JP2005226111A - Method for producing grain-oriented silicon steel sheet excellent in magnetic characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for extreme-stably producing a grain-oriented silicon steel sheet excellent in a magnetic characteristic at a slab heating temperature avoiding extra-high temperature and extra-low temperature. <P>SOLUTION: In the method for producing the grain-oriented silicon steel sheet, by which the grain-oriented silicon steel slab containing Al applies the slab-heating at 1200 to <1350°C and hot-rolling and an annealing to the hot-rolled plate and one time of cold-rolling or two or more times of cold-rolling interposing an intermediate annealing and decarburization annealing and coats annealing separation agent, and a nitriding treatment is applied to the steel sheet at the interval till starting a secondary-crystallization in a finish-annealing after decarburization annealing, and the finish-annealing is applied, the precipitating ratio as AlN in N of the steel sheet after hot-rolling, is made to be ≤30%, and the maximum temperature T1 (°C) of the annealing before the finish-cold-rolling is made to be in the range of the formula 2 with an index AIR regulated with the formula 1 with sAl (soluble Al), N and Ti contents. AIR(ppm)=sAl(ppm)-27/14×N(ppm)+27/47.9×Ti(ppm)...formula 1, -4/3×AIR+3850/3≤T1≤-4/3×AIR+4210/3...formula 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a unidirectional electrical steel sheet mainly used as an iron core of a transformer or the like very stably.

Various techniques for stably producing a unidirectional electrical steel sheet having excellent magnetic properties with a magnetic flux density B ₈ (magnetic flux density in a magnetic field of 800 A / m) exceeding 1.9 T have been proposed. The manufacturing method in the case of containing as an inhibitor can be classified into three types of techniques shown in Table 1 depending on the slab heating temperature.

  The first technique, called the fully solid solution non-nitrided type, is sufficient to heat the slab from 1350 ° C to an extremely high temperature of up to 1450 ° C and uniformly (uniform temperature) throughout the slab. This is a method of keeping the slab at that temperature for a long time. This is to completely dissolve a substance having inhibitor ability such as MnS, AlN and function as an inhibitor necessary for secondary recrystallization. In this respect, it is advantageous for stable secondary recrystallization.

  However, in this technique, the complete solution temperature for securing the amount of inhibitor necessary for secondary recrystallization is not so high in thermodynamics, but in actual industrial production, productivity and uniform solid solution of the entire slab are obtained. In order to ensure the state, the temperature has to be extremely high, and accordingly, various problems are included in actual production. For example, 1) It is difficult to ensure a predetermined hot rolling temperature, and if it cannot be ensured, a secondary recrystallization failure occurs due to a deviation in the slab of inhibitor strength. 2) Coarse grains are formed during hot rolling heating. The coarse grains cannot be recrystallized, and linear secondary recrystallization failure occurs. 3) The slab surface melts and becomes noro, and a great deal of labor is required for the maintenance of the heating furnace. 4) A huge edge crack is generated in the steel strip after hot rolling, and the yield is lowered.

  Further, as disclosed in Non-Patent Document 1, in this technique, if nitriding is performed before decarburization annealing and the start of secondary recrystallization in order to supplement the inhibitor, the magnetic characteristics are deteriorated.

  The second technique is called a (complete) precipitation nitriding type. As disclosed in Patent Documents 1 to 3, the slab heating temperature is less than 1280 ° C., and secondary recrystallization is started after decarburization annealing. The nitriding treatment is performed up to this point. In such a method, for example, as shown in Patent Document 4, it is possible to control the average grain size of primary recrystallized grains after decarburization annealing within a certain range, usually in the range of 18 to 35 μm. It is very important for good performance.

  In addition, in this technology, the amount of solid solution in the steel of a substance having inhibitor ability such as solute nitrogen during slab heating greatly affects the primary recrystallized grain growth, so the size of primary recrystallized grains in the slab is made uniform. For this reason, for example, Patent Document 5 discloses a method in which solid solution nitrogen during slab heating is lowered to suppress non-uniform precipitation that occurs in a subsequent process. From the viewpoint of reducing the amount of solid solution, the actual slab heating temperature is desired to be 1150 ° C. or lower.

  However, with this technique, no matter how strictly the components are adjusted, the inhibitor substance cannot be precipitated completely. Therefore, in actual production activities, the primary recrystallization annealing conditions ( Especially the temperature) is adjusted for each coil. For this reason, the manufacturing process becomes complicated, and since the formation of the oxide layer after decarburization annealing is not constant, the glass film formation may become unstable.

  The third technique is called a mixed type. In actual operation, as shown in Patent Document 6, the slab heating temperature is set to 1200 to 1350 ° C., and nitriding is essential as in the second technique. In order to avoid the slab heating temperature exceeding 1350 ° C. in the first technique, the slab heating temperature is lowered by reducing the initial content of the inhibitor substance, and the insufficient inhibitor strength is supplemented by nitriding treatment. This technology is further classified into two types. One is a partial solid solution nitriding type (partial precipitation nitriding type), and the other is a complete solid solution nitriding type represented by Patent Document 7.

  This technique distinguishes inhibitors from primary inhibitors and secondary inhibitors. Here, the primary inhibitor mainly determines the primary recrystallization particle diameter, but of course this also contributes to the secondary recrystallization. Secondary inhibitors make secondary recrystallization possible. Due to the presence of the primary inhibitor, the variation in the particle size after the primary recrystallization is reduced, so there is no need to change the primary recrystallization annealing conditions for the particle size, and the glass film formation is extremely stable.

  As the primary inhibitor, an inhibitor substance (for example, AlN, MnS, MnSe, Cu—S, Sn, Sb) used in the first technique is used. However, in order to reduce the slab heating temperature, the content is required to be small. The secondary inhibitor is AlN formed by nitriding from the primary inhibitor to the start of secondary recrystallization after decarburization annealing. In Patent Document 7, BN is also described as a primary inhibitor. However, since N also binds to Al, when it contains Al and B at the same time, secondary recrystallization may become unstable.

  A problem common to the above three techniques is that the appropriate range of the content of necessary inhibitor substances (especially Al and N) is narrow. Therefore, conventionally, methods for adjusting production conditions using AlR obtained by subtracting N equivalents from acid-soluble Al (hereinafter referred to as sAl) as an index have been disclosed in the first and second techniques.

  In the first technique, for example, Patent Document 8 stipulates that any one of a series of process conditions is adjusted in addition to the soaking time or cooling rate of the annealing before the final cold rolling depending on the AlR value.

In the second technique, Patent Document 9 defines the ratio of N _{2 in} the atmosphere during finish annealing by the AlR equation. In Patent Document 11, Bi is added, and the annealing temperature before final cold rolling is defined by the AlR equation. In Patent Document 11, Ti is contained, and the amount of nitriding is defined by the AlR equation considering TiN.

ISIJ International, Vol. 43 (2003), No. 3, pp. 400-409 JP 59-56522 A Japanese Patent Laid-Open No. 5-112827 JP-A-9-118964 Japanese Patent Laid-Open No. 2-182866 JP-A-5-295443 JP 2000-199015 A JP 2001-152250 A JP-A-60-177131 JP-A-7-305116 JP-A-8-253815 JP-A-8-279408

  In the case of the third technique, the primary recrystallization annealing temperature dependence on the primary recrystallization grain size is small, but if the content of Ti that affects the formation of the inhibitor component, particularly Al, N, and further AlN, varies, Recrystallization may become unstable.

  When AlR is large, it is necessary to increase the amount of nitriding in the subsequent process in order to ensure magnetic properties. The cause is currently considered as follows. When the AlR is large, a large amount of AlN precipitates after the annealing before the final cold rolling and the primary particle size becomes small, but the secondary inhibitor effect of the primary inhibitor becomes strong, so the secondary recrystallization start temperature becomes high. As it is, the inhibitor strength is not qualitatively sufficient for high temperature, and the balance between the particle size and the inhibitor is lost, resulting in a secondary recrystallization failure. In order to correspond to the increased secondary recrystallization temperature, it is necessary to strengthen the secondary inhibitor by nitriding, and it is necessary to increase the amount of nitriding. That is, it is considered that a coarse inhibitor is required because the degree of change in the inhibitor strength increases as the secondary recrystallization temperature increases. However, when the nitriding amount is increased, the glass film is remarkably deteriorated.

  On the other hand, if the AlR is small, less AlN precipitates after annealing before the final cold rolling, and the primary particle size increases, but the secondary inhibitor effect of the primary inhibitor is small, so the secondary recrystallization start temperature does not increase, and nitriding If the amount of AlR is too small, the secondary recrystallization nucleus generation position spreads over the entire plate thickness as described in Non-Patent Document 1, so that not only the sharp Goss orientation near the surface layer but also the central layer These grains are also secondarily recrystallized and the magnetic properties are deteriorated.

  Thus, when AlR changes, the secondary recrystallization property, and hence the sharpness of Goss orientation, changes. However, since it is difficult to control the Al, N, and Ti component ranges to a narrow range at the melting stage, there has been a strong demand for measures to alleviate the effects of these component variations.

  It is well known that unidirectional electrical steel sheets are produced through a number of processes after hot rolling, but in the present invention, the slab heating temperature is neither extremely high nor low. On the premise that it can be produced by a rolling mill and does not require a special slab heating device, the inhibitor strength is kept constant in the process after hot rolling even if the components inevitably fluctuate, and the magnetic properties are extremely good. A certain unidirectional electrical steel sheet can be manufactured.

The present invention has the following configuration.
(1) In mass%,
C: 0.035 to 0.09%,
Si: 2.5-4.0%
Acid-soluble Al (hereinafter referred to as sAl): 0.018 to 0.033%,
N: 0.003 to 0.007%,
S and / or Se with Seq = S + 0.406Se, 0.005 to 0.018%,
Mn: 0.03 to 0.09%,
Ti is 0.005% or less,
A slab of a unidirectional electrical steel sheet, the balance of which is Fe and inevitable impurities, is slab heated at a temperature of 1200 ° C. or more and less than 1350 ° C., hot-rolled, hot-rolled sheet annealing and one cold rolling, or intermediate Perform cold rolling at least twice with annealing, decarburize and anneal, apply annealing separator, perform nitriding treatment after decarburization annealing and start secondary recrystallization of finish annealing, finish annealing In the method for producing a unidirectional electrical steel sheet, the precipitation rate as AlN is 30% or less in N of the steel strip after hot rolling, and the index AlR defined by the formula 1 according to the sAl, N, and Ti contents A method for producing a unidirectional electrical steel sheet with excellent magnetic properties, characterized in that the maximum temperature T1 (° C.) of annealing before final cold rolling is in the range of Formula 2.
AlR (ppm) = sAl (ppm) −27 / 14 × N (ppm) + 27 / 47.9 × Ti (ppm) ・ ・ ・ Equation 1
−4 / 3 × AlR + 3850/3 ≦ T1 ≦ −4 / 3 × AlR + 4210/3 ・ ・ ・ Equation 2
(2) The annealing temperature of the hot-rolled sheet annealing or the last intermediate annealing is set to two stages, and the first stage is a temperature within a range of T1 (° C.) shown in the above formula 2 for 5 to 120 seconds, and the second stage is a temperature T2 ( The method for producing a unidirectional electrical steel sheet having excellent magnetic properties according to (1), characterized in that the temperature is in the range of 850 to 1000 ° C. for 10 seconds to 240 seconds.
(3) In (1), the annealing temperature of hot-rolled sheet annealing or the last intermediate annealing is set to one stage, and the temperature is set to 20 to 360 seconds in the range of T1 (° C.) shown in the formula 2. A method for producing a unidirectional electrical steel sheet having excellent magnetic properties.
(4) When cooling after hot-rolled sheet annealing or the last intermediate annealing, cooling is performed from 700 ° C. to 300 ° C. at a cooling rate of 10 ° C./second or more. (1) to (3) A method for producing a unidirectional electrical steel sheet having excellent magnetic properties according to any one of the items.
(5) The magnetic property according to any one of (1) to (4), wherein the slab component is mass% and further contains Sb and Sn as Sb + Sn in an amount of 0.02 to 0.30%. The manufacturing method of the unidirectional electrical steel sheet which was excellent.
(6) One direction excellent in magnetic properties according to any one of (1) to (5), characterized in that the slab component is mass% and further contains 0.02 to 0.30% Cu. Method for producing an electrical steel sheet.
(7) An average particle size of primary recrystallized grains after completion of the decarburization annealing is 7 μm or more and less than 18 μm, and the magnetic properties described in any one of (1) to (6) are excellent A method for producing a unidirectional electrical steel sheet.
(8) After the decarburization annealing, nitriding treatment is performed in a mixed gas of hydrogen, nitrogen and ammonia under the strip running condition, and the nitrogen content (tN) (unit: ppm) after nitriding the steel sheet is 0.25 × sAl + 90 The method for producing a unidirectional electrical steel sheet having excellent magnetic properties according to any one of (1) to (7), wherein ≦ tN ≦ 300.
(9) The unidirectional electromagnetic wave having excellent magnetic properties according to any one of (1) to (8), wherein the rolling reduction of the last cold rolling is 80% or more and 95% or less A method of manufacturing a steel sheet.
(10) The magnetic property according to any one of (1) to (9), wherein an average heating rate from the start of temperature rise in decarburization annealing to 600 to 800 ° C. is set to 100 ° C./second or more. Of excellent unidirectional electrical steel sheet.

  In the present invention, it becomes possible to manufacture a unidirectional electrical steel sheet having excellent magnetic properties by removing the ultra-high temperature during hot rolling of a conventional unidirectional electrical steel sheet and removing the adverse effects of low temperature heating.

  The present invention is described in detail below. As a result of intensive studies on the manufacturing method of the complete solid solution nitriding type in the third technique, the inventors have determined that the form of the inhibitor substance dissolved and frozen by hot rolling is the annealing condition immediately before the final cold rolling. I found that it can be changed. In particular, it was found that AlR is effective as a parameter at that time, and the stability of secondary recrystallization is greatly influenced by the annealing temperature.

  Next, the reason for limiting the component range of the slab in the present invention will be described.

  When C is less than 0.035%, the primary recrystallization texture becomes unsuitable, and when it exceeds 0.09%, decarburization becomes difficult and is not suitable for industrial production.

  If Si is less than 2.5%, good iron loss cannot be obtained, and if it exceeds 4.0%, cold rolling becomes extremely difficult and is not suitable for industrial production.

  Al combines with N to form AlN, and mainly functions as a primary and secondary inhibitor. Contained in the melting stage, frozen by hot rolling (forced to cool from the solid solution state and not precipitated in the hot-rolled steel strip), and precipitated by annealing immediately before the final cold rolling, mainly as a primary inhibitor It functions but also functions as a secondary inhibitor. Further, AlN formed by nitriding until the start of secondary recrystallization after decarburization annealing functions as a secondary inhibitor. That is, this AlN is formed before nitriding and formed during high-temperature annealing after nitriding. In order to secure the amount of both AlN, 0.018 to 0.033% of acid-soluble Al is required. is there. Outside this range, even if the technique of the present invention is used, if it is low, secondary recrystallized grains having good Goss orientation cannot be stably obtained because the function as a secondary inhibitor is insufficient. If it is high, the amount of nitridation required in the subsequent process increases, and the glass film is seriously damaged.

  If N exceeds 0.007%, in actual industrial production, the slab heating temperature for hot rolling needs to be higher than 1350 ° C. More preferably, it is 0.006% or less. If it is less than 0.003%, a stable primary inhibitor effect cannot be obtained, resulting in poor secondary recrystallization.

  S and Se combine with Mn and Cu and act mainly as a primary inhibitor. When Seq = S + 0.406 × Se exceeds 0.018%, the slab heating temperature during hot rolling increases. Moreover, when less than 0.005%, the effect as a primary inhibitor will become weak. Desirably, it is 0.010 to 0.015%.

  If Mn is less than 0.03%, cracks are likely to occur after hot rolling, and the yield decreases. On the other hand, if it exceeds 0.09%, MnS and MnSe will increase so much that the slab heating temperature during hot rolling must be increased. Desirably, it is 0.04 to 0.06%.

  When hot rolling is performed under the conditions of the present invention in which the slab is heated at 1200 ° C. or higher, Cu forms fine precipitates together with S and Se and exhibits a primary inhibitor effect. The precipitates also serve as precipitation nuclei that make the dispersion of AlN more uniform and also play a role of secondary inhibitors, and this effect makes secondary recrystallization good. If the content is less than 0.02%, the above effect is reduced and stable production becomes difficult. If the content exceeds 0.30%, the above effect is saturated, and it causes surface flaws such as “copper lashes” during hot rolling.

  Sn and Sb are well-known grain boundary segregation elements. Since the present invention contains Al, depending on the conditions of finish annealing, Al is oxidized by moisture released from the annealing separator, and the inhibitor strength varies at the coil position, and the magnetic characteristics may vary at the coil position. is there. As a countermeasure, there is a method of preventing oxidation by adding a grain boundary segregation element in addition to the early formation of a dense glass film in finish annealing. If Sn + Sb is less than 0.02%, this effect is extremely small. On the other hand, if it exceeds 0.30%, it is difficult to be oxidized at the time of decarburization annealing, and the glass film formation becomes insufficient, and the decarburization annealing property is remarkably inhibited.

  If Ti exceeds 0.005%, secondary recrystallization becomes unstable, and in order to stabilize, it is necessary to make the nitrogen content after nitriding 0.030% or more, which causes a glass film defect.

  In addition, known elements that improve various characteristics of the unidirectional electrical steel sheet can be added. The preferred addition ranges are P and Cr: 0.02 to 0.30%, Mo, Cd: 0.008 to 0.3%, and Ni: 0.03 to 0.30%. Both can be used alone or in combination.

  Next, the reasons for limiting the manufacturing process in the present invention will be described.

  In the method of the present invention, first, a slab having an initial thickness in the range of 150 mm to 350 mm, preferably in the range of 220 mm to 280 mm, is manufactured by a known continuous casting method. Alternatively, the slab may be a so-called thin slab having an initial thickness in the range of about 30 mm to 70 mm, and in this case, when manufacturing a hot-rolled steel strip, there is no need to roughen the intermediate thickness. There are advantages.

  The reason why the slab heating temperature is limited to 1200 to 1350 ° C. is that it is less than 1200 ° C., which corresponds to the second technique described above, and the solid solution of the inhibitor substance for achieving good Goss orientation secondary recrystallization Thermodynamically impossible. In addition, when the slab heating temperature is low, the rolling load of the hot rolling mill is increased, and the cause of misroll and flatness (crown) failure are likely to occur. On the other hand, exceeding 1350 ° C. corresponds to the first technique, which causes a well-known difficulty in industrial production. A desirable range is 1280 ° C to 1330 ° C.

  A gas heating method is usually used as the slab heating method. However, induction heating and direct current heating are desirable in terms of uniform heating, and in order to ensure the shape in these special heating methods, the partial slab is cast into a slab. There is no problem even if given to. Moreover, when heating temperature shall be 1300 degreeC or more, the texture may be improved by this partial rolling and the amount of C may be reduced.

  In the present invention, it is necessary that the inhibitor substance is frozen at the stage after hot rolling. As this index, the precipitation rate of N as AlN is 30% or less. If it exceeds 30%, the form of the inhibitor substance in the hot-rolled steel strip becomes non-uniform in position, and industrially stable production cannot be performed.

Annealing before the final cold rolling, that is, hot-rolled sheet annealing or the final intermediate annealing is important for the homogenization of the structure in the steel strip frozen during the hot rolling and the fine dispersion of the inhibitors. That is, it is indispensable to perform one or more continuous annealings before the final cold rolling in order to cause non-uniformity due to the difference in hot rolling history and fine precipitation of the inhibitor substance. Of these annealing conditions, the maximum temperature is particularly important, and it has been found that variations in secondary recrystallization due to variations in AlR are absorbed. That is, the condition to be satisfied when the maximum temperature is T1 (° C.) is in the range of Equation 2.
AlR (ppm) = sAl (ppm) −27 / 14 × N (ppm) + 27 / 47.9 × Ti (ppm) ・ ・ ・ Equation 1
−4 / 3 × AlR + 3850/3 ≦ T1 ≦ −4 / 3 × AlR + 4210/3 ・ ・ ・ Equation 2
If it is lower than this, the sharpness of Goss decreases, and if it is higher, secondary recrystallization becomes unstable and it is required to significantly increase the amount of nitriding, which is not practical for industrial production.

  Moreover, there are two types of heat patterns for the annealing conditions in this case. One is a two-stage method, and the first stage has a temperature in the range of T1 (° C) shown in Equation 2 for 5 to 120 seconds, and the second stage temperature T2 (° C) is in the range of 850 to 1000 ° C. This is a method of 10 to 240 seconds. The other is a one-stage cycle in which the temperature is set to 20 to 360 seconds in the range of T1 (° C.) shown in Formula 2 above. Since the two methods have different cooling conditions, there is an effect on the texture. However, since the adjustment of the inhibitor state, which is the subject of the present invention, is determined by T1, which method is used depends on the current equipment constraints and the like. I can decide.

  Cooling from the above annealing temperature is important for fixing the inhibitor. In the past, Japanese Patent Publication No. 46-23820 discloses that the temperature from 750 to 950 ° C. to 400 ° C. is carried out in 2 to 200 seconds. In the present invention, it is sufficient if cooling from 700 ° C. to 300 ° C. is ensured at 10 ° C./second or more.

  Cold rolling is performed once or twice or more with intermediate annealing. At this time, if the final cold rolling rate in the final cold rolling is less than 80%, it is difficult to obtain the orientation accumulation degree of Goss orientation grains in the primary recrystallization texture, so that it is difficult to secure a high magnetic flux density. On the other hand, if it exceeds 95%, the number of Goss orientation grains in the primary recrystallization texture becomes extremely small, and secondary recrystallization becomes unstable.

  The final cold rolling may be carried out at room temperature, but if at least one pass is kept in the temperature range of 100 to 300 ° C. for 1 minute or longer, the primary recrystallization texture is improved and the magnetic properties become extremely good.

  Decarburization annealing is performed by a known method. At this time, when the heating rate from room temperature to 600 to 800 ° C. is rapid heating of 100 ° C./second or more, the primary recrystallization texture is improved and the magnetic properties are improved. Various methods are conceivable for securing the heating rate. That is, resistance heating, induction heating, direct energy application heating, and the like. It is disclosed in JP-A-6-51887 and the like that when the heating rate is increased, Goss orientation grains increase in the primary recrystallization texture and the secondary recrystallization grain size decreases. In the present invention, the heating rate is effective even at 100 ° C./second, desirably 120 ° C./second or more. The reason why the temperature range for rapid heating is set to 600 to 800 ° C. is that recrystallization is not completed when the temperature is lower than this, and the effect is small. On the other hand, even if rapid heating is continued beyond this range, primary recrystallization is not possible. Since the formation of Goss nuclei having a great influence on the texture of this material is completed up to 800 ° C., the effect is small.

  In the second technique, the average grain size of primary recrystallized grains after completion of decarburization annealing is disclosed in Japanese Patent Laid-Open No. 7-252532, etc., so that the average grain size of primary recrystallized grains is 18 to 35 μm. However, in the present invention relating to the third technique, the magnetic properties (particularly iron loss) can be further improved by setting the average primary recrystallized grain size to 7 μm or more and less than 18 μm. That is, if the particle size is small, it means that the number of primary recrystallized grains existing in the unit volume increases. Furthermore, when the primary recrystallized grain size is small, from the viewpoint of grain growth, the volume fraction of Goss orientation grains that become the nucleus of secondary recrystallization at the primary recrystallization stage increases (Materials Science Forum Vol.204-206). Part 2: pp: 631) As a result, the absolute number of Goss oriented grains is about 5 times larger than that of, for example, the average grain size of primary recrystallized grains is 18 to 35 μm, and the selective growth of Goss grains is increased. Significantly improved and magnetic properties are improved.

  In addition, when the average particle size of the primary recrystallized grains is small, the driving force for secondary recrystallization is increased, and secondary recrystallization can be started at a lower temperature stage than the temperature raising stage during finish annealing. In the present situation where finish annealing is performed in a coil shape, the temperature difference between the inside and outside of the coil increases as the temperature rises, so the secondary recrystallization due to the coil site is not uniform due to the lowering of the secondary recrystallization temperature described above. Is significantly reduced and the magnetic properties are extremely stable.

  However, when the average grain size of the primary recrystallized grains is less than 7 μm, the grain growth driving force becomes too large, and the dispersion of the secondary recrystallized grain orientation from the Goss orientation becomes large, which leads to a decrease in magnetic flux density. Absent.

  It is essential in the present invention that the steel sheet is subjected to nitriding after decarburization annealing and before the start of secondary recrystallization. As the method, there are a method of mixing a nitride (CrN, MnN, etc.) with an annealing separator at the time of final annealing, and a method of nitriding in an atmosphere containing ammonia in a state where the strip is run after decarburization annealing. Either method may be adopted, but the latter is more industrially stable.

  At this time, the nitrogen content (tN) (unit: ppm) after nitriding the steel sheet is preferably in the range of 0.25 × sAl + 90 ≦ tN ≦ 300 according to the content of sAl. If it is less than this, secondary recrystallization becomes unstable, while if the total nitrogen content after nitriding exceeds 0.030%, excessive N may blow out during finish annealing and destroy the glass film. Desirably, the nitrogen increase is 0.018% to 0.022%.

  After heating the slab which has a component shown in Table 2 at 1300-1330 degreeC, hot rolling was completed as high as possible, the 2.3 mm-thick steel strip was quenched, and it wound up at 500-600 degreeC. The hot-rolled steel strip is heated at a maximum temperature (T1) of 1050, 1080, 1110, 1140, and 1170 ° C. in a nitrogen atmosphere for 150 seconds, cooled, air-cooled to 730 ° C., and then quenched in hot water at 100 ° C. It was. Thereafter, 3 passes were secured at 150 ° C. to 210 ° C., and the thickness was 0.285 mm by cold rolling. Thereafter, soaking and primary recrystallization annealing at 850 ° C. for 150 seconds was performed in an atmosphere with a dew point of 70 ° C. of 75% hydrogen and 25% nitrogen. This was followed by nitriding in a mixed gas of ammonia and nitrogen in the form of a strip running so that the nitrogen content was 0.018 to 0.021%. And the annealing separation agent which has MgO as a main component was apply | coated. Next, heating was performed at 15 ° C./h up to 1200 ° C. in an atmosphere of 25% nitrogen and 75% hydrogen, and after reaching 1200 ° C., purification treatment was performed in a 100% hydrogen atmosphere and finish annealing was performed. Then, after applying a commonly used tensile insulating coating mainly composed of aluminum phosphate, the magnetic properties were measured.

  The results are shown in Table 3.

  After heating the slab which has a component shown in Table 4 at 1300-1330 degreeC, hot rolling was completed as high as possible, the 2.1 mm-thick steel strip was quenched, and it wound up at 500-600 degreeC. The hot-rolled steel strip was heated at a maximum temperature (T1) of 1050, 1080, 1110, 1140, and 1170 ° C. in a nitrogen atmosphere for 15 seconds, cooled to 900 ° C. in 150 seconds, and then air-cooled to 750 ° C. Quenched in hot water at 100 ° C. Thereafter, three passes were secured at 150 ° C. to 230 ° C., and the thickness was 0.220 mm by cold rolling. Thereafter, soaking and primary recrystallization annealing at 850 ° C. for 90 seconds was performed in an atmosphere having a dew point of 69 ° C. with 75% hydrogen and 25% nitrogen. This was followed by nitriding in a mixed gas of ammonia and nitrogen in the form of a strip running so that the nitrogen content was 0.018 to 0.021%. And the annealing separation agent which has MgO as a main component was apply | coated. Next, heating was performed at 15 ° C./h up to 1200 ° C. in an atmosphere of 25% nitrogen and 75% hydrogen, and after reaching 1200 ° C., purification treatment was performed in a 100% hydrogen atmosphere and finish annealing was performed. Then, after applying a commonly used tensile insulating coating mainly composed of aluminum phosphate, the magnetic properties were measured.

  The results are shown in Table 5.

Claims (10)

% By mass
C: 0.035 to 0.09%,
Si: 2.5-4.0%
Acid-soluble Al (hereinafter referred to as sAl): 0.018 to 0.033%,
N: 0.003 to 0.007%,
S and / or Se with Seq = S + 0.406Se, 0.005 to 0.018%,
Mn: 0.03 to 0.09%,
Ti is 0.005% or less,
A slab of a unidirectional electrical steel sheet, the balance of which is Fe and inevitable impurities, is slab heated at a temperature of 1200 ° C. or more and less than 1350 ° C., hot-rolled, hot-rolled sheet annealing and one cold rolling, or intermediate Perform cold rolling at least twice with annealing, decarburize and anneal, apply annealing separator, perform nitriding treatment after decarburization annealing and start secondary recrystallization of finish annealing, finish annealing In the method for producing a unidirectional electrical steel sheet, the precipitation rate as AlN is 30% or less in N of the steel strip after hot rolling, and the index AlR defined by the formula 1 according to the sAl, N, and Ti contents A method for producing a unidirectional electrical steel sheet with excellent magnetic properties, characterized in that the maximum temperature T1 (° C.) of annealing before final cold rolling is in the range of Formula 2.
AlR (ppm) = sAl (ppm) −27 / 14 × N (ppm) + 27 / 47.9 × Ti (ppm) ・ ・ ・ Equation 1
−4 / 3 × AlR + 3850/3 ≦ T1 ≦ −4 / 3 × AlR + 4210/3 ・ ・ ・ Equation 2   The annealing temperature of hot-rolled sheet annealing or the last intermediate annealing is made into two stages, the first stage is the temperature within the range of T1 (° C.) shown in the formula 2 for 5 to 120 seconds, and the second stage is the temperature T2 (° C.). 2. The method for producing a unidirectional electrical steel sheet with excellent magnetic properties according to claim 1, wherein the temperature is in the range of 850 to 1000 [deg.] C. for 10 seconds to 240 seconds.   2. The magnetism according to claim 1, wherein the annealing temperature of the hot-rolled sheet annealing or the last intermediate annealing is set to one stage, and the temperature is set to 20 to 360 seconds in the range of T1 (° C.) shown in the formula 2. A method for producing a unidirectional electrical steel sheet having excellent characteristics.   In the cooling after hot-rolled sheet annealing or the last intermediate annealing, cooling is performed from 700 ° C to 300 ° C at a cooling rate of 10 ° C / second or more. A method for producing a unidirectional electrical steel sheet having excellent magnetic properties.   The slab component further contains Sb and Sn at a mass percentage of 0.02 to 0.30% as Sb + Sn, and the unidirectional excellent magnetic properties according to any one of claims 1 to 4 Method for producing an electrical steel sheet.   The unidirectional electrical steel sheet with excellent magnetic properties according to any one of claims 1 to 5, wherein the slab component is contained by mass% and further contains 0.02 to 0.30% of Cu. Manufacturing method.   The unidirectional electrical steel sheet with excellent magnetic properties according to any one of claims 1 to 6, wherein an average grain size of primary recrystallized grains after completion of the decarburization annealing is 7 µm or more and less than 18 µm. Manufacturing method.   After the decarburization annealing, nitriding treatment is performed in a mixed gas of hydrogen, nitrogen, and ammonia under the strip running condition, and the nitrogen content (tN) (unit: ppm) after nitriding the steel sheet is 0.25 × sAl + 90 ≦ tN ≦ The method for producing a unidirectional electrical steel sheet having excellent magnetic properties according to any one of claims 1 to 7, characterized in that it falls within a range of 300.   The method for producing a unidirectional electrical steel sheet having excellent magnetic properties according to any one of claims 1 to 8, wherein the rolling reduction of the last cold rolling is 80% or more and 95% or less.   The one direction excellent in magnetic characteristics according to any one of claims 1 to 9, wherein an average heating rate from 600 to 800 ° C from a temperature rise start in decarburization annealing is set to 100 ° C / second or more. Method for producing an electrical steel sheet.