Method for reducing brittle fracture of non-oriented silicon steel hot-rolled curled edge part with silicon content of 3.2% or above

Abstract

The invention discloses a method for reducing brittle failure of a non-oriented silicon steel hot-rolled hemming part with the silicon content of 3.2% or above, and belongs to the technical field of metallurgical materials. The method comprises the steps that a converter is adopted for smelting, RH is adopted for vacuum treatment, nitrogen and oxygen content is strictly controlled, generation of an oxide brittle phase is restrained, a plate blank with the thickness of 230 mm is formed through continuous casting, the pulling speed is 0.8-0.9 m / min, the plate blank is placed in a heat preservation pit or stacked in a concentrated mode for slow cooling, and the situation that corner cracks are possibly generated due to the fact that the edge of the plate blank is cooled fast is reduced; plate blank hot charging heating is adopted, and the charging temperature is not lower than 350 DEG C; the heating temperature is 1110 + / -10 DEG C, and the heat preservation time is 180-220 minutes; the rough rolling reduction is greater than 45mm; the reduction rate of the first pass of finish rolling is larger than 35%; the densified laminar cooling adopts post-dispersion, and a grain recrystallization and growth process is carried out for 5-8 seconds from an outlet of a rolling mill to a laminar cooling section. The invention aims to improve the phenomenon that the edge part of the hot-rolled plate is relatively brittle through reasonable measures.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and in particular relates to a method for reducing the brittle fracture of hot-rolled edge of non-oriented silicon steel with a silicon content of more than 3.2%. Background Technology

[0002] Currently, patent application number 202411304380.8 discloses a method for improving the edge quality of cold-rolled high-grade non-oriented silicon steel burr coils, focusing on the goal of controlling edge cracks and reducing edge waviness in the cold rolling process of high-grade non-oriented silicon steel. This invention focuses on improving the edge quality of hot-rolled high-silicon non-oriented silicon steel, reducing edge brittleness, and decreasing the rework rate in subsequent processes due to edge brittleness.

[0003] Patent application number 202310785904.9 discloses a method for controlling transverse crack defects at the edge of cold-rolled non-oriented silicon steel containing ≥3.0% Si. The method focuses on controlling the thickness difference between the edge sections of hot-rolled strip steel to reduce the incidence of transverse cracks at the edge of cold-rolled strips. This invention reduces the edge brittleness of hot-rolled coils and decreases the rework rate in subsequent processes by strictly controlling the oxide phase elements in the composition, the heating regime, and the placement policy of the slab and hot-rolled coil.

[0004] With the rapid development of the new energy and robotics industries, the requirements for non-oriented silicon steel used in core components like motors are becoming increasingly stringent. These requirements extend beyond magnetic properties to include mechanical properties, particularly strength. High-strength non-oriented silicon steel ensures that the motor does not deform during high-speed operation, maintaining a good level of iron loss. High-strength non-oriented silicon steel requires more alloying elements for support; the simplest and most effective method is to increase the silicon content. This improves both strength and magnetic properties without negatively impacting the magnetic properties. However, increasing the silicon content makes the steel coil more brittle, especially at the edges. Summary of the Invention

[0005] The purpose of this invention is to provide a method for reducing the brittle fracture of hot-rolled coil edges of non-oriented silicon steel with a silicon content of more than 3.2%, thereby improving the brittle edge phenomenon of hot-rolled plates through reasonable measures.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses a method for reducing brittle fracture at the edge of hot-rolled non-oriented silicon steel with a silicon content of 3.2% or more, comprising:

[0008] The smelting process is carried out in a converter, and vacuum treatment is performed in RH. The nitrogen and oxygen content is strictly controlled to suppress the formation of brittle oxide phases. The slabs are continuously cast into 230mm thick slabs at a casting speed of 0.8-0.9m / min. The slabs are placed in a heat preservation pit or stacked in a centralized manner for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges of the slabs.

[0009] Hot charging of slabs is adopted, with a charging temperature of not less than 350℃; heating temperature of 1110±10℃, holding time of 180-220min, and maximum exit temperature of not more than 1120℃. In order to minimize the oxidation and iron oxide scale formation during the heating process, the residual oxygen value of the heating furnace is controlled at <1.0%.

[0010] The roughing reduction is greater than 45mm, which on the one hand destroys the surface oxide layer, and on the other hand can destroy the columnar crystals of the slab and promote subsequent recrystallization; the first pass of finishing rolling has a reduction rate of more than 35%, which breaks the initial oxide layer; the dense laminar flow cooling adopts post-dispersion, and there is a 5-8s process of grain recrystallization and growth from the mill exit to the laminar cooling section.

[0011] Furthermore, the chemical composition of the non-oriented silicon steel by mass percentage is as follows: C: ≤0.0025%, Si: 3.20-3.50%, Mn: 0.30-0.60%, P: ≤0.025%, S: ≤0.0020%, Als: 0.80-1.0%, N: ≤0.0020%, O ≤0.0015%, Sn: 0.030-0.050%, Ti: ≤0.0025%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0012] Furthermore, the specific steps include the following:

[0013] Step a: Smelting is carried out in a converter, and vacuum treatment is performed in RH to strictly control the nitrogen and oxygen content and suppress the formation of brittle oxide phases;

[0014] Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting is used to cast 230mm thick slabs at a casting speed of 0.82m / min. The slabs are placed in a heat preservation pit or stacked in a centralized manner for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges of the slabs.

[0015] Step c: Furnace temperature 385℃, total holding time 185min, furnace exit temperature 1118℃, roughing first pass reduction 46mm, finishing first pass reduction 42%; post-dispersion laminar flow cooling is adopted; hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom.

[0016] Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.78%.

[0017] Furthermore, the chemical composition of the non-oriented silicon steel by mass percentage is as follows: C: 0.0024%, Si: 3.28%, Mn: 0.31%, P: 0.014%, S: 0.0014%, Als: 0.91%, Sn: 0.042%, N: 0.0016%, O: 0.0008%, Ti: 0.0014%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0018] Furthermore, the specific steps include the following:

[0019] Step a: Smelting is carried out in a converter, and vacuum treatment is performed in RH to strictly control the nitrogen and oxygen content and suppress the formation of brittle oxide phases;

[0020] Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting is used to cast 230mm thick slabs at a casting speed of 0.85m / min. The slabs are placed in a heat preservation pit or stacked in a centralized manner for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges of the slabs.

[0021] Step c: Furnace temperature 421℃, total holding time 196min, furnace exit temperature 1116℃, roughing first pass reduction 48mm, finishing first pass reduction 45%; post-dispersion laminar flow cooling is adopted; hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom.

[0022] Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.81%.

[0023] Furthermore, the chemical composition of the non-oriented silicon steel by mass percentage is as follows: C: 0.0025%, Si: 3.32%, Mn: 0.42%, P: 0.014%, S: 0.0015%, Als: 0.89%, Sn: 0.045%, N: 0.0014%, O: 0.0007%, Ti: 0.0016%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0024] Furthermore, the specific steps include the following:

[0025] Step a: Smelting is carried out in a converter, and vacuum treatment is performed in RH to strictly control the nitrogen and oxygen content and suppress the formation of brittle oxide phases;

[0026] Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting is used to cast 230mm thick slabs at a casting speed of 0.80m / min. The slabs are placed in a heat preservation pit or stacked in a centralized manner for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges of the slabs.

[0027] Step c: Furnace temperature 455℃, total holding time 205min, furnace exit temperature 1118℃, roughing first pass reduction 47mm, finishing first pass reduction 43%; post-dispersion laminar flow cooling is adopted; hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom.

[0028] Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.93%.

[0029] Furthermore, the chemical composition of the non-oriented silicon steel by mass percentage is as follows: C: 0.0023%, Si: 3.45%, Mn: 0.45%, P: 0.015%, S: 0.0015%, Als: 0.92%, Sn: 0.046%, N: 0.0016%, O: 0.0010%, Ti: 0.0017%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0030] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0031] This invention develops a hot-rolled raw material for producing high-grade non-oriented silicon steel. The composition, process design, and slab and hot-rolled coil placement policy can effectively reduce edge brittleness, reduce the user rework rate to below 2%, and greatly reduce the user's production costs. Detailed Implementation

[0032] The present invention will be further described in conjunction with the embodiments:

[0033] The test material was a hot-rolled sample of high-grade non-oriented silicon steel, with the following chemical composition: C: ≤0.0025%, Si: 3.20-3.50%, Mn: 0.30-0.60%, P: ≤0.025%, S: ≤0.0020%, Als: 0.80-1.0%, N: ≤0.0020%, O ≤0.0015%, Sn: 0.030-0.050%, Ti: ≤0.0025%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass. Examples 1-3 illustrate the process steps used in the preparation of a high-grade non-oriented silicon steel hot-rolled strip according to the present invention.

[0034] Example 1

[0035] Step a: Smelting is carried out in a converter, followed by vacuum treatment with RH to strictly control the nitrogen and oxygen content and suppress the formation of brittle oxide phases. The composition is: C: 0.0024%, Si: 3.28%, Mn: 0.31%, P: 0.014%, S: 0.0014%, Als: 0.91%, Sn: 0.042%, N: 0.0016%, O: 0.0008%, Ti: 0.0014%.

[0036] Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting produces 230mm thick slabs at a casting speed of 0.82m / min. The slabs are placed in a heat preservation pit or stacked for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges.

[0037] Step c: Furnace entry temperature 385℃, total holding time 185min, furnace exit temperature 1118℃, roughing first pass reduction 46mm, finishing first pass reduction 42%. Post-dispersed laminar flow cooling is adopted. Hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom.

[0038] Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.78%.

[0039] Example 2

[0040] Step a: Smelting is carried out in a converter, followed by vacuum treatment with RH to strictly control the nitrogen and oxygen content and suppress the formation of brittle oxide phases. The composition is: C: 0.0025%, Si: 3.32%, Mn: 0.42%, P: 0.014%, S: 0.0015%, Als: 0.89%, Sn: 0.045%, N: 0.0014%, O: 0.0007%, Ti: 0.0016%.

[0041] Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting produces 230mm thick slabs at a casting speed of 0.85m / min. The slabs are placed in an insulation pit or stacked for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges.

[0042] Step c: Furnace entry temperature 421℃, total holding time 196min, furnace exit temperature 1116℃, roughing first pass reduction 48mm, finishing first pass reduction 45%. Post-dispersed laminar flow cooling is adopted. Hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom.

[0043] Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.81%.

[0044] Example 3

[0045] Step a: Smelting is carried out in a converter, followed by vacuum treatment with RH to strictly control nitrogen and oxygen content and suppress the formation of brittle oxide phases. The composition is: C: 0.0023%, Si: 3.45%, Mn: 0.45%, P: 0.015%, S: 0.0015%, Als: 0.92%, Sn: 0.046%, N: 0.0016%, O: 0.0010%, Ti: 0.0017%.

[0046] Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting produces 230mm thick slabs at a casting speed of 0.80m / min. The slabs are placed in a heat preservation pit or stacked for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges.

[0047] Step c: Furnace entry temperature 455℃, total holding time 205min, furnace exit temperature 1118℃, roughing first pass reduction 47mm, finishing first pass reduction 43%. Post-dispersive laminar flow cooling is adopted. Hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom.

[0048] Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.93%.

[0049] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for reducing brittle fracture at the edge of hot-rolled coils of non-oriented silicon steel with a silicon content of 3.2% or more, characterized in that, include: The smelting process is carried out in a converter, and vacuum treatment is performed in RH. The nitrogen and oxygen content is strictly controlled to suppress the formation of brittle oxide phases. The slabs are continuously cast into 230mm thick slabs at a casting speed of 0.8-0.9m / min. The slabs are placed in a heat preservation pit or stacked in a centralized manner for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges of the slabs. Hot charging of slabs is adopted, with a charging temperature of not less than 350℃; heating temperature of 1110±10℃, holding time of 180-220min, and maximum exit temperature of not more than 1120℃. In order to minimize the oxidation and iron oxide scale formation during the heating process, the residual oxygen value of the heating furnace is controlled at <1.0%. The roughing reduction is greater than 45mm, which on the one hand destroys the surface oxide layer, and on the other hand can destroy the columnar crystals of the slab and promote subsequent recrystallization; the first pass of finishing rolling has a reduction rate of more than 35%, which breaks the initial oxide layer; the dense laminar flow cooling adopts post-dispersion, and there is a 5-8s process of grain recrystallization and growth from the mill exit to the laminar cooling section.

2. The method for reducing the brittle fracture of the hot-rolled edge of non-oriented silicon steel with a silicon content of 3.2% or more according to claim 1, characterized in that, The chemical composition of the non-oriented silicon steel by mass percentage is as follows: C: ≤0.0025%, Si: 3.20-3.50%, Mn: 0.30-0.60%, P: ≤0.025%, S: ≤0.0020%, Als: 0.80-1.0%, N: ≤0.0020%, O ≤0.0015%, Sn: 0.030-0.050%, Ti: ≤0.0025%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

3. The method for reducing the brittle fracture of the hot-rolled edge of non-oriented silicon steel with a silicon content of 3.2% or more according to claim 1, characterized in that, Specifically, the steps include the following: Step a: Smelting is carried out in a converter, and vacuum treatment is performed in RH to strictly control the nitrogen and oxygen content and suppress the formation of brittle oxide phases; Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting is used to cast 230mm thick slabs at a casting speed of 0.82m / min. The slabs are placed in a heat preservation pit or stacked in a centralized manner for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges of the slabs. Step c: Furnace temperature 385℃, total holding time 185min, furnace exit temperature 1118℃, roughing first pass reduction 46mm, finishing first pass reduction 42%; post-dispersion laminar flow cooling is adopted; hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom. Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.78%.

4. The method for reducing the brittle fracture of the hot-rolled edge of non-oriented silicon steel with a silicon content of more than 3.2% according to claim 3, characterized in that, The chemical composition of the non-oriented silicon steel by mass percentage is as follows: C: 0.0024%, Si: 3.28%, Mn: 0.31%, P: 0.014%, S: 0.0014%, Als: 0.91%, Sn: 0.042%, N: 0.0016%, O: 0.0008%, Ti: 0.0014%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

5. The method for reducing the brittle fracture of the hot-rolled edge of non-oriented silicon steel with a silicon content of more than 3.2% according to claim 1, characterized in that, Specifically, the steps include the following: Step a: Smelting is carried out in a converter, and vacuum treatment is performed in RH to strictly control the nitrogen and oxygen content and suppress the formation of brittle oxide phases; Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting is used to cast 230mm thick slabs at a casting speed of 0.85m / min. The slabs are placed in a heat preservation pit or stacked in a centralized manner for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges of the slabs. Step c: Furnace temperature 421℃, total holding time 196min, furnace exit temperature 1116℃, roughing first pass reduction 48mm, finishing first pass reduction 45%; post-dispersion laminar flow cooling is adopted; hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom. Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.81%.

6. The method for reducing the brittle fracture of the hot-rolled edge of non-oriented silicon steel with a silicon content of more than 3.2% according to claim 5, characterized in that, The chemical composition of the non-oriented silicon steel by mass percentage is as follows: C: 0.0025%, Si: 3.32%, Mn: 0.42%, P: 0.014%, S: 0.0015%, Als: 0.89%, Sn: 0.045%, N: 0.0014%, O: 0.0007%, Ti: 0.0016%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

7. The method for reducing the brittle fracture of the hot-rolled edge of non-oriented silicon steel with a silicon content of 3.2% or more according to claim 1, characterized in that, Specifically, the steps include the following: Step a: Smelting is carried out in a converter, and vacuum treatment is performed in RH to strictly control the nitrogen and oxygen content and suppress the formation of brittle oxide phases; Step b: Electromagnetic stirring is used in continuous casting. The electromagnetic stirring section is the first section of the continuous casting machine, with a current of 600A and a frequency of 5Hz. The continuous casting is used to cast 230mm thick slabs at a casting speed of 0.80m / min. The slabs are placed in a heat preservation pit or stacked in a centralized manner for slow cooling to reduce the risk of corner cracks caused by rapid cooling at the edges of the slabs. Step c: Furnace temperature 455℃, total holding time 205min, furnace exit temperature 1118℃, roughing first pass reduction 47mm, finishing first pass reduction 43%; post-dispersion laminar flow cooling is adopted; hot-rolled steel coils are stacked in a concentrated manner for slow cooling, with ordinary hot-rolled coils at the bottom. Step d: For this batch of hot-rolled coils, the rework rate in the subsequent normalizing process of the user is controlled at 1.93%.

8. The method for reducing the brittle fracture of the hot-rolled edge of non-oriented silicon steel with a silicon content of 3.2% or more according to claim 7, characterized in that, The chemical composition of the non-oriented silicon steel by mass percentage is as follows: C: 0.0023%, Si: 3.45%, Mn: 0.45%, P: 0.015%, S: 0.0015%, Als: 0.92%, Sn: 0.046%, N: 0.0016%, O: 0.0010%, Ti: 0.0017%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.