JPS6055567B2 - Manufacturing method of non-oriented silicon steel sheet with low iron loss - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a non-oriented silicon steel sheet with low iron loss.

Among the properties required of non-oriented silicon steel, iron loss is one of the most important.

Conventionally, several methods have been known to reduce iron loss, such as adding Si)N to increase the specific resistance of the material, increasing the final annealing temperature, and reducing precipitates and inclusions. It is being As a method for reducing such iron loss, there is also a prior art of the present applicant disclosed in Japanese Patent Publication No. 54-36960. This prior art involves adding rare earth elements (REM) and calcium (Ca) to molten steel to make these sulfides into coarse crystal grains that are agglomerated rather than finely dispersed. In particular, this method is designed to prevent fine crystals from re-precipitating during heat treatment and deteriorating electromagnetic characteristics.

The present invention relates to an improvement over the prior art described above and includes REM
And/or when continuously casting molten steel to which calcium has been added, strong electromagnetic stirring is applied to the drawn slab to further promote the cohesive force and coarsening of REMNCa oxysulfides and sulfides. It was developed with the aim of improving the iron loss value by more than 20%. The details of the configuration will be explained below. It is known that when REM and Ca are added to non-oriented silicon steel, the S in the steel is fixed by these additives and has the effect of preventing sulfide redecipitation and solid solution during hot rolling. ing.

Therefore, by adding REM or the like, fine precipitates such as sulfides that inhibit the growth of crystal grains are eliminated, and iron loss is improved. On the other hand, according to the research of the present inventors, the REM, . It has been found that when electromagnetic stirring is applied during continuous casting of Ca-added steel, the agglomeration phenomenon of REM sulfides, Ca sulfides, etc. becomes noticeable, and the influence of fine precipitates becomes even less.

Therefore, REM. ．． If electromagnetic stirring treatment is performed in the presence of Ca, crystal grain growth will be promoted, and iron loss will be improved by adding to the effect of addition of REM and the like. Note that the preferable position of the continuous casting stage in which electromagnetic stirring is applied is the stage of the secondary cooling zone where the solidified shell thickness ratio is less than 50%. The above-mentioned electromagnetic stirring applied to the drawn slab is ineffective if the applied electromagnetic force is small, and the agglomeration of REM, Ca oxyoxides, and sulfides is not promoted, so it is necessary to maintain the strength above a certain level. .

The drawing shows the relationship between the number of aggregated REM oxysulfides and sulfides and the intensity of electromagnetic stirring when electromagnetic stirring is applied to a steel slab having the composition shown in Table 1. As can be seen from this figure, it is clear that when the stirring intensity is increased, sulfides with small particle sizes decrease and sulfides with large particle sizes increase, promoting the growth of crystal grains. As is clear from the figure, this improvement in stirring strength was achieved at 1000A-Hzll2.
If it is less than this, the effect of electromagnetic stirring will be weak.

Note that the stirring intensity F is related to current and frequency and can be expressed as (Asai: Metal Physics Seminar Vol. 3
), the stirring intensity F in this invention is as follows.

Although the aforementioned electromagnetic stirring further promotes the agglomeration of REM and Ca oxysulfides and sulfides, in this sense the present invention is not applicable to steels to which REM and Ca are not added.

This is because, in the case of steel without additives such as REM, even sulfides that have grown once become atomized during hot rolling.
The following REM, . The reason for limiting the Ca content will be explained together with the reasons for limiting the other components of the steel of the present invention. First, the content of C is limited to 0.05% by weight or less.

Since carbon in steel has a negative effect on magnetic properties, it may eventually decarburize during final annealing, but if it exceeds this level, sufficient decarburization during final annealing becomes difficult.
It takes time to achieve the desired decarburization. When Si exceeds 4% by weight, cold rollability deteriorates, and in low-grade products containing less than 1% by weight, Si contains rare earth elements (REM) or calcium (Si).
Since properties satisfying the grade quality can be easily obtained without adding Ca), the content is set at 1 to 4% by weight. is 0.1
If it is less than 0.15% by weight, fine AlN will precipitate and the crystal grains will become smaller, deteriorating the electromagnetic properties, so the content should be 0.15% by weight or more.

REM and C added to steel with the above composition
The content of a is as follows.

Regarding REM, it is necessary to keep it within the following range.

That is, less than 0.003% by weight, and this REM<
If the ratio to 5S is less than 1, S remains as a solid solution in the steel, deteriorating the rolled plate and making it impossible to achieve the intended purpose. On the other hand, if REM is more than 0.05% by weight and the ratio of REM to S is more than 10, magnetic properties will deteriorate due to excessive REM and rolling properties will deteriorate. The amount should be in the range of 0.003 to 0.05% by weight and the ratio of REM to S should be in the range of 1 to 10. REM has atomic number 57 to 71
up to 15 elements and SC. 17 with the addition of two elements Y
It is a general term for elements, and their chemical properties are extremely similar, and the effects of using each of these elements in the present invention are almost the same.Therefore, there is no need to add rare earth elements as single elements; It may be a mixture of elements, and it is preferable to use a metal containing a cerium group metal or a silicide containing a cerium group metal, which is advantageous in terms of cost.

REM has a large bonding force with S in the molten steel stage and also has a large bonding force with S even at a slab heating temperature of 1200 to 135°C, so it has the function of minimizing the amount of S dissolved in solid solution.

By adding this rare earth element within the above range, S can be fixed as a large rare earth element sulfide, and precipitation of fine sulfides during heat treatment can be prevented. As a result, grain growth is improved and excellent magnetic properties can be obtained in subsequent treatments. Next, regarding calcium, if the Ca content is more than 0.01%, the iron loss value will be high, and if the Ca/S ratio is less than 0.3 or greater than 2.0, the iron loss value will be high. , Ca/S ratio is 0.3-2.0
and the Ca content must be 0.01% or less.

Next, a method for manufacturing a non-oriented silicon steel sheet according to the present invention will be explained.

As the steelmaking furnace, any of an open hearth, a converter, and an electric furnace can be used, and the necessary Si, . Al is added after the decarburization process is completed, that is, after the C content is reduced to 0.05% or less, and the required amount of Si, . Adjust the Al content. Next, a continuous casting method is used to form a slab, which is subjected to electromagnetic stirring treatment. Sho RE
The addition of M and/or Ca may be carried out in a vacuum degassing inner ladle, in a tundish, or in a mold. The obtained slab was heated to 1100 to 130 CfC in a heating furnace.
heated to a temperature of 1.5 to 3.5T by hot rolling! n
A thick hot-rolled plate. Next, a product having a thickness of 0.3 to 0.7 is obtained by a single cooling process or a two-time cold rolling process including intermediate annealing. The effects of the present invention will be described below with reference to Examples.

Example 1 After decarburizing molten steel blown in a 100 ton converter in a vacuum degassing tank, Si, . A], Mn. ．． REM was added to obtain molten steel having the composition shown in Table 11.

When this molten steel is continuously cast by continuous slab casting, we use electromagnetic stirring treatment to change the strength, and for comparison, we manufacture slabs that are not subjected to electromagnetic stirring treatment. did. Slab dimensions are 20" x 1250wI
, it was. After heating the obtained slab, it was made into a hot-rolled plate with a 1.8 ugliness, and after pickling, it was continuously annealed at 850°C for 2 minutes to 0.35? Cold rolled to product thickness, 950℃ x 1min
Finish annealing was performed. The electromagnetic properties of the obtained product are shown in Table 2.
Shown below. It is clear that the magnetic properties are improved by the electromagnetic stirring treatment. Example 2 After decarburizing molten steel blown in a 100 ton converter in a vacuum degassing tank, Si, . Al,. When continuously casting molten steel containing Mn, Ca was added in a tundish.

Table 3 shows the ingredients in the tundish. Further, a slab subjected to electromagnetic stirring at an intensity of F=200A-Hzll2 during continuous casting and a slab not subjected to electromagnetic stirring were produced as comparative examples. The slab dimensions were 200 heads x 1070!1a. The obtained slab was heated and then hot rolled into 2
．． 3? A hot-rolled sheet was obtained, pickled, cold-rolled to a thickness of 0.50 mm, and finish annealed at 900°C. Table 4 shows the electromagnetic properties of the obtained product. Improvement in magnetism was observed by electromagnetic stirring treatment. As explained above, according to the present invention, the electromagnetic properties of the prior art non-oriented silicon steel sheet containing REM and/or Ca can be significantly improved.

[Brief explanation of the drawing]

The drawing shows the electromagnetic stirring intensity and REM. ．． FIG. 2 is a diagram showing the relationship with an index representing the number of Ca sulfides.

Claims (1)

[Claims] 1% by weight, C: 0.05% or less, Si: 1.0-4
．． 0%, Al; 0.150% or more, REM at least one or two or more selected from them, total 0.0
03 to 0.05% and its REM is regulated in the range of 1 to 10 in terms of REM/S ratio, and/or it contains 0.01% or less of Ca and its Ca is regulated in the range of 1 to 10 in terms of REM/S ratio. Continuously cast slabs with an amount regulated within the range of 0.3 to 2.0, with the remainder consisting of Fe and unavoidable impurities, are hot-rolled and cold-rolled according to conventional methods to achieve the final plate thickness. In the method of manufacturing non-oriented silicon steel strip by final annealing, a stirring intensity F of F≧1000A・Hz^1/^2 is applied to the drawn slab during continuous casting. A method for producing a non-oriented silicon steel sheet with low iron loss, characterized by subjecting it to electromagnetic stirring treatment.