KR100957931B1 - Method for manufacturing non-oriented electrical sheets with low core loss - Google Patents

Abstract

The present invention relates to a method for manufacturing a non-oriented electrical steel sheet used as an iron core of electrical equipment such as small and medium motors and transformers.

This manufacturing method is% by weight, C: 0.006% or less, Si: 1.5% or less, Mn: 0.75% or less, P: 0.15% or less, S: 0.02% or less, Cu: 0.01% or less, Al: 0.10 to 0.30% , N: 0.003% or less, B: 0.0003 ~ 0.005%, the slab composed of the remaining Fe and other impurities is reheated to 1100-1250 ° C, hot rolled, wound at 600-750 ° C, and then reduced to 75-85% After cold rolling at a rate, it comprises annealing at 700 to 950 ° C. for 2 minutes or less.

This manufacturing method has the effect of providing non-oriented electrical steel sheet having low iron loss by adding B to prevent precipitation of AlN and to optimize winding temperature, cold reduction rate and annealing conditions.

Iron loss, non-oriented, electrical steel sheet, BN precipitate

Description

Method for manufacturing non-oriented electrical sheets with low core loss

The present invention relates to a method for manufacturing a non-oriented electrical steel sheet used as an iron core of electrical equipment such as small and medium-sized motors and transformers, more specifically to the addition of B to prevent the precipitation of AlN, winding temperature, cold rolling rate and annealing The present invention relates to a method for manufacturing a non-oriented electrical steel sheet having low iron loss under optimized conditions.

Non-oriented electrical steel sheets used as iron cores in electric appliances such as motors, small transformers, and magnetic shields require low iron loss. The iron loss indicates the degree of electrical energy loss per weight of the electrical steel sheet material, expressed in units of W / kg. The method for reducing the iron loss is to increase the content of Si. However, increasing the content of Si can lower the iron loss, there is a problem that the manufacturing cost increases. Therefore, there is a demand for a method for reducing both iron loss and manufacturing cost.                         

Non-oriented electrical steel can lower the iron loss by growing grains in the tissue. Among the elements that suppress the growth of grains, a representative element is N. N combines with Al in the steel to form fine and long AlN to inhibit grain growth. Therefore, even though Al is not added at all or a large amount of Al is added, in this case, there is a problem in that deoxidation is not sufficient or manufacturing cost is increased.

Japanese Patent Laid-Open No. 62-284016 is a related art related to reducing iron loss of non-oriented electrical steel sheet. The prior art relates to lowering iron loss by increasing specific resistance by adding Al, but there is a problem that plate-like defects may be generated by lowering cold rolling to reduce rolling thickness in a hot rolled sheet.

Another prior art is Japanese Patent Laid-Open No. 63-47322. The prior art is to perform light rolling at 2 to 15% after annealing the cold rolled plate to improve magnetic properties, but there is a problem in that the manufacturing process according to the light rolling is lengthened.

Another prior art is Korean Patent Application No. 97-65507. The prior art has a problem that the generation of oxides may increase due to the low content of Sol.Al becomes difficult to deoxidize sufficiently.

The present invention is to solve the above problems of the prior art, to prevent the precipitation of AlN by adding B, to provide a method for producing a non-oriented electrical steel sheet with low iron loss optimized the winding temperature, cold rolling rate and annealing conditions , Its purpose is.

The present invention for achieving the above object by weight, C: 0.006% or less, Si: 1.5% or less, Mn: 0.75% or less, P: 0.15% or less, S: 0.02% or less, Cu: 0.01% or less, Al: 0.10 to 0.30%, N: 0.003% or less, B: 0.0003 to 0.005%, the slab composed of the remaining Fe and other impurities is reheated to 1100 to 1250 ° C, hot rolled, and wound up at 600 to 750 ° C. Cold rolling at a reduction ratio of 75 to 85%, followed by annealing at 700 to 950 ° C. for 2 minutes or less.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The non-oriented electrical steel sheet can lower the iron loss by increasing the specific resistance by adding Si, and by reducing the hysteresis loss by appropriately controlling the amount of impurities, it is possible to lower the total iron loss. Since the method of adding Si causes an increase in manufacturing cost, it is necessary to lower the iron loss as much as possible in the same Si content. Therefore, it is important to lower the hysteresis loss by controlling the amount of impurities. Impurities of the non-oriented electrical steel sheet include finely precipitated AlN, MnS and other oxides. However, the MnS is fixed under the same manufacturing conditions given a component. Therefore, a method of reducing the precipitation of AlN as possible is desirable. AlN does not occur unless Al is added, but Al is added in an amount of 0.005% or less in order to reduce the influence of oxygen in the steel refining process. And Al is added more than the said content because it increases specific resistance. Therefore, by adding B having a strong reaction with N, BN is precipitated instead of AlN. In the present invention, N is AlN, the small amount of precipitation alone, and most of them are precipitated as BN precipitates, and also precipitated as coarse precipitates obtained by mixing various precipitates such as Cu ₂ S in which Cu contained in the steel is precipitated. By growing greatly, the magnetism is improved. In the process of manufacturing the steel as described above, the coiling temperature, cold reduction rate and annealing conditions are important. If the precipitate is excessively large in the process of manufacturing the steel as described above may be destroyed during cold rolling, rather fine, it is essential to carry out the manufacturing conditions according to the present invention.

Hereinafter, the present invention will be described from the reasons for limiting the ingredients.

C: 0.006 wt% or less

The lower the content of C improves the magnetism, and if it is added in excess of 0.006% by weight causes magnetic aging to reduce the magnetic properties during use, it is preferable to limit the content to 0.006% by weight or less.

Si: 1.5 wt% or less

The Si is a component that lowers the iron loss by increasing the specific resistance, and when added in excess of 1.5% by weight causes an increase in manufacturing cost, it is preferable to limit the content to 1.5% by weight or less.

Mn: 0.75 wt% or less

The Mn is an effective ingredient for improving the texture, and when added in excess of 0.75% by weight, the effect is reduced even if it is added, and the content thereof is preferably limited to 0.75% by weight or less.

P: 0.15 wt% or less

The P is a component that forms an advantageous texture for magnetic, and when added in excess of 0.15% by weight, cold rolling property is lowered, it is preferable to limit the content to 0.15% by weight or less.

S: 0.02 wt% or less

S is a harmful component that forms fine precipitates, MnS, thereby suppressing grain growth, and is advantageously managed as low as possible. When the content of S exceeds 0.02% by weight, grain growth is suppressed, so the content is preferably limited to 0.02% by weight or less.

Cu: 0.01 wt% or less

The Cu is a harmful component that forms CuS, which is a fine precipitate, to suppress grain growth, and is advantageously managed as low as possible. When the content of Cu exceeds 0.01% by weight, grain growth is suppressed, so the content is preferably limited to 0.01% by weight or less.

Al: 0.10 to 0.30 wt%

The Al decreases the eddy current loss by increasing the specific resistance, and serves to help B easily bond with N in the B-added steel, when less than 0.10% by weight of AlN may be excessively precipitated, 0.30% by weight If it is added in excess of AlN is less affected even without adding B, it is preferable to limit the content to 0.10 to 0.30% by weight.

N: 0.003 wt% or less

The N is preferably controlled as low as possible to form fine and long AlN precipitates, and in the present invention, it is preferably limited to 0.003% by weight or less.

B: 0.0003 to 0.005 wt%

The B is an effective component for grain growth by combining with N in the material to form coarse precipitate BN instead of fine AlN. When the content of B is less than 0.0003% by weight, excessive AlN may be generated due to the small influence of B addition, and when the content of B is more than 0.005% by weight, the effect is less than the amount of addition, which limits the content to 0.0003 to 0.005% by weight. It is preferable.

In addition to the above compositions, the remainder is composed of Fe and other unavoidable impurities.

The steel slab formed as described above is reheated to 1100 ~ 1250 ° C. and then hot rolled. If the reheating temperature is less than 1100 ° C., the elements in the slab are not sufficiently homogenized, so the load during hot rolling is large, and if the reheating temperature is 1250 ° C. or more, the calorie loss is excessive.

The hot rolled hot rolled sheet is wound at 600 to 750 ° C. and then cold rolled at a reduction ratio of 75 to 85%. The coiling temperature is a temperature at which N is less likely to enter the steel and precipitate into AlN even when the coiling is wound in air. Excess AlN may be formed when the coiling temperature is less than 600 ° C. Since the oxide can be made by combining with Al and the like, the winding temperature is preferably limited to 600 ~ 750 ℃. In addition, when the cold reduction rate is less than 75%, fine air holes, etc., remain in the steel, resulting in deterioration of magnetic properties after final annealing. When the cold reduction rate exceeds 85%, excessively large precipitates are broken, so the cold reduction rate is 75%. It is desirable to limit it to -85%.

The cold rolled sheet is annealed in a continuous process in a mixed atmosphere of nitrogen and hydrogen for 2 minutes at 700 ~ 950 ℃. If the annealing temperature is less than 700 ℃ recrystallization is insufficient, if it exceeds 950 ℃ may be an oxide layer on the surface, the annealing temperature is preferably limited to 700 ~ 950 ℃. In addition, when the annealing time exceeds 2 minutes, since the oxide layer may be formed by combining with oxygen in a small amount of the atmosphere remaining in the atmosphere, the annealing time is preferably limited to 2 minutes or less.

The annealed steel sheet can then be subjected to inorganic or organic-inorganic composite coating treatment.

In addition, the annealed steel sheet can be subjected to stress relief annealing after processing to a desired shape, it can lower the iron loss when performing the stress relief annealing. The stress relief annealing may be performed in a nitrogen atmosphere or a non-oxidizing atmosphere. There is somewhat insufficient grain growth by annealing in a short time by continuous annealing during cold annealing, but the iron loss is lowered by growing the grain through the stress relief annealing, the stress is removed and the permeability is also high. When the annealing temperature is annealing temperature is 750 ~ 850 ℃, annealing time can be carried out for more than 30 minutes, if the annealing temperature is lower than 750 ℃ time is excessively long, if higher than 850 ℃ damage to the insulating film There is a possibility. In addition, if the annealing time is less than 30 minutes, the stress relief annealing may not be sufficiently performed.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

The steel slab formed as shown in Table 1 was reheated to 1150 ° C., hot rolled to be cold rolled at the cold rolling rate of Table 2, wound up in air, and then pickled, followed by the cold rolling rate of Table 2 below. Cold rolling was carried out to prepare a steel sheet to a thickness of 0.50mm. Annealing of the cold rolled plate was performed under the annealing conditions of Table 2 in a mixed atmosphere of 20% hydrogen and 80% nitrogen. Iron loss and grain size of the steel sheet manufactured as described above were measured, and the results are shown in Table 2 below.

As can be seen in Table 2, the invention materials (1 to 6) prepared by the production conditions of the present invention using the invention steel (A ~ C) satisfying the component range of the present invention is a comparative material outside the scope of the present invention Compared with (1-7), the iron loss is small and the grain size is large.

Example 2

After cutting the invention materials (1 to 2, 3) of Example 1 and then stress relief annealing, the magnetic properties were measured. As a result, the invention material (7) which stress-annealed the invention material (1) had an iron loss of 3.62 W / kg, and the invention material (8) which stress-annealed the invention material (2) had an iron loss of 3.50 W / kg, an invention material. The invention material (9) which stress-annealed (3) showed the iron loss of 3.52 W / kg. Therefore, it can be seen that a lower iron loss can be obtained by performing stress relief annealing after cold rolling annealing.

Example 3

By weight, C: 0.002%, Si: 0.82%, Mn: 0.25%, P: 0.015%, S: 0.0023%, Al: 0.16%, N: 0.0015%, Cu: 0.008%, B: 0.0010%, rest Slabs composed of Fe and other impurities were vacuum melted, reheated to 1150 ° C., hot rolled to 2.1 mm, wound at 680 ° C., and cold rolled to a thickness of 0.35 mm and 0.50 mm after pickling. The cold rolled sheet was annealed at 930 ° C. for 60 seconds in an atmosphere of 20% hydrogen and 80% nitrogen. The invention material 10 having a thickness of 0.35mm was 3.1W / kg iron loss (W _15/50 ), the grain size was 80㎛. In addition, the inventive material 11 having a thickness of 0.50 mm had an iron loss (W _15/50 ) of _3.75 W / kg and a grain size of 85 μm.

 As described above, the present invention has the effect of providing a non-oriented electrical steel sheet having a low iron loss by adding B to prevent the precipitation of AlN and optimize the winding temperature, cold reduction rate and annealing conditions.

Claims (2)

By weight%, C: 0.006% or less, Si: 1.5% or less, Mn: 0.75% or less, P: 0.15% or less, S: 0.02% or less, Cu: 0.01% or less, Al: 0.10 to 0.30%, N: 0.003 % Or less, B: 0.0003 ~ 0.005%, slab composed of the remaining Fe and other impurities are reheated to 1100 ~ 1250 ℃, then hot rolled, wound at 600 ~ 750 ℃ and cold rolled at 75 ~ 85% Then, a low iron loss non-oriented electrical steel sheet comprising annealing at 700 ~ 950 ℃ 2 minutes or less. The method of manufacturing a non-oriented electrical steel sheet having low iron loss according to claim 1, wherein the stress relief annealing is further performed after the annealing.