A low temperature slab heating inhibitor oriented silicon steel and a method of making

Abstract

The application discloses a low-temperature slab heating inhibitor oriented silicon steel and a preparation method, and belongs to the field of metallurgy technology. The chemical components of the oriented silicon steel are as follows in percentage by mass: C: ≤0.003%, Si: 2.0-3.5%, Nb: 0.03-0.1%, S: 0.03-0.1%, and the rest is Fe and inevitable impurity elements. The preparation method comprises the following steps: smelting of molten steel, heating of cast slab, hot rolling, two-stage cold rolling, primary recrystallization annealing and secondary recrystallization annealing. Based on the ultra-low carbon component system, the application forms niobium sulfide compound-Nb2S3 as an inhibitor for preparing the oriented silicon steel by adding only two elements of Nb and S in the oriented silicon steel, realizes low-temperature heating of the slab, omits the normalizing and decarburization annealing processes, and adopts a two-stage cold rolling process to prepare the oriented silicon steel plate with high magnetic induction and low iron loss. The energy consumption and production cost are significantly reduced, and the application has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a low-temperature slab heating inhibitor for oriented silicon steel and its preparation method. Background Technology

[0002] Grain-oriented silicon steel possesses excellent magnetic properties such as high magnetic induction intensity and low iron loss. It is primarily used in the manufacture of transformer cores and is a key material for achieving efficient electrical energy conversion, supporting the smooth implementation of major new energy projects in my country, including ultra-high voltage power transmission and distribution, wind power, and photovoltaics. The finely dispersed metastable second-phase particles in grain-oriented silicon steel are called inhibitors. Inhibitors are used to hinder the normal growth of primary recrystallized grains, inducing Goss-oriented grains ({110}). <001> The perfect secondary recrystallization is the key to the excellent magnetic properties of grain-oriented silicon steel.

[0003] Currently, the commonly used inhibitors in grain-oriented silicon steel are MnS, Cu2S, and AlN. Among these, the high-temperature billet heating process using MnS and AlN as the main inhibitors reaches temperatures as high as 1350℃-1400℃, resulting in high energy consumption, severe burn-off, and low product yield. The medium-temperature billet heating process using Cu2S, with its relatively lower solution temperature, as an inhibitor, can reduce the billet heating temperature to 1250-1300℃, while eliminating the normalizing process for hot-rolled plates. The product performance falls between that of ordinary grain-oriented silicon steel and high-magnetic-induction grain-oriented silicon steel, and it is widely used by private enterprises in my country. The low-temperature slab heating process, which uses an inhibitor-obtaining method, involves nitriding after decarburization annealing. This utilizes the combination of free nitrogen atoms and acid-soluble aluminum in the steel to form a large amount of AlN or (Al,Si)N inhibitors, further reducing the billet heating temperature to 1150-1200℃. However, the chemical nitriding process is affected by many factors, has a narrow process window, and a low yield. Therefore, finding inhibitors with high solid solubility to further reduce the billet heating temperature, simplify the production process of grain-oriented silicon steel, replace the existing high-energy-consuming and high-emission grain-oriented silicon steel preparation technology, and produce high-performance grain-oriented silicon steel has always been a research hotspot in the field of grain-oriented silicon steel.

[0004] Nitrogen b (Nb) precipitates are relatively common in steel, and they readily precipitate in fine, dispersed form. Solid-solution Nb atoms (solute drag) can hinder grain growth. The addition of Nb can lower the heating temperature of grain-oriented silicon steel billets, resulting in a more uniform billet microstructure and finer, more uniform grains. Furthermore, Nb is chemically stable, its composition is easily controlled, and residual amounts of Nb do not adversely affect the performance of the final product.

[0005] Chinese invention patent (publication number CN103898409B) discloses an inhibitor for reducing the heating temperature of grain-oriented silicon steel slabs and its preparation method. The main feature of this patent is that it uses Nb(C,N) as the main inhibitor and AlN, Cu2S, (Cu,Mn)S and grain boundary segregating element Cr as auxiliary inhibitors, thereby realizing the preparation of grain-oriented silicon steel by heating slabs at low temperature.

[0006] Chinese invention patent (publication number CN103898409B) discloses a method for producing niobium-containing oriented silicon steel using low-temperature heating of slabs. The main feature of this patent is that by adding the auxiliary inhibitor element Nb, fine and dispersed precipitates with Nb (C, N) as the main component are formed, which reduces the heating temperature of the hot-rolled slab by 6-77°C, reduces the difficulty of controlling the composition of Als, and reduces production energy consumption.

[0007] However, the method of using Nb(C,N) as an inhibitor in grain-oriented silicon steel has not been widely applied. This is because the fine and dispersed precipitates of Nb(C,N) have an excessively strong inhibitory effect, significantly suppressing dynamic recrystallization and leading to a reduction in the number of Goss textures in hot-rolled sheets. Furthermore, the precipitation temperature of Nb(C,N) is relatively low; at a normalizing temperature of 920℃, it actually re-dissolves. After decarburization annealing, some carbon exists in Nb(C,N) in the form of compounds, making it difficult to reduce the carbon content to the level of traditional grain-oriented silicon steel (0.003%). Summary of the Invention

[0008] The purpose of this invention is to provide a low-temperature slab heating inhibitor for grain-oriented silicon steel and its preparation method. Only two elements, Nb and S, are added to the grain-oriented silicon steel, which significantly reduces the cost of steelmaking and the difficulty of controlling the smelting composition. While realizing low-temperature heating of the slab, the normalizing and decarburizing annealing processes are further omitted. A high magnetic induction and low iron loss grain-oriented silicon steel sheet is prepared through a two-stage cold rolling process, which has good application prospects.

[0009] This invention provides a low-temperature slab heating inhibitor oriented silicon steel, which uses an ultra-low carbon oriented silicon steel composition system. Its composition by mass percentage is C: ≤0.003%, Si: 2.0~3.5%, Nb: 0.03~0.1%, S: 0.03~0.1%, with the remainder being Fe and unavoidable impurity elements.

[0010] This invention also provides a method for preparing low-temperature slab heating inhibitor oriented silicon steel, comprising the following process steps:

[0011] Steel smelting process: smelt steel according to the set composition to obtain a billet with a thickness of 150mm~200mm;

[0012] Billet heating process: Heat the smelted billet to 1150~1200℃ and hold for 120 minutes;

[0013] Hot rolling process: divided into rough rolling and finish rolling. After the billet is heated and taken out of the furnace, it is rough rolled to obtain a 30~50mm rough rolled billet, and then finish rolled to a thickness of 2~2.5mm. The initial rolling temperature of rough rolling is 1050℃~1100℃, and the final rolling temperature of finish rolling is 800~950℃.

[0014] Cold rolling process: The hot-rolled plate is pickled to remove the iron oxide scale, and then subjected to two-stage cold rolling; the first stage cold rolling reduction rate is 65~75%, and then intermediate annealing is carried out at 950~1050℃ for 5~7 minutes; then the second stage cold rolling is carried out with a reduction rate of 50~80%, to obtain the cold-rolled plate.

[0015] Annealing process: The cold-rolled sheet is first recrystallized and annealed at 850℃~950℃ for 180s~300s; after coating with MgO release agent, it is subjected to secondary recrystallization and annealing, with the temperature increased to 1050℃~1200℃ at a rate of 10~40℃ / h. The secondary recrystallization and annealing is carried out in an atmosphere with a nitrogen-hydrogen ratio of 1:3.

[0016] Furthermore, the steelmaking process uses an ultra-low carbon oriented silicon steel composition system, with only Nb and S elements added to the oriented silicon steel.

[0017] Furthermore, the chemical composition of the billet by mass percentage is as follows: C: ≤0.003%, Si: 2~3.5%, Nb: 0.03~0.1%, S: 0.03~0.1%, with the remainder being Fe and unavoidable impurity elements.

[0018] Furthermore, in the above preparation method, Nb2S3 is formed in oriented silicon steel as an inhibitor, with precipitates having a size of 15~60nm and being dispersed in the matrix.

[0019] Furthermore, the thickness of the inhibitor-oriented silicon steel product prepared according to the above method is 0.18~0.35mm, the magnetic induction intensity B8 is 1.76~1.89T, and the iron loss P is... 17 / 50 It ranges from 0.9 to 1.4 W / kg.

[0020] The present invention provides a low-temperature slab heating inhibitor for grain-oriented silicon steel and its preparation method, which has at least the following beneficial effects:

[0021] 1. This invention designs an inhibitor, niobium trisulfide (Nb2S3), that can induce perfect secondary recrystallization in oriented silicon steel. This niobium-sulfur compound is easy to smelt and control in terms of composition. Its full solution temperature is below 1200℃, which can realize low-temperature heating of slabs, significantly reducing energy consumption and production costs.

[0022] 2. The present invention provides a method for preparing a low-temperature slab heating inhibitor for grain-oriented silicon steel, breaking through the bottleneck of current low-temperature slab heating technology. The ultra-low carbon composition system employed eliminates the need for a decarburization annealing process, solving the problem of decarburization difficulties caused by the use of Nb(C,N) in existing low-temperature slab heating processes. Furthermore, Nb₂S₃ has a wide precipitation temperature range, allowing for sufficient dispersion and precipitation during hot rolling and subsequent annealing, thus eliminating the need for a normalizing annealing process and further simplifying the production flow. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments.

[0024] Example 1

[0025] A low-temperature slab heating inhibitor oriented silicon steel is provided, which adopts an ultra-low carbon oriented silicon steel composition system. Its composition by mass percentage is C: ≤0.003%, Si: 2.5%, Nb: 0.03%, S: 0.03%, with the remainder being Fe and unavoidable impurity elements.

[0026] The preparation method of low-temperature slab heating inhibitor oriented silicon steel in this embodiment is carried out according to the following steps:

[0027] Steel was smelted according to the above-mentioned composition to produce a 150mm thick billet. The billet was held at 1150℃ for 120 minutes, then rough-rolled to 30mm, and finally finish-rolled to 2mm to obtain a hot-rolled plate. The rough-rolling start temperature was 1050℃, and the finish-rolling finish temperature was 850℃. The hot-rolled plate was pickled to remove iron oxide scale, and then subjected to two-stage cold rolling. The first stage cold rolling was to 0.7mm (65% reduction), followed by intermediate annealing at 1050℃ for 5 minutes. The intermediate-annealed plate was then cold-rolled in a second stage to 0.35mm (50% reduction) to obtain a cold-rolled plate. The cold-rolled plate was first subjected to primary recrystallization annealing at 850℃ for 180 seconds, then coated with an MgO release agent and heated to 1050℃ at a rate of 40℃ / h for secondary recrystallization annealing. The secondary recrystallization annealing was carried out in an atmosphere with a nitrogen-hydrogen ratio of 1:3. The finished inhibitor-oriented silicon steel prepared by the above process has a magnetic induction intensity B8 of 1.86T and an iron loss P. 17 / 50 It is 0.9 W / kg.

[0028] Example 2

[0029] A low-temperature slab heating inhibitor oriented silicon steel is selected, using an ultra-low carbon oriented silicon steel composition system, whose composition by mass percentage is C: ≤0.003%, Si: 3.2%, Nb: 0.05%, S: 0.05%, with the remainder being Fe and unavoidable impurity elements.

[0030] The preparation method of low-temperature slab heating inhibitor oriented silicon steel in this embodiment is carried out according to the following steps:

[0031] Steel was smelted according to the above-mentioned composition to produce a 200mm thick billet. The billet was held at 1200℃ for 120 minutes, then rough-rolled to 40mm, and finally finish-rolled to 2.2mm to obtain a hot-rolled plate. The rough-rolling start temperature was 1100℃, and the finish-rolling finish temperature was 900℃. The hot-rolled plate was pickled to remove iron oxide scale, and then subjected to two-stage cold rolling. The first stage cold rolling was to 0.65mm (65% reduction), followed by intermediate annealing at 950℃ for 5 minutes. The intermediate-annealed plate was then cold-rolled in the second stage to 0.3mm (54% reduction) to obtain a cold-rolled plate. The cold-rolled plate was first subjected to primary recrystallization annealing at 900℃ for 300s, then coated with an MgO release agent and heated to 1200℃ at a rate of 20℃ / h for secondary recrystallization annealing. The secondary recrystallization annealing was carried out in an atmosphere with a nitrogen-hydrogen ratio of 1:3. The finished inhibitor-oriented silicon steel prepared by the above process has a magnetic induction intensity B8 of 1.89T and an iron loss P17 / 50 of 1.0W / kg.

[0032] Example 3

[0033] A low-temperature slab heating inhibitor oriented silicon steel is selected, using an ultra-low carbon oriented silicon steel composition system, whose composition by mass percentage is C: ≤0.003%, Si: 3.2%, Nb: 0.07%, S: 0.07%, with the remainder being Fe and unavoidable impurity elements.

[0034] The preparation method of low-temperature slab heating inhibitor oriented silicon steel in this embodiment is carried out according to the following steps:

[0035] Steel was smelted according to the set composition to produce a 200mm thick billet. The billet was held at 1200℃ for 120 minutes, then rough-rolled to 40mm, and finally finish-rolled to 2.3mm to obtain a hot-rolled plate. The rough-rolling start temperature was 1100℃, and the finish-rolling finish temperature was 900℃. The hot-rolled plate was pickled to remove iron oxide scale and then subjected to two-stage cold rolling. The first stage cold rolling was to 0.6mm (74% reduction), followed by intermediate annealing at 950℃ for 7 minutes. The intermediate-annealed plate was then cold-rolled in a second stage to 0.23mm (62% reduction) to obtain a cold-rolled plate. The cold-rolled plate was first subjected to primary recrystallization annealing at 900℃ for 300s, then coated with an MgO release agent and heated to 1200℃ at a rate of 20℃ / h for secondary recrystallization annealing. The secondary recrystallization annealing was carried out in an atmosphere with a nitrogen-hydrogen ratio of 1:3. The finished inhibitor-oriented silicon steel prepared by the above process has a magnetic induction intensity B8 of 1.82T and an iron loss P17 / 50 of 1.2W / kg.

[0036] Example 4

[0037] A low-temperature slab heating inhibitor oriented silicon steel is selected, which adopts an ultra-low carbon oriented silicon steel composition system. Its composition by mass percentage is C: ≤0.003%, Si: 3.5%, Nb: 0.1%, S: 0.1%, with the remainder being Fe and unavoidable impurity elements.

[0038] The preparation method of low-temperature slab heating inhibitor oriented silicon steel in this embodiment is carried out according to the following steps:

[0039] Steel was smelted according to the set composition to produce a 200mm thick billet. The billet was held at 1200℃ for 120 minutes, then rough-rolled to 50mm. After trimming, it was finish-rolled to 2.5mm to obtain a hot-rolled plate. The roughing rolling temperature was 1100℃, and the finish rolling temperature was 950℃. The hot-rolled plate was pickled to remove iron oxide scale, and then underwent two-stage cold rolling. The first stage cold rolling was to 0.75mm (70% reduction), followed by intermediate annealing at 1000℃ for 5 minutes. The intermediate-annealed plate was then cold-rolled in the second stage to 0.18mm (76% reduction) to obtain a cold-rolled plate. The cold-rolled plate was first subjected to primary recrystallization annealing at 950℃ for 300 seconds, then coated with an MgO release agent and heated to 1200℃ at a rate of 40℃ / h for secondary recrystallization annealing. The secondary recrystallization annealing was carried out in an atmosphere with a nitrogen-hydrogen ratio of 1:3. The finished inhibitor-oriented silicon steel prepared by the above process has a magnetic induction intensity B8 of 1.76T and an iron loss P17 / 50 of 1.4W / kg.

[0040] In the preparation methods of the above embodiments, Nb₂S₃ was formed in oriented silicon steel as an inhibitor. The precipitate size was 15-60 nm and it was dispersed in the matrix. The crystal structure of Nb₂S₃ belongs to the hexagonal crystal system, with space group P₆₃ / mmc (194), and lattice constants a=b=3.31Å and c=12.53Å. The orientation relationship of Nb₂S₃ precipitated relative to the matrix is ​​as follows: The morphology of Nb₂S₃ is mainly ellipsoidal and short rod-shaped, with an average diameter of 30–100 nm and a distribution density of 1–6 μm. -2 .

[0041] The magnetic properties of inhibitor-oriented silicon steels with different Nb and S contents prepared by the above process are shown in Table 1:

[0042] Table 1:

[0043]

[0044] Table 1 shows the relationship between Nb and S content and the magnetic properties of the inhibitor-oriented silicon steel products in four examples. The table shows that the oriented silicon steel prepared using a composition system of 0.05% Nb-0.05% S exhibits the best magnetic properties.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the ideas of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-temperature slab heating inhibitor for grain-oriented silicon steel, characterized in that, The composition system of ultra-low carbon oriented silicon steel is selected, and its composition by mass percentage is C: ≤0.003%, Si: 2.0~3.5%, Nb: 0.03~0.1%, S: 0.03~0.1%, with the remainder being Fe and unavoidable impurity elements; The preparation process steps of the low-temperature slab heating inhibitor oriented silicon steel are as follows: Steel smelting process: smelt steel according to the set composition to obtain a billet with a thickness of 150mm~200mm; Billet heating process: Heat the smelted billet to 1150~1200℃ and hold for 120 minutes; Hot rolling process: divided into rough rolling and finish rolling. After the billet is heated and taken out of the furnace, it is rough rolled to obtain a 30~50mm rough rolled billet, and then finish rolled to a thickness of 2~2.5mm. The initial rolling temperature of rough rolling is 1050℃~1100℃, and the final rolling temperature of finish rolling is 800~950℃. Cold rolling process: The hot-rolled plate is pickled to remove the iron oxide scale, and then subjected to two-stage cold rolling; the first stage cold rolling reduction rate is 65~75%, and then intermediate annealing is carried out at 950~1050℃ for 5~7 minutes; then the second stage cold rolling is carried out with a reduction rate of 50~80%, to obtain the cold-rolled plate. Annealing process: The cold-rolled sheet is first recrystallized and annealed at 850℃~950℃ for 180s~300s; after coating with MgO release agent, it is subjected to secondary recrystallization and annealing, with the temperature increased to 1050℃~1200℃ at a rate of 10~40℃ / h. The secondary recrystallization and annealing is carried out in an atmosphere with a nitrogen-hydrogen ratio of 1:

3.

2. A method for preparing low-temperature slab heating inhibitor oriented silicon steel as described in claim 1, characterized in that, The process includes the following steps: Steel smelting process: smelt steel according to the set composition to obtain a billet with a thickness of 150mm~200mm; Billet heating process: Heat the smelted billet to 1150~1200℃ and hold for 120 minutes; Hot rolling process: divided into rough rolling and finish rolling. After the billet is heated and taken out of the furnace, it is rough rolled to obtain a 30~50mm rough rolled billet, and then finish rolled to a thickness of 2~2.5mm. The initial rolling temperature of rough rolling is 1050℃~1100℃, and the final rolling temperature of finish rolling is 800~950℃. Cold rolling process: The hot-rolled plate is pickled to remove the iron oxide scale, and then subjected to two-stage cold rolling; the first stage cold rolling reduction rate is 65~75%, and then intermediate annealing is carried out at 950~1050℃ for 5~7 minutes; then the second stage cold rolling is carried out with a reduction rate of 50~80%, to obtain the cold-rolled plate. Annealing process: The cold-rolled sheet is first recrystallized and annealed at 850℃~950℃ for 180s~300s; after coating with MgO release agent, it is subjected to secondary recrystallization and annealing, with the temperature increased to 1050℃~1200℃ at a rate of 10~40℃ / h. The secondary recrystallization and annealing is carried out in an atmosphere with a nitrogen-hydrogen ratio of 1:

3.

3. The method for preparing low-temperature slab heating inhibitor oriented silicon steel according to claim 2, characterized in that, Nb2S3 was formed in oriented silicon steel as an inhibitor, with precipitates ranging in size from 15 to 60 nm and dispersed throughout the matrix.

4. The method for preparing low-temperature slab heating inhibitor oriented silicon steel according to claim 2, characterized in that, The prepared inhibitor-oriented silicon steel has a thickness of 0.18~0.35mm, a magnetic induction intensity B8 of 1.76~1.89T, and an iron loss P. 17 / 50 It ranges from 0.9 to 1.4 W / kg.

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