JPH0365001B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing an electrical steel sheet having excellent soft magnetic properties on an industrial scale. [Prior Art] Since silicon steel sheets have excellent soft magnetic properties, they have been used in large quantities as magnetic cores for electric power or in rotating machines. It is known that in this silicon steel sheet, the soft magnetic properties improve as the amount of silicon added increases, reaching a peak at 6.5%. However, when the silicon content in the steel exceeds 4.0%, the elongation decreases rapidly, making normal cold rolling impossible, and it has been difficult to stably produce thin sheets of high-silicon steel industrially. It was said that Several methods have been proposed in the past for manufacturing such high-silicon steel sheets. Ishizaka et al. have reported that cold rolling of high-silicon steel is possible to some extent by appropriately selecting hot rolling conditions after hot forging (Ishizaka et al.: Journal of the Japan Institute of Metals).
Vol.30 (1966) No.6). That is, they are 1-7%
Silicon-containing alloy is melted by high frequency in the atmosphere to 50mm
After making square ingots, they were hot-forged to a thickness of 15 mm, and the surface of the test piece was cut to a thickness of 11 mm, and then heated at 1000℃, 850℃, and 750℃ for 1 hour each.
After isothermal hot rolling at 750°C to a thickness of 5mm, at 600°C to a thickness of 1mm, and at 750°C to a thickness of 5mm.
After constant temperature hot rolling to 3mm thickness, 600mm
Cold ductility was determined by isothermal hot rolling at ℃, then isothermal hot rolling at 450℃ to a thickness of 1 mm, and then pickling and cold rolling of the samples to observe the occurrence of cracks. The influence of hot rolling conditions was investigated. According to this report, the silicon content is approximately 4.7
% or less, cold rolling is possible regardless of the hot rolling conditions, and when the silicon content is around 5%, cold rolling is possible regardless of the hot rolling conditions by shearing the side edges (edges) of the hot rolled sheet. be. However, for steel sheets containing approximately 6% or more silicon, the subsequent cold rolling properties vary depending on the hot rolling temperature, and in particular, steel with a silicon content of around 6.5% must be hot rolled at a constant temperature of 600 to 750°C. It is reported that this makes it possible to perform cold rolling. On the other hand, as a method for manufacturing thin sheets of high silicon steel,
In addition to the rolling method, a method called ultra-rapid solidification method (usually cooling rate is 10 ⁵ °C/sec or more) is also known (for example, Japanese Patent Application Laid-Open No. 59-16926
issue). According to this method, it is possible to produce a thin plate of high silicon steel containing 4% or more silicon,
Moreover, a thin plate obtained by grain refinement by rapid cooling can be cold-rolled to some extent. [Problems to be solved by the invention] However, in order to industrially manufacture thin plates of high-silicon steel using the method of Ishizaka et al., the molten steel after scouring is made into ingots by the ingot-making method, and the ingots are heated after reheating. It is necessary to perform forging and then hot rolling at a constant temperature. Such a manufacturing method has the following problems. First, in this method, hot forging is essential before rolling, and if hot forging is omitted,
Rolling at temperatures below 1000℃ becomes impossible. Therefore, the processing in this case must necessarily be discontinuous, resulting in a complicated manufacturing process and an increase in manufacturing costs. Furthermore, since cracks occur when the cast ingot material is film-formed and forged, the surface must be sufficiently adjusted before hot rolling. In fact, Ishizaka et al. cut the surface by approximately 27% (from 15 mm to 11 mm thick). In addition, Ishizaka et al.'s method requires hot rolling to be carried out at a constant temperature in order to improve cold workability, but this requires the strip to be reheated in the middle of rolling, which is different from the conventional continuous method. It cannot be carried out on a type hot rolling mill. As described above, it is impossible to implement the method of Ishizaka et al. on an industrial scale from the viewpoint of manufacturing cost and yield. On the other hand, the ultra-rapid solidification method jets molten metal from a nozzle onto the surface of a metal cooling moving body and solidifies it, making it possible to manufacture thin metal sheets continuously and with a high yield. The thickness of the thin plate is approximately several hundred micrometers at most, and the width is approximately
The problem is that the limit is 20 to 30 cm, which limits its uses. [Summary of the Invention] The key point of Ishizaka et al.'s method is to perform isothermal hot rolling at a temperature of 600 to 750°C to improve cold workability. However, as already mentioned, it is not possible to immediately roll the steel at such a low temperature, and hot forging is essential as a pretreatment for hot rolling. Forging is a well-known method as a preliminary treatment when processing or rolling difficult-to-process materials, but forging has low productivity and there are restrictions on the shape of the resulting product. Furthermore, as mentioned above, it is impossible to perform constant temperature hot rolling with conventionally used continuous hot rolling mills.
There are also restrictions in terms of equipment. The reason why Ishizaka et al.'s method was not put into practical use is thought to be due to the above-mentioned points. The present inventors have conducted various studies regarding the hot and cold workability of high-silicon steel, and have determined that appropriate hot rolling conditions should be selected when blooming or rough rolling ingots or continuously cast slabs. In particular, grain refinement of the intermediate hot-rolled material is achieved, thereby making continuous hot rolling possible, and that the intermediate hot-rolled material is subsequently continuously hot-rolled at a relatively low temperature. It has been found that by doing so, a hot-rolled sheet structure suitable for cold rolling can be obtained. The present invention is based on the above-mentioned knowledge, and C<
0.01wt%, 4.0wt%<Si7.0wt%, Mn<0.2wt
%, Sol.Al<2.0wt%, N<0.01wt%, balance iron and unavoidable impurities. Blooming or rough rolling is performed at a material temperature of 1000℃ or higher, a cumulative reduction rate of 50% or more, and a rolling reduction rate of 10% or more per pass, and then the material temperature during rolling is 1000℃ or lower, the interpass time is 10 seconds or less, and the cumulative reduction is performed. The electrical steel sheet is manufactured by performing continuous rolling at a rate of 30% or more and coiling at a temperature of 700°C or less, and then subjecting it to the necessary treatments for manufacturing the electrical steel sheet, including cold rolling. It is something. The reasons and effects of limiting the component conditions and manufacturing conditions of the present invention will be explained in detail below. Steel Composition C: C is a harmful element that increases the iron loss of the product and is the main cause of magnetic aging, and also reduces workability, so it is desirable to have as little as possible. Therefore, in the present invention, C is limited to <0.01wt%. Si: As mentioned above, Si is an element that improves soft magnetic properties, and the soft magnetic properties improve when its content reaches a peak of 6.5 wt%. In the present invention, Si>
The target range is 4.0wt%. On the other hand, when the Si content exceeds 7.0wt%, the manufacturing cost increases,
It is also known that magnetic properties, especially maximum magnetic permeability, deteriorate. For this reason, the upper limit for Si is 7.0wt.
%. Mn: Mn is added to fix S as an impurity in steel. However, if the amount of Mn increases, the workability deteriorates, and if the amount of MnS increases, it will have a negative effect on the soft magnetic properties, so Mn was set to <0.2 wt%. Sol.Al: Al is added for deoxidation during steel manufacturing.
Furthermore, Al contains solute N that degrades soft magnetic properties.
It is known that electrical resistance can be increased by fixing and further dissolving in steel. Also
By adding Al, the size of the precipitated AlN can be made coarser to the point where there is almost no resistance to the movement of the domain walls. however
Adding a large amount of Al deteriorates workability and increases cost, so Sol.Al is limited to <2.0wt%. N: As mentioned above, N deteriorates the soft magnetic properties, so it is desirable that it be lower. Therefore, in the present invention, N
Limited to <0.01wt%. Hot Rolling Conditions The present inventors have conducted various studies on the hot and cold rollability of high silicon steel, and have found that when high silicon steel is cold rolled, if a specific pre-structure is formed, cold rolling will be possible. A structure with improved properties and a structure preferable for this cold rolling can be obtained by continuous hot rolling by selecting the conditions, and in order to carry out this continuous hot rolling, it is necessary to further improve the previous structure. We learned that it is necessary to miniaturize the structure. In order to cold-roll high-silicon steel in this way,
First of all, it is necessary to refine the grains of the continuously cast slab or ingot, and then to form a structure suitable for cold rolling. It has been found that this process can be carried out by selecting the conditions for finish rolling. The manufacturing conditions of the present invention will be explained in detail in the order of the steps below. Usually, the grain size of high silicon steel ingots or continuously cast slabs ranges from several mm to more than ten mm. Samples with such coarse grains are heated to 600 to 750℃ proposed by Ishizaka et al.
When hot rolling is carried out at constant temperature, the rolling reduction rate decreases even with a Si content of 4%.
At 10% or less, cracks appeared from the sample side edges, making hot rolling impossible. Therefore, in order to improve the cold rolling properties of high-silicon steel, it is necessary to first refine the crystal grains in the pre-hot rolling stage and then obtain a hot-rolled sheet structure suitable for cold rolling through finish rolling. Considering this to be necessary, we first investigated a method of refining coarse grains by rolling (rough rolling or blooming rolling). Parameters that can be changed during rough rolling include rolling start temperature, pass and
These are the schedule (reduction rate per pass, time between passes, cumulative reduction rate) and rolling end temperature. As a result of studies, it was found that hot rolling high-silicon steel under specific rolling conditions causes recrystallization, which makes it possible to refine the grain. That is, grain refinement using recrystallization is possible by applying a rolling reduction of 50% or more at a material temperature of 1000°C or higher during rolling. In order to achieve this by blooming rolling or rough rolling, the rolling start temperature may be set to 1050°C or higher. This is because the lower limit of recrystallization temperature during hot rolling is around 1000℃, and if sufficient strain is applied to cause recrystallization at a temperature lower than this, cracks will occur in samples with a high Si content. This is because further rolling is no longer possible. Figure 1 shows the influence of rolling start temperature on recrystallization behavior in relation to Si content. The graph in Figure 1 shows the structure of a continuously cast slab of high silicon steel with a thickness of 250 mm with the chemical composition shown in Table 1, which was heated at various temperatures of 900 to 1300°C for 2 hours, immediately rough rolled, and its structure was examined using a microscope. This was obtained as a result of observation. Note that rolling was completed in 5 passes, and the target rough bar thickness was 30 mm. Moreover, the material temperature at the end of rolling was within -100°C from the heating temperature.

〔Example〕

Examples of the present invention will be shown below. A high silicon steel slab having a thickness of 250 mm shown in Table 1 above was hot rolled using a continuous hot rolling mill under the following conditions. Heating 1100℃ x 2 hours Rough rolling start temperature 1100℃ Reduction rate 250mm-30mm (88%) Rough rolling end temperature 1023℃, air cooling after rough rolling Finish rolling start temperature 800℃ Reduction rate 30mm-3mm (90%) Finishing Rolling end temperature
725℃, air-cooled coiling after finish rolling 593℃ When the obtained hot-rolled sheet is recovery annealed at 650℃ for 5 minutes, pickled, and then cold-rolled by 83% (process A), the hot-rolled steel sheet is as it is. In the case of pickling and 83% cold rolling (process B), the hot rolled steel plate is pickled and 50% cold rolling, then recovery annealing is performed at 650°C for 5 minutes, and cold rolling is performed again. The cumulative cold rolling rate is
Cold rollability and materials that could be cold rolled in the case of 83% (Process C) and in the case of annealing the hot rolled sheet obtained for comparison at 800°C for 5 minutes and cold rolling (Process D) Table 2 shows the magnetic properties of a part of the material after annealing at 1000°C for 2 minutes. It can be seen that in the present invention, good cold rollability is obtained in all cases.

【table】

〔Effect of the invention〕

As explained above, according to the method of the present invention, it becomes possible to cold-roll high-silicon steel (Si>4.0%) on an industrial scale, which has been considered difficult in the past.

[Brief explanation of drawings]

Figure 1 is a graph showing the influence of rolling start temperature on recrystallization behavior in relation to Si content, and Figure 2 is a graph showing the relationship between finish rolling start temperature, cumulative rolling reduction, and cold rollability. .

Claims (1)

[Claims] 1 C＜0.01wt%, 4.0wt%＜Si7.0wt%, Mn
<0.2wt%, Sol.Al<2.0wt%, N<0.01wt%, balance iron and unavoidable impurities. Material temperature during rolling is 1000℃ or higher, cumulative reduction rate is 50% or more, and rolling reduction rate is 10 per pass.
% or more, followed by continuous rolling at a material temperature of 1000°C or less during rolling, an interpass time of 10 seconds or less, and a cumulative reduction rate of 30% or more, and then coiling at a temperature of 700°C or less. 1. A method for manufacturing an electrical steel sheet with excellent soft magnetic properties, characterized by manufacturing the electrical steel sheet by subjecting it to treatments necessary for manufacturing the electrical steel sheet, including cold rolling.