JPH03219021A - Production of grain-oriented silicon steel sheet minimal in iron loss - Google Patents

Abstract

PURPOSE:To stably produce a grain-oriented silicon steel sheet minimal in iron loss by reducing C content to a specific value in the course between the conclusion of hot rolling and the initiation of final cold rolling at the time of producing a grain- oriented silicon steel sheet with a specific composition. CONSTITUTION:A hot rolled plate of a silicon steel having a composition consisting of 2.5-4.0% Si, 0.03-0.10% C, 0.015-0.040% acid-soluble Al, 0.0040-0.0100% N, 0.01-0.04% S, 0.02-0.2% Mn, further <=0.4% Sn and/or Cu, and the balance Fe with inevitable impurities is annealed. Subsequently, this hot rolled plate is successively subjected to two-time or more cold rollings including forced final cold rolling at >80-95% rolling reduction, to process annealing performed between the cold rolling stages, to decarburizing annealing after final cold rolling, and to final finish annealing, by which the thin grain-oriented silicon steel sheet of 0.10-0.23mm sheet thickness having high magnetic flux density is produced. At this time, in the course between the conclusion of hot rolling and the initiation of final cold rolling, decarburizing is carried out so that C content is reduced to 0.0070-0.0300%. By this method, the grain-oriented silicon steel sheet used for iron core for transformer, etc., and excellent in iron loss characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a thin, high magnetic flux density unidirectional electrical steel sheet with excellent iron loss characteristics used for the iron core of transformers and the like. be.

(Prior art) - Grain-oriented electrical 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 core loss properties.

B8 (magnetic flux density at a magnetic field strength of 800 A/m) is usually used as a numerical value representing this excitation characteristic, and W + w/so (per 1 kg when magnetized to 1.7 T at 50 Hz) is used as a numerical value representing iron loss characteristics. iron loss) is used.

This unidirectional electrical steel sheet is usually obtained by developing a so-called Goss structure with a 1101 plane and a <001> axis in the rolling direction on the steel sheet surface using a secondary recrystallization phenomenon. In order to obtain these characteristics, it is important to highly align the <001> axis, which is the axis of easy magnetization, in the rolling direction.Also, sheet thickness, grain size, resistivity, surface coating, purity of the steel sheet, etc. have a large effect on magnetic characteristics. affect.

The directionality has been significantly improved by a method characterized by cold rolling under final compression using MnS and AlN as inhibitors, and the iron loss properties have also been improved accordingly.

・In recent years, against the backdrop of rising energy prices, transformer manufacturers have increasingly focused on materials for low core loss transformers. Amorphous alloys and 6.5 as low iron loss materials
Although progress is being made in the development of steels such as %Si steel, there are still problems that need to be solved before they can be used industrially as materials for transformers. Therefore, efforts have been made to reduce iron loss by reducing the thickness of grain-oriented electrical steel sheets.

It has long been known that reducing the thickness of steel plates is effective in reducing eddy current loss, which accounts for over 70% of iron loss, but until now it has been known that reducing the thickness of steel plates is effective in reducing eddy current loss, which accounts for over 70% of iron loss. Due to this request, the main plate thickness was around 0.301IllI+. However, as the demand for energy conservation has become stronger in recent years, the demand for workability has been outweighed, and plates with thicknesses even thinner than 0.20 mm have come to be used.

However, in general, as the plate thickness becomes thinner, secondary recrystallization tends to become less likely to occur. One of the reasons for this is that when a thinner product is obtained from the same hot-rolled sheet thickness, a greater cold rolling reduction is required, resulting in disadvantages in terms of texture. A possible solution to this cause is to reduce the thickness of the hot-rolled sheet according to the product thickness.

However, this method has limitations. That is,
Making the hot-rolled sheet thinner inevitably lowers the hot-rolling finish temperature, which leads to AI! , N, and MnS, resulting in an excessive precipitate size and deterioration of magnetism.

As mentioned above, there is a limit to reducing the thickness of a hot-rolled sheet as a means of solving disadvantages in texture, so an intermediate cold rolling step must be introduced, although the number of steps increases. In other words, after hot rolling, cold rolling is performed, intermediate annealing is performed, and then cold rolling is performed at a predetermined reduction rate to the final plate thickness.This method considerably stabilizes secondary recrystallization, Although it becomes easier to obtain a high magnetic flux density, it is still insufficient as a method for obtaining magnetism with a final plate thickness of 0.18 mm or less and good iron loss. One of the reasons for this insufficiency is that non-uniform regions remain in the structure of the substrate, and linear secondary recrystallization regions described below are likely to occur frequently. As a method for eliminating such drawbacks, a method has been proposed in which the hot-rolled sheet is annealed prior to the first cold rolling (US Pat. No. 819,426). It is true that when this method is added, the annealing process that follows the intermediate cold rolling
The recrystallization rate of the structure increases, and the structure that forms the basis for the development of secondary recrystallization after the final decarburization annealing is greatly improved.
Although secondary recrystallization is stabilized up to a plate thickness of 4 mm, it is difficult to obtain sufficiently satisfactory magnetic properties due to factors such as a decrease in magnetic flux density.

In this way, there are still issues to be solved in the development of thin grain-oriented electrical steel sheets. In addition, it has been reported that magnetic properties are improved by decarburizing a component system that does not use IN as an inhibitor during the process after the hot rolling process but before the end of the final cold rolling process (Japanese Unexamined Patent Publication No. 58-55530).
However, this technology is said to be effective only when the final cold rolling reduction is between 40% and 80%, which is different from the present invention, which is characterized by a high rolling reduction of over 80%. It is understood that

(Problem to be solved by the invention) The present invention is an AI! When thinning an electromagnetic steel sheet with a high magnetic flux density using N as the main inhibitor to a thickness of 0.10 to 0.23 mm, the final cold rolling reduction ratio must be increased in order to stabilize the secondary recrystallization. The present invention provides a method for solving the problem that it is impossible to obtain a high magnetic flux density.

(Means for Solving the Problems) The present invention achieves a final cold rolling reduction of over 80% by decarburizing C by 0.0070 to 0.0300% in a step after hot rolling and before final cold rolling. The present invention provides a method for producing a thin electrical steel sheet having a high magnetic flux density and a low iron loss value.

That is, the present inventors have developed a method for obtaining a high magnetic flux density material by using AfN as the main inhibitor and making the final cold rolling reduction more than 80%.
As a result of examining methods for stably obtaining materials with good magnetic flux density and iron loss while making the plate thickness as thin as 1.0 mm, we found that when the plate thickness is thin, the position of secondary recrystallization after the decarburization annealing process is It is necessary to make the substrate more stable, that is, to make it more grained, and furthermore, the number of secondary recrystallized nuclei, i.e., (1
By increasing the number of primary recrystallized grains with 101<001> orientation, secondary recrystallization is made more stable, and
+1101<001 where the orientation of the next recrystallized grain is sharper
> direction, and (1101 <001> direction 2
It has been found that the size of the recrystallized grains is reduced and improved.

Specifically, in addition to performing a hot-rolled sheet annealing process before intermediate cold rolling to adjust the rolling reduction ratio, C in the steel is removed during the process after hot rolling and before final cold rolling. 0.
It has been discovered that a grain-oriented electrical steel sheet with a thickness of 0.10 to 0.23 mm, which is excellent in both iron loss and magnetic flux density, can be obtained by decarburizing by 0.070 to 0.0300%.

The present invention will be explained in detail below.

The components of the hot rolled sheet which is the starting material of the present invention are Si:
2.5-4.0%, C: 0.03-0.10%, acid solubility 1/! : 0.015-0.040%, N: 0.
0040-0.0100%, S: 0.01-0.0
4%, Mn: 0.02-0.2%, 0.4% or less Sn
, contains one or two types of Cu, and the remainder is F.
e and unavoidable impurities.

The reasons for specifying the components of the hot-rolled sheet as a starting material in the present invention will be explained below.

If Si exceeds 4%, embrittlement becomes severe and cold rolling becomes difficult, which is not preferable. -・If it is less than 2.5%, the electrical resistance is low and it is difficult to obtain good iron loss characteristics.

If C is less than 0.03%, the amount of T before the decarburization process becomes extremely small, making it difficult to obtain a good primary recrystallized structure.
- If it exceeds 0.10%, decarburization will be poor, which is not preferable.

Acid soluble/2. In the present invention, N is a basic component for obtaining the main inhibitor iN, which is essential for obtaining a high magnetic flux density, and if it is out of the above range, secondary recrystallization becomes unstable, which is not preferable, so it should be acid-soluble! is 0.015~0.0
40%, and N is 0.0040 to 0.0100%.

Further, Mn and S are elements necessary to form the inhibitor MnS, and if outside the above range, secondary recrystallization becomes unstable, which is not preferable, so Mn is 0.02 to 0.0.
2%, S is 0. It is set as O1 to 0.04%.

In addition to these inhibitor constituent elements, 0.4%
It is necessary that one or two of the following Sn and Cu be contained. The upper limit value must be strictly adhered to since the growth of secondary recrystallization will be impaired if this value is exceeded.

Incidentally, it is of course possible to use Sb, Cr, Se, etc., which are known per se, as inhibitor constituent elements.

The present invention uses a hot-rolled silicon steel sheet containing the above-mentioned components as a starting material, performs hot-rolled sheet annealing, and then cold-rolls it two or more times to obtain a final sheet thickness of 0.10 to 0.23 Ilm.
It is assumed that the process includes intermediate annealing in between, decarburization annealing after final cold rolling, and final annealing. Although secondary recrystallization up to a plate thickness of 0.14 mm is relatively stable using this manufacturing method, the magnetic flux density tends to decrease.
It is difficult to obtain low iron loss values.

Based on the above process, the present inventors added C from 0.0070 to 0.000 in an intermediate process after hot rolling and before final cold rolling.
By decarburizing by 0.30%, the plate thickness is reduced to 0.10.
This makes it possible to perform secondary recrystallization up to mm, and also significantly improves magnetic flux density and iron content.

Generally, the γ phase in steel that is generated during hot rolling is effective in finely improving the coarsely elongated grain structure that has grown significantly, and it is generated in a linear shape to provide a good substrate for secondary recrystallization to grow. It has the effect of suppressing the occurrence of non-secondary recrystallization regions.

Therefore, in order to generate a sufficient amount of γ phase, it is essential to add an appropriate amount of Cl at the steel manufacturing stage depending on the amount of Si. In addition, C causes magnetic aging if it remains in the product, so
It is necessary to decarburize in the middle of the process. In addition, placing the decarburization process before the final annealing process that causes secondary recrystallization can prevent the generation of γ phase during secondary recrystallization annealing, which inhibits the generation and growth of the desired oriented grains. It is necessary to eliminate it. For the above reasons, the decarburization step is an essential step in the manufacturing process of grain-oriented electrical steel sheets.

Below are the reasons why magnetism improves when C is decarburized by an amount of 0.0070 to 0.0300% in the process from hot rolling to final cold rolling, which is a feature of the present invention, and the reason for regulating the range of C. Explain.

First, Figure 1 shows a photograph of the metallographic structure of a steel sheet before final cold rolling.

The thickness of the hot-rolled sheet as a starting material is 2.3 mm, and (A) is 1.07 m by cold-rolling the hot-rolled sheet at a reduction rate of 53%.
m, then held at 1130°C for 30 seconds in a dry mixed gas of 90% N2 and 11.10%, and then heated to 900°C.
(B) is a hot-rolled sheet that was held at 1100'C for 2 minutes in a dry mixed gas of 90% N2 and 10% N2, and then cooled in hot water at 100°C.
After cooling in hot water at 0°C, cold rolling and annealing were performed under the same conditions as in (A). In (C), the hot rolled sheet was heated in a wet gas containing 90% N2 and 10% Nz (dew point 65°). After being held at 1100°C for 2 minutes in C), it was placed in hot water at 100°C, and then cold rolled and annealed under the same conditions as in (A).

In (B) and (C) of Figure 1, the hot-rolled sheet annealing process has been introduced, so recrystallization has developed sufficiently at this stage compared to (A) where the hot-rolled sheet is not annealed. I found out that there was
It can be seen that the structure becomes more uniform after the subsequent final annealing and decarburization annealing steps.

Also, when comparing the surface parts of the copper sheets in (B) and (C), the surface area of the copper sheets in (C), which was annealed in a decarburized atmosphere, is better.
It can be seen that the crystal grains in the surface area are larger than in (B), which was annealed in a non-decarburizing atmosphere.

In addition, the C content of the starting hot rolled sheet in this case is 0.070%
However, in the case of (A) and (B), clear decarburization is not observed, whereas in the case of (C), the total thickness of the steel plate is 0.0200.
% was decarburized. The difference in structure shown in FIG. 1 greatly affects the stability of secondary recrystallization and magnetism of the product.

Ten specimens each having histories of (A), (B), and (C) were then cold rolled to 0.15 mm at a reduction rate of 86%, and then decarburized and annealed by a known method. A product was obtained by applying an annealing separator containing l'1go as a main component, finishing annealing, applying a tension coating containing phosphoric acid and chromic anhydride as main components, and baking. Table 1 lists the magnetism and secondary recrystallization rate. It can be seen that (C) according to the present invention is much better than other cases.

Table 1 (Average value of n=10) Next, FIG. 2 shows the relationship between the amount of decarburization ΔC and magnetic properties in the process from hot rolling to final cold rolling.

The thickness of the hot-rolled plate in this case is 2.3 mm, and the Si3.2
5%, CO 0,078%, acid soluble 1.027%, NO
, 0083%, and after hot-rolled plate annealing at 1050°C, first cold rolling, intermediate annealing at 1100°C, and final cold rolling under 80-91% elastic pressure. A sample with a final plate thickness of 0.175 mm was obtained, followed by known decarburization annealing, application of an annealing separator mainly composed of MgOa, and final annealing, and finally a tension coating mainly composed of phosphoric acid and chromic anhydride. It has been subjected to

During this process, decarburization is performed by changing the dew point of the atmospheric gas during the hot-rolled plate annealing process, intermediate annealing process, or by changing the dew point of the atmospheric gas, and the steel plate surface is Samples with various amounts of decarburization could be obtained by decarburizing by applying a KzCO:+ aqueous solution to the steel.

From Figure 2, decarburization amount ΔC0,0070~0.0300%
It can be seen that good magnetism can be obtained within the range of . Although the reason for the new findings shown in FIG. 2 is not necessarily clear, the present inventors speculate as follows.

First, (A) KzCOs for hot-rolled sheets for grain-oriented electrical steel sheets.
The one coated with the 30% aqueous solution and the one not coated (B) were each kept at 1050°C for 2 minutes in a dry mixed gas consisting of 90% Nz and 10% Nz, and then placed in hot water at 100°C. Fig. 3 shows an optical micrograph of the sample after cooling. Cl in the hot rolled sheet is 0.072%, and the amount of decarburization in hot rolled sheet annealing is (A): ΔC-〇, 0150%,
In the case of (B): ΔC=0.0030%. From FIG. 3, it can be seen that the recrystallized region on the surface is wider in case (A) than in case (B). On the other hand, in the case of the single compression cold rolling method where the final rolling reduction exceeds 80%, it is known that the secondary recrystallization of the product becomes unstable if the surface recrystallized portion after hot-rolled sheet annealing is removed. . Therefore, as shown in (A), it is thought that increasing the surface recrystallized portion by decarburization leads to stabilization of secondary recrystallization and improvement of magnetism of the product.

As shown in (A), the surface recrystallized layer is increased by decarburization, and as shown in (C) of Figure 1, the recrystallized grains are deeper in the surface than the inner part before the final cold rolling. growing. When the plate thickness becomes as thin as 0.10 to 0.23 mm, the surface layer containing the secondary recrystallization nuclei becomes geometrically thinner.
In addition, since it is close to the outermost surface, the surface layer containing the nuclei of secondary recrystallization becomes susceptible to the influence of the atmosphere during the heating process of finish annealing, and as a result, secondary recrystallization becomes unstable and it is difficult to obtain good magnetism. Become.

In the present invention, by performing decarburization during the process from hot rolling to final cold rolling, the surface recrystallization zone is created deep, thereby successfully allowing the secondary recrystallization nuclei to exist deep down. As a result, even if the final cold rolling was carried out at a high reduction rate of over 80%, it was possible to stabilize secondary recrystallization and improve magnetism in the case of a thinner plate.

The amount of decarburization ΔC from the end of hot rolling to the final cold rolling is 0.0
If it is less than 0.070%, the above effect is not sufficient, and 0.
．． If it exceeds 0300%, the amount of γ phase in hot-rolled sheet annealing and intermediate annealing becomes too small, resulting in an inappropriate primary recrystallized structure after the decarburization annealing process.
It is presumed that the secondary recrystallization becomes unstable because the N precipitation becomes coarse and the effect of the inhibitor is reduced. The present invention solves the problem in manufacturing thin unidirectional electrical steel sheets, and when the thickness exceeds 0.23 mm, the process of the present invention is not necessarily necessary.
When the plate thickness is less than 0 mm, the effect of the present invention is insufficient and instability occurs in secondary recrystallization. The final cold rolling reduction is 80
% is necessary to obtain high magnetic flux density,
If it exceeds 95%, the texture becomes inappropriate, resulting in instability in secondary recrystallization.

The method of decarburization during the final cold rolling after hot rolling is not necessarily limited, but may include a method of annealing with its own heat after hot rolling and winding, or a method of decarburizing in the temperature range of 700 to 1200 ° C. Possible methods include performing rolling annealing and intermediate annealing in a wet gas, or applying 2C03 or the like before these annealing.

Examples will be described below.

(Example) Example I C: 0.065%, Si: 3.25%, Mn:
0.088%, S: 0.026% acid soluble A f
: 0.028%, N: 0.0075%, Sn:
0.10%, Cu: 0.10% (A): Annealed at 980 °C for 2 minutes in a humid atmosphere (point n: 62'C) in N2 gas, (B ):98
Annealing in a dry atmosphere N2 gas for 2 minutes at 0 °C, (C):
After no annealing, it was pickled and cold rolled by about 41% to 1.35 mPA. After that, drying atmosphere N29
0%, ■! After holding at 1130°C for 30 seconds in 10% gas, holding at 900°C for 1 minute and rapidly cooling, then about 83%
Cold rolled to 0.225 no++ finish. The obtained cold-rolled sheet was decarburized and annealed by a known method, coated with an annealing separator, and heated at 15°C/h in an atmosphere of 90% N2 and 10% H2.
Raise the temperature to 1200°C at a rate of r, then continue to 1200°
After performing purification annealing at C for 20 hours, tension coating was applied to obtain a grain-oriented electrical steel sheet. magnetic properties of the product,
The amount of decarburization ΔC (%) from the end of hot rolling to the final cold rolling is calculated as the second
Shown in the table.

Table 2 Example 2 C: 0.081%, Si: 3.35%, Mn
: 0.077%, S: 0.024%, acid soluble ff: 0.027%, N: 0.0082%, Sn
: 0.15%, plate thickness 2.3 including Cu: 0.15%
mm hot-rolled plate (A): 3 minutes at 1050°C,
Humid atmosphere (dew point: 55°c) Nz: 90%, Hz:
Annealed in 10% gas, (B): Annealed at 1050°C for 3 minutes, dry atmosphere N2: 90%, Hz: 10% gas, (C): No annealing, then pickled, approx. 49%
It was cold rolled at a reduction rate of 1.2 mm. After that, it was heated to 1080°C in a dry atmosphere of N290%, 11□10% gas.
After being held for 2 minutes, it was rapidly cooled, and then cold-rolled to a thickness of 0.175 mm at a rolling reduction of about 85%. The obtained cold-rolled sheet was decarburized and annealed by a known method, coated with an annealing separator containing MgO as a main component, and then finished annealed. Next, a tension coating containing phosphoric acid and chromic anhydride as main components was applied to obtain a grain-oriented electrical steel sheet. Table 3 shows the magnetic properties of the product and the amount of decarburization ΔC (%) from the end of hot rolling to the final cold rolling.

Table 3 Example 3 C: 0.072%, Si: 3.25%, Mn:
0.075%, S: 0.028%, acid soluble 7/!
: 0.025%, N: 0.0082%, Sn;
0.12%, Cu: 2.3m thick including 0.19%
(A) Apply a 30% K, CO3 aqueous solution to a hot-rolled sheet of m.
(B) After treatment without coating, annealing at 1100°C for 3 minutes in a dry atmosphere Nz: 90%, Hz: 10% gas, followed by rapid cooling, followed by pickling and cooling at a reduction rate of approximately 53%. It was rolled to a thickness of 1.07 mm. Afterwards drying atmosphere N
It was annealed at 1000°C for 2 minutes in 2 gases and cold rolled to a thickness of 0.150 mm at a reduction of about 86%. The obtained cold-rolled sheet was decarburized and annealed by a known method, coated with an annealing separator, and finished annealed. Next, a tension coating containing phosphoric acid and chromic anhydride as main components was applied to obtain a grain-oriented electrical steel sheet. The magnetic properties of the product and the amount of decarburization ΔC (%) from hot rolling to final cold rolling are shown on the fourth back.

Table 4 Example 4 C: 0.072%, Si: 3.40%, Mn:
0.078%, S2 0.026%, acid soluble^f:
0.029%, N: 0.0080%, Sn: 0
．． 09%, Cu: 0.06%, Sb: 0.02
5% hot rolled at 1000'C to a thickness of 2.3mm containing 8%
After annealing in a dry atmosphere J: 90%, N2: 10% gas for 1 minute, pickling and cold rolling at a reduction rate of about 22%.
．． 8 m+n. Then (A) 4 at 1120°C
minutes, dry atmosphere Ng: 90%, 11□: After annealing in 10% gas, elephant, cold, (B) 4 minutes at 1120°C, humid atmosphere (dew point: 60”C) Nz: 90%, lh: 10%
After annealing in a gas, the material was rapidly cooled, then pickled, and cold-rolled at a rolling reduction of about 89% to form a 0.20 mm ladle. Thereafter, the cold rolled sheet was decarburized and annealed by a known method, coated with an annealing separator, final annealed, and then tension coated to obtain a unidirectional electrical steel sheet. Table 5 shows the magnetic properties of the product and the amount of decarburization ΔC (%) from the end of hot rolling to the final cold rolling.

Table 5 (Effects of the Invention) As described above, according to the present invention, a thin, high magnetic flux density, grain-oriented electrical steel sheet with good iron loss characteristics can be stabilized simply by controlling the carbon content before final cold rolling. Since you can get
Its industrial effects are significant.

[Brief explanation of drawings]

Figure 1 is a comparative micrograph of the metal structure before final cold rolling.
FIG. 2 is a diagram showing the relationship between the amount of decarburization ΔC after hot rolling and the final cold rolling and magnetic properties, and FIG. 3 is a comparative microscopic photograph of the metal composite fibers after annealing the hot rolled sheet. 1st s (A) 3rd f B: 0.2 mm Fig. 2

Claims (1)

[Claims] Si: 2.5-4.0%, C: 0.03-0.10%,
Acid-soluble Al: 0.015-0.040%, N: 0.0
040-0.0100%, S: 0.01-0.04%,
A silicon steel hot-rolled sheet containing Mn: 0.02 to 0.2%, further containing 0.4% or less of one or both of Sn and Cu, and the balance consisting of Fe and inevitable impurities is annealed. The plate thickness is improved by two or more cold rollings including final cold rolling under compression at a rolling reduction of more than 80% to 95%, intermediate annealing performed in between, decarburization annealing after the final cold rolling, and final finish annealing. is 0.10
In a method for manufacturing a thin unidirectional electrical steel sheet with a high magnetic flux density of ~0.23 mm, a step of decarburizing C by 0.0070 to 0.0300% during the process after hot rolling and before final cold rolling. A method for producing a unidirectional electrical steel sheet with low iron loss, characterized by having the following.