JPS643564B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical field) The present invention belongs to the field of hot rolling technology for producing unidirectional silicon steel sheets, and relates to the field of hot rolling technology for manufacturing unidirectional silicon steel sheets, and the present invention relates to the field of hot rolling technology for producing unidirectional silicon steel plates, and is concerned with the rough edges and cracks that occur during hot rolling when oriented silicon steel slabs are heated to high temperatures. This is a proposal for a hot rolling method that can effectively prevent ear flaws such as the above and improve product yield. (Prior art and its problems) Grain-oriented silicon steel sheets are widely used as iron core materials for transformers and the like due to their excellent magnetic properties, including high magnetic flux density and low iron loss. In recent years, even in this type of technical field, it has been desired to supply grain-oriented silicon steel sheets with excellent magnetic properties at a lower cost, and the question for engineers concerned is how to reduce manufacturing costs. This is a common issue. Generally, in order to obtain grain-oriented silicon steel sheets with excellent magnetic properties, {110}<001>
It is necessary to control the secondary recrystallization phenomenon in which the orientation (Goss orientation) selectively grows, and to obtain a uniform secondary recrystallization structure in which the Goss orientation is highly concentrated. In order to obtain a recrystallized texture with Goss orientation, it is effective to utilize an appropriate precipitated dispersed phase, and for this purpose, MnS,
Impurities called inhibitors such as MnSe and AlN are used. This technology first begins when heating the slab.
It is important to obtain a dispersed phase preferable as an inhibitor by sufficiently dissociating MnS, MnSe, etc. into a solid solution and then performing appropriate hot rolling. The slab heating temperature required for this dissociation and solid solution (solution treatment) of the inhibitor is usually in the high temperature range of 1300 to 1420°C for a long period of time. However, long-term heating in a high temperature range of 1300℃ or higher induces abnormal growth of slab grains, and the coarse grains do not recrystallize sufficiently even during hot rolling, leaving coarse grains. This is often the cause of ear scratches, such as cracks in the ears of hot coils. Such edge flaws in hot coils can cause breakage in the next process of cold rolling, and the rough edges must be removed before cold rolling, which greatly reduces yield and increases manufacturing costs. It was the main cause. In short, the above-mentioned phenomenon that is especially noticeable in continuously cast slabs is because columnar crystal structures are easily formed in continuous cast slabs due to rapid solidification, and these columnar crystal structures are more likely to grow abnormally than normal agglomerated materials. They tend to remain as unrecrystallized grains after rough rolling. These coarse unrecrystallized grains have extremely poor toughness and turn into ear flaws in the hot coil in the later stages of hot finish rolling. Conventionally, there is a technique already disclosed in Japanese Patent Publication No. 57-4690 to prevent such ear scratches, which is a method of promoting recrystallization of coarse grains by changing the rolling schedule during rough rolling. With a conventional rolling mill that uses only horizontal rolls, sufficient stress is not applied to the side surfaces of the rolled material, and great effects cannot be expected. In addition, a method for limiting the temperature difference between the start and end of finish rolling disclosed in JP-A No. 55-62124, a longitudinal direction of a material to be rolled during finish rolling disclosed as JP-A-57-165102; Methods based on temperature control, such as a method of limiting the temperature difference in the width direction, have been proposed. All of these methods aim to prevent ear scratches by eliminating temperature unevenness, but when it comes to the phenomenon of the edges (ears) on both sides of the strip, there are rather passive methods that do not require a fundamental solution. I haven't gotten to the point where I can give it. (Introduction to the Invention) The present inventors conducted a follow-up investigation of phenomena during rolling, such as when edge cracking occurs and how it develops, and as a result, the following findings were obtained. That is, in the widthwise side edges (edges) at the stage of the sheet bar after rough rolling, the coarse crystal grains are not sufficiently recrystallized and the coarse drawn grains and fine recrystallized grains are mixed together. This is because the thickness of the coarse grains after heating is large during rough rolling, so the effect is small, and the resistance from both end faces of the plate is small, so slippage occurs at the grain boundaries and sufficient stress is not transmitted. figure,
This is thought to be because they remain as unrecrystallized grains. In this case, the shape of both side edges of the sheet bar is such that coarse grains jump out discontinuously and create complex undulations. Normally, when a plate to be rolled is rolled, triaxial stress is applied to both side edges thereof, and the strip becomes wider. At this time, if the shape of both side edges of the strip, that is, the ears, is irregularly undulating, local stress concentration occurs, causing internal cracks and eventually causing ear cracks. In fact, the higher the flatness of both edges in the width direction at the sheet bar stage, the less severe the edge scratches will be, and the shape of the edges of the rolled material before finish rolling has a large effect on edge scratches (particularly edge cracks). It turned out that it does. (Objective and Summary of the Invention) The present invention is based on the above-mentioned knowledge that the shape of the edges of the rolled material at the initial stage of finish rolling affects the condition of the edges of the hot coil. The main feature of the claim is to mechanically correct both side end surfaces of the sheet bar and strip using an edger roll at the beginning of finish rolling, with the aim of effectively preventing the above-mentioned ear scratches without causing any scratches. By adopting the method described in , the limitations of the prior art described above were exceeded. (Structure of the Invention) The main manufacturing process of grain-oriented silicon steel sheets to which the present invention is applied is to form steel containing 2.5 to 4.1% Si into a slab using an ingot method or continuous casting method, and then hot rolling the steel into a slab. What to do with hot coils. Next 1
After obtaining the final thickness by cold rolling twice or more times with intermediate annealing in between, decarburization annealing and final annealing are performed. It is in the finish rolling process after heating and rough rolling. That is, after finish rolling,
Etching is applied using an edger roll (vertical roll) at either or both of the entrance and exit sides of the first stand, and width reduction is applied to both end surfaces of the seat bar and strip to flatten the shape of both side edges. It is in the point of doing. The reasons for limiting each condition in the above manufacturing process will be described below. The composition of the steel used in the present invention is, in weight%,
Si: 2.5-4.1% as essential component, other C: 0.01
~0.08%, Mn: 0.03~0.1%, S and/or Se:
It contains 0.005 to 0.1%, with the remainder being iron and some unavoidable components. The amount of Si was limited to 2.5 to 4.1% because if it was less than 2.5%, sufficient magnetic properties could not be obtained, and if it was more than 4.1%, cold rolling would be difficult. The amount of C is 0.01
If it is less than 0.08%, a sufficient amount of γ phase will not be generated during hot rolling, and if it is more than 0.08%, it will take a long time to decarburize in the subsequent process, so it was limited to 0.01 to 0.08%. Mn, S and Se form an inhibitor used as a precipitated dispersed phase, so the content of each Mn:
0.03%, S and/or Se: less than 0.005% will cause a quantitative shortage of the precipitated dispersed phase, while each 0.1
If it exceeds Mn: 0.03 to 0.1, insufficient solutionization occurs during slab heating and an appropriate dispersed phase cannot be obtained.
%, S and/or Se: limited to 0.005 to 0.1%.
Other solute atoms such as Cr, Ni, Cu, Mo, Sb, P, and Sn may be intentionally added, but the effects of the present invention are not lost in this case as well. Slabs containing the above components are heated in a pusher or walking beam type slab heating furnace.
The slab is heated to a temperature of 1,300 to 1,420℃, but if the heating temperature of the slab is lower than 1,300℃, solid solution of impurities used as the precipitated dispersed phase will be insufficient, and if it is too high, the yield will be reduced due to the generation of huge scale, and the furnace A temperature range of 1300 to 1420°C is preferable since this results in a decrease in service life. After that, it is rolled in multiple passes in a rough rolling mill for 20~
It is said to be a sheet bar with a thickness of about 60mm. One of the features of the present invention is the etching performed at least one or both of the entry side and exit side of the first stand of the finishing mill.
A correction reduction of 40 mm is applied. As shown in Figure 1, if the width reduction is less than 5 mm, the effect of shape correction will be small, while if it exceeds 40 mm, defective shape will occur due to the formation of dot bones, so the range was limited to 5 to 40 mm. . This straightening reduction is for the purpose of preventing stress concentration on the side edges and suppressing the occurrence of internal cracks, and it is sufficient to flatten the shape of the side edges within a range of 5 to 40 mm regardless of the slab width. Note that this reduction is not essentially limited to the first stand, but from the second stand onward the thickness of the strip becomes thinner and defects in shape due to width reduction are more likely to occur, so it is carried out before and after the first stand. I decided to do so. Next, the reason why the temperature before starting finish rolling is set to 1100° C. or higher is that when the temperature is lower than this temperature, the size of the precipitated dispersed phase often becomes non-uniform and the magnetic properties deteriorate. After that, cold rolling is performed once or twice or more including intermediate annealing to obtain a finished product thickness, and then decarburization annealing, which also serves as primary recrystallization, is performed for 3 times in a wet hydrogen atmosphere at 780 to 850°C.
Perform final annealing at 1200℃ or higher for about 15 minutes. In addition, FIG. 2 shows a preferred embodiment of the present invention, in which 1 is a rough edger, 2 is a rough rolling mill, and 3
is a crop shear, 4 is an inlet edger, 5 is the first stand of the finishing mill, 6 is the second stand, an outlet edger 7 is disposed between them, and 8 is the final stand. (Example) C: 0.04%, Si: 2.95%, Mn: 0.07%, S:
Molten steel with the balance of 0.02% mainly consisting of Fe was continuously cast to obtain a slab with a thickness of 230 mm. This was heated to 1350℃ and hot-rolled under the following three conditions (a) to (c).
A 2.4mm hot coil was manufactured. Condition (a) in the manufacturing process is that no width reduction is performed on both the inlet and outlet edgers of the first stand, and condition (b) is that a width reduction of 10 mm is applied with the edger on the inlet side of the first stand. Condition (c) is that the width reduction is 10 mm each (total 20 mm) on both the input and output edgers. The obtained hot coil was uniformly annealed at 900°C for 3 minutes, then subjected to primary cold rolling of approximately 70%.
After intermediate annealing at 950°C for 3 minutes, secondary cold rolling of approximately 60% was performed to give a finished product thickness of 0.3 mm. Thereafter, decarburization annealing was performed for 4 minutes in wet hydrogen at 820°C. Then,
Apply an annealing separator mainly composed of MgO, and
Final annealing was performed at ℃. The results are shown in the table below.

[Table] (Effects of the Invention) As explained above, according to the hot rolling method of the present invention, in which a grain-oriented silicon steel sheet is subjected to appropriate width reduction by an edger in the early stage of the finish rolling mill, the width of the hot coil can be reduced. Ear scratches on both side edges (ears) can be eliminated.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between edger width reduction and degree of edge cracking, and FIG. 2 is a schematic diagram of hot rolling equipment used to implement the method of the present invention. 1... Rough edger, 2... Rough rolling mill, 3...
Crop shear, 4... First stand entrance edger of finishing rolling mill, 5... First stand of finishing rolling mill, 6... Second stand of finishing rolling mill, 7...
Finishing mill's first stand exit edger, 8...
...The final stand of the finishing rolling mill.

Claims (1)

[Claims] 1% by weight, Si: 2.5-4.1%, C: 0.01-0.08
%, Mn: 0.03~0.1%, S and/or Se: 0.005~
In the method of obtaining a hot rolled steel strip by heating a silicon steel slab consisting of 0.1%, the balance being Fe and unavoidable components to a temperature of 1300 to 1420° and subjecting it to rough rolling and finish rolling, a hot rolled steel strip is obtained. For hot finish rolling, (a) The start temperature of finish rolling shall be 1100℃ or higher; (b) Rolling by an edger roll at either or both of the entry side and exit side of the first stand of the finishing rolling mill. A method for hot rolling a grain-oriented silicon steel sheet, characterized by applying a width reduction of 5 to 40 mm, and rolling to satisfy the following conditions.