CN118638989A - A method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strip - Google Patents

Abstract

The invention relates to a method for realizing continuous annealing treatment of unoriented high-grade high-silicon thin strips, which comprises the following steps: 1) Chemical composition control; controlling C in steel to be less than or equal to 0.0025 percent, S is less than or equal to 0.0010 percent, N is less than or equal to 0.0012%; adding lanthanide rare earth elements, copper elements and grain boundary segregation elements into steel; 2) Continuous annealing treatment control; and adopting a cold-rolled non-oriented silicon steel thin strip continuous annealing unit to perform heat treatment under the protection of a full nitrogen atmosphere. According to the invention, under the condition of the existing production process equipment of the high-grade high-silicon aluminum thin strip, on the basis of strict control of steel cleanliness, the heat treatment of the finished product is carried out in a total nitrogen protective atmosphere by adding various beneficial elements, the surface layer and substrate oxidation nitriding defects of the product are avoided, and the electromagnetic performance is excellent; the continuous annealing unit can be operated with high efficiency and low cost, and a high-performance product with market competitiveness is produced.

Description

A method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strip

Technical Field

The invention relates to the technical field of non-oriented silicon steel production, and in particular to a method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strips at low cost.

Background Art

With the development of frequency conversion technology, high-power density motors designed for high-speed operation, such as new energy vehicle drive motors, drones and micro motors, have developed rapidly, and the demand for cold-rolled non-oriented electrical steel high-silicon and high-aluminum thin strip products has also increased.

In order to meet the functional characteristics of high-frequency, high-speed and high-power density motors for new energy vehicle drive motors (key points include: low loss - corresponding to long cruising range, high strength - corresponding to high power density and high-speed operation, high magnetic flux density - corresponding to fast response and high torque, etc.), the composition design of non-oriented, high-grade, high-silicon thin strip products is usually that the main alloy Si ≥ 3.0%, Als ≥ 0.60%, and the product thickness specification is less than 0.35mm (typical industrial product specifications are 0.30mm, 0.27mm, 0.25mm, 0.23mm, 0.20mm and 0.15mm), and there is a trend of further thinning.

The heat treatment of existing non-oriented silicon steel products is usually completed by a multifunctional continuous annealing unit. In order to quickly raise the temperature of the steel strip, NOF open flame heating is often used (but the surface of the steel strip is easily oxidized). Due to the limitations of the spacing and operating tension of the conveying rollers in the furnace, it is only suitable for the heat treatment of thin strips with specifications above 0.25mm. As the specifications of non-oriented silicon steel thin strip products are further thinned, the specific surface area of the steel strip is increased (the structure is only a single grain under the thickness of the matrix section), and the surface reaction activity is relatively improved. In addition, due to the increase in the content of silicon and aluminum elements in the main alloy components of the product, under the traditional continuous annealing protective atmosphere conditions (such as 80% _N2 +20% _H2 +dew point control under corresponding conditions), oxidation and nitridation are very likely to occur and an oxidation and nitridation layer is formed inside and outside the matrix, which deteriorates the comprehensive performance indicators such as the electromagnetic properties and product strength of the product.

In order to solve the problem of oxidation and nitridation in the heat treatment of high-silicon and high-aluminum thin strips, the NOF open flame heating section was cancelled in the newly developed thin strip continuous annealing unit production line; the protective atmosphere was adjusted, and the _H2 content in the furnace could reach more than 70%, and even full hydrogen production was adopted (such as a "cold-rolled non-oriented silicon steel thin strip continuous annealing cooling control method" disclosed in the Chinese invention patent with authorization announcement number CN 111926171 B), and measures such as shortening the gap between the bottom rollers in the process section were taken. However, with the increase in production scale, the supply of hydrogen, the matching of equipment capacity, the safety of the overall system operation, and the production cost of the product are all affected.

The Chinese invention patent with application number CN202210093017.0 discloses "a high magnetic induction, high strength, cerium-containing, copper-containing non-oriented silicon steel and a manufacturing method". By alloying copper, cerium, etc. and coordinating appropriate rolling and heat treatment processes, the precipitation strengthening of copper and the role of cerium in metamorphic inclusions, grain size regulation, and texture improvement are fully utilized to develop high-strength non-oriented electrical steel with excellent magnetic properties, thereby improving the strength of non-oriented silicon steel while ensuring magnetic properties.

The Chinese patent application with application number CN201911152829.2 discloses "A Ce-containing high magnetic induction non-oriented silicon steel and preparation method", which uses thin slab continuous casting and rolling technology to produce a Ce-containing high magnetic induction non-oriented silicon steel. The mechanism of rare earth Ce metamorphic inclusion, grain size regulation, and favorable texture improvement is fully utilized, and the CSP (thin slab continuous casting and rolling) technology of thin slab hot delivery and hot rolling is used for preparation. The prepared high magnetic induction non-oriented silicon steel containing rare earth element Ce has a magnetic induction intensity B50 of up to 1.804T.

The Chinese patent application with application number CN202011026376.1 discloses "A normalizing treatment method for preventing internal oxidation of non-oriented silicon steel". It is designed for the oxidation of non-oriented silicon steel during the normalizing process. It is mainly achieved by removing the surface oxide scale through straightening and phosphorus breaking and pickling, and annealing in a non-oxidizing atmosphere. It is not suitable for the control of oxidation and nitridation in the annealing process of the finished product.

The Chinese invention patent with application number CN201110415947.5 discloses "a method for producing high-grade non-oriented silicon steel", which mainly uses a lower process heat treatment temperature to control oxidation, but its control of electromagnetic properties increases the difficulty of production and is not easy to achieve.

The Chinese patent application with application number CN202310130637.1 discloses "a method for preparing high-frequency, low-iron-loss non-oriented silicon steel for new energy vehicle drive motors". By controlling the annealing speed and atmosphere, non-oriented silicon steel with good surface condition is obtained.

The technical solution of the present invention is different from that of the above-mentioned patent document. The present invention can realize low-cost production by adding rare earth, copper and segregated elements in the dedicated thin strip continuous annealing production line without hydrogen protection, while improving the safety of unit operation; it can also produce thinner high-silicon aluminum products under the condition of simple modification of the existing thick specification (above 0.25mm) production line (cancelling the non-oxidizing heating section, adjusting the distance between the conveying rollers and the tension control system). In addition, the present invention is also conducive to further improving the electromagnetic and mechanical properties of the product, and can be applied to low-loss, high-efficiency, high-strength and other products.

Summary of the invention

The present invention provides a non-oriented high-grade high-silicon thin strip heat treatment process. Under the existing production process equipment conditions of high-grade high-silicon aluminum thin strips, on the basis of strict control of steel cleanliness, a variety of beneficial elements are added for synergistic effect, so that the finished product heat treatment is carried out in a full nitrogen protective atmosphere, the product has no surface and matrix oxidation and nitridation defects, and has excellent electromagnetic properties; the continuous annealing unit can operate with high efficiency and low cost, and produce high-performance products with market competitiveness.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strips, including chemical composition control and continuous annealing treatment control process; wherein:

1) Chemical composition control: according to the mass percentage, control the C in the steel to be ≤ 0.0025%, S to be ≤ 0.0010%, and N to be ≤ 0.0012%; add lanthanide rare earth elements to the steel, and control the La content to be within the range of 0.05% to 0.15%; add copper elements, and control the Cu content to be within the range of 0.035% to 0.35%; add grain boundary segregation elements, including Sn and/or Sb, and control the addition amount to be within the range of 0.050% to 0.20%;

2) Continuous annealing heat treatment control: The continuous annealing unit adopts a cold-rolled non-oriented silicon steel strip continuous annealing unit, eliminates the open flame heating section, and performs heat treatment under full nitrogen atmosphere protection.

Furthermore, the thickness of the finished non-oriented high-grade high-silicon thin strip is ≤0.25mm.

Furthermore, no decarburization treatment is performed during the annealing treatment.

Furthermore, the running speed of the cold-rolled steel strip entering the continuous annealing unit is ≤100m/min, and the uniform heating temperature of the continuous annealing treatment is 940-960°C.

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

1) The present invention can realize low-cost production by adopting hydrogen-free protection on the thin strip continuous annealing unit, thereby improving the safety of the operation of the continuous annealing unit;

2) The present invention is conducive to further improving the electromagnetic and mechanical properties of products, and can be applied to low-loss, high-efficiency, high-strength and other products;

3) Based on the existing thick specification (above 0.25mm) continuous annealing treatment production line, the present invention can produce thinner specifications of high-silicon aluminum-silicon steel strip products after simple functional improvements (such as eliminating the open flame heating section, adjusting the distance between the conveying rollers and the tension control system).

DETAILED DESCRIPTION

The method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strips described in the present invention includes chemical composition control and continuous annealing treatment control processes; wherein:

1) Chemical composition control: according to the mass percentage, control the C in the steel to be ≤ 0.0025%, S to be ≤ 0.0010%, and N to be ≤ 0.0012%; add lanthanide rare earth elements to the steel, and control the La content to be within the range of 0.05% to 0.15%; add copper elements, and control the Cu content to be within the range of 0.035% to 0.35%; add grain boundary segregation elements, including Sn and/or Sb, and control the addition amount to be within the range of 0.050% to 0.20%;

2) Continuous annealing heat treatment control: The continuous annealing unit adopts a cold-rolled non-oriented silicon steel strip continuous annealing unit, eliminates the open flame heating section, and performs heat treatment under full nitrogen atmosphere protection.

Furthermore, the thickness of the finished non-oriented high-grade high-silicon thin strip is ≤0.25mm.

Furthermore, no decarburization treatment is performed during the annealing treatment.

Furthermore, the running speed of the cold-rolled steel strip entering the continuous annealing unit is ≤100m/min, and the uniform heating temperature of the continuous annealing treatment is 940-960°C.

In order to achieve continuous annealing treatment of non-oriented high-silicon, high-aluminum, high-grade thin-strip silicon steel with a thickness of less than 0.25 mm, the present invention adopts the following technical measures in the steel grade composition design and production process.

1. Strictly control the cleanliness of steel; control C≤0.0025%, no decarburization treatment is performed during the heat treatment of the product, reduce the involvement of oxidizing atmosphere in a wet atmosphere, reduce the magnetic aging of the product, ensure that the functional components of the product (such as the stator and rotor of the motor) operate stably under relatively high temperature (motor operating temperature rise) conditions for a long time, reduce the lattice distortion of the recrystallized structure during the heat treatment, and reduce the involvement of oxygen and nitrogen atoms. Control S≤0.0010%, reduce sulfides and precipitates, reduce the lattice distortion of the recrystallized structure during the heat treatment, reduce the involvement of oxygen and nitrogen, reduce the impact of sulfur on electromagnetic properties, and reduce the "catalyst effect" of sulfur intensifying the reaction on the surface of the thin strip. Control N≤0.0012%, reduce nitrides and precipitates, reduce the lattice distortion of the recrystallized structure, and reduce the impact of nitrogen on electromagnetic properties;

2. Add lanthanide rare earth elements; control the La content to 0.05% to 0.15%, give full play to the corrosion resistance of rare earth elements on iron-based materials, promote the denaturation of inclusions and precipitates, promote favorable organization and favorable texture components, and improve the electromagnetic properties of the product.

3. Add appropriate amount of copper element; control the Cu content at 0.035% to 0.35% to give full play to the corrosion resistance of copper element on iron-based materials; and in the heat treatment process, copper is enriched on the surface under the promotion of high silicon and high aluminum and the control of grain boundary segregation elements, which reduces the oxidation and nitridation of the surface layer (including iron and high silicon and aluminum components) under large surface ratio conditions.

4. Add grain boundary segregation elements; add Sn and/or Sb elements. These elements have similar functions and effects and can be added in combination or separately, with the main focus on controlling the amount of addition; the added content should match the copper content, that is, within the range of 0.050% to 0.20%; utilize the surface enrichment characteristics of grain boundary segregation of these elements to reduce the precipitates formed by residual harmful elements in the steel to pin the grain boundaries, improve the organization and texture, and eliminate the adverse effects of copper and other elements required for process characteristics on production and magnetic properties; strengthen the grain boundaries, increase product strength and improve processing performance. One of the important functions is to prevent copper from segregating at the grain boundaries and promote surface enrichment; the present invention adopts a copper-containing design, and copper is easy to gather at the grain boundaries, resulting in softened grain boundaries (melting of high-temperature grain boundary copper enrichment zone) in the production of hot-rolled steel strips and easy copper brittleness and edge cracking.

In the present invention, the process control of non-oriented high-silicon, high-aluminum and high-grade thin strip series products from continuous casting to cold rolling is the same as the production control process of conventional products. Only by controlling the chemical composition and continuous annealing heat treatment process, heat treatment under full nitrogen atmosphere protection using a thin strip continuous annealing unit can be achieved. The silicon steel thin strip products produced have excellent surface quality, are free of internal and external nitridation and oxidation defects, and have excellent electromagnetic properties.

In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with the examples. The following examples are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto, and any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the protection scope of the present invention.

Example 1:

In this example, by comparing Example 1 and Example 1, a typical non-oriented high-silicon aluminum strip product 30NV1500 is taken as an example to compare the chemical composition, production process and product performance of the product.

In Comparative Example 1, the chemical composition of the non-oriented high silicon thin strip is C: 0.0028%, Si: 3.25%, Als: 0.88%, Mn: 0.311%, P: 0.009%, S: 0.0012%, N: 0.0015% by mass; the rest are Fe and unavoidable impurities.

In Comparative Example 1, after continuous casting, billet heating, hot rolling and cold rolling, the cold-rolled steel strip enters the continuous annealing unit at a running speed of 100 m/min, the soaking temperature of continuous annealing is 950°C, and the _H2 content in the protective atmosphere in the furnace is 30%.

In Comparative Example 1, the thickness of the finished non-oriented high-silicon thin strip is 0.30 mm, the iron loss P10/400 is 14.3 W/kg, the magnetic induction B5000 is 1.656 T, the yield strength Rp0.2 is 395 MPa, and the product surface is light gray and shiny, meeting the factory standard requirements.

In Example 1, the chemical composition of the non-oriented high silicon thin strip is Si: 3.29%, Als: 0.79%, Mn: 0.245%, P: 0.005%, C: 0.0021%, S: 0.0009%, N: 0.0011%, Cu: 0.15%, Sn: 0.085%, La: 0.079%, and the rest is Fe and unavoidable impurities.

In Example 1, after continuous casting, billet heating, hot rolling and cold rolling, the cold-rolled steel strip enters the continuous annealing unit at a running speed of 100 m/min, the soaking temperature of continuous annealing is 950°C, and the protective atmosphere in the furnace is full nitrogen protection.

In Example 1, the thickness of the finished non-oriented high silicon thin strip is 0.30 mm, the iron loss P10/400 is 14.05 W/kg, the magnetic induction B5000 is 1.66 T, and the yield strength Rp0.2 is 410 MPa. The surface of the product is light gray and bright, meeting the factory standard requirements.

Example 2:

In this example, by using Comparative Example 2 and Example 2, a typical non-oriented high-silicon aluminum strip product 27NVP1400 is taken as an example to compare the chemical composition, production process and product performance of the product.

In Comparative Example 2, the chemical composition of the non-oriented high silicon thin strip is C: 0.0031%, Si: 3.28%, Als: 0.85%, Mn: 0.293%, P: 0.007%, S: 0.0012%, N: 0.0016% by mass; the others are Fe and unavoidable impurities.

In Comparative Example 2, after continuous casting, billet heating, hot rolling and cold rolling, the cold-rolled steel strip enters the continuous annealing unit at a running speed of 100 m/min, the soaking temperature of continuous annealing is 940°C, the _H2 content in the protective atmosphere in the furnace is 35%, and the dew point is controlled at -15°C.

In Comparative Example 2, the thickness of the finished non-oriented high-silicon thin strip is 0.27 mm, the iron loss P10/400 is 13.35 W/kg, the magnetic induction B5000 is 1.65 T, the yield strength Rp0.2 is 405 MPa, and the product surface is light gray and matte, meeting the factory standard requirements.

In Example 2, the chemical composition of the non-oriented high silicon thin strip is Si: 3.25%, Als: 0.83%, Mn: 0.325%, P: 0.006%, C: 0.0017%, S: 0.0005%, N: 0.0010%, Cu: 0.085%, Sn: 0.115%, and the rest is Fe and unavoidable impurities.

In Example 2, after continuous casting, billet heating, hot rolling and cold rolling, the cold-rolled steel strip enters the continuous annealing unit at a running speed of 100 m/min, the soaking temperature of continuous annealing is 940°C, and the protective atmosphere in the furnace is full nitrogen protection.

In Example 2, the thickness of the finished non-oriented high silicon thin strip is 0.27 mm, the iron loss P10/400 is 13.42 W/kg, the magnetic induction B5000 is 1.67 T, and the yield strength Rp0.2 is 410 MPa. The surface of the product is light gray and bright, meeting the factory standard requirements.

Example 3:

In this example, by comparing Example 3 and Example 3, a typical non-oriented high-silicon aluminum strip product 25NVPS1300 (high magnetic induction and high strength type) is taken as an example to compare the chemical composition, production process and product performance of the product.

In Comparative Example 3, the chemical composition of the non-oriented high silicon thin strip is, by mass percentage, C: 0.0032%, Si: 3.31%, Als: 0.88%, Mn: 0.297%, P: 0.006%, S: 0.0012%, N: 0.0017%, Ni: 0.120%; the rest are Fe and unavoidable impurities.

In Comparative Example 3, after continuous casting, billet heating, hot rolling and cold rolling, the cold-rolled steel strip enters the continuous annealing unit at a running speed of 95 m/min, the soaking temperature of continuous annealing is 940°C, the _H2 content in the protective atmosphere in the furnace is 40%, and the dew point is controlled at -10°C.

In Comparative Example 3, the thickness of the finished non-oriented high-silicon thin strip is 0.25 mm, the iron loss P10/400 is 12.55 W/kg, the magnetic induction B5000 is 1.658 T, the yield strength Rp0.2 is 425 MPa, and the product surface is light gray and matte, meeting the factory standard requirements.

In Example 3, the chemical composition of the non-oriented high silicon thin strip is Si: 3.29%, Als: 0.91%, Mn: 0.251%, P: 0.006%, C: 0.0022%, S: 0.0006%, N: 0.0010%, Cu: 0.115%, Sn: 0.105%, Ni: 0.118%, and the rest is Fe and unavoidable impurities.

In Example 3, after continuous casting, billet heating, hot rolling and cold rolling, the cold-rolled steel strip enters the continuous annealing unit at a running speed of 95 m/min, the soaking temperature of continuous annealing is 940°C, and the protective atmosphere in the furnace is full nitrogen protection.

In Example 3, the thickness of the finished non-oriented high silicon thin strip is 0.25 mm, the iron loss P10/400 is 12.61 W/kg, the magnetic induction B5000 is 1.658 T, and the yield strength Rp0.2 is 440 MPa. The surface of the product is light gray and bright, meeting the factory standard requirements.

Example 4:

In this example, by comparing Example 4 and Example 4, a typical non-oriented high-silicon aluminum strip product 20NVPS1250 (high magnetic induction and high strength type) is taken as an example to compare the chemical composition, production process and product performance of the product.

In Comparative Example 4, the chemical composition of the non-oriented high silicon thin strip is, by mass percentage, C: 0.0028%, Si: 3.22%, Als: 0.75%, Mn: 0.277%, P: 0.006%, S: 0.0011%, N: 0.0015%; Ni+Cr: 0.25%, and the rest is Fe and unavoidable impurities.

In Comparative Example 4, after continuous casting, billet heating, hot rolling and cold rolling, the cold-rolled steel strip enters the continuous annealing unit at a running speed of 90 m/min, the soaking temperature of continuous annealing is 955°C, the _H2 content in the protective atmosphere in the furnace is 45%, and the dew point is controlled at -30°C.

In Comparative Example 4, the thickness of the finished non-oriented high-silicon thin strip is 0.20 mm, the iron loss P10/400 is 12.20 W/kg, the magnetic induction B5000 is 1.648 T, the yield strength Rp0.2 is 430 MPa, and the product surface is dark gray and matte, meeting the factory standard requirements.

In Example 4, the chemical composition of the non-oriented high silicon thin strip is Si: 3.26%, Als: 0.75%, Mn: 0.271%, P: 0.006%, C: 0.0015%, S: 0.0004%, N: 0.0010%, Cu: 0.25%, Sn: 0.135%, Ni+Cr: 0.25%, and the rest is Fe and unavoidable impurities.

In Example 4, after continuous casting, billet heating, hot rolling and cold rolling, the cold-rolled steel strip enters the continuous annealing unit at a running speed of 90 m/min, the soaking temperature of continuous annealing is 955°C, and the protective atmosphere in the furnace is full nitrogen protection.

In Example 4, the thickness of the finished non-oriented high silicon thin strip is 0.20 mm, the iron loss P10/400 is 12.11 W/kg, the magnetic induction B5000 is 1.646 T, and the yield strength Rp0.2 is 445 MPa. The surface of the product is light gray and bright, meeting the factory standard requirements.

The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims (4)

1. A method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strip, characterized in that it includes chemical composition control and continuous annealing treatment control process; wherein: 1) Chemical composition control: according to the mass percentage, control the C in the steel to be ≤ 0.0025%, S to be ≤ 0.0010%, and N to be ≤ 0.0012%; add lanthanide rare earth elements to the steel, and control the La content to be within the range of 0.05% to 0.15%; add copper elements, and control the Cu content to be within the range of 0.035% to 0.35%; add grain boundary segregation elements, including Sn and/or Sb, and control the addition amount to be within the range of 0.050% to 0.20%; 2) Continuous annealing heat treatment control: The continuous annealing unit adopts a cold-rolled non-oriented silicon steel strip continuous annealing unit, eliminates the open flame heating section, and performs heat treatment under full nitrogen atmosphere protection. 2. A method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strip according to claim 1, characterized in that the thickness of the finished non-oriented high-grade high-silicon thin strip is ≤0.25mm. 3. A method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strip according to claim 1, characterized in that no decarburization treatment is performed during the continuous annealing treatment. 4. A method for realizing continuous annealing treatment of non-oriented high-grade high-silicon thin strip according to claim 1, characterized in that the running speed of the cold-rolled steel strip entering the continuous annealing unit is ≤100m/min, and the soaking temperature of the continuous annealing treatment is 940-960°C.