JP5757693B2 - Low iron loss unidirectional electrical steel sheet manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a unidirectional electrical steel sheet having excellent magnetic properties and used for a transformer core or the like by improving the conditions of a hot-rolled sheet annealing process.

  Unidirectional electrical steel sheets are used as iron core materials for electrical equipment such as transformers, and must have good excitation characteristics and iron loss characteristics as magnetic characteristics. Moreover, in recent years, market demand for low iron loss materials with low energy loss has been increasing particularly due to environmental problems. A steel plate with a high magnetic flux density is a very important development goal because it has a low iron loss and a small iron core.

  This unidirectional electrical steel sheet having a high magnetic flux density is obtained by subjecting a steel sheet having a final thickness from a hot-rolled sheet to finish annealing by appropriate cold rolling and annealing, and is commonly called {110} <001>. It is obtained by so-called secondary recrystallization in which primary recrystallized grains having an orientation are selectively grown.

This secondary recrystallization is caused by the presence of fine precipitates called inhibitors in the steel sheet, such as MnS, AlN, MnSe, Cu ₂ S, BN, (Al, Si) N, or Sn, This is achieved by the presence of grain boundary segregation type elements such as Sb.

  As one method for controlling this secondary recrystallization, there is a method in which fine precipitates are completely dissolved during slab heating before hot rolling, and then finely precipitated in hot rolling and subsequent annealing steps. Has been implemented industrially. However, in this method, it is necessary to heat the slab at a high temperature of 1350 ° C. to 1400 ° C. or more in order to completely dissolve the precipitate.

  This temperature is approximately 200 ° C higher than the slab heating temperature of ordinary steel, and a dedicated heating furnace is required for that purpose, and there is a large amount of melt scale and linear secondary recrystallization failure. Since it is easy, use of a continuous casting slab is difficult.

  Therefore, in order to avoid the above-mentioned problems, research and development has been advanced on a method of manufacturing a grain-oriented electrical steel sheet by heating a slab at a low temperature of 1350 ° C. or lower. As a manufacturing method by low-temperature slab heating, for example, Komatsu et al. Discloses a method using (Al, Si) N formed by nitriding as an inhibitor in Patent Document 1. Moreover, Kobayashi et al. Discloses a method of nitriding in strip form after decarburization annealing as a nitriding method at that time.

Japanese Patent Publication No.62-045285 Japanese Patent Laid-Open No. 02-077525 JP 62-040315 A Japanese Patent Laid-Open No. 02-274812

  As a method for improving the magnetic properties of the unidirectional electrical steel sheet, the {110} <001> goth orientation secondary recrystallization is increased in order to increase the degree of integration of the secondary recrystallization in the primary recrystallization texture. There is known a method of increasing the surface strength such as {111} <112> orientation which is easy.

  For example, by increasing the cumulative reduction rate of the final three passes of finish rolling in hot rolling and the reduction rate of the final pass, the accumulation of strain is promoted, and then, using its own thermal energy, recrystallization is performed as much as possible. Patent Document 4 and the like disclose a manufacturing method that increases the surface strength such as the {111} <112> orientation by primary recrystallization after cold rolling by reducing the crystal size.

  However, in this method, since recrystallization is performed using the thermal energy of the own after hot rolling, the temperature difference between the skid and the skid during slab heating, the temperature difference in the width direction of the steel plate, etc. There is a problem that recrystallization textures and / or variations in magnetic properties are likely to occur.

  For this reason, this invention makes it a subject to provide the method of manufacturing the unidirectional electrical steel plate which has the outstanding magnetic characteristic.

  In order to solve the above problems, the present invention has the following features.

(1) In the present invention, first, by mass, Si: 0.8 to 7%, C: 0.085% or less, acid-soluble Al: 0.01 to 0.065%, N: 0.0075% or less , Mn: 0.02 to 0.20%, Seq. = S + 0.406 × Se: 0.003 to 0.05%, and a silicon steel slab composed of the remaining Fe and inevitable impurities is any of temperatures T1 , T2, and T3 (° C.) represented by the following formula Heat at a temperature of 1350 ° C. or higher, then hot-rolled, anneal the resulting hot-rolled sheet, and perform a single cold-rolling or multiple cold-rolling through the final plate After the steel sheet is decarburized and annealed, the steel sheet is coated with an annealing separator, finish annealing is performed, and the nitrogen content of the steel sheet is increased between the decarburization annealing and the start of secondary recrystallization of the finish annealing. In the method for producing a unidirectional electrical steel sheet comprising performing the treatment, the finishing temperature at the time of finish rolling in hot rolling is 950 ° C. or less, and the cooling rate is 10 ° C./sec or more within 2 seconds after the rolling is finished. Starts rapid cooling and coiling temperature is 700 ℃ or less Winding taken, subsequently, when subjected to hot rolled sheet annealing, characterized in that the heating rate during the sheet temperature 800 to 1000 ° C. and 5 ° C. / sec or higher.

T1 = 10062 / (2.72−log ([Al] × [N])) − 273
T2 = 14855 / (6.82-log ([Mn] × [S]))-273
T3 = 10733 / (4.08-log ([Mn] × [Se]))- 273
In here, [Al], [N] , [Mn], [S], and [Se] are respectively the content of acid-soluble Al, N, Mn, S, and Se (wt%).

  (2) The present invention is characterized in that, in the invention of (1), the cumulative rolling reduction of finish rolling in hot rolling is 93% or more.

  (3) The present invention is characterized in that, in the invention of (1) or (2), the cumulative reduction ratio of the final three passes of finish rolling in hot rolling is 40% or more.

(4) The present invention is the invention of (1), (2), or (3), wherein the silicon steel slab contains Cu: 0.01 to 0.30% in mass% , and In the silicon steel slab, the content of the inhibitor component is adjusted so that all of the temperatures T1 to T3 represented by the above formula and the temperature T4 represented by the following formula are 1350 ° C. or less, and the temperature of T1 to T4 (° C.). As described above, the heating is performed at 1350 ° C. or lower .
T4 = 43091 / (25.09-log ([Cu] * [Cu] * [S]))-273
Here, [Cu] and [S] are the contents (mass%) of Cu and S, respectively.

  (5) The present invention is the invention (1), (2), (3), or (4), wherein the silicon steel slab is in% by mass, Cr: 0.3% or less, P: 0 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, and Bi: 0.01% or less. To do.

  Since the present invention is a low-temperature slab heating method in which the main inhibitor for secondary recrystallization control is formed by nitriding after the decarburization annealing step, without affecting the inhibitor that controls secondary recrystallization, The plate temperature during finish rolling can be easily kept low, and the plate temperature until coil winding in hot rolling is also kept low rapidly, thereby suppressing recrystallization and grain growth, followed by hot rolling. By rapid heating during annealing, recrystallization can be refined uniformly and effectively in both the length and width directions of the steel sheet.

  As a result, the primary recrystallization texture is improved, the degree of integration of {110} <001> -oriented secondary recrystallization is increased, and it is easier to obtain a grain-oriented electrical steel sheet having uniform magnetic properties and excellent magnetic properties in the coil. Can be manufactured.

  Furthermore, in the present invention, by controlling the cumulative reduction ratio of finish rolling in hot rolling more strictly, the primary recrystallization texture is further improved, and secondary recrystallization is performed more stably. An effect of improving magnetic characteristics can be obtained.

  Furthermore, in the present invention, the primary recrystallization texture is further improved by further increasing the reduction ratio of the subsequent pass in the finish rolling in the hot rolling, so that the secondary recrystallization can be performed more stably and further magnetic A characteristic improvement effect can be obtained.

  Furthermore, according to this invention, the unidirectional electrical steel plate which improved the magnetic characteristic according to the additive element can be manufactured.

It is a figure which shows the relationship between the conditions of completion | finish temperature at the time of finish rolling in hot rolling, and magnetic flux density B8. It is a figure which shows the conditions of the temperature increase rate of hot-rolled sheet annealing, and magnetic flux density B8.

  The present invention is premised on heating a slab at a low temperature of 1350 ° C. or lower in a method for producing a unidirectional electrical steel sheet using AlN as a main inhibitor for secondary recrystallization. That is, the present invention is to completely dissolve the inhibitor in the low-temperature slab heating before hot rolling, and to reinforce the inhibitor by nitriding in the subsequent process. For example, disclosed in Patent Document 3 In other words, a technique is used in which an inhibitor necessary for secondary recrystallization is made after completion of decarburization annealing (primary recrystallization) and before the occurrence of secondary recrystallization in finish annealing.

  In the manufacturing method premised on low-temperature slab heating at 1350 ° C. or lower, the plate temperature during finish rolling can be kept low without affecting the inhibitor that controls secondary recrystallization. The present inventors make use of this fact, and further suppress the recrystallization and grain growth by keeping the plate temperature until coil winding in hot rolling low, and subsequently perform hot-rolled sheet annealing. In this case, the recrystallized grains can be effectively refined by rapid heating.

  Although this phenomenon has not been fully elucidated, increasing the strain accumulated during hot rolling and holding it, and then rapidly heating the hot-rolled sheet promotes refinement of recrystallized grains. It is estimated that.

  According to this method, in the primary recrystallization texture after cold rolling, it is possible to increase the {111} <112> orientation generated from the vicinity of the material grain boundary. As a result, the {110} <001> orientation secondary reconstruction The present inventors have found that a unidirectional electrical steel sheet excellent in magnetic properties can be produced effectively by increasing the degree of crystal integration, and completed the present invention.

  Next, the reason for limiting the component composition of the silicon steel material used in the present invention will be described. Hereinafter,% means mass%.

  In the present invention, at least Si: 0.8-7%, C: 0.085% or less, acid-soluble Al: 0.01-0.065%, N: 0.0075% or less, Mn: 0.02- 0.20%, Seq. = S + 0.406 × Se: 0.003 to 0.05%, the component composition consisting of the remaining Fe and inevitable impurities, or this component composition, further Cu: 0.01 to 0.30%, Cr: 0.3% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, and Bi: 0.01% or less Or based on the component composition containing 2 or more types, the silicon steel slab for grain-oriented electrical steel sheets containing another component is used as a raw material as needed. The reasons for limiting the component composition are as follows.

  When Si is added in an increased amount, the electrical resistance increases and the iron loss characteristics are improved. However, if it exceeds 7%, cold rolling becomes extremely difficult, and the steel plate is cracked during rolling. More suitable for industrial production is 4.8% or less. On the other hand, if less than 0.8%, γ transformation occurs during finish annealing and the crystal orientation of the steel sheet is impaired, so the content is made 0.8% or more. Preferably, it is 2.8 to 4.0%.

  C is an effective element for controlling the primary recrystallization structure, but it adversely affects the magnetic properties, so it is necessary to decarburize before finish annealing. When C is more than 0.085%, the decarburization annealing time becomes long and the productivity in industrial production is impaired, so the content is made 0.085% or less. Preferably, it is 0.05 to 0.08%.

In the present invention, acid-soluble Al is an element essential for binding to N and securing the function as an inhibitor as (Al, Si) N. In order to ensure the inhibitor function, it is necessary to contain 0.01% or more. However, if it exceeds 0.065 %, secondary recrystallization becomes unstable, so that acid-soluble Al stabilizes secondary recrystallization. 0.01 to 0.065%. Preferably, it is 0.022 to 0.035%.

  If N exceeds 0.012%, voids called blisters are formed in the steel sheet during cold rolling, and it is necessary to be 0.0075% or less in order to function as an inhibitor. If it exceeds 0.0075%, the dispersion state of the precipitates becomes non-uniform and secondary recrystallization becomes unstable. Preferably, it is 0.006 to 0.0075%.

  If Mn is less than 0.02%, cracking is likely to occur during hot rolling. Mn forms MnS and / or MnSe that functions as an inhibitor. However, if it exceeds 0.20%, the precipitation dispersion of MnS and / or MnSe tends to be uneven, and secondary recrystallization becomes unstable. 0.20% or less. Preferably, it is 0.03 to 0.09%.

  Since S and Se combine with Mn to form MnS and / or MnSe that function as an inhibitor, the content is Seq. = S + 0.406 × Se. Seq. = S + 0.406 × Se is less than 0.003%, the function as an inhibitor is reduced. Is 0.003% or more. On the other hand, if it exceeds 0.05%, the dispersion of precipitates tends to be non-uniform and secondary recrystallization becomes unstable, so 0.05% or less. Preferably, it is 0.005 to 0.05%.

In the present invention, Cu may be further added as an inhibitor constituent element. Cu also binds to S and Se to form precipitates that function as inhibitors. If it is less than 0.01%, the function as an inhibitor is reduced. On the other hand, if it exceeds 0.3%, the dispersion of precipitates tends to be non-uniform and the effect of reducing iron loss is saturated, so the content is made 0.3% or less. Preferably, it is 0.05 to 0.3%.

  In addition to the above components, the silicon steel slab of the present invention further contains at least one of Cr, P, Sn, Sb, Ni, and Bi, if necessary, Cr: 0.3% or less, P: 0.5 %, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, Bi: 0.01% or less.

  Cr improves the decarburization annealing oxide layer and is an effective element for glass coating formation, and is 0.3% or less. Preferably, it is 0.02 to 0.3%.

  P is an element effective for increasing the specific resistance and reducing the iron loss. If it exceeds 0.5%, a problem arises in rollability, so the content is made 0.5% or less. Preferably, it is 0.02 to 0.3%.

  Sn and Sb are grain boundary segregation elements. Since the present invention contains Al, depending on the conditions of final annealing, Al is oxidized by moisture released from the annealing separator, and the inhibitor strength varies at the coil position, and the magnetic characteristics vary at the coil position. There is a case. As one of countermeasures, there is a method of preventing oxidation by adding grain boundary segregation elements of Sn and / or Sb.

  In the present invention, Sn and / or Sb is added in an amount of 0.30% or less in order to suppress fluctuations in magnetic characteristics at the coil position. If it exceeds 0.30%, it is difficult to be oxidized at the time of decarburization annealing, and the formation of the glass film becomes insufficient, and the decarburization annealing property is remarkably inhibited. Preferably, it is 0.02 to 0.30%.

  Ni is an element effective for increasing the specific resistance and reducing the iron loss. It is also an effective element for improving the magnetic properties by controlling the metal structure of the hot-rolled sheet. However, if it exceeds 1%, secondary recrystallization becomes unstable. Preferably, it is 0.02 to 0.30%.

  Bi, when added in an amount of 0.01% or more, has the effect of stabilizing precipitates such as sulfides and strengthening the function as an inhibitor. However, if it exceeds 0.01%, the glass film formation is adversely affected. Preferably, it is 0.0005 to 0.01%.

  Furthermore, the silicon steel slab used in the present invention may contain elements other than those described above and / or other inevitable elements as long as the magnetic properties are not impaired.

  Next, the manufacturing conditions of the present invention will be described.

  A silicon steel slab having the above component composition is obtained by melting steel with a converter or an electric furnace, etc., and vacuum-degassing the molten steel as necessary, and then performing continuous casting or block rolling after ingot forming. .

  The silicon steel slab is usually cast to a thickness of 150 to 350 mm, preferably 220 to 280 mm, but may be a thin slab of 30 to 70 mm. In the case of a thin slab, there is an advantage that when a hot-rolled sheet is manufactured, it is not necessary to perform roughing to an intermediate thickness.

<Slab heating temperature>
The silicon steel slab is then slab heated prior to hot rolling. In the present invention, the slab heating temperature is set to 1350 ° C. or less, and in the slab heating before hot rolling, the inhibitor is completely dissolved, and various problems in high-temperature slab heating (a dedicated heating furnace is necessary, And problems such as a large amount of melt scale).

In the present invention, the inhibitor (AlN, MnS, MnSe, etc.) needs to be completely in solution, so that the slab heating temperature is equal to or higher than all the temperatures T1, T2, and T3 (° C.) represented by the following formulas. In addition, it is necessary to control the amount of the element constituting the inhibitor.

  Regarding the contents of Al and N, the following formula T1 needs to be 1350 ° C. or lower. Similarly, regarding the contents of Mn and S, the contents of Mn and Se, and the contents of Cu and S, the following formulas T2, T3, and T4 are set to 1350 ° C. or lower, respectively. There is a need to.

T1 = 10062 / (2.72−log ([Al] × [N])) − 273
T2 = 14855 / (6.82-log ([Mn] × [S]))-273
T3 = 10733 / (4.08-log ([Mn] × [Se]))-273
T4 = 43091 / (25.09-log ([Cu] * [Cu] * [S]))-273
Here, [Al], [N], [Mn], [S], [Se], and [Cu] are the contents of acid-soluble Al, N, Mn, S, Se, and Cu, respectively. (Mass%).

<Hot-roll finish finish temperature>
As described above, the slab heating is performed at 1350 ° C. or lower, followed by hot rolling to obtain a hot rolled sheet having a required thickness. At that time, by setting the finishing temperature at the time of finish rolling to 950 ° C. or less, the magnetic characteristics are clearly improved.

  Although this effect has not been fully elucidated, if the accumulation of rolling strain increases, the subsequent rapid cooling suppresses recrystallization until the end of hot rolling, and the recrystallization caused by rapid heating in hot-rolled sheet annealing. At this time, the refinement of the crystal is promoted, and the {111} <112> orientation generated from the vicinity of the grain boundary in the primary recrystallization texture after the cold rolling increases, and as a result, the {110} <001> orientation secondary This is thought to be because recrystallization tends to grow.

  The lower end temperature during finish rolling is preferably lower for magnetic properties, so a lower limit is not set. However, if it is too low, production problems such as rolling properties will occur. Therefore, the lower limit temperature should be selected so as not to cause this problem. . A preferable temperature range of the end temperature during finish rolling is 750 to 900 ° C.

  Hereinafter, experiments in which knowledge that forms the basis of the present invention has been obtained will be described. The magnetic measurement is performed by a single plate magnetic property test method (SST test method) described in JIS C 2556 using a single plate of 60 × 300 mm, and B8 (magnetic flux density at 800 A / m, unit is Tesla). It was measured.

(Experimental example 1)
First, the relationship between the condition of the end temperature during finish rolling in hot rolling and the magnetic flux density B8 was investigated.

  Si: 3.26%, C: 0.055%, acid-soluble Al: 0.028%, N: 0.005%, Mn: 0.05%, S: 0.01%, the balance Fe and A 40 mm thick slab composed of inevitable impurities was heated at a temperature of 1320 ° C. and then hot rolled to a thickness of 2.3 mm. At that time, the finishing temperature of finish rolling was changed in the range of 760 to 1010 ° C.

  The cumulative rolling reduction of finish rolling in hot rolling was 94.3%, and the cumulative rolling reduction of the final three passes of finish rolling was 45%. The cooling rate from finish rolling to winding was 16 ° C./s.

  The hot-rolled sheet was heated at a temperature of 1100 ° C. by heating at a rate of temperature increase of 800 to 1000 ° C. at a rate of 7.2 ° C./sec. Then, the annealed hot-rolled sheet is cold-rolled to a thickness of 0.23 mm, then decarburized and annealed at 850 ° C., and then annealed in an ammonia-containing atmosphere to increase the nitrogen in the steel sheet to 0.019%. Then, an annealing separator containing MgO as a main component was applied, and then finish annealing was performed at 1200 ° C. for 20 hours.

  The magnetic properties of the obtained steel sheet after finish annealing are shown in FIG. From FIG. 1, it can be seen that a high magnetic flux density of 1.91 T or more can be obtained with B8 by setting the finish rolling finishing temperature to 950 ° C. or lower.

<Cumulative rolling reduction of finish rolling>
By setting the cumulative rolling reduction of finish rolling to 93% or more, the magnetic properties are further improved. This effect is thought to be due to an increase in the strain accumulation effect, as in the case of lowering the finishing temperature during finish rolling. A preferred range of the cumulative rolling reduction of finish rolling is 93 to 97%.

<Cumulative rolling reduction of final 3 passes of finish rolling>
By setting the cumulative rolling reduction ratio of the final three passes to 40% or more, the same action is obtained and the magnetic characteristics are improved.

  Neither of the above-mentioned rolling reductions defines an upper limit, but is limited for production reasons such as rolling capacity. A preferable range of the rolling reduction is 45 to 60%.

<Time from finish rolling to cooling start>
Even if the strain accumulation is increased by the above method, if cooling is not started within 2 seconds after the end of rolling, recrystallization is suppressed by hot rolling, and the effect of crystal refining accompanying rapid heating by hot-rolled sheet annealing Magnetic properties cannot be improved sufficiently. This is presumably because recrystallization begins unevenly due to temperature variations in the length and width of the steel sheet.

<Cooling rate from finish rolling to winding>
If the cooling rate from finish rolling to winding is not 10 ° C./sec or more, the magnetic properties cannot be sufficiently improved due to recrystallization suppression and crystal refining effects due to the same action as the cooling start time. The upper limit of the cooling rate is not stipulated, but is limited for production reasons such as cooling facility capacity.

<Taking-up temperature>
If the coiling temperature is not set to 700 ° C. or lower, the magnetic characteristics cannot be sufficiently improved by the crystal refining effect due to the same action as the cooling start time and cooling rate. The lower the temperature, the more effective and not the lower limit, but it is limited for production reasons such as hot-rolled plate shape. Preferably, it is 450-600 degreeC.

<Temperature increase rate during hot-rolled sheet annealing>
The magnetic properties can be effectively improved by rapidly heating the temperature increase rate between 800 to 1000 ° C. to 5 ° C./sec or more during the temperature increase in the annealing process of the hot-rolled sheet. . Although this effect has not been fully elucidated, the rolling strain accumulated by strengthening the rolling process and suppressing recrystallization in hot rolling is utilized to promote the refinement of recrystallized grains by rapid heating and continuous annealing. Therefore, the steel sheet can be uniformly recrystallized without temperature variations in the length and width directions of the steel sheet, so that cold rolling preferable for obtaining a {110} <001> -oriented secondary recrystallization with a high degree of integration as described above. It is considered to be a pre-material.

(Experimental example 2)
The relationship between the temperature rise rate condition of the hot-rolled sheet annealing and the magnetic flux density B8 was investigated.

  Si: 3.25%, C: 0.057%, acid-soluble Al: 0.027%, N: 0.004%, Mn: 0.06%, S: 0.011%, Cu: 0.1% A 40 mm thick slab containing the remaining Fe and inevitable impurities was heated at a temperature of 1320 ° C. and then hot rolled to a thickness of 2.3 mm. At that time, the finish temperature of finish rolling was set to 840 ° C.

  The cumulative rolling reduction of finish rolling in hot rolling was 94.3%, the cumulative rolling reduction of the final three passes of finish rolling was 45%, and the cooling rate from finish rolling to winding was 16 ° C./s.

  This hot-rolled sheet was annealed at a temperature of 1100 ° C. by heating at a heating rate of 800 to 1000 ° C. at a temperature of about 3 to 8 ° C./sec. Then, the annealed hot-rolled sheet is cold-rolled to a thickness of 0.23 mm, then decarburized and annealed at 850 ° C., and then annealed in an ammonia-containing atmosphere to increase the nitrogen in the steel sheet to 0.017%. Then, an annealing separator containing MgO as a main component was applied, and then finish annealing was performed at 1200 ° C. for 20 hours.

  The magnetic properties of the obtained steel sheet after finish annealing are shown in FIG. From FIG. 1, it is understood that a high magnetic flux density of 1.91 T or more can be obtained with B8 by setting the heating rate between 800 to 1000 ° C. of the plate temperature to 5 ° C./sec or more during hot-rolled sheet annealing. .

<Heating temperature for hot-rolled sheet annealing>
Annealing of the hot-rolled sheet is performed in a temperature range of 1000 to 1150 ° C. in order to eliminate non-uniformity of the crystal structure / precipitate dispersion due to the difference in temperature history caused by hot rolling.

<Cold rolling>
A cold-rolled sheet having a final thickness is obtained by cold rolling at least once with or without annealing. The number of cold rollings is appropriately selected in consideration of the desired product characteristic level and cost. In the cold rolling, the primary recrystallization orientation such as {111} is advantageous in order to increase the accumulation degree of secondary recrystallization of {110} <001> orientation by setting the final cold rolling rate to 80% or more. Necessary for development.

<Decarburization / Nitriding>
In order to remove C contained in the steel, the steel sheet after cold rolling is subjected to decarburization annealing in a humid atmosphere. After that, before secondary recrystallization appears, N is allowed to penetrate into the steel to form (Al, Si) N that functions as an inhibitor, and a product with high magnetic flux density is stably manufactured.

  As the nitriding treatment for increasing nitrogen, in the decarburization annealing step, a method of annealing in an atmosphere containing a nitriding gas such as ammonia, and adding a nitriding powder such as MnN into the annealing separator. For example, there is a method performed during finish annealing.

  In the decarburization annealing step, heating is performed at 800 to 900 ° C. so that the primary recrystallized grain size becomes 7 to 18 μm. By this heating, secondary recrystallization can be expressed more stably and a more excellent grain-oriented electrical steel sheet can be produced. Thereafter, an annealing separator containing magnesia as a main component is applied, and then finish annealing is performed to preferentially grow {110} <001> oriented grains by secondary recrystallization.

  As described above, according to the present invention, the silicon steel slab is heated at a temperature not lower than the temperature at which a predetermined precipitate is completely solutionized and not higher than 1350 ° C., and then hot-rolled and hot rolled. Sheet annealing, then multiple cold rolling through a single cold rolling or annealing to the final sheet thickness, after decarburization annealing, apply annealing separator, perform finish annealing and decarburization annealing When the unidirectional electrical steel sheet is manufactured by nitriding the steel sheet from the start of secondary recrystallization to finish annealing, the finish temperature at the time of finish rolling in the hot rolling process is 950 ° C. or less, and In addition, the rapid cooling is started within 2 seconds after the end of rolling, and the coiling temperature is set to less than 700 ° C. When the hot-rolled sheet annealing is subsequently performed, the temperature increase rate between 800 to 1000 ° C of the plate temperature is set to 5 ° C. / Sec or more to produce a grain-oriented electrical steel sheet with a high magnetic flux density. It can be.

  Examples of the present invention will be described below. The conditions employed in the examples are one example of conditions for confirming the feasibility and effects of the present invention. Therefore, the present invention is not limited to this one condition example, and various conditions can be adopted as long as the object of the present invention is achieved without departing from the present invention.

  Magnetic measurement was performed by the SST test method (described above), and B8 (magnetic flux density at 800 A / m, unit is Tesla) was measured.

<Example 1>
A 40 mm thick silicon steel slab having the chemical components shown in Table 1 was heated at a temperature of 1320 ° C. and then hot rolled to a thickness of 2.3 mm. At that time, finish hot rolling finish temperature is 875-885 ° C., time from finish rolling to cooling start is 1 second, cooling rate from cooling start to winding is 13-14 ° C./sec, winding temperature is 580 ˜610 ° C. The cumulative rolling reduction of finish rolling in hot rolling was 94%, and the cumulative rolling reduction of the final three passes of finish rolling was 45%.

  About these hot-rolled sheets, it heated at the temperature increase rate between 800-1000 degreeC of plate temperature at 7 degreeC / sec, and annealed at the temperature of 1100 degreeC. Thereafter, the hot-rolled sheet that has been annealed is cold-rolled to a thickness of 0.23 mm, then decarburized and annealed at 850 ° C., and subsequently annealed in an ammonia-containing atmosphere to reduce the nitrogen in the steel sheet by 0.016%. Then, an annealing separator containing MgO as a main component was applied, followed by a finish annealing at 1200 ° C. for 20 hours.

  The magnetic properties (B8) of the steel plates after finish annealing are shown in Invention Examples B10 to B16 in Table 2. Both the finish hot rolling and the hot rolled sheet annealing satisfy the conditions of the present invention, and a high magnetic flux density was obtained in the case of any of the component compositions of the present invention.

<Example 2>
A 40 mm-thick silicon steel slab having the component composition of steel code A1 in Table 1 was produced under the conditions shown in Table 2. Conditions other than those shown in Table 2 are as follows. After the hot-rolled sheet is annealed, the hot-rolled sheet is cold-rolled to a thickness of 0.23 mm, and then decarburized and annealed at 850 ° C., followed by annealing in an ammonia-containing atmosphere, so that the nitrogen in the steel sheet is 0.016. %, And then an annealing separator mainly composed of MgO was applied, followed by finishing annealing at 1200 ° C. for 20 hours.

  The magnetic properties of the obtained steel sheets after finish annealing are shown in Invention Examples B1 to B9 and Comparative Examples C1 to C6 in Table 2. A high magnetic flux density was obtained when the conditions of the present invention were satisfied for both finish hot rolling and hot rolled sheet annealing.

  According to the present invention, a low iron loss unidirectional electrical steel sheet having excellent magnetic properties, in particular, a high magnetic flux density can be produced. Therefore, the present invention has high applicability in the manufacture and use industries of electrical steel sheets.

Claims (5)

In mass%, Si: 0.8-7%, C: 0.085% or less, acid-soluble Al: 0.01-0.065%, N: 0.0075% or less, Mn: 0.02-0. 20%, Seq. = S + 0.406 × Se: 0.003% to 0.05% of silicon steel slab composed of the balance Fe and inevitable impurities, so that all the temperatures T1 to T3 represented by the following formulas are 1350 ° C. or less. The content of the inhibitor component is adjusted and heated at a temperature of T1 to T3 (° C.) or higher and 1350 ° C. or lower, and then hot-rolled, and the obtained hot-rolled sheet is annealed and cooled once. The steel sheet of the final thickness is obtained by performing cold rolling or multiple cold rolling processes through annealing, and after decarburizing and annealing the steel sheet, it is applied with an annealing separator, subjected to finish annealing, and finished from decarburizing annealing. In the method for producing a unidirectional electrical steel sheet, which includes a treatment for increasing the amount of nitrogen in the steel sheet before the start of secondary recrystallization of annealing, the end temperature at the time of finish rolling in hot rolling is set to 950 ° C. or less. And cool down within 2 seconds after rolling. When rapid cooling at a rate of 10 ° C./sec or more is started, the coil is wound at a coiling temperature of 700 ° C. or less, and subsequently subjected to hot-rolled sheet annealing, the temperature increase rate between 800 to 1000 ° C. is increased to 5 ° C. / The manufacturing method of the low iron loss unidirectional electrical steel sheet characterized by setting it as sec or more.
T1 = 10062 / (2.72−log ([Al] × [N])) − 273
T2 = 14855 / (6.82-log ([Mn] × [S]))-273
T3 = 10733 / (4.08-log ([Mn] × [Se]))- 273
In here, [Al], [N] , [Mn], [S], and [Se] are respectively the content of acid-soluble Al, N, Mn, S, and Se (wt%).   2. The method for producing a low iron loss unidirectional electrical steel sheet according to claim 1, wherein a cumulative rolling reduction during finish rolling in the hot rolling is 93% or more.   The method for producing a low iron loss unidirectional electrical steel sheet according to claim 1 or 2, wherein the cumulative reduction ratio of the final three passes during finish rolling in the hot rolling is 40% or more. The silicon steel slab further contains Cu: 0.01 to 0.30% by mass% , and all of the temperatures T1 to T3 represented by the above formula and the temperature T4 represented by the following formula are used. The content of the inhibitor component is adjusted so that the temperature is 1350 ° C. or lower, and heating is performed at a temperature of T1 to T4 (° C.) or higher and 1350 ° C. or lower. The manufacturing method of the low iron loss unidirectional electrical steel sheet as described in claim | item.
T4 = 43091 / (25.09-log ([Cu] * [Cu] * [S]))-273
Here, [Cu] and [S] are the contents (mass%) of Cu and S, respectively.   The silicon steel slab further includes, in mass%, Cr: 0.3% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, And Bi: 0.01% or less of 1 type or 2 types or more are contained, The manufacturing method of the low iron loss unidirectional electrical steel sheet of any one of Claims 1-4 characterized by the above-mentioned.

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