JPS6318087A - Production of grain-oriented silicon steel sheet having small iron loss - Google Patents

Abstract

PURPOSE:To stably produce a grain-oriented silicon steel sheet having superior iron loss characteristics by pickling a grain-oriented silicon steel sheet subjected to finish annealing to form a surface having proper relative-specular glossiness and a proper amount of oxygen stuck and by carrying out mirror polishing. CONSTITUTION:A purified grain-oriented silicon steel sheet subjected to finish annealing is pickled with hydrochloric acid or the like to remove an oxide film remaining on the surface of the steel sheet and to form a surface having <=30% relative-specular glossiness at 20 deg. and <=0.1g/m<2> oxygen stuck. The surface of the steel sheet is then then mirror-finished by mirror polishing. Thus, a satisfactory smooth surface is formed and a grain-oriented silicon steel sheet having further improved iron loss characteristics is obtd.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing unidirectional silicon steel sheets, and the present invention relates to a method for producing unidirectional silicon steel sheets, and the present invention provides an advantageous method for improving iron loss characteristics by adding innovations to the pickling process during the production process and (to). This is an attempt to make further improvements.

(Prior art) The magnetic properties required of unidirectional silicon steel sheets, which are mainly used for iron cores such as transformers, are high magnetic flux density at a constant magnetizing force (represented by the e+ value). , and low iron loss at a constant magnetic flux density (represented by the value WI?/S). Particularly recently, there has been an increasing demand for products with low heat loss and low core loss characteristics from an energy cost perspective.

As a conventional method for manufacturing a unidirectional silicon steel sheet, Si is, for example, 2.0 to 4. A material containing Owtχ (hereinafter simply expressed as %) was hot-rolled, the final thickness was obtained by cold rolling once or twice including intermediate annealing, and after decarburization annealing, M
After applying an annealing separator mainly composed of gO, it is wound into a coil, and then secondary recrystallization annealing and purification annealing are performed.
Thereafter, a phosphate-based insulating coating is usually applied as needed.

In addition, during the purification annealing described above, the oxidation layer mainly composed of 5i02 generated on the surface of the steel sheet after decarburization annealing is reacted with MgO in the annealing separator to form forsterite.
(Mg2SiO4) coating is also formed.

By the way, iron loss consists of hysteresis loss and eddy current loss. Of these, eddy current loss can be reduced by introducing artificial grain boundaries by laser irradiation, but hysteresis loss can be reduced by introducing artificial grain boundaries such as those described above. Once present, it is difficult to reduce it. Regarding this point, for example, as disclosed in Japanese Patent Publication No. 52-24499 and Japanese Patent Publication No. 56-4150, substances that increase hysteresis loss such as a forsterite film are removed and the surface is mirror-finished by an appropriate method. It is known that iron loss can be reduced by this.

Furthermore, if a laser method or the like is applied to such a mirror-finished material, further reduction in iron loss value can be achieved.

(Problems to be Solved by the Invention) This invention was developed in view of the above-mentioned circumstances, and is a unidirectional technology that achieves further improvement in iron loss characteristics by obtaining a good smooth surface. The purpose of this paper is to propose a method for manufacturing silicon steel sheets.

(Means for solving problems) First, the background to the elucidation of this invention will be explained.

After removing the oxide film present on the surface of the steel sheet, possible methods of mirror-finishing the surface include mechanical polishing using a puff or brush, chemical polishing that dissolves the surface chemically, and electrolytic polishing that dissolves the surface electrochemically. .

Among these methods, when using mechanical methods, it is difficult to polish the steel plate without causing distortion, so processing distortion remains.
Such residual strain cannot be completely removed even if strain relief annealing is performed afterwards, and therefore, due to the residual strain and the oxidized layer on the surface layer generated by annealing, chemical polishing or electrolytic polishing with the same smoothness cannot be achieved. Its magnetic properties are inferior to other materials. Therefore, in order to obtain a stable reduction in core loss, mirror polishing by chemical polishing or electrolytic polishing is preferred.

As a mirror material, there is a method of mirror polishing without pickling using a material without a forsterite undercoat as disclosed in Japanese Patent Publication No. 60-39123, but according to the research of the inventors. It has been found that even for such materials, if appropriate pickling is performed, the amount of reduction in iron loss after subsequent polishing is greater.

The reason for this is that when mirror polishing is performed without pickling, oxides mainly consisting of SiO2 that remain partially on the surface impair the uniformity of polishing, and as a result, the reduction in iron loss is small ( considered to be a thing.

Conventionally, the surface condition after pickling was not controlled, so a stable mirror surface condition could not be obtained.

Therefore, the inventors studied various pickling conditions and found a new method that can achieve a good reduction in core loss by subsequent mirror polishing, and have completed this invention.

That is, the present invention provides a unidirectional silicon steel plate which has a finish-annealed unidirectional silicon steel plate, removes the oxidized layer on the surface by pickling treatment, and then performs mirror polishing treatment to provide a mirror finish surface. During manufacturing, the copper plate surface is polished to a 20 degree specular gloss of 30% in the above pickling treatment.
This is a method for producing a low core loss unidirectional silicon steel sheet, which comprises finishing the sheet to an oxygen basis weight of 0.1 g/aa" or less.

The experimental results that led to this invention will be explained below.

A 0.23 m thick steel plate containing 3.35% St was decarburized and annealed, then wound into a coil using an annealing separator mainly composed of alumina, and then subjected to secondary recrystallization annealing and purification annealing. The finished annealed plate was subjected to strain relief annealing at 800°C in Nt in order to remove the coil winding curl, and then
Figure 1 summarizes the results of investigating the amount of change in iron loss when pickling was performed in a 0% hydrochloric acid bath at various treatment temperatures and times.

After pickling, the amount of surface oxygen on both sides of the steel sheet, that is, the amount of oxygen per unit area, was less than O.1 g/m''.In addition, changes in iron loss due to reduction in sheet thickness were corrected, and the influence of surface conditions on iron loss was In the figure, negative values indicate that the iron loss is lower after pickling than after strain relief annealing.

Figure 2 also shows JIS Z of the same material after pickling.
The results of examining 20 specular gloss using the gloss measurement method specified in 8741 are shown below.

As is clear from the results shown in Figures 1 and 2,
The iron loss reduction effect is more pronounced as the pickling treatment is carried out at higher temperatures and for longer periods of time, and the gloss is also increased.

According to these results, it is expected that performing mirror polishing after long-term pickling at high temperatures is advantageous in obtaining a good iron loss value.

Therefore, we investigated the iron loss value after chemically polishing the same material after pickling to a depth of 6 μm per side in a Hgo□10F bath, and found that it was actually pickled at a low temperature as shown in It was found that the effect of reducing iron loss by polishing was greater in the case of polishing.

In order to elucidate the cause of this, we observed the surface after pickling using a scanning electron microscope and found that when pickling is carried out at high temperatures and for a long time, although the smoothness within the secondary recrystallized grains progresses, the ridge-like steps remain. It was observed that they were formed in some places. During polishing, this part dissolves preferentially, resulting in insufficient mirror polishing as a whole.On the other hand, when the temperature is low, fine oxygen parts exist all over the surface, but their depth is Because it is shallower than pickling, the mirror-like state becomes more uniform after polishing, which is thought to have a greater effect of reducing iron loss.In addition, this phenomenon is also responsible for the phenomenon in which the gloss level increases with pickling at high temperatures. Consistent with observations.

Next, FIG. 4 shows the final change in iron loss after pickling and mirror polishing in relation to the 20 degree specular gloss after pickling.

As is clear from this figure, a stable reduction in iron loss is observed when the specular gloss after pickling treatment is 30% or less. On the other hand, if it exceeds 30%, the effect of reducing iron loss will be small.

Therefore, in this invention, the surface condition after pickling treatment is
The range was limited to 30% or less in terms of 0 degree surface gloss.

However, according to the inventors' research, simply specifying the surface glossiness cannot necessarily improve the iron loss characteristics as much as expected, and in order to stably achieve the iron loss reduction effect, it is necessary to It was found that the amount of oxygen on the surface of the steel sheet after pickling (hereinafter referred to as oxygen basis weight) also needs to be regulated.

Figure 5 shows that the 20 degree specular gloss was all below 30%, but the oxygen basis weight was variously changed after pickling.
Thereafter, the iron loss change of the product plate obtained by chemical polishing of 6μ on one side in a H,0□÷HF bath is shown in relation to the oxygen basis weight after pickling.

As is clear from the figure, even if the 20 degree specular gloss after pickling is less than 30%, if the oxygen basis weight exceeds 0.1 g/m'' on both sides of the steel plate, it will be satisfactory. No reduction in iron loss can be expected, and a stable reduction in iron loss cannot be achieved by simply reducing the 20 degree specular gloss to 30% or less (and limiting the oxygen basis weight to 0.1 gemz or less) It is.

Therefore, in this invention, the oxygen basis weight on the surface of the steel sheet after pickling is also limited to 0.1 g/s+'' or less.

(Function) Next, the manufacturing process of the unidirectional silicon steel sheet according to the present invention will be explained.

The starting material is a conventionally known unidirectional silicon steel material, such as ■C: 0.01~0.05%, St: 2.0~
4.0%, Mn: 0.01-0.2%, Mo:
0.003-0.1%, Sb: 0.005-0.
2%, one or two types of S or Se, 0.0
Composition containing 05-0.05% ■C: 0.01-0
．． 08%, Si: 2.0-4.0%, S: o
, oos~0.05%, N: 0.001~0.01
%, Sol Al: 0.01-0.06χ, Sn:
0.01-0.5%, Cu: 0.01-0.3
%, Mn: Composition containing 0.01 to 0.2% ■C
: 0.01-0.06%, Si: 2.0-4.
0%, S: 0.005-0.05%, B: 0.
0003-0.0004%, N: 0.001-0.
Composition containing 0.01%, Mn: 0.01-0.2% ■C: 0.01-0.06χ, St: 2.0-4
．． 0%, Mn: 0.01-0.2% O, oos-0.0% in total of one or both of S or Se.
Next, the hot-rolled sheet is subjected to homogenization annealing at 800 to 1100°C.
One-time cold rolling method, in which the final plate thickness is obtained by two cold rolling steps, or two-step cold rolling method, in which intermediate annealing is usually performed at 850°C to 1050°C, and then further cold rolling is performed.In the latter case, the first rolling rate is 50
% to about 80%, the final rolling reduction is about 50% to 85%, and the final cold rolled plate thickness is 0.15 m to 0.35 m.

After finishing the final cold rolling, the steel plate finished to the product thickness is subjected to decarburization and primary recrystallization annealing treatment in wet hydrogen at 750°C to 850°C after surface degreasing.

After that, Al tOs＊Zro□ or T is applied to the surface of the steel plate.
Apply an annealing separator mainly composed of iO□ or the like. In the case of this invention, since it is advantageous not to form a forsterite film after final annealing, AI! It is desirable to increase the content of an inert annealing separator such as TO3.

After that, secondary recrystallization annealing is performed, but this step is (110)
This is done to sufficiently develop secondary recrystallized grains with <001> orientation, and is usually box annealed to immediately
This is done by raising the temperature above ℃ and maintaining it at that temperature.

In this case, in order to develop a highly uniform secondary recrystallized grain structure in the (110) <001> orientation, the
It is more advantageous to carry out retention annealing at a low temperature of 00°C, and in addition, for example, 0.5-b annealing may be used.

Purification annealing after secondary recrystallization annealing is performed at 1100°C in dry hydrogen.
It is necessary to perform annealing for 1 to 20 hours to achieve purification of the steel plate.

Next, pickling treatment is performed to remove the oxide film remaining on the surface of the steel sheet, and in this invention, the pickling process reduces the 20' specular gloss to 30% or less and reduces the oxygen basis weight to O.
, Ig/mz or less.

In order to keep the glossiness condition and oxygen basis weight within the specified range, various acids such as hydrochloric acid, sulfuric acid, nitric acid,
It is important to use phosphoric acid or the like and determine the concentration, treatment temperature, and time appropriately depending on the material and equipment. Preferred concentrations are 5-25% for hydrochloric acid, 5-70% for sulfuric acid, 5-40% for nitric acid, and 5-85% for phosphoric acid. Further, a suitable treatment temperature is room temperature to 95°C.

Thereafter, the surface of the steel plate is finished to a mirror-like state, that is, to a center line average roughness Ra of approximately 0.4 μm or less, by chemical polishing or electrolytic polishing.

(Example) Example I C: 0.045%, Si: 3.33%, Se
: 0.020%, sb: 0.025% and MO:
After hot rolling a steel slab with a composition containing 0.0% and 0.000%, it is cold rolled twice including intermediate annealing to achieve a composition of 0.000%.
The final plate thickness was 23 m.

Then, after decarburization annealing, A f 2 was applied to the surface of the steel plate.
After applying an annealing separator containing O3 as a main component, it was wound into a coil, and subjected to secondary recrystallization annealing and then purification annealing.

This material was then treated with 10% hydrochloric acid (temperature 85°C) under various pickling conditions shown in Table 1.
Subsequently, chemical polishing of 6 μm per side was performed in a HzOg+HF bath.

The results of investigating the magnetic properties of the product board thus obtained are shown in Table 1 along with the 20 degree specular gloss after pickling treatment, the oxygen basis weight, and the magnetic properties after pickling.

As is clear from the same table, particularly good magnetic properties are obtained when the 20 degree specular gloss and oxygen basis weight after pickling satisfy the appropriate ranges of the present invention.

Actual mλ C: 0.042%, Si: 3.18%, Se:
0.019%, Sb: 0.024% and Mo
: A steel slab with a composition containing 0.012% is hot-rolled and then cold-rolled twice including intermediate annealing to achieve a composition of 0.23%.
The final plate thickness was M. After decarburization annealing,
An annealing separator containing AIIZO3 as a main component was applied to the surface of the steel plate, the steel plate was wound into a coil, and subjected to secondary recrystallization annealing and then purification annealing.

Thereafter, this material was treated with 15% sulfuric acid (temperature 60°C) under various pickling conditions shown in Table 2, and then electrolytically polished in a mixed solution of phosphoric acid and chromic acid to a 6 μm roughness on one side. Polished the rock.

The results of investigating the magnetic properties of the product board thus obtained are shown in Table 2 together with the 20 degree specular gloss after pickling treatment, the oxygen basis weight, and the magnetic properties after pickling.

(Effects of the Invention) Thus, according to the present invention, a grain-oriented silicon steel sheet having excellent magnetic properties, particularly iron loss properties, can be stably obtained.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the pickling time in the pickling process and the change in iron loss of the steel plate after pickling, using the pickling temperature as a parameter, during the manufacturing process of grain-oriented silicon steel sheets. Figure 2 is a graph showing the relationship between pickling time and 20 degree specular gloss after pickling, using pickling temperature as a parameter. Figure 3 is a graph showing the relationship between pickling time and 20 degree specular gloss after pickling. A graph showing the relationship between the change in iron loss using pickling temperature as a parameter. Figure 4 is a graph showing the relationship between the 20 degree specular gloss after pickling and the change in iron loss of the product board. FIG. 5 is a graph showing the relationship between the oxygen basis weight on the surface of the steel sheet and the amount of change in iron loss after pickling.

Claims (1)

[Scope of Claims] 1. A unidirectional silicon steel plate having a finish-annealed unidirectional silicon steel plate, the oxidation layer on the surface of which is removed by pickling treatment, and then subjected to mirror polishing treatment to provide a mirror-finished surface. In manufacturing a steel plate, the above pickling treatment is characterized in that the surface of the steel plate is finished to a state where the 20 degree specular gloss is 30% or less and the oxygen basis weight is 0.1 g/m^2 or less. A method for producing a low iron loss unidirectional silicon steel sheet.