JP3338257B2 - Manufacturing method of high magnetic flux density unidirectional electrical steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are mainly used for core materials of transformers and generators. Recently, steel sheets with higher magnetic flux density and less iron loss have been required from the market for energy saving. Has been requested. In order to obtain a unidirectional magnetic steel sheet having a high magnetic flux density, it is necessary to obtain a secondary recrystallized structure highly integrated in the {110} <001> direction, that is, the so-called Goss direction. It is known that the inhibitor and the primary recrystallization texture have a great influence on the secondary recrystallization. As for the inhibitor, 100% in steel before finish annealing is performed.
It is necessary to make the precipitated dispersed phase of about 1000 ° exist uniformly and finely, and AlN, MnS, MnSe and the like are generally known. Since these are coarsely precipitated in continuous casting, the slab is heated to a high temperature of 1250 ° C. or more to sufficiently form a solution, and then MnS and MnSe are uniformly and finely precipitated by hot rolling. AlN is uniformly and finely precipitated by precipitation annealing, and furthermore, Sb, Sn, C of grain boundary segregation elements are formed at grain boundaries from hot rolling to decarburization and primary recrystallization annealing.
It is effective to segregate u, Mo, Ge, B, Te, As, Bi and the like.

Conventionally, slab heating has generally been performed in a gas heating furnace. However, this method requires a long slab heating, so that a magnetic characteristic defect called line mixing caused by abnormal grain growth of slab crystal grains may occur. In order to solve this problem, a method has been proposed in which a slab is rapidly heated using induction heating as described in Japanese Patent Publication No. 56-18654. However, when slab heating is performed by induction heating, Japanese Unexamined Patent Publication No. Hei.
As disclosed in Japanese Unexamined Patent Publication No. 2, the end of a slab (the end rolled first by hot rolling is the hot rolled head, and the other end rolled last by hot rolling is the hot rolled tail) In addition, the hot rolled head, hot rolled central portion, and hot rolled tail portion of the annealing before final strong cold rolling described below are coils rolled as hot rolled head, hot rolled central portion, and hot rolled tail portion in hot rolling. In some cases) did not rise to a predetermined temperature due to heat dissipation, resulting in poor magnetic properties at the ends. Japanese Patent Application Laid-Open No. 3-31422 proposes a method of improving the magnetic defect at the end by installing a conductive heat insulating plate near the end of the slab. However, the heat insulating plate is exposed to high temperatures. Therefore, there is a problem in durability, and there is a problem that the heat-insulating plate must be replaced frequently, which leads to an increase in costs and a heavy burden on facility management, and also causes poor magnetism when the heat-insulating plate deteriorates and wears out. I was

[0004] Incidentally, cooling during annealing before final strong cold rolling has a great effect on the precipitation of AlN, and secondary recrystallization,
It is known that it greatly affects magnetic properties. Japanese Patent Publication No. 46-23820 discloses that after annealing at a temperature of 750 to 1200 ° C.,
A method of rapidly cooling to 2 ° C. in 2 seconds to 200 seconds has been proposed. JP-B-62-56923 discloses that 900 to 1
A method has been proposed in which the temperature is kept at 200 ° C. and then cooled to room temperature at a cooling rate higher than that of air cooling and lower than that of 30 ° C. water cooling. JP-A-2-138419 discloses 800
After primary soaking at ~ 1200 ° C, primary cooling is performed, and 850-9
In secondary soaking at 50 ° C., 100% in primary soaking
A method has been proposed in which the holding time at 0 ° C. or more is set to 20 to 120 seconds, and the cooling rate from the temperature of 850 to 950 ° C. during secondary cooling to 500 ° C. is set to 20 to 100 ° C./second.
Japanese Patent Publication No. Sho 62-1458 discloses that when a slab is heated to a high temperature by gas heating, a magnetic defect due to wire mixing of a portion rolled at a hot rolled head and fine grains at a portion rolled at a hot rolled tail are caused. A method has been proposed to improve the magnetic defect by cooling the annealing before the final strong cold rolling by rapidly cooling the hot rolling head and slowly cooling the hot rolling tail portion with respect to the central portion of the hot rolling.

[0005]

The magnetic properties of the product obtained by the above-mentioned prior art method, 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, which occurs specifically when the slab is heated using an induction heating furnace, the magnetic defect of the portion rolled at the tail portion, and the cooling in the annealing before the final strong cold rolling is performed at the hot-rolling central portion. The present invention proposes a method for solving the problem by making the hot-rolled head and the hot-rolled tail different from each other, and is capable of inexpensively obtaining a product having excellent magnetic properties and being stable in the longitudinal direction of the coil.

[0006]

Namely, the gist of the present invention is as follows. (1) By weight%, C: 0.015 to 0.100%,
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
%, With the remainder being a slab heated to 1320 to 1490 ° C., followed by hot rolling, annealing the hot rolled sheet and final strong cold rolling, or preliminary cold rolling and precipitation annealing. After any of the following steps: final strong cold rolling, or hot rolled sheet annealing, preliminary cold rolling, precipitation annealing and final strong cold rolling, the final sheet thickness is determined, decarburization / primary recrystallization annealing, and final finishing In the method of manufacturing a high magnetic flux density unidirectional magnetic steel sheet by annealing, slab heating in a high temperature region of 1200 ° C. or more is performed using an induction heating furnace at a heating rate of 5 ° C./min or more, and before the final strong cold rolling. After holding the annealing at 800 to 1200 ° C., cooling from a temperature of 800 to 1200 ° C. to 400 ° C. is performed at a cooling rate of 20 to 120 ° C./s in the portion of the coil rolled at the center of the hot rolling. Cooling is applied to the part of the coil rolled at the head and hot rolled tail. A method for producing a high magnetic flux density unidirectional magnetic steel sheet having little variation in magnetic properties in a longitudinal direction of a coil, which is performed at a cooling rate of 0 ° C./s or more and a cooling rate lower than that of a central portion of a hot rolled sheet. And (2) the continuous cast slab is made of Sb, Sn, Cu, Mo, Ge, B, Te, As,
And one or two or more selected from Bi and 0.003 to 0.3% in each element amount, and the variation in the magnetic characteristics in the longitudinal direction of the coil described in (1) above is small. A method for manufacturing high magnetic flux density unidirectional magnetic steel sheets.
(3) A hot deformation is applied at a rolling reduction of 50% or less before slab heating in a high temperature range of 1200 ° C. or more, wherein the coil is deformed in the longitudinal direction of the coil as described in (1) or (2) above. This is a method for producing a high magnetic flux density unidirectional magnetic steel sheet with less variation in magnetic properties.

The inventor of the present invention has solved a problem that when a slab is heated by using an induction heating furnace, the slab ends can be free from poor magnetic characteristics without a heat-insulating plate, and have excellent magnetic characteristics and are stable in the longitudinal direction of the coil. After earnestly studying a method that can be obtained at low cost,
It has been found that it is very effective to make the cooling speed in the hot rolling head and the tail of the hot rolling slower than the central portion of the hot rolling in the annealing before the final strong cold rolling.

FIGS. 1 and 2 show examples of the results of experiments conducted by the present inventors. [C] in the component range according to the invention
0.070%, [Si] 3.22%, [Mn] 0.07
1%, [S] 0.021%, [Sol.Al] 0.030
%, [N] is continuously cast to a thickness of 250 mm to a thickness of 250 mm, heated in a gas-fired furnace at 1100 ° C. × 3 h, then temperature-controlled at the center in the longitudinal direction of the slab, and heated 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 sheet having a thickness of 2.40 mm. Then, an experiment was performed by collecting samples from the hot rolled head, the center, and the tail. 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. Thereafter, the steel sheet was cold-rolled to 0.30 mm, decarburized and subjected to primary recrystallization annealing, and then subjected to final finish annealing and insulating coating.

At this time, the hot rolled head, central portion,
The relationship between the tail cooling rate and B ₈ 1.88T or more incidence of Figure 1, and hot rolling head of hot-rolled sheet annealing, the central portion, the cooling rate and B ₈ tail has been expressed above 1.88T FIG. 2 shows the relationship between the average iron loss W _17/50 of the sample. Hot rolling the head, the tail is seen that when the cooling rate is slower than the central portion B ₈ 1.88T or more occurrence rate increases. The central part of the hot rolling is 2
It can be seen that when the cooling rate of the hot rolled head and tail at 0 ° _C./s is lower than 10 ° _C./s , the iron loss W _17/50 deteriorates. In addition,
The hot-rolled head, hot-rolled central portion, and hot-rolled tail portion of the hot-rolled sheet annealing refer to portions of the coil rolled at the hot-rolled head, hot-rolled central portion, and hot-rolled tail portion in hot rolling. Also, it was confirmed that similar results were obtained even in the presence of preliminary cold rolling.

Next, various conditions of the present invention and reasons for limiting the conditions 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 the lower limit of Si is less than 2%, good iron loss cannot be obtained, and if the upper limit of 4% is exceeded, the cold rolling property 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 them is less than the lower limit of 0.005%, the absolute amounts of MnS and MnSe are insufficient, and the upper limit is 0.050%. If the temperature exceeds the limit, hot cracking will occur, and it will be difficult to purify the final finish annealing.

Sol. Al is an element necessary for forming AlN. When the lower limit is less than 0.010%, the absolute amount of AlN is insufficient, and when the upper limit is more than 0.065%, an appropriate dispersion state of AlN is obtained. I can't. N is an element necessary for forming AlN. If the lower limit is less than 0.0040%, the absolute amount of AlN is insufficient, and if the upper limit is more than 0.0100%, an appropriate dispersion 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 amount of each element is less than the lower limit of 0.003%, the amount of segregation will be insufficient, and the upper limit of 0.3% will be economical. This is due to the deterioration of decarburization. One type of element may be added, or two or more types may be added.

The slab is heated in a high temperature range of 1200 ° C. or more by using an induction heating furnace at a rate of 5 ° C./min or more. 5 ℃
If the rate of temperature rise is lower than / min, a magnetic defect called linear mixing due to abnormal grain growth of the slab will occur. Slab heating is 13
Perform at 20 ° C to 1490 ° C. If the temperature is lower than 1320 ° C., poor magnetic properties occur due to insufficient solid solution of inhibitors such as MnS and AlN, and if it is higher than 1490 ° C., the slab melts.

Before the slab is heated in a high temperature range of 1200 ° C. or more, hot deformation may be applied at a rolling reduction of 50% or less, which breaks columnar crystals of the slab and improves the effect of improving iron loss. Have. The reason why the upper limit of the rolling reduction is set to 50% is that the effect is saturated.

The 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 deposition, size, and distribution density are adjusted. If the temperature is lower than 800 ° C. or higher than 1200 ° C., good magnetic properties cannot be obtained. The temperature cycle in this holding is described in
As proposed in Japanese Patent Application Laid-Open No. 7-198214, a temperature cycle in which the first half temperature and the second half temperature are different can be employed.

[0017] The cooling rate of the portion of the coil rolled at the center of the hot-rolled part of the annealing before the final strong cold rolling from a temperature of 800 to 1200 ° C to 400 ° C is 20 to 120 ° C / s. During this cooling, a part of AlN is precipitated, and the amount, size and distribution density of the deposited AlN are adjusted. As shown in FIG.
° C. / If faster than s will lower B ₈ 1.88T or more incidence can not be obtained excellent magnetic characteristics when the cooling rate as shown in FIG. 2 is slower than 20 ° C. / s. The hot-rolled head, hot-rolled central portion, and hot-rolled tail of the annealing before the final strong cold rolling are the portions of the coil rolled at the hot-rolled head, hot-rolled central portion, and hot-rolled tail in hot rolling. Point.

[0018] The cooling rate of the portion of the coil rolled at the hot rolling head and the tail of the hot rolling before the final strong cold rolling from a temperature of 800 to 1200 ° C to 400 ° C is 10 ° C / s or more and the hot rolling is performed. Slower than the center. The hot-rolled head and tail are in the range of a ² / b (a: slab thickness at the time of induction heating, b: plate thickness at the time of annealing before final strong cold rolling) in the longitudinal direction from the head and the tail of the coil. Part. As shown in FIG. 1, the hot rolling head, when the cooling rate of the tail slower than hot rolled center portion B ₈ 1.88T or more incidence increases, improved yield of product. Preferably, it is slowed down by 10 ° C./s or more. As shown in FIG.
If the temperature is lower than ° C / s, good magnetic properties cannot be obtained. As a method of making the cooling speed of the hot rolled head and tail lower than that of the hot rolled 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] 0.022-0.024%, [Sol.
l] 0.033-0.034%, [N] 0.0072-
0.0079%, [Sn] 0.12%, [Cu] 0.0
A slab containing 6% is continuously cast to a thickness of 250 mm,
The slab was heated in a gas heating furnace at 0 ° C. × 3 h, and then the temperature was controlled at the center of the slab in the longitudinal direction with an induction heating furnace.
The temperature was raised at a rate of 1 / min, the slab was heated at 1380 ° C. for 40 minutes, and hot-rolled to a thickness of 2.40 mm. Then, it was pre-cold rolled to 1.65 mm, and the precipitation annealing was kept at 1100 ° C. × 10 seconds, and then kept at 950 ° C. for 120 seconds and cooled. At this time, 400
The cooling rate of the part of the coil rolled at the center of hot rolling to 100 ° C is 100 ° C / s, and the part of the coil rolled at the head and tail of the hot rolling changes the cooling water flow rate and changes various cooling rates. did. Thereafter, the product was subjected to final strong cold rolling to 0.22 mm to obtain a product plate thickness, decarburization and primary recrystallization annealing were performed, and then an annealing separator was applied, followed by final finish annealing and application of a coating liquid.

[0020] pass as a product, B ₈ is 1.88
It means those expressed T or more. The portions rolled at the hot-rolled head and tail are the portions at the top of the coil and 37.8 m from the tail. 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.
Hot rolling head of precipitation annealing at this time, the cooling rate of the tail, the iron loss W of the average of the sample product yield and B ₈ is expressed above 1.88T
_17/50 is shown in Table 1. From this, it can be seen that when the cooling speed of the hot-rolled head and tail is lower than that of the central portion of the hot-rolling, the yield of the product increases, and when the cooling speed is lower than 10 ° C./s, the iron loss worsens.

[0021]

[Table 1]

[Example 2] [C] 0.079 to 0.08
2%, [Si] 3.39 to 3.42%, [Mn] 0.0
70 to 0.071%, [S] 0.010%, [Se]
0.018 to 0.019%, [Sol. Al] 0.022 to
0.023%, [N] 0.0090-0.0095%,
A slab containing 0.017% of [Sb] and 0.012% of [Mo] is continuously cast to a thickness of 250 mm, and is 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 ratio, temperature-controlled at the center in the longitudinal direction of the slab in an induction heating furnace, heated at various speeds, 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. × 2 minutes and then quenched, pre-rolled to 1.35 mm, and kept at 1090 ° C. × 90 seconds for precipitation annealing and cooled. At this time,
The cooling rate up to 400 ° C. was varied by changing the flow rate of the cooling water at the portion of the coil rolled at the hot rolled center, hot rolled head, and hot rolled tail. Thereafter, the steel sheet was subjected to final strong cold rolling to 0.17 mm, subjected to decarburization / primary recrystallization annealing, and then applied with an annealing separator, followed by final finish annealing and application of a coating liquid.

[0023] pass as a product, B ₈ is 1.88
It means those expressed T or more. The hot-rolled head and tail are portions of the top of the coil and a range of 42.3 m from the tail when no hot rolling is performed before induction heating, and 12% before induction heating.
The one with a thickness of 220 mm by hot rolling is the top of the coil,
It is a part in the range of 35.9 m from the tail. At this time, the heating rate of the induction heating furnace of the slab, the central part of the hot rolling, the head of the hot rolling,
The cooling rate of the precipitation annealing of the hot-rolled tail, the product yield, and B ₈ are 1.
Table 2 shows the average iron loss W _17/50 of those expressed at 88T 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 at the head and tail of the hot rolling is made slower than that at the center of the hot rolling, It can be seen that the product yield of the head and tail is high. In addition, it can be seen 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, a product having a high magnetic flux density can be manufactured industrially stably in the longitudinal direction of the coil, and the industrial effect is very large.

[Brief description of the drawings]

[1] hot rolling the central portion, hot rolling head is a relationship diagram of the cooling rate and B ₈ 1.88T or more occurrences of the final strong cold rolling prior to annealing Netsunobeo portion.

FIG. 2 is a graph _showing the relationship between the cooling rate of the central hot rolling, the hot rolling head, and the hot rolling tail before the final strong cold rolling and the average W _17/50 of the sample in which B ₈ is 1.88 T or more. It is.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kenichi Nishiwaki 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works (72) Inventor Yasuhiro Mayumi Fujimachi, Hirohata-ku, Himeji-shi, Hyogo No. 1 Nippon Steel Corporation Hirohata Works (56) References JP-A-58-164725 (JP, A) JP-A-1-230720 (JP, A) (58) Fields investigated (Int. . ^7, DB name) C21D 8/12 C22C 38/00 303 C22C 38/06 C22C 38/60 H01F 1/16

Claims (3)

(57) [Claims] C .: 0.015 to 0.100%, Si: 2.0 to 4.0%, Mn: 0.03 to 0.12%, Sol.Al: 0.010% by weight. 0.065%, N: 0.0040 to 0.0100%, one or two selected from S and Se:
A step of continuously rolling a continuously cast slab having a composition of 0.005 to 0.050%, with the balance being substantially Fe, after slab heating to 1320 to 1490 ° C., hot rolling, annealing this hot rolled sheet and final strong cold rolling. , Or pre-cold hot-rolled sheet, precipitation annealing and final strong cold-rolling, or annealed hot-rolled sheet, pre-cold rolled,
After any of the steps of precipitation annealing and final strong cold rolling, the final sheet thickness is determined, and a method for producing a high magnetic flux density unidirectional magnetic steel sheet by decarburization / primary recrystallization annealing and final finish annealing is used. Slab heating in a high temperature range of at least 5 ° C. using an induction heating furnace at a rate of 5 ° C./min or more, and holding the annealing before final strong cold rolling at 800 to 1200 ° C .;
Cooling from a temperature of 1200 ° C to 400 ° C, the part of the coil rolled at the center of the hot rolling is cooled at a cooling rate of 20 to 120 ° C.
/ S, and the portion of the coil rolled at the hot rolled head and the hot rolled tail is cooled at 10 ° C./s or more and at a slower cooling rate than the central portion of the hot rolled roll. A method for producing a high magnetic flux density unidirectional electrical steel sheet with less variation in magnetic properties. 2. The continuous cast slab is made of 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 magnetic steel sheet according to claim 1, wherein the magnetic properties in the longitudinal direction of the coil are small. 3. The coil according to claim 1, wherein a hot deformation is applied at a rolling reduction of 50% or less before heating the slab in a high temperature region of 1200 ° C. or more. A method for producing high-flux-density unidirectional electrical steel sheets with little variation.