JPH032323A - Manufacture of nonoriented silicon steel sheet having high magnetic flux density - Google Patents

Abstract

PURPOSE:To manufacture the nonoriented silicon steel sheet having high magnetic flux density by properly heating a slab having specified compsn. constituted of C, Si, Mn, P, S, Al, N and Fe to execute hot rolling, subjecting it to annealing and cold rolling and thereafter executing specified final annealing. CONSTITUTION:A slab contg., by weight, <=0.005% C, 0.7 to 1.7% Si, 0.1 to 1.5% Mn, 0.005 to 0.10% P, <=0.005% S, 0.3 to 1.3% Al (where <2.0% Si+Al is regulated), <=0.005% N and the balance Fe with inevitable impurities is heated to a temp. within a gamma loop in an Fe-(Si+Al) series to execute hot rolling. The hot rolled steel sheet is subjected to hot rolled sheet annealing within an alphaphase areal temp. of 800 deg.C to the AC3 point. Next, the hot rolled sheet is subjected to cold rolling at >=50% and is thereafter to final annealing. As the final annealing, continuous annealing of 800 to 1000 deg.CX0.5 to 5 min or box annealing of 700 to 850 deg.CX1 to 10hr is executed. In this way, the nonoriented silicon steel sheet having excellent magnetic characteristics of remarkably high magnetic flux density and low core loss can be obtd. at low cost.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a non-oriented electrical steel strip with excellent magnetic properties, and in particular to a method for manufacturing a non-oriented electrical steel strip with extremely high magnetic flux density and low iron loss. Regarding the manufacturing method. (Prior Art) Non-directional electromagnetic m-band is used as core material for generators, electric motors, small transformers, ballasts, etc. However, in recent years, there has been a strong demand for energy conservation, and in order to improve the efficiency or downsize electrical equipment, there has been an increasing demand for iron core materials with high magnetic flux density and low core loss. Texture is one of the factors that governs magnetic flux density, but in the case of non-oriented steel sheets, there is almost no known method for improving the texture to improve magnetic flux density.As for non-oriented steel sheets, (100) So-called in-plane non-direction, in which the plane is parallel to the plate surface, is ideal, and several manufacturing methods have been proposed, but none have been applied to industrial production due to high manufacturing costs. For this reason, it was not possible to fully bring out the magnetic properties of the material. For example, regarding the improvement of magnetic flux density by improving the texture, in JP-A-54-68716, a hot coil of silicon steel added with sb was annealed at 800°C for 5 hours in an HNx gas, and after cold rolling, It is disclosed that the accumulation in the vicinity of (100)<uvW> becomes stronger by processing the process using a known method. However, this method requires a long annealing time for the hot coil, resulting in high costs. Furthermore, as a conventional technique for producing non-oriented electrical steel sheets, it has been shown that increasing the grain size of the material before cold rolling is effective in improving magnetic properties. For example, Japanese Patent Application No. 55-110314 proposes a method of coarsening grains before cold rolling. In this method, when hot-rolling a steel ingot or slab having a specific chemical composition into a hot-rolled steel strip, the hot-rolling end temperature is set to a temperature equal to or higher than the temperature expressed by the following formula (1) according to the chemical composition of the magnetic steel. and (891-900(C%)+50(S j%)-88(
Mn%) + 190 (P%) + 380 (A Q Z))
('C) ・= - (1) Next, this hot rolled steel strip is heated in Ar of magnetic steel at below the transformation point temperature for 30 seconds or more.
The main feature is that annealing is performed under conditions of less than 1 minute. Furthermore, in JP-A No. 58-204126, in a method for manufacturing a non-oriented electrical steel sheet, c:Q, Q2% or less, either Si or (Si+Al) is 1°5% or less, Mn
: 1. For steel containing 0% or less, P: 0.20% or less, and the remainder consisting of Fe and unavoidable impurities, the rolling end temperature in the hot rolling process is 600 to 700°C. 1 coiling temperature is 500°C. A method for producing a patented magnetic steel strip is disclosed, which is characterized in that the above temperature range is used, and then the rolled steel strip is annealed at a temperature not higher than the A3 transformation point for 30 seconds or more and 15 minutes or less. However, these methods all involve hot rolling at low temperatures, and in the case of high-Si steel, there is a risk of cracking or breaking during hot rolling. On the other hand, conventionally, silicon steel sheets have generally been used as non-oriented electrical steel sheets. A silicon steel plate is a steel type to which Si is added to increase specific resistance and reduce iron loss. As a result, the higher the Si content, the higher the Si content, so the magnetic flux density tends to be lower. In addition, when the amount of Si is increased, the Fe-Si system phase diagram leaves the γ loop and enters the α single phase region, so that coarse α grains can be obtained even at the normal pre-hot rolling heating temperature. However, coarse α grains are required before cold rolling.
For this reason, coarsening the α grains before hot rolling brings about many disadvantages. For example, the structure distribution in the sheet thickness direction becomes uneven, which not only deteriorates the magnetic properties after cold rolling and annealing, but also
Brings ridging and sawing. The present invention was made to solve the problems of the prior art described above, and it is possible to easily increase the crystal grain size of the material before cold rolling, and in particular, the magnetic flux density is extremely high, and the iron loss is reduced. The object of the present invention is to provide a method that can continuously produce a Ti magnetic steel strip with low non-orientation. (Means for Solving the Problems) In order to achieve the above object, the present inventors have conducted intensive research on measures that can easily increase the crystal grain size of the material before cold rolling by a full process or a semi-process. Layered. As a result, especially the amount of Si and AQfl. In order to obtain a hot-rolled steel strip with a fine and uniform crystal structure after hot rolling, and to coarsen the grain size of this hot-rolled steel strip, conventional annealing methods are used. It is possible to coarsen the grains of a hot-rolled steel strip relatively cheaply and easily in a short time of 15 minutes or less, without requiring long annealing time such as box annealing, and without the need for decarburization. This is where the present invention is made. That is, the method according to the present invention provides C:0. O O 5%
Below, Si: 0.7 to 1.7%, Mn: 0.1 to 1.
5%, P:O. O O 5 ~0.1 0%, S:O.
005% or less. AQ: 0.3 to 1.3% (However, Si+
When hot rolling a slab containing AI2 (2.0%) and [0.005% or less, with the remainder consisting of iron and unavoidable impurities, it is heated to a temperature within the γ loop in the Fe-(Si+Al) system. After hot rolling, the obtained hot rolled steel sheet is annealed at a temperature of 800°C or higher and within the α phase region temperature of 3 points or less, further cold rolled by 50% or more, and then The summary is a method for producing a non-oriented electrical steel sheet with low core loss and high magnetic flux density, which is characterized by performing final annealing at 800-b or box annealing at 700-850@c for 1-10 hours. It is something to do. The present invention will be explained in more detail below. (Operation) The present invention is based on a combination of the above-mentioned conditions, and its basic configuration is as follows. First, in order to obtain a hot rolled steel strip having a fine and uniform crystal structure, the heating temperature before hot rolling is set to a low temperature γ phase region,
Hot rolling is completed in the γ phase region as much as possible. This can also suppress the refinement of precipitates and promote grain growth in the primary hot-rolled sheet annealing6. During plate annealing, a pre-cold-rolled material having a coarse crystal structure can be obtained by heating to the α region as high as possible. This results in (100)<uvw>+ in the final annealing.
Since a (110)<001> texture is obtained, an extremely high magnetic flux density can be obtained compared to a conventional non-oriented electrical steel sheet having the same core loss value. Considering the balance between iron loss and magnetic flux density, the component system to realize these conditions is as follows. Si: 0.7-1.7% AQ: 0.3-1.3% Si+Al≦2.0% In other words, the total amount of Si + AQ is determined by heating before hot rolling in the γ phase region (e.g. Point a in Figure 1), and subsequent hot-rolled sheet annealing is regulated in the α phase region (e.g., point 5 in Figure 1), with a Si content of 2.0% or less. is regulated in order to achieve the necessary balance between iron loss value and magnetic flux density. Furthermore, the AQ amount is determined by locating the Si amount very close to the γ loop (point C in FIG. 1) under the condition that the Si amount is regulated by the balance between the iron loss value and the magnetic flux density. The above effect is achieved most efficiently, and furthermore, it is regulated from the viewpoint of suppressing fine precipitation of AQN precipitates due to the solubility product with N. Note that if the AQ amount is small, good core loss cannot be obtained, and if it is large, the magnetic flux density decreases. Next, the reasons for limiting the chemical components in the present invention will be explained. C: C is a harmful element in order to maintain magnetic properties, and the content must be kept at 0.01% or less, but the lower the content, the better. Furthermore, in order to prevent magnetic aging, the content is preferably 0.005% or less. Therefore, the C content is set to 0.005% or less. Si: Si is regulated from the viewpoint of fully exhibiting the effects of the present invention. That is, S and L are elements necessary for improving iron loss by increasing specific resistance, but their content is 0.
If it is less than 7%, there is little effect, and if it exceeds 1.7%, S
Even when i alone, not only does it exceed the γ loop of the Fe-8i system, but also the magnetic flux density decreases. Therefore, the Si content is in the range of 0.7 to 1.7%. Mn: Mn is an element that is effective in preventing red heat during hot rolling and improving magnetism by improving texture. However, the content is 0
．． If it is less than 1%, the effect will be small, and if it exceeds 1.5%, the magnetic properties will deteriorate. Therefore, 1Mn content is 0.
The range % is 1 to 1.5. P: P is an element that is effective in improving iron loss. However, this effect is small when the content is less than 0.005%, and 0.1%
If the content exceeds 20%, the magnetic flux density will decrease. therefore,
The P content is in the range of 0.005 to 0.1%. S is an element that generates nonmetallic inclusions such as MnS that are harmful to improving magnetism, and the smaller the amount, the better.
% or less, a stable magnetic improvement effect cannot be obtained. Therefore, the S content is set to 0°005% or less. AQ: Like Si, AQ is an important element constituting the present invention. In other words, in addition to developing components in the (100) crystal direction and increasing resistivity like Si, AQ also increases the solubility product of AQN, which is harmful to the magnetic properties of non-oriented silicon steel sheets. This is an element necessary to suppress fine precipitation. However, if the content is less than 0.3%, such effects are small and good iron loss cannot be obtained, while if the content exceeds 1.3%, the magnetic flux density decreases. Therefore, the Afl content should be in the range of 0.3 to 1.3%. However, regarding the above Si and AQ, the total amount of Si + A9 is set to 2.0% or less from the viewpoint that heating before hot rolling is performed in the γ phase region as described above, and subsequent hot rolled sheet annealing is performed in the α phase region. It needs to be regulated. Next, a manufacturing process in the present invention will be explained. First, steel having the above chemical composition is melted by a normal method and then cast into a steel slab by continuous casting, or a steel ingot is made by an ingot method, and then made into a steel slab by blooming. may be formed. The steel slab produced in this way is heated to a temperature in the γ loop in the Fe-(Si+AQ) system and hot-rolled to form a hot-rolled plate with a thickness of 1.5 to 3.0 mm. obtain. Since most of the reduction in this hot-rolled sheet is performed in the γ phase region, a fine crystal structure (α) can be obtained uniformly in the thickness direction, and remarkable grain growth can be achieved in the subsequent hot-rolled sheet annealing. The plate texture is also favorable for magnetic properties. Next, by subjecting the hot-rolled sheet to hot-rolled sheet annealing, coarse crystal grains are obtained and the texture is improved. The annealing conditions are 800°C or higher, Ac, the desired temperature (within the α phase region temperature), and preferably continuous annealing is performed by holding at this temperature for 0.5 to 5 minutes.
At a low temperature of less than 800° C., a good hot-rolled sheet crystal structure cannot be obtained in continuous annealing, and no annealing effect can be expected. Furthermore, annealing at a high temperature exceeding the Ac point is not preferable because α→γ transformation occurs during annealing of the hot rolled sheet, resulting in finer grains and deterioration of pickling properties in subsequent steps. Next, the hot-rolled plate that has undergone the hot-rolled plate annealing is pickled to remove scale by a conventional method, and then cold-rolled at a rolling reduction of 50% or more. This is the optimum annealed plate grain size for iron loss and magnetic flux density, and high agglomeration (100) <
This is because a cold rolling rate of 50% or more is required to obtain a texture of uvw>. By final annealing the cold-rolled sheet, the texture develops and the magnetic properties are improved. As the annealing conditions, continuous annealing is performed at a temperature of 800 to 1000°C for 0.5 to 5 minutes, or box annealing is performed at a temperature of 700 to 850°C and held for 1 to 10 hours. In this case, if the continuous annealing is less than 800°C and the five-box annealing is less than 700°C, grain growth during annealing is poor and good magnetic properties cannot be obtained. In addition, in continuous annealing, 100
When the temperature exceeds 0°C, and exceeds 850°C in box annealing, the magnetic flux density decreases, and an excessive increase in the furnace temperature is disadvantageous from the viewpoint of furnace maintenance, management, and economic efficiency. The holding time for this final annealing varies depending on the annealing method and can be selected appropriately depending on the respective temperature, but in the case of continuous annealing, a recrystallized structure cannot be obtained if it is less than 0.5 minutes, which further leads to poor magnetic properties. Moreover, if the holding time exceeds 5 minutes, the line speed will become excessively slow in the operation of the continuous annealing furnace. On the other hand, in the case of box annealing, if it is less than 1 hour, there is a problem similar to the reason for limiting the lower limit of the holding time in continuous annealing, and if it exceeds 10 hours, there is an economical problem. Next, examples of the present invention will be shown. (Example) A lot of test steel having the chemical composition shown in Table 1 was melted in a vacuum melting furnace to form a steel ingot, which was then heated to a temperature of 1150°C and then a slab with a thickness of 200+++m was produced. did. This slab was heated to a temperature of 1150°C and 2°OLI
Hot rolling was performed to a thickness of Im. After hot rolling, 755
Hot rolled sheets were annealed for 2 minutes at a temperature of ~1060°C. Furthermore, after pickling, cold rolling is performed to a thickness of Q, 5 mm, and this cold rolled plate is subjected to continuous annealing (840°C x 1.5 minutes, 945°C x 1.5 minutes) or box annealing (750°C x 3 time) was applied. Epstein test pieces were taken from the obtained annealed plates by shearing and their magnetic properties were measured. The results are also listed in Table 1. In Table 1, tests Ha 3 to Ha 4, Ha 8,
&11 to Nα13 and Nα15 are examples of the present invention. As is clear from Table 1, it can be seen that in each of the examples of the present invention, the magnetic flux density can be increased while reducing the iron loss. That is, a non-oriented electrical steel sheet with low iron loss and high magnetic flux density can be manufactured. On the other hand, comparative examples 1 to Nα2 with chemical components outside the scope of the present invention,
Nα5 to Nn 7, &9. Comparative example Nα1 whose chemical components are within the scope of the present invention but whose manufacturing conditions are outside the scope of the present invention
0 and Nα14 cannot reduce iron loss and cannot obtain high magnetic flux density.

[Left below]

(Effects of the Invention) As detailed above, according to the present invention, the grain size of the material before cold rolling can be easily and economically increased in a short time, so that the magnetic flux density is extremely high. A non-oriented electrical steel strip with low core loss and excellent magnetic properties can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a Fe-(Si+Al) system phase diagram schematically showing the relationship between the amount of Si+AI2 and temperature. Patent applicant Takashi Nakamura, Patent attorney representing Kobe Steel, Ltd. 5i+Al(%n)

Claims (2)

[Claims] (1) In weight% (the same applies hereinafter), C: 0.005% or less, Si: 0.7 to 1.7%, Mn: 0.1 to 1.5%,
P: 0.005 to 0.10%, S: 0.005% or less,
Al: 0.3 to 1.3% (However, Si+Al<2.0%
) and N: 0.005% or less, and the balance is iron and unavoidable impurities.
After heating to a temperature within the γ loop in the e-(Si+Al) system and hot rolling, the obtained hot rolled steel sheet has a
Hot-rolled plate annealed within the alpha phase region temperature of ℃ or higher and Ac_3 point or lower, further cold rolled by 50% or higher, and then continuous as final annealing under the conditions of 800-1000℃ x 0.5-5 minutes. A method for producing a non-oriented electrical steel sheet with low iron loss and high magnetic flux density, which comprises performing annealing. (2) As the final annealing, 700-850°C x 1-1
The method according to claim 1, wherein box annealing is performed under conditions of 0 hours.