JPH09143561A - Production of grain oriented silicon steel sheet with high magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively produce a grain oriented silicon steel sheet with high magnetic flux density, stable in a longitudinal direction, by subjecting a continuously cast slab, containing specific amounts of C, Si, Mn, Al, N, S, and Se, to specific slab heating and to specific annealing prior to final heavy cold rolling. SOLUTION: A continuously cast slab, which has a composition consisting of, by weight, 0.015-0.100% C, 2.0-4.0% Si, 0.03-0.12% Mn, 0.010-0.065% Sol.Al, 0.0040-0.0100% N, 0.005-0.050% S or Se, and the balance essentially Fe and further containing, if necessary, 0.003-0.3% of Sn, Cu, Mo, Ge, B, Te, As, and Bi, is subjected to slab heating to 1320-1490 deg.C and hot-rolled. At this time, after 1200 deg.C is reached, temp. is raised at a rate of >=5 deg.C/min in an induction heating furnace. The resultant hot rolled plate is annealed and then subjected to final heavy cold rolling. At the time of this annealing, the hot rolled plate is held at 800-1200 deg.C and cooled down to 400 deg.C. At this time, the central part of coil is cooled at a rate of 20 to 120 deg.C/s, and the head and the tail are cooled at a rate not lower than 10 deg.C/s and lower than that for the central part. After the resultant cold rolled sheet is formed to the final sheet thickness, decarburizing and primary recrystallization annealing and final annealing are performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a high magnetic flux density unidirectional magnetic steel sheet used for an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are mainly used as iron core materials for transformers and generators, but with the recent demand for energy saving, steel sheets with higher magnetic flux density and less iron loss are available from the market. Is required. In order to obtain a grain-oriented electrical steel sheet having a high magnetic flux density, it is necessary to obtain a secondary recrystallized structure highly integrated in the {110} <001> orientation, the so-called Goss orientation. It is known that the inhibitor and the primary recrystallization texture have a great influence on the secondary recrystallization. As for inhibitors, 100 is added to the steel before finish annealing.
It is necessary to make the precipitation-dispersed phase of about 1000 Å evenly and finely present, and AlN, MnS, MnSe, etc. are generally known. Since these are coarsely precipitated in continuous casting, the slab is heated to a high temperature of 1250 ° C. or higher and sufficiently solutionized, and then MnS and MnSe are uniformly and finely precipitated by hot rolling, and hot-rolled sheet annealing, AlN is uniformly and finely precipitated by precipitation annealing, and further, Sb, Sn, C of grain boundary segregation elements are present in the crystal grain boundaries from hot rolling to decarburization / primary recrystallization annealing.
It is effective to segregate u, Mo, Ge, B, Te, As, Bi and the like.

Conventionally, slab heating is generally performed in a gas heating furnace. However, in this method, since slab heating is required for a long time, there is a case where a magnetic characteristic defect called line mixing due to abnormal grain growth of slab crystal grains occurs. In order to solve this, a method of rapidly heating a slab by using induction heating has been proposed as described in Japanese Patent Publication No. 56-18654. However, when the slab heating is performed by induction heating, Japanese Patent Laid-Open No. 3-3142
As disclosed in Japanese Patent Laid-Open No. 2 (1994), the end of the slab (the end rolled first in hot rolling is the hot rolling head, and the other end rolled last in hot rolling is the hot rolling tail). The hot-rolled head, the hot-rolled central portion, and the hot-rolled tail portion of the annealing before the final strong cold rolling, which will be described later, are the coil rolled as the hot-rolled head portion, the hot-rolled central portion, and the hot-rolled tail portion in hot rolling. In some cases, the temperature does not rise to a predetermined temperature due to heat dissipation, and magnetic defects may occur at the ends. Japanese Unexamined Patent Publication No. 3-31422 proposes a method of installing a conductive heat insulation plate near the end of the slab to improve the magnetic defect of the end, but the heat insulation plate is exposed to high temperature. Therefore, there is a problem in durability, and there is a problem that the heat insulation plate must be replaced frequently, which increases costs and burdens equipment management.In addition, when the heat insulation plate deteriorates and wears out, it causes magnetic defects. Was there.

By the way, the cooling in the annealing before the final strong cold rolling has a great influence on the precipitation of AlN, and the secondary recrystallization,
It is known that magnetic properties are greatly affected. Japanese Examined Patent Publication No. 46-23820 discloses that after annealing at a temperature of 750 to 1200 ° C., a temperature range of 750 to 950 ° C.
A method of rapidly cooling the temperature to 2 ° C to 200 seconds has been proposed. Japanese Patent Publication No. 62-56923 discloses 900-1
A method has been proposed in which the temperature is maintained at 200 ° C. and then cooled to room temperature at a cooling rate faster than atmospheric cooling and slower than 30 ° C. underwater cooling. In Japanese Patent Laid-Open No. 2-138419, there is 800
Primary soaking at ~ 1200 ° C followed by primary cooling to 850-9
When soaking at 50 ℃, 100 at the first soaking
A method has been proposed in which the holding time at 0 ° C. or higher is 20 to 120 seconds, and the cooling rate from the temperature of 850 to 950 ° C. to 500 ° C. at the time of secondary cooling is 20 to 100 ° C./second.
Further, Japanese Patent Publication No. 62-1458 discloses a magnetic defect due to wire mixing in a portion rolled by a hot rolling head that occurs when a slab is heated to a high temperature by gas heating, and fine grains in a portion rolled by a hot rolling tail. It has been proposed to improve the magnetic deficiency by cooling the annealing before the final strong cold rolling by quenching the hot rolling head part with respect to the hot rolling central part and slowly cooling the hot rolling tail part.

[0005]

The magnetic properties of the products obtained by the above-mentioned prior art methods, the stability of the magnetic properties in the longitudinal direction of the coil, and the cost are not satisfactory.
The present invention is a hot rolling head that occurs peculiarly when slab heating is performed using an induction heating furnace, and a magnetic defect of a portion rolled at the tail is a hot rolling central portion for cooling in annealing before final strong cold rolling. The present invention proposes a method for solving the problem by making the hot-rolled head and the hot-rolled tail different so as to obtain a product which has excellent magnetic properties and is stable industrially in the coil longitudinal direction at low cost.

[0006]

That is, the present invention has the following structures. (1) C: 0.015 to 0.100% by weight,
Si: 2.0-4.0%, Mn: 0.03-0.12
%, Sol. Al: 0.010-0.065%, N:
0.0040 to 0.0100%, one or two selected from S and Se: 0.005 to 0.050
%, The balance is a continuous cast slab having a substantially Fe composition, heated to slab at 1320 to 1490 ° C., hot-rolled, hot-rolled sheet annealed and finally cold-rolled, or pre-cold-rolled, precipitation annealed. After the final strong cold rolling step, or hot-rolled sheet annealing, preliminary cold rolling, precipitation annealing and final strong cold rolling, the final sheet thickness is obtained, and decarburization / primary recrystallization annealing and final finishing are performed. In the method of producing a high magnetic flux density unidirectional electrical steel sheet by annealing, slab heating in a high temperature region of 1200 ° C or higher is performed at a temperature rising rate of 5 ° C / min or higher using an induction heating furnace, and before the final strong cold rolling. After holding the annealing at 800 to 1200 ° C., cooling from the temperature of 800 to 1200 ° C. to 400 ° C. is performed at the cooling rate of 20 to 120 ° C./s at the portion of the coil rolled in the hot rolling central portion, and the hot rolling is performed. 1 part for cooling the coil part rolled in the head and hot rolled tail A method for producing a high magnetic flux density unidirectional electrical steel sheet with little variation in magnetic properties in the coil longitudinal direction, which is performed at a cooling rate of 0 ° C./s or more and slower than that of a hot rolled central portion. And (2) the continuous cast slab is Sb, Sn, Cu, Mo, Ge, B, Te, As,
1 or 2 or more selected from Bi and Bi in the amount of each element in an amount of 0.003 to 0.3% is included, and there is little variation in magnetic properties in the longitudinal direction of the coil according to the above item (1). Manufacturing method of high magnetic flux density grain-oriented electrical steel sheet.
In addition, (3) before the slab heating in a high temperature range of 1200 ° C. or higher, hot deformation is applied at a rolling reduction of 50% or less, in the coil longitudinal direction described in the above item (1) or (2). This is a method for producing a high magnetic flux density unidirectional electrical steel sheet with little variation in magnetic properties.

The present inventor eliminates the magnetic characteristic defect at the end of the slab when the slab is heated using an induction heating furnace without a heat insulating plate, has excellent magnetic characteristics and is stable in the longitudinal direction of the coil. After diligently examining the method that can be obtained at low cost,
It was found that it is very effective to make the cooling rate in the annealing before the final strong cold rolling slower in the hot rolling head and hot rolling than in the hot rolling central part.

FIG. 1 and FIG. 2 show an example of the results of an experiment conducted by the present inventor. Within the range of ingredients according to the invention [C]
0.070%, [Si] 3.22%, [Mn] 0.07
1%, [S] 0.021%, [Sol.Al] 0.030
%, [N] 0.0071% is continuously cast to a thickness of 250 mm, heated at 1100 ° C. for 3 hours in a gas combustion furnace, and the temperature is controlled at the central portion in the longitudinal direction of the slab to raise the temperature at 12 ° C./h. Then, the slab was heated at 1380 to 1385 ° C. for 30 minutes and then hot-rolled to prepare a hot-rolled plate having a plate thickness of 2.40 mm. Then, samples were taken from the hot rolled head portion, the central portion, and the tail portion to perform the experiment. The hot-rolled sheet annealing was soaked at 1000 ° C for 2 minutes, and thereafter the cooling rate from 1000 ° C to 400 ° C was variously changed. Then, it was cold rolled to 0.30 mm, decarburized and subjected to primary recrystallization annealing, final finish annealing and insulating coating.

At this time, the hot rolling head portion of the hot rolled sheet annealing, the central portion,
The relationship between the cooling rate of the tail portion and the incidence of B ₈ 1.88 T or more is shown in FIG. 1, and the cooling rate of the hot rolling head, the central portion and the tail portion of the hot rolled sheet annealing and B ₈ of 1.88 T or more were developed. The relationship between the average iron loss W _17/50 of the samples is shown in FIG. It can be seen that when the cooling rate of the hot rolled head and tail is slower than that of the central portion, the rate of occurrence of B ₈ 1.88T or higher becomes higher. Also, the hot rolled central part is 2
It can be seen that the core loss W _17/50 deteriorates at 0 ° _C./s , the hot rolling head and the tail when the cooling rate is slower than 10 ° _C./s . In addition,
The hot-rolled head, hot-rolled central portion, and hot-rolled tail portion of hot-rolled sheet annealing refer to the parts of the coil rolled by the hot-rolled head, hot-rolled central portion, and hot-rolled tail portion in hot rolling. It was also confirmed that similar results could be obtained with the preliminary cold rolling.

Next, the conditions and the reasons for limiting the present invention will be described. If the lower limit of C is less than 0.015%, the secondary recrystallization becomes unstable, and the upper limit of 0.100% is that if C is more than this, the time required for decarburization becomes longer, which is economically disadvantageous. Limited. If Si is less than the lower limit of 2%, good iron loss cannot be obtained, and if it exceeds the upper limit of 4%, cold ductility is significantly deteriorated.

Mn causes hot embrittlement when the lower limit is less than 0.03%, and degrades magnetic properties when the upper limit exceeds 0.12%. S and Se are elements necessary for forming MnS and MnSe. If the total of one or two of these is less than the lower limit of 0.005%, the absolute amount of MnS and MnSe is insufficient, and the upper limit is 0.050%. If it exceeds the range, hot cracking occurs and it becomes difficult to purify in the final finish annealing.

Sol.Al is an element necessary for forming AlN. If the lower limit is less than 0.010%, the absolute amount of AlN is insufficient, and if the upper limit is more than 0.065%, a suitable dispersed state of AlN is obtained. I can't. N is an element necessary for forming AlN, and if the lower limit is less than 0.0040%, the absolute amount of AlN is insufficient, and if it exceeds the upper limit of 0.0100%, a proper dispersed state of AlN cannot be obtained.

Sb, Sn, Cu, Mo, Ge, B, T
e, As, and Bi segregate at the grain boundaries to stabilize the secondary recrystallization, but if the content of each element is less than the lower limit of 0.003%, the segregation amount is insufficient, and the upper limit of 0.3% is economical. And the deterioration of decarburization. The element to be added may be one kind or two or more kinds.

The slab heating in the high temperature range of 1200 ° C. or higher is carried out using an induction heating furnace at a temperature rising rate of 5 ° C./min or higher. 5 ℃
If the heating rate is slower than / min, a magnetic defect called line mixing occurs due to abnormal grain growth of the slab. Slab heating is 13
It is carried out at 20 ° C to 1490 ° C. If the temperature is lower than 1320 ° C, magnetic failure occurs due to insufficient solid solution of inhibitors such as MnS and AlN, and if the temperature is higher than 1490 ° C, the slab melts.

Prior to slab heating in a high temperature range of 1200 ° C. or higher, hot deformation may be applied at a rolling reduction of 50% or less, which destroys columnar crystals of the slab and improves iron loss. Have. The upper limit of the rolling reduction is set to 50% because the effect is saturated.

Annealing before the final strong cold rolling is 800 to 1200 ° C.
Hold with. Thereby, a part of AlN is precipitated, and the amount of precipitation, size, and distribution density are adjusted. When the temperature is lower than 800 ° C or higher than 1200 ° C, good magnetic properties cannot be obtained. The temperature cycle for this holding is disclosed in Japanese Patent Laid-Open No.
As proposed in Japanese Patent Publication No. 7-198214, it is of course possible to employ a temperature cycle in which the temperatures of the first half and the second half are different.

The cooling rate of the portion of the coil rolled in the hot rolled central portion of the annealing before the final strong cold rolling from the temperature of 800 to 1200 ° C. to 400 ° C. is set to 20 to 120 ° C./s. During this cooling, a part of AlN is precipitated, and the precipitation amount, size and distribution density are adjusted. As shown in FIG. 1, the cooling rate is 120
When it is faster than ℃ / s, the generation rate of B ₈ 1.88T or higher becomes low, and as shown in FIG. 2, when the cooling rate is slower than 20 ℃ / s, good magnetic properties cannot be obtained. The hot rolling head, the hot rolling central portion, and the hot rolling tail portion of the annealing before the final strong cold rolling are the hot rolling head portion, the hot rolling central portion, and the portion of the coil rolled by the hot rolling tail portion in the hot rolling. Point to.

The cooling rate of the coil portion rolled at the hot rolling head and the hot rolling tail of the annealing before the final strong cold rolling from the temperature of 800 to 1200 ° C. to 400 ° C. is 10 ° C./s or more and the hot rolling is performed. Be slower than the central part. The hot-rolled head and tail are the top of the coil and the range of a ² / b (a: slab thickness during induction heating, b: sheet thickness during final strong cold rolling annealing) in the longitudinal direction from the backmost portion. It is a part. As shown in FIG. 1, when the cooling rate of the hot rolled head and tail is slower than that of the hot rolled central portion, the occurrence rate of B ₈ 1.88T or higher is increased and the product yield is improved. Preferably, it is slowed down by 10 ° C./s or more. As shown in FIG.
If it is slower than ° C / s, good magnetic properties cannot be obtained. As a method of lowering the cooling rate of the hot rolling head portion and the tail portion than that of the hot rolling central portion, means for controlling the flow rate of the cooling medium in the longitudinal direction of the steel sheet can be adopted.

[0019]

【Example】

[Example 1] [C] 0.070 to 0.074%, [S
i] 3.35-3.38%, [Mn] 0.064-0.
066%, [S] 0.022 to 0.024%, [Sol.A
1] 0.033 to 0.034%, [N] 0.0072 to
0.0079%, [Sn] 0.12%, [Cu] 0.0
Continuously cast a slab containing 6% to a thickness of 250 mm,
Heat the slab in a 0 ° C x 3h gas heating furnace, and then control the temperature at the center of the slab in the induction heating furnace at 10 ° C.
The temperature was raised at a rate of / min, slab heating was performed at 1380 ° C. for 40 minutes, and hot rolling was performed to a thickness of 2.40 mm. Then, it was pre-cold rolled to 1.65 mm, precipitation annealing was held at 1100 ° C. for 10 seconds, and then held at 950 ° C. for 120 seconds to cool. At this time, 400
The cooling rate of the coil part rolled in the central part of hot rolling up to ℃ is 100 ° C / s, and the cooling rate of the coil part rolled in the hot rolling head and tail is changed by changing the cooling water flow rate. did. After that, final strong cold rolling was performed to 0.22 mm to obtain a product sheet thickness, decarburization and primary recrystallization annealing were performed, and then an annealing separator was applied, followed by final finishing annealing and application of a coating solution.

The product passed is B ₈ of 1.88.
It means that T or more is expressed. The hot-rolled head portion and the portion rolled by the tail portion are the top portion of the coil and the portion within the range of 37.8 m from the tail portion. The yield of the product in the central part of the hot rolling is 100%, and the average iron loss W _17/50 is 0.782 W / kg.
At this time, the hot rolling head of precipitation annealing, the cooling rate of the tail, the product yield, and the average iron loss W of the sample in which B ₈ was 1.88 T or more.
_17/50 is shown in Table 1. From this, it can be seen that when the cooling rate of the hot-rolled head portion and the tail portion is slower than that of the hot-rolled central portion, the product yield is high, and when the cooling rate is slower than 10 ° C./s, the iron loss is deteriorated.

[0021]

[Table 1]

[Embodiment 2] [C] 0.079 to 0.08
2%, [Si] 3.39 to 3.42%, [Mn] 0.0
70-0.071%, [S] 0.010%, [Se]
0.018 to 0.019%, [Sol.Al] 0.022 to
0.023%, [N] 0.0090 to 0.0095%,
A slab containing 0.017% of [Sb] and 0.012% of [Mo] is continuously cast to a thickness of 250 mm and slab-heated in a gas heating furnace at 1150 ° C. for 3 hours. It was hot-rolled to a thickness of 220 mm at a reduction rate, temperature-controlled in the center part of the slab longitudinal direction in an induction heating furnace, heated at various speeds, slab heated at 1380 ° C. for 40 minutes, and hot rolled to a thickness of 2.60 mm. . Then, the hot-rolled sheet was annealed by soaking at 1130 ° C. for 2 minutes and then rapidly cooled, pre-cold rolled to 1.35 mm, and the precipitation annealing was held at 1090 ° C. for 90 seconds and cooled. At this time,
As for the cooling rate up to 400 ° C., the flow rate of cooling water was changed at various portions of the coil rolled in the hot rolling central portion, hot rolling head portion, and hot rolling tail portion to change various cooling rates. After this, final strong cold rolling to 0.17 mm was performed, decarburization and primary recrystallization annealing were performed, and then an annealing separator was applied, followed by final finishing annealing and application of the coating liquid.

The product passed is B ₈ of 1.88.
It means that T or more is expressed. The hot-rolled head and tail are the parts within the range of 42.3 m from the top and the tail of the coil without hot rolling before induction heating, and 12% before induction heating.
220mm thick by hot rolling is the top of the coil,
It is a part within a range of 35.9 m from the tail. Temperature rising rate of induction heating furnace of slab at this time, hot rolling center, hot rolling head,
Cooling rate of precipitation annealing of hot rolled tail, product yield, B ₈ is 1.
Table 2 shows the average iron loss W _17/50 expressed in 88 T or more. As a result, good iron loss can be obtained when the heating rate of slab heating is 5 ° C./s or more, and when the cooling rate of precipitation annealing of the hot rolling head and tail is slower than that of the hot rolling central portion, hot rolling is performed. It can be seen that the product yield of the head and tail is high. Further, it is understood that iron loss is improved by applying hot deformation of 50% or less before induction heating.

[0024]

[Table 2]

[0025]

As described above, according to the present invention, it is possible to industrially manufacture a product having a high magnetic flux density in the longitudinal direction of the coil, and the industrial effect thereof is very large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the cooling rate of annealing at the center of hot rolling, the head of hot rolling, and the tail of hot rolling before final strong cold rolling and the incidence of B ₈ 1.88 T or more.

FIG. 2 is a diagram _showing the relationship between the cooling rate of annealing at the center of the hot rolling, the head of the hot rolling, and the tail of the hot rolling before final strong cold rolling and the average W _17/50 of the samples in which B ₈ is 1.88 T or more. Is.

Front page continued (72) Kenichi Nishiwaki, 1st Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Shin-Nihon Steel Co., Ltd. Hirohata Works (72) Inventor Yasuhiro Mayumi 1st Fuji-machi, Hirohata-ku, Himeji-shi Hyogo Japan Hirohata Works, Ltd.

Claims (3)

[Claims] 1. By weight%, C: 0.015 to 0.100%, Si: 2.0 to 4.0%, Mn: 0.03 to 0.12%, Sol.Al: 0.010 to 0.065%, N: 0.0040 to 0.0100%, one or two kinds selected from S and Se in total:
A step in which a continuously cast slab having a composition of 0.005 to 0.050% and the balance substantially Fe is heated to 1320 to 1490 ° C., then hot rolled, and this hot rolled sheet is annealed and finally strongly cold rolled. , Or the step of pre-cold rolling the hot rolled sheet, precipitation annealing and final strong cold rolling, or annealing the hot rolled sheet, pre-cold rolling,
A method for producing a high magnetic flux density unidirectional electrical steel sheet by decarburization / primary recrystallization annealing or final finishing annealing after any of the steps of precipitation annealing and final strong cold rolling Slab heating in a high temperature range of ℃ or more is performed at a temperature rising rate of 5 ℃ / min or more using an induction heating furnace, and after annealing at 800 to 1200 ℃ before final strong cold rolling,
Cooling from a temperature of 1200 ° C to 400 ° C is performed at a cooling rate of 20 to 120 ° C at the portion of the coil rolled in the hot rolled central portion.
/ S, and the portion of the coil rolled at the hot rolling head and the hot rolling tail is cooled at a cooling rate of 10 ° C / s or more and slower than the central portion of the hot rolling. A method of manufacturing a high magnetic flux density unidirectional electrical steel sheet with little variation in magnetic properties. 2. The continuous casting slab is Sb, Sn, Cu, M.
1 selected from o, Ge, B, Te, As, and Bi
Species or two or more kinds of each element amount 0.003 to 0.3
%, The method for producing a high magnetic flux density unidirectional electrical steel sheet according to claim 1, wherein there is little variation in magnetic properties in the coil longitudinal direction. 3. The coil longitudinal magnetic properties according to claim 1 or 2, wherein hot deformation is applied at a rolling reduction of 50% or less before slab heating in a high temperature range of 1200 ° C. or higher. A method for manufacturing a high magnetic flux density unidirectional electrical steel sheet with little variation.