JPH0569910B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a non-oriented electrical steel sheet with excellent iron loss characteristics, which is characterized by using an oxide to render harmless fine MnS that is harmful to iron loss characteristics. (Conventional technology) In recent years, increasing the efficiency of electrical equipment has become a global power
There is a strong demand for this in the energy saving movement. For this reason, there is an increasing demand for non-oriented electrical steel sheets, which are widely used as core materials for rotating machines and small and medium-sized transformers, to have excellent magnetic properties, especially low iron loss. It's coming. Precipitates such as MnS and AlN and B-based inclusions are important factors that affect the magnetic properties of non-oriented electrical steel sheets. In other words, fine MnS, AlN, and Al ₂ O ₃ clusters that precipitate during the hot rolling process and B-based inclusions that spread during rolling form crystals during finish annealing or strain relief annealing at the customer. It inhibits grain growth and significantly deteriorates iron loss characteristics. In order to reduce the number of fine MnS that precipitates during the hot rolling process, it is possible to reduce S as much as possible during the melting stage, and to precipitate MnS before hot rolling to aggregate and coarsen the pieces, thereby reducing the number. . Of these, for the former, ultra-high purity refining can be considered from the hot metal pretreatment to the secondary refining process, but this will inevitably lead to an increase in melting costs. Also,
When considering desulfurization in the secondary refining process, the use of strong deoxidizing elements such as Al is a prerequisite, but it is also necessary to take measures to prevent fine precipitation of AlN. As described in JP-A-54-163720, by adding B in Al deoxidation,
There is a method to suppress fine precipitation of AlN by fixing N as BN, but there is a concern that BN itself may cause magnetic deterioration. In addition, in Al deoxidation,
Colonial Al ₂ O ₃ is generated and causes deterioration of iron loss. On the other hand, in the method of deoxidizing with Si,
By regulating the ratio of SiO ₃ and MnO-based inclusions as disclosed in Japanese Patent No. 152239, it is possible to reduce the inclusions that spread during rolling, and this has been shown to be quite effective. (Problems to be Solved by the Invention) However, the above-mentioned prior art does not mention conditions for effectively coagulating and coarsening MnS. The present inventors focused on the conditions of oxides as precipitation nuclei of MnS, and as a result of elucidating and examining them based on many experimental results, we found that by appropriately controlling the size and number of oxides, He also invented an excellent non-oriented electrical steel sheet with low iron loss. (Means for Solving the Problems) The present inventors have conducted extensive research in an attempt to utilize oxides in order to control the precipitation of MnS in non-oriented electrical steel sheets. As a result, by leaving a large number of oxides with a size of 0.5 μm or more and 5 μm or less in the steel ingot, MnS is agglomerated and precipitated using these oxides as nuclei, and the number of fine MnS precipitates is significantly reduced. It was discovered that a non-oriented electrical steel sheet with extremely excellent iron loss characteristics could be obtained. Furthermore, by significantly shortening the time from deoxidation to injection, a large number of oxides of the above size are present in the steel, and MnS is agglomerated and precipitated using these oxides as nuclei, reducing the number of fine MnS precipitates. It was found that the iron loss characteristics of non-oriented electrical steel sheets were significantly improved. Experiments have shown that in order to leave a large number of oxides of this size in steel, it is necessary to keep the time from injecting molten steel to completion of solidification after adding a deoxidizing agent to within 3 minutes, preferably within 60 seconds. This is what I found. The present invention will be explained in detail below. If this oxide is smaller than 0.5 μm, it will adversely affect core loss for the same reason as fine MnS. Moreover, if the diameter is larger than 5 μm, it is difficult to form a precipitation nucleus of MnS, and the present purpose cannot be achieved. It has been experimentally found that with regard to the number of oxides of this size, it is very effective to have 1000 or more oxides per cm ² in the steel. On the other hand, if the number exceeds 50,000, oxides will aggregate and accumulate in the injection nozzle, clogging the nozzle and making it impossible to operate stably. In the production of non-oriented electrical steel sheets, molten steel is generally deoxidized by deoxidizing with Al and deoxidizing with Si, but oxides as deoxidizing products are Those that are generated and already exist in molten steel (primary deoxidation products) and those that crystallize as the solubility product decreases during solidification and cooling (secondary deoxidation products)
It can be broadly divided into Among these, secondary deoxidation products are caused by solidification segregation.
Since most of the dendrites exist between dendrite trees where Mn and S are concentrated, they tend to become nuclei for MnS precipitation. It has been experimentally found that the size of this secondary deoxidation product is mostly 5 μm or less. Therefore, in order to increase the number of oxides serving as MnS precipitation nuclei, it is effective to utilize secondary deoxidation products. When using a deoxidizing agent such as Si, which has a relatively weak deoxidizing power and a large temperature dependence of its solubility product, a large amount of secondary deoxidation products can be made to act as precipitation nuclei of MnS. Furthermore, when the Si content is the same, it is effective to increase the amount of secondary deoxidation products by increasing the temperature when injecting into the mold and increasing the solubility product. When the injection temperature is low, primary deoxidation products that are generated in the molten steel stage before injection and grow to a larger size increase, and secondary deoxidation products decrease accordingly. However, by raising the injection temperature, the proportion of secondary deoxidation products that are effective as MnS precipitation nuclei increases at a cooling rate similar to that of current continuous casting machines. For example, it has been found that by increasing the injection temperature by 20°C from 1560°C, the amount of secondary deoxidation products increases by about 40%. It is also possible to add oxide powder of the above-mentioned size to molten steel before injection to increase the number of oxides and use it as precipitation nuclei of MnS. It has been found that some of the added oxide powders coalesce with each other and float to the surface, but the remaining oxide powders of the same size remain in the steel ingot. It goes without saying that it is advantageous from the viewpoint of steel cleanliness to reduce as much as possible oxides with a diameter of 5 μm or more and inclusions that spread during rolling. On the other hand, in the method of shortening the holding time after deoxidation, when a strong deoxidizing element such as Al is used, the amount of secondary deoxidation products is very small, but it is necessary to pour the molten steel into the mold immediately after deoxidation. For example, the time for growth and flotation of primary deoxidation products is reduced, and a large number of oxides of the relevant size remain in the steel, which is effective. If molten steel is held for more than 3 minutes after deoxidation, oxides, which are deoxidation products, will grow and become large, and most of them will float and separate. By specifying the holding time after deoxidation, the oxide is injected into the mold before it grows and floats to separate, so that a large number of oxides that become MnS precipitation nuclei are present in the steel. This method is particularly effective when strong deoxidizing elements such as Al, Zr, etc. are used as the deoxidizing agent. It has been experimentally found that the present invention is effective even when using a relatively weak deoxidizing agent such as Si, but the effect is smaller than when using a strong deoxidizing element. it is,
This is thought to be because in the case of Si deoxidation, the secondary deoxidation products that crystallize during solidification and cooling account for a large proportion of the oxides of 8 μm or less, so the influence of the holding time after deoxidation is small. However, even in the case of Si deoxidation, practical effects can be expected, so it is included in the present invention. Next, a method for producing 100 tons of molten steel using a continuous casting machine will be explained. When molten steel is deoxidized using a pot, the molten steel at the final stage of casting has already been deoxidized for several tens of minutes, and most of the oxides float to the surface and serve as precipitation sites for MnS. Due to the insufficient number of oxides, sufficient magnetic properties cannot be obtained. Therefore, the molten steel is continuously poured in a tandate or continuous casting machine, and the addition rate of deoxidizing agent is controlled according to the casting speed. By manufacturing it, it is possible to increase the number of oxides that effectively function as MnS precipitation sites, and the magnetic properties are improved. As a deoxidizing agent, Si is recommended unless there is a problem with cleanliness.
The most desirable is one that produces a large number of secondary deoxidation products, but strong deoxidizing elements such as Ti, Al, and Zr can be used if the size and number of oxides can be controlled as described above. It is something. Next, the reasons for limiting the steel components of the present invention will be described. C is a harmful component that increases core loss and causes magnetic aging, so it should be kept at 0.010% or less. As is well known, Si is a component that has the effect of reducing iron loss, and in order to achieve this effect, it is necessary to
It is necessary to contain 0.1% or more. On the other hand, if the content increases, the magnetic flux density will decrease, the rolling operation will deteriorate, and furthermore, the cost will increase, so 2.0
% or less. Mn also has the effect of increasing specific resistance and lowering iron loss, and for this purpose it is necessary to contain it in an amount of 0.1% or more. On the other hand, as the content increases, the ferrite-austenite transformation temperature decreases, making it impossible to maintain a sufficiently high annealing temperature, which necessitates long-term annealing at a relatively low temperature, resulting in decreased productivity. Therefore, it should be 1.5% or less. Al is necessary when used as a deoxidizing agent, but if the content exceeds 0.1%, it causes a decrease in magnetic flux density and increases in cost, so it is set to 0.1% or less. However, for the action of deoxidizing, 0.005%
It is necessary to contain the above amount. Zr is also necessary when used as a deoxidizing agent, but it is set at 0.05% or less in consideration of high cost. However, for the deoxidizing effect, it is necessary to contain 0.005% or more. P is a necessary component to increase the hardness of steel and improve punching properties, but if its content exceeds 0.15%, the steel will become brittle and rolling workability and workability will deteriorate. % or less. Components other than those mentioned above are iron and unavoidable impurity elements. Example 1 A steel ingot for non-oriented electrical steel sheet containing the components shown in Table 1 was produced using a 20 kg scale high frequency vacuum melting furnace, then hot rolled and cold rolled to a thickness of 0.50 mm. Final annealing was performed at 750℃ for 30 seconds, and
Magnetic annealing was performed at 750°C for 2 hours. As a result of investigating the oxide particle size distribution and MnS precipitation status of the steel ingot, observing the crystal grains of the product plate, and measuring the iron loss characteristics, it was found that 0.5 μm or more in the steel ingot
The amount of fine MnS precipitated is very small, the crystal grains after magnetic annealing are large, and the iron loss W _15/50 is 4.5W/cm ² or more.
Kg and very low. The results are summarized in Table 2. In the present invention, A, B, and C are deoxidized with Si, Al, and Zr, respectively, and A is the one in which the injection temperature is increased by 30°C.
For B and C, oxide powders of Al ₂ O ₃ and ZrO ₂ are added, and the number of oxides with a size of 0.5 μm or more and 5 μm or less per cm ²
There are 1600 pieces. D and E are produced by the comparative method by deoxidizing Si and Al, respectively. In addition, for F, add SiO ₂ oxide powder before injection to form an oxide of 1 cm ² of the above size.
There were 80,000 pieces per cast, but the injection nozzle was blocked and casting was extremely difficult.

【table】

[Table] Example 2 A steel ingot for non-oriented electrical steel sheet containing the ingredients shown in Table 3 was manufactured using a 20 kg scale high frequency vacuum melting furnace, then hot rolled and cold rolled to a thickness of 0.50 mm. After rolling, final annealing is performed at 750℃ for 30 seconds, and
Magnetic annealing was performed at 750°C for 2 hours. As a result of investigating the oxide particle size distribution and MnS precipitation status of the steel ingot, observing the crystal grains of the product plate, and measuring the iron loss characteristics, we found that the retention time after deoxidation is 30% as in the present invention.
The amount of fine MnS precipitated in the steel ingot is very small, the crystal grains are large after magnetic annealing, and the iron loss W _15/50 is very low at 4.4 W/Kg. The results are summarized in Table 4. In the present invention, the retention times for A, B, and C after deoxidation are 2 minutes, 30 seconds, and 30 seconds, respectively. Deoxidation methods are A and B.
Al deoxidation, and (c) Si deoxidation. D and H are respectively
This is a conventional method for Al deoxidation and Si deoxidation.

【table】

[Table] Example 3 For non-oriented electrical steel sheets containing the ingredients shown in Table 5
100 tons of molten steel is cast using a continuous casting machine, then hot rolled, then cold rolled to a thickness of 0.50mm, finish annealed at 750℃ for 30 seconds, and
Magnetic annealing was performed at 750°C for 2 hours. The deoxidizer is Al
Deoxidation is performed continuously according to the casting speed in the tandate just before pouring the molten steel, and the thickness is 50 mm.
A thin slab was directly cast (P method). For comparison, a slab obtained by deoxidizing in a pot was hot rolled, then cold rolled to a thickness of 0.50 mm, and then heated at 750°C.
Final annealing is performed for 30 seconds at 750℃
Magnetic annealing was performed for 2 hours (Q method). As a result of investigating the oxide particle size distribution and MnS precipitation status of the slab, observing the crystal grains of the product plate, and measuring the iron loss characteristics, we found that the time required to complete solidification after deoxidation can be significantly reduced as in the present invention. The amount of fine MnS precipitated in the shortened (P method) slab is very small, and the crystal grains after magnetic annealing are also large.
Furthermore, the iron loss W _15/50 is extremely low at 4.6W/Kg. The results are summarized in Table 6.

【table】

【table】

[Table] (Effects of the Invention) As described above, according to the present invention, by appropriately controlling the size and amount of oxide, it is possible to significantly improve iron loss after magnetic annealing.

Claims (1)

[Claims] 1% by weight: C: 0.01% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or more and 1.5% or less, and, depending on the steel deoxidation method, Al: 0.1% or less, Or Zr: In a non-oriented electrical steel sheet containing 0.05% or less, with the balance consisting of iron and unavoidable impurity elements, the number of oxides in the steel with a diameter of 0.5 μm or more and 5 μm or less is 1000 or more per cm ² A non-oriented electrical steel sheet with excellent magnetic properties characterized by less than 50,000 pieces. 2 By weight: C: 0.01% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or more and 1.5% or less, and depending on the steel deoxidation method, Al: 0.1% or less, or Zr: 0.05% or less. In a method for producing a non-oriented electrode steel sheet, the steel containing iron and inevitable impurity elements is hot rolled, followed by cold rolling and final annealing.
A method for producing a non-oriented electrical steel sheet with excellent magnetic properties, characterized in that when deoxidizing molten steel, casting and solidification are completed within 3 minutes after adding a deoxidizing agent. 3. A non-oriented electrical steel sheet with excellent magnetic properties according to claim 1 or 2, which contains P: 0.15% or less in weight percent.