Soft magnetic steel smelting method

Abstract

The invention relates to the technical field of metallurgy, in particular to a soft magnetic steel smelting method which comprises the following process steps: 1) raw material pretreatment; 2) vacuum induction melting; (3) carrying out multi-stage vacuum degassing; 4) continuously casting and forming; 5) cooling and annealing; (6) surface treatment; the nitrogen source is strictly controlled from the source, so that the denitrification pressure in subsequent treatment is reduced, and the risk of nitride inclusion is reduced; molten steel obtained after smelting is treated through a multi-stage vacuum degassing device, harmful gas (such as hydrogen and oxygen) in the molten steel is effectively removed, meanwhile, the nitrogen content is greatly reduced, and the purity and magnetic performance of materials are ensured; the nitrogen content of the process product is low, and the influence of nitride inclusion on the material is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and more specifically to a method for smelting soft magnetic steel. Background Art

[0002] The introduction of nitrogen and other nitrogen-containing substances is a common problem in the smelting process of soft magnetic steel. Nitrogen will cause nitride inclusions to form at the grain boundaries of soft magnetic steel, reducing the magnetic permeability of the material and increasing the coercive force, thereby affecting the magnetic properties of soft magnetic steel; nitride inclusions may also change the hardness and toughness of the material, especially in the case of high nitrogen content, which may increase the brittleness of soft magnetic steel; nitride inclusions will affect the plasticity and weldability of the material, making subsequent processing more difficult.

[0003] It is difficult to effectively control the nitrogen content by traditional smelting methods, which is mainly reflected in the following aspects: In the smelting stage: if the raw materials (such as scrap steel, alloy additives) contain a high nitrogen content, these nitrogen may be released during high-temperature smelting and mixed into the molten steel; in the refining stage, in order to remove harmful gases (such as hydrogen and oxygen) in the steel, argon blowing or vacuum treatment is often used, but if the operation is improper or the equipment is not tightly sealed, nitrogen in the outside air may also enter the system; in the casting and rolling stages, if the cast billet is exposed to the air during the cooling process, a small amount of nitrogen may be absorbed on the steel surface; the rolling oil or lubricant used in the cold rolling process sometimes contains nitrogen-containing compounds, which may release nitrogen after decomposition at high temperatures.

[0004] Therefore, developing a soft magnetic steel smelting method that can efficiently and stably achieve ultra-low nitrogen content has important practical significance and technical value. Summary of the invention

[0005] The object of the present invention is to provide a soft magnetic steel smelting method, the nitrogen content of the product is low, and the influence of nitride inclusions on the material is avoided.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A soft magnetic steel smelting method comprises the following process steps:

[0008] 1) Raw material pretreatment: Select iron ore and scrap steel with low nitrogen content as the main raw materials, and add appropriate amounts of alloy elements such as silicon, aluminum, and nickel to ensure that the nitrogen content in the raw materials is less than 0.005wt%;

[0009] 2) Vacuum induction melting: Place the raw materials in a vacuum induction furnace for melting, maintain the absolute pressure in the furnace at no more than 10Pa, the melting temperature is 1450°C to 1550°C, the melting time is 60 minutes to 90 minutes, and argon is used for protection during the melting process;

[0010] 3) Multi-stage vacuum degassing: The molten steel after smelting is treated by a multi-stage vacuum degassing device, with each stage of degassing time not less than 40 minutes and the total degassing time not less than 150 minutes;

[0011] 4) Continuous casting: The degassed molten steel is directly cast into slabs or strips through a continuous casting machine;

[0012] 5) Cooling and annealing: The as-cast billet is cooled rapidly, followed by a low-temperature short-time annealing treatment;

[0013] 6) Surface treatment: Apply protective coating on the surface of the finished product according to application requirements.

[0014] Furthermore, the purity of the argon gas in step 2) is ≥ 99.999%.

[0015] Furthermore, in step 3), a nitrogen trap is provided in the vacuum degassing device.

[0016] Furthermore, in step 4), electromagnetic stirring technology is used during the continuous casting process to promote uniform flow of molten steel.

[0017] Furthermore, in step 5), the cooling method is spray cooling or gas quenching to rapidly cool the cast billet to room temperature, the temperature range of the low-temperature short-time annealing treatment is 450° C. to 550° C., and the annealing time is 1.5 hours to 2.5 hours.

[0018] Furthermore, in step 6), the protective coating is a polyurethane insulating coating.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention selects iron ore and scrap steel with nitrogen content lower than 0.005wt% as main raw materials, and adds appropriate amounts of alloy elements such as silicon, aluminum, nickel, etc., to ensure strict control of nitrogen source from the source, thereby reducing denitrification pressure in subsequent treatment and reducing the risk of nitride inclusions; the molten steel after smelting is treated by a multi-stage vacuum degassing device, which effectively removes harmful gases (such as hydrogen and oxygen) in the molten steel, and at the same time greatly reduces the nitrogen content, ensuring the purity and magnetic properties of the material; the nitrogen content of the product of this process is low, avoiding the influence of nitride inclusions on the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is an operation flow chart of the smelting process of the present invention. DETAILED DESCRIPTION

[0022] like Figure 1 As shown, a soft magnetic steel smelting method includes the following process steps:

[0023] 1) Raw material pretreatment: Select iron ore and scrap steel with low nitrogen content as the main raw materials, and add appropriate amounts of alloy elements such as silicon, aluminum, and nickel to ensure that the nitrogen content in the raw materials is less than 0.005wt%;

[0024] 2) Vacuum induction melting: Place the raw materials in a vacuum induction furnace for melting, maintain the absolute pressure in the furnace at no more than 10Pa, the melting temperature is 1450°C to 1550°C, the melting time is 60 minutes to 90 minutes, and argon is used for protection during the melting process;

[0025] 3) Multi-stage vacuum degassing: The molten steel after smelting is treated by a multi-stage vacuum degassing device, with each stage of degassing time not less than 40 minutes and the total degassing time not less than 150 minutes;

[0026] 4) Continuous casting: The degassed molten steel is directly cast into slabs or strips through a continuous casting machine;

[0027] 5) Cooling and annealing: The as-cast billet is cooled rapidly, followed by a low-temperature short-time annealing treatment;

[0028] 6) Surface treatment: Apply protective coating on the surface of the finished product according to application requirements.

[0029] The purity of the argon gas in step 2) is ≥ 99.999%.

[0030] In step 3), a nitrogen trap is provided in the vacuum degassing device.

[0031] In step 4), electromagnetic stirring technology is used during the continuous casting process to promote uniform flow of molten steel.

[0032] In step 5), the cooling method is spray cooling or gas quenching to quickly cool the cast billet to room temperature. The temperature range of the low-temperature short-time annealing treatment is 450° C. to 550° C., and the annealing time is 1.5 hours to 2.5 hours.

[0033] In step 6), the protective coating is a polyurethane insulating coating.

[0034] Process flow:

[0035] Iron ore and scrap steel with low nitrogen content are selected as the main raw materials, and appropriate amounts of alloying elements such as silicon, aluminum, and nickel are added to ensure that the nitrogen content in the raw materials is less than 0.005wt%; the raw materials are placed in a vacuum induction furnace for smelting, and the absolute pressure in the furnace is maintained at no more than 10Pa. The smelting temperature is 1450°C to 1550°C, and the smelting time is 60 minutes to 90 minutes. During the smelting process, argon gas with a purity of ≥99.999% is used for protection to ensure that the smelting atmosphere is pure and free of nitrogen; the smelted molten steel is treated by a multi-stage vacuum degassing device, with each stage of degassing time being no less than 40 minutes and the total degassing time being no less than 150 minutes. A nitrogen trap is set in the degassing device to absorb nitrogen. The residual nitrogen molecules are attached and removed to ensure that the nitrogen content is reduced to a minimum; the degassed molten steel is directly poured into slabs or strips through a continuous casting machine. Electromagnetic stirring technology is used during the continuous casting process to promote uniform flow of molten steel, reduce internal defects, and ensure that the surface of the cast billet is smooth and the internal structure is uniform and dense; the cast billet is rapidly cooled to room temperature by spray cooling or gas quenching, and then subjected to low-temperature annealing treatment in the range of 450°C to 550°C for 1.5 to 2.5 hours to restore the material's optimal magnetic properties; according to application requirements, a polyurethane insulating coating is applied to the surface of the finished product to ensure uniform coating thickness, strong adhesion, good weather resistance, and enhance the product's protective performance.

[0036] This process ensures that the material has excellent magnetic permeability and coercivity by strictly controlling the nitrogen content, improves the magnetic properties of soft magnetic steel, and avoids the impact of nitride inclusions on the material.

[0037] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for smelting soft magnetic steel, characterized in that The process steps include: 1) Raw material pretreatment: Select iron ore and scrap steel with low nitrogen content as the main raw materials, and add appropriate amounts of alloy elements such as silicon, aluminum, and nickel to ensure that the nitrogen content in the raw materials is less than 0.005wt%; 2) Vacuum induction melting: Place the raw materials in a vacuum induction furnace for melting, maintain the absolute pressure in the furnace at no more than 10Pa, the melting temperature is 1450°C to 1550°C, the melting time is 60 minutes to 90 minutes, and argon is used for protection during the melting process; 3) Multi-stage vacuum degassing: The molten steel after smelting is treated by a multi-stage vacuum degassing device, with each stage of degassing time not less than 40 minutes and the total degassing time not less than 150 minutes; 4) Continuous casting: The degassed molten steel is directly cast into slabs or strips through a continuous casting machine; 5) Cooling and annealing: The as-cast billet is cooled rapidly, followed by a low-temperature short-time annealing treatment; 6) Surface treatment: Apply protective coating on the surface of the finished product according to application requirements.

2. The soft magnetic steel smelting method according to claim 1, characterized in that: The purity of the argon gas in step 2) is ≥ 99.999%.

3. The soft magnetic steel smelting method according to claim 1, characterized in that: In step 3), a nitrogen trap is provided in the vacuum degassing device.

4. The soft magnetic steel smelting method according to claim 1, characterized in that: In step 4), electromagnetic stirring technology is used during the continuous casting process to promote uniform flow of molten steel.

5. The soft magnetic steel smelting method according to claim 1, characterized in that: In step 5), the cooling method is spray cooling or gas quenching to quickly cool the cast billet to room temperature. The temperature range of the low-temperature short-time annealing treatment is 450° C. to 550° C., and the annealing time is 1.5 hours to 2.5 hours.

6. The soft magnetic steel smelting method according to claim 1, characterized in that: In step 6), the protective coating is a polyurethane insulating coating.

Images