JPH0331422A - Heating method and heating furnace for slab for grain oriented silicon steel - Google Patents

Abstract

PURPOSE:To uniformly heat a silicon steel slab over the entire part thereof and to improve the electromagnetic characteristics of the grain oriented silicon steel sheet to be obtd. by the cold rolling after the heating by heating the slab in an induction type heating furnace in the state of disposing exothermic heat insulating plates at both ends of the slab at the time of heating the slab prior to a hot rolling. CONSTITUTION:The silicon steel slab 1 contg. Si at a high ratio and contg., for example, 0.005 to 0.10% at least one kind of inhibitor components, such as S, Se and Al, is disposed in an induction coil 2 of the induction type heating furnace and this coil is energized to heat the slab to >=1300 deg.C. The exothermic heat insulating plates 3, 3 consisting of a stock, such as Fe, which can be induction-heated by the current of the coil 2 are disposed at both ends of the slab 1 in proximity to each other within 200mm in such a manner that the spacings from both ends of the slab 1 can be adjusted by rotation of a supporting rod 4, by which the cooling of both ends of the slab to the temp. lower than the temp. in the central part by heat radiation is prevented and the inhibitor components are uniformly solutionized over the entire part of the slab. The inhibitor components, such as MnS, MnSe and AlN, are uniformly and finely deposited at the time of forming the slab to the sheet material by the hot rolling and cold rolling. The electromagnetic characteristics of the silicon steel sheet which is the final product are thus improved.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a heating method and a heating furnace for grain-oriented silicon steel slabs, and in particular to a method for reducing temperature due to heat radiation from the end of the slab when heating the slab. The aim is to improve the electromagnetic properties of the final product board by preventing this from occurring.

It is known that the excellent magnetic properties of grain-oriented silicon steel sheets are obtained by developing secondary recrystallized grains with (110) planes on the sheet surface and [100] axes aligned in the rolling direction during final annealing. It is being For this purpose, fine precipitates called inhibitors, such as MnS+ MnSe
, AIN, etc. must be finely dispersed. Control of the dispersion form of the inhibitor can be obtained by once dissolving these precipitates into solid solution during slab heating prior to hot rolling, and then hot rolling under an appropriate cooling pattern.

Slab heating, which is carried out to meet such demands, usually takes 1
A high temperature of 300°C or higher is used, and the coldest point of the slab must satisfy this condition in order to sufficiently dissolve the inhibitor. On the other hand, if the heating temperature becomes too high, a large amount of molten scale is generated, which not only hinders the operation of the heating furnace, but also causes surface flaws such as baldness, which impairs the surface quality of the product. Magnetic variation also increases. Therefore, it is not preferable to perform heating at an unnecessarily high temperature for a long period of time, and it is important to maintain the temperature necessary for solid solution of the inhibitor over the entire length of the slab in a short period of time.

(Prior Art) As a heating method that satisfies the above requirements, the inventors previously proposed a method of heating silicon steel slabs in a non-oxidizing atmosphere using a vertical slab heating furnace (Japanese Patent Application Laid-open No. 60-145
Publication No. 318). This method achieved remarkable improvement effects by enabling high-temperature heating in a short period of time and by enabling the dissociation and solid solution of the inhibitor without the generation of slag.

(Problem to be Solved by the Invention) However, in the above method, if the slab length is shorter than the specified value, the end of the slab will not rise to the specified temperature due to heat dissipation, and the end will have poor magnetic properties. In some cases, this may occur.

Regarding ensuring the temperature at the end of the slab in a slab induction heating furnace, for example, Japanese Patent Publication No. 52-47179 describes a method of covering the end of the material to be heated with a refractory;
Publication No. 50447 proposes a method of placing an iron core on the outside of the coil to focus the induced magnetic flux to heat the end of the material, but in these methods, the installation position of the end temperature drop prevention device is fixed. Therefore, when the slab length changed, it was still not possible to maintain a stable end temperature.

The present invention advantageously solves the above-mentioned problems, and provides a slab for grain-oriented silicon steel that can secure the temperature necessary for solid solution of the inhibitor over the entire length of the slab in a short period of time, regardless of the length of the slab. The purpose of this study is to propose a heating method that can be used directly for its implementation, together with a suitable heating furnace.

(Means for Solving the Problem) That is, the present invention provides the following steps when heating a grain-oriented silicon steel slab to 1300°C or higher using an induction heating method.
Place a conductive heat generating heat insulating plate 200mm from the end of the slab.
This is a method for heating a grain-oriented silicon steel slab (first invention), which comprises heating a grain-oriented silicon steel slab in a state where the slab is placed in close proximity to each other.

The present invention also provides a vertical induction heating furnace for heating slabs, in which a conductive heating heat insulating plate is provided at the end of the slab introduced into the furnace to prevent a temperature drop due to heat radiation from the end of the slab. On the other hand, this is a heating furnace (second invention) that is installed so as to be movable forward and backward.

゛Hereinafter, this invention will be explained in detail.

FIG. 1 schematically shows the main parts of a heating furnace according to the present invention,
In the figure, numeral 1 is a slab, 2 is a coil, 3 is a conductive heat-generating heat-insulating plate, and 4 is a support rod for this heat-generating heat-insulating plate 3. Here, if the hanger of the heat-generating and heat-insulating plate 3 is provided with a female thread, and the support rod 4 is provided with a male thread, and the direction of the screw lead of the support rod 4 is reversed with the center as the boundary,
By simply rotating the support rod 4, the heat-generating heat-retaining plates 3 can be brought closer to each other or separated from each other. Then, the movable heat insulating plate 3 is installed in the induction heating furnace,
If induction heating is performed with the heat insulating plate 3 placed close to the end of the slab, the heat insulating plate 3 will also be heated, effectively preventing heat dissipation at the end of the slab. This prevents the temperature from decreasing.

Since the heat generating heat insulating plate 3 must generate heat by the induced current from the outer circumferential coil, its material may be an iron-based metal that has both conductivity and heat resistance, or a ceramic containing a conductive substance. Materials etc. are advantageously compatible. In order to control the amount of heat generated, it is necessary to choose an appropriate thickness. Furthermore, in order to effectively prevent heat dissipation at the ends of the slab, it is necessary to control the distance between the slab and the heat-generating heat insulating plate.

Next, Figure 2 shows the degree of magnetic deterioration at the end of the coil (difference between iron loss at the center of the coil and iron loss at the end) when heated while varying the distance between the heating plate and the end of the slab. shows.

The sample was a grain-oriented silicon steel slab with (AIN + MnS) as an inhibitor, heated at 1420 °C in an induction heating furnace.
After heating at ℃ for 10 minutes and finishing it into a 2.4 am hot-rolled plate, it was cold-rolled twice by final strong reduction and warm rolling to give a 0.2
It is finished in three layers.

As is clear from the figure, the distance between the heating plate and the slab is 2
00! If it is within MI, magnetic deterioration at the end of the slab is completely eliminated.

Next, in order to find out how much heating the end of the slab needs to be done using the heat-generating heat-retaining plate to obtain uniform magnetism, we changed the material and thickness of the heat-generating plate and controlled the amount of heat generated to achieve a uniform magnetic property. I investigated the relationship.

Since it is extremely difficult to accurately measure the temperature at the end of the slab, it is determined based on the temperature of the slab after rough rolling (RDT). The evaluation was made based on the temperature difference between the position corresponding to

FIG. 3 shows the difference in iron loss between a position corresponding to the rear end and a position corresponding to the longitudinal center during hot rolling, with respect to the difference between the end and center of the RDT.

The sample was made with (MnSe + Sb) as an inhibitor, and was heated in an induction heating furnace at 1420°C for 10 minutes, then made into a 2.4 mm thick hot rolled sheet, and then finished to a 0.23 mm thick sheet by two passes of cold rolling. It is something that

As is clear from Fig. 3, the slab end heat generating plate allows the end RDT to exhibit uniform magnetism as long as it is within a range of ±10°C with respect to the average temperature of the RDT at the center in the longitudinal direction. found.

(Function) The preferred composition of the grain-oriented silicon steel slab in this invention is as follows: Si: 4.5 wt% (hereinafter simply expressed as %) or less Mn
: Contains 0.02 to 0.10%, as well as S, Se, and AI as inhibitor components.
At least one selected from among 0.005 to 0.
It is contained within a range of 10%.

Here, the upper limit of Si was determined from the limit of processability, and the range of Mn was determined as the amount necessary to provide an inhibitor function in the form of MnS and MnSe. Furthermore, the reason for regulating the amount of inhibitor is that if it is less than 0.005%, the absolute amount of inhibitor will be insufficient and the development of secondary recrystallization will be insufficient, and the upper limit is mainly based on economic reasons. In addition to this, Sb, Sn, Cu, Mo
, B, and other grain boundary segregation elements are known, but there is no problem in adding these in addition to the above components.

The slab containing the above components is heated to 130° or more, preferably 14°, in a vertical induction heating furnace for the purpose of solid dissolving the inhibitor.
The slab is heated to a temperature range of 00 to 1450°C, and the object of the present invention is to uniformly heat the slab temperature over the entire length. Normally, when a slab is heated in this type of vertical induction heating furnace, as the length of the slab becomes shorter than the furnace length, both ends are not sufficiently heated due to heat dissipation, and magnetic defects may occur due to insufficient solid solution of the inhibitor. Often.

As a preventive measure against this, a feature of the present invention is to install a heat insulating plate at the end of the slab that can be moved according to the length of the slab, and to keep the distance between the slab and the heat generating plate within 200 mm as long as they do not come into contact with each other. be. In addition, in order to make the slab temperature uniform, it is recommended to preheat the slab in a normal gas heating furnace before charging it into the induction heating furnace, or to charge it into the induction heating furnace immediately in the hot slab state after casting. , which is more effective in making the slab temperature uniform. The slab extracted from the slab induction heating furnace is immediately processed into a rough rolling mill and a finishing tandem mill with a 1.5
A hot-rolled sheet with a thickness of ~3.0 mrn is finished, but the degree to which the temperature drop at the end of the slab can be prevented by the end heating and insulation plate can be evaluated by the rough rolling exit temperature (RDT). In other words, the sheet bar temperature after rough rolling corresponding to both ends of the slab (500 mm from both ends of the slab is defined as the end) is heated so that the temperature of the sheet bar after rough rolling is within ±10 ° C. from the average value at the center of the slab. This is important in obtaining uniform and good properties over the entire length of the final product.

The thus obtained hot-rolled steel strip is subjected to a cold rolling process of 0.15 to 0.15 or twice including intermediate annealing according to a known method.
It is made into a cold rolled sheet with a thickness of 0.35 mm, then subjected to decarburization and primary recrystallization annealing, and final finish annealing to be finished into a grain-oriented silicon steel sheet.

(Example) Example I Si: 3.15%, C: 0.075%, Mn:
0.080%, S: 0.020%, Al: 0.0
25%, N: 0.0085% and Cu: 0.08
A 200 mm thick silicon control slab (20 tons) containing 0% silicon was heated at 1200°C13 in a combustion type heating furnace.
After heating for 1450 hr, it was heated in a vertical slab induction heating furnace.
The mixture was heated and maintained at ℃ for 10 minutes. At this time, two types of stainless steel end heat generating plates with a wall thickness of 150,011 mm were installed at a position of 50 mm from the slab edge (A) and one without (B).
The conditions were compared. The heated slab was finished into a hot-rolled plate with a thickness of 2.4 mm by rough rolling and finish rolling. After that, it was first cold-rolled to a thickness of 1.511I11, and then rolled to a temperature of 1130°C1.
After performing intermediate annealing for 3 minutes, secondary cold rolling was performed for 200. '
C warm rolling was carried out to give a product plate thickness of 0.23 mm. After decarburization annealing at 850°C for 3 minutes in wet hydrogen, an annealing separator containing MgO as a main component was applied, and final annealing was performed at 1200°C for 110 hours in a 2 atmosphere. Furthermore, after removing the separating agent, a tension coating was applied.

The results of investigating the magnetic properties (5 locations in the longitudinal direction) of the final product thus obtained are as shown in Table 1.
All slags subjected to heat treatment under the conditions of this invention exhibited uniform magnetism over the entire length.

Table 1 Compatible with both ends of the slab Example 2 Sl j 3.30%, C: 0.050%, Mn:
0.075%, Se: 0.021% and Sb?
After continuous casting, a silicon steel slab with a thickness of 200+a+s having a composition containing 0.030% was heated to a temperature of 800%.
The sample was charged into a vertical induction heating furnace before the temperature dropped below 0.degree. C., and heated at a surface temperature of 1440.degree. C. for 10 minutes. At this time, the wall thickness is 12
0mm stainless steel charcoal heating plate 1 from the slab edge
Two types were compared: one installed at a position of 00 mm and one installed at a position of 250 m (B). After that, it was finished into a hot-rolled sheet with a thickness of 2.4 am by hot rolling, and then it was made into a 0.6 m thick sheet by the first cold rolling.
Following intermediate annealing at 000°C for 3 minutes, secondary cold rolling
It was set to 3 mm. Next, decarburization annealing was performed at 800°C for 15 minutes in wet hydrogen, MgO was applied, and then annealing was performed at 1200°C for 15 minutes.
Finish BOX annealing was performed for 0 hours. Furthermore, after removing the separating agent, a tension coating was applied.

The magnetic properties of the thus obtained final product coil at five locations in the length direction are as shown in Table 2, and all of the coils obtained according to the present invention exhibited uniform and good characteristics over the entire length.

Table 2

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the main parts of the heating furnace according to the present invention, and FIG. 2 is a diagram showing the distance between the slab end and the heat insulating plate and ΔWl'
1156, the graph shown in Figure 3 shows the relationship between ΔRDT
and Δ1. /,. This is a graph showing the relationship between 1... Slab 2... Coil 3... Heat generating heat insulating plate 4... Support rod (effect of the invention) (According to the present invention, when heating a grain-oriented silicon steel slab, Regardless of the length of the slab, it is possible to heat the entire length of the slab to the temperature required for solid solution of the inhibitor in a short period of time, which in turn greatly contributes to eliminating variations in magnetic properties in the product plate.

Claims (1)

[Claims] 1. When heating a slab for grain-oriented silicon steel to 1,300°C or higher using an induction heating method, a conductive heating heat insulating plate is installed within 200 mm from the end of the slab. A heating method for a grain-oriented silicon steel slab, characterized by heating the slab. 2. In a vertical induction heating furnace for heating slabs, a conductive heat generating heat insulating plate for preventing temperature drop due to heat radiation from the end of the slab introduced into the furnace is advanced against the end of the slab. ,
A heating furnace characterized by being installed so that it can be moved backwards.