JP4267439B2 - Non-oriented electrical steel sheet with excellent magnetic properties, manufacturing method thereof and strain relief annealing method - Google Patents

Description

  The present invention relates to a non-oriented electrical steel sheet used as an iron core material for electrical equipment, a manufacturing method thereof, and a stress relief annealing method, and particularly to a non-oriented electrical steel sheet having excellent magnetic properties after stress relief annealing. It is.

Increasing the grain size of non-oriented electrical steel sheets is extremely effective as a means of reducing iron loss, but on the other hand, sagging and burrs become large, and there is a problem that the punching workability of the motor core is remarkably deteriorated. It was. For this reason, there is provided a product that achieves both punching workability and magnetic characteristics by reducing the crystal grain size before strain relief annealing and growing crystal grains by strain relief annealing. In this case, it is most important to improve the grain growth during strain relief annealing, and a method for detoxifying precipitates that inhibit grain growth has been proposed. For example, Patent Document 1 discloses a method in which S: 50 ppm or less and Ti: 50 ppm or less, and Patent Document 2 discloses a method in which Ti is reduced to 15 ppm or less and sulfide is coarsened by adding REM. However, many non-oriented electrical steel sheets contain 0.2% or more of Al, and Al, which is a strong deoxidizing element, reduces TiO ₂ in slag and increases the amount of Ti in steel in steelmaking. There was a problem. Further, when REM is added, since it is a strong deoxidizing element like Al, the amount of Ti in the steel further increases, and the expected effect may not be obtained. In order to reduce the Ti in such a situation, it is necessary to reduce the TiO ₂ concentration in the slag as much as possible, which is an unavoidable increase in manufacturing cost and a decrease in productivity. On the other hand, Patent Document 3 discloses a method for improving grain growth after strain relief annealing even if mixing of Ti: 15 to 50 ppm is allowed, but for that purpose, 700 to 900 ° C. before final cold rolling. Therefore, annealing for 30 minutes to 10 hours and slow cooling to 500 ° C. at 50 ° C./min or less are necessary, and the productivity is remarkably deteriorated.

JP-A-6-108149 JP-A-8-325678 JP-A-11-158589

  In view of the above-mentioned problems, the present invention provides a non-oriented electrical steel sheet having excellent magnetic properties after strain relief annealing without sacrificing cost and productivity, a manufacturing method thereof, and a strain relief annealing method. is there.

  In order to solve the above-described problems, the present invention has the following (1) to (5).

(1) By mass%, C: 0.0010% to 0.010%, Si: 3.5% or less, Al: 0.2% to 3.0%, Mn: 1.5% or less, Ti: 0.0015% to 0.010%, S: 0.0030% Below, N: 0.0030% or less, consisting of the balance Fe and inevitable impurities, the grain size before strain relief annealing is 40 μm or less, and the precipitate containing Ti with a diameter of 0.01 μm or more is less than 10000 pieces / mm ² A non-oriented electrical steel sheet characterized by being.
(2) A non-oriented electrical steel sheet characterized by containing Sn: 0.01% or more and 0.10% or less in (1).

  (3) When manufacturing the electrical steel sheet of (1) or (2), in the manufacturing process in which finish annealing is performed following hot rolling, pickling, and cold rolling, the finishing temperature of hot rolling is 850 ° C or higher, and the coiling temperature Is made to be less than 650 ° C., and the temperature raising rate of finish annealing is set to 15 ° C./sec or more.

  (4) When manufacturing the electrical steel sheet of (1) or (2), the hot rolling finish temperature is set to 850 ° C. in the manufacturing process in which hot annealing, hot rolling sheet annealing, pickling and cold rolling are followed by finish annealing. As described above, the coiling temperature is set to less than 650 ° C., the hot-rolled sheet annealing is performed at 900 ° C. to 1150 ° C. for 60 seconds or more, and the cooling rate to at least 650 ° C. is set to 15 ° C./sec or more. A method for producing a non-oriented electrical steel sheet, wherein the speed is 15 ° C / sec or more.

  (5) When performing stress relief annealing after machining the electrical steel sheet produced in (3) or (4) into a core, the temperature is raised at 15 ° C / sec or less, and 750 to 900 ° C for 30 minutes to 3 hours. A strain relief annealing method for a non-oriented electrical steel sheet, characterized by performing the following annealing.

  The present invention improves the magnetic properties after strain relief annealing without lowering Ti or annealing for a long time, and there is no problem of cost increase or productivity.

  The inventors conducted intensive research on a method for improving iron loss after strain relief annealing without extremely reducing Ti and without annealing for a long time during the manufacturing process. As a result, by preventing precipitation containing Ti with a diameter of 0.01 μm or more (hereinafter referred to as Ti precipitate) as much as possible before strain relief annealing, the crystal grains after strain relief annealing are coarsened. The inventors have found that low iron loss can be realized, and have completed the present invention. Hereinafter, the experimental results that led to the present invention will be described.

(Experiment 1)
In a laboratory vacuum melting furnace, contained by mass: C: 0.0020%, Si: 2.0%, Al: 0.3%, Mn: 0.2%, Ti: 0.0020%, S: 0.0010%, N: 0.0020% A steel piece was prepared. This steel slab was hot rolled at a heating temperature of 1100 ° C., a finishing temperature of 870 ° C., and a coiling temperature of 550 to 700 ° C. to obtain a plate thickness of 2.7 mm. This hot-rolled sheet is pickled, cold-rolled to a thickness of 0.50 mm, and then subjected to finish annealing at a heating rate of 5,15,30 ° C / sec and at a heating rate of 10 ° C / sec for 2 hours at 750 ° C. The strain relief annealing was performed. With respect to the sample thus prepared, the crystal grain size and iron loss were measured, and Ti precipitates were observed with a transmission electron microscope.

As a result, as shown in Table 1, the crystal grain size before strain relief annealing is the same in all samples, but the sample with a coiling temperature of less than 650 ° C and a temperature increase rate of finish annealing of 15 ° C / sec or more. For 2, 3, 5, and 6, the crystal grain size after strain relief annealing was coarsened, and the iron loss was remarkably reduced. Therefore, when Ti precipitates before strain relief annealing were observed, in Samples 2, 3, 5, and 6 where grain growth was good, the precipitate density was less than 10 × 10 ³ pieces / mm ² compared to other samples. And found that it is extremely few.

(Experiment 2)
The sample before stress relief annealing in Experiment 1 was subjected to strain relief annealing at 700 ° C. for 1 hour at a temperature increase rate of 10 ° C./sec, and then immediately cooled with water to observe the crystal grain size and precipitates. The results are shown in Table 2. Although the crystal grain size did not change from about 30 μm before strain relief annealing in any of the samples, Ti precipitates with a diameter of 0.01 μm or more were observed in Samples 2, 3, 5, and 6. Precipitation along the grain boundaries was confirmed.

  On the other hand, although Ti precipitates were observed in Samples 1, 4, 7-12, the distribution was not much different from that before strain relief annealing, and was uniformly dispersed regardless of the grain boundaries.

  This result is considered as follows. In Samples 2, 3, 5, and 6, the coiling temperature of hot rolling was as low as less than 650 ° C, and the temperature increase rate of finish annealing was as fast as 15 ° C / sec or more. It is thought that it was not precipitated after the finish annealing, but was precipitated at the grain boundaries during the temperature increase of the strain relief annealing. On the other hand, in Samples 7 to 12, where the hot rolling coiling temperature was high, most of Ti was deposited before recrystallization in Samples 1 and 4 where the temperature increase rate of finish annealing was slow after winding. It is thought that it was unrelated to the grain boundary before annealing.

(Experiment 3)
The sample before strain relief annealing in Experiment 1 was subjected to strain relief annealing at 800 ° C. for 1 hour at a heating rate of 10 ° C./sec, and then immediately cooled with water to observe precipitates. The results are shown in Table 3. Almost no Ti precipitate having a diameter of 0.01 μm or more was observed in any sample. This is thought to be because Ti precipitates decomposed by 800 ° C strain relief annealing and dissolved in steel.

  From the above results, it was found that during precipitation annealing, Ti precipitates with a diameter of 0.01 μm or more were precipitated at the grain boundaries and then solid-dissolved to achieve coarse grains and low iron loss. This is because the grain growth is remarkably suppressed by the Ti precipitates, and the deterring power is abruptly lost by the Ti solid solution, so that significant crystal grain growth occurs.

  In the strain relief annealing of non-oriented electrical steel sheets, the above-mentioned technical technique for improving the grain growth by continuously causing precipitation and solid solution of Ti precipitates was first discovered in the present invention. This is completely different from the conventional knowledge of reducing grain size and improving grain growth. Needless to say, Patent Documents 1 and 2, but also for Patent Document 3 which improves the grain growth after strain relief annealing by allowing mixing of Ti: 15 to 50 ppm, 700 to 900 ° C. applied before the final cold rolling The purpose of this invention is to reduce the grain growth deterrence by precipitating Ti precipitates coarsely before strain relief annealing and annealing at 50 ° C / min or less. Are completely different.

  Next, the reason for limiting the numerical values of the components in the present invention will be described.

  C is an element necessary for producing Ti precipitates, and for that purpose, it is necessary to contain 0.0010% or more. However, if it exceeds 0.010%, the amount of carbide increases and iron loss is remarkably deteriorated, so the upper limit was made 0.01%.

  Si is an effective element for increasing the electric resistance, but if added excessively, the cold rolling property is remarkably deteriorated, so 3.5% was made the upper limit.

  Al is an element necessary for deoxidation and fixing nitrogen in steel. For that purpose, it is necessary to add 0.2% or more. In addition, it is an element effective for increasing electrical resistance like Si, but if the added amount exceeds 3.0%, it causes hardness increase like Si and deteriorates castability. The upper limit was 3.0%.

  Mn is effective in increasing the electrical resistance like Si and Al, but the upper limit is 1.5% in consideration of cost.

  S and N are both 0.0030% or less in order to inhibit grain growth during strain relief annealing.

  Ti is a constituent element of the precipitate that expresses the present invention, and for that purpose, it is necessary to contain 0.0015% or more. However, if it exceeds 0.010%, the amount of precipitates increases and iron loss deteriorates, so the upper limit was made 0.01%.

Sn has an effect of improving the texture and an effect of suppressing nitridation and oxidation at the time of strain relief annealing. Therefore, Sn may be added in a range of 0.01% or more and 0.10% or less that can enjoy these effects.

  Next, the reason for limiting the numerical values of the size and number of Ti precipitates and the crystal grain size in the present invention will be described.

Ti precipitates having a diameter of 0.01 μm or more are the most important in achieving the effects of the present invention. The purpose of the present invention is to precipitate this during strain relief annealing.To that end, it is important that Ti is dissolved as much as possible before strain relief annealing, so the number of precipitates is 10,000 / mm. ^It is necessary to suppress to less than ² .

  The crystal grain size before strain relief annealing needs to be 40 μm or less because when it exceeds 40 μm, punching workability deteriorates and grain growth during strain relief annealing deteriorates.

  Next, the reasons for limiting the manufacturing conditions in the present invention will be described. In the present invention, it is necessary to dissolve Ti as much as possible and prevent it from precipitating before the strain relief annealing.

  The hot rolling conditions were such that the finishing temperature was 850 ° C. or higher in order to maintain the solid solution of Ti, and the winding temperature was lower than 650 ° C. in order to avoid Ti precipitation.

  Although hot-rolled sheet annealing can be omitted, it is performed for the purpose of magnetism and shape improvement. For this purpose, it is necessary to perform annealing at 900 ° C. or more for 60 seconds or more. However, if the annealing temperature is too high, the cost increases, so the upper limit was set to 1150 ° C. In order to avoid Ti precipitation as in hot rolling, the cooling rate to at least 650 ° C. was set to 15 ° C./sec or more.

  In finish annealing, if the rate of temperature rise is slow, Ti is uniformly dispersed and precipitated before recrystallization, so the rate of temperature rise was set to 15 ° C./sec or more.

  As manufacturing conditions other than those specified above, known conditions for non-oriented electrical steel sheets can be used.

  Next, the reason for the limitation of strain relief annealing is that Ti cannot be sufficiently precipitated at the grain boundaries at a temperature rising rate exceeding 15 ° C / sec. . As for the annealing temperature and time, Ti precipitates were not dissolved at less than 750 ° C. and less than 30 minutes. The upper limit was set to 900 ° C or less and 3 hours or less in consideration of cost and productivity.

  In a laboratory vacuum melting furnace, contained by mass: C: 0.0030%, Si: 1.5%, Al: 0.5%, Mn: 0.5%, Ti: 0.0025%, S: 0.0015%, N: 0.0025% A steel piece was prepared. The steel slab was hot-rolled at a heating temperature of 1150 ° C., a finishing temperature of 800-900 ° C., and a coiling temperature of 500-700 ° C. to a thickness of 2.0 mm. This hot-rolled sheet is pickled, cold-rolled to a thickness of 0.35 mm, and then finish-annealed at a heating rate of 15 ° C / sec. Was given. With respect to the sample thus prepared, the crystal grain size and iron loss were measured, and Ti precipitates were observed with a transmission electron microscope.

As a result, as shown in Table 4, in samples 6 to 8, 11 to 13 whose finishing temperature was 850 ° C. or higher and the coiling temperature was less than 650 ° C., Ti precipitates having a diameter of 0.01 μm or more before strain relief annealing Is less than 10000 pieces / mm ² , and it has been found that coarse grains can be obtained after strain relief annealing and low iron loss can be achieved.

  In a laboratory vacuum melting furnace, in mass%, C: 0.0050%, Si: 3.0%, Al: 1.0%, Mn: 0.2%, Ti: 0.0045%, S: 0.0025%, N: 0.0030%, Sn: A steel slab containing 0.020% was prepared. This steel slab is heated to 1130 ° C, the finishing temperature is 875 ° C, the coiling temperature is 630 ° C, hot rolled to a thickness of 1.8mm, and the cooling rate to 650 ° C in 950 ° C x 90 seconds is 1,15,30 ° C / sec hot-rolled sheet annealing was performed, pickling was performed, and the sheet was cold-rolled to a thickness of 0.30 mm. Then, finish annealing is performed at a heating rate of 20 ° C / sec, the crystal grain size before strain relief annealing is changed to 20-50μm, and then strain relief annealing is performed at 800 ° C for 1 hour at a temperature elevation rate of 15 ° C / sec. gave. With respect to the sample thus prepared, the crystal grain size and iron loss were measured, and Ti precipitates were observed with a transmission electron microscope.

As a result, as shown in Table 5, the cooling rate of hot-rolled sheet annealing is less than 10000 pieces / mm ² of Ti precipitates with a diameter of 0.01 μm or more before strain relief annealing in samples 5 to 12 of 15 ° C./sec or more, It was also found that in Samples 5, 6, 9 to 11 whose crystal grain size before strain relief annealing was 40 μm or less, coarse grains were obtained after strain relief annealing, and low iron loss was achieved.

  In a laboratory vacuum melting furnace, by mass%, Si: 2.0%, Al: 2.3%, Mn: 0.3%, S: 0.0005%, N: 0.0014%, Sn: 0.015%, C: 0.0005 ~ Steel pieces with 0.0020% and Ti changed to 0.0005 to 0.0020% were produced. These steel slabs were hot-rolled at a heating temperature of 1050 ° C, a finishing temperature of 860 ° C, a coiling temperature of 620 ° C to a thickness of 2.3 mm, and a cooling rate of 30 ° C / sec to 1000 ° C x 60 seconds to 650 ° C. After hot-rolled sheet annealing, it was pickled and cold-rolled to a thickness of 0.50 mm. Then, finish annealing was performed at a temperature increase rate of 15 ° C./sec, and strain relief annealing was performed at a temperature increase rate of 3 ° C./sec at 750 ° C. for 1 hour. With respect to the sample thus prepared, the crystal grain size and iron loss were measured, and Ti precipitates were observed with a transmission electron microscope.

  As a result, as shown in Table 6, in samples 7, 8, 11, 12, 15, and 16 where C is 0.0010% or more and Ti is 0.0015% or more, coarse grains are obtained after strain relief annealing, and low iron It was found that loss could be achieved.

  In a laboratory vacuum melting furnace, by mass, C: 0.0030%, Si: 2.4%, Al: 0.6%, Mn: 0.2%, Ti: 0.0020%, S: 0.0025%, N: 0.0030%, Sn: A steel slab containing 0.020% was prepared. This steel slab was heated to 1120 ° C, the finishing temperature was 880 ° C, the coiling temperature was 590 ° C and rolled to a thickness of 2.7mm, and the heat rate was 950 ° C x 90 seconds to 650 ° C with a cooling rate of 20 ° C / sec. After performing sheet annealing, pickling was performed, and after cold rolling to a sheet thickness of 0.50 mm, finish annealing was performed at a temperature rising rate of 15 ° C./sec. The sample thus prepared was subjected to stress relief annealing at a temperature rising rate of 5 ° C./sec and 700 ° C. to 850 ° C. for 0.2 hours to 2 hours, and the iron loss and crystal grain size were measured.

  As a result, as shown in Table 7, coarse grains can be obtained in samples 6 to 8, 10 to 12, 14 to 16 where the stress relief annealing temperature is 750 ° C. or more and 0.5 hours or more, and low iron loss can be achieved. I found out.

  In a laboratory vacuum melting furnace, contained by mass: C: 0.0020%, Si: 3.0%, Al: 0.6%, Mn: 0.2%, Ti: 0.0030%, S: 0.0020%, N: 0.0021% A steel piece was prepared. This steel slab is heated to 1140 ° C, the finishing temperature is 890 ° C, the coiling temperature is 600 ° C, hot rolled to a sheet thickness of 2.3mm, and the cooling rate to 650 ° C at 1050 ° C for 90 seconds is 20 ° C / sec. After performing sheet annealing, pickling was performed, and after cold rolling to a sheet thickness of 0.50 mm, finish annealing was performed at a heating rate of 25 ° C./sec. The sample thus prepared was subjected to strain relief annealing at 700 to 850 ° C. for 2 hours while changing the temperature rising rate to 1 to 20 ° C./sec, and the iron loss and the crystal grain size were measured.

  As a result, as shown in Table 8, coarse grains are obtained in samples 5 to 7, 9 to 11, 13 to 15 in which the temperature raising rate of strain relief annealing is 15 ° C./sec or less and the temperature is 750 ° C. or more, We found that low iron loss can be achieved.

Claims (5)

In mass%, C: 0.0010% to 0.010%, Si: 3.5% or less, Al: 0.2% to 3.0%, Mn: 1.5% or less, Ti: 0.0015% to 0.010%, S: 0.0030% or less, N : Containing 0.0030% or less, balance Fe and unavoidable impurities, crystal grain size before strain relief annealing is 40 μm or less, and precipitates containing Ti with a diameter of 0.01 μm or more are less than 10000 pieces / mm ² A non-oriented electrical steel sheet. 2. The non-oriented electrical steel sheet according to claim 1, containing Sn: 0.01% or more and 0.10% or less .   In manufacturing the non-oriented electrical steel sheet according to claim 1 or 2, in the manufacturing process in which finish annealing is performed subsequent to hot rolling, pickling, and cold rolling, the finishing temperature of hot rolling is 850 ° C. or more, and the winding temperature is 650. A method for producing a non-oriented electrical steel sheet, characterized in that the temperature is raised below 15 ° C. and the rate of temperature increase in finish annealing is 15 ° C./sec or more.   In producing the electrical steel sheet according to claim 1 or 2, in the production process of performing hot annealing, hot rolled sheet annealing, pickling, and cold rolling followed by finish annealing, the hot rolling finishing temperature is 850 ° C or higher, the winding temperature Is heated to 900 ° C or higher and 1150 ° C or lower for 60 seconds or longer, the cooling rate to at least 650 ° C is set to 15 ° C / sec or higher, and the temperature increase rate of finish annealing is 15 ° C / second. The manufacturing method of the non-oriented electrical steel sheet characterized by making it into sec or more.   When performing stress relief annealing after machining the electrical steel sheet produced in claim 3 or claim 4 into a core, the temperature is increased at 15 ° C / sec or less, and annealing is performed at 750 ° C to 900 ° C for 30 minutes to 3 hours. A method for strain relief annealing of a non-oriented electrical steel sheet, characterized in that: