JPS58123825A - Manufacture of nonoriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To manufacture a nonoriented electrical steel sheet with a small iron loss by holding a continuously cast slab contg. specified percentages of Si, Mn, P, Al, C, S, Ca and a rare earth element in Fe at a specified temp. under specified conditions and by hot rolling it at once. CONSTITUTION:A continuously cast hot slab consisting of 1.5-4% Si, 0.1-1.5% Mn, <=0.1% P, 0.2-2% Al, <=0.008% C, 0.003-0.015% S, 0.003-0.03% at least one of Ca and a rare earth element, and the balance essentially Fe is held at 900-1,150 deg.C for <=30min. It is hot rolled at once and cold rolled to obtain a steel sheet. Thus, the time for holding the slab at said temp. can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a non-oriented electrical steel sheet with a low core loss, and particularly the present invention relates to a method for producing a non-oriented electrical steel sheet with a lower core loss than a continuously cast slab.

The conventional method for manufacturing non-oriented electrical steel sheets involves tapping molten steel produced in a converter, degassing it, and adjusting the composition by adding ferroalloys and the like. The molten steel after the composition adjustment is poured into an independent mold, and the resulting steel ingot is either bloomed into a slab or directly formed into a slab by continuous casting. The slab thus obtained requires a large amount of thermal energy because it is once cooled to room temperature and then subjected to precious heating (slab heating) and hot rolling. In response to this, a recent technology has been developed to make the continuous casting process and hot rolling process continuous, and to utilize the sensible heat of the slab to save energy. That is, this method involves hot rolling continuously cast slabs on a high-temperature platform to improve thermal energy efficiency and operational efficiency. This manufacturing method is generally called the continuous casting direct piezoelectric method, but when applied to the manufacturing of non-oriented electrical steel sheets, it has a serious drawback in that the desired magnetic properties cannot be obtained in the final product.

The reason for this is that a large amount of AAN is finely dispersed and precipitated in the hot-rolled steel sheet, suppressing grain growth during final annealing of the cold-rolled steel sheet.

As a means to avoid this, in the conventional slab heating method, for example, as disclosed in JP-A No. 49-38814, there is a method of reducing the heating temperature to 1200 C or less, and a continuous casting direct heating method. Regarding the rolling method, the Special Publication Act of 1986-
As disclosed in No. 18015 and % Kosho No. 56=33451, hot-rolled 1M1K high-temperature slade was
Insulate for 40 minutes or more in the temperature range of oo-1oso'e,
There is a method to coarsen AN.

However, such long heat retention treatment in continuous cast direct rolling goes against the improvement of operational efficiency, which is one of the advantages of continuous cast direct rolling, so it was necessary to shorten this heat retention treatment time by some means. .

An object of the present invention is to provide a method for producing a non-oriented electromagnetic copper plate having lower iron loss than a continuous casting slab, which can eliminate the disadvantage of long heat retention treatment time according to the conventional method. , the said object can be achieved by providing the method according to the claims.

Next, the present invention will be explained in detail.

In order to shorten the heat retention treatment time, the present inventors have tried various experiments and found that among the components of steel, C, S, +
This book is based on the new finding that the heat retention treatment time can be shortened by adjusting the content of C or by adjusting the content of C and Aj and adding a special element. )4 Completed the invention.

According to the present invention, since a continuous casting slab containing 2 to 2% of AAo is used, the slab contains! 'dN is precipitated as a precipitate.

By the way, the mechanism by which AJLN deteriorates the magnetic properties of a product by suppressing the grain growth of the steel sheet and the mechanism by which the magnetic properties are improved by coarsening AtN have been known for a while. Kaisho 49-388
It is disclosed in No. 14. As can be seen from this disclosure, K
AAN has a relatively low solid solution temperature, and at the normal slab heating temperature of 1200 to 1300C, most of the M balls are in solid solution, which causes a large number of fine At
On the other hand, if the slab is heated below 1200C, AjN causes large precipitates that do not suppress grain growth and deteriorate the magnetic properties. It is present in the steel in the form of grains, and its subsequent processing provides good magnetic properties.

Therefore, in continuous casting direct pressure [also in
It was believed that it was necessary to coarsen νN to a large size by heat retention treatment at a temperature of 800 to 1050 C for 40 minutes or more as described in Japanese Patent Publication No. 18045 and Japanese Patent Publication No. 56-33451.

On the other hand, in the conventional slab heating method, A
Methods of reducing the solid solution amount of AN at a constant temperature have been known for some time, and in principle, the following methods a) and b) are possible.

a) Trans, A8M 461470~, whose main purpose is to increase the amount of added steel and reduce the amount of solid solution of AjN
1499 (1954).

b) A method disclosed in JP-A-49-38814, characterized in that the amount of C in the steel is reduced, thereby reducing the amount of solid solution of /UN.

In the conventional slab heating method, the mechanism by which magnetic properties are improved by reducing the amount of νN in solid solution is already clear. In other words, a decrease in the solid solution amount of AtN at a certain slab heating temperature means that the number of fine AjNOs that are dissolved and precipitated during the next step of hot rolling is reduced. As a result, the absolute number of AtN is reduced, and the effect of inhibiting the growth of crystal grains by AjN on the growth of crystal grains in the negative plate can be sufficiently rendered harmless.

The present inventors thought that the component adjustment method described in a) t or b) above would also be effective in continuous casting direct rolling, but the mechanism that brings about this effect is different from that of the conventional slab heating method. I found out something completely different. That is, a)
Or, because the solid solution temperature of klN increases by means of b), /UN starts to precipitate at a higher temperature than a slab that has not been subjected to composition adjustment during the cooling process of a slab cast at a high temperature, and Fortunately, at such high temperatures, the diffusion rate of rainbow and N is high, and /UN grows into coarse grains with a small number. Therefore, by appropriately selecting the amount of M and the amount of C, it is possible to make the steel plate sufficiently harmless to grain growth in the subsequent process.

The present inventors confirmed this through the following experiment.

Experiment 1 After melting in a converter, vacuum degassing treatment was performed, and the amount of M was adjusted. Various types of molten copper having the thickness shown in Table 1 were continuously cast into slabs with a thickness of 200 mm.

When the surface temperature of the high-temperature slab that comes out of the continuous casting machine reaches the set heat retention temperature, a heat insulating material is placed on the surface of the high-temperature slab at a temperature of approximately 1200c, and the sample is cut out while changing the heat retention time while preventing heat radiation. Inter-rolling was performed to produce a 2-thick hot rolled sheet.

Table 1 (%) This hot-rolled sheet was normalized at 900C for 1 minute, pickled, cold piezoelectrically processed to a thickness of Q, 5Qw, and decarburized annealed at 900C for 4 minutes (atmosphere H26096, N240 %, dew point 5°C)
The final product was obtained by subjecting it to the following steps, and its magnetic properties were investigated. Some of the results are shown in FIG. Note that the C content after decarburization and purification is 0.004% or less in all cases, and its effect on magnetic properties is extremely small.

Figure 2 shows the relationship between heat retention temperature and heat retention time on iron loss for steel ingot DK. In the figure, the O mark indicates a point with good iron loss, and the X mark indicates a point with poor iron loss, and the hatched frame is an area where good iron loss can be obtained in a short time.

From the results in Figures 1 and 2, the amount of S should be 0.003% or less.
If the amount of C is regulated to be less than o, 'oos, and the amount of At is regulated to be more than 0.20%, the effective heat retention temperature range is 900 to 1.
It becomes 150U, and the heat retention time is shortened to less than 30 minutes.

The fact that the effective heat retention temperature range has shifted to a higher temperature side than the known temperature range of continuous casting direct rolling indicates that the method of the present invention utilizes the increase in the solid solution temperature of AAN to obtain the effect of improving iron loss. It shows that

However, if the concentration of 8 in the steel is high, as shown by the steel ingot symbol E in FIG. , C was found to be impossible to shorten the heat retention time.

However, in actual manufacturing, suppressing the S content to 0.003% or less would result in a significant cost increase, so we developed a technology that can shorten the heat retention time of high-temperature slabs even when the S content is high. is necessary. As a result of various investigations, the present inventors found that the reason why the heat retention time shortening effect could not be obtained in the case of a high 8fi like the steel ingot E was the grain growth suppressing effect due to Mn8 precipitates. . Also AJLN
9, it was concluded that with MnS, it is difficult to shorten the heat retention time of a high-temperature slab due to an increase in the solid solution temperature. The most effective method is to combine S as a compound with another element that is harmless in terms of magnetic properties.
Moreover, we tried to select elements whose solid solution temperature is high for the compound. In other words, most of the S is combined with other elements, and the concentration of [S] that can exist as Mn8 is reduced to substantially 0.
．． Rare earth elements and Ca are known as elements that fix 8 in molten steel, which is a method of suppressing the S content to 0.006% or less. An experiment similar to Experiment I was conducted. Table 2 shows the components of each slab and some of the experimental results.

As seen in Table 2, steel ingots in which S was fixed by introducing Ca or rare earth elements into molten steel were able to shorten the heat retention time to within 30 minutes.

Table 2) Heat retention temperature 11001:' Here, as a method of adding rare earth elements, 50qb of Ce
A method was used in which metals were added into molten steel, with the remainder mainly consisting of rare earth elements such as Lm, Nd, and Sm.

Next, the reason for limiting the component composition in the present invention will be explained.

8i is an element necessary to improve magnetic properties, but 1
．． If it is less than 5%, the desired magnetic properties cannot be obtained, while if it is more than 4.0%, the cold rollability will deteriorate significantly and it cannot be put to practical use. It is necessary to keep it within the range of i to 4.0%.

Pigeon is an element that contributes to improving hot brittleness, but 0
．． If it is less than 1%, the above improvement cannot be obtained;
%, it becomes difficult to reduce the amount of C at the steel manufacturing stage, so it is necessary to keep it within the range of 0.1 to 1.5%.

P is an element that is unavoidably contained in steel unless special treatment is applied, and it does not have a negative effect on magnetic properties in small amounts, but if it exceeds a factor of 0.1, it may cause grain growth. P must be kept at 0.1% or less since it impairs the properties.

If the C content exceeds 0.008%, the heat retention time cannot be shortened, so the C content must be at most 0.00%.

If Niji is less than 0.2%, it will not be possible to shorten the heat retention time, while if it is more than 2%, cold piezoelectricity will deteriorate.
Red should be within the range of 0.2 to 2.0%.

If S is greater than 0.0034, the heat retention time cannot be shortened, so S needs to be 396 or less. However, if the amount of s is 0.003% to 0.01
Between 596 and 8@, Ca or 1 rare earth element (
Atomic numbers 57 to 71) or 2 or more selected from atomic numbers 57 to 71) in the case of two or more, the total amount is 0.003
By adding 0.03% from 96 to fix 8,
The heat retention time shortening effect of the present invention can be exhibited.

When S is o, ots 4 or more, there will be a large amount of inclusions in the steel, which is unfavorable in terms of magnetic properties. Ca or rare earth elements can be added to molten steel by any of the following methods. Can be used.

The reason for limiting the manufacturing conditions in the present invention will be explained.

The heat retention temperature of the continuously cast high-temperature slab is set at 900 to 1150 C, since the temperature range of 900 to 1150 C is effective as shown in FIG. Regarding the heat retention time, since it takes about 10 minutes to cast 101% of the slab length, adopting a heat retention time of more than 30 minutes will reduce operational efficiency, so the heat retention time should be kept within 30 minutes. do. In addition, the higher the slab temperature, the better the hot rolling properties.
Hot rolling is performed immediately after heating at 150C.

Next, the present invention will be explained by comparing examples with comparative examples.

Example: Molten in a converter, subjected to vacuum degassing treatment, and various components were removed from the third
Molten steel prepared as shown in H, I, J and L in the table was continuously cast into slabs.

In this ζ, the addition of rare earth elements contains 50% Ce, and the rest is mainly composed of rare earth elements such as La, Nd, Pr, etc.Otsush metal is added to the molten steel, and the amount of addition is confirmed by analyzing the amount of Ce and checking its value. was doubled to obtain the total amount of rare earth elements.

When this high-temperature slab was cooled to 1104)C, a heat insulating material was placed on it, the slab was kept warm for 20 minutes, and then immediately hot-rolled to produce a hot-rolled plate with a thickness of 2.01. This hot-rolled plate is heated to 900C
After normalizing for 2 minutes at
b%N2304, dew point 60%) to make the final product,
We investigated the magnetic properties. The results are shown in Table 4. In addition, the C content after decarburization annealing has a φ deviation of 0.00A al
b or less, and the influence on magnetic properties is extremely small. In addition, steel ingot symbols 4, H, I, J, and N are examples in which the composition was adjusted according to the present invention, and K, L,
M is a comparative example.

Table 3 and above According to the present invention, a non-oriented electrical steel sheet with low iron loss can be manufactured.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between iron loss W2O15Q and heat retention time @), and FIG. 2 is a diagram showing the relationship between heat retention temperature (C) and heat retention time (minutes).

Claims (1)

[Claims] t, 8j 1.5-4%, Mn 0.1-1.5%,
P 0.1% or less, red 0.2-2'! ,80.003
1. In a method of producing a non-oriented electrical steel sheet through a normal hot rolling process and a cold process, a continuously cast slab of 1 or less, CG, 00B or less, and the remainder substantially consists of Fe. Heat the continuously cast high-temperature slab within the temperature range of 900-1150C, and limit the heat retention time to within 30 minutes,
A method for producing a non-oriented electrical steel sheet with low iron loss, characterized by immediately hot rolling. Yu8i 1.5-4%, Mn0.1-1.5
%, P 0.1% or less, I't10.2-2%
, co, oos% or less, 80.003 to 0.015%,
Ca, one selected from rare earth elements, at least t
In the method of manufacturing a non-oriented electrical steel sheet by subjecting a continuously cast slab consisting of 0.003 to 0.03% ill and the remainder substantially Fe to a normal hot rolling process and a cold heron process, A method for producing a non-oriented electrical steel sheet with low iron loss, characterized by retaining a high temperature slab within a temperature range of 900 to 1150 C, limiting the heat retention time to 30 minutes or less, and immediately hot rolling. .