sheet to 500-670 ℃ and soaking and nitriding, wherein the nitriding atmosphere is NH3+N2+H2The mixed gas of (3);
2) controlling the steel strip nitriding increment delta N after the nitriding-decarburization annealing is finished according to the soaking nitriding treatment time, wherein the steel strip nitriding increment delta N satisfies the following mathematical relation formula I:
Figure FDA0002108790540000011
wherein, the Delta N, the nitriding increment of the steel strip, unit and ppm;
t, nitriding treatment time, unit, s;
d, steel strip thickness, unit, mm;
3) soaking the steel strip at 820-860 ℃ and carrying out decarburization annealing treatment, wherein the decarburization annealing time is 120-360 s, detecting the carbon content and the nitriding increment delta N of the steel strip after decarburization is finished, controlling the carbon content in the decarburized steel strip to be lower than 5ppm, and controlling the nitriding increment delta N of the steel strip to meet the following formula II mathematical relation:
(185) -155 XD- Δ N-198-91 XD formula II;
4) after the nitriding and decarburization annealing processes are finished, the grain distribution on the rolled section of the steel strip is characterized in that the ratio n of the average size of grains from the upper surface and the lower surface of the steel strip to the 1/4 thickness intervals of the steel strip to the average size of grains from the upper surface and the lower surface of the steel strip to the 1/4 thickness intervals of the rolled section of the steel strip is less than or equal to 0.76; and the ratio n satisfies the following formula III mathematical relation:
Figure FDA0002108790540000012
wherein n is2The number of crystal grains in the thickness interval of 1/4 above and below the central line of the rolling direction section;
n1the number of crystal grains in the interval from the upper surface to the lower surface of the steel strip to 1/4 thickness distances from the upper surface to the lower surface.
2. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel as claimed in claim 1, wherein the process method comprises the following steps: in step 1), the NH3The volume percentage content A satisfies the following formula IV mathematical relation:
A＝0.165×10-6×T2-0.962×10-4x T +0.055 formula IV;
wherein T is nitriding temperature in DEG C.
3. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel as claimed in claim 1, wherein the process method comprises the following steps: in step 1), the N is2And H2Is 1: 3.
4. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel as claimed in claim 1, wherein the process method comprises the following steps: in the step 3), the decarburization annealing atmosphere is wet N2+H2Mixed gas, wherein the partial pressure ratio p of water vapor is pSteam of water/pHydrogen gas0.27 to 0.35.
5. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel according to any one of claims 1 to 4, characterized by comprising the following steps of: the high magnetic induction oriented silicon steel comprises the following components in percentage by mass;
0.035-0.060% of C, 2.55-3.55% of Si, 0.0100-0.0350% of Als, 0.03-0.2% of Mn, 0.0020-0.0100% of S, 0.0040-0.0100% of N, less than 0.07% of Cu, 0.03-0.2% of Cr and the balance of Fe and inevitable impurities.
6. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel as claimed in claim 5, wherein the process method comprises the following steps: the high magnetic induction oriented silicon steel comprises the following components in percentage by mass;
0.035-0.060% of C, 3.0-3.3% of Si, 0.0100-0.0350% of Als, 0.085-0.095% of Mn, 0.0020-0.0100% of S, 0.0062-0.0086% of N, less than 0.04% of Cu, 0.03-0.16% of Cr and the balance of Fe and inevitable impurities.
7. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel according to any one of claims 1 to 4, characterized by comprising the following steps of: the casting blank heating process comprises the step of controlling the heating temperature to be 1100-1250 ℃.
8. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel according to any one of claims 1 to 4, characterized by comprising the following steps of: the hot rolling process comprises the step of conventionally hot rolling to form a hot rolled coil with the thickness of 1.5-3.8 mm.
9. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel according to any one of claims 1 to 4, characterized by comprising the following steps of: the cold rolling process comprises the step of cold rolling to a finished product with the thickness of not more than 0.30mm according to the reduction rate of 87-92%.
10. The process method for preparing the low-temperature high-magnetic-induction oriented silicon steel according to any one of claims 1 to 4, characterized by comprising the following steps of: the high-temperature annealing comprises the step of controlling the purification temperature to be 1150-1250 ℃, and the nitrogen content and the sulfur content in the steel strip are not higher than 10ppm after the annealing is finished.
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