JPS62149815A - Production of low iron loss grain oriented silicon steel sheet having decreased surface defect - Google Patents

Abstract

PURPOSE:To produce a low iron-less grain oriented silicon steel sheet having decreased surface defects by subjecting a silicon steel slab contg. specific compsn. ratios of C, Si, Se and S to a preliminary hot rolling treatment under specific conditions then to hot and cold rolling, etc. CONSTITUTION:The silicon steel slab contg. 0.010-0.060wt% C, 2.5-4.0% Si, and contg. 0.010-0.10% Se and/or S as an inhibitor forming element is subjected to the preliminary hot rolling treatment under the conditions satisfying the formula; 130X(R+5)<1/4>XlogL<=T<=360, 800/(110+R).logL (where, T; the surface temp. of the slag, deg.C, L; the thickness of the slag, mm, R' the draft at the 1st pass, %) prior to hot rolling. The above-mentioned slab is thereafter subjected to hot rolling and cold rolling, then to decarburization, primary recrystallization annealing and final finish annealing. The low-rion loss grain oriented silicon steel sheet which obviates the generation of the surface defects such as scabs and cracks is thus obtd.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing unidirectional silicon steel sheets, and specifically aims to further reduce iron loss without deteriorating surface properties. It is something.

(Prior Art) Unidirectional silicon steel sheets are mainly used as iron cores for transformers and large power generators, and their characteristics include high magnetic flux density (represented by ego) and iron loss (WI715).
(represented by 0) is required to be low.

As a means of achieving high magnetic flux density and low core loss in such unidirectional silicon steel sheets, a method is known in which a slab is hot rolled prior to normal hot rolling. (Special Publication No. 54-27820, No. 50-3700
No. 9 publications).

All of the above methods are used to destroy the columnar crystal structure and refine the crystal grains.
- No crystal grain growth occurs in Publication No. 278201
By rolling at a temperature of 200°C or less, on the other hand, the latter Japanese Patent Publication No. 50-37009 aims to form a fine-grained recrystallized structure by rolling at a relatively high reduction rate (up to 70%). ing.

By the way, as another means to reduce the iron loss of silicon steel sheets,
It is possible to increase the content of the inhibitor, but when the above method is applied to increase the amount of the inhibitor, there are problems as described below.

(Problem to be solved by the invention) That is, (1) When rolling at high temperatures, baldness occurs frequently.

(2) However, when rolled at low temperatures, cracks occur during subsequent hot rough rolling, and sag occurs during finish rolling.

(3) The incidence of surface defects in (1) and (2) above tends to increase as the slab thickness increases and as the rolling reduction rate increases.

Regarding the problem of sagging, Japanese Patent Application Laid-Open No. 59-80719 proposes a method of slowly cooling the slab to 1250°C or less before transporting it, but this method does not eliminate the sagging generated during rolling as described above. It is not possible to prevent warping and cracking.

The present invention advantageously solves the above-mentioned problems, and even when the amount of inhibitor is increased, it effectively prevents the occurrence of surface defects such as bald spots and cracks, and has excellent iron loss characteristics. The purpose is to propose a manufacturing method that can advantageously obtain grain-oriented silicon steel sheets.

(Means for Solving the Problem) In order to solve the above problem, the inventors once again carefully examined the rolling conditions prior to hot rolling, and found that low temperature hot rolling is effective against line curling. On the other hand, in addition to finding that high-temperature hot rolling is preferable for cracking and flaking, we also found that the conditions under which cracking and flaking do not occur change depending on the slab thickness and the rolling reduction in the first pass. Ta.

This invention is based on the above knowledge.

Sunarichiko's invention is C: 0.010~0.060w
t% (hereinafter shown in % on cars), Si: 2.5 to 4.0
% and at least one of Se and S as an inhibitor-forming element in an amount of 0.010 to 0.10 wt.
A silicon steel slab with a silicon content in the range of In producing a raw steel plate, prior to the above-mentioned hot rolling, the silicon steel slab is subjected to a preliminary hot rolling treatment under conditions that satisfy the following formula (1). This is a method for producing a grain-oriented silicon steel sheet.

Record L: Slab thickness (mm) R: 1st pass rolling reduction rate (%) This invention will be explained in detail below.

First, the experimental results that formed the basis of this invention will be explained.

Slabs having the chemical compositions shown in Table 1 and having various thicknesses L (mm) and surface temperatures T (t) were subjected to various rolling reductions (first pass rolling reduction R%) prior to hot rolling. Rolling, that is, preliminary hot rolling was performed.

After such preliminary rolling, hot rough rolling is carried out according to a conventional method.
Finish rolling, cold rolling, decarburization/primary recrystallization annealing, and final finish annealing were performed.

During the above manufacturing process, the occurrence rate of cracks that occurred in some slab corners during pre-hot rolling and line baldness that appeared on the surface after annealing was measured. In addition, if the hot rolling temperature is too low, scabbing may occur, so we also investigated whether this occurred.

Here, the occurrence rate of line baldness is per unit length of 1 m in the longitudinal direction of the steel plate.
If there is a line sag in the area (even if there are multiple lines), it is set as 1, and the sum is divided by the total length of the steel plate, which is 1. It was calculated by multiplying 1 by 100.

Among the results obtained in this way, the rolling reduction ratio R of the first pass is 2
The presence or absence of cracks and the incidence of sagging in the case of 0% are summarized in FIG. 1 in relation to the slab thickness and the slab surface temperature T.

Now, regarding line baldness, it is extremely difficult to completely eliminate it, so the immediate goal is to suppress the incidence to less than 1%. As such, it is necessary to start rolling under conditions that satisfy the following formula (a): T≦2774/log L ·(a).

The Tamade formula (a) suggests that the larger the slab thickness, the lower the temperature it is necessary to perform rolling.

Although the mechanism by which line baldness occurs has not been clearly elucidated to date, intergranular cracks and flaws occur due to the impact received when the slab is bitten by the rolling roll, and these cracks and flaws The larger the thickness, the higher the surface temperature and the softer the surface layer, and the higher the rolling reduction rate in the first bath, the more the amount will increase. It is estimated that

Therefore, the slab surface temperature is especially important for line shedding.

Next, regarding slab corner cracks, it can be seen from FIG. 1 that the thicker the slab thickness is, the more likely cracks are to occur in low-temperature rolling. If we look for conditions where no cracking occurs, we get
The following formula (1)) is as follows.

The reason why corner cracks are more likely to occur when rolling at a lower temperature is considered to be due to insufficient ductility within the grains, and the reason why the thicker the slab is, the more likely it is to crack is due to the difference in the form of deformation between the surface layer and the center layer, that is, the edge of the slab. This is because the morphological difference in which the surface layer of the rolled surface is mainly caused by shear deformation due to frictional force, whereas the center layer of the slab is mainly deformed in the rim direction due to compressive force, which becomes larger as the slab thickness increases. Presumed.

Next, with the composition shown in Table 1, the thickness L is 100 ++++n and 300 mm (For the Q slab, the relationship between the slab surface temperature T and the rolling reduction ratio R of the first pass against cracks and line curling is summarized in 2- show.

In order to suppress the incidence of line baldness to less than 1%, it is necessary to satisfy the following formula (C) where T≦, /(110+R)... (C), and here the above-mentioned A comparison with equation (a) shows that 1 is proportional to 1/1ogL.

On the other hand, regarding cracks, it is understood that as the rolling reduction ratio R of the first pass increases, it is necessary to increase the surface temperature. From Figure 2, the relationship between the slab surface temperature T (℃) at which no cracking occurs and the rolling reduction ratio R (%) of the first pass is expressed by the following formula (d): T≧2X (5+R)I/4 ・... It can be expressed as (d).

Here again, 2 is calculated as log L by comparison with equation (b) above.
It is clear that it is proportional to , and when we calculated the values of the proportionality constants Kl and K2 in equations (c) and (d) by numerical calculation, we found that the conditions under which neither line peeling nor cracking occurs are the following equation (1).
It turns out that it can be expressed as follows.

In order to prevent sagging, which is thought to occur when the slab temperature decreases during pre-hot rolling and the resulting hot-rolling finishing temperature drops too much, the slab was reheated in the pre-hot rolling mill and then subjected to the subsequent process. , Regardless of the conditions of subsequent hot rough rolling, products subjected to such reheating do not have any cracks, let alone sagging, and the incidence of line sagging is 0.05%. It was significantly reduced to:

Although the reason for this is not yet clearly understood, one of the causes of flaking and cracking is that the extreme surface layer of reheated materials is affected by rolling, heating, and descaling.
This is presumed to be due to a decrease in the content of Se and S.

The preferred conditions for reheating after preliminary hot rolling as described above are 100
The temperature is 0 to 1400°C for about 15 minutes or less.

(Function) The reason why the component composition of the material is limited to the above range in this invention is as follows.

C: 0.010-0.060% In order to reduce C to less than 0.010%, it is necessary to strengthen degassing in the melting stage, but such treatment causes a decrease in yield and an increase in cost. On the other hand, if it exceeds 0°060%, M n Se and! In order to dissolve AnS into solid solution, it is necessary to heat the slab to a high temperature (1400°C or higher), and the decarburization process takes a long time, leading to an increase in cost. 060
% range.

Si: 2.5 to 4.0% Si must be contained in an amount of at least 2.5% in order to reduce iron loss, but if it exceeds 4.0%, workability deteriorates, so 2. It was limited to a range of 5 to 4.0%.

Se and/or S: 0.010-0.10%Se
Both of S and S are useful as inhibitor-forming elements, and in this invention, these elements are contained in relatively larger amounts than conventionally in order to obtain a secondary recrystallized texture with sufficiently uniform crystal orientation. . However, 0.1
If the content exceeds 0%, the heating temperature for solid solution treatment becomes extremely high, which is undesirable. On the other hand, if the content is less than 0.010%, the effect of the addition is poor, so 0.010 to 0.
．． The content was set to be within 10%.

Note that if the hot-rolling finishing temperature falls too low, burrs will occur, so even if the slab surface temperature T satisfies the range of formula (1) above, if this T decreases and there is a risk of burlap occurring, It is preferable to perform reheating after preliminary hot rolling.

(Example) The chemical composition (steel D-F) shown in Table 2 was obtained, and the thickness L was 15
Each slab of 0, 250, and 350 mm was subjected to pre-hot rolling under conditions where the slab surface temperature T (t>) and the first pass rolling reduction R (%) are shown in Table 3.

Then, hot rolling was completed according to a conventional method with or without reheating, and after pickling, a cold rolled sheet of 0.70 mm was obtained by the first cold rolling, and heated at 950 degrees, 5 m1.
After n intermediate annealing, the final plate thickness is 0.2 by second cold rolling.
After finishing it into a 3mm cold-rolled plate, it was heated to 820 degrees and 10m1n.
decarburization, primary recrystallization annealing, and final annealing at 1200°C for 50 hours.

Table 3 summarizes the results of examining the magnetic properties and sagging occurrence rate of each product sheet thus obtained, as well as the presence or absence of cracking during the hot rolling process.

As shown in Table 3, when the slab surface temperature T, the slab thickness, and the rolling reduction ratio R of the first pass in pre-hot rolling deviate from the conditions of formula (1), that is, when T is less than the lower limit, sample N014 and Cracks occurred in all samples No. 7, while samples No. 003 and No. 6, which exceeded the upper limit, both had a high occurrence of bald spots.

Further, when steel F in which the amounts of S and Se are less than the lower limit (sample No. 9.1O) is used, the magnetic properties are poor even if the condition of equation (1) is satisfied.

On the other hand, sample No. 1 obtained according to the present invention
.

No. 2.5, 8.11, and 12 had no cracks, a low rate of sagging, and excellent magnetic properties.

(Effects of the Invention) Thus, according to the present invention, a unidirectional silicon steel sheet having excellent magnetic properties, particularly iron loss properties, can be obtained without deterioration of surface properties.

Furthermore, in the present invention, there is no need to carry out surface care, which was conventionally considered unavoidable when preliminary hot rolling was performed under the condition of increasing the amount of inhibitor, thereby greatly contributing to labor saving and improvement in yield.

[Brief explanation of drawings]

Figure 1 is a graph showing the presence or absence of cracks and the incidence of sagging in relation to the slab thickness and the slab surface temperature T of the first pass. Figure 2 is a graph showing the slab surface temperature for cracks and line sagging. T and 1
It is a graph showing the relationship between the rolling reduction ratio R of the pass.

Claims (1)

[Claims] 1. Contains 0.010 to 0.060 wt% of C, 2.5 to 4.0 wt% of Si, and 0.010 wt% of at least one of Se and S as an inhibitor-forming element. ~0.10wt%
A unidirectional silicon steel slab containing silicon steel in the range of In manufacturing steel plates, the following (1) is applied to silicon steel slabs prior to the above hot rolling.
A method for producing a unidirectional silicon steel sheet with few surface defects and low iron loss, characterized by performing preliminary hot rolling treatment under conditions satisfying the formula. Note 130×(R+5)^1^/^4×logL≦T≦36
0800/[(110+R)・logL]...(1) where T: Slab surface temperature (℃) L: Slab thickness (mm) R: 1st pass rolling reduction (%)