JPS63195217A - Nonoriented electrical steel sheet having small iron loss after magnetic annealing - Google Patents

Abstract

PURPOSE:To manufacture a nonoriented electrical steel sheet having small iron loss after magnetic annealing, by specifying the ratio of the amt. of MnO to the total amt. of SiO2 MnO and Al2O3 in a nonoriented electrical steel sheet contg. specified percentages of C, Si, sol.Al, Mn, S, N and T.O. CONSTITUTION:When a nonoriented electrical steel sheet contg., by weight, <=0.015% C, 0.1-1.0% Si, 0.001-0.005% sol.Al, <=1.5% Mn, <=0.008% S, <=0.0050% N and <=0.02% T.O contains SiO2, MnO and Al2O3 as inclusions, the amt. of MnO is regulated to <=15% of the total amt. of SiO2, MnO and Al2O3. Thus, a nonoriented electrical steel sheet capable of attaining >=50mum average grain size after magnetic annealing and having small iron loss is easily obtd. at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties. Non-oriented electrical steel sheet is a full-process product manufactured so that the steel sheet already has the final magnetic properties when it is shipped from the steel mill, and a non-oriented electrical steel sheet that is manufactured in such a way that it already has the final magnetic properties when the sheet is shipped from the steel mill. It is classified into semi-processed products in which predetermined magnetic properties are revealed for the first time through magnetic annealing after processing, and the present invention relates to the latter.

(Prior Art) Non-oriented electrical steel sheets are widely used in electrical equipment such as generators, electric motors, and small transformers. However, recently there has been a demand for materials with even lower iron loss from the standpoint of energy conservation.

The main factor that determines the iron loss of non-oriented electrical steel sheets is Si+
It is known that the iron loss is the lowest when the An content and the crystal grain size are the same, and the crystal grain size is about 120 μm. This class of non-oriented electrical steel sheet has an average crystal grain size of about 5 to 20 μm at the time of shipment from the manufacturer, so the crystal grain size can be increased by magnetic annealing after processing such as punching at the customer. This will reduce iron loss.

By the way, inclusions in steel sheets include sulfides, nitrides, oxides, etc. These inclusions, especially fine inclusions, impede crystal grain growth during magnetic annealing in the customer, so must be reduced. First, desulfurization is essential as a method to reduce sulfides, and commonly known methods include adding various desulfurization agents during hot metal pretreatment, tapping, or vacuum degassing of molten steel. As a method for reducing zero-order nitrides, it is essential to reduce the N content, and a low nitrogen blowing method is generally known.

A generally known method for further reducing oxides is to vacuum degas the starting molten steel and deoxidize it with Aj, 3i, or the like. Furthermore, in addition to these general methods, fine Aj
Conventionally, the method of making N harmless is 5oLjV10
．． A method is known in which the content is set at 15% or more and fine AjN is not precipitated. On the other hand, Japanese Patent Publication No. 48-3055 discloses that silicon steel containing 0.3 to 2.0% of 5ijc has an acid-soluble M content of 0.001% or more (0.014-0.4X
(S, i) )% or less has been proposed.

This means that the content of soL At is (0,014-0,4
If it exceeds X (St)% and is less than 0.15%, it is difficult to coarsen the crystal grains during magnetic annealing due to the adverse effects of fine /'JN, resulting in unstable and inferior magnetic properties. Also,
In JP-A-61-119652, M is 0.15~
0.60%, and N is 0.60%. OO20% or less, S 0.
A method has been proposed in which 0 is set to 0.0025% or less, and 0 is set to 0.0020% or less. This means that N is less than 0.0020% and S
It is estimated that this is due to the effects of high purification by reducing the content to 0.0025% or less and prevention of precipitation of fine nitrides by adding M. In JP-A-54-163720, the IV is 0.
1% or less and B/N (boron content/nitrogen content) is 0.
．． 5 to 2.5, and a method of controlling N to 0.0100% or less has been proposed. This means that B is more N than AI.
This is because BN is generated because it has a strong affinity with BN, and BN does not precipitate finely and does not inhibit crystal grain growth.

On the other hand, in Japanese Patent Publication No. 56-43294, molten steel is vacuum degassed to reduce the carbon content in the steel to 0.015% or less and the oxygen content to 0.02% or less, and then silicon is removed without using aluminum for deoxidation. silicon content in the steel from 0.1 to 1.0.
%, the total aluminum amount is adjusted to 0.007% or less, and the iron loss is excellent, and the average magnetic permeability μI of the steel plate's warp and width
A method for obtaining a silicon steel plate with an S/So of 2500 or more is proposed. This is because the aluminum remaining in the steel exists in the form of various precipitates and inclusions, and these develop unfavorable crystal orientations that lower magnetic permeability during grain growth due to annealing. I'm imagining it.

(Problems to be Solved by the Invention) The iron loss obtained by the above-mentioned conventional technology is not satisfactory, and the present invention solves the drawbacks of the above-mentioned conventional technology and can be manufactured at an industrially low cost. This is a semi-processed non-oriented electrical steel sheet.

(Means for Solving the Problems) The present invention provides c:o, ots% or less, St: 0.1 to
1.0%, soj, Aj: 0.001-0.00
5%, Mn: 1.5% or less, S: 0.008% or less, N: 0.0050% or less, T, O: 0.02% or less, 5iOz+ in the steel
Non-directional with low iron loss that can make the average grain size after magnetic annealing 50 μm or more, characterized in that the ratio of the weight of MnO to the total weight of the three types of inclusions MnO and Ajz03 is 15% or less It is a magnetic steel sheet.

The present inventor has proposed that the content of 5oLA1 is 0.1% or less, and B
To provide a semi-processed non-oriented electrical steel sheet that does not contain additives and can be produced at low cost and has low iron loss after magnetic annealing (,75
After magnetic annealing at 0° C. for 2 hours, the core loss, average grain size, and inclusions of the product were investigated. Magnetic annealing is 750
℃ × 2 hours is the standard, but there are cases where continuous annealing is performed or the temperature conditions change by about ±50°C. In particular, it is important that excellent magnetic properties can be obtained even when the magnetic annealing conditions are shifted to the lower temperature side. The newly obtained findings will be explained below using 0.1% Si steel as an example.

■ Metal phase structure (1) in Figure 1 shows a product with poor iron loss after magnetic annealing (WI
S/S. ≧6.0 W/kg), (21 is a product with medium iron content (4.8 W/-≦W+s/so <6.
0 W/kg), (3) is a product with low iron loss (VL
An example of a gold phase structure with s/so < 4.8 W/kg) is shown. As is well known, the iron loss after magnetic annealing shows a good correlation with the crystal grain size, and the average crystal grain size of products with poor iron loss is approximately 1.
0 to 20 μl, the average grain size of products with medium iron loss is approximately 20 to 50 μl, and the average grain size of products with low iron loss is 5
It was found that it was more than 0μ.

■ Inclusions Figure 2 (a) is a scanning electron micrograph of inclusions in a product with poor iron loss after magnetic annealing, and Figure 2 (d) shows the inclusions taken using an energy dispersive X-ray analyzer W (EDX). The figure showing the results of the analysis using an energy dispersive X-ray analyzer (Fig. EDX), the same figure (C1 is a scanning electron micrograph of inclusions in a product with low iron loss, the same figure <n is an energy dispersive X-ray analysis system! It is a figure which shows the result of analysis using EDX).

In products with poor iron loss, many inclusions extending along the rolling direction were observed, which suppressed grain growth. These inclusions were also observed in products with medium iron loss, but the amount was smaller than in products with poor iron loss. In products with low iron loss, inclusions extending in the rolling direction were hardly observed, most of them were spherical, and grain growth was not suppressed.

As a result of analyzing these inclusions by EDX, it was found that StO□-M
It turned out to be an inclusion of the nO-u,o system.

Then, Aj, SlSMn are quantified, and from this, Sin,
, find the composition of Mn01AlzO1 and convert it to Si01S
The results plotted on a 10l-/V2O3 ternary system phase diagram are shown in FIG.

From this, inclusions in products with poor iron loss have a melting point of 1140
Many have a low melting point of ~1200℃, and the composition of inclusions in products with medium core loss is lower than that in products with low core loss.
It was found that inclusions in products with low iron loss and low nO content were found to have compositions with very low MnO content. Figure 4 shows the Sing-MnO phase diagram, which shows that the inclusions of products with medium iron loss contain more substances with low melting points than the inclusions of products with low iron loss. I know the name.

Therefore, the 5tOz-'MnOI'JzOz-based inclusions observed in products with poor iron loss and products with medium iron loss become molten or semi-molten during slab heating, and are rolled in the rolling direction during hot rolling. It has been newly discovered that this suppresses grain growth during magnetic annealing.

Figure 5 shows the chemical analysis of the content of Sing, Mn02A7to, in the product, the ratio of MnO to the total weight of three types of inclusions: SiO, MnO, and Altos, the average grain size, and the iron loss after magnetic annealing. W+s/s. This shows the relationship between Sin,,Mn01jV,0. M for the total weight of
If the nO ratio is 15% or less, the average grain size after magnetic annealing can be 50 μI or more, and for example, in a 0.1% Si steel, the iron loss is WIS/S. It can be seen that a low core loss of <4.8 W/kg can be obtained.

As stated above, the present inventor has discovered that SiO□, MnO in steel
.

By adjusting the weight ratio of MnO to the total weight of the three types of inclusions, IV and O, to 15% or less, the average crystal grain size after magnetic annealing can be made to be 50 μm or more. He invented non-oriented electrical steel sheets.

Now, here is an example of a method for manufacturing such a non-oriented electrical steel sheet.
The case where 00 is manufactured using a converter and a vacuum degassing device will be described. In the conventional method, 150 kg of Fe-Mn alloy was added at the time of steel tapping in the converter, but in the present invention, 300 kg of Fe-Mn alloy was added.
Added. As a result, molten steel is deoxidized by Mn, and Mn
Although nO is generated, MnO and MnO float to the surface during transport of molten steel from the converter to the vacuum degassing treatment equipment or during the first half of the vacuum degassing treatment for decarburization. Then, Al deoxidation is performed in the latter half of the vacuum degassing treatment, and then SL and Mn are added for the purpose of composition adjustment, but since Mn is added at the time of steel extraction from the converter, the Mn in the molten steel is Since the content of Mn is increased, the amount of Mn added for component adjustment during this period can be reduced, and the generation of MnO can be reduced. Through these series of treatments, in the method of the present invention, SiO2, MnO%M2
0. The ratio of MnO to the total weight of the steel was 15% or less, and low melting point inclusions were not generated, making it possible to facilitate crystal grain growth during magnetic annealing.

[Relationship with conventionally known technology]

Japanese Patent Publication No. 3055 is a technique for making /VN harmless, and the present invention also uses Sol and kl of 0.001.
% to 0,005%. However, in the present invention, it is essential to adjust the weight ratio of MnO to the total weight of the three types of inclusions of SiO□+MnO and AlzO3 in the steel to 15% or less.
Iron loss after magnetic annealing for i0.1% steel Wtszvo<4.
It is impossible to create a product with low core loss such as 8 W 7 kg, and the present invention is considered to be a step ahead in technology.

JP-A-61-119652 also discloses a technique for preventing the precipitation of fine AjN, and Aβ is 0.15% to 0.60%.
This is considered to be a technology different from the present invention, and M
Since the amount of addition is large, an increase in cost is unavoidable.

JP-A-54-163720 discloses the addition of B in order to prevent the precipitation of fine AjN, which is considered to be a different technology from the present invention, and also adds an expensive amount of B to avoid an increase in cost. No way.

Japanese Patent Publication No. 56-43294 is a technique for dealing with the adverse effects of aluminum precipitates and inclusions on core loss and magnetic permeability, and does not mention MnO at all. However, in the present invention, not only AlzO, but also (
Control of MnO is essential, and SiOz9 in steel
M relative to the total weight of three types of inclusions: MnO, kl, and 0+
Good core loss can only be obtained by adjusting the weight ratio of nO to 15% or less, and this can be interpreted as a different technology.

(Conditions of the present invention) The conditions and reasons for limitations of the present invention will be explained below.

[C]: If C exceeds 0.015%, it is not only harmful to the magnetic properties, but also causes significant magnetic aging due to the precipitation of C, deteriorating the magnetic properties.
% or less.

(Si): St is an element that increases the degree of decrease in iron loss as the amount added increases, but in the present invention, the grains are made coarser by magnetic annealing at about 700 to 800°C to reduce iron loss. To achieve this goal, the SL was set to 0.1 to 1.0%.

(soL Aj): If 5oLN is less than 0.001%, the amount of oxygen in the steel will be too large, and if it exceeds 0.005%, there will be a sufficient amount of Aj2N to suppress grain growth during magnetic annealing. For generation, 5oLAI was o,ooi~0.005%.

(Mn): Mn increases the hardness of the steel plate and improves the punching property.
However, the upper limit of 1.5% is for economic reasons.

[S]: S combines with Mn and Cu of the Trump element to form Mn.
Since it becomes S and CuzS and hinders crystal grain growth during magnetic annealing, it is preferable to have a small amount, and the content is set to 0.008% or less.

[N]: If N exceeds 0.008o%, a sufficient amount of IVN is generated to suppress grain growth after magnetic annealing, so N was set to 0.008o% or less. Preferably 0.0030
% or less.

(T, O): When T and O exceed 0.2%, oxides increase and hinder crystal grain growth during magnetic annealing, so 'r,0 was set to 0.02% or less. 7.0 amount within the range not exceeding the upper limit of 5oLN
It is desirable to reduce it as much as possible, and the effect is particularly significant when it is reduced to 0.015% or less.

(MnO) + (/VtO+) + (Sing)
: As already stated<, MnO+A7zOa+5i
If the weight ratio of MnO to the total weight of the three types of Oz inclusions exceeds 15%, inclusions with a low melting point will be generated, and these will melt or soften during slab heating, causing fine particles to form in the rolling direction during hot rolling. MnO+81z is divided into MnO+81z and a+
The ratio of the weight of MnO to the total weight of the three types of Sing inclusions was set to 15% or less.

MnO, A7zOs, other than siog, such as MgO,
There are oxides such as CaO and ZrOz that are unavoidably mixed in during steel manufacturing operations. Of course, it is preferable that the amount of these oxides be as small as possible.

Average grain size after magnetic annealing: It is known that when the ingredients are the same, the iron loss is the lowest when the grain size is approximately 120 μm, and the average grain size at the time of shipment from the manufacturer is 5. ~20μm, so the grain size is increased by magnetic annealing (doing so reduces iron loss, and the average grain size after magnetic annealing is 50μm).
If it is more than μm, for example, in the case of Si0.1% steel, WIS
/S. Since a product with low iron loss such as <4.8 W/kg can be obtained, the average grain size after magnetic annealing was set to 50 μm or more.

(Example) [Example 1] Slabs for non-oriented electrical steel sheets having various compositions containing 0.1% St were manufactured. Next, this was heated to 1180° C. in a continuous heating furnace and hot rolled to a thickness of 2.0 mm. This hot-rolled sheet was pickled, cold-rolled to a thickness of 0.5fi, and then final annealed in a continuous furnace at 775°C for 60 seconds.
Furthermore, magnetic annealing was performed at 750°C for 2 hours. Table 1 shows the component composition, content of inclusions, average grain size and magnetic properties after magnetic annealing of the product thus obtained. From this, the product of the present invention has an average grain size of 50μ after magnetic annealing.
It can be seen that the product can be made more than m and has low iron loss. In addition, according to the method of the present invention, slabs for non-oriented electrical steel sheets having various compositions containing Fe [Example 2] 0.7% St at the time of steel tapping in a converter were manufactured. Next, this was heated to 1150° C. in a continuous heating furnace and hot rolled to a thickness of 2.0 mm. This hot-rolled sheet was pickled, cold-rolled to a thickness of 0.5fl, and then final annealed in a continuous furnace at 780°C for 60 seconds.
Furthermore, magnetic annealing was performed at 750°C for 2 hours. Table 2 shows the component composition, content of inclusions, average crystal grain size after magnetic annealing, and magnetic properties of the product thus obtained. From this, the product of the present invention has an average grain size of 50μ after magnetic annealing.
It can be seen that it is a product that can be made even better than Yai and has less iron loss. In addition, in the method of the present invention, 300 kg of Fe-Mn alloy was added at the time of steel tapping in the converter, which is larger than the conventional method. In the subsequent vacuum degassing treatment, M deoxidation was performed in the latter half of the treatment, and then Si and Mn were added for the purpose of component adjustment, but in the present invention, Mn addition for component adjustment at this stage was The amount was reduced. On the other hand, the comparative method was conducted using a normal steel manufacturing method.

(Effects of the Invention) As detailed above, the present invention limits the composition and content of inclusions in a non-oriented electrical steel sheet, which facilitates grain growth during magnetic annealing and reduces iron loss at low cost. It is a non-oriented electrical steel sheet.

[Brief explanation of the drawing]

Fig. 1 (1) is a metallurgical micrograph showing the gold phase structure of a product with poor iron loss after magnetic annealing, (2) a product with medium iron loss, and (3) a product with low iron loss, respectively. Figure 2 (a) is a scanning electron metallurgical micrograph of inclusions in a product with poor core loss after magnetic annealing, and Figure 2 (d) is a scanning electron metallurgical micrograph of the inclusions in a product with poor iron loss after magnetic annealing. Figures showing the analysis results. Figure (b) is a scanning electron metallurgical micrograph of inclusions in a product with medium iron loss, and Figure (e) is a scanning electron metallurgical micrograph of the inclusions in a product with an energy dispersive X-ray analyzer (EDX). (C1 is a scanning electron metallurgical micrograph of inclusions in a product with low iron loss, and (f) is a scanning electron metallurgical micrograph of the inclusions in a product with low iron loss.) Figure 3 is a diagram showing the results of the analysis using the EDX). The composition of 5ift, MnO, and l'dt03 of the SiOz-MnOAJ!03 system inclusion is determined, and this is converted into the SiOSlol--Al2O2 ternary system phase diagram. A diagram showing the plotted results, Figure 4, shows 5fOz MnO
Figure 5 shows the state diagram of SiO2, MnO, and AZ in the product.
,0. Chemically analyzed the content of Sin, , Mn01IV
, the ratio of MnO to the total weight of the three types of inclusions, O,
Average grain size and iron loss WIS/S after magnetic annealing. FIG. Figure 3 MJNn(-'lI'flW)・J'711is
'・Jtl'' /, 7,755p (hmi
匈(〃-女) 0, fO, /(:40 Procedural Amendment (Spontaneous April 24, 1985 Commissioner of the Patent Office Black 1) Ming Xiong 1, Indication of Case 1988 Patent Application No. 29364 2 , Name of the invention: Non-oriented electrical steel sheet with low core loss after magnetic annealing 3, Relationship with the amended case Patent applicant: Nippon Steel Corporation, 2-6-3 (665) Otemachi, Chiyoda-ku, Tokyo Company Representative Takeshi 1) Toyoshi 4, Agent Address: 2-4-1-5 Marunouchi, Chiyoda-ku, Tokyo 100, Date of Amendment Order: Month, Day, 6, 1939, Detailed Description of the Invention in the Specification Subject to Amendment ( 1) Specification page 3 line 12 “sob, 8710.15
%” to “sat, IV to 0.15%”. (2) End of page 15 of the same paper: ``In addition, in the method of the present invention, FeJ is
300 kg of Mn alloy was added, which is more than before. In the subsequent vacuum degassing treatment, M deoxidation was carried out in the latter half of the treatment, followed by the addition of St and Mn for the purpose of component adjustment. The amount of Mn added was reduced.On the other hand, the comparative method was carried out using a normal steel manufacturing method.'' Procedural amendment (voluntary) August 19, 1988

Claims (1)

[Claims] 1) C: 0.015% or less, Si: 0.1 to 1.0%,
sol. Al: 0.001-0.005%, Mn: 1.
5% or less, S: 0.008% or less, N: 0.0050%
Below, T. In a non-oriented electrical steel sheet containing O: 0.02% or less, SiO_2, MnO, Al_2O_3 in the steel
A non-oriented electrical steel sheet with low core loss and capable of having an average grain size of 50 μm or more after magnetic annealing, characterized in that the ratio of the weight of MnO to the total weight of the three types of inclusions is 15% or less.