JPH0518900B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a silicon steel plate with excellent surface properties and a method for manufacturing the same. [Prior art and its problems] The electrical steel sheets that are widely used today are called non-oriented electrical steel sheets, and are mainly used for the iron cores of rotors or stators of motors, and the iron cores of general-purpose small transformers. Materials with low crystal orientation used for cores, ballasts of certification equipment, etc., and grain-oriented electrical steel sheets, which are mainly used in large transformers and high-frequency transformers that require excellent soft magnetic properties. It is broadly classified into materials with high crystal orientation. The quality of the magnetic properties of these materials is largely determined by the Si content in the steel sheet. In other words, the higher the grade of electrical steel sheet, the higher the Si content. These,
Many studies have already been conducted on the mechanism of magnetic property improvement due to Si inclusion, and the results can be summarized as follows. (1) Si is a ferrite stabilizing element and at the same time
It has the effect of increasing the electrical resistance of steel. By annealing in the ferrite single-phase region expanded by the addition of Si, ferrite grain growth can be achieved, making it possible to achieve high magnetic permeability and low coercive force. This is effective in reducing hysteresis loss. However, as the ferrite grain size increases, the domain wall movement distance during the alternating magnetization process increases, resulting in an increase in eddy current loss. Therefore, Si contributes to reducing this eddy current loss through increasing electrical resistance. Therefore, Si enables excellent soft magnetic properties and low iron loss. (2) Furthermore, in a region where the amount of Si added exceeds 3%, the magnetocrystalline anisotropy and magnetostriction decrease significantly, and the high frequency magnetization characteristics are improved. In contrast to these effects, the addition of Si causes a decrease in the density and magnetic flux density of steel, resulting in a decrease in energy conversion efficiency. However, even if such negative effects are taken into consideration, Si addition exhibits a significant effect of improving magnetic properties. As mentioned above, when Si is added to steel, the magnetic properties of the material itself are improved, but many restrictions are imposed on the process due to the addition of Si. Important points in the process are listed below. As the amount of Si added increases, the formation of a low melting point fayalite layer (Fe ₂ SiO ₄ ) is promoted during the slab heating stage during hot rolling, causing scale melting. The formation of such a low melting point scale layer causes scale surface defects during the hot rolling stage. In particular, for grain-oriented silicon steel sheets, complete melting of MnS, AlN, etc., which play important roles as inhibitors, during final annealing is essential during hot rolling. High-temperature heating is performed, and the formation of a scale layer as described above is undesirable not only in terms of surface defects but also in terms of yield reduction. Further, the formation of such a scale layer also occurs during decarburization annealing. Generally called the subscale layer. The surface oxidation layer produced by the reaction with water vapor in the decarburization annealing atmosphere impedes domain wall movement during the magnetization process, thereby deteriorating the magnetic properties. The presence of such subscale layers is not a major problem in the case of grain-oriented silicon steel sheets that are ultimately purified in a high-temperature hydrogen atmosphere, but semi-processed non-grained silicon steel sheets are often made into products after decarburization. This is a big problem for magnetic steel sheets. On the other hand, an increase in the amount of Si added causes deterioration of weldability. In particular, welding defects during pickling welding and continuous annealing of hot rolled sheets are a direct cause of in-line fractures. These welding defects are caused by the formation of oxides in the weld zone and the coarsening of ferrite grains in the heat affected zone. An increase in the amount of Si added deteriorates the ductility of steel.
In particular, deterioration in toughness due to coarsening of crystal grains promotes slab cracking and edge cracking during rolling. Furthermore, in steels with Si additions exceeding 4 wt%, DO ₃ type Fe ₃ Si intermetallic compounds are formed, and it is generally believed that rolling becomes impossible. The electrical steel sheets are finally used by being laminated after being coated with an inorganic or organic insulating coating.
In that case, the steel surface becomes inert due to the increase in the amount of Si added, and the wettability between the insulating film and the steel plate surface decreases. As a result, spot-like coating defects occur due to the coating being repelled when the coating is baked. For this reason, when the amount of Si is large, it is necessary to improve the adhesion of the coating by brushing the surface of the steel sheet in advance before applying the insulation coating. Although the above-mentioned individual problems must be dealt with in each process, no technology has yet been disclosed to completely eliminate these problems. In particular, for the purpose of suppressing the formation of the above-mentioned subscale layer, the technology of applying iron plating before decarburization annealing (Japanese Patent Publication No. 59-10412) is considered to be noteworthy, but this technology is also used in the previous process. cannot solve the problem. In addition, with the aim of improving the magnetic properties of grain-oriented electrical steel sheets, Japanese Patent Application Laid-Open No. 127829/1982 and Japanese Patent Publication No. 37367/1983 have proposed increasing the Si concentration in the inner layer compared to the surface layer. . Of these,
The former steel plate has a Si content of 3.0wt% or more in the surface layer and a low Si concentration in the center, and the latter steel plate has a Si content of 1.8 to 3.5wt% in the surface layer, so it does not have the above problems. It is difficult to say that it will solve all the problems. In particular, it cannot be expected to have a subscale suppression effect comparable to that of the above-mentioned iron plating technology. In view of the above-mentioned problems, the present invention can improve various problems such as scale layer formation, weldability, strip edge cracking, and affinity with insulating coatings, and makes manufacturing by rolling, which was conventionally considered difficult, practically possible. The present invention aims to provide a high-silicon steel plate and a method suitable for manufacturing the same. [Means for solving the problem] Therefore, the present invention provides a multilayer silicon-containing steel plate having a shell layer with a thinner alloy concentration than the inner layer on the surface layer of the steel plate with a specified thickness, This is intended to improve the surface, reduce edge cracking, improve weldability, and improve the adhesion of the insulating coating while maintaining the excellent magnetic properties of the inner layer. That is, the silicon steel plate of the present invention has a thickness of 20% or less of the total thickness of the steel plate on both sides, and a thickness of 20% or less on one side of the total thickness of the steel plate.
The alloy composition in a limited surface layer portion of 3 μm or more is C≦0.010wt%, 0.05wt%≦Mn≦0.5wt%,
Si<1.0wt%, P≦0.1wt%, S≦0.05wt%, N≦
0.005wt%, 0.005wt%≦Sol.Al≦0.1wt%, remainder
Composed of Fe and unavoidable impurities, the alloy composition in the remaining inner layer in the thickness direction is C≦0.010wt
%, 0.05wt%≦Mn≦0.5wt%, 1.0wt%≦Si≦
7.0wt%, P≦0.1wt%, S≦0.05wt%, N≦
0.005wt%, 0.005wt%≦Sol.Al≦0.1wt%, balance
Its basic feature is that it has a multilayer structure composed of Fe and unavoidable impurities. In addition, in order to suitably manufacture such a silicon steel plate, the present invention casts a shell with a total thickness of 20% or less of both sides of the steel ingot and a wall thickness of 2.5 mm or more. The alloy composition of the shell layer is C≦0.060wt by the step of casting and the step of casting the inside of the steel ingot.
%, 0.05wt%≦Mn≦0.5wt%, Si＜1.0wt%, P
≦0.1wt%, S≦0.05wt%, N≦0.005wt%,
0.005wt%≦Sol.Al≦0.1wt%, the balance consists of Fe and unavoidable impurities, and the alloy composition of the inner layer of the steel ingot is
C≦0.060wt%, 0.05wt%≦Mn≦0.5wt%, 1.0wt
%≦Si≦7.0wt%, P≦0.1wt%, S≦0.05wt%,
N≦0.005wt%, 0.005wt%≦Sol.Al≦0.1wt%,
A steel ingot composed of the remainder Fe and unavoidable impurities is formed into an ingot, and the steel ingot is hot rolled directly or after heating and soaking, and then subjected to cold rolling and annealing one or more times after descaling treatment. This is another basic characteristic. The details of the present invention will be explained below. Basically, the present invention suppresses scale formation, improves malleability, improves weldability, and improves insulation coating by making the alloy composition of the extremely limited surface layer of a silicon-containing steel sheet thinner than that of the inner layer. The aim is to simultaneously improve the adhesion of the adhesive. In particular, the manufacturing method of the present invention solves various problems associated with Si content that occur in subsequent steps by controlling the alloy composition of the surface layer and inner layer of the steel ingot during the ingot making process. The silicon steel sheet of the present invention has a limited Si content of less than 1.0wt% in the surface layer, and a Si content of less than 1.0wt% in the inner layer.
1.0 to 7.0wt%, and the thickness of the surface layer is 20% or less of the total thickness of the steel plate on both sides, and 3 μm or more on one side. The steel plate of the present invention is obtained by rolling a steel ingot having a structure in which an inner layer with a high Si content is covered with a shell layer with a low Si content, and the shell layer constitutes the surface layer of the steel plate. In order to reduce cracking resistance during hot working by covering with a shell, it is necessary to increase the ductility of the shell layer compared to the inner layer. For this purpose, it is necessary to control the Si layer of the shell layer. Third
The figure shows a slab in which the inner layer having the composition of Steel-6 in Table 2 is cast into a shell with an increased amount of Si based on the composition of Steel-1 in Table 1 at 1150℃.
After heating for 2 hours, hot rolling was immediately performed to a thickness of 2 mm, and the effect of the amount of Si in the shell layer on edge cracking of the hot rolled sheet at that time is shown. As is clear from the figure, the effect of reducing edge cracking decreases when the amount of Si in the shell layer is 1.0 wt% or more. Therefore, the present invention aims at reducing Si in the shell layer, that is, the surface layer.
The amount should be less than 1.0wt%. Furthermore, by controlling the Si content to less than 1.0 wt%, it is possible to appropriately avoid the occurrence of ridging defects that inevitably occur in high-Si electrical steel sheets. The alloy composition of the inner layer is determined with consideration to the original magnetic properties. Considering the essential effect of improving magnetic properties by adding Si, it can be expected that up to about 6.5 wt% of Si can reduce magnetostriction, improve magnetic permeability, and reduce iron loss. On the other hand, when the amount of Si added exceeds 7.0 wt%, the magnetic permeability decreases conversely, and the advantages in terms of alloy design decrease. Therefore, in the present invention, the upper limit of the amount of Si in the inner layer is 7.0 wt%.
Regarding the lower limit, we also take into account the fact that the magnetic properties of the entire material must be maintained by the magnetic properties of the inner layer, and that if the composition is the same as that of the shell layer, the advantage of a multilayer structure is lost. 1.0wt
% is the lower limit of the amount of Si. The thickness of the surface layer is first regulated from the viewpoint of maintaining and improving the final magnetic properties. Figure 4 shows hot-rolled sheets with shell compositions of Steel-1 in Table 1, inner layer compositions of Steel-7 and Steel-8 in Table 2, and with various shell thicknesses. After cold rolling to
This figure shows the relationship between the ratio of the shell layer to the total thickness of the material obtained by finishing annealing for seconds (= the ratio of the surface layer of the steel plate) and the iron loss at a magnetic flux density of 1.5T at 50Hz. . According to the figure, for any material, there is almost no increase in iron loss up to a shell ratio of about 10%. This is because the presence of a shell layer with a low Si composition lowers the resistivity of the surface layer and tends to increase eddy current loss, but on the other hand, the shell layer suppresses the formation of subscale layers during decarburization annealing. However, in order to effectively reduce the iron loss caused by the irreversible movement of the domain wall near the surface layer of the material due to the subscale layer, the positive and negative effects of both cancel each other out and there is almost no change in iron loss. it is conceivable that. Therefore, in the present invention, from a practical point of view, the upper limit of the ratio of the surface layer portion is set to 20%, preferably 10% or less, which is a region in which no significant deterioration of magnetic properties appears. Next, the thickness of the surface layer is regulated from the viewpoint of suppressing the formation of subscale layers. Figure 5 shows a 1.0 mm thick hot rolled sheet with a shell layer composition of Steel-1 in Table 1, an inner layer of Steel-8 in Table 2, and a shell ratio of 3% (1.5% per side). Materials whose surface layer (shell) thickness is varied by rolling from 0.1 mm to 0.1 mm, and steel
The relationship between the thickness of the subscale layer immediately below the surface layer and the thickness of the surface layer was investigated using a material obtained by decarburizing the No. 8 shell-less material at 800°C for 5 minutes.
From the figure, it can be seen that if the surface layer thickness is 3 μm or more, the formation of the subscale layer is considerably suppressed, and if the surface layer thickness is 5 μm or more, the subscale layer is hardly formed in a short time decarburization treatment. Therefore, in the present invention, the thickness of the surface layer is 3 μm or more on one side,
Preferably it is 5 μm or more. Next, reasons for limiting other compositional components in the present invention will be explained. Regarding magnetic properties, C acts as a barrier to domain wall movement when precipitated as Fe ₃ C, and as a direct cause of magnetic aging when in a solid solution C state, so it is preferable to have a small amount after final annealing. Therefore, in the present invention, the content is set to 0.010 wt% or less in both the surface layer portion and the inner layer portion. Mn contributes to reducing iron loss by increasing the resistivity of steel, but its effect is smaller than that of Si, and this effect cannot be expected in steel containing 1.0 wt% or more of Si. Furthermore, if it is contained in a large amount, it causes deterioration of magnetic properties such as magnetic permeability, so the upper limit is set at 0.5 wt%. The lower limit is set for the purpose of fixing S, which has a negative effect on magnetic properties.
The content shall be 0.05wt%. Like Si, P is a ferrite stabilizing element and at the same time increases resistivity, so it is an effective element for improving AC magnetic properties. However, on the other hand, it is also an element that segregates at ferrite grain boundaries and makes steel brittle. In particular, in steel with Si exceeding 1.0wt%,
The embrittlement effect of P becomes a problem. Therefore, in the present invention, P is regulated to 0.1 wt% or less. Since S is an element harmful to magnetic properties, it is preferable to minimize the amount of S. Therefore, in the present invention, the upper limit is set in consideration of fixation by Mn.
The content shall be 0.05wt%. Since N is an element that participates in magnetic aging like C, it is preferable that the amount of N be as small as possible. However, it is also possible to fix it with Al etc.
In the present invention, the upper limit is set to 0.005wt from a practical point of view.
%. Al contributes to the improvement of AC magnetic properties through the same effect as Si, but when added in large amounts compared to Si, the formation of alumina inclusions during the steelmaking stage becomes significant, and conversely it impairs the cleanliness of the material. lower.
Therefore, the maximum amount of Al added in the inner layer is 1.0 wt%. In the surface layer (shell layer), high Al content increases the ferrite grain size and further promotes the formation of a subscale layer during the decarburization annealing process.
The upper limit of is regulated to 0.1wt%. Furthermore, the lower limit of Al is set to 0.005% or more for the purpose of fixing N in the steel in both the surface layer and the inner layer. Next, the manufacturing method of the present invention will be explained. In the method of the present invention, a steel ingot as described above is obtained by manufacturing a steel ingot from an inner layer with a high Si content and a shell layer with a low Si content, and rolling this ingot under predetermined conditions. Steel ingots are manufactured by first casting a shell and then casting steel that will become the inner layer of the steel ingot, or by casting steel that will become the inner layer of the steel ingot and then casting the shell. Figure 1 shows the steel ingots manufactured in this way (shell layer: Table 1 Middle Steel-1, inner layer: Table 2 Middle Steel-1).
5) shows the cross-sectional macrostructure (photo taken from direction A in Figure 2), and it can be seen that the shell layer has a finer ferrite structure than the inner layer by regulating its Si content. . As mentioned above, this plays an important role in preventing edge cracking of the material. In such a steel ingot, the total thickness of the shell on both sides of the steel ingot is 20% or less of the total thickness of the steel ingot for the reasons mentioned above. Furthermore, the thickness of the shell layer (thickness on one side)
It should be 2.5mm or more. Steels having the compositions of Steel-5 and Steel-6 in Table 2 were cast into a solidified shell having a thickness of 2 mm to 15 mm having the composition of Steel-1 in Table 1 to prepare a clad slab. For comparison, slabs of Steel-5 and Steel-6 without shells were also cast. Four such slabs were heated at 1150° C. for 2 hours, immediately hot rolled to a thickness of 2 mm, and rolled up. For the steel strip obtained in this way, the degree of edge cracking that occurred on both edges of the steel strip was measured using ordinary low carbon hot rolled steel strip (SPHC).
The condition of the edge in the class) was evaluated on a five-point scale, with the condition being 5. The results are shown in FIG. According to this, whether the internal composition is Steel-5 or Steel-6, the shell layer is 2
It can be seen that the effect of reducing edge cracking is remarkable in the region increasing from mm to 3 mm. This is to prevent exposure of the inner layer due to scaling off during the slab heating stage and cracking of the shell layer during hot rolling.
This indicates that a minimum shell layer must be ensured, and in the present invention, based on these results, the lower limit of the shell thickness was determined to be 2.5 mm. The composition of the steel ingot is basically the same as described for the steel plate, but when decarburizing annealing is performed in the post-manufacturing process, C can be reduced to 0.010wt% or less by short-time decarburizing annealing. The upper limit to which the amount of C can be reduced is set at 0.060wt%. In the present invention, such a steel ingot is directly or
After heating and soaking to a temperature of 1000 to 1350°C, hot rolling is performed. After the scale removal treatment, this hot-rolled sheet is cold-rolled and annealed at least once, resulting in a final product with a surface layer (shell layer) thickness of 3 μm or more, and usually 1.0 mm or less. . In addition, in the present invention, at least one of the two or more annealing times can be decarburization annealing to reduce C in the steel to 0.010 wt% or less.

【table】

[Table] [Example] ● Example 1 For the purpose of manufacturing non-oriented electrical steel sheets, the first
Slabs made by appropriately combining the steels shown in Tables 2 and 2,
After heating to 1150°C, it was rolled to a thickness of 2.0 mm using a continuous hot rolling mill and wound at 700°C. After evaluating the surface and edge characteristics of this hot-rolled sheet, the thickness was reduced to 0.35 mm through a pickling and cold pressing process, and then the amount of C in the core (inner layer) was reduced according to the C level.
Items below 0.010wt% are directly annealed continuously at 850℃ for 2 minutes, and items over 0.01wt% are decarburized at 800℃ for 5 minutes, followed by 900℃ x
Finish annealing was performed for 30 seconds. The magnetic properties of the steel sheet thus obtained and the characteristic evaluation at the hot-rolled sheet stage are shown in Table 3 together with the manufacturing conditions. From the same table, it can be seen that the non-oriented electrical steel sheet manufactured based on the method of the present invention is superior in both sheet properties and electromagnetic properties as compared to the conventional method. ● Example 2 For the purpose of manufacturing grain-oriented electrical steel sheets, slabs made by appropriately combining the steels listed in Tables 1 and 2 were heated to 1300°C.
After heating to , it was rolled to a thickness of 2.0 mm using a continuous hot rolling mill and rolled up at 550°C. After evaluating the surface and edge cracks of the hot-rolled sheet, it was subjected to cold process rolling including normalization treatment at 1100°C for 5 minutes, pickling, and intermediate annealing.
The thickness was reduced to 0.35mm. After that, decarburization annealing was performed at 800°C for 5 minutes, and after coating with MgO as the main component, the first stage was heated to 850°C, and the second stage was heated to 850°C.
A two-stage finish annealing was performed at 1150°C, and finally a flattening annealing was performed at 850°C for 2 minutes. The magnetic properties of the steel sheet thus obtained and the characteristic evaluation at the hot-rolled sheet stage are shown in Table 3 together with the manufacturing conditions. From the same table, by using a slab with a multilayer structure with shells as a material, scale melting during high temperature heating is reduced, and as a result, the surface quality and edge cracking of the hot rolled sheet are significantly improved.
It can be seen that excellent values can be obtained in terms of magnetic properties.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a photograph showing the metallographic structure of a cross section of a steel ingot, which is the raw material for the steel plate of the present invention. FIG. 2 is an explanatory diagram showing the cross-sectional direction and dimensions of the steel ingot shown in FIG. 1. Third
The figure shows the effect of the Si concentration in the shell layer of a steel ingot consisting of a shell layer and an inner layer on edge cracking during rolling. FIG. 4 shows the influence of the ratio of the total shell layer thickness to the total thickness on the magnetic properties of the final product in a steel ingot consisting of a shell layer and an inner layer. FIG. 5 shows the influence of the thickness of the surface layer of a silicon steel plate, which consists of an inner layer and a surface layer, on the formation of a subscale layer. FIG. 6 shows the influence of the shell layer thickness of a steel ingot consisting of a shell layer and an inner layer on edge cracking during rolling.

Claims (1)

[Claims] 1. The alloy composition in a limited surface layer portion whose thickness is 20% or less in total on both sides of the steel plate and 3 μm or more on one side of the total thickness of the steel plate is C≦0.010wt%,
0.05wt%≦Mn≦0.5wt%, Si＜1.0wt%, P≦
0.1wt%, S≦0.05wt%, N≦0.005wt%,
0.005wt%≦Sol.Al≦0.1wt%, the remainder consists of Fe and unavoidable impurities, and the alloy composition in the remaining inner layer in the thickness direction is C≦0.010wt%, 0.05wt%≦
Mn≦0.5wt%, 1.0wt%≦Si≦7.0wt%, P≦
0.1wt%, S≦0.05wt%, N≦0.005wt%,
A silicon steel sheet with excellent surface properties and a multilayer structure consisting of 0.005wt%≦Sol.Al≦0.1wt%, the balance being Fe and unavoidable impurities. 2 20% of the total thickness of both sides of the steel ingot
Through the process of casting a shell with the following thickness and a wall thickness of 2.5 mm or more, and the process of casting the inside of the steel ingot, the alloy composition of the shell layer is C≦0.060wt%,
0.05wt%≦Mn≦0.5wt%, Si＜1.0wt%, P≦
0.1wt%, S≦0.05wt%, N≦0.005wt%,
0.005wt%≦Sol.Al≦0.1wt%, the balance consists of Fe and unavoidable impurities, and the alloy composition of the inner layer of the steel ingot is
C≦0.060wt%, 0.05wt%≦Mn≦0.5wt%, 1.0wt
%≦Si≦7.0wt%, P≦0.1wt%, S≦0.05wt%,
N≦0.005wt%, 0.005wt%≦Sol.Al≦0.1wt%,
A steel ingot composed of the balance Fe and unavoidable impurities is formed into an ingot, and the steel ingot is directly or hot rolled after being heated and soaked, and then subjected to a scale removal treatment, and then cold rolled and annealed one or more times. The total thickness of both sides of the steel plate is 20% or less of the total thickness of the steel plate, and the thickness of one side is 20% or less of the total thickness of the steel plate.
The alloy composition in a limited surface layer portion of 3 μm or more is C≦0.010wt%, 0.05wt%≦Mn≦0.5wt%,
Si<1.0wt%, P≦0.1wt%, S≦0.05wt%, N≦
0.005wt%, 0.005wt%≦Sol.Al≦0.1wt%, remainder
Composed of Fe and unavoidable impurities, the alloy composition in the remaining inner layer in the thickness direction is C≦0.010wt
%, 0.05wt%≦Mn≦0.5wt%, 1.0wt%≦Si≦
7.0wt%, P≦0.1wt%, S≦0.05wt%, N≦
0.005wt%, 0.005wt%≦Sol.Al≦1.0wt%, balance
A method for manufacturing a silicon steel sheet with excellent surface properties, which comprises manufacturing a silicon steel sheet with a multilayer structure composed of Fe and unavoidable impurities. 3. The method for producing a silicon steel sheet with excellent surface properties according to claim 2, wherein at least one of the two or more annealings is decarburization annealing to reduce C in the steel to 0.010 wt% or less. .