JPH03215627A - Production of nonoriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To obtain a medium- or low-grade nonoriented silicon steel sheet having superior magnetic properties by subjecting a steel in which Si content is reduced and respective contents of S, Ca, and REM are specified to hot rolling and then to low temp. finishing under specific conditions. CONSTITUTION:A steel having a composition consisting of, by weight, <=0.005% C, 0.10-1.40% Si, <=1.50% Mn, <=0.15% P, <=0.005% S, <0.20% Al, <=0.0030% N, Ca and/or REM so that Ca/S is 1-2 and Rem/S is 3-8, and the balance Fe with inevitable impurities is refined. This steel is cast continuously and then hot-rolled immediately. The resulting rolled plate is finish-rolled at a temp. of the Ar3 point or below and coiled at >=600 deg.C. After cold rolling, annealing is exerted at a temp. of the recrystallization temp. or above. Further, skin pass rolling is carried out at 2-15% rolling reduction, if necessary.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a non-oriented electrical steel sheet with excellent magnetic properties by directly hot rolling (hereinafter referred to as direct rolling) after continuous casting. It is something.

(Prior Art) Non-oriented electrical steel sheets are used as core materials for electrical equipment such as motors and transformers. There are intermediate to low grade materials with a JIS standard of less than 330%.

Intermediate to low-grade materials are required to have good magnetic properties and workability, and to be inexpensive. In addition, even if it is a low-grade material, high performance and power saving are required in refrigerators, vacuum cleaners, automobiles, compressors, etc. in which the motor is incorporated, so the magnetic properties of the material must be improved to fully meet this demand. This is very important.

In the conventional production of non-oriented electrical steel sheets, the slab is heated at a temperature of 1200°C or less prior to hot rolling to facilitate the growth of crystal grains and reduce core loss.
Prevent pN from solid solution during the slab heating step, and then
Prevents fine A and QN from precipitating (Unexamined Japanese Patent Publication No. 4
9-38814).

In the past, slab heating was essential before hot rolling.

By the way, recently, the so-called direct rolling method, which directly connects continuous casting and hot rolling, has been studied as a new technology, and efforts have begun to be made to save energy, but the target steel types are general steels that do not require relatively good material properties. Among these, JP-A-58-123825 proposes a method for manufacturing non-oriented electrical steel sheets in which a continuously cast high-temperature slab is kept at 900 to 1150°C for within 30 minutes and then hot rolled. There is. Although this proposal has the effect of shortening the heat retention time, this steel has a St content of 1.5 to 4.0% and an AΩ
: It is an electromagnetic steel containing 0.2 to 2%, and because it has a high transformation point, it is easily affected by transformation behavior during hot rolling, and the magnetic properties of the steel sheet vary in the width direction or length direction. Steel sheets with excellent properties cannot be obtained.

For these reasons, the current situation is that non-oriented electrical steel sheets are not manufactured using the direct rolling method.

(Problems to be Solved by the Invention) The present invention is a non-oriented electrical steel sheet of low St, intermediate to low grade, with good magnetic properties, by a direct rolling method in which continuously cast hot slabs are continuously hot rolled. The purpose is to obtain.

(Means for Solving the Problems) The present invention sets the St content as low as 0.1 to 1.2%, further defines the S content as a steel component, and adds Ca to this.
Alternatively, new knowledge has been found that non-oriented electrical steel sheets with good magnetic properties can be manufactured by the direct rolling method due to the synergistic effect of adding Rea in a specific ratio to the S content, specifying hot rolling conditions, and finishing at a low temperature. This was done based on. That is, in the present invention, in weight %, C: 0.005% or less, Si: 0.10
~1.40% or less, Mn: 1.50% or less, P: 0
．． 15% or less, S2 0.005% or less, Aj7:0.2
Less than 0%, N:. 0.0030% or less, further Ca,
Ca/S-1 to 2, ReII with one or two types of Rem
A steel containing 1/S-3 to 8 with the remainder consisting of iron and unavoidable impurities is melted and made into a slab by continuous casting, and the hot slab is immediately hot rolled to a temperature below Ar3 point. A non-oriented electrical steel sheet, which is finished by winding at a temperature of 600°C or higher, cold rolling, annealing at a temperature higher than the recrystallization temperature, and optionally skin bath rolling at a rolling reduction of 2 to 15%. The gist is the manufacturing method.

Next, the present invention will be explained in detail.

Since C is harmful to magnetic properties, it is limited to 0.005% or less.

Si has the effect of increasing specific resistance and lowering iron loss, but when its content increases, not only does the magnetic flux density decrease, but also the stability of the magnetic properties decreases when continuously cast hot slabs are directly rolled. Therefore, it should be set at 1.2% or less.

Mn is necessary to prevent hot embrittlement and is contained at an upper limit of 1.5% in order to have the effect of reducing iron loss.

P is contained in order to improve the punching property, but if the amount is too large, it will become brittle and cause edge cracking, so the content should be 0.1% or less.

When S forms fine sulfides, it inhibits grain growth during annealing, but in the present invention, as described later, 1 of Ca and Rem
Since it contains one or two species to make the sulfide harmless, 0.
Content up to 0.005% is permitted.

Allium is an effective element for reducing iron loss, but if it increases, it deteriorates the magnetic flux density, especially in the direct rolling method.
．． It needs to be less than 20%.

Since N deteriorates iron loss, it should be kept at 0.0030% or less.

Ca and Rem form sulfides at higher temperatures and in a shorter time than Mn, and these sulfides are less deformed during hot rolling and have the effect of reducing iron loss, so they are included. In relation to the S content, Ca/S must be 1 or more and Rem/S must be 3 or more. on the other hand,
If its content increases, not only will it increase costs, but it will also deteriorate iron loss, so Ca/S should be 2 or less, ReIII
/S shall be 8 or less.

Steel having the above-mentioned composition is melted using a conventional method such as a converter, and after continuous casting is made into a slab, the hot slab is immediately hot-rolled. In the present invention, one or two of Ca and Rem
Since it contains seeds, sulfides that inhibit crystal grain growth are not generated, and since SiA and Q are reduced, the magnetic flux density is high and the magnetic properties are stable.

Note that an auxiliary heating device such as an edge heater may be used to recover the temperature drop at the end of the slab after casting and before hot rolling.

In hot rolling, finish rolling is performed at a temperature below the Ar point,
This is to set the finishing temperature to below the Ar3 point in order to obtain a high magnetic flux density. Although the lower limit is not limited, it is desirable to be at least Ar, from the viewpoint of workability during hot rolling.

The winding temperature is set at 600° C. or higher to improve the growth of crystal grains due to precipitates.

After hot rolling, cold rolling is performed by a conventional method, and annealing may be performed after hot rolling or during cold rolling, if necessary. Note that the cold rolling reduction rate should not be too high from the viewpoint of magnetic flux density.

Annealing is performed at a temperature higher than the recrystallization temperature, and this is done to improve workability and magnetic properties.

After annealing, skin pass rolling is performed at a reduction rate of 2 to 15% as required. The lower limit of the rolling reduction is set at 2% to improve grain growth during strain relief annealing. However, if the rolling reduction rate is too high, grain growth becomes difficult, so the upper limit is set at 15%.

(Example) Slabs having the steel components shown in Table 1 were hot rolled using two methods: direct rolling and conventional reheat rolling. The hot rolling conditions are also shown in the same table. Next, 0.5m from 2.3+nm
After cold rolling to +g, continuous annealing was performed at 800°C. The magnetic properties of the obtained steel plate were measured and the results are shown in Table 2. As is clear from Table 2, the steel sheets manufactured by the method according to the present invention exhibited magnetic properties equivalent to those of the conventional reheat rolling method even in direct rolling, and good results were obtained.

Table 2 Next, samples 1 and 2.3 in Table 1 were subjected to a 6% skin bath after annealing, and the magnetic properties after strain relief annealing were measured. The results are shown in Table 3.

Table 3 As shown in Table 3, the steel sheets produced by the method of the present invention exhibit the same level of magnetic properties as those produced by the conventional method after skin pass rolling and strain relief annealing.

(Effect of the invention) According to the present invention, a non-oriented electrical steel sheet that has magnetic properties equivalent to those of the conventional reheating method can be produced by so-called direct rolling, which directly connects continuous casting and hot rolling. This can be achieved while fully enjoying the benefits.

Claims (1)

[Claims] 1) In weight%, C: 0.005% or less, Si: 0.10
~1.40% or less, Mn: 1.50% or less, P: 0.1
5% or less, S: 0.005% or less, Al: less than 0.20%, N: 0.0030% or less, and 1 of Ca and Rem.
species or two species, Ca/S=1-2, Rem/S=3-8
After melting the steel containing iron and unavoidable impurities in the range of 100 to 300 ml and making the steel into slabs by continuous casting, the hot slabs are immediately hot-rolled and finished at a temperature of Ar_3 or below6.
A method for producing a non-oriented electrical steel sheet, which comprises winding and cold rolling at a temperature of 00°C or higher, and annealing at a recrystallization temperature or higher. 2) In weight%, C: 0.005% or less, Si: 0.10
~1.40% or less, Mn: 1.50% or less, P: 0.1
5% or less, S: 0.005% or less, Al: less than 0.20%, N: 0.0030% or less, and 1 of Ca and Rem.
species or two species, Ca/S=1-2, Rem/S=3-8
After melting the steel containing iron and unavoidable impurities in the range of 100 to 300 ml and making the steel into slabs by continuous casting, the hot slabs are immediately hot-rolled and finished at a temperature of Ar_3 or below6.
1. A method for producing a non-oriented electrical steel sheet, which comprises winding and cold rolling at a temperature of 00° C. or higher, annealing at a recrystallization temperature or higher, and then skin pass rolling at a rolling reduction of 2 to 15%.