JPH0347601A - Hot edging method for continuously cast and unidirectionally oriented magnetic steel slab - Google Patents

Abstract

PURPOSE:To allow high-draft edging without promoting the edge crack of a unidirectionally oriented electrical hot rolled sheet and to improve productivity by subjecting a slab to the high-draft edging by using an edging mill at a specific high temp. of the slab surface temp. right after extraction of the slab after heating. CONSTITUTION:The unidirectionally oriented magnetic steel slab produced by continuous casting is heated to a high temp. of >=1,300 deg.C and is then subjected to the hot high-draft edging to >=60mm by using the edging mill, by which the hot rolled sheet of a desired size is obtd. The slab is subjected to the high-draft edging by using the edging mill at the high temp. of >=1,200 deg.C and <=1,380 deg.C surface temp. of the slab right after the extraction of the slab after heating in this case. The high-draft edging is enabled in this way while the edge crack is improved. The productivity is thus improved.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention belongs to the field of hot rolling technology for producing unidirectional electrical steel, and more specifically, the present invention belongs to the field of hot rolling technology for producing unidirectional electrical steel. A hot rolling method that makes it possible to heat wide continuous cast slabs of unidirectional electromagnetic steel at high temperatures and then perform large reduction rolling over a wide range of hot widths in order to obtain hot rolled sheets of various sizes from the continuous cast slabs. It is related to.

(Prior Art) Unidirectional electrical steel is widely used as an iron core material for transformers and the like due to its excellent magnetic properties including high magnetic flux density and low iron loss.

In recent years, in this type of technical field, there has been a desire not only to have even better magnetic properties but also to supply materials at a lower cost.In other words, how can we improve productivity and yield? , the problem to be solved by these engineers is how to reduce manufacturing costs.

As is well known, most unidirectional electromagnetic steel slabs are currently manufactured by the continuous casting method from the viewpoint of improving productivity and stabilizing material quality.

Productivity in a continuous casting method is determined by its casting speed and casting size. Regarding the former casting speed, the maximum speed is selected as it is constrained by casting stability, but the latter casting size is In the normal hot rolling process, the most suitable slab size for producing the desired hot-rolled sheet size is determined, and since the hot-rolled sheet sizes are diverse, the slab sizes to be supplied must also be diverse. Unavoidably, it cannot be said that casting is always performed at the maximum width, which is restricted by casting stability.

In other words, in order to further improve productivity in the continuous casting method, it is desired to expand and consolidate the width of continuous casting slabs to a size that is restricted by equipment capacity.

As an example, although there is no mention of electromagnetic steel,
For example, Japanese Patent Publication No. 59-42561 proposes a wide reduction rolling technology that uses vertical large-diameter rolls to achieve a high yield, while Japanese Patent Publication No. 1-12581 proposes cracking of medium-low carbon steel. Techniques regarding optimal material composition, slab cooling rate, and heat retention temperature and time have been proposed in order to perform hot width reduction rolling while preventing the occurrence of defects.

(Problems to be Solved by the Invention) The present inventors have discovered that hot wide reduction rolling of continuous cast slabs
Considering that it is extremely effective in improving the productivity of the continuous casting process, we considered applying the above-mentioned wide reduction rolling technology to continuously cast unidirectional electrical steel slabs to improve the productivity of the continuous casting process. .

However, in order to develop the magnetic properties of the finished product, the unidirectional electrical steel that is the object of the present invention is manufactured by continuously casting slabs of 13
Hot rolling is performed after heating at a high temperature of 00°C or more for a long period of time, and in this case, a defect called edge cracking occurs in the edges of the hot rolled sheet obtained by hot rolling, resulting in a decrease in yield and This causes a decrease in the operating rate during pickling and cold rolling.

In addition, in recent years, unidirectional electrical steel has been developed with s
In addition to increasing i, m and (l, Cu.

Additions of Sn, Sb, etc. have come to be carried out, but there is a tendency for edge cracking to occur frequently in hot-rolled sheets, especially due to an increase in the amount of 5ljl and C.

If the continuously cast unidirectional electrical steel slab is subjected to wide reduction rolling, that is, rolling that mainly involves heavy working on the ends of the continuous cast slab, with the above problems, the edge cracking will be further promoted. The fact that continuous casting slabs can be rolled with a large width reduction without promoting edge cracking in hot-rolled sheets is an important factor in improving productivity in the production of unidirectional electrical steel slabs in the continuous casting process. extremely important.

The present invention not only does not promote edge cracking in hot-rolled unidirectional electrical steel sheets, but also improves the edge cracking of unidirectional electrical steel slabs by making the wide reduction rolling of unidirectional electromagnetic steel slabs nJ-capable, thereby making continuous casting process possible. The aim is to improve productivity in the production of unidirectional electrical steel slabs.

(Means for Solving the Problems) The gist of the present invention is as follows. That is, a unidirectional electrical steel slab manufactured by continuous casting is heated to a high temperature of 1300°C or higher, and then subjected to hot wide reduction rolling of 60 degrees or more using a width reduction rolling mill to form a hot rolled plate of a desired size. In the hot width reduction rolling method of continuously cast unidirectional electrical steel slabs, which aims to improve productivity in the continuous casting process by obtaining This is a method for hot width reduction rolling of a continuously cast unidirectional electrical steel slab, characterized in that the above-described large width reduction rolling is performed using a width reduction rolling mill at a high temperature of 1380° C. or lower.

(for production) The present invention will be explained in detail below.

As is well known, the reason why edge cracks occur in the edges of hot-rolled sheets during the production of grain-oriented electrical steel sheets is due to sufficient solid solution of the inhibitor-forming elements contained in the continuously cast grain-oriented electrical steel slabs. Because the slab is heated at a high temperature for a long period of time, the crystal grains of the slab become large and coarse.
It is thought that edge cracking occurs because this is rolled into a hot rolled sheet without recrystallizing.

By the way, in the rough rolling stage of the hot rolling process of the continuously cast slab after heating it to a high temperature, the bar IV is approximately 40 m + m.
By reducing the width of the bar using an edger roll and promoting recrystallization at the ends of the bar in the width direction,
As a method for preventing edge cracking in a hot rolled sheet caused by coarsened crystal grains, techniques such as those disclosed in Japanese Patent Laid-Open No. 200918/1983 and Japanese Patent Laid-Open No. 1113721/1988 are already known.

However, in the manufacturing method of unidirectional electrical steel as intended by the present inventors, 1. For the purpose of improving productivity in the continuous casting process, wide casting j2 is performed, and then in order to perform wide reduction rolling in the hot rolling process, k1
It is necessary to increase the bus reduction and perform wide reduction rolling with a small number of passes. This is because, in order to exhibit the desired magnetism of the unidirectional electrical steel sheet in the finished product, it is necessary to maintain the temperature of the sheet during rolling as high as possible. In this regard, in the rough rolling stage of the hot rolling process, the bar thickness is thin, so the amount of width reduction is usually 8.
Only 0 mm or less can be obtained, and it is impossible to reduce the width further. That is, in order to perform wide reduction rolling with a minimum number of baths, it must be performed at a stage where the slab thickness is thick before the rough rolling stage, and it is difficult to apply the above-mentioned known technique.

The present invention has established a wide reduction rolling technique that reduces edge cracking by examining various measures against edge cracks that are exacerbated by wide reduction rolling of continuously cast slabs heated at high temperatures.

Figure 1 shows 0.07%C-3,25%Sl-0.13%
After heating a Sn-0,05% Cu composition-based unidirectional electrical steel test piece to 1400°C, a high-temperature tensile test was conducted at each temperature from 900°C to 1400°C, and the cross-sectional shrinkage rate at each temperature was measured. These are the so-called Greeple test results. As can be seen from this figure, the unidirectional electrical steel in this composition system exhibits a significantly low cross-sectional shrinkage ratio, that is, a low ductility in the temperature region around 1100°C.

Furthermore, when the slab is rapidly cooled in this ductile low temperature region (1100° C.) and the state of segregation at the grain boundaries is observed, a large amount of S segregation near the grain boundaries is seen as shown in FIG.

Considering this in comparison with the state diagram in Figure 3, we get
Unidirectional electrical steel undergoes phase transformation into α phase - σ + γ phase - α phase during the cooling process from high temperature, and in the α + γ 2 phase region during this process, the solubility product of S of each phase changes. Dense segregation of S at grain boundaries occurs due to the difference. It is thought that as the ratio of the γ phase increases, the ratio occupied by grain boundary segregated portions increases, and as a result, a significant decrease in ductility occurs in the temperature range of around 1100° C. where the γ ratio is maximum.

Based on the above results, the present inventors have determined that in order to prevent edge cracks in unidirectional electrical steel and to perform large hanging width reduction rolling, it is necessary to That is, it has been found that a hot rolled sheet with fewer edge cracks can be obtained by performing wide reduction rolling in a temperature range of 1200° C. to 1380° C., which is a good ductility region.

In the present invention, the reason why the continuously cast unidirectional electrical steel slab is heated at a high temperature of 1300°C or higher before hot rolling is to sufficiently dissolve the inhibitor-forming elements contained in the continuously cast slab, This is to impart excellent magnetic properties to the final product.

Figure 4 shows the Mn5la remaining in the α and γ phases at each heating temperature when a material containing 0.05% Mn, 0.25% S:Q, and 0.25% S is heated to a temperature higher than goo'c. There is. As is clear from this figure, heating of 1300° C. or higher is required for sufficient solid solution of MnS. In other words,
If the heating temperature of the continuously cast slab is less than 1300° C., the inhibitor-forming elements will not be sufficiently solid-dissolved, so that excellent magnetic properties of the finished product cannot be obtained.

In addition, the temperature range for wide reduction rolling is 1200℃~
One reason why 1380°C is optimal is that, as mentioned above, in the temperature range below 1200°C, dense segregation of S, etc. progresses to the grain boundaries, and at this time, if strong processing is added to the end of the continuous casting slab, A lower temperature limit of 1200°C has been set because it promotes edge cracking. On the other hand, the grain boundaries of continuously cast slabs that are hotter than 1380"c are close to the melting temperature, causing problems such as melting of the slab. Therefore, the upper limit temperature was set at 1380°C.

Next, the purpose of the present invention is to aim for a width reduction amount of 60 degrees or more during wide reduction rolling, which is the object of the present invention. A width reduction of On the other hand, the main purpose of the present invention is to perform wide reduction rolling of B0 or more, which can improve the productivity of the continuous casting process by at least about 10% or more, and to reduce the heat generated when such wide reduction rolling is performed. This is because it is characterized by not only preventing an increase in edge cracking of the rolled sheet, but also improving it.

Regarding the selection of a hot width reduction mill for performing wide reduction rolling that greatly improves continuous casting productivity as intended by the present invention, it is possible to perform wide reduction rolling of 60 mm or more during width reduction rolling. Etcher, which is a reinforced version of Caliber roll or flat roll, is suitable, but is not limited thereto. However, as mentioned above, since width reduction rolling under high temperature is optimal for IL to prevent edge cracking, it is preferable to be able to perform width reduction to the desired size in one bath to ensure the temperature of the slab. It is desirable that the distance between the equipment and the heating furnace be as short as possible. In addition, it has already been proposed in Japanese Patent Publication No. 42561/1983 that the use of large diameter rolls is effective in reducing the area of fishtails that occur when wide reduction rolling is performed, so this was adopted. It is desirable to do so.

The composition of the unidirectional electrical steel slab is not limited in any way in the present invention, but is preferably in the following range.

(C) is preferably in the range of 0.025 to 0.085%.

This is because if it is less than 0.025%, secondary recrystallization becomes unstable, and if it exceeds 0.085%, the time required for decarburization annealing becomes longer, which is economically disadvantageous. [S1
] is preferably in the range of 2.5 to 4.5%. This is 2,5
This is because good iron loss cannot be obtained if it is less than 4.5%.
This is because if it exceeds %, cold rollability will be significantly deteriorated. (
Mn), (S), (Soffi, AR)
, (N).

[Cu), (S, n) are added as inhibitor elements if necessary, and are 0, old to 0, respectively.
．． IO%, Q,, OI~0.04%, 0.005~
0.085%, 0.002~o, oio%, 0
．． Old to 0.50%, preferably 0.05 to 0.5096. Others (Sb), (Bi), (V).

(Ni), [Cr], (B1, etc.) are added as necessary.

Examples will be described in detail below.

(Example 1) Component composition: C: 0.09%, S 1: 3.25
%, Mn: 0.07%, P; 0.01%, S: 0
．． 028%, Al: 0.027%, N: 0.00
90%, Cu: 0.05%, Sn: o, 10%, remainder substantially made of Fe, size 250 x 120
A continuously cast slab with a width of 0 mm was gas heated to 1400°C, and the temperature during width reduction rolling was set to 1100°C, 1250°C,
Three levels of +300'C and width reduction rolling amount, Omm,
After hot width reduction rolling at three levels: 100 mm and 400 mm, the plate is rolled to a thickness of 2.
A hot rolled sheet of 5 ms+ was obtained. After that, pickling, preliminary cold rolling, and hot rolled sheet annealing are performed using a known method for manufacturing unidirectional electrical steel sheets.
A cold-rolled plate with a plate thickness of 0.220+am was obtained by cold rolling. The obtained cold-rolled sheet was decarburized and annealed by a known method, coated with a baking separator, final annealed, and tension coated to produce a high magnetic flux density unidirectional electrical steel sheet. Table 1 shows the worst value of the edge crack depth of the hot rolled sheet in this manufacturing process and the magnetic properties of the finished product.

From Table 1, ■ indicates significantly inferior ear cracking and magnetic properties.

■The productivity of the continuous casting process is poor.

■ - [Stocks] all have good edge cracking, improve productivity in the continuous casting process, and have no problems in terms of magnetic properties (among them, ■ and ■ are particularly good in continuous casting while maintaining good edge cracking and magnetic properties. productivity has improved).

(Implementation M2) Component composition: C: 0.044%, Si: 3.0%, M
n: 0.06%, P: 0.01%, S: 0.02
0%, Al: 0.002%, N: 0.0040%
, Cυ: 0.17%, the remainder substantially consists of FO, a continuous casting slab of size 250 m thick x 1200 + u + width,
Gas heated to 1400°C, and the temperature during width reduction rolling was set to 1i
After performing hot width reduction rolling at three levels: oo℃, 1250℃, and 1300℃, and the width reduction rolling amount at three levels: Ou+, 100Ryu, and 400U+, the plate is processed through a rough rolling process and a finish rolling process. A hot rolled sheet with a thickness of 2.5 mm was obtained. Thereafter, by a known manufacturing method for unidirectional electrical steel sheets, pickling, preliminary cold rolling, intermediate annealing, and cold rolling are performed to obtain a plate thickness of 0.
, a cold-rolled sheet of AOO was obtained. The obtained cold-rolled sheet was decarburized by a known method, coated with a seizing separator, final annealed, and tension coated to produce a unidirectional electrical steel sheet. Table 2 shows the worst value of the edge cracking depth of the hot rolled sheet and the magnetic properties of the finished product during the production of this unidirectional electrical steel sheet.

All of the products from (1) to (2) within the scope of the present invention have good edge cracking, improve productivity in the continuous casting process, and have no problems in terms of magnetic properties.

(Effects of the Invention) According to the present invention, it is possible not only to not promote edge cracking in hot-rolled unidirectional electrical steel sheets, but also to improve the width of continuous casting slabs of unidirectional electrical steel. It is possible to improve the productivity in the production of continuously cast slabs of unidirectional electromagnetic steel in the continuous casting process, and the industrial effect is great.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between each test temperature of a unidirectional electrical steel test piece and the cross-sectional shrinkage rate at that time. FIG. 2 is a diagram showing the S concentration near the grain boundaries of a unidirectional electrical steel test piece. FIG. 3 is a Fe-8i phase diagram at 0.07%C. Fourth
The figure is a diagram showing the relationship between the heating temperature of unidirectional electrical steel and the solid solution curve of Mn5 (α, γ phase). Sub-agent Patent attorney Hiroaki Tamura 6- and #da θO Sectional shrinkage = l (%) SLCwtZ)

Claims (1)

[Claims] A unidirectional electrical steel slab manufactured by continuous casting is
After heating to a high temperature of 0℃ or higher, use a width reduction rolling mill to reduce the width to 60m.
A method for hot width reduction rolling of continuously cast unidirectional electrical steel slabs, which aims to improve productivity in the continuous casting process by performing hot width large reduction rolling of m or more to obtain a hot rolled sheet of a desired size. Continuous casting unidirectional, characterized in that immediately after heating and extracting the slab, the above-mentioned wide reduction rolling is performed using a width reduction rolling mill at a high temperature where the surface temperature of the slab is 1200°C or more and 1380°C or less. Hot width reduction rolling method for magnetic steel slabs.