JPH02240215A - Production of thin grain-oriented magnetic steel sheet - Google Patents

Abstract

PURPOSE:To improve magnetic properties and film characteristics by rolling a slab of silicon steel in which respective contents of C, Si, Mn, S, sol.Al, N, Cu, and Sn and applying decarburizing treatment and heat treatment in a nonoxidizing atmosphere under respectively specified temp. and time conditions. CONSTITUTION:A slab of silicon steel having a composition consisting of 0.06-0.10% C, 2.5-4.5% Si, 0.01-0.10% Mn, 0.01-0.04% S, 0.01-0.065% sol.Al, 0.005-0.01% N, 0.03-0.50% Cu, 0.03-0.50% Sn, and the balance essentially Fe is rolled to 0.25-0.15mm final thickness, to which decarburizing treatment is applied at a temp. represented by an equation for 1-10min. Subsequently, the resulting rolled sheet is subjected to heat treatment in a nonoxidizing atmosphere at 850-1050 deg.C for <=10min and then to final finish annealing, by which a grain-oriented silicon sheet is produced. By this method, a product in which secondary recrystallization is stabilized and which has excellent magnetic properties and superior film characteristics can be obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a thin unidirectional electrical steel sheet for the purpose of stabilizing secondary recrystallization of a thin unidirectional electrical steel sheet and improving magnetic properties and film properties. This is a method for manufacturing electrical steel sheets.

(Prior Art) Unidirectional electrical steel sheets used as core materials for transformers, etc. are produced by: - Finally, a steel billet containing predetermined necessary components is hot-rolled, then annealed once or twice or more. After repeated cold rolling to obtain the final plate thickness, decarburization annealing is performed, M,
It is manufactured by applying an annealing separator such as O and subjecting it to final annealing.

The main purposes of this decarburization annealing are: ■Decarburization;■
Three points are considered: forming primary recrystallized grains that lead to secondary recrystallization, and (2) generating a Sigh-based oxide layer to generate a forsterite film. For such decarburization annealing, the method described in JP-A-54-35117 improves magnetic properties by regulating the temperature increase rate of the temperature increase process in a decarburization atmosphere at 750 to 870'C. The method described in Japanese Patent Publication No. 54-24686, in which heat treatment is performed in a non-oxidizing atmosphere at 890 to 1050°C after decarburization treatment and before final annealing, and the atmosphere at the front and rear parts of the decarburization annealing process. The method described in Japanese Patent Publication No. 57-1575 and the like for changing the degree of oxidation are disclosed.

(Problems to be Solved by the Invention) In recent years, there has been an increasing demand for lower iron loss in grain-oriented electrical steel sheets, and for this reason, measures have been taken to reduce the thickness of the product sheets. However, due to thinning, conventional manufacturing methods inevitably lead to unstable secondary recrystallization behavior during the final annealing process, making it difficult to produce products with excellent magnetic properties with a thickness of 0.250 m or less. However, the present invention stabilizes secondary recrystallization by specifying the annealing temperature for each product plate thickness, compared to the conventional decarburization annealing technology, which has had the problem of being difficult to manufacture.
The present invention provides a method for manufacturing a thin grain-oriented electrical steel sheet that has good magnetic properties and film properties.

(Means for Solving the Problems) The present invention relates to decarburization annealing conditions in the manufacturing process of grain-oriented electrical steel sheets as described above.

Conventionally, the final plate thickness range is annealed at a temperature within a predetermined range, and secondary recrystallization becomes unstable. , had not been disclosed. For example, the method described in Japanese Patent Publication No. 571,575 can also be used when the final plate thickness becomes thinner.
By changing the degree of oxidation in the atmosphere, it is possible to reduce the
This paper presents a manufacturing method for the final plate thickness of
Although the method described in JP-A-57-41326 specifies the amount of forsterite, the method only indicates the atmosphere during decarburization annealing, the amount and quality of Mg0O, and the atmosphere for final finish annealing. In contrast, the present invention adopts an annealing temperature that corresponds to the final plate thickness.
The present invention presents a method for stably manufacturing thin unidirectional electrical steel sheets with a thickness of 250 rsta or less.

First, the experiments that led to the present invention and their results will be explained.

The electromagnetic steel slab having the composition range according to claim 1 is 1.8 to 2.
After hot rolling to 3 m, homogenizing annealing → cold rolling → intermediate annealing, the steel was heated at 100 to 400°C with a rolling reduction of 80 to 95%.
The steel sheet was rolled to a final thickness of 0.13 to 0.22 tm while maintaining the temperature of the sheet. Stability of secondary recrystallization of the products obtained by decarburizing them for 3 minutes at a temperature range of 760 to 860 degrees Celsius, followed by heat treatment for 1 minute in a non-oxidizing atmosphere at 900 degrees Celsius, and then final annealing. and iron... are shown in Figure 1. It can be seen that in the temperature range of 760 to 860°C, decarburization was performed well in almost all the samples, but as the final plate thickness became thinner, the temperature range in which secondary recrystallization was stabilized became narrower. Furthermore, it has been revealed that the level of iron loss varies depending on the decarburization treatment temperature, and that secondary recrystallization is stable and iron loss is good at decarburization annealing temperatures that vary depending on the final plate thickness.

Ta.

Inferring the reason for this experimental result, it seems that among the three main purposes of decarburization annealing mentioned earlier, it improves "■generating a Sing-based oxide layer to generate a forsterite film". Conceivable. First of all, with regard to ``performing decarburization'', in this annealing temperature range, decarburization is fairly stable, and decarburization itself is not improved. In addition, "■ Forming primary recrystallized grains that lead to secondary recrystallization" is ensured by heat treatment in a non-oxidizing atmosphere at 900°C following decarburization annealing, and is due to the difference in the previous decarburization temperature. It can be said that the impact is small. Now, regarding the improvement of "■Generating a 5-inch oxide layer to generate a forsterite film," it is assumed that there is an optimal quality and quantity of the SiO□-based oxide layer depending on the final plate thickness. Ru. That is, the Sth-based acid layer that affects the stability of secondary recrystallization (near the secondary recrystallization start temperature during the final annealing process, atmospheric nitrogen
The amount of 5i02-based oxide layer that penetrates into the steel sheet through the Sing-based oxide layer and exists as an inhibitor/'JN fluctuates) and the amount of the 5i02-based oxide layer that affects the iron loss value (correlation between the tension effect of the forsterite film and the space factor) differs depending on the final plate thickness, and it is thought that it became possible to manufacture thin unidirectional electrical steel sheets only when it was optimized.

The basis for limiting the range will be explained below.

The lower limit of C is 0.0 as the limit at which secondary recrystallization becomes unstable.
060%, and the upper limit was set to 0.100% because the time required for decarburization annealing would be too long, which would be economically disadvantageous.

Si is added to increase electrical resistance and reduce iron loss value, and its lower limit is 850~ after decarburization treatment in the decarburization annealing process.
During heat treatment at 1050°C in a non-oxidizing atmosphere, α-γ
The content was set at 2.5% so that there would be no structural change due to transformation, and the upper limit was set at 4.5% due to the workability limit of cold rolling, etc.

Mn, Cu, S are Mn3. as inhibitors.
These are the elements necessary to form CuxS, and the lower limit is 0.0 to ensure the absolute amount of each as an inhibitor.
01%, 0.03%, 0.01%, and the upper limit is M
n is 0.10% at compaction temperature, Cu is 0.50 at pickling property.
%, S is 0.04% to avoid hot cracking troubles.
limited to.

sol, N, and N are elements necessary to form A7N as an inhibitor.
, kl is 0.010~0.065%, N is 0.005~
It was limited to 0.010%.

Sn segregates at grain boundaries and stabilizes secondary recrystallization, but the lower limit is set at 0.03% as the limit at which the amount of segregation becomes insufficient.
The upper limit was set at 0.50% because it would be economically disadvantageous.

Next, the decarburization annealing in the invention according to claim 1 employs the method described in Japanese Patent Publication No. 54-24686 disclosed by the present inventor, that is, decarburization in a decarburization atmosphere at 750 to 870°C. It is based on two-stage annealing in which carbon treatment is followed by heat treatment in a non-oxidizing atmosphere at 890-1050°C. Regarding the decarburization treatment temperature, the final plate thickness is 0.
780 based on experimental results for products specified as 25mm or less
The heat treatment in a non-oxidizing atmosphere is limited to ~850°C.
Similarly, based on the results of experiments with products in which the final plate thickness was specified to be 0.25 tm or less, the limit was set at 850 to 1050°C. The invention of claim 1 expresses the basic content of the present invention, and the invention of claim 1 represents the basic content of the present invention.
As derived from the results in the figure, when the final plate thickness is 0.25 m or less (0.15 am or more), the decarburization treatment temperature is determined according to the final plate thickness as follows: This shows that there is an optimal value for representing the value.

On the other hand, the time for the decarburization process is set at a lower limit of 1 minute, which is the minimum time required to complete decarburization and to generate an appropriate Sin and oxide layer, and an upper limit of 1 minute to limit excessive oxide layer formation. for 10 minutes. In addition, in heat treatment in a non-oxidizing atmosphere, the
The duration was limited to 0 minutes or less. This is because if the heating time is longer than that, deterioration of magnetism and reduction in productivity will occur. The decarburization annealing atmosphere is 780 to 850℃ during decarburization treatment.
It is sufficient as long as the degree of oxidation allows decarburization to proceed sufficiently, and in the subsequent heat treatment at 850 to 1050°C, it is sufficient as long as it is a non-oxidizing atmosphere that suppresses the progress of oxidation as much as possible; these are not particularly restricted. .

The invention of claim 2 takes into consideration the improvement of productivity in addition to the improvement of characteristics provided by the invention of claim 1. That is, the invention of claim 2 optimizes the decarburization temperature according to the thickness of the plate like the invention of claim 1, but in the latter half of the decarburization process, by raising the temperature to 835 to 850°C. ,5i02
The time required for the generation of the system oxide layer is shortened, making it possible to improve productivity. However, if productivity is to be improved by the three-step temperature conditions in the invention of claim 2, the decarburization treatment temperature is lowered from 780 to 850 depending on the final plate thickness.
The required time at ℃ may be determined based on the following consideration.In other words, the required time at the decarburization treatment temperature, which is lowered according to the final plate thickness, is the time needed to complete the decarburization process. It is sufficient to increase the time, and after that, it is possible to increase the temperature and shorten the time to the time necessary to ensure the production of the 5ta2-based oxide layer in the optimum quantity and quality, thereby improving productivity. On the other hand, when carrying out the process under three-stage temperature conditions, the initial temperature is as claimed in claim 1.
Good results may not be obtained if the temperature is outside the range, or if the time is too short even if it is within the range, this is because decarburization is not completed and a 5iO1-based oxide layer is formed. It is hypothesized that this is caused by an increase in the quality of the StO□-based oxide layer, which affects the density of the forsterite film.

The reason why the plate thickness was limited was that the upper limit was set to 0.25 am in order to obtain good magnetic properties, and the lower limit was set to 0.15 m in view of secondary recrystallization and magnetic stability based on experimental results.

Regarding the manufacturing process, a hot-rolled sheet manufactured by a conventional method is subjected to precipitation treatment, and then cold-rolled at a strong rolling rate of 80 to 95% to obtain the final sheet thickness, or if the rolling method is performed twice or more, 40% After performing rolling→precipitation treatment at a rolling rate of 80 to 95%, final cold rolling is performed at a hard rolling rate of 80 to 95% to obtain a predetermined final plate thickness, and the decarburization annealing of the present invention is performed.

Next, an annealing separator containing MgO as a main component is applied to this steel plate, and then final annealing is performed to perform secondary recrystallization and purification, followed by tension coating.

(Example 1) c: o, oso%, St: 3.23%, M
n: 0.076%, SX0.025%, so
l, fiJ: 0.025%, N: 0.
0086%+ Sn: 0.12%, Cu: 0.07%
2, 30 mm hot rolled sheet containing
Cold rolling (intermediate thickness 1.55m1, final thickness 0.22111
111) ■860℃×180sec■850℃×180sec
■835℃×180sec0800″(: X 180
A decarburization annealing experiment was performed by performing decarburization treatment under various conditions for 10 seconds, followed by heat treatment at 880° C. for 60 seconds in a non-oxidizing atmosphere. Thereafter, a known annealing separator application, final finish annealing, and tension coating were applied to obtain a unidirectional electrical steel sheet. The results are shown in Table 1.

From the results in Table 1 and Table 2, it can be seen that by following the method of the present invention, better magnetic properties and film properties can be obtained than by the conventional method.

(Example 2) C: 0.080%, Si: 3.23%, Mn
: 0.076%, 880.025%, sol, k
l: 0.025%, N: 0.0086%,
A hot rolled sheet of 2,3011m+ containing Sn: 0.12% and Cu: 0.07% was annealed twice and cold rolled (intermediate sheet thickness 1.40 mm, final sheet thickness 0.17 aa), 0835℃X 180sec■820℃X 180sec
c■800℃×180sec■800℃×90sec
A decarburization annealing experiment was performed by performing decarburization treatment under various conditions of +835°C for 60 seconds, followed by heat treatment at 880°C for 60 seconds in a non-oxidizing atmosphere. Thereafter, a known annealing separator application, final finish annealing, and tension coating were performed to obtain a unidirectional electromagnetic w4ttyi. The results are shown in Table 2.

Table 2 From the results in Table 2, it can be seen that according to the present invention, better magnetic properties can be obtained compared to the conventional method, and according to the second invention, productivity can be improved by reducing time. I understand that.

(Effects of the Invention) According to the present invention, there is an effect that secondary recrystallization is stable, and thin products of unidirectional electrical steel sheets with excellent magnetic properties and good film properties can be manufactured.

[Brief explanation of drawings]

FIG. 1 shows the stability of secondary recrystallization and iron loss values when the decarburization treatment temperature is changed for materials with different final plate thicknesses. 〔Usage Guide〕

Claims (1)

[Claims] (1) C: 0.060~0.100%, Si: 2.5~
4.5%, Mn: 0.01-0.10%, S: 0.01
~0.04%, sol. Al: 0.010-0.065
%, N: 0.005-0.010%, Cu: 0.03-
A magnetic steel slab containing 0.50%, Sn: 0.03-0.50%, balance iron and unavoidable impurities is hot rolled, and cold rolled once or twice or more with intermediate annealing in between. , final plate thickness of 0.25-0.15mm, 780-8
After decarburizing for 1 to 10 minutes in a decarburizing atmosphere at 50°C, heat treatment for 10 minutes or less in a non-oxidizing atmosphere at 850 to 1050°C, and then final annealing to produce unidirectional electromagnetic A method for manufacturing a thin unidirectional electrical steel sheet, characterized in that the decarburization treatment temperature of the decarburization annealing is carried out at a temperature that satisfies the following formula [1] depending on the final sheet thickness. T-807 = 700 (t-0.186) [T: annealing temperature (°C), t: final thick plate (0.15-0.251)] [1
] (2) The decarburization process of the decarburization annealing is divided into two stages, the first stage being carried out at a temperature according to formula [1] of claim 1, and the second stage being carried out at a temperature of 835°C.
The method for manufacturing a thin grain-oriented electrical steel sheet according to claim 1, which is carried out at a temperature of ~850°C.