JP3362077B2 - Smelting method of molten steel for non-oriented electrical steel sheets with low iron loss - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing molten steel for producing low-Si non-oriented electrical steel sheets, and more particularly to a method for obtaining a product with low iron loss. To propose the results of research and development on out-of-pile refining methods such as pot refining. [0002] Non-oriented electrical steel sheets are used as iron cores for rotating machines and transformers. In order to increase the energy efficiency of these rotating machines and transformers to achieve energy saving and high efficiency, it is necessary to reduce the iron loss of the non-oriented electrical steel sheet. Here, to reduce the iron loss of the non-oriented electrical steel sheet, it is effective to optimize the crystal grain size.
It is well known that iron loss is minimized at 50 μm. However, the grain size of non-oriented electrical steel sheets at the time of product shipment is at most about 20 μm. [0003] Therefore, it has been practiced in customers to reduce the iron loss by growing crystal grains by strain relief annealing at 750 ° C for 2 hours performed after the punching process. The crystal grain size was about 60 μm, which was far from the particle size of 150 μm at which the above-mentioned iron loss was minimized.
Therefore, in response to the recent demand for higher efficiency of electrical equipment for energy saving, research and development of ladle refining method of molten steel for non-oriented electrical steel sheet with the aim of reducing iron loss of non-oriented electrical steel sheet Was advanced. Conventional Si: 1.0 wt% or less, Al: 0.1 wt%
The following methods are used as ladle refining methods for molten steel used in the production of low-Si, low-Al non-oriented electrical steel sheets as described below. 1) A method of deoxidizing with Si or Mn without adding Al. (JP-B-56-43294, JP-A-3-249115) 2) A method of deoxidizing with a rare earth metal without adding Al. (Japanese Patent Laid-Open No. 60-145310) 3) A method of adding Si after adding Al. (Japanese Patent Publication No. 54-3443) 4) A method of adding Al after adding Si. [0005] However, of the ladle refining methods described above, the method of 1) deoxidizing with Si, Mn or C without adding Al uses a weakly deacidifying element. Therefore, there is a problem in operation that a large amount of deoxidized product is generated during continuous casting and nozzle clogging is likely to occur. Also, 2) Al
The method of deoxidizing with a rare earth metal without adding any of them is not suitable for economic reasons because a large amount of expensive rare earth metal is used. Furthermore, although the methods 3) and 4) have no operational or economical problems, there is a problem that iron loss is inferior to the methods 1) and 2). Incidentally, with respect to a non-oriented electrical steel sheet having a Si content of 1.0 wt% or less, a non-oriented electrical steel sheet with low iron loss can be obtained by reducing the sol.Al content in the steel to 0.0010 wt% or less. This is disclosed in Japanese Patent Publication No. 58-55210. If the amount of sol.Al in the steel is set to 0.0010 wt% or less, a non-oriented electrical steel sheet having good iron loss can be obtained. The iron loss characteristics disclosed in Japanese Patent Publication No. 58-55210 have become insufficient. [0007] The present invention advantageously solves the above-mentioned problems, and provides a low-Si non-oriented electrical steel sheet having a low iron loss and is economical and excellent in operability. The purpose is to propose a manufacturing method. Means for Solving the Problems The inventors of the present invention have conducted intensive studies to obtain a non-oriented electrical steel sheet having excellent iron loss characteristics. Was found to significantly affect the iron loss of the electrical steel sheet. The present invention is based on the above findings. That is, according to the present invention, C: 0.01 wt% or less, Si: 0.05 to 1.0 wt%, Mn: 0.05 to 0.5 wt%, P: 0.
3 wt% or less and sol.Al: 0.0010 wt% or less, with the balance being
This is a method of melting molten steel for non-oriented electrical steel sheets comprising Fe and unavoidable impurities, and performing a vacuum degassing process to reduce the dissolved oxygen concentration in the molten steel to 700 before the adjustment of the Si component in out-of-pile refining. wtppm or less, and then further deoxidation with Al to reduce the dissolved oxygen concentration in the molten steel to 50 wtppm or more and 200 wtppm or less.
This is a method for producing molten steel for non-oriented electrical steel sheets having a low iron loss, which is performed with an Fe-Si alloy whose content is limited to 0.3 wt% or less. The findings that led to the present invention and the experimental results leading to them will be described below. The inventors have noted that the ladle refining method of adding Si after adding Al is excellent in operability and economic efficiency, and conventionally, iron loss characteristics of the product were considered to be inferior.
The iron loss improvement method of the ladle refining method in which Si was added after Al addition was examined. As a result, compared to Fe-Si alloys conventionally used for melting low-Si, low-Al non-oriented electrical steel sheets,
The following experiments revealed that iron loss can be remarkably improved by adding a low-concentration Fe-Si alloy during ladle refining. In ladle refining after converter refining, first,
After adjusting the composition of Mn in the -Mn alloy, performing a vacuum degassing process to bring the dissolved oxygen concentration in the molten steel to 350 to 400 wtppm, then adding metallic Al to bring the dissolved oxygen concentration in the molten steel to 200 wtpp.
m or less. Thereafter, Al was added in an amount of 1.2 wt% and 0.13%, respectively.
The Fe-Si alloys containing wt% were added to adjust the components of Si, and after the ladle refining was completed, slabs were formed by continuous casting. The slab was hot-rolled after slab heating to form a 2 mm hot-rolled sheet, then cold-rolled to a sheet thickness of 0.5 mm, and then 780 mm.
Finish annealing was performed at 1 ° C. for 1 minute to obtain a product plate. The composition of this product plate is C: 0.003 wt%, Si: 0.12 wt%, Mn: 0.2 wt%
%, P: 0.01 wt%. This product plate has an additional 750
After the strain relief annealing at 2 ° C. for 2 hours, the sample was subjected to iron loss measurement and crystal grain size measurement. FIG. 1 shows the relationship between the sol. Al analysis value of the product sheet and the iron loss characteristics after strain relief annealing. As can be seen from FIG.
Good iron loss characteristics could be obtained by using a Fe-Si alloy with a small content. In particular, it is noted that good iron loss can be obtained by using Fe-Si having a small Al content for adjusting the Si concentration even at the same sol.Al concentration. In order to find the cause, the crystal grain size after strain relief annealing is examined in relation to the sol.Al content analysis value of the product sheet, and is shown in FIG. As a result, even with the same sol.Al content in the product plate, good crystal grain growth was exhibited when the Fe-Si alloy having a low Al content was used as the Fe-Si alloy. Such improvement in grain growth is considered to be a cause of improvement in iron loss. Based on these experiments, the effect of Al content in the Fe—Si alloy on iron loss was investigated in more detail. In the ladle refining after the converter refining, first, the composition of Mn is adjusted with Fe-Mn alloy, then the vacuum oxygen degassing is performed to adjust the dissolved oxygen concentration in the molten steel to 350 to 400 wtppm, and then the metal Al Was added to reduce the dissolved oxygen concentration in the molten steel to 200 wtppm or less. Thereafter, the composition of Si was adjusted using various Fe-Si alloys containing Al in an amount ranging from 0.01 wt% to 0.7 wt%, and after the ladle refining was completed, a slab was formed by continuous casting. The slab was hot-rolled after slab heating to form a hot-rolled sheet of 2 mm, then cold-rolled to a sheet thickness of 0.5 mm, and then subjected to finish annealing at 780 ° C for 1 minute to obtain a product sheet. The composition of this product plate is C: 0.00
3 wt%, Si: 0.12 wt%, Mn: 0.2 wt%, P: 0.01 wt%,
sol.Al: 2-5 wtppm. This product plate has 7 more
After performing the strain relief annealing at 50 ° C. for 2 hours, it was subjected to iron loss measurement and crystal grain size measurement. FIG. 3 shows that the Fe-Si alloy used in the ladle refining
The relationship between Al content and iron loss characteristics is shown. As can be seen from the figure, good iron loss was obtained when the Al content in the Fe-Si alloy was 0.3 wt% or less. It is not clear why the iron loss characteristics are significantly different depending on the Al content in Fe-Si, but it is necessary that the oxygen content be contained in molten steel whose oxygen concentration is sufficiently low due to Al deoxidation and addition of Fe-Si alloy. Al in the turned Fe-Si alloy forms fine Al ₂ O ₃ and remains in the steel without floating during ladle refining, and as a result, becomes an inhibitory factor for grain growth and domain wall movement, Eventually, it is presumed that iron loss deterioration was caused. From the above findings, in the ladle refining of low-Si, low-Al non-oriented electrical steel sheets, the content of Fe was 1 to 2 wt% conventionally.
It has been clarified that by limiting the Al content in -Si to 0.3 wt% or less, a non-oriented electrical steel sheet with remarkably excellent iron loss can be manufactured. As described above, the present invention uses a Fe-Si alloy with a suppressed Al content in molten steel in which the dissolved oxygen concentration is reduced as much as possible by vacuum gas treatment and Al deoxidation treatment in order to eliminate iron loss deterioration. Is the first time. Conventionally known Fe-Si alloys have a reduced Al content of at most 0.4 wt%.
It was not conventionally known that the iron loss characteristics were significantly different from the 0.3 wt% content. Next, various conditions defined in the present invention will be described. First, the reason for limiting the components of the product plate will be described. C: 0.01 wt% or less When the C content exceeds 0.01 wt%, magnetic aging occurs and the magnetic characteristics deteriorate, so the content was made 0.01 wt% or less. Si: 0.05 wt% or more and 1.0 wt% or less Si has a function of increasing the specific resistance and is a useful component that can reduce iron loss. However, if the added amount increases, the cost increases, so that 0.05 wt% or more and 1.0 wt% or less. wt% or less. Mn: 0.05 wt% or more and 0.5 wt% or less Mn has a function of fixing S as coarse MnS and detoxifying it. However, addition of 0.5 wt% or more increases the cost, so that 0.05 wt% or more and 0.5 wt% or less. It was as follows. P: 0.3 wt% or less P can be added to improve the punching property.
Since the addition of more than wt% deteriorates the cold rolling property, the content is desirably 0.2 wt% or less. sol.Al: 0.0010wt% or less If sol.Al is contained in an amount exceeding 0.0010wt%, fine Al
N forms, and iron loss deteriorates remarkably. So 0.0010wt%
It was as follows. In the present invention, components other than those described above are not particularly limited, but the allowable ranges of impurity components are as follows. S: 0.01 wt% or less S forms MnS together with Mn, and hinders domain wall movement and grain growth. N: 0.01 wt% or less N forms nitrides and hinders domain wall movement and grain growth. Therefore, it is preferable that N be 0.01 wt% or less. T. O: 0.025 wt% or less If O exceeds 0.025 wt%, the oxide will hinder domain wall movement and grain growth, so it is desirable that the content be 0.025 wt% or less. Next, preferable manufacturing conditions and reasons for limiting the manufacturing conditions in the present invention will be described. Molten steel from a steelmaking furnace such as a converter (for example, C: 0.04wt%,
Dissolved oxygen: 800 wtppm, Si: tr., Mn: 0.1 wt%, P:
0.01 wt%, sol.Al tr.), And the molten steel is subjected to ladle refining by a known vacuum degassing apparatus. In ladle refining, first, if necessary,
The components except Al and Si are adjusted with metallic Mn, Fe-Mn alloy, Fe-P alloy, etc., and then the dissolved oxygen concentration in the molten steel is reduced to 700 wtppm or less by vacuum degassing. If the concentration of dissolved oxygen in the molten steel exceeds 700 wtppm, a large amount of deoxidized products will be generated, causing nozzle clogging during continuous casting. More preferably, it is at most 600 wtppm. The dissolved oxygen concentration may be measured using an oxygen concentration cell. Thereafter, Al is added for deoxidation. At this time, when the amount of Al added is small, and as a result, the dissolved oxygen concentration in the molten steel after the addition of Al exceeds 200 wtppm, nozzle clogging occurs during continuous casting. On the other hand, when the added amount of Al is large and the dissolved oxygen concentration after the addition of Al becomes 50 wtppm or less, Al remains in the steel, sol.Al of the product plate exceeds 10 wtppm, and iron loss deteriorates. Therefore, Al is added so that the dissolved oxygen concentration in the molten steel after Al addition is 200 wtppm or less and 50 wtppm or more. More preferably, it is in the range of 60 to 160 wtppm. After the addition of Al, an Fe-Si alloy is added for adjusting the Si concentration. At this time, as described above, the Fe-Si alloy
If the Al content exceeds 0.3 wt%, iron loss will deteriorate.
l: Use Fe-Si alloy limited to 0.3 wt% or less. More preferably, it is at most 0.2 wt%. Further, if necessary, components other than Al and Si are adjusted by using metal Mn, Fe-Mn alloy, Fe-P alloy, or the like. Although the preferred ladle refining conditions have been described above, adjustment of components other than Si and Al may be performed by any method, not by the above method. EXAMPLES (Example 1) A 200-ton bottom-blowing converter, C: 0.04 to 0.06 wt%
%, Dissolved oxygen: 800 wtppm, Si: tr., Mn: 0.04 wt%,
A molten steel of P: 0.01 wt%, sol. Al: tr. Was melted, and then ladle refining was performed by a vacuum degassing apparatus. In this ladle refining, the components of Mn and P are first adjusted with Fe-Mn alloy (25wt% Fe-74% Mn) and Fe-P alloy (67% Fe-32% P), and then with oxygen probe. Measure dissolved oxygen concentration, then add Al, then add Fe-Si alloy to Si
The concentration was adjusted to obtain molten steel for non-oriented electrical steel sheets. Table 1 shows the conditions for ladle refining. [Table 1] Next, the obtained molten steel was continuously cast into a slab, and the slab was hot-rolled to obtain a hot-rolled sheet. These hot-rolled sheets were pickled, cold-rolled to a thickness of 0.5 mm, subjected to finish annealing at 780 ° C. for 1 minute, and then coated with an insulating film to form a product sheet. This sheet was subjected to strain relief annealing at 750 ° C. for 2 hours, and then subjected to magnetic measurement. Table 1 also shows the components of the product sheet and the magnetic properties after the strain relief annealing. It can be seen from Table 1 that the conforming example according to the present invention has excellent iron loss. Example 2 In a 100-ton bottom blow converter, C:
0.04 to 0.06 wt%, dissolved oxygen: 750 wtppm, Si: tr., M
A molten steel of n: 0.1 wt%, P: 0.01 wt%, sol. Al: tr. was smelted, and then ladle refining was performed by a vacuum degassing apparatus. In this ladle refining, first, an Fe-Mn alloy (25% Fe-74%
(Mn) to adjust the composition of Mn, then measure the dissolved oxygen concentration with an oxygen probe, then add Al, and then
A Fe-Si alloy was added to adjust the Si concentration to obtain a smelted steel for non-oriented electrical steel sheets. Table 2 shows the conditions for ladle refining.
Was as shown in FIG. [Table 2] Next, the obtained molten steel was continuously cast into a slab, and the slab was hot-rolled to obtain a hot-rolled sheet. These hot-rolled sheets were pickled, cold-rolled to a thickness of 0.5 mm, subjected to finish annealing at 780 ° C. for 1 minute, and then subjected to 8% skin pass rolling to obtain product sheets. 75 on this product plate
After subjecting to strain relief annealing at 0 ° C. for 2 hours, the sample was subjected to magnetic measurement. Table 2 also shows the components of the product sheet and the magnetic properties after the strain relief annealing. From Table 2, it can be seen that the conforming example according to the present invention provides excellent iron loss. According to the present invention, a low-Si non-oriented electrical steel sheet having a low iron loss can be obtained with good operability and economical efficiency. It can sufficiently meet the demand for low iron loss in non-oriented electrical steel sheets used as iron core materials, and has great industrial effects.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the effect of the Al content in the Fe—Si alloy and the sol.Al content of the product on the iron loss W _15/50 . FIG. 2 is a graph showing the effect of the Al content in the Fe—Si alloy and the product sol.Al content on the crystal grain size of the product. FIG. 3 is a graph showing the relationship between the Al content in the Fe—Si alloy and the iron loss W _15/50 .

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-B-54-3443 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) C21C ^7/ 00-7/ ¹⁰

Claims (1)

(57) [Claims] [Claim 1] C: 0.01 wt% or less, Si: 0.05 to 1.0 wt%, Mn: 0.05 to 0.5 wt%, P: 0.3 wt% or less, and sol.Al: 0.0010 wt% % Or less,
The remainder is a method of smelting molten steel for non-oriented electrical steel sheets consisting of Fe and unavoidable impurities.Before adjusting the Si composition in out-of-pile refining, vacuum degassing is performed to dissolve the dissolved oxygen concentration in the molten steel. To 700 wt
ppm, and then further deoxidation with Al to reduce the dissolved oxygen concentration in the molten steel to 50 wtppm or more and 200 wtppm or less. Then, the above Si component adjustment was restricted to an Al content of 0.3 wt% or less. A method for smelting molten steel for non-oriented electrical steel sheets having low iron loss, which is performed using an Fe-Si alloy.