JP6319586B2 - Method for producing non-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for manufacturing a non-oriented electrical steel sheet, and specifically relates to a method for manufacturing a non-oriented electrical steel sheet having a high magnetic flux density.

  In recent years, energy saving has been promoted from the viewpoint of protecting the global environment, and in the field of electrical equipment, high efficiency and miniaturization are actively directed. Therefore, high magnetic flux density and low iron loss have been strongly desired for non-oriented electrical steel sheets that are widely used as iron core materials for electrical equipment.

  In order to improve the magnetic flux density of the non-oriented electrical steel sheet, it is possible to improve the texture of the product plate, that is, reduce {111} orientation grains or increase {110} or {100} orientation grains. It is valid. Therefore, in the manufacture of non-oriented electrical steel sheets, conventionally, the crystal grain size before cold rolling is increased, the cold rolling reduction ratio is optimized, and the like.

  As another means for improving the texture, there is a technique for increasing the heating rate in the recrystallization annealing. This technique is a technique often used in the production of grain-oriented electrical steel sheets. When the heating rate in decarburization annealing (primary recrystallization annealing) is increased, the {110} orientation grains of the steel sheet after decarburization annealing are increased. It is utilized that the steel loss after secondary recrystallization is refined and iron loss is improved (see, for example, Patent Document 1). Similarly, even in non-oriented electrical steel sheets, a technique has been proposed in which the texture is changed and the magnetic flux density is improved by increasing the heating rate of finish annealing (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 01-290716 Japanese Patent Laid-Open No. 02-011728

  However, the technique disclosed in Patent Document 1 relates to a grain-oriented electrical steel sheet and cannot be applied to a non-oriented electrical steel sheet as it is. Further, it has been clarified that the technique disclosed in Patent Document 2 cannot stably obtain the effect of improving the magnetic flux density, as a result of examination by the inventors.

  The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to stably achieve a high magnetic flux density even in the case of rapid heating for the purpose of improving the texture in finish annealing. It is in proposing the manufacturing method of the non-oriented electrical steel sheet which can do.

  In order to solve the above-mentioned problems, the inventors have made extensive studies focusing on trace components contained in steel and a temperature rising pattern in finish annealing. As a result, in addition to limiting the trace components contained in the steel material (slab), particularly Ti, Nb and As, to a very small amount, an appropriate holding treatment is performed between 250 and 630 ° C. in the heating process of finish annealing. As a result, it was found that a non-oriented electrical steel sheet having a high magnetic flux density can be obtained stably by rapidly heating between 630 and 700 ° C., and the present invention has been developed.

That is, the present invention includes C: 0.0050 mass% or less, Si: 8.0 mass% or less, Mn: 0.03 to 3.0 mass%, P: 0.1 mass% or less, S: 0.005 mass% or less, Al : 3.0 mass% or less, N: 0.005 mass% or less, Ni: 3.0 mass% or less, Cr: 5.0 mass% or less, Ti: 0.003 mass% or less, Nb: 0.003 mass% or less, As: 0 A steel slab containing 0.005 mass% or less and O: 0.005 mass% or less, with the balance being composed of Fe and inevitable impurities, hot-rolled, hot-rolled sheet annealed, or hot-rolled sheet annealed In the method of manufacturing a non-oriented electrical steel sheet that is subjected to finish annealing after one or two or more cold rolls sandwiching intermediate annealing, in the heating process of the finish annealing. Kicking the arbitrary temperature _{T i} of between two hundred fifty to six hundred thirty ° C., number of times or more once retention process for holding between 0.5 seconds or longer _{t i,} and the sum of the _{t i} is 0.5 to 10 seconds After the application, a method for producing a non-oriented electrical steel sheet is proposed, characterized by heating between 630 and 700 ° C. at an average heating rate of 50 ° C./s or more. Here, the holding time t _i refers to the time during which the temperature T _i is held at a temperature within ± 2 ° C.

  The method for producing a non-oriented electrical steel sheet according to the present invention is characterized in that the ferrite grain size before the final cold rolling in the cold rolling is controlled to 50 μm or less.

  Moreover, in addition to the said component composition, the said steel slab used for the manufacturing method of the non-oriented electrical steel sheet of this invention is further 0.005-0.20mass, respectively 1 type or 2 types chosen from Sn and Sb. % Content.

  Moreover, the steel slab used in the method for producing a non-oriented electrical steel sheet of the present invention further includes one or more selected from Ca, Mg, and REM in addition to the above component composition. It contains in the range of 0.010 mass%.

  According to the present invention, a non-oriented electrical steel sheet having a high magnetic flux density can be stably produced even when rapid heating is performed in finish annealing, which greatly contributes to energy saving of electrical equipment.

The average heating rate and retention process between 630-700 ° C. is a graph showing the effect on the magnetic flux density _{B 50.} Between retention temperature and the coercive scheduled in retention process is a graph showing the effect on the magnetic flux density B _50. As content and retention process conditions is a graph showing the effect on the magnetic flux density B _50. It is a diagram illustrating a retention treatment temperature T _i.

First, a series of experiments that triggered the development of the present invention will be described.
<Experiment 1>
C: 0.0021 mass%, Si: 1.01 mass%, Mn: 0.29 mass%, P: 0.06 mass%, S: 0.0012 mass%, Al: 0.0005 mass%, N: 0.0016 mass%, Ni : Steel containing 0.01 mass%, Cr: 0.01 mass%, Ti: 0.0012 mass%, Nb: 0.0004 mass%, As: 0.001 mass% and O: 0.0018 mass% are melted in the laboratory. Then, after forming a steel ingot, it was hot-rolled to obtain a hot-rolled sheet having a thickness of 2.4 mm. When the steel sheet structure of the hot-rolled sheet was examined, it was completely recrystallized and the ferrite grain size was 22 μm. Here, the ferrite particle diameter is an average value when the ferrite particle diameter of the entire plate thickness is measured by a cutting method (hereinafter the same).

Next, the hot-rolled sheet was pickled and cold-rolled to obtain a cold-rolled sheet having a thickness of 0.35 mm, and then subjected to finish annealing at a soaking temperature of 900 ° C. and a soaking time of 10 s.
At this time, heating from room temperature to 740 ° C. in the finish annealing is performed using a heating device in which a plurality of induction heating devices are arranged in series, and from room temperature to 630 ° C., the average temperature increase rate is 30 ° C./s. In addition to heating, at the temperatures T ₁ , T ₂ , and T ₃ in the middle of heating shown in Table 1, the holding treatment is performed for the times t ₁ , t ₂ , and t ₃ , respectively, and the subsequent induction from 630 ° C. to 740 ° C. Heating was performed by changing the output of the heating device and changing the average temperature increase rate between 630 and 740 ° C. in various ways within the range of 30 to 400 ° C./s (the same is true for the average temperature increase rate of 630 to 700 ° C.). Subsequently, from 740 degreeC to soaking temperature (900 degreeC), it heated with the average temperature increase rate of 10 degree-C / s using the electric furnace.

Here, the holding time t ₁ is a time within a range of ± 2 ° C. with respect to the temperature of T ₁ , t ₂ is a time within a range of ± 2 ° C. with respect to the temperature of T ₂ , and t ₃ is T a ₃ times in the range of ± 2 ℃ relative temperature, the average heating rate of up to 630 ° C. from the room temperature, in the time other than the sum of the dwelling scheduled to _{(t 1 + t 2 + t} 3) Average heating rate. The atmosphere in the finish annealing was a hydrogen-nitrogen mixed atmosphere having a vol% ratio of H ₂ : N ₂ = 2: 8 and a dew point of −20 ° C. (PH ₂ O / PH ₂ = 0.006).

From each of the finish annealed plates thus obtained, when the rolling direction is L and the plate width direction is W, two L: 180 mm × W: 30 mm test pieces, L: 30 mm × W: 180 mm test Two pieces were collected and evaluated for magnetic properties (magnetic flux density B ₅₀ ) by an Epstein test.

FIG. 1 shows the influence of the average heating rate between 630 and 700 ° C. and the holding treatment during heating on the magnetic flux density B ₅₀ . From this figure, it can be seen that the magnetic flux density is improved by applying the retention treatment during heating after setting the average temperature rising rate between 630 and 700 ° C. to 50 ° C./s or more.

  Therefore, when the primary recrystallized texture was examined with an X-ray diffractometer for the test piece obtained in the above experiment, the one with a high magnetic flux density had a lower {111} strength than the one with a low magnetic flux density. I understood. That is, conventionally, it is known that the magnetic flux density of the non-oriented electrical steel sheet is improved by rapidly heating the finish annealing, but in order to obtain a higher magnetic flux density, the holding treatment is performed at a temperature during heating. It was found that it was effective to apply

The inventors consider the following reason as follows.
{111} grains have high strain energy accumulated by rolling, and recrystallization proceeds preferentially from a low temperature in the heating process. Therefore, if the rate of temperature increase is increased, the steel sheet reaches a high temperature before the recrystallization of {111} grains proceeds, so that crystal grains having orientations other than {111} grains also cause recrystallization. The frequency of {111} grains that adversely affect the magnetic properties in the recrystallized structure after finish annealing is relatively reduced. Here, when the holding treatment is performed at a temperature lower than the temperature at which recrystallization in the middle of heating starts, recovery preferentially proceeds from {111} grains having a large accumulated strain energy, and recrystallization is prioritized. Sex is reduced. Thereby, the reduction effect of {111} orientation grains when applying rapid heating is further enhanced.

Next, the inventors conducted an experiment to investigate the influence of the temperature and time of the retention treatment applied during the rapid heating on the magnetic properties.
<Experiment 2>
C: 0.0025 mass%, Si: 1.10 mass%, Mn: 0.40 mass%, P: 0.05 mass%, S: 0.0005 mass%, Al: 0.0005 mass%, N: 0.0010 mass%, Ni : Steel containing 0.01 mass%, Cr: 0.01 mass%, Ti: 0.0010 mass%, Nb: 0.0005 mass%, As: 0.002 mass% and O: 0.0012 mass% are melted in the laboratory. Then, after forming a steel ingot, it was hot-rolled to obtain a hot-rolled sheet having a thickness of 2.4 mm. When the steel sheet structure of the hot-rolled sheet was examined, it was completely recrystallized and the ferrite grain size was 20 μm.

Next, the hot-rolled sheet was pickled and cold-rolled to obtain a cold-rolled sheet having a thickness of 0.35 mm, and then subjected to finish annealing at a soaking temperature of 900 ° C. and a soaking time of 10 s.
At this time, heating from room temperature to 740 ° C. in the finish annealing is performed using a heating device in which a plurality of induction heating devices are arranged in series, and until various temperatures T ₁ between 100 to 680 ° C. during heating are performed. Then, after heating at an average temperature increase rate of 30 ° C./s and performing a single holding treatment at the temperature T ₁ , holding the holding time t ₁ in various ranges in the range of 0.2 to 20 seconds, From the holding temperature T ₁ to 740 ° C., heating was performed at an average temperature increase rate of 630 to 740 ° C. at 200 ° C./s (the same is true for the average temperature increase rate of 630 to 700 ° C.). Subsequently, from 740 degreeC to soaking temperature (900 degreeC), it heated with the average temperature increase rate of 10 degree-C / s using the electric furnace.

Here, the holding time t ₁ is a time within a range of ± 2 ° C. with respect to the temperature of T ₁ . The atmosphere in the finish annealing was a hydrogen-nitrogen mixed atmosphere having a vol% ratio of H ₂ : N ₂ = 2: 8 and a dew point of −20 ° C. (PH ₂ O / PH ₂ = 0.006).

Test pieces were collected from each finish-annealed plate thus obtained in the same manner as in <Experiment 1>, and magnetic properties (magnetic flux density _B50 ) were evaluated by an Epstein test.
FIG. 2 shows the influence of the holding temperature T ₁ and the holding time t ₁ on the magnetic flux density B ₅₀ . From this figure, retention temperature _{T 1} is the range of two hundred fifty to six hundred and thirty ° C., and, holding constant-time _{t 1} it was found that good magnetic flux density at a range of 0.5 to 10 seconds is obtained.

Next, the inventors conducted an experiment to investigate the influence of impurity elements in steel on the magnetic property improvement effect by rapid heating.
<Experiment 3>
C: 0.0015 mass%, Si: 1.20 mass%, Mn: 0.60 mass%, P: 0.07 mass%, S: 0.0015 mass%, Al: 0.0010 mass%, N: 0.0007 mass%, Ni : 0.02 mass%, Cr: 0.03 mass%, Ti: 0.0018 mass%, Nb: 0.0011 mass% and O: 0.0011 mass%, further, As is 0.002 to 0.010 mass% The steel added with various changes in the range was melted in the laboratory to form a steel ingot, and then hot rolled to obtain a hot rolled sheet having a thickness of 2.4 mm. In addition, when the steel plate structure | tissue of the said hot rolled sheet was investigated, it recrystallized completely and the ferrite particle size was the range of 17-23 micrometers.

Next, the hot-rolled sheet was pickled and cold-rolled to obtain a cold-rolled sheet having a thickness of 0.35 mm, and then subjected to finish annealing at a soaking temperature of 900 ° C. and a soaking time of 10 s.
At this time, heating from room temperature to 740 ° C. in the finish annealing is performed using a heating device in which a plurality of induction heating devices are arranged in series, and from room temperature to 630 ° C., the average temperature increase rate is 30 ° C./s. In addition to heating, at the temperatures T ₁ , T ₂ , T ₃ in the middle of heating shown in Table 2, after holding treatment for the time t ₁ , t ₂ , t ₃ , respectively, from 630 ° C. to 740 ° C., Heating was performed by changing the output of the induction heating device and changing the average temperature increase rate between 630-740 ° C. to two levels of 30 ° C./s and 200 ° C./s (the same is true for the average temperature increase rate of 630-700 ° C.) . Subsequently, from 740 degreeC to soaking temperature (900 degreeC), it heated with the average temperature increase rate of 10 degree-C / s using the electric furnace.

Here, the holding time t ₁ is a time within a range of ± 2 ° C. with respect to the temperature of T ₁ , t ₂ is a time within a range of ± 2 ° C. with respect to the temperature of T ₂ , and t ₃ is T a ₃ times in the range of ± 2 ℃ relative temperature, the average heating rate of up to 630 ° C. from the room temperature, the sum of the dwelling scheduled _{(t 1 + t 2 + t} 3) excluding the time The average temperature increase rate, and the average temperature increase rate from 630 ° C. to 740 ° C. is an average temperature increase rate between 630 and 700 ° C. The atmosphere in the finish annealing was a hydrogen-nitrogen mixed atmosphere having a vol% ratio of H ₂ : N ₂ = 2: 8 and a dew point of −20 ° C. (PH ₂ O / PH ₂ = 0.006).

Test pieces were collected from each finish-annealed plate thus obtained in the same manner as in <Experiment 1>, and magnetic properties (magnetic flux density _B50 ) were evaluated by an Epstein test.
Figure 3 shows the effect of As content on the magnetic flux density _{B 50.} From this figure, it was found that when the As content exceeds 0.0050 mass%, the effect of improving the magnetic flux density by rapid heating and the retention treatment during heating is weakened.

  Then, in order to investigate said cause, when the primary recrystallization texture of the said test piece was investigated, even if it carried out rapid heating and holding process, what has high As content has high {111} intensity | strength. I found out that That is, As is a harmful element that increases the ratio of {111} -oriented grains and lowers the magnetic flux density. In order to stably realize a high magnetic flux density, the content of As mixed in as impurities is reduced to 0. It was found that it was necessary to limit to 0.005 mass% or less.

  The inventors further conducted the same experiment for trace components other than the above As, and investigated the influence on {111} strength after finish annealing. As a result, similar to As, it was found that there are Ti and Nb as harmful elements that adversely affect the magnetic flux density, and it is necessary to limit each to 0.003 mass% or less.

As described above, the inventors consider the reason why Ti, Nb, and As adversely affect the {111} strength after finish annealing as follows.
Ti, Nb, and As are elements that delay recovery / recrystallization in finish annealing, but {111} oriented grains that are recrystallized quickly are not easily affected. , {110} and {100} oriented grains have a relatively superior predominance of {111} oriented grains. Therefore, even if the heating rate is increased, the generation of {111} oriented grains cannot be suppressed, and the effect of improving the magnetic flux density by rapid heating cannot be obtained.
Therefore, it has been found that in order to obtain a high magnetic flux density stably when rapid heating is performed by finish annealing, it is necessary to use a high-purity steel material in which Ti, Nb, and As are reduced to an extremely small amount.
The present invention has been developed based on the above-described novel findings.

Next, the component composition of the steel material (slab) used for manufacturing the non-oriented electrical steel sheet of the present invention will be described.
C: 0.0050 mass% or less C is an element that causes magnetic aging and forms carbides to deteriorate iron loss characteristics. Therefore, in the present invention, C is limited to 0.0050 mass% or less. Preferably it is 0.0040 mass% or less. In addition, although a minimum is not prescribed | regulated, it is preferable to set it as about 0.0001 mass% from a viewpoint of suppressing decarburization cost.

Si: 8.0 mass% or less Si is an element effective for increasing the specific resistance of steel and reducing iron loss, and is preferably added in an amount of 0.5 mass% or more. However, since addition exceeding 8.0 mass% makes it difficult to roll and manufacture, an upper limit shall be about 8.0 mass%. In addition, 4.0 mass% or less is preferable from a viewpoint of manufacturability. Moreover, since magnetic flux density will fall when Si content is high, in order to obtain a high magnetic flux density, 2.0 mass% or less is preferable.

Mn: 0.03-3.0 mass%,
In addition to the effect of fixing S to prevent hot brittleness, Mn has the effect of increasing the specific resistance of steel and reducing iron loss. In order to acquire the said effect, addition of 0.03 mass% or more is required. However, when it exceeds 3.0 mass%, the magnetic flux density is significantly reduced. Therefore, Mn is set to a range of 0.03 to 3.0 mass%. Preferably it is the range of 0.05-1.0 mass%.

P: 0.1 mass% or less P is an element used for adjusting the strength of steel because of its high solid solution strengthening ability. However, if it exceeds 0.1 mass%, the steel becomes brittle and difficult to roll, so the upper limit of P is set to 0.1 mass%. Preferably it is 0.08 mass% or less. In addition, although a minimum is not prescribed | regulated, it is preferable to set it as about 0.001 mass% from a viewpoint of suppressing removal P cost.

Al: 3.0 mass% or less Al, like Si, has the effect of increasing the specific resistance of steel and reducing iron loss. However, if it exceeds 3.0 mass%, it becomes difficult to roll, so the upper limit of Al is about 3.0 mass%.
However, when the Al content is in the range of 0.01 to 0.1 mass%, fine AlN precipitates and the iron loss increases, and therefore, preferably 0.01 mass% or less or 0.1 to 2.0 mass%. It is a range. Note that, if Al is reduced, the texture is improved and the magnetic flux density is improved. Therefore, when it is desired to obtain the above effect, Al is preferably 0.01 mass% or less.

S, N, O: 0.005 mass% or less for each S, N, O is a harmful element that forms fine precipitates and increases iron loss. Especially when the content exceeds 0.005 mass%, the adverse effect is remarkable. become. Therefore, S, N, and O are limited to 0.005 mass% or less, respectively. More preferably, each is 0.003 mass% or less.

Ni: 3.0 mass% or less Ni is an element added for adjusting the strength of steel. However, addition exceeding 3.0 mass% leads to an increase in raw material cost, so the upper limit of Ni is about 3.0 mass%. Preferably it is 2.5 mass% or less. In addition, although a minimum is not prescribed | regulated in particular, it is preferable to set it as about 0.001 mass% from a viewpoint of suppressing Ni removal cost.

Cr: 5.0 mass% or less Cr is an element having an effect of increasing the specific resistance of steel and reducing iron loss. However, if it exceeds 5.0 mass%, the iron loss deteriorates, so the upper limit of Cr is set to about 5.0 mass%. Preferably it is 3.0 mass% or less. The lower limit is not particularly defined, but is preferably about 0.001 mass% from the viewpoint of reducing Cr removal cost.

Ti and Nb: each 0.003 mass% or less Ti and Nb delay recovery and recrystallization in finish annealing, increase {111} orientation grains after finish annealing, and lose the effect of rapid heating to increase magnetic flux density It is a harmful element. In particular, the above-mentioned adverse effects become significant when the amount exceeds 0.003 mass%. Therefore, Ti and Nb are limited to 0.003 mass% or less, respectively. Preferably, it is 0.002 mass% or less, respectively.

As: 0.005 mass% or less As is the case with Ti and Nb, As is delayed recovery and recrystallization in finish annealing, increasing the {111} orientation grains after finish annealing, and the effect of improving the magnetic flux density by rapid heating is lost. It is a harmful element. In particular, the above-mentioned adverse effects become significant when the amount exceeds 0.005 mass%. Therefore, As is limited to 0.005 mass% or less. Preferably it is 0.003 mass% or less.

The slab used for producing the non-oriented electrical steel sheet of the present invention can contain the following components in addition to the above components.
Sn, Sb: 0.005 to 0.20 mass% each
Sn and Sb have the effect of improving the recrystallization texture and improving the magnetic flux density and iron loss. In order to acquire said effect, it is preferable to add 0.005 mass% or more, respectively. However, the above effect is saturated even if added over 0.20 mass%. Therefore, when adding any one or more of Sn and Sb, it is preferable to add in the range of 0.005-0.20 mass%, respectively.

Ca, Mg, REM: 0.0001 to 0.010 mass% each
Ca, Mg, and REM have the effect of forming stable sulfides and selenides and improving the grain growth of crystal grains. In order to acquire said effect, it is preferable to add 0.0001 mass% or more, respectively. However, if added over 0.010 mass%, the iron loss deteriorates. Therefore, when adding any one or more of Ca, Mg, and REM, it is preferable to set it as the range of 0.0001-0.010 mass%, respectively.
In addition, the remainder other than the said component in the slab used for manufacture of the non-oriented electrical steel sheet of this invention is Fe and an unavoidable impurity.

Next, the manufacturing method of the non-oriented electrical steel sheet of this invention is demonstrated.
The non-oriented electrical steel sheet of the present invention is a continuous casting method in which molten steel is melted in a converter or electric furnace, and is adjusted to the above-described component composition in a conventional refining process in which secondary refining is performed with a degassing facility or the like. After making into a slab, it can be manufactured by a method of hot rolling, subjecting it to hot-rolled sheet annealing as necessary, pickling, cold rolling, and finishing annealing.

  Here, although the conditions for the above hot rolling are not particularly defined, it is preferable that the finish rolling finish temperature is in the range of 700 to 900 ° C. and the winding temperature is in the range of 600 to 800 ° C. from the viewpoint of enhancing the magnetic properties. Moreover, what is necessary is just to perform the hot-rolled sheet annealing after hot rolling as needed.

Subsequently, the hot-rolled sheet after the hot rolling or after the hot-rolled sheet annealing is made into a cold-rolled sheet having a final thickness by one or more cold rollings sandwiching the intermediate annealing.
Under the present circumstances, it is preferable to control the ferrite grain size of the steel plate before the last cold rolling of the said cold rolling (in the case of a single rolling method) to 50 micrometers or less.

Because, in the recrystallization in finish annealing, the recrystallized grains having a {111} orientation, for generating from the grain boundary near the final cold rolling before tissue, the more the ferrite grain size of the final cold rolling before the tissue is less This is because {111} recrystallized grains increase in the structure after cold rolling and recrystallization, so that the {111} reduction effect by rapid heating becomes remarkable. A more preferable ferrite particle size is 40 μm or less. In addition, the said ferrite particle diameter means the average crystal grain measured with the cutting method about the whole board thickness.

  Here, the ferrite grain size can be controlled by adjusting the finish rolling end temperature in hot rolling, the coiling temperature (self-annealing temperature), the hot-rolled sheet annealing temperature, the intermediate annealing temperature, and the like. From the viewpoint of preventing ridging, it is desirable that the steel sheet structure before the final cold rolling has a recrystallization rate of 80% or more.

The cold-rolled sheet having the final thickness is subjected to finish annealing to obtain a non-oriented electrical steel sheet.
At this time, in order to increase the magnetic flux density, the finish annealing requires that the average heating rate between 630 and 700 ° C. in the heating process be 50 ° C./s or more, preferably 100 ° C./s or more. It is. The upper limit of the rate of temperature rise is not particularly specified, but the upper limit is about 1000 ° C./s from the viewpoint of reducing the equipment cost.
The rate of temperature rise in the temperature range exceeding 700 ° C. after the rapid heating is not particularly specified, but is preferably 30 ° C./s or more.

  Here, the temperature range defining the average rate of temperature rise as described above is between 630 and 700 ° C., the temperature range is a region where recrystallization proceeds, and the average rate of temperature rise in this temperature region is This is because the magnetic flux density is greatly affected. That is, since the recrystallization hardly occurs in the temperature range below 630 ° C., the influence of the average heating rate does not appear, whereas in the temperature range above 700 ° C., the recrystallization proceeds sufficiently, This is because the effect cannot be obtained even if the average temperature increase rate is changed.

  The rapid heating between 630 and 700 ° C. may be performed by radiant heat from a radiant tube or an electric heater, but the furnace needs to be heated to a considerably high temperature, and the furnace life is shortened. Or using an electric heating apparatus. The heating from the end of rapid heating to the soaking temperature is preferably performed using a radiant tube or an electric heater. In the soaking zone, it is preferable to heat by radiant heat from a radiant tube or an electric heater from the viewpoint of reducing temperature unevenness.

Moreover, what is important in the present invention is that the holding treatment for holding time t _i of 0.5 seconds or more at an arbitrary temperature T _i between 250 to 630 ° C. until the rapid heating section of the finish annealing is performed. the sum of the retention time t _i is that it is necessary to perform one or more times to be 0.5 to 10 seconds.

As shown in FIG. 4, the holding time t _i is a time during which the temperature T _i is kept within ± 2 ° C. The temperature is kept constant as shown in FIG. 4 (a). As shown in FIG. 4 (b), it may be possible to hold continuously within a range of T _i ± 2 ° C.

In addition, the retaining process need not be performed once, and may be performed a plurality of times as long as the total retaining time is in the range of 0.5 to 10 seconds. For example, the temperature _{T i} of between two hundred and fifty to six hundred and thirty ° C. (retention _{temperature: T 1, T 2, ···} T N) at the time is maintained at a temperature of ± 2 ℃ relative to the retention temperature _{T i t} i ( retention _time: t _1, t 2, the sum of · · · _{t N)} may be performed more than once as long as it is within the range of 0.5 to 10 seconds. However, if each holding time T _i is too short, a recovery effect cannot be obtained.

The reason for the 250 to 630 ° C. The range of temperature _{T i} to carry out the retention process, when retaining the temperature _{T i} is lower than 250 ° C., since no progress has {111} grain recovery, the effect of retaining the processing On the other hand, if the temperature exceeds 630 ° C., recrystallization proceeds during the retention treatment, and the {111} strength increases on the contrary. A preferable holding temperature is in the range of 280 to 550 ° C.

The reason why the sum of the coercive constant-time _{t i} the _{(t 1 + t 2 + ···} + t N) and 0.5 to 10 seconds, is less than 0.5 seconds, does not proceed is {111} grain Recovery Therefore, the effect of the retention treatment cannot be obtained. On the other hand, if it exceeds 10 seconds, the recovery proceeds too much during the retention treatment, the recrystallization temperature rises, and the effect of the retention treatment is effective in the temperature range where rapid heating is applied. This is because it cannot be obtained. A preferable sum of the holding times is in the range of 1 to 6 seconds.

Incidentally, in a temperature range between two hundred fifty to six hundred thirty ° C., and retaining the temperature T _i when performing retention process a plurality of times, heating rate between subsequent retention temperature T (i _{+ 1),} i.e., the time except for the dwelling scheduled In order to clarify the difference between the heating rate in the heating process and the retention treatment, if it is too slow, or 10 ° C./s or more is desirable. The rate of temperature increase from room temperature to 250 ° C. is a region where the recovery of {111} grains does not proceed, and is not particularly specified. However, the heating rate should be 10 ° C./s or more so that the heating equipment does not become too long. desirable.

  In addition, although there are no particular restrictions on the equipment for performing the retention treatment, for example, there are devices in which a plurality of induction heating devices and direct current heating devices are arranged, and a section in which the temperature is uniformly maintained by an electric heater or the like is provided therebetween Can be mentioned. Moreover, the heating equipment from room temperature to the temperature which performs a retention process should just obtain the said temperature increase rate, and is not specifically limited.

The annealing atmosphere in the finish annealing is preferably a reducing atmosphere, for example, a hydrogen-nitrogen mixed atmosphere having a P _H2O / _PH2 of 0.1 or less.

  Next, the steel sheet after the finish annealing is formed into a product plate by applying an insulating coating as necessary. The said insulating film can use well-known organic, inorganic, organic-inorganic mixed coating according to a required characteristic. For example, in order to ensure good punchability, it is preferable to apply an organic coating containing a resin, or a semi-organic or inorganic coating when emphasizing weldability.

The steel slab having the various composition shown in Table 3 was reheated to a temperature of 1100 ° C. for 20 minutes, and then hot-rolled to a finish rolling finish temperature of 750 ° C. and a coiling temperature of 630 ° C. After making a hot rolled sheet of 7 mm, the hot rolled sheet is subjected to hot rolled sheet annealing, or without being subjected to hot rolled sheet annealing, pickling and cold rolling to obtain a final sheet thickness of 0.5 mm. Cold-rolled sheet was used. In addition, it was confirmed that all the steel plates before the final cold rolling had a recrystallization rate of 100%.
Next, the hot-rolled sheet was pickled and cold-rolled once or twice with intermediate annealing in between to obtain a cold-rolled sheet having a thickness of 0.5 mm. Under the present circumstances, the ferrite particle size (average particle diameter) in the steel plate total thickness before the last cold rolling of the said cold rolling was measured with the cutting method.
Next, the cold-rolled sheet was 920 ° C. in a vol-% ratio of H ₂ : N ₂ = 2: 8 under a hydrogen-nitrogen mixed atmosphere with a dew point of −40 ° C. (PH ₂ O / PH ₂ = 0.001). A finish annealing of × 10 s was performed, and then an insulating coating was formed to obtain a product plate (non-oriented electrical steel sheet).
At this time, in the above finish annealing, heating from room temperature to 740 ° C. is performed using a heating device in which a plurality of induction heating devices are arranged in series, and the heating from room temperature to 630 ° C. is shown in Table 4. After carrying out the holding treatments of holdings 1 to 4 at a predetermined temperature and time, the average heating rate between 630 to 700 ° C. is the value shown in Table 4 from the last holding treatment temperature T _N to 740 ° C. Heated. The average heating rate from room temperature up to the first retention temperature _{T 1} of the 10 to 20 ° C. / s, the average heating rate from the first retention temperature T1 to the end of the retention temperature _{T N} 10~20 ℃ / s, The average temperature increase rate from the last retention treatment temperature T _N to 630 ° C. was 10 to 20 ° C./s, and the average temperature increase rate from 700 ° C. to 740 ° C. was in the range of 30 to 40 ° C./s. Subsequently, from 740 degreeC to soaking temperature (920 degreeC), it heated with the average temperature increase rate of 15 degree-C / s with the radiant tube.

From each of the product plates thus obtained, when the rolling direction is L and the plate width direction is W, two L: 180 mm × W: 30 mm test pieces, L: 30 mm × W: 180 mm test pieces Two samples were collected and magnetic properties (iron loss W _15/50 , magnetic flux density B ₅₀ ) were measured by an Epstein test.
Table 4 shows the measurement results of the magnetic properties, together with the hot-rolled sheet annealing conditions, the ferrite grain diameter before the final cold rolling, the retention treatment conditions in the finish annealing, and the average temperature increase rate between 630 to 700 ° C.
From this result, the non-oriented electrical steel sheet manufactured under the conditions suitable for the present invention using the steel material having the component composition suitable for the present invention has excellent magnetic properties, in particular, It can be seen that the magnetic flux density B ₅₀ is greatly improved in the steel sheet in which the ferrite grain size before final cold rolling is controlled to 50 μm or less.

Claims (3)

C: 0.0050 mass% or less, Si: 8.0 mass% or less, Mn: 0.03 to 3.0 mass%, P: 0.1 mass% or less, S: 0.005 mass% or less, Al: 3.0 mass% or less N: 0.005 mass% or less, Ni: 3.0 mass% or less, Cr: 5.0 mass% or less, Ti: 0.003 mass% or less, Nb: 0.003 mass% or less, As: 0.005 mass% or less, and O : Steel slab containing 0.005 mass% or less, the balance being composed of Fe and inevitable impurities , hot-rolled, and cold-rolled twice or more sandwiching intermediate annealing without hot-rolled sheet annealing In the method for producing a non-oriented electrical steel sheet that is subjected to finish annealing after hot rolling,
The ferrite grain size before the final cold rolling in the cold rolling is controlled to 50 μm or less,
While heating at 250 to 630 ° C. in the heating process of the above-mentioned finish annealing at an average temperature rising rate of 10 ° C./more , hold at an arbitrary temperature T _i between 250 to 630 ° C. for a time t _{i of} 0.5 seconds or more. The holding treatment is performed at least once, and after the number of times that the total of t _i is 0.5 to 10 seconds is applied, the temperature between 630 and 700 ° C. is heated at an average temperature increase rate of 50 ° C./s or more. A method for producing a non-oriented electrical steel sheet. Here, the holding time t _i refers to the time during which the temperature T _i is held at a temperature within ± 2 ° C. The steel slab, in addition to the above chemical composition, in claim 1, characterized in that it contains in one or two, respectively 0.005～0.20Mass% range selected from among Sn and Sb The manufacturing method of the non-oriented electrical steel sheet of description. The steel slab further contains one or more selected from Ca, Mg and REM in the range of 0.0001 to 0.010 mass% in addition to the above component composition. Item 3. The method for producing a non-oriented electrical steel sheet according to Item 1 or 2 .

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