Thin strip cast niobium sulphide inhibitor oriented silicon steel and method of making

Abstract

The present application relates to the metallurgical technical field, propose a kind of thin strip continuous casting niobium sulphur inhibitor oriented silicon steel and its preparation method, the oriented silicon steel is composed of the following weight percentage components: C≤0.003%, Si 2%~3.5%, Nb 0.03%~0.1%, S 0.03%~0.1%, Mn 0.002%~0.025%, Cu 0.002%~0.025%, the rest is Fe and inevitable impurity element;By weight percentage, Nb, S, Mn and Cu satisfy the following relationship formula: (Nb+S) / (Mn+Cu)=4~15. By the above technical scheme, the problems such as secondary recrystallization imperfect, Goss texture proportion low, magnetic property is poor and the like of oriented silicon steel in the related art are solved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a thin strip continuous casting niobium sulfur inhibitor oriented silicon steel and its preparation method. Background Technology

[0002] Thin-strip continuous casting technology is a highly promising green and short-process technology in the field of steel continuous casting. Its unique physical metallurgical processes, such as near-net-shape forming and sub-rapid solidification, can endow materials with a completely new microstructure control mechanism and performance advantages that are unmatched by conventional processes, and it is gradually moving towards industrialization. In the preparation of electrical steel, the sub-rapid solidification characteristics of thin-strip continuous casting can control the supersaturated solid solution or fine dispersed precipitation of second-phase particles in grain-oriented silicon steel casting strips, fundamentally solving the drawbacks of conventional processes that use high-temperature heating of the billet to control the precipitation of inhibitors, and significantly reducing production costs.

[0003] However, in existing technologies, the thin strip continuous casting process does not involve hot rolling. The solidification structure and defects of the cast billet have a significant impact on the performance of the final product. Obtaining fine and uniform equiaxed crystals is key to improving the magnetic properties of grain-oriented silicon steel. Existing grain-oriented silicon steel suffers from problems such as imperfect secondary recrystallization, low Goss texture ratio, and poor magnetic properties. For example, the magnetic induction B8 is usually below 1.7T, which cannot meet the requirements of high-end electrical equipment. Summary of the Invention

[0004] This invention proposes a thin strip continuous casting niobium sulfur inhibitor oriented silicon steel and its preparation method to solve or alleviate at least one of the above problems.

[0005] The technical solution of the present invention is as follows: This invention proposes a thin-strip continuous casting niobium-sulfur inhibitor oriented silicon steel, which is composed of the following components by weight percentage: C≤0.003%, Si 2%~3.5%, Nb 0.03%~0.1%, S 0.03%~0.1%, Mn 0.002%~0.025%, Cu 0.002%~0.025%, with the remainder being Fe and unavoidable impurity elements; By weight percentage, the Nb, S, Mn and Cu satisfy the following relationship: (Nb+S) / (Mn+Cu)=4~15.

[0006] Preferably, the precipitates of the oriented silicon steel include NbS.

[0007] Preferably, the average diameter of the NbS is 20~40 nm.

[0008] Preferably, the average diameter of the secondary recrystallized grains in the oriented silicon steel is 40~70mm.

[0009] This invention also proposes a method for preparing thin-strip continuous casting niobium-sulfur inhibitor oriented silicon steel, comprising the following steps: S1. After the molten steel is poured, it is cooled by water and air to room temperature to obtain the casting strip; S2. The cast strip is cold rolled in two stages to obtain a cold-rolled sheet; S3. The cold-rolled sheet is subjected to primary recrystallization annealing and secondary recrystallization annealing to obtain the oriented silicon steel.

[0010] Preferably, in step S1, the water cooling specifically involves cooling to 800-900°C at a cooling rate of 40-60°C / s.

[0011] Preferably, in step S2, the two-stage cold rolling includes a first-stage cold rolling, intermediate annealing, and a second-stage cold rolling. The reduction rate of the first stage cold rolling is 80%~85%, and the reduction rate of the second stage cold rolling is 40%~45%. The intermediate annealing temperature is 950~1000℃, and the time is 5~7 minutes.

[0012] Preferably, the reduction rate of the first stage cold rolling is twice the reduction rate of the second stage cold rolling.

[0013] Preferably, the initial recrystallization annealing temperature is 800~900℃ and the time is 3~7min.

[0014] Preferably, the secondary recrystallization annealing temperature is 1100~1200℃ and the time is 8~12h.

[0015] The beneficial effects of this invention are as follows: This invention achieves a synergistic effect of Nb, S, Mn, and Cu by controlling the elemental composition and weight content in grain-oriented silicon steel and maintaining the (Nb+S) / (Mn+Cu) ratio between 4 and 15. This effectively promotes the formation of fine, dispersed NbS precipitates and maximizes the pinning effect of the inhibitor. The dispersed NbS precipitates pin to the grain boundaries, effectively suppressing grain coarsening during solidification and cooling of the cast strip. This directly results in a uniform and fine equiaxed primary solidification structure, which is beneficial for the full development of subsequent secondary recrystallization and the formation of Goss texture. Ultimately, this significantly reduces iron loss, improves magnetic induction, and gives grain-oriented silicon steel excellent comprehensive magnetic properties. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a microstructure image of the oriented silicon steel of Example 3. Detailed Implementation

[0018] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will be described through embodiments.

[0020] A specific embodiment of the first aspect of the present invention provides a thin-strip continuous casting niobium-sulfur inhibitor oriented silicon steel, which is composed of the following components by weight percentage: C≤0.003%, Si 2%~3.5%, Nb 0.03%~0.1%, S 0.03%~0.1%, Mn 0.002%~0.025%, Cu 0.002%~0.025%, with the remainder being Fe and unavoidable impurity elements; by weight percentage, Nb, S, Mn and Cu satisfy the following relationship: (Nb+S) / (Mn+Cu)=4~15.

[0021] In this invention, the oriented silicon steel adopts an ultra-low carbon composition system with few element types. This not only significantly reduces steelmaking costs and the difficulty of controlling the smelting composition, but also eliminates the need for subsequent decarburization annealing, thus avoiding the adverse effects of C on magnetic properties from the perspective of composition. Among them, the high Nb and S content, combined with a small amount of Mn and Cu, under a specific relationship, can promote the precipitation of NbS. NbS belongs to the cubic crystal system, with space group P-6m2 (187), lattice constant a=b=c=3.32 Å, and its orientation relationship with the matrix α-Fe along the (100) zone axis is

[100] . α-Fe / /

[110] NbS It has the effect of hindering the growth of recrystallized grains and can effectively refine the solidification structure of the cast strip, so that the cast strip obtains a fine and uniform equiaxed initial structure with an average grain size of ≤70μm, which lays a good foundation for subsequent Goss control and secondary recrystallization.

[0022] In one embodiment of the present invention, the average diameter of the NbS precipitate is 20-40 nm.

[0023] In this invention, the average diameter of NbS refers to the statistical average of the particle size of NbS precipitates, which can be observed and measured using a transmission electron microscope on the cast strip sample. During testing, at least 10 fields of view are randomly selected under bright or dark field conditions, and the equivalent circular diameters of at least 50 NbS precipitates (i.e., the circular diameters converted from the precipitate area) are statistically analyzed using image analysis software, and their arithmetic mean is calculated. During testing, the NbS phase can be confirmed by selected area electron diffraction or energy dispersive spectroscopy (EDS).

[0024] In one embodiment of the present invention, the average diameter of the secondary recrystallized grains of the oriented silicon steel is 40-70 mm.

[0025] In this invention, abnormally large secondary recrystallized grains are revealed by macroscopic etching of grain-oriented silicon steel. These secondary recrystallized grains exhibit a Goss texture, clearly distinguishable from the surrounding fine iron matrix grains. The average diameter of the secondary recrystallized grains is the statistical average of the counted grains. During testing, at least five regions are randomly selected on the etched sample surface, and at least ten secondary recrystallized grains are measured in each region. The equivalent circle diameter is statistically analyzed using image analysis software, and its arithmetic mean is calculated.

[0026] A second aspect of the present invention provides a method for preparing thin-strip continuous casting niobium-sulfur inhibitor oriented silicon steel, used to prepare the oriented silicon steel provided in the first aspect of the present invention, comprising the following steps: S1. After the molten steel is poured, it is cooled by water and air to room temperature to obtain the casting strip; S2. The cast strip is cold rolled in two stages to obtain a cold-rolled sheet; S3. Cold-rolled sheet is subjected to primary recrystallization annealing and secondary recrystallization annealing to obtain oriented silicon steel.

[0027] This invention utilizes a short-process technology for thin-strip continuous casting to produce grain-oriented silicon steel. It eliminates the need for hot rolling, significantly reducing energy consumption and production costs. Furthermore, it eliminates the need for decarburization annealing, reducing redundant steps and improving production efficiency. Specifically, in step S1, a vertical twin-roll thin-strip continuous casting machine is used to form the cast strip. Circulating water flows through the casting rolls to improve their thermal conductivity and accelerate steel solidification. During continuous casting, molten steel is guided through the casting nozzle to a preheated tundish at approximately 1190-1210°C. The molten steel in the tundish then flows through the gating nozzle into the molten pool formed by the crystallizing roll and the side sealing plate, where it rapidly solidifies at a cooling rate of 2000-4000°C / s. The side sealing plate is preheated to 700-1000°C before installation to prevent cracking from contact between the molten steel and the cold side sealing plate. The casting temperature is controlled at 1530~1540℃, and the casting superheat is 30~40℃. This superheat range effectively avoids the formation of coarse columnar crystals in the cast strip. The casting and rolling speed is set at 0.25~0.35m / s to ensure uniformity of the cast strip thickness. After exiting the casting roll, the cast strip is guided by a guide rail to a secondary cooling device. It is first cooled by water at a cooling rate of 40~60℃ / s to 800~900℃, and then air-cooled to room temperature.

[0028] Compared to the conventional one-stage cold rolling process, step S2 of this invention employs a two-stage cold rolling process, which can further improve the Goss texture ratio and secondary recrystallization rate, weaken the secondary cold rolling texture, and avoid non-Goss textures that occur in the one-stage cold rolling process ({112}). <110> The problem of abnormal grain growth. The specific process of the two-stage cold rolling process is as follows: the cast strip is pickled to remove the iron oxide scale, and then subjected to two-stage cold rolling. The reduction rate of the first stage cold rolling is 80%~85%, followed by intermediate annealing at 950~1000℃ for 5~7 minutes, and then the second stage cold rolling is performed with a reduction rate of 40%~45%. After the two-stage cold rolling, a cold-rolled sheet is obtained.

[0029] In step S3 of this invention, the cold-rolled sheet is held at 800-900℃ for 3-7 minutes for primary recrystallization annealing, allowing the cold-rolled deformed structure to fully recrystallize and form fine and uniform primary recrystallized grains. After the primary recrystallization annealing, an MgO release agent is applied to prevent oxidation of the sheet during high-temperature annealing and to provide lubrication. Subsequently, in a protective atmosphere of hydrogen and nitrogen in a volume ratio of 3:1, the temperature is slowly increased to 1100-1200℃ at a heating rate of 20-30℃ / h and held for 8-12 hours to complete the secondary recrystallization annealing. The slow heating process allows the NbS inhibitor to fully exert its effect, inhibiting the normal growth of matrix grains and promoting the abnormal growth of Goss grains. After the secondary recrystallization annealing, oriented silicon steel is obtained.

[0030] In one embodiment of the present invention, the reduction rate of the first stage cold rolling is twice the reduction rate of the second stage cold rolling.

[0031] In this invention, the inventors unexpectedly discovered that when the reduction rate of the first stage cold rolling is twice that of the reduction rate of the second stage cold rolling, the proportion of Goss texture and the secondary recrystallization rate can be further improved.

[0032] The present invention will now be described in detail with reference to preferred embodiments and comparative examples. The preferred embodiments of the invention described below can be modified in various ways, and therefore the scope of the invention should not be construed as limited to the preferred embodiments described in detail below. Preferred embodiments are provided to help those skilled in the art to more readily understand the invention.

[0033] Unless otherwise specified, the process conditions are all common knowledge or conventional choices in the field and have no substantial impact on the core technical effects of the present invention. Those skilled in the art can reasonably determine them, so they will not be described in detail here.

[0034] Example 1 A method for preparing thin-strip continuously cast niobium-sulfur inhibitor oriented silicon steel includes the following steps: S1. A vertical twin-roll thin strip continuous casting machine is used for continuous casting. During continuous casting, molten steel is guided through the casting nozzle to the tundish which has been preheated to 1190°C. The molten steel in the tundish then flows through the nozzle into the molten pool formed by the crystallizing roll and the side sealing plate. The molten steel solidifies rapidly at a cooling rate of 2000°C / s. The side sealing plate is preheated to 700°C before installation to prevent cracks from forming when the molten steel comes into contact with the cold side sealing plate. The casting temperature is controlled at 1530°C, the casting superheat is 30°C, and the casting and rolling speed is set to 0.25m / s. After the strip exits the casting roll, it is guided by the guide rail to the secondary cooling device. It is first cooled by water at a cooling rate of 40°C / s to 900°C, and then air cooled to room temperature. Molten steel is composed of the following components by weight percentage: C 0.003%, Si 2%, Nb 0.03%, S 0.03%, Mn 0.002%, Cu 0.002%, with the remainder being Fe and unavoidable impurity elements, (Nb+S) / (Mn+Cu)=15; S2. The cast strip is pickled to remove the iron oxide scale, and then subjected to two-stage cold rolling. The reduction rate of the first stage cold rolling is 80%, and then intermediate annealing is carried out at 950℃ for 7 minutes. Then, the second stage cold rolling is carried out with a reduction rate of 45%. After two-stage cold rolling, a cold-rolled sheet is obtained. S3. The above cold-rolled sheet is held at 800℃ for 7 minutes for the first recrystallization annealing. After the first recrystallization annealing, MgO release agent is coated. Then, in a mixed protective atmosphere of hydrogen and nitrogen with a volume ratio of 3:1, the temperature is slowly increased to 1100℃ at a heating rate of 20℃ / h and held for 12 hours to complete the second recrystallization annealing, thus obtaining oriented silicon steel.

[0035] Example 2 A method for preparing thin-strip continuously cast niobium-sulfur inhibitor oriented silicon steel includes the following steps: S1. A vertical twin-roll thin strip continuous casting machine is used for continuous casting. During continuous casting, molten steel is guided through the casting nozzle to the tundish which has been preheated to 1210°C. The molten steel in the tundish then flows through the nozzle into the molten pool formed by the crystallizing roll and the side sealing plate. The molten steel solidifies rapidly at a cooling rate of 4000°C / s. The side sealing plate is preheated to 1000°C before installation to prevent cracks from forming when the molten steel comes into contact with the cold side sealing plate. The casting temperature is controlled at 1540°C, the casting superheat is 40°C, and the casting and rolling speed is set to 0.35m / s. After the strip exits the casting roll, it is guided by the guide rail to the secondary cooling device. It is first cooled by water at a cooling rate of 60°C / s to 800°C, and then air cooled to room temperature. Molten steel is composed of the following components by weight percentage: C 0.001%, Si 3.5%, Nb 0.1%, S 0.1%, Mn 0.025%, Cu 0.025%, with the remainder being Fe and unavoidable impurity elements, (Nb+S) / (Mn+Cu)=4; S2. The cast strip is pickled to remove the iron oxide scale, and then subjected to two-stage cold rolling. The reduction rate of the first stage cold rolling is 85%. Then, it is annealed at 1000℃ for 5 minutes. Then, it is subjected to the second stage cold rolling with a reduction rate of 40%. After the two-stage cold rolling, a cold-rolled sheet is obtained. S3. The above cold-rolled sheet is held at 900℃ for 3 minutes for the first recrystallization annealing. After the first recrystallization annealing, MgO release agent is coated. Then, in a mixed protective atmosphere of hydrogen and nitrogen with a volume ratio of 3:1, the temperature is slowly increased to 1200℃ at a heating rate of 30℃ / h and held for 8 hours to complete the second recrystallization annealing, thus obtaining oriented silicon steel.

[0036] Example 3 A method for preparing thin-strip continuously cast niobium-sulfur inhibitor oriented silicon steel includes the following steps: S1. A vertical twin-roll thin strip continuous casting machine is used for continuous casting. During continuous casting, molten steel is guided through the casting nozzle to the tundish which has been preheated to 1200°C. The molten steel in the tundish then flows through the nozzle into the molten pool formed by the crystallizing roll and the side sealing plate. The molten steel solidifies rapidly at a cooling rate of 3000°C / s. The side sealing plate is preheated at 900°C before installation to prevent cracks from forming when the molten steel comes into contact with the cold side sealing plate. The casting temperature is controlled at 1535°C, the casting superheat is 35°C, and the casting and rolling speed is set at 0.3m / s. After the strip exits the casting roll, it is guided by the guide rail to the secondary cooling device. It is first cooled by water at a cooling rate of 50°C / s to 850°C, and then air cooled to room temperature. Molten steel is composed of the following components by weight percentage: C 0.002%, Si 3%, Nb 0.04%, S 0.04%, Mn 0.01%, Cu 0.01%, with the remainder being Fe and unavoidable impurity elements, (Nb+S) / (Mn+Cu)=4; S2. The cast strip is pickled to remove the iron oxide scale, and then subjected to two-stage cold rolling. The reduction rate of the first stage cold rolling is 85%. Then, it is annealed at 980℃ for 6 minutes. Then, it is subjected to the second stage cold rolling with a reduction rate of 41%. After the two-stage cold rolling, a cold-rolled sheet is obtained. S3. The above cold-rolled sheet is held at 850℃ for 5 minutes for the first recrystallization annealing. After the first recrystallization annealing, MgO release agent is coated. Then, in a mixed protective atmosphere of hydrogen and nitrogen with a volume ratio of 3:1, the temperature is slowly increased to 1150℃ at a heating rate of 25℃ / h and held for 10 hours to complete the second recrystallization annealing, thus obtaining oriented silicon steel.

[0037] Example 4 The only difference between this embodiment and Embodiment 3 is that in this embodiment, the molten steel is composed of the following components by weight percentage: C 0.002%, Si 3%, Nb 0.04%, S 0.04%, Mn 0.0027%, Cu 0.0027%, with the remainder being Fe and unavoidable impurity elements, and (Nb+S) / (Mn+Cu)=14.8.

[0038] Example 5 The only difference between this embodiment and embodiment 3 is that in this embodiment, the reduction rate of the first stage cold rolling is 80%, and the reduction rate of the second stage cold rolling is 41%.

[0039] Example 6 The only difference between this embodiment and embodiment 3 is that in this embodiment, the reduction rate of the first stage cold rolling is 82%, and the reduction rate of the second stage cold rolling is 41%.

[0040] Comparative Example 1 The only difference between this comparative example and Example 3 is that the molten steel in this comparative example is composed of the following components by weight percentage: C 0.002%, Si 3%, Nb 0.04%, S 0.04%, Mn 0.002%, Cu 0.002%, with the remainder being Fe and unavoidable impurity elements, and (Nb+S) / (Mn+Cu)=20.

[0041] Comparative Example 2 The only difference between this comparative example and Example 3 is that the molten steel in this comparative example is composed of the following components by weight percentage: C 0.002%, Si 3%, Nb 0.04%, S 0.04%, Mn 0.025%, Cu 0.025%, with the remainder being Fe and unavoidable impurity elements, and (Nb+S) / (Mn+Cu)=1.6.

[0042] Experimental Example 1 Microstructural analysis was performed on the grain-oriented silicon steels prepared in Examples 1-6. The results showed that the precipitates in the grain-oriented silicon steel of this invention included NbS with an average diameter of 20-40 nm, and the average diameter of the secondary recrystallized grains was 40-70 mm. The microstructure morphology of the grain-oriented silicon steel in Example 3 is shown in the image below. Figure 1 As shown.

[0043] Experimental Example 2 The magnetic induction B8 and iron loss P1.7 / 50 of the oriented silicon steels prepared in Examples 1-6 and Comparative Examples 1-2 were measured according to GB / T 3655-2022. The test results are shown in Table 1 below.

[0044] Table 1 Test results of magnetic induction and iron loss

[0045] Example 3 The secondary recrystallization rate and Goss texture orientation density f(g) of Examples 3 and 5-6 were tested. The secondary recrystallization rate was tested by etching 150mm × 100mm oriented silicon steel with 40% hydrochloric acid at 50℃ for 5 minutes. Under a microscope, the coarse Goss grains appeared as rectangular patches, representing the secondary recrystallization region, while the fine-grained matrix represented the non-recrystallized region. The percentage of the secondary recrystallized region area to the total area was used as the secondary recrystallization rate. The Goss texture orientation density was tested by acquiring three pole figures ({110}, {200}, and {211}) using an X-ray diffractometer (Cu target), calculating the three-dimensional ODF using series expansion, and reading the Goss orientation density f(g). The test results are shown in Table 2 below.

[0046] Table 2. Test results of secondary recrystallization rate and Goss texture orientation density

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit 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 thin-strip continuously cast niobium-sulfur inhibitor oriented silicon steel, characterized in that, It is composed of the following components by weight percentage: C≤0.003%, Si 2%~3.5%, Nb 0.03%~0.1%, S 0.03%~0.1%, Mn 0.002%~0.025%, Cu 0.002%~0.025%, with the remainder being Fe and unavoidable impurity elements; By weight percentage, the Nb, S, Mn and Cu satisfy the following relationship: (Nb+S) / (Mn+Cu)=4~15.

2. The thin-strip continuously cast niobium sulfur inhibitor oriented silicon steel according to claim 1, characterized in that, The precipitates in the oriented silicon steel include NbS.

3. The thin-strip continuously cast niobium sulfur inhibitor oriented silicon steel according to claim 2, characterized in that, The average diameter of the NbS is 20~40 nm.

4. A thin-strip continuously cast niobium sulfur inhibitor oriented silicon steel according to any one of claims 1 to 3, characterized in that, The average diameter of the secondary recrystallized grains in the oriented silicon steel is 40~70mm.

5. A method for preparing thin-strip continuously cast niobium-sulfur inhibitor oriented silicon steel according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. After the molten steel is poured, it is cooled by water and air to room temperature to obtain the casting strip; S2. The cast strip is cold rolled in two stages to obtain a cold-rolled sheet; S3. The cold-rolled sheet is subjected to primary recrystallization annealing and secondary recrystallization annealing to obtain the oriented silicon steel.

6. The method for preparing thin-strip continuously cast niobium sulfur inhibitor oriented silicon steel according to claim 5, characterized in that, In step S1, the water cooling specifically refers to cooling to 800-900℃ at a cooling rate of 40-60℃ / s.

7. The method for preparing thin-strip continuously cast niobium sulfur inhibitor oriented silicon steel according to claim 5, characterized in that, In step S2, the two-stage cold rolling includes a first-stage cold rolling, intermediate annealing, and a second-stage cold rolling. The reduction rate of the first stage cold rolling is 80%~85%, and the reduction rate of the second stage cold rolling is 40%~45%. The intermediate annealing temperature is 950~1000℃, and the time is 5~7 minutes.

8. The method for preparing thin-strip continuously cast niobium sulfur inhibitor oriented silicon steel according to claim 7, characterized in that, The reduction rate of the first stage cold rolling is twice that of the second stage cold rolling.

9. The method for preparing thin-strip continuously cast niobium sulfur inhibitor oriented silicon steel according to claim 5, characterized in that, The initial recrystallization annealing temperature is 800~900℃, and the time is 3~7min.

10. The method for preparing thin-strip continuously cast niobium sulfur inhibitor oriented silicon steel according to claim 5, characterized in that, The secondary recrystallization annealing temperature is 1100~1200℃, and the time is 8~12h.

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