WO2008032483A1

WO2008032483A1 - Process for manufacturing grain-oriented silicon steel sheet of high magnetic flux density

Info

Publication number: WO2008032483A1
Application number: PCT/JP2007/062183
Authority: WO
Inventors: Akira Sakakura; Hiroshi Takechi
Original assignee: Nippon Steel Corporation
Priority date: 2006-09-13
Filing date: 2007-06-11
Publication date: 2008-03-20
Also published as: KR20090057010A; CN101516537A; US20090199935A1; EP2077164A1; JP5001611B2; JP2008069391A

Abstract

A process comprising casting a bar of intermediate thickness by the use of continuous casting-hot rolling equipment; causing the bar to reach an entrance of hot finish rolling while keeping a temperature exceeding 1200°C at which the bar retains its state of containing AlN in solid solution; and carrying out hot rolling and quenching of the bar so as to effect precipitation of fine AlN, thereby accomplishing efficient production of a grain-oriented silicon steel sheet of high magnetic flux density at low cost without the need to perform high-temperature heating of the bar at all.

Description

Method for producing high magnetic flux density grain-oriented silicon steel sheet

Technical field

The present invention relates to a method for producing a directional silicon steel sheet having excellent magnetic properties, particularly magnetic flux density, used for iron core materials for power transformers and iron core materials for rotating equipment.

It is related.

Rice field

book

Background art

As disclosed in U.S. Pat.No. 1,965,559, NP Goss's two-stage cold rolling method has been developed for the production technology of grain-oriented silicon steel sheets, and the production principle is the presence of fine precipitates MnS. The second secondary recrystallization phenomenon was revealed in 1958 by JE May & D. Turnbull (Trans. AIME., 212 (1958), 769). Apart from this, the present inventors have developed a grain-oriented electrical steel sheet using the effectiveness of fine precipitate A1N in the one-stage strong cold rolling method containing A1 (Japanese Patent Publication No. 33-4710, US Pat. No. 3). 159, 511). On the other hand, unlike solid precipitates, solid elements such as Sb, Nb, Se, S, Mo, Cu, and Sn have strong primary recrystallized grain growth inhibiting action, which promotes secondary recrystallization. Saito et al. Developed this (Journal of the Japan Institute of Metals, 27 (1963), 191). In this way, the secondary recrystallization phenomenon used in actual manufacturing technology requires the presence of precipitates or solid trace elements, but as a secondary recrystallization phenomenon in the absence of any precipitates, The secondary recrystallization phenomenon in the presence of a texture consisting of a stable crystal structure solidified in a certain crystal orientation was revealed by CG Dunn (Acta M etallurgica, 1 (1953) , 163).

Furthermore, the manufacturing principle of the high magnetic flux density grain-oriented silicon steel sheet is determined by the present inventors. It was clarified by the effect on the secondary recrystallization of A1N (Feramu, Vol.9, No.2 (2004), 52)). That is, (110) [001] — Regarding the effect of A1N on the cold rolling and recrystallization phenomena of Goss-oriented single crystals, when the starting single crystal contains a small amount of extremely fine MN of 5 nm or less, {111} <110> — C-oriented primary recrystallized growth structure. When a large amount of fine A1N around 10 nm is included, secondary recrystallization reproduces the first orientation (110) [001], Similarly, in the case of containing a large amount of relatively large A1N, three types of {120} <001> —A orientation, {362} <012>-B orientation, {111} <110> —C orientation are similarly obtained by secondary recrystallization. Secondary recrystallized grains appearing in this direction.

This is in complete agreement with the results of the C.G. Dunn 3% Si-silicon steel single crystal that do not contain any impurities. From these research results, it is clear that securing A1N around lOnm in the state of hot-rolled sheet is crucial for the production of high magnetic flux density grain-oriented silicon steel sheet. However, secondary recrystallization does not occur with very fine A1N below 5nm and should be avoided. The coarse A1N around 1 m is meaningless.

Conventionally, in order to secure A1N before and after lOnnt, which is indispensable for the production of high magnetic flux density grain-oriented silicon steel sheets, in the state of hot-rolled sheets, slabs obtained by split rolling or continuous forging ( Reheat (approx. 200 mm or more in thickness) to a high temperature of 1 300 ° C or more (fired heating) to completely dissolve A1N once, and then use a rough rolling mill of a continuous hot rolling machine to 20 to 70 mm. The thickness of the bar was changed to a final thickness after rolling with a continuous hot finishing mill, and the steel was rolled up at about 500 ° C. It was cooled. However, for thick slabs around 200mm thick, when the flame is heated at a high temperature of 1350 ° C or higher, the temperature difference between the slab surface and the bottom surface is large, and the surface temperature needs to be extremely high in order to achieve the desired effect. Therefore, abnormal growth of slab grains and silicon steel surface There were also operational problems due to melting of the surface scale and accumulation in the furnace.

Although it is very difficult to solve this problem, the low temperature slab heating method (Material Science Forum, 204/206, No. P tl (1996), 143) is adopted as one manufacturing method. There is a method (for example, Japanese Patent Laid-Open No. 5-117751) for preventing dissolution of oxide scale by performing induction heating at the final stage after flame heating. Furthermore, in order to secure a preferable A1N of around 10 nm with the same thickness as the hot-rolled sheet, the idea of adopting a thin-wall continuous manufacturing method with a thickness of several mm (JP-A-2-258922) has been announced. The conventional method of once cooling a thick CC slab and then reheating the cold slab has problems in productivity and workability, and improvement is desired.

In addition, a method for producing grain-oriented electrical steel sheets by manufacturing thin slabs with a thickness of 20 to 80 mm by continuous forging and employing hot rolling with a rolling start temperature of 1 100 to 1200 ° C is shown in Table 2000. This is disclosed in Japanese Patent No. 500568. However, in this method, A 1N having a large grain size is formed during hot rolling, and sufficient magnetic properties cannot be obtained in a normal processing process. Therefore, there is a problem that nitriding after decarburization annealing is required. is there. Disclosure of the invention

As mentioned above, the effect of dispersion and precipitation of fine A1N, which is conventionally required for the production of high magnetic flux density grain-oriented silicon steel sheet, is due to the fact that A1 N is once contained in silicon steel by high-temperature reheating work using a hot slab for thick slabs. This was achieved by the rapid cooling effect by hot rolling after the solid solution, but there was a problem due to the high temperature heating scale melting of the thick slab, and the problem of crystal orientation in the thin continuous manufacturing method of several mm thick There is a problem of brittleness of the structure, which is a big problem that hinders practical use.

Furthermore, hot rolling of medium-sized continuous slabs started at temperatures below 1200 ° C In this method, A1 N precipitates before hot rolling and becomes coarse, and has not yet reached a state where it is sufficiently effective in improving magnetism.

The present invention produces a medium-thick slab by a continuous forging method, maintains the slab at a temperature that is at least the minimum that can be hot-rolled, and performs continuous hot rolling of A1N that is already solid solution in the molten steel state The thick CC slab is once cooled by holding it in the steel without precipitation until it is finely precipitated by the rapid cooling effect during continuous hot rolling. Can solve the problems in the conventional method of heating to high temperature, can greatly improve work efficiency and energy efficiency, and produce high magnetic flux density directional silicon steel sheet with more uniform crystal orientation and iron loss than conventional It aims to provide a method.

In order to achieve the above object, the configuration of the present invention is as follows.

(1) By mass, C: 0.0010 to 0.075%, Si: 2.95 to 4.0%, acid solubility A1: 0.010 to 0.040%, N: 0.0010 to 0.150%, S or Se alone or in both 0.005 to 0.1%, the remaining steel and molten steel consisting of unavoidable impurities are continuously forged and the thickness is 20 to 70mm. A thick bar is manufactured, and after the forging, the medium thickness bar is maintained at a temperature of over 1200 ° C, and within 500 seconds from the completion of the forging, it reaches the inlet of the hot finishing mill to start hot continuous rolling. Use hot-rolled sheets with a thickness of 1.5 mm to 5 mm by hot rolling, cool the cooling time to 600 ° C after hot-rolling at 150 seconds or less, then perform normal cold rolling, intermediate annealing, decarburization annealing A method for producing a high magnetic flux density directional silicon steel sheet, characterized by performing finish annealing or the like.

(2) In the above molten steel, further praying to the grain boundary to suppress crystal growth, Sb: 0.005 to 0.2%, Nb: 0.005 to 0.2%, Mo: 0.003 to It is characterized by containing at least one selected from the group of 0.1, Cu: 0.02-0.2%, Sn: 0.02-0.3%. Magnetic flux density directional silicon steel sheet manufacturing method. (3) When the medium-thickness bar is maintained at a temperature of 1250 ° C or higher, the maximum thickness is 500 seconds or less, and when it is maintained at a temperature of 1200 ° C or higher, it is heated within 150 seconds. The method for producing a high magnetic flux density directional silicon steel sheet according to (1), characterized in that it reaches the entrance of a finishing mill.

(4) When it takes more than 200 seconds to reach the inlet of the hot finishing mill after the medium thickness bar manufactured by continuous forging exceeds 200 seconds, or When the temperature is as low as 1000 ° C, these medium thickness bars are heated in a heating furnace to maintain the temperature at 1300-1350 ° C (1). The manufacturing method of the high magnetic flux density grain-oriented silicon steel sheet of description. Brief Description of Drawings

Figure 1 is a schematic diagram showing an example of continuous forging-hot rolling continuous equipment.

Fig. 2 is a schematic diagram showing another example of continuous forging-hot rolling continuous equipment. Figure 3 shows the effect (3.20% Si) of the retention temperature and time on the magnetic properties after A1N solid solution treatment.

Fig. 4 shows a typical thermal history curve (3. 10% Si) in hot rolling after iN solid solution treatment.

Figure 5 shows the rapid cooling (tandem rolling) in hot rolling after A1N solid solution treatment

) Diagram showing the relationship between starting temperature and magnetic properties U, 10% Si).

Figure 6 shows the cooling curve after A1N solid solution treatment and the effect of Si content on A1N precipitation. BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below.

First, the reason for limitation of each component contained in the molten steel of the present invention will be described. C is necessary to cause a certain transformation during hot rolling depending on the amount of Si. It is an important element, and if it is less than 0.010%, secondary recrystallization cannot be generated stably. If it exceeds 0.075%, the decarburization annealing time becomes longer, which is not preferable for production, so the content was made 0.010 to 0.075%.

If Si is less than 2.95%, an excellent iron loss value cannot be obtained as a high-grade high magnetic flux density grain-oriented silicon steel sheet. Further, if added over 4%, it is not preferable because cracks and the like occur during cold rolling due to brittleness, and its content was set to 2.95 to 4: 0%.

Oxidation-soluble A1 and N are elements necessary for producing an appropriate A1N as an inhibitor, and a sufficient amount for the purpose is 0.010 to 0.040% and 0.0010 to 0.0150%.

S and Se form Mn, MnS, and MnSe, and act as a precipitation dispersed phase for secondary recrystallization. Therefore, 0.005% to 015% of these are contained alone or both. In addition, for the purpose of strengthening the inhibitor, it is selected from the group of Sb: 0.005-0.2%, Nb: 0.005-0.2%, Mo: 0.003-0.1, Cu: 0.02-0.2%, Sn: 0.02-0.3% as necessary. At least one species can be included.

In order to produce the high magnetic flux density directional silicon steel sheet of the present invention, it is essential that A1N of about 10 nm (5 to 50 nm) exists in the hot rolled sheet state. A medium-thickness bar of 20 to 70 mm is manufactured, and the bar temperature is 1200C while maintaining the solid solution state of A1N by the heating means that prevents the heat held by this bar or temperature drop of the heat insulation furnace etc. In the above case, transfer to the hot rolling mill entrance within 150 seconds at the maximum after extraction from the heat-retaining furnace, and within 500 seconds at the maximum in the case of 1250 ° C or more, and 1.5 mm to 5 mm by hot rolling. Thick A1N is deposited in the vicinity of lOim (5 to 500 nm) by using a thick hot-rolled sheet and setting the cooling time to 600 ° C after hot-rolling to 150 seconds or less.

In the present invention, the thickness of the bar is limited to a medium thickness of 20 to 70 mm. If it is less than 70 mm, large equipment is required for heat retention, and if it exceeds 70 mm, it is not possible to obtain hot-rolled sheets with only a finish rolling mill, and a rough rolling mill is required, so that economical production cannot be achieved.

The means for producing and rolling a 20 to 70 mm thick bar is not particularly limited. An example of the known continuous forging-hot rolling continuous equipment is shown schematically in Figs. Figure 1 shows the continuous slab 2 extracted from the mold 1 and the cut slab 3 placed in the heat-retaining furnace 4 to maintain a constant temperature. Rolled and rolled thin hot rolled steel strip 6. Fig. 2 shows the continuous production of the medium slab 2 and then winding it into a coil 7. After the coil is placed in the coil box 8 to equalize the temperature, the continuous finishing hot rolling machine 5 is used. This is a rolling and winding device.

Next, the processing conditions for the medium-thickness bar will be described with reference to FIGS.

In mass%, 0.045% C, 3. 20% Si, 0. 025% AK Resin iron ingot containing the balance Fe and unavoidable impurities is rolled into a 40 mm thick bar as the starting material. This was divided into 4 and the following experiment was tried. These were kept in a bar heating furnace at 1300 C for 3 hours, and A1N was completely dissolved in the steel and then allowed to cool.These four bars were 1250 ° C, 1210 ° C, 1100 ° C, Immediately after reaching the temperature of 1000 C, they were charged in furnaces maintained at 1250 ° C, 1210 ° C, 1100 ° C, and 1000 ° C, respectively, and 480 seconds at 1250 ° C (par heating furnace extraction) After 500 seconds), 1210 ° C for 120 seconds (same total of 150 seconds), U00 ° C for 50 seconds (same total of 100 seconds), 1000 for 20 seconds (same total of 50 seconds) After holding hot rolling and rolling After completion, it was allowed to cool to the atmosphere. Fig. 4 shows the overall thermal history. In this figure, curve (A) is the cooling curve when rolling immediately after extraction in the bar furnace, and the cooling curves of (B), (C), (D), and (E) are as described above. is there.

This hot-rolled sheet is cold-rolled, decarburized, and finally annealed to obtain the final product. Measure the magnetic properties (B 10) of the product and determine the relationship between this property and the thermal history (the total time from the extraction of the bar heating furnace to the finish rolling mill inlet, including the time in the incubator). This is shown in Fig. 3.

As is apparent from Fig. 3, when the hot rolling shown in the cooling curve of Fig. 4 (A) is performed, the retention time is 0, so the magnetic characteristics are the best as shown by black circle 1 in Fig. 3. Fig. 4 (B) shows the B10 characteristics, and the magnetic properties when hot-rolled after holding at 1000 ° C for 20 seconds are short, although the holding time is short as shown by the white circle 2 in Fig. 3. The B10 characteristic shows considerable deterioration, and if it exceeds 100 seconds, the secondary recrystallization itself becomes unstable. Furthermore, when it is kept at 1100 ° C for 50 seconds as shown in Fig. 4 (C), As shown by the half-black circle 3 in Fig. 3, the magnetic characteristics are slightly improved due to the long holding time but high temperature. Furthermore, as shown in the black circle 4 in Fig. 3, the magnetic properties when holding for 120 seconds above 1200 ° C in Fig. 4 (D) are shown in Fig. 3. Shows a value close to the best value.

Finally, the magnetic properties of the case of hot rolling after holding at 1250 ° C for 480 seconds in (E) of Fig. 4 are very long holding times as shown by small black circles 5 in Fig. 3. Regardless, the value is slightly inferior to the best value.

In this way, the lowering of the bar temperature is fatal to the B 10 characteristics, but if a high temperature exceeding 1200 ° C is secured, it is possible to give a hold time, and excellent characteristics can be obtained. I understood that. '

When the hot rolling shown in the cooling curves of (B) and (C) in Fig. 4 is performed, as is clear from Fig. 3, the holding temperature before rolling is not sufficient. It has been shown that precipitation of A1N progresses and causes magnetic deterioration. In the case of the cooling curve (C) in Fig. 4, It is possible to secure a certain degree of magnetism if it can reach the hot rolling mill inlet in a short time, but judging from the conditions at the manufacturing site, at least the cooling of Fig. 4 (D) or Fig. 4 (E) It is clear that production work cannot be done without a thermal history along the curve.

Iron loss values are regarded as important for high magnetic flux density grain-oriented silicon steel plates.3.0-4.0% Si has a lower Si content of less than 3%. The processing conditions are rather strict and the time allowed for production operations is relatively short. The reason is that in the case of low Si, precipitation can be prevented because the solid solubility of A1N is increased by the transformation. Therefore, when the amount of Si is high, the only way to prevent precipitation is to use temperature. The meaning is that the higher the temperature of A1N precipitation, the more rapidly it delays. Therefore, if it takes time to reach the inlet of the finishing hot rolling machine, it is sufficient to consider increasing the holding temperature. That is, as described in claim 4, when the required time to reach the inlet of the hot finishing mill after the medium thickness bar manufactured by continuous forging exceeds 200 seconds The bar may be passed through a heating furnace for maintaining the bar at a temperature of 1250 to 1350 ° C., and when the bar temperature is as low as 1000 ° C. Precipitation of A1N can be prevented by means such as passing through a heating furnace to keep the temperature at ~ 1350 ° C.

Figure 5 shows a 0.040% C, 3.10% S i, 0.029% AK balance silicon steel ingot consisting of Fe and unavoidable impurities rolled into a 40mm thick bar at 1350 ° C for 30 minutes Immediately after heating, it is rolled into a 3.5-thick hot-rolled sheet at approximately 1000 ° C, and this is water-cooled from the cooling process immediately after the end of hot-rolling to create five types of hot-rolled sheets. The figure shows the relationship between the magnetic properties and the thermal history when decarburized and finish-annealed into the final product. The thick line in the figure indicates the starting point of cooling (water cooling) after hot rolling, and the thin line indicates the magnetic properties (B10).

From this result, the material after hot rolling is rapidly Cooling treatment, that is, within a range not exceeding 150 seconds after the end of hot rolling, can be done from a high temperature such as b.c.d.e instead of slow cooling like (a). Cooling at the fastest possible speed is necessary to obtain magnetic properties. For example, in the case of e, B 10 == 1.95 T, which is a high value. The temperature for cooling in a range not exceeding 150 seconds shall be at least 600 ° C. Normally, hot-rolled steel sheets are wound up at 600 ° C or lower and are slowly cooled, so A1N does not precipitate.

Figure 6 shows the relationship between the hot rolling cooling cycle and the amount of A1N precipitation. For reference, the precipitation curves for low Si (1.12% Si, 2.17% Si) are also shown. As can be seen from the comparison with this, when the Si content is 3.10%, the A1N starts from around 1250 ° C. Precipitation starts and proceeds rapidly below 1200 ° C, whereas in the case of 1% Si, A1N deposition hardly progresses up to 1000 ° C, and it begins for the first time below 1000 ° C. This is because the α-a transformation region of the material varies depending on the amount of C and Si contained, and the precipitation behavior of A1N is closely related to the amount of this transformation.

In summary, the hot rolling conditions for producing an excellent high magnetic flux density grain-oriented silicon steel sheet using the crystal growth suppression effect of A1N are as follows.

(1) When hot-rolling a medium-thickness bar in which A1N is completely dissolved in a silicon steel material containing 2.95 to 4% Si, the holding temperature after the bar is forged or extracted in a heating furnace If the temperature is 1250 ° C or higher, the hot rolling should reach the inlet of the hot finishing mill within 150 seconds at the longest, and if it exceeds 1200 ° C, preferably within 150 seconds. To start.

(2) Cooling after the end of hot rolling should not exceed 150 seconds at the maximum to 600 ° C. A1N precipitates due to cooling from a high temperature, but if it is gradually cooled over time, A1N becomes coarser with time and becomes about 1 m in extreme cases. It becomes a completely meaningless form. When A1N in a completely solid solution is cooled to 600 ° C. for a time not exceeding 150 seconds, the precipitation size becomes approximately 10 ηm, which is a preferable state for the present invention. Example

[Example 1]

Mass steel, 0.045% C, 3.05% Si, 0.032% A1 and the remainder Fe and unavoidable impurities in silicon steel molten steel is made into a 60-thick bar with a continuous forging machine (hereinafter referred to as CC machine) and immediately finished with heat The thickness was 3.0mm. The finishing heat inlet temperature was 1210 ° C for the bar head and 1205 ° C for the bottom. The amount of C in the hot-rolled sheet is 0.041%, and decarburization is slightly occurring. This was first cold-rolled at a rolling reduction of 30% to a thickness of 2.1 mm, then annealed at 1100 ° C for 2 minutes in nitrogen, and then cooled by blowing a jet stream. The cooling rate was about 18 seconds from 1100 ° C to 850 ° C, and about 27 seconds from 850 ° C to 400 ° C. The A1N after this annealing was analyzed as 0.0055% (NasAIN). Next, this was cooled at a rolling rate of 83.3% to a thickness of 0.35 mm, decarburized at 800 ° C for 3 minutes in hydrogen, and then annealed at 1200 ° C for 20 hours. The B 10 characteristics in the rolling direction of the product were 1.93T and W17 / 50 was 1.15W / kg.

[Comparative Example] A bar having the same composition as in Example 1 was allowed to stand for about 40 seconds in front of the finishing hot rolling machine inlet, and then finishing hot rolling was started. The finishing rolling temperature of the bar at that time was 1150 ° C for the bar head and 1120 ° C for the bottom. Thereafter, the same treatment as in Example 1 was carried out, and the occurrence rate of secondary recrystallization in the final product was examined. As a result, it was almost 50% and did not become a product.

[Example 2]

By mass, 0.048% (, 3.13% Si, 0.10% Mn, 0.029% AK 0.029% S containing the balance Fe and unavoidable impurities made of molten steel is made into a 50 mm thick bar with the CC machine. Finished hot rolled to a thickness of 2.8 mm. The upper hot rolling entrance temperature is 1210 ° C for the bar head and 1200 ° C for the bottom, and after 10 seconds and 50 seconds, the hot rolling ends, and the temperature at that time is 1010 ° C and 1000 ° C. The winding was completed after about 75 seconds. After hot rolling, C was 0.040%, and A IN was 0.0040% (NasAIN). The hot-rolled sheet was pickled, cold-rolled at a rolling rate of 87.5% to a final gauge of 0.35 mm thickness, decarburized at 850 for 3 minutes in wet hydrogen, and then annealed at 1200 ° C in hydrogen for 15 hours. The B10 characteristics in the rolling direction of the product were 1.92T and 1.05WZkg, respectively.

[Example 3]

By mass, 0.050% C, 3.18% Si, 0.075% Mn, 0.021% AK 0.035% S, and the balance of iron and unavoidable impurities made of molten steel is made into a 40mm thick bar with the CC machine. Finished hot rolled to a thickness of 3.0 mm. The finishing hot rolling inlet temperature was 1210 ° C at the bar head and 1205 ° C at the bottom, and the hot rolling was finished after 12 seconds and 53 seconds, respectively. The temperatures at that time were 1020 ° C and 990 ° C, respectively. After about 80 seconds, the collection was completed.

This is continuously annealed at 1100 ° C for 1 minute in a nitrogen atmosphere, then forcibly cooled to 930 ° C with a nitrogen gas blowing device at the furnace outlet, and further rapidly cooled to 200 ° C with a laminar flow device. did. C was 0.045% and A1N was 0.0040% (NasAIN). This was pickled, cold rolled at a rolling rate of 88.3% to a final gauge of 0.35M thickness, decarburized at 850 ° C for 3 minutes in wet hydrogen, and then annealed at 1200 ° C in hydrogen for 15 hours. The magnetic properties of the product in the rolling direction were 1.92T for B10 and 1.05W / kg for ¥ 17/50.

[Comparative Example] A bar having the same composition as in Example 3 was allowed to stand for about 150 seconds in front of the finishing hot rolling machine inlet, and then finishing hot rolling was started. At that time, the finish rolling start temperature of the bar was 950 ° C at the bar head and 930 ° C at the bottom. After that, as a result of processing up to the final product under the same conditions as in Example 3 above, secondary reconstitution When the crystallinity generation rate was examined, it was 20%, which was not a product.

[Example 4]

60% thick silicon steel molten steel containing 0.050% C, 3.12% Si, 0.041% AK 0.030% S, 0.050% Se, 0.030% Te, balance Fe and unavoidable impurities in the CC machine. Immediately finished and hot rolled to a thickness of 3.0 mm. The finish hot rolling inlet temperature was 1230 ° C at the head and 1210 ° C at the bottom, and the hot rolling was finished after 15 seconds and 60 seconds, respectively. The temperatures at that time were 1050 ° C and 1020, respectively. The winding was completed after about 90 seconds.

This was continuously annealed at 1100 for 2 minutes in a nitrogen atmosphere, then cold-rolled 50%, then annealed for 1 minute for primary recrystallization, and further 0.28 mm at a rolling rate of 84.7%. This was decarburized and annealed for 20 hours at 1200 ° C with de-Se, de-Te, and de-S. The magnetic properties of the product were 1.93T for B 10 and 1.05 WZ kg for W 17/50.

[Example 5]

In mass%, 0.046% (:, 3.20% Si, 0.031% AK 0.025% S inclusive, the remaining Fe and inevitable impurities silicon steel molten steel is made into a 50 dragon-thick bar with the CC machine and immediately finished hot rolled Finishing hot rolling The inlet temperature of the bar head is 1220 ° C and the bottom is 1205 ° C, and the hot rolling was finished after 12 seconds and 50 seconds respectively. They were 1005 ° C and 990 ° C, respectively, and the winding was completed after about 85 seconds.

This was continuously annealed at 1130 ° C for 2 minutes, then pickled, cold-rolled to a final thickness of 0.23 mm, and then decarburized and annealed in wet hydrogen at 850 for 2 minutes. MgO by weight in the steel sheet: 100 against Ti0 _2: 10, Mn0 _2: in proportions of 5, applied to further distinguish the annealing separator of boric acid from 0.1 to 3% additives, and annealing separator which is not boric acid added And then annealed in hydrogen at 1200 ° C for 20 hours.

As shown in Table 1, the addition of boric acid to MgO improves the B 10 characteristics and at the same time decreases the iron loss value and reduces the variation. The properties of the glass film, which is very important as a grain-oriented silicon steel sheet, have been improved.

table 1

[Example 6]

In mass%, 0.04% C, 3. 30% Si 0 · 029% A1 containing the balance Fe and unavoidable impurities made of molten steel is made into a 60 mm thick bar with the CC machine and finished immediately. Hot rolled to 2.3mm thick. The finishing hot rolling inlet temperature was 1230 ° C at the top of the bar and 1205 ° C at the bottom, and the hot rolling was finished after 12 seconds and 45 seconds, respectively. The temperatures at that time were 1010 ° C and 995 ° C, respectively. The winding was completed after about 85 seconds.

This hot-rolled sheet is continuously annealed at 1150 ° C for 2 minutes, then rapidly cooled, pickled, and cold-rolled to a final sheet thickness of 0.27mm, and then decarburized and annealed in hydrogen at 850 ° C, 1200 ° C was finally annealed. For cold rolling, the same pass schedule (1.6 mm, 1.2 mm, 1.0 mm, 0.8 mm, 0.6 mmni, 0.45 mm) was applied while aging treatment was performed at five different temperatures. 6 passes). That is, the relationship between the conditions and magnetic properties is as shown in Table 2.

From this, it can be seen that aging between passes at around 200 ° C is effective. Table 2

(1) 50: x 5 min heat treatment per cold rolling pass B10 = 1. 920 (T) 17/50 = 1.024 (W / kg)

(2) Heat treatment at 150 ° CX for 5 minutes per cold rolling pass B10 = 1.944 (T) W17 / 50 = 1.001 (W / kg)

(3) 200 ° CX 5 min heat treatment per cold rolling pass B10 = 1. 951 (T) W17 / 50 = 0.998 (W / kg)

(4) 350 ° C x 5 minutes heat treatment per cold rolling pass B10 = 1. 925 (T) W17 / 50 = 1.012 (W / kg)

(5) Heat treatment at 500 ° C for 5 minutes per cold rolling pass B10 = 1. 880 (T) W17 / 50 = 1. '195 (W / kg)

[Example Ί]

Silicon steel containing 0.085% (:, 3.20% Si 0.073% Mn, 0.025% S, 0.025% acid-soluble Al, 0.0085% N, 0.08 Sn, 0.07% Cu with the balance Fe and inevitable impurities The molten steel was made into a 60mm thick bar with the CC machine and immediately finished hot rolled to 2. The finished hot rolling inlet temperature was 1220 ° C at the head and 1201 at the bottom, after 15 seconds each. After 55 seconds, the hot rolling was finished, and the temperatures at that time were 990 ° C and 985 ° C, respectively.

This hot-rolled sheet was continuously annealed at 1130 ° C for 2 minutes, then rapidly cooled in hot water at 100 ° C, subjected to precipitation heat treatment, pickled, and then subjected to aging treatment between passes at 250 ° C for 5 minutes. However, it was cold-rolled to a final thickness of 0.22. Then in 2 minutes Graced- NH ₃ in 850 ° C, have rows decarburization annealing in an atmosphere of a dew point of 62 ° C, and final baking blunt with further MgO and Ti0 ₂ was coated with an annealing separating agent mixture 1200 ° C . Tension coating was applied after final annealing.

The magnetic properties and grain size of the product were B 10- 1.92 (T), W17 / 50 = 0.88 W / kg, ASTM No. 5. When Sn and Cu were not added, B 10 = 1.92 (T), W17 / 5 = 0.95 W / kg> ASTM No. 3.

[Example 8]

Silicon containing 0.05% C, 3.05% Si, 0.07% Mn, 0.03% S, 0.026% acid-soluble Al, and the balance Fe and unavoidable impurities. Molten steel was forged as a 40 mm thick bar with the CC machine. After forging, it was cut into a single bar and the bar temperature at that time was 1255 ° C. In order to prevent the temperature from falling below 1250 ° C, the temperature reached the inlet of the finishing hot rolling machine in about 300 seconds while maintaining the temperature with a heating device, and hot rolling was started immediately to a thickness of 30 mm. The finishing hot rolling inlet temperature was 1220-1230 ° C, and the hot rolling was completed after 15 seconds and 60 seconds at the front and rear ends of the hot rolled sheet, respectively. The temperatures at that time were 1030 ° C and 1020, respectively.

This hot-rolled sheet was continuously annealed at 1130 ° C for 3 minutes, then forced-cooled to immerse the bath containing boiling water at the furnace outlet, then pickled, and rolled at a rolling reduction of 90% to obtain 0.3 The thickness was mm. This was decarburized and annealed at 1200 ° C for about 20 hours in H ₂ . The magnetic properties of the product in the rolling direction were B 10 = 1.93 (T), W 17/50 = 1. OlWZkg.

As a comparative example, after forging a bar having the same components as in Example 8 above, the temperature was lowered to 1100 ° C when transported to the finishing hot rolling machine without holding the temperature by the heating device. The hot-rolled sheet that was immediately hot-rolled was processed to the final product under the same conditions as in Example 3 above, and when the secondary recrystallized grain ratio occurrence rate was examined, it was 30% or less for the entire coil, resulting in a product. I could n’t.

[Example 9]

A molten steel containing 0.055% C, 3.20% Si, 0.025% S, 0.30% acid-soluble Al, and the balance Fe and unavoidable impurities in a mass% was forged as a 30 mm thick bar with the CC machine. After fabrication, the bar temperature was 1150 ° C when cut into a single bar. This bar was immediately put into a heating furnace heated to 1330 ° C to dissolve the side A1N, then extracted from the furnace, allowed to reach the inlet of the finishing hot rolling mill for about 120 seconds, and immediately started hot rolling The thickness was 25mm. The finishing hot rolling inlet temperature was 1210-1220 ° C, and the hot rolling was completed after 16 seconds and 50 seconds at the leading edge and trailing edge of the hot rolled sheet, respectively. The temperature at that time is They were 1010 ° C and 998 ° C, respectively, and the winding was completed after about 70 seconds.

This hot-rolled sheet was continuously annealed at 1130 ° C for 2 minutes, then forcedly cooled with a spraying device at the outlet of the furnace, pickled, cold-rolled to a thickness of 0.3 miii, and then 3 ° C at 835 ° C. Decarburized and annealed in wet hydrogen for minutes. MgO containing 800 ppm of B was applied as a slurry to this steel sheet, wound on a coil, and annealed in hydrogen at 1200 ° C for 20 hours. The magnetic properties of the product in the rolling direction were B 10- 1.92 (T), W 17/50 = 0.89 WZkg.

As a comparative example, the bar having the same composition as in Example 8 was immediately transported to the finishing hot rolling machine inlet, and the temperature further decreased to 1080 ° C. The hot rolled sheet that was immediately finished and hot rolled was processed to the final product under the same conditions as in Example 3 above, and when the secondary recrystallization rate occurrence rate was examined, it was found that only 20% was generated, which could be a product. There wasn't. Industrial applicability

As in the present invention, A.1N obtained by rapid cooling in a hot rolling finish rolling mill (tandem mill) from a state in which it is completely dissolved in a medium-sized piece produced by continuous forging is uniform and It is finely dispersed and sufficient to generate primary recrystallization nuclei with excellent crystal orientation, and at the same time, it has a sufficient effect of suppressing crystal growth, and the crystal structure obtained by fabrication is hot rolled. Therefore, there is no adverse effect of abnormally grown grains of the slab by conventional high-temperature heating, and uniform and complete secondary recrystallized grains are formed by final annealing, and the magnetic flux density B 10≥ 1.90T is excellent. It is possible to obtain a high magnetic flux density directional silicon steel sheet having excellent characteristics. Moreover, the high-temperature reheating operation at 1350 ° C in the conventional slab furnace is completely unnecessary, and the retained heat of the steel slab is fully utilized, resulting in a significant improvement in energy efficiency. It was possible to solve the major problems in the work due to high-temperature heating of the slab.

Claims

The scope of the claims

1. By mass, C: 0.010-0.075%,

Si: 2.95 to 4.0%,

Acid soluble A1: 0.010-0.040%,

N: 0.0010 to 0.0150%,

S or Se alone or both, 0.005 to 0.1%, and the remaining steel and molten steel consisting of unavoidable impurities are continuously produced to produce a medium thickness bar having a thickness of 20 to 70 mm, The bar is kept at a temperature of over 1200 ° C after forging, and it reaches the inlet of the hot finishing mill within 500 seconds after the forging is completed, and hot continuous rolling is started. Thick hot-rolled sheet, 60 (after cooling is completed, cool down to 150 seconds or less after hot rolling, and then perform normal cold rolling, intermediate annealing, decarburization annealing, finish annealing, etc. A method for producing a high magnetic flux density directional silicon steel sheet.

2. In the molten steel, the crystal growth is further restrained by praying to the grain boundary, Sb: 0.005 to 0.2%, Nb: 0.005 to 0.2%, Mo: 0.003 to 0, and Cu: 0.02 to 0.2% 2. The method for producing a high magnetic flux density grain-oriented silicon steel sheet according to claim 1, comprising at least one selected from the group of Sn: 0.02 to 0.3%.

3. If the medium-thickness bar maintains a temperature of 1250 ° C or higher, it will be hot within 500 seconds at the longest. If it holds a temperature of 120D ° C or higher, it will be hot within 150 seconds. The method for producing a high magnetic flux density directional silicon steel sheet according to claim 1, wherein the method reaches the entrance of a finishing mill.

4. When it takes more than 200 seconds to reach the entrance of the hot finishing mill from the medium thickness bar manufactured by continuous forging and start the hot continuous rolling, or the temperature of the par When the temperature is as low as 1000 ° C, these bars are passed through a heating furnace to keep the temperature at 1300-1350 ° C. The method for producing a high magnetic flux density directional silicon steel sheet according to claim 1, wherein: