JP3458682B2 - Non-oriented electrical steel sheet excellent in magnetic properties after strain relief annealing and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties after strain relief annealing and a method for producing the same, particularly when Ti, which is a harmful element, is mixed in the steel during the production process. Even so, it is intended to stably obtain excellent magnetic characteristics without variations in characteristics after the strain relief annealing.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are mainly used as iron cores for rotating equipment, transformers, etc. In order to improve the energy efficiency of these devices, the iron loss of the non-oriented electrical steel sheet which is the iron core material is taken into consideration. It is important to lower it. In recent years, along with the increasing demand for higher efficiency in rotating equipment, the demand for improved magnetic properties, especially high magnetic flux density and low iron loss, has also increased in non-oriented electrical steel sheets. Regarding loss characteristics, materials with W _15/50 and 3.5 W / kg or less are required.

Conventionally, the above-mentioned materials having a low iron loss have not been considered so much in the strain relief annealing process, and have been used by steel sheet manufacturers.
It was annealed in a high temperature range exceeding 00 ° C, controlled to obtain a predetermined grain size, that is, iron loss, and supplied to the motor manufacturer.

On the other hand, recently, as a utilization form of a high-performance electromagnetic steel sheet, a product steel sheet is punched into a predetermined shape by a motor maker or the like and then subjected to strain relief annealing at 750 ° C. for 2 hours to be used as a motor component. The method of doing so is becoming more common. The original purpose of applying strain relief annealing was to recover the deterioration of magnetism (about 0.1 to 2.0 W / kg) caused by strain during shearing. However, at present, in order to ensure the punching precision during shearing, the particle size is
On the other hand, the idea of improving the characteristics by growing the crystal grains by subsequent strain relief annealing is becoming generalized while the thickness is set to about 20 to 30 μm.

As a magnetic characteristic improving technique based on the above-mentioned idea, the present inventors have previously described in JP-A-8-3699 and JP-A-8-325678 that the impurity elements Ti and Zr are used.
We have proposed a manufacturing technique that is mainly based on the reduction of the amount and inclusion control by adding REM, and showed that it is possible to manufacture a non-oriented electrical steel sheet with excellent magnetic properties after strain relief annealing.

[0006]

However, when manufacturing a non-oriented electrical steel sheet according to the above-mentioned manufacturing technique, there are occasional cases where the Ti content in the steel fluctuates greatly and the target characteristics cannot be achieved accordingly. It was Such a change in characteristics not only causes a reduction in product yield, but also poses a problem because it threatens a stable supply of products.

[0007] Therefore, as a result of proceeding with the analysis, paying attention to the behavior of Ti in particular, in order to solve the above problems, the inventors have found that steel containing a relatively large amount of Al has a slag content in the slag during molten steel refining.
When Ti is reduced by Al and returned to the steel, the Ti concentration increases, and when the Ti concentration increases in this way, 750
It was found that the magnetic characteristics of the product are likely to vary because the magnetic deterioration occurs after the strain relief annealing at ℃ for 2 hours. Such Ti recovery Ti is an unavoidable phenomenon in the current refining metallurgy when the Al content is large, so in order to suppress the characteristic deterioration due to the variation of Ti as much as possible, auxiliary raw materials, flux and slag are used. Strict refining management of the Ti contained in it is necessary, which inevitably leads to cost increase and productivity deterioration due to yield reduction.

The present invention advantageously solves the above-mentioned problems. Even when Ti is contained to some extent, excellent magnetic characteristics can be stably obtained without causing magnetic deterioration after strain relief annealing. The aim is to propose a non-oriented electrical steel sheet together with its advantageous manufacturing method.

[0009]

Means for Solving the Problems The clarification process of the present invention will be described below. Table 1 shows the amount of Al in the steel and the ratio of the magnetic deterioration coil (the iron loss after strain relief annealing is 0.5 W from the target iron loss.
The result of investigation on the relationship with the increase of Ti content in steel (Ti ≧ 15 ppm) is shown below. In addition,
Components other than Al were constant.

[0010]

[Table 1]

As shown in Table 1, with the increase of Al,
The ratio of magnetic deterioration coils increased. Especially, Al is 0.6wt%
In the materials exceeding 1.0, the effect of improving magnetism after annealing decreased due to the increase of Ti. It is considered that the increase of Ti in the high Al component system is due to the reduction of Ti oxide in the auxiliary raw material and slag with Al and returning to Ti in the steel. It turned out to be a problem.

As described above, such a phenomenon is unavoidable in the current refining and metallurgy process, and in order to suppress the characteristic deterioration due to the variation of Ti as much as possible, the strict content of Ti contained in the auxiliary raw material, the flux and the slag should be suppressed. Refining management is required, but it is very limited by the current technology, so the problems of yield reduction and instability of characteristics due to variations in Ti are unavoidable. Therefore, in order to realize stable production of products, it is essential to obtain stable magnetic properties excellent after strain relief annealing even in steel containing Ti to some extent.

Under the background as described above, the inventors have found that Ti
As a result of intensive studies on the relationship between the amount and the low temperature grain growth property, even if Ti is conventionally considered to be extremely harmful to the grain growth property as long as the content is 0.0050 wt% or less, O, S,
If N is reduced as much as possible and the processes after hot rolling are optimized, grain growth can be secured in strain relief annealing at 750 ° C. for 2 hours, and eventually the characteristics are stabilized. I got the knowledge. The present invention is based on the above findings.

That is, according to the present invention, C: 0.005 wt% or less, Si: 0.1-3.5 wt%, Mn: 0.1-1.5 wt%, Al: 0.
6-2.0 wt% and Ti: 0.0015-0.
0050 wt% (excluding 0.0015 wt%) is allowed, and S, O and N are suppressed to S: 40 ppm or less, O: 30 ppm or less, N: 50 ppm or less, respectively. , The balance is composed of Fe and unavoidable impurities , the grain size before strain relief annealing is 35 μm or less, and 750
A non-oriented electrical steel sheet having excellent magnetic properties after stress relief annealing, characterized by having a grain size of 65 μm or more after stress relief annealing at 2 ° C. for 2 hours.

The present invention is also characterized in that C: 0.005 wt% or less,
Si: 0.1-3.5 wt%, Mn: 0.1-1.5 wt%, Al: 0.6-
Contains 2.0 wt% and Ti: 0.0015 to 0.0050 as impurities
wt% (excluding 0.0015 wt% ) is allowed, and S, O and N are suppressed to S: 40 ppm or less, O: 30 ppm or less, N: 50 ppm or less, respectively. , The balance is a steel slab having a composition of Fe and unavoidable impurities , hot-rolled, then cold-rolled, and then subjected to finish annealing to produce a non-oriented electrical steel sheet. Before cold rolling, heat at least once in the temperature range of 700 to 900 ℃ for 30 minutes to 10 hours, and then anneal at least 500 ℃ at a cooling rate of 50 ℃ / min or less. The magnetic properties after stress relief annealing are characterized by a steel structure in which the grain size before strain relief annealing is 35 μm or less and the grain size after strain relief annealing at 750 ° C. for 2 hours is 65 μm or more. It is a method for producing a non-oriented electrical steel sheet having excellent heat resistance.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Below, the experimental results which are the basis of the present invention will be explained. Si: 0.6 wt%, Al: 1.5 wt
%, Mn: 0.6 wt%, P: 0.02 wt%, C: 15-20 ppm,
A steel ingot containing S: 20 to 26 ppm, O: 12 to 15 ppm, N: 30 to 35 ppm and having Ti changed from 5 ppm to 90 ppm was prepared, and after hot rolling, A: at 810 ° C. After heating for 2.5 h, cooling to 500 ° C at 20 ° C / min B: After heating at 810 ° C for 2.5 h, cooling to 500 ° C at 100 ° C / min C: After heating at 950 ° C for 30 s, 100 ° C / min to 500 ° C After annealing treatment to cool with 0.5mm, cold rolling to 0.5mm thickness, then
The product was annealed at 850 ° C for 10 seconds to obtain a product. At this time, the particle size of the obtained product plate was 24-29 μm. Then 750
After performing stress relief annealing for 2 hours at ℃, measure the magnetic field,
The effect of Ti content on grain growth was investigated.

FIG. 1 shows the relationship between the Ti amount and the iron loss after strain relief annealing. It is understood that under the conditions of B and C, the magnetism after annealing is not improved, and only under the condition of A, the magnetism after annealing is improved. From this, it was found that in the Al-added steel, the temperature and cooling rate of the heat treatment before cold rolling are important in order to stably improve the inhibition of grain growth by Ti. This phenomenon is caused by the appropriate annealing before cold rolling.
It is considered that the grain growth at 750 ° C was improved as a result of coarsening and detoxifying the system precipitates.

It has been a well-known phenomenon for low-Ti materials to reduce iron loss more than annealing at low temperature for a short time when hot-rolled sheet annealing is carried out. About Ti by hot-rolled sheet annealing with controlled cooling rate
It is a fact that was discovered for the first time in the present invention that the adverse effects of the above can be eliminated, and this eliminates the need for the conventional Ti reduction efforts for high Al materials, and although there are some additional steps, stable operation is possible without variations in operation. As a result, a low iron loss non-oriented electrical steel sheet was obtained.

Further, according to the research conducted by the inventors, in order to secure the above-mentioned hot rolled sheet annealing effect, S, O,
It was also determined that the reduction of N is important. In Table 2, Si:
1.1 wt%, Al: 1.5 wt%, Mn: 0.6 wt%, P: 0.02 wt%
%, Ti: 25 to 30 ppm, and various ingots of S, O, and N were subjected to strain relief annealing under the condition A, and magnetic measurements were performed on the obtained annealed sheet. The results are shown below.

[0020]

[Table 2]

As is apparent from the table, this effect cannot be obtained unless S, O and N are all reduced. Therefore, in order to effectively improve the magnetic deterioration phenomenon of strain relief annealing, the reduction of S, O and N is also an important factor.

Next, the reason why the composition of the steel sheet is limited to the above range in the present invention will be explained. C: 0.005 wt% or less C deteriorates the magnetic properties due to the precipitation of carbides.
It was limited to 0.0050wt% or less. Si: 0.1-3.5 wt% Si is a main element of electrical steel sheets and effectively reduces iron loss by increasing the specific resistance, but the content is 0.1
If less than wt%, the effect is not sufficient, while 3.5 wt%
, The cold workability deteriorates, so Si is 0.1 to 3.5.
It was limited to the wt% range. Mn: 0.1 to 1.5 wt% Mn has a function of fixing S as coarse MnS, and for this purpose, 0.1 wt% or more must be contained. On the other hand, the increase in the amount of Mn added deteriorates the magnetic flux density, so its upper limit is 1.
It was set to 5 wt%. Al: 0.6 to 2.0 wt% Al, like Si, is a useful element that effectively contributes to the reduction of iron loss by increasing the specific resistance and does not increase the height as much as Si. If the amount of Al is less than 0.6 wt%, the increase in Ti as described above does not occur, and therefore the hot-rolled sheet annealing treatment of the present invention is not particularly required. Therefore, the lower limit of the amount of Al is set to 0.6 wt%. . However, if it exceeds 2.0 wt%, the decrease in magnetic flux density will increase, so the upper limit is 2.0
It was set to wt%.

S: 40 ppm or less, O: 30 ppm or less, N: 50
ppm or less S, O, and N are all mixed in steel as impurity elements, and it is desirable to reduce them as much as possible. In particular, S
At> 40 ppm, O> 30 ppm, N> 50 ppm, sulfides, oxides, and nitrides hinder domain wall migration and grain growth,
Since it is difficult to improve the magnetic properties, it was limited to the above range.

Ti: 0.0015 to 0.0050 wt% (however, 0.0015 wt
Except) Ti is%, carbides, nitrides, to form a sulfide, a great influence component grain growth during strain relieving annealing. In the past, it was necessary to reduce it as much as possible.
In Al-containing steel, it is difficult to reduce it stably.
Here, if the amount of Ti is less than 0.0015 wt%, the product yield is reduced and the cost is high, but even if the hot-rolled sheet annealing as in the present invention is not performed, the harmful effect due to Ti does not particularly occur . , If the Ti content exceeds 0.0050 wt%, the Ti precipitates impede domain wall movement and grain growth, leading to deterioration of magnetic properties.
Ti amount is 0.0015 to 0.0050wt% (excluding 0.0015wt%)
Limited to the range .

Other components are not particularly limited, but Zr, Mo, V, Cu, Nb and B, which are elements forming sulfides, oxides, nitrides, etc., should be reduced as much as possible. Is desirable. In addition, even when the conventionally known Sb, Sn, or Ca is added, the effect obtained is not affected.
In particular, Sb is well known for its effect of suppressing nitriding during annealing, and can be advantageously applied to this material.

Next, the manufacturing process will be described. Converter-
It is melted by a steelmaking method according to a conventional method such as a degassing method, and is made into a slab by continuous casting or the ingot-casting method. Then, the slab is hot-rolled, and any of a method of reheating the slab and then hot-rolling, and a method of continuously casting without heating the slab and directly hot-rolling are suitable.

The point of the present invention is the heat treatment of the hot rolled sheet after the hot rolling, and the annealing treatment as described below is performed at least once after the hot rolling is completed and before the cold rolling is started. . Regarding the heating conditions, the temperature shall be from 700 to 900 ° C and the time shall be 30 minutes or longer and 10 hours or shorter. If the heating temperature is less than 700 ° C, the grain growth improving effect is not observed, while if it exceeds 900 ° C, the processing in the post-process increases due to the development of scale and the like, which causes a problem in productivity. Because. If the treatment time is less than 30 minutes, the effect of improving the magnetism cannot be obtained, while if it exceeds 10 hours, the productivity is deteriorated.

Next, cooling is performed. In the present invention, this cooling treatment is particularly important, and at least 500
Cooling rate up to ℃: It is necessary to cool slowly at 50 ℃ / min or less. In such cooling treatment, the cooling rate is 50 ° C.
The reason for limiting the growth rate to less than / min is to improve the grain growth inhibition caused by Ti, and the effect of improving grain growth is not seen at cooling rates over 50 ° C / min. Is considered to be related to the growth of Ti precipitates, and even if a relatively large amount of Ti is contained, it is possible to eliminate the adverse effect of Ti by annealing under the appropriate conditions described above. is there.

The hot-rolled sheet annealing as described above may be carried out as a heat treatment immediately after the hot-rolling, or the hot-rolled sheet may still be annealed.
It may be annealed at a high temperature of about 00 ° C. for a short time (10 s) to control the grain size before cold rolling, or may be an ordinary box annealing furnace. Although such hot-rolled sheet annealing causes a slight increase in cost due to an increase in the number of steps, it is low in cost as compared with the reduction in yield due to the deviation of Ti in steelmaking and the deterioration in productivity, and thus has a great total merit.

After that, cold rolling and finish annealing are performed. These treatments include a method in which the product thickness is obtained by cold rolling once and then finish annealing, and a method in which cold rolling including intermediate annealing is performed twice or more to obtain product thickness and then finish annealing is performed. Is also good. It should be noted that the grain size must be 35 μm or less at the time of finish annealing. This is indispensable for obtaining the punching accuracy of the product, and the punching accuracy is deteriorated when the particle diameter is larger than this. In order to obtain such a grain size, it is important to properly select the finish annealing temperature, and annealing in the range of 700 to 900 ° C is appropriate. This is because when the finish annealing temperature exceeds 900 ° C, grain growth becomes noticeable, causing problems with punching accuracy, and the grains grow too much during finish annealing, and the subsequent low temperature strain relief annealing at 750 ° C causes grain growth. This is a product that does not grow at all, and is no different from the conventionally known full-process material with low iron loss. Needless to say, an insulating film may be formed on the surface of the steel sheet by a known method thereafter.

Further, according to the present invention, it is necessary that the crystal grain size becomes 65 μm or more after the strain relief annealing at 750 ° C. for 2 hours. This is the minimum required grain size for obtaining a predetermined iron loss, and iron loss of W _15/50 = 3.5 W / kg or less cannot be stably obtained unless it is 65 μm or more. The steel structure that causes such grain growth can be formed by the annealing treatment in consideration of the cooling rate as described above. Conventionally, in high-Ti steels, it was extremely difficult to set the grain size after finish annealing to 35 μm or less, and to set the grain size to 65 μm or more by strain relief annealing at 750 ° C. Even if the amount is large, a predetermined particle size can be obtained.

[0032]

Example 1 Molten steel having the composition shown in Table 3 was continuously cast by converter refining and degassing, and the obtained continuous cast slab was reheated and hot rolled, The hot rolled sheet was annealed under the conditions shown in Table 4. Then, it was cold-rolled once to form a cold-rolled sheet having a thickness of 0.5 mm, then subjected to finish annealing at 800 ° C. for 12 s, and then an insulating film was formed to obtain a product. The particle diameters of the obtained products were all 35 μm or less. Then, after shearing to a predetermined size, strain relief annealing was performed at 750 ° C. for 2 hours in a nitrogen atmosphere, and then the crystal grain size was measured and magnetic measurement by the 25 cm Epstein method was performed. The obtained results are also shown in Table 4.

[0033]

[Table 3]

[0034]

[Table 4]

No. 1 is a low Al material in which the amount of Ti is reduced. However, in order to reduce such Ti, as described above, strict refining management of Ti is required, so the operation is It was extremely difficult. Moreover, even though the Ti content was reduced, the content was more than the upper limit of 15 ppm, which was the upper limit, so that sufficient magnetic improvement effect could not be obtained even by strain relief annealing. No.3 is No.6 because the annealing temperature of hot-rolled sheet was too low.
Since the cooling rate up to 500 ° C was too fast, it was still impossible to obtain a sufficient magnetic improvement effect by strain relief annealing. No. 10 is an example where the hot-rolled sheet annealing time was too long, and N
o.12 is an example in which the annealing temperature of the hot-rolled sheet was too high. However, although the iron loss characteristics were good, the pickling was extremely difficult because the scale development was remarkable. No. 13 is an example of hot-rolled sheet annealing at high temperature for a short time, and No. 14
Is an example of cooling at a higher speed, but none of them could obtain good iron loss characteristics.

On the other hand, the products obtained according to the present invention (No. 2, 4-5, 7-9, 11, 15-17) are all Ti
Although it was contained in a relatively large amount of 20 to 30 ppm, excellent iron loss characteristics could be obtained under good grain growth. From this also, in order to improve the magnetic properties by strain relief annealing in a steel material containing a relatively large amount of Al and therefore an increase in Ti is unavoidable, according to the present invention, annealing temperature: 700-900 ℃, Annealing time: It can be seen that an annealing treatment of heating for 0.5 to 10 hours and then gradually cooling at a cooling rate of 50 ° C./min or less is extremely effective.

Example 2 A continuous casting slab having the composition shown in Table 5 and manufactured in the same manner as in Example 1 was hot-rolled, and then hot-rolled sheet was annealed under the conditions shown in Table 6, and then, 0.5mm after one cold rolling
After making a thick cold-rolled sheet, finish annealing was performed at 800 ° C for 12 s, and an insulating film was formed to obtain a product. The particle diameters of the obtained products were all 35 μm or less. Then, after shearing to a specified size, in a nitrogen atmosphere at 750 ℃, 2
After performing the strain relief annealing of h, the crystal grain size was measured and the magnetic measurement was performed by the 25 cm Epstein method. The obtained results are also shown in Table 6.

[0038]

[Table 5]

[0039]

[Table 6]

As shown in Table 6, the amount of Ti and the amount of S, O and N in the steel each exceeded the allowable upper limit (No.
3), 4), 6), 8) did not have good iron loss characteristics, but those of which Ti, S, O, and N contents were suppressed to predetermined levels, respectively, had good iron loss characteristics. I was able to get

[0041]

As described above, according to the present invention, it is possible to effectively eliminate the deterioration of grain growth during strain relief annealing due to the increase in the amount of Ti mixed with the addition of a large amount of Al, and to improve the dispersion of characteristics. It is possible to stably obtain a non-oriented electrical steel sheet having excellent magnetic properties.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the amount of Ti in steel on iron loss characteristics after strain relief annealing, using the conditions of hot-rolled sheet annealing as a parameter.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-3699 (JP, A) JP-A-5-5126 (JP, A) JP-A-59-100217 (JP, A) JP-A-11- 158550 (JP, A) Tokuyo Hyo 6-503609 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22C 38/00 303 C21D 8/12 H01F 1/16

Claims (2)

(57) [Claims] 1. C: 0.005 wt% or less, Si: 0.1-3.5 wt%, Mn: 0.1-1.5 wt%, Al: 0.6-2.0 wt%, and Ti: 0.0015-0.0050 wt% as impurities (however, , 0.0015 wt%), and the mixture of S, O and N is suppressed to S: 40 ppm or less, O: 30 ppm or less, N: 50 ppm or less, and the balance is Fe. And the composition of unavoidable impurities, the grain size before strain relief annealing is 35 μm or less, and 750 ° C,
A non-oriented electrical steel sheet having excellent magnetic properties after stress relief annealing, which has a crystal grain size of 65 μm or more after stress relief annealing for 2 hours. 2. C: 0.005 wt% or less, Si: 0.1-3.5 wt%, Mn: 0.1-1.5 wt%, Al: 0.6-2.0 wt% and Ti: 0.0015-0.0050 wt% (however, as impurities) , 0.0015 wt%), and the mixture of S, O and N is suppressed to S: 40 ppm or less, O: 30 ppm or less, N: 50 ppm or less, and the balance is Fe. The steel slab with the composition of unavoidable impurities is hot-rolled, then cold-rolled, and then finish-annealed to manufacture a non-oriented electrical steel sheet.After finishing hot-rolling and before final cold-rolling , At least once in the temperature range of 700 to 900 ℃ for 30 minutes to 10 hours, and then at least 500 ℃ is cooled at a cooling rate of 50 ℃ / min or less to remove strain. The grain size before annealing is 35μm or less, and the grain size is 6 after strain relief annealing at 750 ℃ for 2h. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties after strain relief annealing, characterized by having a steel structure of 5 μm or more.