JPH07126754A - Heating method of slab for grain oriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To obtain a grain oriented electrical steel sheet without the deficient solid solution of an inhibitor and excellent in magnetic properties by subjecting a grain oriented electrical steel slab to a specified primary heating to in a gas burner heating furnace, thereafter subjecting the slab to hot rolling in an electromagnetic induction heating furnace. CONSTITUTION:After the grain oriented electrical steel slab contg. >=2% Si is subjected to at <=1350 deg.C in the gas burner heating furnace, the grain oriented electrical steel sheet is manufactured by subjecting the slab to the hot rolling after the slab is further heated at 1400-1480 deg.C in the electromagnetic introduction heating furnace. At this time, the ranges within 1m from both ends of the slab which is arranged in an I-shape in the gas burner heating furnace are heated at a temp. higher by >=10 deg.C than the temp. of the other middle part and the temp. of the middle part is suppressed within + or -10 deg.C of the average temp. of the entire length of slab. Thus, the temp. distribution in the longitudinal direction of the slab on the outlet side of the electromagnetic introduction heating furnace is made uniform and the solid solution of the inhibiter is sufficiently uniformized again. In this way, the inhibitor is uniformly finely precipitated in the steel by hot rolling and the magnetism of the obtained grain oriented electrical steel sheet is prevented from degrading.

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 grain-oriented electrical steel sheet, and more particularly to a heating technique before hot rolling the slab for production.

[0002]

2. Description of the Related Art As is well known, the excellent magnetic properties of grain-oriented electrical steel sheets include (100) plane on the sheet surface and <001
It is obtained by selectively developing the secondary recrystallized grains of the> axis by the final annealing. For that purpose, fine precipitates called inhibitor in the steel, such as MnS and MnS.
It is important to precipitate e, AlN and the like, and the dispersion morphology of the inhibitor is controlled by once solid-solving these precipitates and then hot rolling.

By the way, the slab heating before hot rolling which is carried out for such a purpose is, for example, at a temperature of 1350 ° C. or lower by a gas burner heating type furnace (hereinafter “gas furnace”) due to re-solution of the inhibitor component. After the first heating of
Induction heating type furnace (hereinafter referred to as "I furnace". This is a slab having a bottom in the thickness direction, and is placed in the furnace in a so-called I shape.
It is a name for heating, and the slab width direction corresponds to the height in the furnace. ) Was done in. The secondary heating temperature is
The temperature is from 1400 ° C to 1480 ° C, which makes it possible to re-dissolve the coarsely precipitated inhibitor in the slab. After this secondary heating, the slab was hot-rolled.

In the I-furnace stage of the above process, as shown in FIG.
Since the radiant heat is large due to the structure of the furnace, the E and TE ends) tend to be lower by 5 ° C to 30 ° C than the other central side. Therefore, conventionally, insufficient re-solution of the inhibitor occurred near both ends of the slab, and the grain-oriented electrical steel sheet of the final product was apt to have a magnetic defect. As a method for solving this problem, Japanese Patent Laid-Open No. 5-59437 discloses a space 4 formed between the slabs at both ends in the I furnace 3.
Discloses a technique of arranging an induction heating plate and a heat insulating material and performing auxiliary heating. Further, JP-A-59-193216 teaches a so-called taper heating technique as shown in FIG. 3 in the longitudinal direction of the slab during the primary heating of the gas burner heating. This is a technique of heating the slab before hot rolling so that the temperature at the rear end in the rolling direction becomes higher than that at the front end within a range of 200 ° C.

However, when these known methods are carried out, a portion having a temperature higher than necessary is generated in the secondary heating. That is, when the secondary heating of the slab is completed, the surface temperature distribution becomes as shown in FIG. 4, the temperature in the range indicated by “A” in FIG. 4 rises more than necessary, and in the worst case, the A part locally melts. There is a problem that the slab structure is coarsened in the portion A even if it does not occur until it melts, causing conversely the magnetic deterioration of the final product due to high temperature.

[0006]

In view of the above circumstances, the present invention provides a method for heating a slab in a gas burner heating furnace so as to prevent insufficient solid solution of an inhibitor during hot rolling of grain-oriented electrical steel sheet. Is intended.

[0007]

In order to achieve the above-mentioned object, the inventor has made earnest studies and has focused on adjusting the temperature distribution in the longitudinal direction of the slab by primary heating. The present invention has been made after many experiments and researches have been carried out in order to materialize the viewpoint. That is, according to the present invention, a slab for producing a grain-oriented electrical steel sheet containing Si in an amount of 2% or more is first heated in a gas burner heating furnace at a temperature of 1350 ° C. or lower, and further in an electromagnetic induction heating furnace at a temperature of 1400 ° C. to 1480 ° C. In the production of grain-oriented electrical steel sheet that is heated and then hot rolled,
In the gas burner heating furnace, a range within 1 m from both ends of the slab is heated to 10 ° C. or more higher than the temperature of the other central portion, and the temperature of the central portion is ± 1 of the average value of the slab length.
It is a method for heating a slab for grain-oriented electrical steel sheets, which is characterized by suppressing the temperature within 0 ° C. In this case, known temperature control means may be used as the temperature control means for heating the slab and suppressing the temperature.

[0008]

According to the present invention, in the gas burner heating furnace, the range within 1 m from both ends of the slab is overheated by about 10 ° C. or more higher than the average temperature of the other central portion, and the temperature of the central portion is further overheated. Since the temperature is controlled to be within ± 10 ° C of the average value, the temperature distribution in the longitudinal direction of the slab becomes uniform on the outlet side of the electromagnetic induction heating furnace, and the re-dissolution of the inhibitor is sufficiently uniform. As a result, it has become possible to prevent the magnetic deterioration of the directional electromagnetic plate of the final product. Hereinafter, FIG. 1 and FIGS.
Based on this, a supplementary explanation will be given regarding the contents of the present invention.

FIG. 1 shows the temperature distribution of the slab measured at the outlet of the gas burner heating furnace by applying the present invention. LE, T
E The slab temperature within 1 m of both ends is higher than the average temperature in the longitudinal direction of other parts by 10 ° C or more. The reason is that during the secondary heating in the subsequent I furnace, there is no temperature drop in that region, the inhibitor is almost completely re-dissolved over the entire length of the slab, and the magnetic deterioration at the end is reduced by the iron loss value. ≦ 0.005 w / kg (when the iron loss further deteriorates, about half or more of them can be reduced by one grade). This is shown in FIG. In addition, the vertical axis of FIG. 5 represents the amount of increase in the iron loss value of the LE end portion with respect to the iron loss value of the central portion in the slab longitudinal direction, and the horizontal axis represents the degree of overheating of the slab end portion. That is, the graph of FIG. 5 clearly shows that the iron loss increase is small when the overheating degree of the slab end portion is 10 ° C. or more.

Next, as shown in FIG. 6, the heating temperature of the central portion corresponding to the outside of each 1 m from both ends is within ± 10 ° C. of the average value of the total length, + 10 ° C. from the target heating temperature.
In the overheated part deviated above, during rough rolling in the hot rolling process,
The occurrence rate of surface defects due to grain boundary cracking increases, and conversely, when heated at a low temperature of −10 ° C., re-dissolution of the coarsely precipitated inhibitor precipitate in the slab stage becomes insufficient, and the magnetic property of that part is reduced. Because it deteriorates. In the measurement results of FIG. 6, the solid line graph shows the relationship between the target heating temperature and the iron loss, and the dotted line graph shows the relationship between the target heating temperature and the serious surface defect occurrence rate.

[0011]

EXAMPLES C: 0.05%, Si: 3.5%, Mn:
0.081%, Se: 0.025%, Sb: 0.03
%, N: 25 ppm of the grain-oriented electrical steel sheet manufacturing slab was primarily heated in a gas burner heating furnace so as to have a temperature distribution in the longitudinal direction as shown in FIG. 7. For heating, both ends of the slab are extracted in the cauldron of the heating furnace 10
From both sides, heat the both ends intensively with a side burner,
The temperature distribution is set as shown in. Primary heating of this slab is completed when the average temperature of the so-called central portion reaches 1220 ° C., and the slab is charged into an I furnace for secondary heating to 144
Heated to 0 ° C. After that, immediately pull out the slab,
After carrying out hot rolling, pick → normalization → first cold rolling → intermediate annealing → second cold rolling → surface cleaning → annealing →
After the normal electromagnetic steel sheet manufacturing process of separate coating → final annealing → flattening (surface coating), the plate thickness becomes 0.
A 23 mm grain-oriented electrical steel sheet was manufactured. FIG. 8 shows changes in the iron loss value of the product in the longitudinal direction, and an absolute value suitable for the product and a uniform distribution were obtained.

The results in FIG. 8 show that, in order to suppress local melting, concentrated heating of both ends of the slab was performed at a temperature higher than the average value by 10 ° C. or more and less than 50 ° C.

[0013]

As described above, in the present invention, in order to prevent the magnetic deterioration of the slab that affects the product yield in the production of grain-oriented electrical steel sheet, the slab heating before hot rolling is devised. As a result, a product without magnetic deterioration in the longitudinal direction can be obtained, and there is great expectation for improving the yield.

[Brief description of drawings]

FIG. 1 is a temperature distribution diagram in the longitudinal direction of a slab at the time of completion of primary heating to which the present invention has been applied.

FIG. 2 is a surface temperature distribution diagram in the longitudinal direction of the slab when the secondary heating is completed in the I furnace by the conventional method.

FIG. 3 shows the slab that was first heated by the taper heating method,
It is a slab longitudinal direction temperature distribution figure at the time of completing secondary heating in a furnace.

FIG. 4 is a temperature distribution diagram in the longitudinal direction of the slab when heating is completed in the I furnace.

FIG. 5 is a diagram showing the relationship between the overheating level of the slab end and the increase in the end iron loss value with respect to the slab central part iron loss value.

[Fig. 6] Central part of the slab (excluding the 1m part at each end)
It is a figure showing the relationship between the heating level deviation and the quality level of.

FIG. 7 is a temperature distribution diagram in the longitudinal direction of the slab upon completion of primary heating according to the application of the present invention.

FIG. 8 is an iron loss change diagram in the longitudinal direction of the grain-oriented electrical steel strip manufactured by applying the present invention.

[Explanation of symbols]

 1 Slab (for production of grain-oriented electrical steel sheet) 2 Induction coil 3 Electromagnetic induction furnace (I furnace) 4 Space between both ends of slab and furnace end wall of I furnace

Claims (1)

[Claims] 1. A slab for producing a grain-oriented electrical steel sheet containing Si in an amount of 2% or more is first heated in a gas burner heating furnace at a temperature of 1350 ° C. or lower, and then in an electromagnetic induction heating furnace at 1400 ° C. to 1 ° C.
In the production of a grain-oriented electrical steel sheet which is heated at a temperature of 480 ° C. and then hot-rolled, in the gas burner heating furnace, the range within 1 m from both ends of the slab is higher than the temperature of the other central portion by 10 ° C. or more. After heating, the temperature of the central part is ± 1 of the average value of the total length of the slab.
A method for heating a slab for grain-oriented electrical steel sheet, which is controlled within 0 ° C.