JPH04304315A - Method for preventing generation of edge flaw in hot-rolled steel sheet for grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To drastically reduce the development of edge flaw of edge crack, etc., feared in the case of using a slab for silicon steel, particularly a continuously cast slab and to improve the yield of a product. CONSTITUTION:In the continuous casting process for Si-incorporating steel slab, to both edge parts of this slab, high deformable range satisfying the range of 1.02-1.15 relative deformability is formed with the width having 0.5-2.0 edge part high deformable range index and successively, after heating relevant slab at >=1250 deg.C, width rolling reduction having 3-60mm is applied at least once among before passing, during passing and after passing in hot rougher rolling process.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to the improvement of hot-rolled materials in the field of manufacturing technology for grain-oriented silicon steel sheets, and particularly relates to the improvement of hot-rolled materials when grain-oriented silicon steel slabs are heated to high temperatures. The purpose of this invention is to effectively prevent the occurrence of ear flaws such as ear roughness and ear cracking, and to obtain a grain-oriented silicon steel sheet with excellent magnetic properties at a high yield.

Grain-oriented silicon steel sheets are widely used as iron core materials for transformers and the like because of their excellent magnetic properties, including high magnetic flux density and low iron loss. Especially since the recent energy crisis, it has become a major issue to supply grain-oriented silicon steel sheets with excellent magnetic properties at low prices.How can we reduce manufacturing costs and spread products with excellent magnetic properties? is of great interest to those skilled in the art.

0003

[Prior Art] Generally, in order to obtain grain-oriented silicon steel sheets with excellent magnetic properties, crystal grains having the (110) [001] orientation (Goss orientation) are selectively grown during final annealing, which is called secondary recrystallization. It is necessary to control the phenomena that occur. For this purpose, it is necessary to finely and uniformly disperse precipitated dispersed phases called inhibitors such as MnS, MnSe, AlN, etc. into the steel. This is done by heating the slab to a high temperature before hot rolling to dissolve these inhibitors in solid solution. It becomes possible only by doing so. For this reason, slabs are usually 1250 to 1
Although it was heated to a high temperature range of 470°C, the slab crystal grains grew abnormally due to such high temperature heating, and the coarse crystal grains did not recrystallize sufficiently during the subsequent hot rolling stage, leaving coarse crystal grains. This will cause deterioration of magnetic properties.

[0004] As a countermeasure against the above problem, measures such as recrystallizing the structure by modifying the temperature and pass schedule of rough rolling, and performing light rolling before heating the slab to prevent coarsening of the slab structure are available. However, such measures are ineffective at both edges of the strip. This is because metal flow occurs in the direction of width expansion at both edges (edges) of the strip when rolling with rolls, so the amount of strain accumulated due to processing is small, and the amount of strain accumulated during hot rolling or after light rolling of the slab is small. This is because recrystallization does not proceed sufficiently even with heating. As a result, on both side edges of the coil after hot rolling, not only deterioration of magnetic properties but also frequent ear flaws such as edge cracks and rough edges occur, and these ear flaws are likely to cause breakage in the next cold rolling process. Since it is also a cause, it has to be removed before cold rolling, which is a major cause of a decrease in yield.

The above-mentioned phenomenon is particularly noticeable in the case of continuously cast slabs, and this phenomenon is due to the columnar crystal structure associated with rapid solidification, which is a feature of continuously cast slabs. In other words, columnar crystal structures tend to grow abnormally more easily than other structures, and are difficult to recrystallize after rough rolling, but such columnar crystal structures are particularly developed at the width ends of continuous casting slabs. . The structure remaining as unrecrystallized grains during hot rough rolling has poor toughness, so cracks are generated during hot finish rolling, which causes edge cracks and other edge flaws.

[0006] As a measure to prevent such ear scratches, rolling in the sheet width direction during hot rolling has been proposed. This method aims to suppress the metal flow (width expansion) in the width direction by the rolling rolls and accumulate strain at the side edges of the strip, while at the same time increasing processing strain by actively applying rolling reduction. This is intended to promote crystallization. For example, Tokuko Sho 6
4-3564, using an edger roll,
A technique for applying a width reduction of ~40 mm and setting the start temperature of hot rolling finish rolling to 1100°C or higher was also disclosed in JP-A-60-20.
No. 0916 discloses a technique for performing at least one width reduction in the range of 5 to 40% during hot rough rolling, and JP-A-61-71104 discloses a technique for applying an edger before hot finishing rolling. A technique is disclosed in which the width reduction is performed in the range of 5 to 60 mm and the temperature of the side surface of the seat cover is maintained in the range of 1150 to 1250°C.

[0007]

[Problem to be solved by the invention] With each of the above technologies,
Regarding the improvement of edge scratches on hot-rolled coils, some effects were obtained, but when the amount of width reduction was small, the effect of improving edge scratches was poor, but when the amount of width reduction was increased, a defect called edge heave occurred. A new occurrence. As a result, the properties of the ears deteriorate, and the ears have to be cut and scrapped, resulting in a decrease in yield.

This invention was developed in view of the above-mentioned circumstances, and it solves the effect of ear scratches caused by coarse grains at the edges of hot-rolled coils, which is a particular problem when continuous cast slabs are used as the raw material. The purpose of this study is to propose effective prevention methods.

[0009]

[Means for Solving the Problems] Now, as a result of extensive research to achieve the above object, the inventors have found that in addition to actively applying stress in the width direction of the slab during the hot rough rolling stage, By changing the deformability of the material in the width direction, coarse grains at the edges are not only effectively refined, but also recrystallization is promoted, without causing the aforementioned edge heave. We have obtained knowledge that the occurrence of ear scratches can be prevented. This invention is based on the above knowledge.

[0010] That is, the present invention provides Si: 2.5 to 4
．． In the continuous casting process of a grain-oriented silicon steel slab containing 5 wt% (hereinafter simply indicated as %), both edges of the slab have a relative deformability (edge deformability/center deformability). The high deformability region satisfying the range of 1.02 to 1.15 is defined by the edge high deformability region index (edge high deformability region width/
After forming the slab with a width such that the slab thickness is 0.5 to 2.0, and then heating the slab to a temperature of 1250°C or higher,
A hot-rolled steel sheet for grain-oriented silicon steel comprising performing width reduction at least once in the range of width reduction: 3 to 60 mm before, between and after passes in a hot rough rolling process. This is a method for preventing ear scratches (first invention).

[0011] Further, the present invention provides, in the first invention,
The formation of a high deformability region makes the region more 0 than the central region.
．． This is a method for preventing ear scratches in a hot-rolled steel sheet for grain-oriented silicon steel (second invention), which comprises containing 03 to 0.25% more Cu.

[0012] The experimental results that led to this invention will be explained below. As a result of investigating the structure of the edge when rolling down with an edger for the purpose of improving edge cracks, the inventors found that when the rolling amount is within 20 mm, the relative rolling amount (so-called rolling ratio) with respect to the entire width direction It was found that since the amount of strain accumulated at the edge was small, it could not serve as a driving force for recrystallization.

[0013] However, if the reduction amount is 20 mm or more, the shape of the edge before rolling as shown in Fig. 3 (a) will change to a dogbone shape as shown in Fig. 3 (b). It was found that as a result of this being rolled in the next pass, collapse as shown in FIG.

Based on the above findings, the inventors conducted the following experiments. (Experiment 1) That is, thickness 1 containing 0.05% C
00 mm of 3% Si steel slab with the same thickness.
Width of the edge of a 3% Si steel slab containing 0.03%: 1
00 mm was cut and welded. This joint slab is 13
After heating to 50°C, one pass of rough rolling was performed.
As shown in FIG. 4(a), the thickness decreased toward the edge. When width reduction was applied to this slab, the edge structure was sufficiently recrystallized and grained even with a reduction of 5 mm. Further, even when a reduction of 25 mm was applied, the edge shape was rectangular as shown in Figure (B), and even in the next pass of rolling, no edge hedding was observed as shown in Figure (C). By rolling as described above, it was possible to obtain a hot-rolled coil in which no edge cracking occurs due to a width reduction of 3 to 60 mm, and also no edge curling occurs.

The success described above is due to the fact that a slab material with greater deformability than the central part of the slab is used for the edges, which results in a thickness taper at the edges as shown in Figure 4 (a), which makes it difficult to reduce the amount of width reduction. It is presumed that even if the size was increased, the dogbone shape shown in FIG. 3(b) would not have occurred. In addition, since the mechanical properties of the material differ in the width direction, the only areas where strain is concentrated due to reduction in the width direction are the edges, where the deformability is large, so recrystallization at the edges is promoted even with a small amount of width reduction. It is assumed that this resulted in

[0016] Next, the inventors investigated the most important area for obtaining the desired effect, the appropriate area of the slab edge where the deformability should be increased, and the appropriate size of the deformability. In addition, in the following experiment, when making a slab from ordinary molten grain-oriented silicon steel containing 3.4% Si by continuous casting,
Approximately 0.12% Cu was contained at the edge of the slab by inserting a Cu wire into the edge of the mold.

(Experiment 2) The edge region where the amount of Cu should be increased was variously changed while adjusting the thickness and number of Cu wires introduced. Here, the Cu-containing region is a region from the edge of the slab to the width center direction, and is a region where the Cu content is reduced by half. Now, the ratio of the deformability of the Cu-containing region to the deformability of the central part of the slab width not containing Cu at the hot rolling temperature (hereinafter referred to as relative deformability) is 1.04 to This was equivalent to 1.07 times. The deformability was evaluated by the rate of decrease in thickness when a constant load was applied at a constant temperature (for example, hot rolling temperature). In addition, in order to take into account the shape effect of the slab,
It was decided to use the length of the Cu-containing region divided by the thickness of the slab as an index of the size of the edge of the slab with high deformability (hereinafter referred to as edge high deformability region index).

(Experiment 3) While adjusting the thickness and number of Cu wires, the Cu content area was kept at the same value as the slab thickness (edge high deformability area index = 1.0), and the Cu content was varied. Different slabs were manufactured. At this time, the relative deformability of the edge was 1.01 to 1.15.

After heating the slabs produced in Experiments 2 and 3 above to 1420°C, the slabs were rolled in three rough passes to give a total of 83.
% rolling to make a sheet bar. At this time, a width reduction of 30 mm was performed after the first pass of rolling. In addition, the sheet bar was made into a hot-rolled coil by ordinary finish rolling. Maximum ear cracking depth, occurrence rate of edge baldness, and edge drop rate at Hot crown of each coil thus obtained {(Thickness at the center of the board width - Thickness of the edge) ÷ Thickness at the center of the board width x
100} was measured. These results for Experiment 2 are shown in FIG. 1, and those for Experiment 3 are shown in FIG. 2.

As is clear from FIG. 1, if the edge high deformability region index is 0.5 or more, that is, if the high deformability region is provided at the slab edge over a length of 0.5 times the slab thickness or more, Ear splitting is significantly reduced. However, when the edge high deformability region index exceeds 2.0, edge drop begins to increase rapidly and edge heave begins to occur. Therefore, in this invention, the edge region to which high deformability is to be imparted has an edge high deformability region index of 0.5 to 2.0.
limited to the range of

Next, according to FIG. 2, the Cu content at the edge is 0.
．． When it is 0.3% or more, it is very effective in reducing ear cracking. However, if the Cu content exceeds 0.25%, edge curling will occur frequently, so the appropriate Cu content is 0.
．． 03 to 0.25%. Here, when the range of the above-mentioned Cu amount is expressed in terms of relative deformability, it corresponds to a range of 1.02 to 1.15. Therefore, in this invention, the range of relative deformability is set to 1.0.
It was limited to 2 to 1.15.

[0022]

[Operation] Next, the present invention will be specifically explained in the order of manufacturing steps. First, the components of the continuously cast slab used in this invention will be described. The test slab must contain Si in a range of 2.5 to 4.5%. This is because the amount of Si is 2.5
%, the desired magnetic properties cannot be obtained; on the other hand, 4.
This is because if it exceeds 5%, cold workability deteriorates. Regarding the amount of C, if it is less than 0.02%, sufficient γ phase will not be generated during hot rolling, while if it exceeds 0.09%, decarburization will be insufficient in the subsequent decarburization process. .02-0.09
The content is preferably within the range of %. In addition, AlN, MnS, Mn as inhibitors
Any one or more of Se can be effectively used. At this time,
In the case of AlN-based, the content suitable as an inhibitor is: Al: 0.010 to 0.030%, N: 0.00%
4 ~ 0.012%%, and in the case of MnS, MnSe type, Mn: 0.03 ~ 0.12, S: 0.005 ~
0.10%, Se: 0.010 to 0.12%. In addition, as auxiliary elements of the inhibitor, Cu, Ni, C
Solute atoms such as r, Sn, Mo, Sb and P can also be added.

Now, the molten steel adjusted to the proper composition as described above is made into a slab with a thickness of 100 to 850 mm by a continuous casting method. At this time, the composition of both edges in the width direction of the slab is changed, and the central part of the slab is The most important point of this invention is to improve the deformability even more than the above. As a means for changing the deformability, it is advantageous to introduce a composition-adjusting alloy into regions corresponding to both edges of the slab in the mold during slab casting. Here, as alloys for composition adjustment, high-Si iron alloy rods, Cr iron alloy rods, Cu
and Cu alloy rods.

From the viewpoint of ease of charging into the mold, it is best to use Cu wire rods or Cu alloy wire rods such as brass, cupronickel, bronze, and phosphor bronze. Good uniformity. At this time, the increase in Cu content at the edge of the slab needs to be 0.03 to 0.25%. This is because, as mentioned above, if the increase in Cu content is less than 0.03%, the effect of improving the edge cracks in the hot rolled coil is insufficient, and on the other hand, if it exceeds 0.25%, the occurrence of edge curling cannot be avoided. That's because there isn't.

[0025] At this time, the relative deformability is 1.02 to 1.15.
As described above, it is necessary to control the edge high deformability region index within the range of 0.5 to 2.0.

The slab thus obtained is heated in a pusher type or walking beam type gas heating furnace, or in a heating furnace using a direct current or induction heater.
Heated to a temperature of 1250°C or higher. The heat-treated high-temperature slab is then hot-rolled. During the rough rolling stage of hot rolling, a vertical roll such as an edger roll or a width roll is used between multiple passes including before the first pass. By pressing at least one width reduction from 3 to 60
Apply in the range of mm. If the amount of width reduction is less than 3 mm, the edge scratches cannot be sufficiently improved even in the slab obtained according to the present invention, while if it exceeds 60 mm, edge hedding occurs.

[0027] In applying the present invention, further effects can be obtained if heat treatment is also applied to the edge of the hot steel plate between the slab and rolling passes.

[0028] Thereafter, the plate was finish rolled according to a conventional method, then wound into a hot coil, and then cold rolled once or twice or more including intermediate annealing to obtain a final thickness, and then heated at 780 to 900°C. 1 in an atmosphere containing wet hydrogen.
Next, decarburization annealing that also serves as recrystallization is performed, and then 1200
A final annealing is performed at around ℃ to produce a product plate. This product board is supplied to customers with a tension insulation coating, if necessary.

[0029]

[Example] Example 1 When manufacturing slabs by continuous casting from molten steel with the composition shown in Table 1, Cu wire was introduced into both edges of the mold in the long side direction of some of the slabs to enrich the Cu concentration. While doing this, a slab with a thickness of 250 mm and a width of 1000 mm was obtained. At both edges of the obtained slab, edge high deformability regions were formed in which the Cu content was increased by 0.10 to 0.15% compared to the central region, and the edge high deformability region index was 1. 0-1
．． 5, the relative deformability was 1.07-1.10. For comparison, a slab of the same size was produced without adding Cu wire and used as a conventional example.

After heating these slabs to 1440° C., they were roughly rolled into a 50 mm sheet bar in 4 passes. At that time, an edger was applied between each pass and after the 4 passes.
A width reduction of 10 mm was applied each time. Thereafter, a hot-rolled coil having a thickness of 2.5 mm was obtained by hot finish rolling according to a conventional method. The results of measuring the maximum amount of edge cracking of each coil thus obtained are also listed in Table 1. In addition, there is no edge heave on each coil, and there are 2 edge drops.
It was good at ~4%.

[0031]

[Table 1]

As is clear from the table, the hot-rolled coil manufactured from the slab manufactured by applying the present invention has a small amount of edge cracking, and the edge flaws are effectively improved. When we investigated the magnetic properties of the edges and center of products manufactured using these hot-rolled coils, no difference was found between the two.

Example 2 C: 0.08%, Mn: 0.075%, P: 0.01
0%, S: 0.020%, Al: 0.025%,
Slabs were manufactured from molten steel containing 3.35% Si and 0.006% N by continuous casting in various ways as shown below. Note that each slab shape has a thickness of 210 mm and a width of 1050 mm. A. Cast as is. B. Casting was carried out while a plurality of Cu wires were introduced into both edges of the mold in the longitudinal direction at a charging speed of 2.5 m/min. C. Casting was performed while a plurality of Cu wires were introduced into both edges of the mold in the longitudinal direction at a charging speed of 1.1 m/min. D. Similar to C, there are multiple Cu on both edges in the long side direction of the mold.
The wire was introduced at a speed of 1.1 m/min, but the Cu wire was introduced over a wider area in the long side direction than in C for casting. E. Casting was carried out while a plurality of brass wires were introduced into both edges of the mold in the longitudinal direction at a charging speed of 1.1 m/min. F. Casting was carried out while a plurality of bronze wires were introduced into both edges of the mold in the longitudinal direction at a charging speed of 1.1 m/min.

When examining the component distribution across the width of each obtained slab, it was found that slab A was relatively homogeneous except for the segregated areas, whereas slabs B to F had edges containing a high concentration of Cu. It has high deformability regions at both ends, and its index is 0.9 to 1.4 for B to C, E and F, and 2 for D.
．． It was 4. The average Cu content in the edge high deformability region is 0.24% for B, 0.18% for C, 0.09% for D, and 0 for E.
．． 08% and 0.11% for F, while the Cu content in the other central part is 0.01-0.02%, and the relative deformability is 1.14 for B and 1.11 for C, respectively. , D with 1.
05, 1.05 in E and 1.08 in F.

[0035] These slabs were then heated to 1400°C and then roughly rolled into a 40 mm sheet bar in 3 passes. At that time, a width reduction of 20 mm was applied using a width press before rolling, and a 25 mm width reduction was applied after the 3 passes. A width reduction of 200 mm was applied with an edger. Furthermore, for a portion of each coil, the temperature at both edges was increased by 20° C. using an edge heater before the third rolling pass. Thereafter, it was made into a 2.2 mm hot rolled coil by normal hot finish rolling. Table 2 shows the results of measuring the maximum amount of edge cracking, edge hedding occurrence rate, and edge drop rate of each coil thus obtained.

[0036]

[Table 2]

As is clear from the table, the hot-rolled coils manufactured from slabs B, C, E, and F according to the present invention had an extremely small amount of ear scratches. When we investigated the magnetic properties of the edges and center of products manufactured using these hot-rolled coils, no difference was found between the two.

[0038]

[Effects of the Invention] Thus, according to the present invention, it is possible to significantly reduce the occurrence of edge cracks and other flaws that were a concern in the past, especially when continuous casting slabs were used, and it is highly effective in improving product yield. play.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the edge high deformability region index, the maximum ear crack depth, the edge heave occurrence rate, and the edge drop rate.

FIG. 2 is a graph showing the relationship between the Cu content of the edge deformability region, the maximum ear crack depth, the edge heave occurrence rate, and the edge drop rate.

FIG. 3 is a cross-sectional view showing a change in the shape of the edge of a rolled material when a slab whose material is homogeneous in the width direction is subjected to rolling treatment including width reduction.

FIG. 4 is a cross-sectional view showing a change in the shape of the edge of a rolled material when a slab having a high deformability region at the edge is subjected to rolling treatment including width reduction.

Claims (2)

[Claims] Claim 1: In the continuous casting process of a grain-oriented silicon steel slab containing 2.5 to 4.5 wt% of Si, both edges of the slab have a relative deformability (edge deformability/ The high deformability region satisfying the range of 1.02 to 1.15 (center deformability) is defined as the high deformability region where the edge high deformability region index (edge high deformability region width/slab thickness) satisfies the range of 0.5 to 2. After heating the slab to a temperature of 1250°C or higher, width reduction is performed at least once before, between passes, or after the pass in the hot rough rolling process. A method for preventing the occurrence of ear scratches on a hot rolled steel sheet for grain-oriented silicon steel, characterized in that the method is carried out within the range of 3 to 60 mm. 2. In claim 1, the formation of the high deformability region is such that the region is 0.03 to 0.25 more deformable than the central region.
A method for preventing ear scratches on a hot-rolled steel sheet for grain-oriented silicon steel, which method involves containing a large amount of Cu by wt%.