DE3107942A1 - Non-oriented silicon-steel sheeting having uniform magnetic properties - Google Patents

Abstract

The invention relates to non-oriented silicon-steel sheeting having low watts loss and uniform magnetic properties, which contains from 1.5 to 3.5% of Si, has a particularly low C content and a low content of soluble Al and has a ratio of B to N in the range from 0.4 to 2.0 and further contains at least one rare-earth metal. The relationship between the watts loss and the Ce content is shown in Figure 2. <IMAGE>

Description

The subject of the invention is a high quality non-orient

oriented silicon steel sheet, in particular a non-oriented silicon steel sheet with excellent magnetic properties, containing 1.5 to 3.5% Si, not more than 0.015% C and not more than 0.08% acid-soluble Al (hereinafter referred to as "soluble Al") and which has an addition of B in such an amount that a balanced Ratio of B to N is achieved, and which also contains a rare earth element.

Among the silicon steel sheets that are soft magnetic materials, There are the following types: Grain-oriented silicon steel sheets that are recrystallized Have collective texture, which crystallographically with the designation (110) [001] is expressed and its (110) plane in the rolling plane and its [001] orientation in the rolling direction, and non-oriented silicon steels with negligible Orientation. These materials are used as iron cores for electrical equipment which are used for specific applications depending on their magnetic and mechanical Properties and their manufacturing costs are selected.

For example, grain-oriented silicon steel sheet is used in spite of it high cost due to its excellent magnetic properties in general used for transformers and mast transformers of large capacity. Because it is very easily magnetizable in the rolling direction, i.e. in the 0017 direction, has a very low wattage loss and very high permeability.

On the other hand, non-oriented silicon steel sheet is commonly used divided into the following two classes: Low-quality non-oriented silicon steel sheet with a Si content between almost 0 and 1.5%, and high quality non-oriented Silicon steel sheet with over 1.5% Si. Because these materials have such a low orientation show that it is negligible and its cost is low they are used extensively for small-sized electric motors and medium-sized transformers and medium to large rotating machines.

A key property found in non-oriented silicon steel sheet what is required is a low watt loss value. The watt loss is mainly there from the hysteresis loss and the eddy current loss. . With non-oriented silicon steel sheet the hysteresis loss is prevented most effectively by adjusting the crystal grain size is increased.

The eddy current loss can be increased by increasing the specific resistance of the steel, i.e. in other words by adding alloying elements, such as Si.

One means of increasing the crystal grain size is high temperature annealing that is carried out over a long period of time. However, this is for cost reasons disadvantageous.

In addition, long annealing times are usually carried out continuous annealing process difficult to achieve.

The inhibition of the growth of crystal grains is known to be closely related Inclusions and precipitates that are distributed in the steel, connected. The size the inclusions and precipitates and their state of dispersion are very important.

In general, it is believed that the presence of a lot of fine Inclusions and precipitates are not favorable for the growth of crystal grains is. As substances that are dispersed in non-oriented silicon steel sheet may contain various oxides, such as Al 2 O 3 or SiO 2, as well as different Sulfides and nitrides such as MnS and AlN can be mentioned. As for the oxides, must these are only collected during steel production and presented as deoxidized products be allowed to swim. In addition, there must be oxidation during the pouring of the molten steel into the slab molds can be prevented. As a result of recent advances in the In steel making, oxide inclusions can be prevented easily.

A widely used method of eliminating sulfides consists in carefully carrying out desulphurisation in steel production, at the same time a sufficient amount of Mn or a similar element is added. Then the heating temperature of the slab before hot rolling becomes so low held that the MnS is converted into a substance that stimulates the growth of crystal grains not adversely affected. By using this procedure, sulfides make up no difficulty.

In order to keep the inclusion of nitrides low, it is best to to keep the nitrogen content in steel production as low as possible. One consequent reduction of the nitrogen content in silicon steel to values below 10 p.m. however, it is very difficult. The nitrogen content is usually included about 30 2.p.M.

The reaction of N with Al, which is used for deoxidation, or with Al contained in silicon alloys leads to the formation of AlN. Because an Al content in the range of 0.005 to 0.15% is detrimental to the growth of the crystalline bodies, was used in the manufacture of low quality non-oriented silicon steel sheet with less than about 1.0 to 1.5% Si, the amount of Al for deoxidation reduced as much as possible, preferably to values below 0.005%. at high quality non- oriented silicon steel sheet with a grade from more than about 1.0 to 1.5% Si, the Al content is adjusted to values above 0.15% and the AlN is precipitated in a form that allows crystal grains to grow does not bother when the steel slab is heated.

In the first case, however, there are such difficulties such as insufficient deoxidation in steel production or the occurrence of surface defects in sheet steel. In the latter case, they increase due to the consumption of a large one Amount of expensive Al inevitably increases the cost of manufacture.

As an effective method of stabilizing deoxidation in the Steel production while avoiding the use of large quantities The increase in cost caused by Al has already become an inexpensive method of production of non-oriented silicon steel sheet with excellent watt loss values suggested by adding boron. However, it was found that in the manufacture of sheet steel with a very low carbon content (max. 0.015%) using this method the product does not have completely uniform magnetic properties.

The invention is based on the object of a non-oriented silicon steel sheet with uniform magnetic properties. This task will solved by the invention.

The invention relates to a non-oriented silicon steel sheet with uniform magnetic properties, consisting essentially of at most 0.015% C, 1.5 to 3.5% Si, 0.05 to 1.0% Mn, 0.005 to 0.08% acid-soluble Al, a maximum of 0.015% S, a maximum of 0.010o 0, a maximum of 0.005% N, B in such an amount, that a ratio of B to N in the range of 0.4 to 2.0 is obtained, 0.001 to 0.02% at least a rare earth metal, the remainder being iron and unavoidable impurities.

In the accompanying drawing: FIG. 1 is a graphic representation the relationship between the Si content and the ratio of precipitated nitride to total nitrogen; Fig. 2 is a graph showing the relationship between the Ce content and watt loss; Fig. 3 is a graphical representation of the change in Watt loss.

Investigations into the precipitation behavior of nitride at very low C content (at most 0.015%) have shown that in a steel with a Content of at least 1.5% Si, in particular at least 2.0% Si, and at most 0.010% C is the amount of N that is precipitated as nitride in the hot-rolled sheet, is very low; see Fig. 1.

Fig. 1 is a graph showing the relationship between the Ratio (in%) of the nitride excretion to the total nitrogen content and the Si content (in%). The chemical composition of the sample is such that the content of C not more than 0.010o, of soluble Al 0.008 to 0.050%, of N not more than 0.005% and of B is 0.0010 to 0.0050% o.

The insufficient nitride precipitation in the hot rolled steel sheet is therefore probably the cause of the inequality of the watt loss values in very low a content.

Based on this assumption, studies were carried out in which it was found that the tendency to slight changes in the watt loss was eliminated and the magnetic properties can be made uniform when using silicon steel with a very low C content and a low content of soluble Al boron is added, so that the ratio of B to N is in a certain range, and if more at the same time a small amount of a rare earth element is present.

The present invention is explained in detail below.

The steel that is used according to the invention for the production of the magnetic material is used is in a steel fresh furnace, for example an electric furnace, Siemens-Martin furnace or a converter melted, and then, if necessary, further refined in a vacuum refining furnace to reduce its C content to a maximum of 0.015% to diminish. Then the required amounts of Al, Si, Mn, B and the rare earth metal added.

The carbon content of the steel is determined by decarburization in the post-treatment stage set to 0.015% or less because C has a deteriorating effect on the magnetic Properties and magnetic compensation. If the C content is over 0.015% is, the time required for decarburization is extended, which is for reasons of cost is unfavorable.

The Si content depends on the required amount of watt loss controlled. However, if the Si content is over 3.5%, the cold rollability of the Steel deteriorates. Because the invention provides a high quality non-oriented Silicon steel sheet is to be obtained, the Si content is reduced to the range of Concentrated 1.5 to 3.5%.

Al is added to deoxidize the steel. A content of soluble Al less than 0.005% results in insufficient deoxidation. An inadequate one Soluble Al content also causes difficulty in slab casting, leads to an increase in the formation of splinters on the surface of the steel and causes poor results for the addition of B and the rare earth element.

The Al content is therefore set to be at least 0.005po. A In contrast, a high Al content not only leads to an increase in costs, but also destroys it also the effect of the addition of B and the rare earth metal. The Al content should therefore not exceed 0.08%. Is preferred for the content of rural Al Range from 0.015 to 0050 / o.

Mn is added in an amount of at least 0.05% to prevent brittle fracture during hot rolling and for the specific resistance of the steel as a result to compensate for the low Al content in order to reduce its watt loss. On the other hand, the upper limit of the Mn content is set to 1.0% because the magnetic Properties of the steel are impaired by an excessively high Mn content.

Since S deteriorates the magnetic properties, its content becomes set to a maximum of 0.015%, preferably a maximum of 0000 / o.

After 0 also the magnetic properties in general and in addition, useless consumption of B and rare earth elements caused, its content is limited to a maximum of 10%.

If the N content exceeds 0.005%, it causes deterioration of the magnetic properties and has a cost due to the increase in the required B salary. The upper limit for the N content is therefore set at 0.005%.

The B content of the steel is adjusted so that the weight ratio from B to N lies in a certain range. The weight ratio of B to N is set to the range from 0.4 to 2.0 because the watt loss increases when this ratio assumes a higher or lower value. If a rare earth metal contained in steel is that from the point of view of reducing watt loss preferred range of the ratio B / N 0.6 to 1.5.

Another important element besides B described above is the rare earth metal. At least 0.001% of at least one rare earth element is necessary to prevent the unevenness of magnetic properties, those to some extent in very low C and low soluble silicon steel Al content is observed.

If the content of the rare earth element is over 0.020 / 0, then it increases the amount of inclusions so strongly that a deterioration of the'magnetischen Properties is caused. The content of rare earth metal is therefore on the Range defined from 0.001 to 0.020h.

The results of the research carried out on the values of the Loss of wattage in silicon steels with a very low carbon content and low content on soluble Al, which contain Ce as a rare earth metal together with B. are shown in FIG.

In addition to Ce and B, the steel samples contain 0.003 to 0.008% C, 0.005 to 0.080 whether soluble Al and 2s3 / o Si.

In Fig. 2: X means no addition of boron, ratio B / N below 0.4 or above 2.0 O ratio B / N in the range of 0.4 to 2.0.

In Fig. 2 it can be seen that silicon steels with a ratio B / N in the range of 0.4 to 2.0, which also contain Ce, a small watt loss exhibit. In particular, silicon steels with 0.001 to 0.0200 / 0 Ce have one low wattage loss and excellent magnetic properties. The effect the simultaneous presence of B and Ce is remarkable in steels with very low C content of 0.005% or less.

On the other hand, the watt loss in silicon steels is the Ce alone or have a B / N ratio of less than 0.4 or more than 2.0, high.

A mixture of metals with an atomic number can be used as the rare earth metal between 57 and -71 can be used. Misch metal, about 50 'from Ce, remainder mainly composed of lanthanum and neodymium, is an inexpensive example of such a mixture. Ce is preferably used.

The addition of the rare earth metal is effective when the Deoxidation is complete and the setting of the additives is completed is. According to the invention, a steel melt with an adjusted composition becomes poured into a slab. Casting is done by continuous casting or pouring into one Form into a block, which is then rolled into a slab. It can also be a slab obtained by sizing rolling a continuously cast slab can be used.

The steel slab is usually heated to a certain temperature in a furnace heated in the range of 1050 to 1250 ° C and to a thickness in the range of about 1.5 rolled up to 3.0 mm. After removing the oxidized surface layer of the hot rolled Sheet metal is rolled to the thickness of the final product.

The hot rolled sheet can be annealed or cold rolled twice / In This will be the glow between the two cold rolling steps carried out. A combination of these process steps can also be used.

The cold-rolled sheet is continuously annealed and coated with an insulating Film coated. The final product is obtained.

According to the invention, there are all suitable methods for pouring the steel melt into a slab or a block and for processing the block or the slab in question.

The examples illustrate the invention.

Example 1 Steel slabs with the composition given in Table I. are produced in the converter, refurbished in a vacuum degassing vessel and thoroughly cleaned Continuous casting produced.

The slabs obtained are heated to 115,000 in a furnace hot rolled to a thickness of 2.3 mm, annealed at 90000, descaled and then cold rolled to a thickness of 0.5 mm. After that, the cold rolled sheets Annealed for 60 seconds at 900 or 95000. The magnetic properties of Epstein samples of each steel sheet are summarized in Table II.

Table 1 Sample classification C Si Mn soluble Al SNBB / N Ce O 1 Invention 0.003 2.20 0.25 0.025 0.001 0.0022 0.0020 0.91 0.004 0.003 2 "0.004 2.22 0.30 0.065 0.007 0.0018 0.0030 1.67 0.008 0.002 3 "0.003 2.15 0.41 0.028 0.006 0.0026 0.0020 0.77 0.014 0.002 4 "0.003 2.25 0.66 0.018 0.007 0.0021 0.0030 1.43 0.017 0.004 5 "0.004 2.88 0.30 0.022 0.007 0.0026 0.0022 0.85 0.005 0.002 6 "0.005 2.93 0.62 0.043 0.005 0.0023 0.0031 1.35 0.009 0.002 7 "0.003 2.92 0.22 0.032 0.005 0.0023 0.0020 0.87 0.016 0.002 8 "0.004 2.83 0.18 0.044 0.004 0.0020 0.0024 1.20 0.011 0.002 9 Comparison 0.004 2.30 0.26 0.031 0.004 0.0026 0.0022 0.85 0.026 0.004 10 "0.004 2.16 0.20 0.022 0.007 0.0031 - - 0.009 0.003 11 "0.003 2.27 0.36 0.024 0.006 0.0022 0.0022 1.00 - 0.002 12 "0.021 2.19 0.33 0.021 0.007 0.0033 0.0029 0.88 0.010 0.004 13 "0.004 3.01 0.22 0.033 0.006 0.0024 0.0020 0.83 0.024 0.002 14 "0.004 2.88 0.22 0.038 0.004 0.0026 - - 0.013 0.002 15 "0.003 2.95 0.26 0.035 0.004 0.0023 0.0024 1.04 - 0.004 16 "0.005 2.83 0.21 0.041 0.004 0.0026 0.0020 0.77 0.008 0.002 Table II Sample Classifi- Process stage after hot rolling Temp. Of the magnetic property Numbering of the steel sheet final shafts glowing, W15 / 50, B50, T ° CW / kg 1 Invention Descaling cold rolling final annealing 900 3.89 1.67 2 """" 900 3.95 1.66 3 """" 900 3.98 1.65 4 """" 900 4.05 1.66 5 "Annealing-Descaling-Cold Roll-Shot Annealing 950 3.25 1.68 6 """" 950 3.25 1.68 7 """" 950 3.30 1.68 8 """" 950 3.31 1.68 9 Comparison of descaling / cold rolling final annealing 900 4.52 1.66 10 """" 900 4.66 1.67 11 """" 900 4.42 1.67 12 """" 900 4.42 1.67 13 "Annealing-Descaling-Cold Rolling-School Annealing 950 3.88 1.69 14 """" 950 3.94 1.69 15 """" 950 3.55 1.69 16 """" 950 3.69 1.68 Note, T = Teala Example 2 Samples Nos. 3 and 11 of Example 1 are selected because of their very low C content. 20 hot-rolled sheets are produced, descaled, cold-rolled to a thickness of 0.5 mm and then annealed at 90,000 for 60 seconds. The average value of the watt loss and its change is measured on these sheets.

In Fig. 3 is the change in the value for the watt loss over the Samples No. 3 (unshaded) and 11 (hatched) are shown.

In Fig. 3 it can be seen that the steel sheet of the invention at watt loss values W 15/50 between 3.6 and 4.0 W / kg is outstanding compared to the comparative sheet is.

The analysis values, the average values of the watt loss and the standard deviation of the samples are summarized in Table III.

Table III Sample chemical analysis values,% watt loss, W / kg No. C Si Mn soluble Al SNBB / N Ce through-standard cut deviation 3 0.003 2.15 0.41 0.028 0.006 0.0026 0.0020 0.77 0.014 3.93 0.15 11 0.003 2.27 0.36 0.024 0.007 0.0022 0.0022 1.00 - 4.18 0.25 The results of Examples 1 and 2 show that silicon steel sheets with little watt loss and little variation are obtained by the invention.

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Claims (2)

"Non-oriented silicon steel sheet with uniform magnetic Properties "claims 1. Non-oriented silicon steel sheet with uniform magnetic properties consisting essentially of at most 0.015%, preferably at most 0.010% G, 1.5 to 3.5% Si, 0.05 to 1.0% Mn, 0.005 to 0.08% acid soluble Al, not more than 0.015% S, not more than 0.010% 0, not more than 0.005% N, B in such an amount, that the ratio of B to N is in the range from 0.4 to 2.0, 0.001 to 0.020% at least one rare earth element, the remainder being Fe and unavoidable impurities. 2. Non-oriented silicon steel sheet according to claim 1, containing at most 0.005% C, 0.005 to 0.03 / o acid-soluble Al and 0.001 to 0.020% Ce.