JPS6254846B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a high magnetic flux density unidirectional silicon steel sheet with excellent iron loss. Unidirectional silicon steel sheets are soft magnetic materials that are mainly used as core materials for transformers and other electrical equipment, and must have good magnetic properties in terms of excitation properties and iron loss properties. In order to obtain a material with excellent magnetic properties, it is important that the <001> axis, which is the axis of easy magnetization, is highly aligned in the rolling direction, but other factors such as crystal grain size, specific resistance, and surface coating also have a large influence. come. The degree of directionality is determined by Satoru Taguchi et al.
With the development of the one-time cold rolling method disclosed in Publication No. 15644, there has been a significant improvement, and now products with magnetic flux densities of approximately 96% of the theoretical value are being manufactured. Along with this, the iron loss characteristics have also improved significantly, but further improvements in the future cannot be solved by improving this direction alone, increasing the specific resistance and making the secondary recrystallized grains of the product finer. There is a growing need for manufacturing technology to achieve this. In particular, in the case of high magnetic flux density unidirectional silicon steel sheets, which are characterized by strong reduction during final cold rolling, the secondary recrystallized grains of the product tend to become larger as the magnetic flux density increases, and the directionality is The improvement in iron loss due to the improvement in iron loss is canceled out. Therefore, the development of technology to reduce the crystal grain size has been awaited. However, in the manufacturing method of high magnetic flux density unidirectional silicon steel sheet, which uses AlN as a precipitate necessary for the occurrence of secondary recrystallization and is characterized by strong reduction during final cold rolling, a manufacturing process that reduces the grain size of the product is difficult. If these conditions were adopted, secondary recrystallization failures frequently occurred, making stable industrial production impossible. For example, acid solubility in the material
Increasing the amount of Al, lowering the hot-rolling temperature, and increasing the cooling rate during cooling after hot-rolled sheet annealing are particularly effective in refining the grains of the product, but in any case, secondary The frequency of occurrence of recrystallization defects increases. In the present invention, secondary recrystallization defects that occur under manufacturing process conditions that aim to refine the crystal grain size of the product are solved by Cr in the molten steel.
It was discovered that the problem could be solved by adding . However, the problem with the addition of Cr is the deterioration of the surface film of the product. As is well known, on the surface of a unidirectional silicon steel sheet, it is common practice to provide a fulterite-based film whose main components are MgO applied as an annealing separator and Si in the steel sheet. This surface film not only plays an important role as an insulating film when silicon steel sheets are laminated in transformers, etc., but also applies tension to the steel sheet due to the difference in expansion coefficient between the steel sheet and the film, reducing iron loss. This effect is greater for materials with better directionality. Therefore, even if manufacturing process conditions are adopted that aim at refining the crystal grains of the finished product by adding Cr, if this results in deterioration of the film properties, it may be difficult to make full use of the refining effect on iron loss. I can't say that. In order to solve these problems, the present inventors conducted various studies and found that an excellent surface film can be formed by adding Cu to molten silicon steel. Thus, one feature of the present invention is that
The purpose is to add elements effective for film formation to molten steel. Conventional methods for improving coatings have mainly involved improving the properties of the annealing separator applied before final high-temperature annealing, or adding elements to the annealing separator. However, in the case of materials containing Cr, the formation of an oxidized layer on the surface of the steel sheet formed during the decarburization annealing process performed before applying the annealing separator is affected, so this method alone is not a drastic solution. Thinking that this would not lead to improvement, they attempted a method of adding elements to molten steel and utilizing this effect. This method of adding elements to molten steel has generally been rarely used because it has a large effect on secondary recrystallization, but in the present invention, the characteristics of each element can be adjusted by adding Cr and Cu in combination. As a result, it has become possible to stably manufacture products with small crystal grains, and to manufacture grain-oriented silicon steel sheets with good film properties and good iron loss. The present invention will be described in detail below. The ingredients of the silicon steel material used in the present invention are as follows. i.e. C0.025~0.100%, Si2.5
~4.0%, Mn0.03~0.15%, S0.010~0.050%, acid-soluble Al0.010~0.050%, N0.0030~0.0100% as basic components, and Cr, which is a feature of the present invention.
It contains 0.03 to 0.30% Cu, 0.02 to 0.30% Sn, and 0.02 to 0.30% Sn as necessary. If C is less than 0.025%, secondary recrystallization becomes unstable, and if it exceeds 0.100%, the annealing time in the decarburization annealing step becomes longer, which is not preferable. If Si is less than 2.5%, the low core loss that is the object of the present invention cannot be obtained. On the other hand, if it exceeds 4.0%, the occurrence of cracking during cold rolling becomes significant, which is not preferable. Acid-soluble Al and N are used in the present invention, which uses strong reduction cold rolling with a final cold rolling reduction of 80% or more as the basic process condition.
It is necessary to form AlN, which is essential for secondary recrystallization, and the lower limit is 0.010% acid-soluble Al.
N0.0030%. When acid-soluble Al exceeds 0.050%, secondary recrystallization defects increase. N is 0.0100
If it exceeds %, bulge-like defects called blisters will occur on the surface of the finished steel sheet, which is undesirable. Mn and S are elements necessary to form MnS, which is necessary to further stabilize secondary recrystallization.
If the amount of MnS is less than 0.03% or S is less than 0.010%, the amount of MnS is insufficient, and if the amount of Mn exceeds 0.15% or S is 0.050.
If it exceeds %, the dispersion state of MnS becomes inappropriate,
In either case, secondary recrystallization defects increase. The amount of Cr added, which is one of the features of the present invention, is 0.03~
0.30%, and Cu needs to be added in a combined amount in the range of 0.02 to 0.30%. As mentioned above, Cr suppresses secondary recrystallization defects that occur when manufacturing process conditions that aim to refine product crystal grains, and as a result, achieves refinement of product crystal grains, and is less than 0.03%. On the other hand, if it exceeds 0.30%, decarburization performance deteriorates in the decarburization annealing process, making it impossible to lower C sufficiently. Figure 1 shows C0.060%, Si3.10%, Mn0.07%,
S0.025%, acid soluble Al0.032%, N0.0085%,
A Cr-containing silicon steel slab containing 0.10% Cu was heated to 1380℃, hot-rolled to a thickness of 2.3mm, annealed at 1120℃×2min, rapidly cooled, cold-rolled to a thickness of 0.30mm, and debonded at 840℃. Charcoal annealing, applying MgO as an annealing separator,
Influence of secondary recrystallization defects and iron loss in molten steel of products obtained by final high-temperature annealing at 1200°C x 20 hours
FIG. 3 is a diagram showing the influence of Cr. The higher the Cr content, the less secondary recrystallization defects occur, and there are no secondary recrystallization defects at 0.03% or more. The iron loss at this time is approximately W _17/50
It was 1.01w/Kg. This value is the highest grade 1.05w/Kg specified by the Japanese Industrial Standards (JIS).
(G6H) is in the following range, indicating that the highest grade of iron loss can be stably obtained under the conditions of the present invention. Figure 2 shows C0.060%, Si3.10%, Mn0.07%,
S0.025%, acid soluble Al0.023%, N0.0085%,
A silicon steel slab containing 0.10% Cu was heated to 1380℃, hot rolled to a thickness of 2.3mm, annealed at 1120℃×2min, rapidly cooled, cold rolled to a thickness of 0.30mm, and decarburized at 840℃. Annealed, coated with MgO as an annealing separator,
Influence of secondary recrystallization defects and iron loss in molten steel of products obtained by final high-temperature annealing at 1200°C x 20 hours
FIG. 3 is a diagram showing the influence of Cr. In the case of Figure 1, the acid-soluble Al in the molten steel is 0.032%, while in the case of Figure 2 it is as low as 0.023%, so secondary recrystallization failure does not occur even when the Cr content is low, but iron loss is around 1.06w/Kg at W _17/50 , which is a problem in stably obtaining the highest quality iron loss.
By increasing the amount of acid-soluble Al, the crystal grains of the product become smaller and the magnetic flux density improves, but since the occurrence of secondary recrystallization defects increases, acid-soluble Al is not suitable for stable industrial production. I couldn't do much. Therefore, as shown in Figure 2, it has been difficult to obtain a product with the highest quality iron loss. However, as shown in FIG. 1, when Cr is contained, secondary recrystallization is stable even if the acid-soluble Al content is high, so it is possible to industrially stably produce top-grade products. A phenomenon similar to that of increasing the amount of acid-soluble Al (product crystal grains become finer,
Alternatively, the phenomenon in which the magnetic flux density improves, but if the limit is exceeded, the occurrence of secondary recrystallization defects increases) can be solved by lowering the hot rolling temperature, increasing the cooling rate after annealing the hot rolled sheet, or increasing the cooling rate during the cold rolling process. This occurs when the conditions of increasing the aging temperature between multiple passes and increasing the heating rate during decarburization annealing are adopted. Incidentally, although it is possible to reduce grain growth by employing these conditions alone, the same effect can be achieved by appropriately combining each condition. Therefore, even if the amount of acid-soluble Al added is such that it is impossible to achieve refinement of crystal grains in the product, grain growth can be reduced by adopting the above conditions. It also helps eliminate secondary recrystallization defects that occur when these conditions are adopted.
Cr addition is effective. Recently, attempts have been made to improve core loss by making the product plate thinner than 0.30 mm, for example 0.23 or 0.15 mm, but thinning increases secondary recrystallization defects and reduces product crystal grains. There are problems that come with growing up. The technique of the present invention is particularly effective as a countermeasure against this problem. By the way, in addition to selecting the manufacturing process conditions in a direction that makes the crystal grains of the product finer, an effective method for refining the crystal grains of the product is to add Sn to the molten steel, as shown in Japanese Patent Application Laid-Open No. 134722/1983. Add only the appropriate amount. Therefore, with materials added with Sn,
Furthermore, the iron loss obtained is extremely good when the manufacturing process conditions are selected so that the crystal grains of the product become fine and Cr is added to eliminate secondary recrystallization defects that occur at that time. At this time, if Sn is less than 0.03%, the effect of refining the crystal grains of the product will be small;
If it exceeds 0.03, cracking during cold rolling will become significant.
It needs to be ~0.30%. Cu is an excellent element for forming an insulating film on the surface of a product (an oxide mainly composed of MgO as an annealing separator and Si in steel), and can provide a film with good adhesion and insulation. Because of its good adhesion, the difference in expansion coefficients between the steel plate and the coating increases the tension applied to the steel plate, which has the effect of reducing iron loss. However, when Cu is added alone, the crystal grains of the product become coarse and the iron loss deteriorates. The present invention makes it possible to manufacture a product with extremely good iron loss by adding the film-improving effect of Cu to the above-mentioned Cr additive. In other words, the manufacturing process conditions adopt the direction of making the crystal grains of the product finer, the secondary recrystallization defects that occur at that time are resolved by adding Cr, the film deterioration caused by the addition of Cr is improved by the addition of Cu, and the product is improved by adding Cu. We have found an organic combination in which coarsening of crystal grains can be eliminated by optimizing the manufacturing process conditions. Figure 3 shows C0.060%, Si3.15%, Mn0.07%,
S0.025%, acid soluble Al0.031%, N0.0085%,
A Cu-containing silicon steel slab containing 0.10% Sn and 0.15% Cr was heated to 1350°C and hot rolled to a thickness of 2.3mm.
Annealed at ℃×2min, rapidly cooled, cold rolled to 0.30mm thickness, decarburized annealed at 840℃, used as an annealing separator.
This figure shows the influence of Cu on the tension and iron loss of the surface film of a product obtained by applying MgO and finishing high-temperature annealing at 1200°C for 20 hours. Here, the tension of the coating is determined by applying a coating liquid containing phosphoric acid, chromic anhydride, and aluminum phosphate as main components to the plate after finishing high-temperature annealing, and applying acid to the coating on one side of the steel plate after flattening annealing. This is calculated from the amount of curvature caused by removal. This figure shows that Cu has a stable and large film tension.
The amount ranges from 0.02 to 0.30%, and the iron loss is stable and good. Although it is not clear why Cu has the effect of forming a high-quality film on the surface of a product, it is speculated as follows. In order to form a high-quality film on the surface of a product, the underlying oxide layer after decarburization annealing must be appropriate. From the experimental results
When Cu is added, an oxide layer with a uniform thickness and no breaks is formed compared to when Cr is added alone. This oxide layer is mainly composed of oxides of Fe, Si, and Al, and is thought to contain Cr and Cu, but the presence of Cu puts this oxide layer in an appropriate state for forming an insulating film on the surface of the product. It is thought that the Any melting method may be used for silicon-containing molten steel having the above-mentioned components, and any casting method may be used. Next, this silicon steel slab is hot-rolled into a hot-rolled plate, and subsequently cold-rolled once or multiple times including intermediate annealing to obtain the final thickness. Since the present invention aims to obtain a high magnetic flux density unidirectional electrical steel sheet, a strong rolling reduction of 80% or more is required during final cold rolling. The annealing performed before this strong reduction cold rolling (corresponds to hot rolled plate annealing in the single cold rolling method and intermediate annealing in the multiple cold rolling method) at 950 to 1200°C for 30 seconds to
The AlN precipitation state is controlled by annealing for 30 min and rapid cooling. The plate thus cold-rolled to the final thickness is subjected to decarburization annealing. Decarburization annealing has the role of decarburizing and primary recrystallization and at the same time generating an oxide layer necessary for forming an insulating film on the surface of the product. An annealing separator is applied to the surface of the steel sheet after decarburization annealing to prevent seizure during final high-temperature annealing and to form an insulating film on the surface of the product. The main component of the annealing separator is MgO, and other substances such as TiO ₂ , Al ₂ O ₃ , CaO, and B are also used depending on the purpose.
A compound to which a compound, an S compound, or an N compound is added can be used. Following this decarburization annealing, finish high-temperature annealing is performed. This annealing involves secondary recrystallization,
The main component of purification and product surface is forsterite, which is a mixture of MgO and SiO ₂ (in steel).
Cr, Al, Cu, or added to annealing separator
The purpose is to form an insulating film (containing elements such as Ti, B, etc.), and it is usually carried out at 1100° C. or higher for 5 hours or more in hydrogen or a mixed atmosphere containing hydrogen. After finishing high-temperature annealing, a coating liquid (tension coating) containing, for example, phosphoric acid, chromic anhydride, or aluminum phosphate as the main components is applied.
The product is made by continuous annealing for the purpose of flattening. This coating completes the surface film as a film that is even stronger and has greater tension. Hereinafter, the present invention will be explained based on examples. Example 1 C0.070%, Si3.08%, Mn0.075%, S0.025%,
Molten steel containing acid-soluble Al 0.030%, N 0.0085%, and Cu 0.08% was poured into two steel ingots, and the amount of Cr was determined in each ingot.
0.01% and 0.08%. Next, it was hot rolled to a thickness of 2.3 mm, annealed at 1130°C for 2 minutes, and then heated at 60°C.
Precipitation annealing was performed by rapid cooling in hot water. It was then pickled and cold rolled to 0.30 mm in 10 passes. Aging treatment was performed at 250°C for 5 minutes between each pass during this cold rolling. Decarburization annealing was then performed at 850°C for 120 seconds in wet hydrogen. Next, an annealing separator containing a mixture of MgO and TiO ₂ was applied, and after finishing high temperature annealing at 1200°C for 20 hours, tension coating was applied. The magnetic properties and secondary recrystallization failure rate of this product are shown in Table 1.

[Table] Example 2 C0.065%, Si3.10%, Mn0.075%, S0.025%,
Molten steel containing acid-soluble Al 0.031%, N 0.085%, and Cr 0.11% was poured into two steel ingots, and the amount of Cu was determined in each.
0.01% and 0.10%. It was then hot rolled to a thickness of 2.3mm, annealed at 1130°C for 2 minutes, and then heated at 60°C.
Precipitation annealing was performed by rapid cooling in hot water. It was then pickled and cold rolled to 0.30 mm in 10 passes. Aging treatment was performed at 250°C for 5 minutes between each pass during this cold rolling. Decarburization annealing was then performed at 850°C for 120 seconds in wet hydrogen. Next, an annealing separator containing a mixture of MgO and TiO ₂ was applied, and after finishing high temperature annealing at 1200°C for 20 hours, tension coating was applied. The magnetic properties and film tension of this product are shown in Table 2.

[Table] Example 3 C0.080%, Si3.25%, Mn0.075%, S0.025%,
Acid soluble Al0.028%, N0.0085%, Cr0.100%,
Hot-rolled steel ingot containing 0.08% Cu and 0.04% Sn.
A hot rolled sheet of mm was obtained. After annealing at 1130°C for 7 minutes, precipitation annealing was performed by rapidly cooling in hot water at 100°C. Then pickled, then 250℃×5min
It was cold rolled to a thickness of 0.22 mm while undergoing aging treatment. Then, decarburization annealing was performed at 850°C for 120 seconds in a wet hydrogen atmosphere. Subsequently, an annealing separator containing a mixture of MgO and TiO ₂ was applied, and after finishing high temperature annealing at 1200°C for 20 hours, tension coating was applied.
The magnetic properties and crystal grain size of this product are as follows.

【table】 [Brief explanation of the drawing]

Figure 1 shows C0.060%, Si3.10%, Mn0.07%,
S0.025%, SolAl0.032%, N0.0085%, Cu0.10%
Figure 2 shows the influence of Cr in molten steel on the incidence of secondary recrystallization defects and iron loss of products from Cr-containing silicon steel slabs containing SolAl 0.032% and other chemical components as 1. Figure 3 is a diagram showing the influence of Cr in molten steel on the incidence of secondary recrystallization defects and iron loss of products made from Cr-containing silicon steel slabs, which is the same as in the case shown in the figure.
C0.060%, Si3.15%, Mn0.07%, S0.025%,
SolAl0.031%, N0.0085%, Sn0.10%, Cr0.15%
FIG. 2 is a diagram showing the influence of Cu on the tension and core loss of the surface film of a product made from a Cu-containing silicon steel slab containing Cu.

Claims (1)

[Claims] 1% by weight, C: 0.025~0.100%, Si: 2.5~
4.0%, Mn: 0.03~0.15%, acid soluble Al: 0.010~
0.050%, N: 0.0030-0.0100%, and further
A silicon steel material with a composite addition of Cr: 0.03 to 0.30% and Cu: 0.02 to 0.30%, the balance consisting of Fe and unavoidable impurities, is hot rolled, then precipitation annealed, and cold rolled with a final cold rolling ratio of 80% or more. After rolling to the final thickness, decarburization annealing is performed in a moist hydrogen-containing atmosphere at a temperature range of 800 to 900℃, then an annealing separator is applied, and then
A method for producing a grain-oriented silicon steel sheet, characterized by performing high-temperature finish annealing at 1100°C or higher. 2 Weight%: C: 0.025~0.100%, Si: 2.5~
4.0%, Mn: 0.03~0.15%, acid soluble Al: 0.010~
0.050%, N: 0.0030~0.0100%, Sn: 0.02~0.30
%, further Cr: 0.03~0.30% and Cu: 0.02~
A silicon steel material with a composite addition of 0.30% and the balance consisting of Fe and unavoidable impurities is hot rolled, then precipitation annealed, and cold rolled at a final cold rolling rate of 80% or more to obtain the final plate thickness. Under a humid hydrogen-containing atmosphere,
A method for producing a grain-oriented silicon steel sheet, which comprises decarburizing annealing in a temperature range of 800 to 900°C, then applying an annealing separator, and further performing high-temperature finishing annealing at 1100°C or higher.