JP2011132558A - Method for manufacturing non-oriented electromagnetic steel sheet - Google Patents

Abstract

A method for manufacturing a non-oriented electrical steel sheet in which the magnetic flux density in the rolling direction is dramatically increased is proposed.
C: 0.0050 to 0.03 mass%, Si: 2 to 7 mass%, Mn: 0.05 to 3 mass%, Al: 0.01 mass% or less, V: 0.003 to 0.05 mass%, S: 0.0050 mass% or less, N: 0.0050 mass% or less, the steel slab having a composition composed of Fe and inevitable impurities in the balance is hot-rolled and hot-rolled sheet annealed, once or in the middle The rolling reduction in two or more cold rollings with annealing interposed therebetween is set to 50 to 75% to obtain a final sheet thickness, and then finish annealing and decarburization annealing to C: less than 0.005 mass%, or decarburization. Finish annealing after annealing to C: less than 0.005 mass%.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a non-oriented electrical steel sheet, and more particularly, to a method for producing a non-oriented electrical steel sheet having excellent magnetic flux density in the rolling direction of the steel sheet.

  In recent years, there has been a strong demand for higher efficiency and downsizing of electrical equipment in the global trend of reducing energy including electric power. Non-oriented electrical steel sheets are widely used as iron core materials for electrical equipment, so in order to achieve miniaturization and higher efficiency of electrical equipment, improvement of magnetic properties of non-oriented electrical steel sheets, High magnetic flux density and low iron loss have become indispensable issues.

  Therefore, the non-oriented electrical steel sheet has conventionally been made with a high magnetic flux density by optimizing the alloying elements to be added, increasing the grain size before cold rolling, and optimizing the cold rolling reduction ratio. On the other hand, the iron loss has been reduced by adding an element for increasing electrical resistance or reducing the plate thickness.

  By the way, in a drive motor such as a hybrid vehicle, a split core has begun to be adopted from the viewpoint of improving the yield. This split core is not punched as a single piece from the material steel plate as in the past, but the core is divided into several parts and punched so that the length direction of the teeth of each part is the rolling direction of the steel sheet. Technology to assemble the core. In this split core, the length direction of the teeth where the magnetic flux concentrates is the rolling direction of the electrical steel sheet. Therefore, in order to improve the characteristics of the motor, the characteristics in the rolling direction of the electrical steel sheet are extremely important.

  An example of the material having an increased magnetic flux density in the rolling direction is a grain-oriented electrical steel sheet having the Goss orientation aligned in the rolling direction. However, since the grain-oriented electrical steel sheet is manufactured through a secondary recrystallization process, the manufacturing cost is high, and the fact is that it is hardly adopted for the split core. Therefore, in an inexpensive non-oriented electrical steel sheet, if the magnetic flux density in the rolling direction can be improved, it can be considered that it can be an optimum material for the split core.

  As a technique to meet such a requirement, for example, after finishing annealing disclosed in Patent Document 1, Si: 2.0 mass% or less, Al: 1.0 mass% or more, and the crystal grain size is 50 μm or less. A technique for obtaining a non-oriented electrical steel sheet in which the magnetic flux density in the rolling direction is increased by subjecting the steel sheet to skin pass rolling with a rolling reduction of 3 to 10% can be mentioned.

JP 2006-265720 A

However, the non-oriented electrical steel sheet obtained by the technique of Patent Document 1 has a magnetic flux density B _{50-L in} the L direction of about 1.78 T at most, which surpasses the magnetic characteristics of the conventional non-oriented electrical steel sheet. is not. Therefore, development of a non-oriented electrical steel sheet with improved magnetic properties for the split core is desired.

Accordingly, an object of the present invention is to propose a method for manufacturing a non-oriented electrical steel sheet in which the magnetic flux density in the rolling direction is dramatically increased in view of the above-described problems in the prior art. Here, a specific development target of the present invention is a non-oriented electrical steel sheet having a magnetic flux density B50 _-L in the rolling direction (L direction) of 1.80 T or more.

  In order to solve the above-mentioned problems, the inventors have conducted intensive studies on the composition of steel and the production conditions of the electrical steel sheet. As a result, the Al content is reduced to 0.01 mass% or less, and after using a steel material to which V is added in an appropriate range, the rolling reduction in two or more cold rollings with intermediate annealing is controlled within the appropriate range. As a result, it has been found that the Goss accumulation degree in the recrystallization texture in the finish annealing can be increased and the magnetic flux density in the rolling direction can be remarkably increased, and the present invention has been completed.

  That is, the present invention includes C: 0.0050 to 0.03 mass%, Si: 2 to 7 mass%, Mn: 0.05 to 3 mass%, Al: 0.01 mass% or less, V: 0.003 to 0.05 mass. %, S: 0.0050 mass% or less, N: 0.0050 mass% or less, the steel slab having a composition composed of Fe and unavoidable impurities in the balance is hot-rolled and hot-rolled sheet annealed once. Alternatively, the rolling reduction in two or more cold rollings sandwiching the intermediate annealing is set to 50 to 75% for the final sheet thickness, and then the final annealing is followed by decarburization annealing to C: less than 0.005 mass%, or It is a manufacturing method of the non-oriented electrical steel sheet which carries out finish annealing after decarburizing annealing and making it C: less than 0.005 mass%.

  The manufacturing method of the non-oriented electrical steel sheet according to the present invention may be one selected from Sn: 0.005 to 0.1 mass% and Sb: 0.005 to 0.1 mass% in addition to the above component composition. It contains two types.

  According to the present invention, a non-oriented electrical steel sheet having a high magnetic flux density in the rolling direction can be provided at a low cost, and can be widely used for applications such as a split core and a transformer core that can make use of the characteristics.

It is a graph which shows the influence which V content has on the magnetic flux density of a rolling direction.

First, the component composition that the steel material should have in producing the non-oriented electrical steel sheet of the present invention will be described.
C: 0.0050 to 0.03 mass%
Solid solution C has an effect of fixing dislocations introduced by cold rolling and promoting the formation of deformation bands. This deformation band increases the accumulation degree of Goss orientation {110} <001> in the recrystallized texture formed by finish annealing, and thus significantly improves the magnetic properties (magnetic flux density) in the rolling direction. Therefore, in order to increase the magnetic flux density in the rolling direction, it is necessary to have a sufficient amount of solute C present during cold rolling, and for that purpose, C of the steel material needs to be 0.0050 mass% or more. is there. On the other hand, in order to prevent magnetic steel from causing magnetic aging and increase in iron loss, C in the product stage needs to be less than 0.0050 mass%. However, if C of the steel material exceeds 0.03 mass%, decarburization annealing after cold rolling may not be sufficiently decarburized to the above level. Therefore, C of a steel raw material shall be the range of 0.0050-0.03 mass%. Preferably it is the range of 0.008-0.02 mass%.

Si: 2 to 7 mass%
Si is an element that increases the electrical resistance of steel and reduces iron loss. On the other hand, when Si is less than 2 mass%, high-temperature annealing by finish annealing after the final cold rolling causes γ transformation, and good magnetic properties cannot be obtained. On the other hand, if Si exceeds 7 mass%, the steel becomes hard and difficult to roll, and the saturation magnetic flux density is lowered, which is not preferable. Therefore, the amount of Si added is in the range of 2-7 mass%.

Al: 0.01 mass% or less Al is an important element in the present invention, and is an element effective for increasing the electrical resistance like Si. However, in the present invention, when the Al content exceeds 0.01 mass%, the texture formed by finish annealing is randomized, and the Goss orientation {110} <001> is not sufficiently developed. Magnetic properties cannot be obtained. Therefore, in the present invention, Al is limited to 0.01 mass% or less. Preferably it is 0.005 mass% or less.

Mn: 0.05-3 mass%
Mn is an element necessary for fixing S and improving the hot workability of steel. However, if it is less than 0.05 mass%, the effect of addition cannot be obtained, while addition exceeding 3 mass% causes an increase in raw material cost. Therefore, Mn is set to a range of 0.05 to 3 mass%.

V: 0.003-0.05 mass%
V is an essential additive element of the present invention that enhances the accumulation degree of Goss orientation in the rolling direction in the recrystallization texture in the finish annealing. The reason why the Goss orientation accumulation degree is increased by the addition of V is not yet fully clarified, but when V is precipitated as VC or VN, the texture after cold rolling is improved. It is estimated that this is because the improvement effect of the texture due to the reduction is superimposed, and the degree of accumulation in the Goss orientation in the recrystallized texture after finish annealing is further increased. The effect of improving the magnetic flux density cannot be obtained when the amount of addition of V is less than 0.003 mass%. On the other hand, the addition exceeding 0.05 mass% only saturates the effect. Therefore, in the present invention, V is added in the range of 0.003 to 0.05 mass%.

Here, the reason for limiting the addition amount of V to the above range will be described.
C: 0.0180 mass%, Si: 3.3 mass%, Al: 0.001 mass%, Mn: 0.16 mass%, N: 0.0025 mass%, S: 0.0017 mass% Then, after melting and adding steel to which V was added in the range of 0.001 to 0.1 mass% to obtain a steel slab, this steel slab was heated at 1100 ° C. for 30 minutes and then hot-rolled. A hot-rolled sheet with a thickness of 2.3 mm is subjected to hot-rolled sheet annealing at 950 ° C. for 30 seconds, and then an intermediate sheet thickness of 0.85 mm is obtained by the first cold rolling, followed by intermediate annealing at 850 ° C. for 30 seconds. After that, a cold rolled sheet having a final thickness of 0.35 mm is obtained by cold rolling for the second time, and then decarburized and annealed at 850 ° C. for 30 seconds in an atmosphere at a fog point of 30 ° C., and 1000 ° C. × 30 Non-oriented electrical steel sheet obtained by finish annealing in seconds Then, an L direction Epstein test piece having a rolling direction L of 180 mm × plate width direction C of 30 mm was sampled, and a magnetic flux density B _50-L in the rolling direction _L was measured.

FIG. 1 shows the above results as a relationship between the amount of addition of V and the magnetic flux density B _{50-L in the} rolling direction. In the range where the content of V is 0.003 to 0.05 mass%, It can be seen that the magnetic flux density in the rolling direction is good.

S: 0.0050 mass% or less, N: 0.0050 mass% or less S and N are unavoidable impurity elements mixed in the steel, and if both contain more than 0.0050 mass%, the magnetic properties are reduced. descend. Therefore, in the present invention, S and N are limited to 0.0050 mass% or less, respectively. Preferably, each is 0.003 mass% or less.

The non-oriented electrical steel sheet of the present invention may further contain Sn and Sb in the following ranges in addition to the above essential components.
Sn: 0.005-0.1 mass%, Sb: 0.005-0.1 mass%
Both Sn and Sb have the effect of improving the magnetic properties of the non-oriented electrical steel sheet by improving the recrystallized texture or preventing oxidation and nitridation during annealing. can do. However, in any case, if the content is less than 0.005 mass%, the above effect cannot be obtained sufficiently. On the other hand, if the content exceeds 0.1 mass%, the above effect is saturated, so Sn and Sb are Sn: It is preferable to make it contain in 0.005-0.1 mass% and the range of Sb: 0.005-0.1 mass%.

  In the non-oriented electrical steel sheet of the present invention, the balance other than the above components is composed of Fe and inevitable impurities.

Next, the manufacturing method of the non-oriented electrical steel sheet according to the present invention will be described.
The method for producing a non-oriented electrical steel sheet according to the present invention comprises melting a steel having a component composition compatible with the above-described component composition of the present invention by a normal refining process including a converter, an electric furnace, or a vacuum refining equipment. The steel slab is made into a steel slab by a continuous casting method or ingot-splitting rolling method, and then the steel slab is reheated in a heating furnace or the like, then hot-rolled, hot-rolled sheet annealed, and sandwiched once or intermediately. After the final thickness is obtained by cold rolling more than once, finish annealing and decarburization annealing, or decarburization annealing and then finish annealing, and if necessary, an insulating coating is applied to make the final product This is a method for obtaining a grain-oriented electrical steel sheet. Here, the important steps in the production method of the present invention are from hot-rolled sheet annealing to finish annealing or decarburization annealing, and the other steps may be conventionally known conditions.

Hereinafter, the manufacturing conditions of each of the important steps will be described.
Hot-rolled sheet annealing Although the hot-rolled sheet annealing in the production method of the present invention may be carried out under conditions that are usually performed in non-oriented electrical steel sheets, the annealing temperature is preferably in the range of 750 to 1050 ° C, more preferably. Is in the range of 800-1000 ° C. If the annealing temperature is less than 750 ° C., an unrecrystallized structure may remain. On the other hand, if the annealing temperature exceeds 1050 ° C., a great load is applied to the annealing equipment.

Cold rolling Cold rolling in the production method of the present invention needs to be performed once or twice or more with intermediate annealing, and the rolling reduction of each cold rolling is 50 to 75% of each. Must be limited to range. This is because if the cold rolling reduction ratio is out of the above range, the Goss texture does not sufficiently develop due to recrystallization in finish annealing, and the magnetic properties deteriorate. The range of a preferable cold reduction rate is the range of 55 to 70%, respectively. In addition, the reduction ratio distribution of the cold rolling does not change even if the number of cold rolling is 3 or more.

Intermediate annealing The intermediate annealing performed between the two or more cold rollings may be performed at a temperature higher than the recrystallization temperature, but is preferably performed in a temperature range of 750 to 1050 ° C, more preferably 800 to 1000 ° C. It is desirable to do. If the temperature is lower than 750 ° C, an unrecrystallized structure may be formed. On the other hand, if the temperature exceeds 1050 ° C, a burden is imposed on the annealing equipment.

Finish annealing Finish annealing may be performed at the recrystallization temperature or higher, but a temperature range of 750 to 1050 ° C is preferable, and a temperature range of 800 to 1000 ° C is more preferable.

Decarburization annealing Decarburization annealing is a process for reducing C in a steel sheet to less than 0.0050 mass% in order not to cause a decrease in magnetic properties (an increase in iron loss) due to aging deterioration. There are no particular restrictions on the conditions, but for example, it is preferably performed in an oxidizing atmosphere with a dew point of 20 to 40 ° C in a temperature range of 800 to 900 ° C. This decarburization annealing may be performed at any stage before or after the finish annealing as long as it is after the final cold rolling.

  No. having the component composition shown in Table 1. 1 to 21 steel was melted to form a steel slab. The steel slab was heated at 1100 ° C. for 30 minutes and then hot rolled to form a hot-rolled sheet having a thickness of 2.3 mm. After hot-rolled sheet annealing for 30 seconds, cold rolled (1R) to an intermediate sheet thickness of 0.80 mm, after intermediate annealing at 900 ° C. for 30 seconds, second cold rolled (2R), and finally A cold-rolled plate having a plate thickness of 0.35 mm was used. Next, the cold-rolled sheet is subjected to finish annealing at 1000 ° C. × 30 seconds, and then decarburized annealing at 850 ° C. × 30 seconds in an atmosphere with a dew point of 30 ° C. to reduce C to less than 0.0050 mass%. A non-oriented electrical steel sheet was used.

Next, an L-direction Epstein test piece having a rolling direction L: 180 mm × plate width direction C: 30 mm was taken from the above-mentioned various non-oriented electrical steel sheets, and magnetic properties in the rolling direction (magnetic flux density B _50-L ) by the Epstein test. Was measured. The results thus obtained are also shown in Table 1.

From Table 1, the steel sheet of the invention example manufactured using the steel having the component composition suitable for the present invention and the condition suitable for the present invention has a magnetic flux density B50 _{-L in the} rolling direction of 1.80 T or more. It can be seen that an excellent value of is obtained.

  C: 0.0180 mass%, Si: 3.3 mass%, Al: 0.001 mass%, Mn: 0.16 mass%, N: 0.0025 mass%, S: 0.0017 mass%, V: 0.009 mass%, balance A steel slab having a composition suitable for the present invention consisting of Fe and unavoidable impurities is heated at 1100 ° C. for 30 minutes, and then hot-rolled to obtain a hot-rolled sheet having the thickness shown in Table 2, followed by 900 ° C. * Hot-rolled sheet annealing for 30 seconds was performed. Then, the hot-rolled sheet is made into a final sheet thickness by one cold rolling, or first cold-rolled (1R) at a rolling reduction shown in Table 2 and subjected to intermediate annealing at 950 ° C. for 30 seconds. After that, the second cold rolling (2R) was performed at the rolling reduction shown in Table 2 to obtain a cold-rolled sheet having a final sheet thickness of 0.35 mm or 0.50 mm. Next, contrary to Example 1, these cold-rolled plates were subjected to decarburization annealing at 850 ° C. for 30 seconds in an atmosphere with a dew point of 30 ° C. to reduce C to less than 0.0050 mass%, Finish annealing was performed at 1000 ° C. for 30 seconds to obtain a non-oriented electrical steel sheet.

Next, an L-direction Epstein test piece having a rolling direction L: 180 mm × plate width direction C: 30 mm was taken from the above-mentioned various non-oriented electrical steel sheets, and magnetic properties in the rolling direction (magnetic flux density B _50-L ) by the Epstein test. Was measured. The results thus obtained are also shown in Table 2.

From Table 2, regardless of the order of decarburization annealing and finish annealing, good magnetic properties (magnetic flux density _B50-L ) are obtained only when the cold rolling reduction ratios of 1R and 2R are both in the range of 50 to 75%. It turns out that it is obtained.

Claims (2)

C: 0.0050 to 0.03 mass%, Si: 2 to 7 mass%, Mn: 0.05 to 3 mass%, Al: 0.01 mass% or less, V: 0.003 to 0.05 mass%, S: 0.00. A steel slab having a composition of 0050 mass% or less and N: 0.0050 mass% or less, the balance being Fe and inevitable impurities, is hot-rolled and hot-rolled sheet annealed, and then sandwiched once or intermediately. The rolling reduction in cold rolling more than 50 times is set to 50 to 75% respectively to obtain the final sheet thickness, and then finish annealing and decarburization annealing to C: less than 0.005 mass%, or decarburization annealing to C : The manufacturing method of the non-oriented electrical steel sheet which carries out finish annealing after setting it as less than 0.005 mass%. 2. In addition to the said component composition, 1 type or 2 types chosen from Sn: 0.005-0.1 mass% and Sb: 0.005-0.1 mass% are contained, It is characterized by the above-mentioned. The manufacturing method of the non-oriented electrical steel sheet described in 1.

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