JPH0456731A - Production of grain-oriented silicon steel sheet excellent in iron loss characteristic - Google Patents

Abstract

PURPOSE:To provide remarkably low iron loss characteristics to a grain-oriented silicon steel sheet by first applying flattening annealing to a grain-oriented silicon steel sheet and then subjecting this sheet, simultaneously or independently, to stress relief annealing for removing the strain resulting from flattening annealing and coating baking annealing. CONSTITUTION:First, as a tension necessary to remove coil set in flattening annealing, a tension of 0.3-1.0kgf/mm<2> is applied to the cross section of a strip and continuous heat treatment is exerted at 650-850 deg.C for 10-60sec. Then, coating is applied to the flattened strip and a tension of <=0.3kgf/mm<2> introducing no strain to the strip is given, and this steel sheet is subjected to continuous annealing treatment which doubles as coating baking annealing and stress relief annealing at 750-900 deg.C for 10-60sec.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a grain-oriented silicon steel sheet having excellent magnetic properties, especially iron loss properties.

<Prior Art> Unidirectional silicon steel sheets, which are mainly used as iron core materials for transformers, are required to have both excellent magnetic properties and insulating film properties. In recent years, from the viewpoint of energy saving, it has been desired to have particularly good iron loss properties among magnetic properties.

The unidirectional silicon i-plate is cast into a slab, hot-rolled, cold-rolled and annealed, then wound into a coil and annealed at a high temperature of about 1200°C for a long period of time. At this stage of high-temperature, long-time annealing, a secondary recrystallized structure having (110)(001), ie, Goss orientation, is formed and a forsterite film forming a part of the insulating film is formed. The coil has coil sets (curling curls) due to long-term annealing at high temperatures, so in order to remove these and flatten the coil, flattening annealing is usually performed at about 800°C, which is a continuous heat treatment while applying tension to the strang. be done. In this case, a tension coating forming another part of the insulating film is applied prior to the planarization annealing, and this coating is baked simultaneously with the planarization annealing.

<Problems to be Solved by the Invention> In the prior art, the strang is heat-treated while applying sufficient tension to straighten the coil set, resulting in a so-called hot working state, and distortion remains in the strip. This distortion deteriorates the magnetic properties, especially the iron loss properties. When such a finished coil is formed into a transformer core and used, the wound core is strain-relief annealed at about 800°C, which reduces the deterioration of iron loss characteristics, but does not improve it sufficiently. Since the iron core is not subjected to strain relief annealing, it is used with deteriorated iron loss characteristics. In addition, in the case of wound iron cores, strain can be sufficiently removed if strain relief annealing is performed at a sufficiently high temperature exceeding 850°C, but in this case, the chemical components forming the tension coating, such as P and C.
It diffuses into the steel plate and becomes an impurity, which not only deteriorates the iron loss characteristics but also destroys the insulation film, impairing the adhesion to the steel plate.

An object of the present invention is to provide an annealing method for flattening a unidirectional silicon steel sheet that does not cause residual strain and therefore does not cause deterioration of iron loss characteristics.

<Means for solving the problem> Conventionally, flattening annealing and coating baking annealing were performed simultaneously under the same conditions, but in the present invention, flattening annealing is first performed, and then the strain introduced by flattening annealing is removed. It is intended to perform strain relief annealing and coating baking annealing simultaneously or separately.

That is, in the present invention, in the flattening annealing of a unidirectional silicon steel plate, firstly, a tension of 0.3 to 1.0 kgf/s is applied and held at 650 to 850°C for 10 to 60 seconds.
Continuous annealing is performed for the first time, and then a tension coating is applied at 750 to 900 °C while applying a tension of 0.3 kg f /mm2 or less, and 50 °C from the first annealing temperature.
This method of manufacturing a patent plate is characterized by performing a second continuous annealing at a temperature higher than 10°C for 10 to 60 degrees.

<Function> First, in flattening annealing, the tension required to remove the coil set is 0.3 to 1.0 k to the strip cross section.
gf/*- and subjected to continuous heat treatment for 10 to 60 seconds at a temperature range of 650 to 850''C.

If the tension is less than 0.3 kgf/1, the removal of the coil set is insufficient, while if it exceeds 1.0 kgf/1, the strain becomes too large to be removed in the subsequent strain relief annealing.

In addition, the lower limit of the flattening annealing temperature is limited because flattening will be insufficient if it is lower than 650"C.The strain relief effect will not be obtained unless the strain relief annealing temperature is increased by 50°C or more than the flattening annealing temperature. Therefore, the upper limit of the flattening annealing is set at 850°C, which is 50°C lower than the upper limit of the strain relief annealing temperature of 900°C, which will be described later.

The coating is then applied to the flattened strip, and the coating is baked and annealed for 60 hours at a temperature of 750° C. to 900° C. under a tension of 0.3 kgr/1 or less, which does not introduce strain to the strip. A continuous annealing treatment that also serves as strain relief annealing is performed.

The reason for limiting the annealing temperature is as follows.

The lower limit of strain relief and coating baking annealing is limited because if the temperature is lower than 750°C, the tension effect of the coating will not be obtained and the strain relief effect will be insufficient. Further, the upper limit is limited because the coating will be destroyed if the temperature is higher than 900°C.

Further, residual strain cannot be sufficiently removed unless strain relief annealing is performed at a temperature 50°C or more higher than the first annealing temperature.

In the present invention, it is also possible to independently insert strain relief annealing between the first annealing treatment and the second annealing treatment, that is, to perform the treatment in the order of flattening annealing → strain relief annealing → coating baking annealing. In this case, the higher the stress relief annealing is, the more advantageous it is, and the upper limit temperature can be 1200°C.

In any case, the objective can be achieved as long as the soaking time for annealing is 10 seconds or more. However, even if it is held for more than 60 volts, the effect is saturated, so the upper limit was set to 60 sec.

Next, the present invention will be explained based on experimental results.

First, the unreacted separating agent adhering to the surface of a 0.23 mm thick unidirectional silicon steel plate that had been finish annealed in a coil shape was washed with water and brushed. Next, the temperature was changed for each coil in the range of 600 to 900° C., and continuous heat treatment was performed for 10 seconds while applying a tension of 0.6 kg/1. Next, a tension coating was applied, and continuous heat treatment was performed at 10 temperatures while changing the temperature for each coil in the range of 700 to 900°C and applying a tension of 0.2 kgf/tJ.

Regarding these coils, we observed their shape in strip form, took cut samples to evaluate their coating properties, and measured their iron loss properties.

As a result, as shown in FIG. 1, it was found that low iron loss, good shape, and good coating properties could be obtained at the temperature opening indicated by the dotted line.

On the other hand, the coil after washing and brushing was subjected to the conventional method, that is, after applying the coating, continuous heat treatment was applied to the strip, which also served as flattening and baking the coating (0.6 kgf/ml).
For products that have been subjected to tensioning and fusing at 800°C for 110 days,
Iron loss W+7zs. =0.93w/kg, good shape and coating properties.

It is clear that the method of the present invention provides much better iron loss characteristics than the conventional method.

<Example> Example I First, the unreacted separating agent on the surface of a coil of 0.20 myn thick unidirectional silicon steel sheet that had been processed using known techniques from slab casting to final annealing was removed by water washing plunging. . This coil was divided into two parts, and one half was subjected to the conditions of the present invention, that is, 700' while applying a tension of 0.4 kgf/■-.
Continuous annealing was performed at C120 sec, then a tension coating was applied, and continuous annealing was performed at 820°C for 11 Osec while applying a tension of 0.1 kgf/-.

The other half was applied using the conventional method, that is, tension coating.
Then, continuous annealing was performed at 820° C. for 110 seconds while applying a tension of 0.4 kg f/mj.

As a result, good strip shape and coating characteristics were obtained for both coils, but the iron loss characteristics were WI7/811 = 0.91w/kg in the conventional method, whereas
In the method of the present invention, WIT/S. =0.81w/kg, which was extremely excellent.

Example 2 0 and 3 processed through the steps up to final annealing using known technology
First, unreacted separating agent was removed from a coil made of a unidirectional silicon steel plate having a thickness of 0 mm by water washing and brushing. Next, this coil was divided into two parts, and one half was processed using the method of the present invention, that is, 0.5k.
Apply a tension of gf/wj and perform continuous annealing at 800°C for 520 seconds, then apply a tension coating, then apply a tension of 0.1kgf/- and apply a static 900'C12
Continuous annealing was performed at 0 Scc.

The other half of the coil was subjected to a conventional method, that is, first, a tension coating was applied, and then continuous annealing was performed at 840° C. for 130 seconds while applying a tension of 0.6 kgf/−.

As a result, good strip shape and coating properties were obtained for all coils, but the conventional method had better strip properties than 1A'B7s. -1.13w/kg, whereas in the method of the present invention, W177s. -1.02w/kg, which was extremely excellent.

<Effects of the Invention> The present invention achieves extremely low iron loss characteristics at once by dividing the conventional continuous annealing that combines flattening and coating baking into continuous annealing that also serves as flattening annealing and strain relief coating baking. This makes it possible to apply this to grain-oriented silicon steel sheets. Therefore, it becomes possible to significantly reduce energy loss in the transformer, which is of great industrial value.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the temperature of flattening annealing, strain relief/coating baking annealing, strip shape, coating properties, and iron one-member properties.

Claims (1)

[Claims] In flattening annealing of unidirectional silicon steel sheet, first 0.3
650~ while applying a tension of ~1.0kgf/mm^3
The first continuous annealing was performed at 850°C for 10 to 60 seconds, and then a tension coating was applied and the weight was 0.3 kgf.
/mm^2 or less at a temperature of 750 to 900℃, and at a temperature 50℃ or more higher than the first annealing temperature.
A method for manufacturing a unidirectional silicon steel sheet having excellent core loss characteristics, characterized by performing a second continuous annealing for ~60 seconds.