CN118726708A - Annealing method for non-oriented silicon steel ultra-thin strip - Google Patents

Abstract

The invention relates to an annealing treatment method of a non-oriented silicon steel ultrathin strip, belongs to the field of metal material heat treatment, and solves at least one of the problems of complex process, high cost, high iron loss, bending, oxidation, insufficient magnetic induction and the like of the conventional annealing method for a plane cast silicon steel ultrathin strip. An annealing treatment method for non-oriented silicon steel ultrathin strips comprises the following steps: s1, carrying out vacuum treatment on a vacuum tube furnace, introducing inert gas, and heating; s2, when the annealing temperature is reached, placing the sample in a cooling area of a vacuum tube furnace, closing a furnace door, and introducing reducing gas; the sample is a non-oriented silicon steel ultrathin strip obtained by adopting a plane casting method; s3, pushing the sample to a heat preservation area, and annealing; s4, pushing the sample to a cooling area, stopping introducing the reducing gas, introducing the inert gas only, and taking out the sample after the reducing gas is exhausted completely. The invention provides an annealing method with simple process and lower cost, which improves the comprehensive performance of the non-oriented silicon steel ultrathin strip: p _1.0/1000Hz≤40W/kg,B₅₀₀₀ is more than or equal to 1.66T, and has good flatness and quality.

Description

Annealing method for non-oriented silicon steel ultra-thin strip

Technical Field

The invention relates to the technical field of heat treatment of metal materials, and in particular to an annealing method for an ultra-thin strip of non-oriented silicon steel.

Background Art

Planar flow casting is an advanced manufacturing technology that can be used to prepare non-oriented silicon steel ultra-thin strips. Non-oriented silicon steel is an important soft magnetic material and is widely used in the manufacture of iron cores for motors and transformers. Planar flow casting has the characteristics of short process and high efficiency. By quickly solidifying the molten metal on a high-speed rotating cooling roller, it can directly produce silicon steel ultra-thin strips, and then obtain the final product through subsequent processing.

According to existing literature reports, the post-processing steps for preparing non-oriented silicon steel ultra-thin strips by planar flow casting mainly include two key links: flattening and annealing. The existing problems and difficulties include: (1) Easy to bend and deform during annealing: During the annealing process, the silicon steel ultra-thin strip is very thin and has low strength, so it is extremely easy to bend, deform or sag during annealing, resulting in damage to the product surface quality and reduced dimensional accuracy; (2) Easy to oxidize during annealing: In the prior art, some people have tried to first press down and flatten the silicon steel ultra-thin strip obtained by the planar flow casting method, then coat it with an insulating layer and wind it into a roll, and anneal the silicon steel ultra-thin strip under a protective atmosphere. However, this method is not only cumbersome in process (including flattening + coating of an insulating layer + annealing), but also has a high risk of oxidation due to the lack of reducing gas in the protective atmosphere. The proportion of the body or reducing gas is small, and the oxidation of the silicon steel ultra-thin strip cannot be effectively avoided. Although some rare elements other than silicon and iron are added, the comprehensive performance of the final product (especially high-frequency iron loss, magnetic induction, etc.) is still not ideal; (3) The comprehensive performance of the sample after annealing is affected by improper setting of process parameters during annealing: In the prior art, for the silicon steel ultra-thin strip with simpler composition obtained by the plane flow casting method, the annealing process parameters (including annealing temperature, time, cooling time, and rate) with the best synergistic effect are not given, because the optimal ratio of these parameters is not easy to obtain. In the actual annealing process, there is an interactive influence between these parameters, and the influence on the annealing treatment results is often complex and nonlinear. During the annealing process, if the annealing temperature, time and cooling parameters are improperly set, it is easy to cause uneven temperature in different parts of the silicon steel ultra-thin strip, thereby causing stress concentration and uneven structure, and then affecting the plate shape and surface quality of the silicon steel ultra-thin strip, as well as iron loss, magnetic induction, etc.

Therefore, it is necessary to study and develop an annealing method suitable for the non-oriented silicon steel ultra-thin strip prepared by the plane flow casting technology, which has a relatively simple process, low cost and excellent comprehensive performance.

Summary of the invention

In view of the above analysis, the present invention aims to provide an annealing method for non-oriented silicon steel ultra-thin strip, so as to solve at least one of the problems of the existing annealing method for silicon steel ultra-thin strip prepared by planar flow casting, namely, complicated process, high cost, high iron loss after annealing (especially high-frequency iron loss), surface defects such as bending and oxidation, insufficient magnetic induction, etc.

The objective of the present invention is achieved through the following technical solutions:

The present invention provides an annealing method for a non-oriented silicon steel ultra-thin strip, comprising the following steps:

S1. Vacuum the vacuum tube furnace, introduce inert gas, and then heat the insulation zone in the vacuum tube furnace;

S2. When the temperature in the holding zone reaches the preset annealing temperature, the sample is placed in the cooling zone of the vacuum tube furnace through the furnace door of the vacuum tube furnace, the furnace door is closed, and reducing gas is introduced;

Among them, the sample is a non-oriented silicon steel ultra-thin strip obtained by plane flow casting;

S3, when the volume ratio K of the reducing gas in the vacuum tube furnace to the annealing atmosphere is ≥30%, the sample is pushed to the insulation zone and annealed at the annealing temperature;

Wherein, the annealing atmosphere is set to a mixed gas of reducing gas and inert gas;

S4. After annealing, push the sample to the cooling zone for cooling. Stop introducing reducing gas during the cooling process and only introduce inert gas. After the reducing gas is cleaned from the vacuum tube grate, open the furnace door and take out the sample.

Furthermore, in the entire process from step S2 to step S4, a porous ceramic plate is used to clamp the sample from top to bottom.

Furthermore, the thickness of the ceramic plate is 8 mm to 20 mm, the pore size of the ceramic plate is 80 μm to 150 μm, and the porosity of the ceramic plate is 16% to 22%.

Furthermore, in S3, the volume ratio K of the reducing gas in the vacuum tube furnace to the annealing atmosphere is ≥50%.

Furthermore, in S2 and S3, the annealing temperature is 950°C to 1050°C.

Furthermore, in S3, the annealing treatment time is 1.0 h to 1.8 h.

Furthermore, in S4, the cooling time T is ≥ 6 min.

Furthermore, in S4, the cooling rate is 1.8°C/s to 3°C/s.

Furthermore, the flow rate of the inert gas is 0L/min to 7L/min, and the flow rate of the reducing gas is 1.5L/min to 5L/min; by controlling the flow rates of the inert gas and the reducing gas, the proportion of the annealing atmosphere inside the vacuum tube furnace is regulated to maintain a positive pressure inside the vacuum tube furnace.

Further, the chemical composition of the non-oriented silicon steel ultra-thin strip is Si: 2.8% to 4.0% by mass, and the rest is Fe and unavoidable impurities; and/or,

In S1, the main step of the vacuum treatment includes evacuating the vacuum tube furnace to make the vacuum degree in the furnace Pa≤150Pa.

Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

(1) The present invention provides an annealing method for non-oriented silicon steel ultra-thin strips with relatively simple process (no need to press down flattening/coating insulating layer, direct annealing), low cost (no need to add expensive trace elements, and simplified steps), by using an annealing atmosphere in which the reducing gas accounts for at least 30% and in combination with a preferred annealing device (vacuum tube furnace) and an operation sequence (steps S1-S4) to ensure safety and operational feasibility when the reducing gas accounts for a high proportion, thereby effectively improving the comprehensive performance of the non-oriented silicon steel ultra-thin strip, including: reducing iron loss, improving magnetic induction (B ₅₀₀₀ ≥1.66T), excellent surface quality, etc., especially effectively reducing high-frequency iron loss (P _1.0/1000Hz ≤40W/kg), which has important practical value for silicon steel ultra-thin strips in high-frequency applications (for example: high-frequency motors, radio equipment, radar systems), and reducing high-frequency iron loss can better meet the strict requirements of high-frequency applications. Compared with the ultra-thin silicon steel strip in the prior art (P _1.0/1000Hz is difficult to control below 50W/kg, and even if it is below 50W/kg, the annealing process is often complicated, or expensive trace elements need to be added, resulting in high costs), the annealing method of the present invention has a simpler process, lower costs, and the obtained ultra-thin silicon steel strip has better comprehensive performance.

(2) The present invention uses porous ceramic plates to clamp the ultra-thin silicon steel strip up and down for annealing treatment, which is simple and easy to operate and can further effectively improve the comprehensive performance of the non-oriented silicon steel ultra-thin strip, including: improving flatness (for example: reducing deformation and stress), reducing iron loss, and improving magnetic induction. Using ceramic plates with appropriate thickness, pore size and porosity to clamp the sample up and down for annealing treatment is conducive to obtaining the best annealing treatment effect.

(3) By using an annealing atmosphere with a high proportion of reducing gas (K ≥ 50%), the comprehensive performance of the non-oriented silicon steel ultra-thin strip is further effectively improved, including: reducing iron loss, increasing magnetic induction, and improving surface quality and flatness.

(4) By selecting preferred process conditions/parameters with synergistic effects, including annealing temperature, annealing time, cooling time, cooling rate, etc., the comprehensive performance of the non-oriented silicon steel ultra-thin strip is further effectively improved. For example, the embodiment using the preferred process parameters shown in Table 1 has lower iron loss and higher magnetic induction.

In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be achieved and obtained through the contents particularly pointed out in the description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

FIG1 is a grain structure diagram of a non-oriented silicon steel ultra-thin strip provided in an embodiment of the present invention, wherein (a) is before annealing treatment, and (b) is after annealing treatment;

FIG2 is a photo of a non-oriented silicon steel ultra-thin strip provided in an embodiment of the present invention, wherein (a) is before annealing treatment, and (b) is after annealing treatment;

FIG3 is a photograph of the non-oriented silicon steel ultra-thin strip after annealing in Comparative Example 1 (no ceramic plate is used);

FIG. 4 is a photograph of the non-oriented silicon steel ultra-thin strip after annealing in Comparative Example 2 (using nitrogen only).

DETAILED DESCRIPTION

The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

The present invention provides an annealing method for a non-oriented silicon steel ultra-thin strip, comprising the following steps:

S1. Vacuum the vacuum tube furnace, introduce inert gas, and then heat the insulation zone in the vacuum tube furnace;

S2. When the temperature in the holding zone reaches the preset annealing temperature, the sample is placed in the cooling zone of the vacuum tube furnace through the furnace door of the vacuum tube furnace, the furnace door is closed, and reducing gas is introduced;

Wherein, the sample is a non-oriented silicon steel ultra-thin strip obtained by plane flow casting method;

S3, when the volume ratio K of the reducing gas in the vacuum tube furnace to the annealing atmosphere is ≥30%, the sample is pushed to the insulation zone and annealed at the annealing temperature;

Wherein, the annealing atmosphere is set to a mixed gas of reducing gas and inert gas;

S4. After annealing, push the sample to the cooling zone for cooling. Stop introducing reducing gas during the cooling process and only introduce inert gas. After the reducing gas is cleaned from the vacuum tube grate, open the furnace door and take out the sample.

It is noteworthy that the present invention provides an annealing method for non-oriented silicon steel ultra-thin strips with a relatively simple process (no need to press down flattening/coating insulating layer, direct annealing), low cost (no need to add expensive trace elements, and simplified steps), by using an annealing atmosphere in which the reducing gas accounts for at least 30% and in combination with preferred annealing equipment (vacuum tube furnace) and operation sequence (steps S1-S4) to ensure safety and operational feasibility when the reducing gas accounts for a high proportion, thereby effectively improving the comprehensive performance of the non-oriented silicon steel ultra-thin strip, including: reducing iron loss, improving magnetic induction (B ₅₀₀₀ ≥1.66T), excellent surface quality, etc., especially effectively reducing high-frequency iron loss (P _1.0/1000Hz ≤40W/kg), which has important practical value for silicon steel ultra-thin strips in high-frequency applications (for example: high-frequency motors, radio equipment, radar systems), and reducing high-frequency iron loss can better meet the strict requirements of high-frequency applications. Compared with the ultra-thin silicon steel strip in the prior art (P _1.0/1000Hz is difficult to control below 50W/kg, and even if it is below 50W/kg, the annealing process is often complicated, or expensive trace elements need to be added, resulting in high costs), the annealing method of the present invention has a simpler process, lower costs, and the obtained ultra-thin silicon steel strip has better comprehensive performance.

Preferably, during the entire process from step S2 to step S4, a porous ceramic plate is used to clamp the sample from top to bottom.

In some preferred embodiments, the porous ceramic plate is a micro-leakage sintered microporous ceramic plate. The micro-leakage sintered microporous ceramic plate is a porous ceramic material with micron or submicron pore sizes.

It is worth noting that by using porous ceramic plates to clamp the silicon steel ultra-thin strip up and down for annealing, the comprehensive performance of the non-oriented silicon steel ultra-thin strip can be further effectively improved, including: improving flatness (for example, reducing deformation and stress), reducing iron loss, improving magnetic induction, etc. Specifically, a) Improving flatness: Clamping the silicon steel strip can prevent it from bending due to stress during annealing, effectively reduce deformation during annealing, maintain the flatness and dimensional accuracy of the material, and improve the plate shape of the silicon steel strip. The ceramic plate has excellent thermal insulation performance, which can ensure that the silicon steel ultra-thin strip is annealed. The ceramic plate can heat the ultra-thin silicon steel strip evenly during the annealing process, which helps to release the internal stress of the ultra-thin silicon steel strip evenly and reduce the residual stress after annealing. b) Prevent oxidation: The loose and porous design on the ceramic plate allows the annealing atmosphere to fully contact the sample, preventing oxidation and improving the surface quality. c) Reduce iron loss and improve magnetic induction: The ceramic plate can make the ultra-thin silicon steel strip evenly heated during the annealing process, which helps to reduce iron loss and improve magnetic induction. d) Simple and easy to operate: The ceramic plate is used to clamp the sample directly. The clamping and unloading process of the sample is very simple and convenient, and excellent annealing effect can be obtained without additional fixtures.

In some preferred embodiments, a porous ceramic plate is used to clamp the sample up and down, and then the sample and the ceramic plate are placed in a container with an upper opening. During the annealing process, the container is moved by a conveying device in a vacuum tube furnace, and the sample is conveniently moved between the heat preservation zone and the cooling zone while ensuring that the ceramic plate and the sample are fixed in position. Exemplarily, the container with an upper opening includes, but is not limited to, a tray. Exemplarily, the conveying device includes, but is not limited to, a conveyor belt and a push rod.

In some preferred embodiments, ceramic plates with appropriate thickness, pore size and porosity are used to clamp the sample from top to bottom for annealing, which is conducive to obtaining the best annealing effect.

Preferably, the thickness of the ceramic plate is 8 mm to 20 mm, the pore size of the ceramic plate is 80 μm to 150 μm, and the porosity of the ceramic plate is 16% to 22%.

More preferably, the thickness of the ceramic plate is 10 mm to 20 mm, the pore size of the ceramic plate is 90 μm to 120 μm, and the porosity of the ceramic plate is 18% to 20%.

Exemplarily, the thickness of the ceramic plate is 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, the pore size of the ceramic plate is 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, and the porosity of the ceramic plate is 18.0%, 18.4%, 18.6%, 18.8%, 19.0%, 19.4%, 19.6%, 20.0%.

Using the above-mentioned preferred thickness, pore size and porosity ceramic plates to clamp the sample up and down for annealing treatment is conducive to obtaining the best annealing treatment effect and ensuring sufficient contact between the annealing atmosphere and the sample; specifically, (a) the thickness of the ceramic plate: a ceramic plate of appropriate thickness can effectively conduct heat to ensure that the ultra-thin silicon steel strip is heated evenly during the annealing process, reduce thermal stress and potential crack risks, and a suitable thickness can provide sufficient downward pressure and upward support for the ultra-thin silicon steel strip to prevent it from deforming, bending or wrinkling at high temperatures; (b) the pore size of the ceramic plate: if the pore is too small, the annealing atmosphere cannot fully contact the ultra-thin silicon steel strip; if the pore is too large, the force is uneven; a suitable pore size can ensure that the annealing atmosphere fully contacts the silicon steel strip. The surface of the silicon steel ultra-thin strip can effectively prevent oxidation and other unwanted chemical reactions, while making the surface of the silicon steel ultra-thin strip evenly stressed, reducing the risk of stress concentration and deformation; (c) Porosity of the ceramic plate: If the porosity is too low, the annealing atmosphere cannot fully contact the silicon steel ultra-thin strip; if the porosity is too high, the force is uneven, and the ceramic plate may not be able to provide sufficient downward pressure and upward support for the silicon steel ultra-thin strip to control deformation; The appropriate porosity can ensure that the annealing atmosphere flows in the pores of the ceramic plate, and fresh annealing atmosphere is replenished in time, which helps the annealing atmosphere to evenly cover the silicon steel ultra-thin strip and reduce the risk of oxidation and other surface defects; The appropriate porosity can speed up the heating and cooling process, shorten the annealing cycle, and improve production efficiency.

Optionally, in step S1, the inert gas includes nitrogen, argon, or a combination thereof. Preferably, the inert gas is nitrogen.

Preferably, in step S1, the main step of the vacuum treatment includes evacuating the vacuum tube furnace to make the vacuum degree in the furnace Pa≤150Pa.

Preferably, in step S2, the thickness of the non-oriented silicon steel ultra-thin strip is 50 μm to 70 μm. Exemplarily, the thickness of the non-oriented silicon steel ultra-thin strip is 50 μm, 55 μm, 60 μm, 65 μm, or 70 μm.

Optionally, the chemical composition of the non-oriented silicon steel ultra-thin strip is Si: 2.8% to 4.0% by mass, and the rest is Fe and unavoidable impurities. In some preferred embodiments, the Si content is 3.0%, 3.2%, 3.4%, 3.6%, 3.8%.

It can be understood that in step S2, the main steps of the planar flow casting method include: melting the alloy raw material into molten steel, the molten steel flows through a straight slit onto a high-speed rotating copper roller, is rapidly cooled and thrown out, and obtains an alloy thin strip.

Preferably, the reducing gas is hydrogen.

It should be noted that in step S2 and step S3, the annealing temperature is 950° C. to 1050° C. Exemplarily, the annealing temperature is 950° C., 960° C., 970° C., 980° C., 990° C., 1000° C., 1010° C., 1020° C., 1030° C., 1040° C., 1050° C. Preferably, the annealing temperature is 1000° C. to 1050° C.

It can be understood that in step S3, during the annealing process of the silicon steel ultra-thin strip, the use of a mixed gas of an inert gas and a reducing gas can bring the following benefits: (1) Preventing oxidation: Inert gases such as nitrogen or argon have good chemical inertness and will not react chemically with silicon steel. They can be used as a protective atmosphere to prevent silicon steel from oxidizing at high temperatures; (2) Improving magnetic properties: The reducing property of reducing gases such as hydrogen can reduce the oxide scale on the surface of the silicon steel ultra-thin strip and ensure the surface quality. At the same time, compared with inert gases such as nitrogen, reducing gases such as hydrogen are more conducive to reducing the proportion of harmful {111} oriented grains in the silicon steel ultra-thin strip, reducing iron loss, and improving magnetic induction. Especially in high-frequency applications, reducing iron loss and increasing magnetic induction intensity are conducive to energy saving and consumption reduction and improving equipment performance; (3) Improving production efficiency and yield rate: Using a mixed gas can speed up the annealing speed, shorten the production cycle, and improve production efficiency; by precisely controlling the proportion of the annealing atmosphere, material defects caused by oxidation or other chemical reactions can be reduced and the yield rate can be improved.

Optionally, in step S3, the ratio of the mixed gas can be adjusted as needed to control the redox property of the annealing atmosphere, optimize the annealing conditions, and improve the performance of the ultra-thin silicon steel strip.

Preferably, in step S3, the volume ratio K of the reducing gas in the vacuum tube furnace to the annealing atmosphere is ≥50%.

It is worth noting that by using an annealing atmosphere with a high proportion of reducing gas (K ≥ 50%), the comprehensive performance of non-oriented silicon steel ultra-thin strips can be further effectively improved, including: reducing iron loss, improving magnetic induction, improving surface quality, flatness, etc. Specifically, a) Reducing iron loss: Using a reducing atmosphere with a high proportion can effectively reduce oxidation, thereby reducing the iron loss of silicon steel ultra-thin strips, especially in high-frequency applications, reducing oxidation can reduce eddy current loss, thereby reducing iron loss; b) Improving comprehensive magnetic properties: Using a reducing atmosphere with a high proportion can help improve the comprehensive magnetic properties of silicon steel ultra-thin strips, by reducing the negative impact of oxidation on grain orientation and microstructure, improving magnetic permeability and reducing hysteresis loss; c) Improving surface quality and preventing oxidation: A higher proportion of reducing gas can prevent the surface of silicon steel ultra-thin strips from oxidizing during the annealing process, thereby improving surface quality and reducing scale and decarburization; d) Improving flatness and reducing stress: Annealing treatment under a higher proportion of reducing atmosphere can reduce the stress inside the material, and reducing oxidation can reduce surface unevenness, which helps to improve the flatness of silicon steel ultra-thin strips.

The higher the ratio of reducing gas (such as hydrogen) to inert gas (such as nitrogen), the greater the positive impact on the comprehensive properties of the silicon steel ultra-thin strip (such as iron loss, magnetic induction, flatness and surface quality) during the annealing process, which helps to produce silicon steel ultra-thin strip with better performance.

It should be noted that, taking into account the safety issues when the proportion of reducing gas (such as hydrogen) is high (for example, K ≥ 50%), the present invention adopts the preferred annealing equipment (vacuum tube furnace) and combines it with the preferred operation sequence (the operation sequence and steps described in S1-S4). It can improve the magnetic induction of ultra-thin silicon steel strip, reduce iron loss, and improve flatness and surface quality while ensuring safety and operability, which has important industrial application value for the production of high-quality ultra-thin silicon steel strip.

A. Using a vacuum tube furnace can bring the following benefits: a) The vacuum tube furnace has an over-temperature protection function and can accurately control the pressure inside the furnace, thereby avoiding safety problems caused by high temperature and high pressure. The vacuum tube furnace is equipped with a gas leak detection (such as a hydrogen detection device) and a flame detection alarm system, which can promptly detect and deal with potential safety problems; b) Due to the good sealing performance of the vacuum tube furnace, the mixing ratio of reducing gas and inert gas in the annealing atmosphere can be accurately controlled to optimize the annealing process while ensuring safety.

B. Adopting the preferred operation sequence (specific steps described in S1-S4) can ensure safety and operational feasibility, improve the magnetic induction of the silicon steel ultra-thin strip, reduce iron loss, and improve surface quality and flatness; specifically:

a) In steps S1 and S2, an inert gas is first introduced to ensure that the furnace is always under positive pressure. After the furnace door is opened to place the sample, the furnace door is closed and a reducing gas (such as hydrogen) is introduced. This can prevent the danger caused by the reducing gas (such as hydrogen). When the reducing gas (such as hydrogen) is introduced, if the furnace door is opened, there will be a safety hazard of explosion.

b) In steps S2 and S3, the sample is first placed in a cooling zone and a reducing gas (such as hydrogen) is passed through for a period of time to effectively ensure that the ratio of reducing gas and inert gas in the furnace has reached a stable level when the sample enters the insulation zone, thereby avoiding directly placing the sample in the insulation zone, where the reducing gas ratio is insufficient and the sample is oxidized at a higher temperature, thereby improving the surface quality.

c) In step S4, after annealing, first stop introducing reducing gas (such as hydrogen), only introduce inert gas, wait for reducing gas to be exhausted, open the furnace door, so as to prevent the danger caused by reducing gas (such as hydrogen), because when reducing gas (such as hydrogen) in the furnace is not exhausted, if the furnace door is opened, there will be a potential safety hazard of explosion. In the cooling process, introducing inert gas can prevent oxidation from occurring during the cooling process, and by controlling the flow rate of inert gas, the cooling rate can be accurately controlled, the thermal stress and residual stress caused by the excessively fast cooling rate of the silicon steel ultra-thin strip can be reduced, and cracks or deformation can be avoided, thereby improving the flatness and surface quality.

It should be noted that in step S3, the annealing time is 1.0h to 1.8h. Exemplarily, the annealing time is 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h. Preferably, the annealing time is 1.2h to 1.8h. More preferably, the annealing time is 1.4h to 1.6h.

It is worth noting that in step S2 and step S3, the use of the above-mentioned preferred annealing temperature and annealing time with synergistic effects can significantly improve the comprehensive performance of the silicon steel ultra-thin strip, for example, reduce iron loss, improve magnetic induction, reduce deformation and stress, and improve plate shape and surface quality. Specifically, (a) Reduce iron loss: The use of the above-mentioned preferred annealing temperature and time can obtain an ideal grain size, which helps to reduce iron loss (especially high-frequency iron loss); annealing temperature is too low or annealing time is too short, which may lead to incomplete recrystallization, thereby increasing iron loss; while annealing temperature is too high or annealing time is too long, it may lead to coarse grains and increase iron loss; (b) Improve magnetic induction: The use of the above-mentioned preferred annealing temperature and time can increase the proportion of favorable {100} oriented grains in the silicon steel ultra-thin strip and reduce the proportion of harmful {111} oriented grains, thereby improving magnetic induction; (c) Reduce deformation and stress, improve flatness (d) Improving surface quality: The preferred annealing temperature and time mentioned above can effectively reduce or eliminate the internal stress generated during the processing (for example, the process of manufacturing ultra-thin silicon steel strip by planar flow casting), thereby preventing deformation of the material; using a suitable annealing temperature and time can help promote the recrystallization process inside the material and restore the microstructure of the material, thereby reducing stress and maintaining the flatness of the material to obtain an ideal plate shape; (d) Improving surface quality: Using the preferred annealing temperature and time mentioned above can help obtain a uniformly grown grain structure, reduce material defects such as cracks, holes, etc., and further improve the surface quality and uniformity of the material.

Preferably, in step S4, the cooling time T is ≥ 6 min. More preferably, the cooling time T is ≥ 8 min. The above preferred cooling time can ensure that the sample sandwiched between the ceramic plates is fully cooled to avoid oxidation after the sample is taken out.

If the cooling time in the furnace is too short and the ultra-thin silicon steel strip is not cooled to room temperature in time, it will react with the air when taken out to form an oxide film on the surface, resulting in a decrease in its magnetic properties, especially an increase in iron loss.

Preferably, in step S4, the cooling rate is 1.8°C/s to 3°C/s. More preferably, the cooling rate is 2.0°C/s to 2.5°C/s.

By adopting the above-mentioned preferred cooling rate, the comprehensive performance of the silicon steel ultra-thin strip can be significantly improved, for example, iron loss can be reduced, magnetic induction can be improved, deformation and stress can be reduced, and plate shape and surface quality can be improved. Specifically, (a) reducing iron loss: adopting the above-mentioned preferred cooling rate helps to ensure that the silicon steel ultra-thin strip forms a uniform microstructure during the cooling process, reduces the obstruction of the movement of the magnetic domain wall, thereby reducing iron loss, and avoiding internal stress and structural defects caused by too fast or too slow cooling rate. These defects may increase hysteresis loss and eddy current loss, resulting in increased iron loss; (b) improving magnetic induction: adopting the above-mentioned preferred cooling rate can ensure that the silicon steel ultra-thin strip forms the desired microstructure and texture during the cooling process, thereby improving the magnetic induction; (c) improving flatness/plate shape and surface quality: adopting the above-mentioned preferred cooling rate can ensure that the temperature of the material drops uniformly at a relatively appropriate rate during the cooling process, reduce the internal stress caused by the temperature difference, thereby reducing the risk of deformation, helping to maintain the uniformity of the material's microstructure, avoiding stress concentration in local areas due to too fast cooling, and also helping to uniformly carry out the recrystallization process inside the material, reducing the internal stress difference caused by uneven recrystallization, which is beneficial to maintaining the flatness of the silicon steel ultra-thin strip, obtaining an ideal plate shape, reducing defects such as micro cracks, and improving surface quality.

Preferably, in steps S1-S4, the flow rate of the inert gas is 0L/min to 7L/min, and the flow rate of the reducing gas is 1.5L/min to 5L/min. By controlling the flow rates of the inert gas and the reducing gas, the ratio of the annealing atmosphere inside the vacuum tube furnace is regulated, so that the sample is placed in a stable annealing atmosphere, effectively protecting the sample from oxidation and contamination during the annealing process, and maintaining a positive pressure in the vacuum tube furnace. Specifically, in S2 and S3, by controlling the flow rates of the inert gas and the reducing gas, it is ensured that the volume ratio of the reducing gas to the annealing atmosphere (a mixture of reducing gas and inert gas) meets the set value K.

It is understood that maintaining a positive pressure in a vacuum tube furnace means maintaining a pressure level higher than atmospheric pressure in the furnace. Such a setting has at least the following beneficial effects on the annealing of ultra-thin silicon steel strips: (a) Improving safety: When a reducing gas (such as hydrogen) is used in the protective atmosphere, maintaining a positive pressure can avoid the mixing of the reducing gas (such as hydrogen) with air, thereby avoiding the risk of explosion and fire, especially when the proportion of hydrogen is high. This is particularly important; (b) Improving magnetic induction: By maintaining a constant positive pressure protective atmosphere, the oxidation of the ultra-thin silicon steel strip during the annealing process can be minimized, which helps to improve its magnetic induction; (c) Reducing Low iron loss: Uniform atmosphere under positive pressure helps to reduce oxidation of ultra-thin silicon steel strip, thereby reducing iron loss, especially high-frequency iron loss; (d) Improve flatness: Positive pressure and gas flow within a suitable range help to reduce the uneven pressure of the furnace atmosphere on the ultra-thin silicon steel strip, thereby reducing deformation or stress concentration caused by uneven atmosphere pressure, and helping to maintain the flatness and plate shape of the ultra-thin silicon steel strip; (e) Improve surface quality: The protective atmosphere under positive pressure can effectively isolate the air, reduce oxidation of ultra-thin silicon steel strip at high temperature, and other surface defects such as cracks, pores, etc., thereby improving the surface quality of the sample after annealing.

Preferably, inert gas (such as nitrogen) and reducing gas (such as hydrogen) are introduced into the cylindrical furnace of the vacuum tube furnace from one side, which can provide uniform and stable atmosphere protection for the annealing treatment of ultra-thin silicon steel strips and ensure the safety and efficiency of the annealing process; specifically, at least the following beneficial effects can be brought about: (a) precise control: introduction from one side can more easily centrally control the gas flow rate and facilitate precise control of the ratio of the two gases; (b) simple operation: introduction from one side can reduce equipment cost and operation complexity; (c) improved annealing uniformity: introduction of gas from one side helps to optimize the gas flow pattern in the furnace, especially in the cylindrical furnace, where natural convection of gas can be used to achieve uniform heating; (d) improved safety: when the proportion of reducing gas (such as hydrogen) is high, introduction from one side helps to better control the distribution of hydrogen and reduce the risk of hydrogen leakage.

It should be noted that in S4, the main step of "after the reduced gas is exhausted from the vacuum tube furnace" includes: determining whether it is exhausted through a reducing gas (such as hydrogen) detection device equipped with the vacuum tube furnace.

The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and comparative examples.

Embodiment 1:

This embodiment provides an annealing method for an ultra-thin Fe-3% Si non-oriented silicon steel strip, comprising the following steps:

S1. Evacuate the vacuum tube furnace to make the vacuum degree in the furnace Pa < 100Pa, introduce nitrogen with a nitrogen flow rate of 6L/min, and then heat the insulation zone in the vacuum tube furnace at a heating rate of 20°C/min;

Among them, the manufacturer of the vacuum tube furnace is Luoyang Juxing Kiln Co., Ltd., and the model is GWL-1200GA.

S2. When the temperature in the heat preservation zone reaches the preset annealing temperature of 1000°C, the sample is clamped up and down by using micro-leakage sintering microporous ceramic plates and placed in a tray; wherein the thickness of the ceramic plate is 10 mm, the pore size of the ceramic plate is 100 μm, and the porosity of the ceramic plate is 18.6%.

Open the door of the vacuum tube furnace, place the tray containing the sample and the ceramic plate in the cooling area of the vacuum tube furnace, close the door, and introduce hydrogen at a flow rate of 4 L/min. Both hydrogen and nitrogen are introduced into the furnace from one side of the cylindrical furnace chamber of the vacuum tube furnace.

The sample is a non-oriented silicon steel ultra-thin strip obtained by a planar flow casting method, the thickness of the non-oriented silicon steel ultra-thin strip is 65 μm, and the chemical composition of the sample is Si: 3% by mass, and the rest is Fe and unavoidable impurities.

S3. When the volume ratio K of hydrogen in the vacuum tube furnace to the annealing atmosphere reaches 40% and the annealing atmosphere is stable, the push rod in the vacuum tube furnace is used to push the tray containing the sample and the ceramic plate to the insulation zone, and annealing is performed at 1000°C for 1.5 hours;

Wherein, the annealing atmosphere is set to a mixed gas of hydrogen and nitrogen;

S4. After annealing, use the push rod in the vacuum tube furnace to push the tray containing the sample and ceramic plate to the cooling zone. Cool for 6 minutes at a cooling rate of 2°C/s. Stop introducing hydrogen during the cooling process and only introduce nitrogen. Use the hydrogen detection device on the vacuum tube furnace to detect the furnace atmosphere. After confirming that the hydrogen has been removed from the vacuum tube furnace, open the furnace door, take out the tray (with the sample and ceramic plate inside), open the ceramic plate pressed on the top, and remove the sample.

Example 2

The difference between this embodiment and embodiment 1 is that in S1, the flow rate of nitrogen is 7 L/min; in S2, the flow rate of hydrogen is 3 L/min; in S3, K is 30%; the other steps and parameters are the same as those in embodiment 1.

Example 3

The difference between this embodiment and embodiment 1 is that in S1, the flow rate of nitrogen is 5 L/min; in S2, the flow rate of hydrogen is 5 L/min; in S3, K is 50%; the other steps and parameters are the same as those in embodiment 1.

Example 4

The difference between this embodiment and embodiment 1 is that in S1, the flow rate of nitrogen is 2.8 L/min; in S2, the flow rate of hydrogen is 4.2 L/min; in S3, K is 60%; the other steps and parameters are the same as those in embodiment 1.

Example 5

The difference between this embodiment and embodiment 1 is that in S1, the flow rate of nitrogen is 1.8 L/min; in S2, the flow rate of hydrogen is 4.2 L/min; in S3, K is 70%; the other steps and parameters are the same as those in embodiment 1.

Example 6

The difference between this embodiment and embodiment 1 is that in S1, the flow rate of nitrogen is 1.2 L/min; in S2, the flow rate of hydrogen is 4.8 L/min; in S3, K is 80%; the other steps and parameters are the same as those in embodiment 1.

Example 7

The difference between this embodiment and embodiment 1 is that in S1, the flow rate of nitrogen is 0.5 L/min; in S2, the flow rate of hydrogen is 4.5 L/min; in S3, K is 90%; the other steps and parameters are the same as those in embodiment 1.

Example 8

The difference between this embodiment and embodiment 1 is that in S2, the annealing temperature is 950°C; the other steps and parameters are the same as those in embodiment 1.

Example 9

The difference between this embodiment and embodiment 1 is that in S2, the annealing temperature is 980°C; the other steps and parameters are the same as those in embodiment 1.

Example 10

The difference between this embodiment and embodiment 1 is that in S2, the annealing temperature is 1020°C; the other steps and parameters are the same as those in embodiment 1.

Embodiment 11

The difference between this embodiment and embodiment 1 is that in S2, the annealing temperature is 1050°C; the other steps and parameters are the same as those in embodiment 1.

Example 12

The difference between this embodiment and embodiment 1 is that in S3, the annealing treatment time is 1.0 h; the other steps and parameters are the same as those in embodiment 1.

Example 13

The difference between this embodiment and embodiment 1 is that in S3, the annealing treatment time is 1.2 hours; the other steps and parameters are the same as those in embodiment 1.

Embodiment 14

The difference between this embodiment and embodiment 1 is that in S3, the annealing treatment time is 1.4 hours; the other steps and parameters are the same as those in embodiment 1.

Embodiment 15

The difference between this embodiment and embodiment 1 is that in S3, the annealing treatment time is 1.6 hours; the other steps and parameters are the same as those in embodiment 1.

Example 16

The difference between this embodiment and embodiment 1 is that in S3, the annealing treatment time is 1.8 hours; the other steps and parameters are the same as those in embodiment 1.

Embodiment 17

The difference between this embodiment and embodiment 1 is that in S4, cooling is performed for 8 minutes; the other steps and parameters are the same as those in embodiment 1.

Embodiment 18

The difference between this embodiment and embodiment 1 is that in S4, cooling is performed for 10 minutes; the other steps and parameters are the same as those in embodiment 1.

Embodiment 19

The difference between this embodiment and embodiment 1 is that in S4, the cooling rate is 1.8°C/s; the other steps and parameters are the same as those in embodiment 1.

Embodiment 20

The difference between this embodiment and embodiment 1 is that in S4, the cooling rate is 2.5°C/s; the other steps and parameters are the same as those in embodiment 1.

Embodiment 21

The difference between this embodiment and embodiment 1 is that in S4, the cooling rate is 3.0°C/s; the other steps and parameters are the same as those in embodiment 1.

Comparative Example 1

The difference between this comparative example and Example 1 is that, in S2-S4, no ceramic plate is used to clamp the sample; the other steps and parameters are the same as those in Example 1.

Comparative Example 2

The difference between this comparative example and Example 1 is that in S3, the annealing atmosphere is only nitrogen; the other steps and parameters are the same as those in Example 1.

Comparative Example 3

The difference between this comparative example and Example 1 is that in S1, the flow rate of nitrogen is 8.0 L/min; in S2, the flow rate of hydrogen is 2.0 L/min; in S3, the volume ratio of hydrogen to annealing atmosphere is K=20%; other steps and parameters are the same as in Example 1.

Comparative Example 4

The difference between this comparative example and Example 1 is that in S2, the preset annealing temperature is 900° C.; the other steps and parameters are the same as those in Example 1.

Comparative Example 5

The difference between this comparative example and Example 1 is that in S2, the preset annealing temperature is 1100° C.; the other steps and parameters are the same as those in Example 1.

Comparative Example 6

The difference between this comparative example and Example 1 is that in S3, the annealing treatment time is 0.8 h; the other steps and parameters are the same as those in Example 1.

Comparative Example 7

The difference between this comparative example and Example 1 is that in S3, the annealing treatment time is 2.0 h; the other steps and parameters are the same as those in Example 1.

Comparative Example 8

The difference between this comparative example and Example 1 is that in S4, cooling is performed for 5 minutes; the other steps and parameters are the same as those in Example 1.

Comparative Example 9

The difference between this comparative example and Example 1 is that in S4, the cooling rate is 1.5°C/s; the other steps and parameters are the same as those in Example 1.

Comparative Example 10

The difference between this comparative example and Example 1 is that in S4, the cooling rate is 3.5°C/s; the other steps and parameters are the same as those in Example 1.

Comparative Example 11

The difference between this comparative example and Example 1 is that in S2, the thickness of the ceramic plate is 6 mm; the other steps and parameters are the same as those in Example 1.

Comparative Example 12

The difference between this comparative example and Example 1 is that in S2, the pore size of the ceramic plate is 70 μm; the other steps and parameters are the same as those in Example 1.

Comparative Example 13

The difference between this comparative example and Example 1 is that in S2, the porosity of the ceramic plate is 24%; the other steps and parameters are the same as those in Example 1.

In order to more clearly show the parameter variables of the above embodiments and comparative examples, see Table 1. The performance results shown in Table 2 were obtained by performing performance tests and quality inspections on the non-oriented silicon steel ultra-thin strips obtained by annealing in Embodiments 1-21 and Comparative Examples 1-13.

As can be seen from Table 2, by adopting the annealing method provided by the present invention, Examples 1-21 can make the grain size uniformly increase to a suitable size, increase the proportion of favorable {100} oriented grains (increase by more than 10%), and reduce the proportion of harmful {111} oriented grains (decrease by more than 20%). The embodiments of the present invention adopt a simple "one-step" annealing process to complete annealing at one time and ensure flatness and non-oxidation of the surface, and the cost is low (due to the low silicon content and no expensive trace elements added). The obtained non-oriented silicon steel ultra-thin strip has excellent comprehensive performance. In particular, compared with the silicon steel strip for high-frequency applications obtained by the existing annealing method, the present invention has higher magnetic induction (B ₅₀₀₀ ≥1.66T), smaller high-frequency iron loss (P 1.0/1000Hz), and lower high-frequency iron loss (P _1.0/1000Hz). ≤40W/kg), which is of great significance for energy saving and consumption reduction and improving equipment performance. With the development of information technology and high-frequency power electronics technology, the demand for high-performance silicon steel that can work stably in a high-frequency environment is increasing. The annealing method provided by the present invention can obtain an ultra-thin silicon steel strip with high magnetic induction and low iron loss under high frequency, which just meets this demand and has great industrial application prospects and value.

It can also be seen from Table 2 that, in comparison, the microstructure and comprehensive performance of Comparative Examples 1-13 are inferior to those of Examples 1-21;

(a) In Comparative Example 1, since a porous ceramic plate was not used to press the sample, the plate shape/flatness and surface quality of the sample after annealing were poor.

(b) In Comparative Example 2, since only nitrogen was used in the annealing process without mixing hydrogen, an obvious oxide film appeared on the surface of the sample after annealing, and the degree of grain growth was also lower than that of the method provided in the embodiment of the present invention. Therefore, the magnetic induction measured in Comparative Example 2 was low.

(c) Since Comparative Example 3 does not adopt the preferred reducing gas ratio provided by the present invention, a certain degree of oxide film appears on the surface of the sample after annealing. The ratio of favorable {100} oriented grains is lower than that of the method provided by the present invention, and the ratio of harmful {111} oriented grains is higher than that of the method provided by the present invention. The magnetic induction measured in Comparative Example 3 is low and the iron loss is high.

(d) Comparative Examples 4-10 do not adopt the preferred annealing temperature, annealing time, cooling time, and cooling rate with synergistic effects provided by the present invention, resulting in low magnetic induction and/or high iron loss in Comparative Examples 4-10 after sample annealing.

(e) Comparative Examples 11-13 do not use the ceramic plates of the preferred thickness, pore size, and porosity provided by the present invention, resulting in low magnetic induction and/or high iron loss in Comparative Examples 11-13 after sample annealing.

Table 1: Specific process parameters in Examples 1-21 and Comparative Examples 1-13

Table 2: Performance results of non-oriented silicon steel ultra-thin strips obtained after annealing in Examples 1-21 and Comparative Examples 1-13

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 changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims (10)

1. A method for annealing a non-oriented silicon steel ultra-thin strip, characterized in that it comprises the following steps: S1. Vacuum the vacuum tube furnace, introduce inert gas, and then heat the insulation zone in the vacuum tube furnace; S2. When the temperature in the holding zone reaches the preset annealing temperature, the sample is placed in the cooling zone of the vacuum tube furnace through the furnace door of the vacuum tube furnace, the furnace door is closed, and reducing gas is introduced; Wherein, the sample is a non-oriented silicon steel ultra-thin strip obtained by plane flow casting method; S3, when the volume ratio K of the reducing gas in the vacuum tube furnace to the annealing atmosphere is ≥30%, the sample is pushed to the insulation zone and annealed at the annealing temperature; Wherein, the annealing atmosphere is set to a mixed gas of reducing gas and inert gas; S4. After annealing, push the sample to the cooling zone for cooling. Stop introducing reducing gas during the cooling process and only introduce inert gas. After the reducing gas is cleaned from the vacuum tube grate, open the furnace door and take out the sample. 2 . The annealing method according to claim 1 , characterized in that during the entire process of steps S2 to S4 , a porous ceramic plate is used to clamp the sample from top to bottom. 3 . The annealing method according to claim 2 , characterized in that the thickness of the ceramic plate is 8 mm to 20 mm, the pore size of the ceramic plate is 80 μm to 150 μm, and the porosity of the ceramic plate is 16% to 22%. 4 . The annealing method according to claim 1 , wherein in S3 , the volume ratio of the reducing gas in the vacuum tube furnace to the annealing atmosphere is K ≥ 50%. 5 . The annealing method according to claim 1 , wherein in S2 and S3 , the annealing temperature is 950° C. to 1050° C. 6 . The annealing method according to claim 1 , characterized in that, in S3 , the annealing time is 1.0 h to 1.8 h. 7 . The annealing method according to claim 1 , characterized in that, in S4 , the cooling time T is ≥ 6 min. 8 . The annealing method according to claim 1 , wherein in S4 , the cooling rate is 1.8° C./s to 3° C./s. 9. The annealing method according to claim 1 is characterized in that the flow rate of the inert gas is 0 L/min to 7 L/min, and the flow rate of the reducing gas is 1.5 L/min to 5 L/min; by controlling the flow rates of the inert gas and the reducing gas, the annealing atmosphere ratio inside the vacuum tube furnace is regulated to maintain a positive pressure in the vacuum tube furnace. 10. The annealing method according to claim 1, characterized in that the chemical composition of the non-oriented silicon steel ultra-thin strip is Si: 2.8% to 4.0% by mass, and the rest is Fe and unavoidable impurities; and/or, In S1, the main step of the vacuum treatment includes evacuating the vacuum tube furnace to make the vacuum degree in the furnace Pa≤150Pa.