JPS5974258A - Nondirectional silicon steel plate with small iron loss - Google Patents

Abstract

PURPOSE:To obtain a nondirectional silicon steel plate with a remarkably reduced iron loss value by restricting the amounts of O, N and S as impurities in a low C steel plate contg. specified amounts of Si, Al and Mn, and regulating the average grain size. CONSTITUTION:The amounts of impurity elements contained in a steel consisting of, by weight, <=0.005% C, 2.5-4.0% Si, 0.25-1.0% Al, 0.1-1.0% Mn and the balance essentially Fe are restricted to <=15ppm S, <=20ppm O and <=25ppm N. The average grain size which is affected by the relation between the Si and Al contents after annealing is regulated to 100+3.5X[Si%+Al%]<2>-170+5.0X [Si%+Al%]<2>. A nondirectional silicon steel plate of the regulated steel shows a very small iron loss value.

Description

[Detailed Description of the Invention] This invention relates to a non-oriented silicon steel plate with low iron loss,
Especially S, 0. The present invention relates to a non-oriented silicon steel sheet which exhibits an extremely small iron loss value and is made of a material having an extremely low N content and an average crystal grain size within a predetermined range.

Non-oriented silicon steel sheets are often used in the cores of rotors, stators, etc. of rotating machines.In particular, core materials for large rotating machines aim to reduce power loss and heat generation from the perspective of energy conservation and safe operation. This trend is strong, and there is a strong demand for the development of non-oriented silicon steel sheets with low iron loss.

By the way, in order to lower the iron loss value of a non-oriented silicon steel sheet, a method is known in which the amounts of Si and Al added are increased to increase the electrical resistance and thereby reduce the iron loss overall. However, when it is necessary to further improve iron loss from the current level,
If the amount of 81 or AI added is increased more than the current level, the cold workability will deteriorate, so it is difficult to increase the amount added above the current level. In addition, Mn, which is added to improve hot workability, has a small effect on magnetic properties.
Moreover, if added in a large amount, it will deteriorate the magnetic properties, so it is not suitable as an element that lowers the iron loss value.

Therefore, the present inventors determined that S, 0. By focusing on impurities in steel, such as N, and studying the relationship between these impurities and iron loss, as well as the relationship between these impurities, grain size, and iron loss, we have achieved extremely low non-directional iron loss, which was not possible with conventional technology. It has been found that it is possible to obtain a silicon steel plate.

That is, S as an impurity in steel, 0. The N content is S
≦15 ppm, O≦20 ppm, N (at 25 ppm, the iron loss is small, and in such a material with good purity, the crystal grain size value that brings about the best iron loss value is the crystal grain size that was conventionally thought to be optimal. The present invention was completed based on the discovery that the particle size is different from the value of the particle size.

In short, the present invention can produce a non-oriented silicon steel sheet in which only the iron loss value is lower than the US standard without impairing the mechanical properties, by reducing the impurities: S, O, N on an average This was achieved by adjusting the crystal grain size to an optimum range.

From this, the present inventors first determined the impurity component (S, 0
．． In order to understand the influence of N) on iron loss, the concentrations of each of the above impurities were variously changed. 3, 2% S1-〇, 60% AJI
! - Steel containing 0.20% Mnf was tapped and subjected to rolling and heat treatment according to conventional methods to produce a powerless isotropic silicon steel plate with a thickness of 0.85 mm. As a result, if C is 0.005% or less, the effect on iron loss is small, whereas S, O,
Regarding H, its influence was large and an extremely strong correlation with iron loss was observed. Of these, regarding S and 0, it has already been shown in the 1980s that reducing the content directly leads to improvement in iron loss.
22931 and JP-A-53-66816, it is disclosed that the 0 content is 25 ppm or less and the S content is 5 oppm or less (preferably ia o
It has been proposed that the amount of carbon dioxide (ppm or less) be regulated. It is also known that it is a desirable embodiment to regulate the N content to less than a o ppm.

However, the content in these reports and examples is, for example, taking S as an example, even if the content is low, the content is 20 to 20%.
It has been reported that the level of impurities is around ao ppm, but the influence of impurities down to even lower levels is unknown.

Therefore, the present inventors conducted a side investigation on the influence of impurities at lower levels. According to the results, S:
15 ppm, O: 20 ppm, N:
If it is reduced to level 1 of 25 ppm, the effect of reducing iron loss becomes remarkable, for example, S = 15 ppm, O =
201) I) When lowering m, N = 25 ppm, the iron loss value is WloA.

0.90, W15150-r 2.20, that is, it was found that an iron loss of 88 class Somura could be obtained.

However, even if the content is lowered to a lower level, the reduction in iron loss is not as great as expected, and it is equivalent to class 87 (WIO150≦0.85, W15150≦2).
．． 00) could not be obtained.

The present inventors conducted various studies to understand the cause of this, and found that the appropriate crystal grain size of the steel plate that exhibits the best iron loss value is approximately 1.
It has been found that iron loss is low when the thickness is larger than the conventional value of 30 μm. Figure 1 shows the final annealing conditions in the above experiment: 950° 0 x 5 minutes, which has been conventionally used, and J030° OX 5 minutes, in order to thicken the grains t-i. , impurity S.

The relationship between the 0 and N contents and iron loss is shown.

As can be seen from this figure, S<15ppm, O≦20ppm
In the region containing impurities of m, N≦25 ppm, steel that is annealed at a higher temperature instead of the conventionally employed annealing conditions to cause the crystal grains to tend to coarsen exhibits a lower iron loss value. Furthermore, the present inventors found that S≦15ppm, Q≦
20 ppm, N≦25 ppm (7) As a result of conducting research on various annealing times and temperatures using high-purity materials, it was found that only the selection of annealing times and annealing temperatures is effective in improving iron loss. By increasing the purity, the optimum grain size to bring about the best iron loss value is achieved.
It was newly discovered that the cause was a shift to the coarse grain side.

This will be explained in detail using FIG.

FIG. 2 shows the relationship between iron loss and average grain size (Al is an impurity, S=82 ppm.

The conventional material containing 0 = 22 ppm, N = 26 ppm, 0) contains S = 8 ppm as impurities,
In the materials of the present invention containing O = 7 ppm and N = 14 ppm, both 81 was 8.2% and A7t was 0.
60%, and Mn is 0.20%. Iron loss consists of hysteresis loss and eddy current loss. Hysteresis loss rapidly decreases as the grain size increases, while eddy current loss increases as the grain size increases. As shown in FIG. 2, at a certain appropriate crystal grain size, both are balanced, and the iron loss value takes a minimum value at that position. The average crystal grain size exhibiting the lowest iron loss value is called the optimum average crystal grain size.

It is generally known that the optimum average crystal grain size varies depending on the content of Si + A6, and increases as the content of Si and Aβ increases. However, as shown in FIG. 2, it was not previously known that the optimum average grain size changes depending on the S and 0°N contents of the material.

Therefore, S≦15ppm, o which is within the composition range of the present invention.
The relationship between (Si + kl)% and the optimal average crystal grain size of a material that satisfies ≦20 ppm and N≦25 ppm and the optimal average crystal grain size of a conventionally used material was determined. As a result, as shown in Fig. 3, the optimum average crystal grain size of the present invention material, which exhibits a low core loss value of class 87, shifts to the coarse grain side compared to the optimum average crystal grain size of conventionally used materials. There is a clear distinction between the particles, and the value of the particle size judged in the figure is 10.
Q+3.5 X (S'i+i%]2 and 170 +
The range is narrowed by 50×[Si+A1%]2.

The reason why the range is wider than that of conventional materials is that, as shown in FIG. 2, the change in characteristics near the minimum value is small. Third
In the figure, the most frequent ranges of optimal average grain size are 120+3.5X (Si+Ajl1%)2 and 160+
Since this is a narrow range of 50X(Si+AJ%)2, it can be estimated that there is a region with the best characteristics in this range if statistical processing is performed.

In short, in order to obtain a material with a low iron loss value aimed at by the present invention, S
In addition to extremely reducing the contents of , N, and O, it is necessary to adjust the average crystal grain size to within a certain limited range toward the coarse grain side in order to make the most of its properties.

The reason why a material with extremely low S, O, and N contents exhibits a low iron loss value when the optimum average crystal grain size shifts to the coarse grain side is presumed as follows. That is, although it was mentioned above that iron loss consists of hysteresis loss and eddy current loss, eddy current loss does not involve impurities such as S, O, and N.

On the other hand, hysteresis loss increases as impurities in the material and grain boundary density increase. However, on the fine grain side where the grain boundary density is high, the grain boundary density is the main cause of hysteresis loss deterioration, so the effect of impurity reduction is difficult to appear.On the other hand, on the coarse grain side where the grain boundary density is low, impurities deteriorate. This is the main cause of
The effect of impurity reduction is significant. In short, the reduction in hysteresis loss due to the reduction of impurities is smaller on the fine grain side and larger on the coarse grain side. Moreover, since the eddy current loss does not change and only the hysteresis loss changes in this way, the optimum average grain size, which exhibits minimal iron loss as a total sum, naturally shifts to the coarse grain side, resulting in the phenomenon of the present invention. It is assumed that this caused the

As explained above, the present inventors found that S≦15ppm,
In steel in the extremely reduced impurity region of O(: 20 ppm, N≦25 ppm, the average grain size D (μm) is ]00+3.5X(Si%+AJ1%)”≦5≦170
It has been newly discovered that a non-oriented silicon steel sheet with extremely low core loss can be obtained by manufacturing a steel sheet that contains trenches in the range of +5, ox(Si'l/crl-AJ%).

Incidentally, a non-oriented silicon steel sheet having such properties may be produced by conventional general manufacturing methods as long as the composition is limited to the above-mentioned composition. For example, molten steel that has been soft wired is degassed,
After adjusting the composition to a specified composition, it is poured into a mold and subjected to ingot-forming and blooming rolling to form a slab (steel billet), or it is made into a slab by continuous casting, followed by hot rolling and cold rolling according to conventional methods. It is made into a product through a rolling process.

The range of the component composition of the present invention will be described below.

If C exceeds 0.005% by weight, aging will occur and the properties will deteriorate, so the content should be 0.005% by weight or less.

If Si exceeds 4.0% by weight, cold rollability deteriorates, so the Si content is limited to 4.0% by weight. If the amount is less than 2.5% by weight, the electrical resistance will be low and the iron loss will increase, making it impossible to obtain a non-oriented silicon steel sheet with low iron loss, which is the desired effect of the present invention. is the lower limit.

Like Si, AJI increases electrical resistance and is effective in reducing iron loss, but if it exceeds 1.0% by weight, cold workability becomes poor like 81, and if it is less than 0.25% by weight, iron loss decreases. Since this results in significant deterioration, the content is set at 0.25% by weight to 1.0% by weight.

Mn is required in an amount of 0.1% by weight or more from the viewpoint of hot workability, but if it exceeds 1.0% by weight, magnetism deteriorates, so 0.
．． From 1% by weight to 1.0% by weight.

Furthermore, the steel of the present invention particularly contains 25pp as an impurity.
It is necessary to satisfy both m in order to realize low iron loss, and the average grain size D (
μm) is related to (Si + AJ)%, 100 + 3.5X (Si% + A1%) 2≦stone≦170+
5. A non-oriented silicon steel sheet that is required to be adjusted to a size of 5, ox (Si% + A1%)2, and exhibits an extremely low iron loss value by having such a composition and crystal grain size. The use of such an average grain size works synergistically with the ultra-low S, O, and N component compositions mentioned above to achieve the desired effect. FIG. 4 shows a comparison between the average grain size (124 μm) of a conventional non-oriented silicon steel sheet (bl) and the average grain size (208 μm) of the steel (a) of the present invention.

Next, the test results regarding the characteristics of the steel of the present invention will be explained based on Table 1.

After blowing in a converter, degassing treatment is performed, and then Sl:
3.2%, i: 0.60%, Mn: 0.20
%, and the molten steel that has been adjusted by adding alloying ingredients,
A slab was made by continuous casting. At this time, deoxidation treatment and desulfurization treatment are performed using desulfurization flux using Ca etc. or REM.
(Rare earth elements: about 50% oe) are desulfurized using a desulfurizing agent used in combination with the above desulfurizing flux, and by changing the deoxidizing and desulfurizing conditions of -'e, the amount of S and 0 can be controlled. The amount of 0 and N was controlled by changing the degree of oxidation and nitridation caused by the atmosphere during casting by changing the degree of lr sealing. As a result, a slab having the components shown in Table 1 was obtained. These slabs were heated at 1200" O, then hot rolled into coils with a thickness of 2.0", and after pickling, they were divided into two parts.
One of the sheets was continuously annealed at 950° C. for 3 minutes, cold rolled to a thickness of 0.50 mm, and subjected to continuous finish annealing to obtain a product sheet using a single cold rolling method, and magnetic measurements were performed on the product sheet. The other side is cold rolled to a thickness of 0.70mm, and after intermediate continuous annealing at 950°C for 3 minutes, the thickness is further cold rolled to a thickness of 0.35111111mm, and continuous finish annealing is performed. A product plate was prepared by the double cold rolling method, and total magnetic measurements were performed on this product. In addition, in the above manufacturing process, the annealing conditions are controlled, that is, the temperature and time are adjusted so that the average grain size (D) falls within the predetermined range aimed at by the steel of the present invention at a stage before continuous finish annealing. This is very important. Table 1 shows the results of measuring the magnetic properties of each test plate obtained through the above manufacturing process. Table 1 also lists the average crystal grain size measured in the cross section of the plate. At the same time, FIG. 4 shows examples of microphotographs of plate thickness cross sections of these steel plates after finish baking.

In Table 1, the code 1. n was completely compared with a steel whose component composition was within the claimed range of the present invention, a steel whose average grain size was 15θ to 250 μm within the range of the present invention, and a comparative example outside that range. case 0.851
1 steel plate W1o15o≦0.85, “15150≦2
．． 00, which showed an extremely good iron loss. Also, code 1,
For Iv and V, S and O, respectively.

This is an example of a comparative steel within the conventional range in which N was increased outside the range prescribed by the present invention, but the average grain size was set to an appropriate average grain size, and the iron loss was also WO with a steel plate of 0.35 mm. 15OL:, 0
．． 95, wl 515 o#2, 25, which was the original value.

As explained above, according to the present invention, by regulating the optimum average grain size to a predetermined size on the overall coarse grain side for steel with a composition that has decreased by 5 poles in S and 0°N', It is possible to obtain a non-oriented silicon steel sheet metal with significantly lower iron loss.

[Brief explanation of the drawing]

FIG. 1 shows plate N-o, a5myrtv Si: a,
2%, Mn: 0.2%, Al: o, e% It is a graph showing the relationship between S , 0 , N content and iron loss for a non-oriented silicon steel sheet containing gold. Figure 2 shows plate thickness o, a5mts no si: 3.2%, J
It is a graph showing the entire relationship between average grain size and iron loss for a non-oriented silicon steel sheet containing 0.2% on: 0.6% Al. FIG. 3 is a graph showing the relationship between the optimum average grain size and (S, i-+A71)% for obtaining the best iron loss value. Figure 4 shows the non-oriented silicon steel sheet (a) of the present invention and the comparative steel (
It is a micrograph of the metallographic structure showing a comparison of the crystal grain size of (b) and (b). Patent applicant Kawasaki Steel Corporation Figure 1 0 10 20 30 40S, 0. Nfil (pp paddy Figure 2 0 Cane pot material (d) ・ , Book #: tJR's end I ↓ (b) 0 50 100 150 200 250 Burnt crystals attached (ttqn) Figure 8 0ne #light material Si +AI (%) Figure 4

Claims (1)

[Claims] L in weight%, 0: 0.005% or less, Si:
2.5-4.0%, Al: 0.25-1.0%, Mn
: Contains 0.1 to 1.0% with the remainder consisting of unavoidable impurities and Fe, the content of O9N and S as impurities i'i, S≦15ppm, O≦20ppm
, In addition to suppressing N < 25 ppm, the above S
The average grain size shown in relation to 1 and AIN content is l oo+8 , 5x[Si%+-A1%]2≦D≦1
70+5, OX (Si-AJ%) A non-oriented silicon steel plate with low iron loss, which is made of a material having a value within the range of 2.