EP0392535A2 - Procédé pour produire de tôle d'acier électrique à grain orienté possédant des caractéristiques magnétiques améliorées - Google Patents

Procédé pour produire de tôle d'acier électrique à grain orienté possédant des caractéristiques magnétiques améliorées Download PDF

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EP0392535A2
EP0392535A2 EP90107030A EP90107030A EP0392535A2 EP 0392535 A2 EP0392535 A2 EP 0392535A2 EP 90107030 A EP90107030 A EP 90107030A EP 90107030 A EP90107030 A EP 90107030A EP 0392535 A2 EP0392535 A2 EP 0392535A2
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Prior art keywords
hot
hot rolling
rolled
weight
reduction ratio
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EP0392535B2 (fr
EP0392535A3 (fr
EP0392535B1 (fr
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Yasunari C/O R&D Lab. Iii Nippon Steel Yoshitomi
Takehide C/O R&D Lab. Ii Nippon Steel Senuma
Yozo C/O R&D Lab. Iii Nippon Steel Suga
Nobuyuki C/O R&D Lab. Iii Nippon Steel Takahashi
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Nippon Steel Corp
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Priority claimed from JP1094412A external-priority patent/JPH0788531B2/ja
Priority claimed from JP1094413A external-priority patent/JP2787776B2/ja
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
    • C21D8/1233—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
    • C21D8/1222—Hot rolling

Definitions

  • a grain-oriented electrical steel sheet is used as a core material for electric devices such as a transformer and this grain-oriented electrical steel sheet should have superior magnetic properties such as exciting characteristics and core loss characteristics.
  • the magnetic flux density B8 at a magnetic field intensity of 800 A/m is generally used as the numerical value representing the exciting characteristics, and the core loss W 17/50 per kg observed when the sheet is magnetized to 1.7 Tesla (T) at a frequency of 50 Hz is used as the numerical value representing the core loss characteristics.
  • the magnetic flux density is a factor having the most influence on the core loss character­istics, and in general, the higher the magnetic flux density, the better the core loss characteristics. Nevertheless, an increase of the magnetic flux density generally results in an increase of the size of secondary recrystallized grains, and sometimes the core loss characteristics are lowered. In contrast, the core loss characteristics can be improved, regardless of the size of the secondary recrystallized grains, by con­trolling the magnetic domain.
  • This grain-oriented electrical steel sheet is prepared by a secondary recrystallization at the final finish annealing step, to develop the Goss structure in which a ⁇ 110 ⁇ plane is formed on the surface of the steel sheet and a ⁇ 001> axis is produced in the rolling direction.
  • the easy magnetization axis ⁇ 001> must be arranged precisely in line with the rolling direction.
  • MnS is once solid-­dissolved at the step of heating a slab before hot rolling and MnS is precipitated at the hot rolling step.
  • a temperature of about 1400°C is necessary for com­pletely solid-dissolving MnS in an amount necessary for the secondary recrystallization, and this temperature is higher by more than 200°C than the slab-heating tempera­ture adopted for a usual steel.
  • This high-temperature slab-heating treatment has the following disadvantages.
  • the slab-heating temperature is lowered to the level adopted for a usual steel, but this means that the amount of MnS effective as the inhibitor must be reduced or MnS not used at all, which results in an unstable secondary recrystallization. Accordingly, to realize a low-­temperature heating of the slab, the inhibitor must be intensified by precipitates other than MnS, by one means or another and the growth of normal grains at the finish annealing properly controlled.
  • the inhibitor sulfides, nitrides, oxides, and grain boundary-precipi­tated elements are considered to be effective, and for example, the following known techniques can be mentioned.
  • Japanese Examined Patent Publication No. 54-24685 discloses a method in which the slab-­heating temperature is adjusted to 1050 to 1350°C by incorporating into a steel a grain boundary-segmented element such as As, Bi, Sn or Sb
  • Japanese Unexamined Patent Publication No. 52-24116 discloses a method in which the slab-heating temperature is adjusted to 1100 to 1260°C by incorporating a nitride-forming element such as Al, Zr, Ti, B, Nb, Ta, V, Cr or Mo.
  • Japanese Unexamined Patent Publication No. 57-89433 discloses a method in which a low-temperature heating of a slab at 1100 to 1250°C is realized by incorporating an element such as S, Se, Sb, Bi, Pb, Sn or B in addition to Mn, and simultaneously, controlling the columnar crystal ratio in the slab and the reduction ratio at the second cold rolling step. Furthermore, Japanese Unexamined Patent Publication No.
  • 59-190324 proposes a technique of stabilizing the secondary recrystallization by incorporating S and Se, forming an inhibitor mainly by Al, B and nitrogen, and carrying out a pulse annealing at the primary recrystallization annealing conducted after cold rolling.
  • the present inventors previously proposed a technique of realizing a low-temperature heating of a slab by controlling the Mn content to 0.08 to 0.45% and the S content to less than 0.007%, in Japanese Unexamined Patent Publication No. 59-56522. According to this method, the problem of an insufficient linear secondary recrystallization in a product, which is due to a coarsening of the crystal grains of the slab during the high-temperature heating of the slab, can be solved.
  • the primary object of this low-temperature slab-heating method is to reduce the manufacturing cost, but the method cannot be industrialized unless good magnetic properties can be stably obtained. If the slab-heating temperature is lowered, changes at the hot rolling step, such as lowering of the hot rolling, should naturally be made, but the continuous production process comprising a low-temperature heating of a slab, including the hot rolling step, has not been investigated.
  • the main roles of hot rolling are the following three rolls, that is, (1) a division of coarse crystal grains by recrystallization, (2) a precipitation of fine MnS and AlN or control of the precipitation, and (3) a formation of ⁇ 110 ⁇ 001> oriented grains by shear deformation.
  • the role (1) is not necessary, and the role (2) is sufficiently exerted if an appropriate microstructure is produced after decarburization annealing, as taught by in Japanese Patent Application No. 1-1778, and therefore, a control of the precipitates in the hot-­rolled sheet is not necessary. Accordingly, the restrictions of the conventional hot rolling method are moderated in the low-temperature heating of the slab.
  • the inventors examined the hot rolling method in which, to control the secondary recrystallization, the microstructure of a hot-rolled steel sheet is rationalized to a high level not attainable by the conventional high-temperature slab-­heating method. For example, in connection with metal-­physical phenomena after the final pass of hot rolling, a precipitation of fine MnS and AlN or control of the precipitation is a most important control item in the conventional method, and other phenomena are not taken into consideration.
  • the inventors noted the recrystallization phenomenon after the final pass of the finish hot rolling, not taken into consideration in the conven­tional techniques, and examined the hot rolling method for obtaining a product having good and stable magnetic properties by utilizing this phenomenon for controlling the microstructure of a hot-rolled steel sheet in the preparation process in which the low-temperature heating of the slab is carried out as the premise step and the final high-reduction cold rolling is carried out at a reduction ratio of at least 80%.
  • the above-mentioned coarsening of crystal grains caused by the high-temperature heating of the slab is not caused, and therefore, the recrystal­lization high-reduction rolling for a division of coarse crystal grains is not necessary.
  • a primary object of the present invention is to obtain a grain-oriented electrical steel sheet stably by the method in which the low-temperature heating of a slab is carried out at a temperature lower than 1280°C as the premise operation and the final cold rolling is carried out at a high reduction ratio of at least 80%.
  • the recrystal­lization after the final pass of finish hot rolling which has not been taken into consideration in the conventional methods, is utilized for attaining this object.
  • the hot rolling-terminating temperature is adjusted and the hot tolling is carried out at a specific cumulative reduction ratio at final three passes, or the hot-rolled sheet is maintained at a predetermined temperature for a predetermined time after termination of the hot rolling and is then wound, whereby the recrystallization of the hot-rolled steel sheet is advanced and the strain in the hot-rolled steel sheet is reduced or the crystal grain diameter is made finer, and the hot-rolled steel sheet is cold-rolled and recrystallized and superior magnetic properties can be obtained.
  • a process for the prepara­tion of a grain-oriented electrical steel sheet which comprises heating at a temperature lower than 1280°C a slab comprising 0.021 to 0.075% by weight of C, 2.5 to 4.5% by weight of Si, 0.010 to 0.060% by weight of acid-soluble Al, 0.0030 to 0.0130% by weight of N, up to 0.014% by weight of S + 0.405Se and 0.05 to 0.8% by weight of Mn, with the balance consisting of Fe and unavoidable impurities, hot-rolling the hot-rolled sheet, subsequently annealing the hot-rolled sheet according to need, subjecting the hot-rolled steel sheet to at least one cold rolling including final cold rolling at a reduction ratio of at least 80% and, if necessary, intermediate annealing, and subjecting the cold-rolled sheet to decarburization annealing and final finish annealing, wherein the hot rolling-terminating temperature is adjusted to 700 to 1150°C and the cumulative reduction
  • the hot rolling-terminating temperature is adjusted to 750 to 1150°C, the hot-rolled sheet is maintained at a temperature higher than 700°C for at least 1 second after termination of the hot rolling, and the winding temperature is adjusted to a level lower than 700°C.
  • the cumulative reduction ratio at the final three passes of the finish hot rolling is adjusted to at least 40%, a grain-­oriented electrical steel sheet having further superior magnetic properties can be obtained.
  • the reduction ratio at the final pass of the finish hot rolling is adjusted to at least 20% in the above-­mentioned process, the magnetic properties are further improved in the obtained grain-oriented magnetic steel sheet.
  • Figure 1 shows the influences of the hot rolling-­terminating temperature and the cumulative reduction ratio at the final three passes of the hot rolling on the magnetic flux density of a product. More specifi­cally, a slab having a thickness of 20 to 60 mm and comprising 0.054% by weight of C, 3.27% by weight of Si, 0.029% by weight of acid-soluble Al, 0.0080% by weight of N, 0.007% by weight of S and 0.14% by weight of Mn, with the balance consisting of Fe and unavoidable impurities, was heated at 1100 to 1280°C, hot-rolled to a hot-rolled sheet having a thickness of 2.3 mm through 6 passes, and subjected to a winding simulation in which the hot-rolled sheet was water-cooled to 550°C about 1 second after the hot rolling and maintained at 550°C for 1 hour to effect furnace cooling.
  • the hot-­rolled sheet was maintained at 1120°C for 30 seconds, maintained at 900°C for 30 seconds, and rapidly cooled to effect annealing of the hot-rolled sheet.
  • final high-reduction rolling was carried out at a reduction ratio of about 88% to obtain a cold-rolled sheet having a final thickness of 0.285 mm.
  • a decarburization annealing was carried out at a tempera­ture of 830 to 1000°C, an anneal separating agent composed mainly of MgO was coated on the cold-rolled sheet, and a final finish annealing was carried out.
  • Figure 2 is a graph illustrating the relationship between the reduction ratio at the final pass of the hot rolling and the magnetic flux density, observed in runs giving a high magnetic flux density in Fig. 1, where the hot rolling-terminating temperature was 700 to 1150°C and the cumulative reduction ratio at the final three passes of the hot rolling was at least 40%.
  • Figures 3, 4, and 5 show examples of microstruc­tures of hot-rolled steel sheets, microstructures of hot-rolled and annealed steel sheets, and textures (at the point of 1/4 thickness), observed under different hot rolling conditions. More specifically, slabs having a thickness of 33.2 or 26 mm and the same composition as described above with respect to Fig.
  • hot-rolled sheets having a thickness of 2.3 mm through a pass schedule of (A) 33.2 mm ⁇ 18.6 mm ⁇ 11.9 mm ⁇ 8.6 mm ⁇ 5.1 mm ⁇ 3.2 mm ⁇ 2.3 mm or (B) 26 mm ⁇ 11.8 mm ⁇ 6.7 mm ⁇ 3.5 mm ⁇ 3.0 mm ⁇ 2.6 mm ⁇ 2.3 mm. Then, the hot-rolled sheets were cooled under the same conditions as described above with respect to Fig. 1.
  • the hot rolling-terminating temperature was (A) 925°C or (B) 910°C, and the hot-rolled sheets were subjected to annealing and final high-reduction rolling to obtain cold-rolled steel sheets having a thickness of 0.285 mm. Then decarburization annealing was carried out by maintaining the cold-rolled steel sheets at 830°C for 150 seconds in an atmosphere comprising 25% of N2 and 75% of H2 and having a dew point of 60°C.
  • the recrystallization ratio (at the point of 1/4 thickness) was measured by the method developed by the inventors for measuring the crystal strain by the image analysis of ECP (electron channelling pattern) [Collection of Outlines of Lectures Made at Autumn Meeting of Japanese Metal Association (November 1988), page 289], and the area ratio of low-strain grains having a higher sharpness than that of ECP obtained when an annealed sheet of a reference sample was cold-rolled at a reduction ratio of 1.5% was designated as the recrystallization ratio. According to this method, a much higher precision can be obtained than the precision attained by the conventional method of determining the recrystallization ratio by the naked eye observation of the microstructure.
  • the potential nucleus of ⁇ 110 ⁇ 001> secondary recrystallized crystal grains is formed by shearing deformation on the surface layer at the hot rolling, and that the method of coarsening the ⁇ 100 ⁇ 001> oriented crystal grains and keeping them in the strain-reduced state in the hot-rolled steel sheet is effective for enriching the ⁇ 110 ⁇ 001> oriented grains in the steel sheet after cold rolling and recrystallization.
  • the crystal grain diameter in the hot-rolled steel sheet is small, the crystal grains are kept in the strain-­reduced state, and this tendency is maintained after the annealing of the hot-rolled steel sheet, and therefore, the number of the ⁇ 110 ⁇ 001> oriented grains in the steel sheet after the decarburization annealing is not influenced by the present invention hot-rolling method.
  • the main orientations ⁇ 111 ⁇ 112> and ⁇ 100 ⁇ 025> in the decarburized steel sheet are orientations having influences on the growth of ⁇ 110 ⁇ 001> secondary recrystallized crystal grains, and it is considered that the larger the number of ⁇ 111 ⁇ 112> oriented grains and the smaller the number of ⁇ 100 ⁇ 025> oriented grains, the easier reduction the growth of ⁇ 110 ⁇ 001> secondary recrystallized grains.
  • the present invention by applying a high at final three passes of the hot rolling, the number of sites for formation of nuclei at the recrystallization subsequent to the final pass is increased, the recrystallization is advanced, and the crystal grains are made finer.
  • this hot-rolled steel sheet is subjected to the hot-­rolled sheet annealing, many nuclei present in the hot-rolled sheet are changed to recrystallized grains, and these recrystallized grains and fine recrystallized grains already formed in the hot-rolled steel sheet occupy the majority of the steel sheet, with the result that a microstructure composed of fine crystal grains is formed. If this sheet, which has passed through the hot-rolled sheet, is cold-rolled and recrystallized, since the grain diameter before the cold rolling is fine, nucleation in ⁇ 111 ⁇ 112> becomes vigorous from the vicinity of the grain boundary while nucleation in ⁇ 100 ⁇ 025> from the interiors of grains is relatively reduced.
  • the present invention by the recrystallization subsequent to the final pass of the hot rolling, many low-strain recrystallized grains are formed in the hot-rolled steel sheet, and the diameter of the crystal grains is reduced.
  • This influence is taken over after the subsequent hot-rolled sheet annealing, cold rolling and decarburization annealing, and in the decarburized sheet, the number of ⁇ 111 ⁇ 112> oriented grains advantageous for the growth of ⁇ 110 ⁇ 001> oriented grains is increased without any influence on the ⁇ 110 ⁇ 001> oriented grains while the number of ⁇ 100 ⁇ 025> oriented grains inhibiting the growth of ⁇ 110 ⁇ 001> oriented grains is reduced. Due to this characteristic feature, good magnetic properties can be stably obtained according to the present invention.
  • cooling step-adjusting method The method of the holding treatment conducted after termination of the hot rolling (hereinafter referred to as “cooling step-adjusting method”) will now be described in detail with reference to the experimental results.
  • Figure 6 is a graph illustrating the influences of the hot rolling-terminating temperature and the time of maintenance of the steel sheet at a temperature not lower than 700°C after the hot rolling on the magnetic flux density.
  • the hot-rolled sheets were water-cooled, air-cooled for a certain time, then subjected to various coolings such as water cooling and air cooling, and cooling was completed at 550°C, the sheets were maintained at 550°C for 1 hour, and furnace cooling was carried out to effect a winding simulation.
  • the hot-rolled sheets were subjected to the hot-­rolled sheet annealing by maintaining them at a tempera­ture of 900 to 1120°C and the sheets were subjected to final high-reduction rolling at a reduction of about 88% to obtain cold-rolled steel sheets having a final thickness of 0.285 mm. Thereafter, decarburization annealing was carried out at a temperature of 830 to 1000°C, and subsequently, an anneal separating agent was coated on the sheets and the final finish annealing was carried out.
  • Figure 7 is a graph illustrating the relationship between the cumulative reduction ratio at the final three passes of the finish hot rolling and the magnetic flux density, observed in runs giving a high magnetic flux density in Fig. 6, where the hot rolling-termi­nating temperature was 750 to 1150°C and the steel sheet was maintained at a temperature not lower than 700°C for at least 1 second after termination of the hot rolling.
  • Figure 8 is a graph illustrating the relationship between the reduction ratio at the final pass of the finish hot rolling and the magnetic flux density, observed in runs giving a high magnetic flux density in Fig. 7, where the hot rolling-terminating temperature was 750 to 1150°C, the steel sheet was maintained at a temperature not lower than 700°C for at least 1 second after termination of the hot rolling and the cumulative reduction ratio at the final three passes of the finish hot rolling was at least 40%.
  • Figure 9-(a) and 9-(b) illustrate examples of hot-rolled microstructures and recrystallization ratios (at the point of 1/4 thickness) obtained under different hot rolling conditions. Namely, slabs having a thick­ness of 26 mm and the same composition as described above with reference to Fig. 6 were heated at 1150°C, hot rolling was started at 1000°C, and the slabs were hot-rolled according to a pass schedule of 26 mm ⁇ 11.8 mm ⁇ 6.7 mm 3.5 mm ⁇ 3.0 mm ⁇ 2.6 mm ⁇ 2.3 mm.
  • the hot-rolled sheets were air-cooled for (C) 6 seconds or (D) 0.2 second, water-cooled to 550°C at a rate of 200°C/sec, maintained at 550°C for 1 hour, and subjected to furnace cooling to effect a winding simulation and obtain hot-rolled sheets having a thickness of 2.3 mm.
  • the hot rolling-terminating temperature was 846°C and the time of maintenance of the steel sheet at a temperature higher than 700°C was 6 seconds in the case of (C) or 0.9 second in the case of (D).
  • the recrystal­lization ratios (at the point of 1/4 thickness) of the hot-rolled sheets were measured by the same measurement method as described above with reference to Figs. 3 and 4.
  • the matrix of ⁇ 110 ⁇ 001> secondary recrystallized crystal grains is formed by shearing deformation on the surface layer at the hot rolling, and that the method of coarsening the ⁇ 110 ⁇ 001> oriented crystal grains and keeping them in the strain-reduced state in the hot-rolled steel sheet is effective for enriching the ⁇ 110 ⁇ 001> oriented grains in the steel sheet after cold rolling and recrystallization.
  • Figures 10-(a), 10-(b), 11-(a), 11-(b) and 12 show examples of microstructures and recrystallization ratios (at the point of 1/4 thickness) of hot-rolled sheets obtained under different hot rolling conditions, microstructures after the hot-rolled sheet annealing and textures (at the point of 1/4 thickness) after the decarburization annealing (decarburized sheets).
  • the hot-rolled sheets were air-cooled for 2 seconds, water-cooled to 550°C at a rate of 100°C/sec, maintained at 550°C for 1 hour, and subjected to furnace cooling to effect a winding simula­tion, whereby hot-rolled steel sheets having a thickness of 2.3 mm were obtained.
  • the hot rolling-terminating temperature was (E) 930°C or (F) 916°C, and the time of maintenance of the sheet at a temperature not lower than 700°C was (E) 4 seconds or (F) 4 seconds.
  • the hot-­rolled steel sheets were maintained at 1120°C for 30 seconds and maintained at 900°C for 30 seconds, and then rapid cooling was carried out to effect the hot-rolled sheet annealing.
  • the high-reduction rolling was then carried out at a reduction ratio of about 88% to obtain cold-rolled sheets having a final thickness of 0.285 mm, and the cold-rolled sheets were maintained at 840°C for 150 seconds in an atmosphere comprising 25% of N2 and 75% of H2 and having a dew point of 60°C, to effect the decarburization annealing.
  • the main orientations ⁇ 111 ⁇ 112> and ⁇ 100 ⁇ 025> in the decarburized steel sheet are orientations having influences on the growth of ⁇ 110 ⁇ 001> secondary recrystallized crystal grains, and it is considered that the larger the number of ⁇ 111 ⁇ 112> oriented grains and the smaller the number of oriented grains, the easier the growth of ⁇ 110 ⁇ 001> secondary recrystallized grains.
  • the present invention by applying a high reduction at the final three passes of the hot rolling, the number of sites for a formation of nuclei at the recrystallization subse­quent to the final pass is increased, the recrystallization is advanced, and the crystal grains are made finer.
  • this hot-rolled steel sheet is subjected to the hot-rolled sheet annealing, many nuclei present in the hot-rolled sheet are changed to recrystallized grains, and these recrystallized grains and fine recrystallized grains already formed in the hot-rolled steel sheet occupy the majority of the steel sheet, with the result that a microstructure composed of fine crystal grains is formed. If this sheet which has passed through the hot-rolled sheet is cold-rolled and recrystallized, since the grain diameter before the cold rolling is fine, nucleation in ⁇ 111 ⁇ 112> becomes vigorous from the vicinity of the grain boundary while nucleation in ⁇ 100 ⁇ 025> from the interiors of grains is relatively reduced.
  • the recrystallization subsequent to the final pass of the hot rolling by the recrystallization subsequent to the final pass of the hot rolling, many low-strain recrystallized grains are formed in the hot-rolled steel sheet, and the diameter of the crystal grains is reduced.
  • This influence is taken over after the subsequent hot-rolled sheet annealing, cold rolling and decarburization annealing, and in the decarburized sheet, the number of ⁇ 111 ⁇ 112> oriented grains advantageous for the growth of ⁇ 110 ⁇ 001> oriented grains is increased without any influence on the ⁇ 110 ⁇ 001> oriented grains while the number of ⁇ 100 ⁇ 025> oriented grains inhibiting the growth of ⁇ 110 ⁇ 001> oriented grains is decreased.
  • the lower limit of the C content is set as at least 0.021% in the present invention. If the C content is too high, the decarburization time becomes too long and the process is disadvantageous from the economical point of view. Therefore, the upper limit of the C content is set as 0.075%.
  • the Si content is higher than 4.5% cracking becomes conspicuous at the cold rolling, and thus the upper limit of the Si content is 4.5%. If the Si content is lower than 2.5%, the resistivity of the material is too low and a core loss required for a core material of a transformer cannot be obtained.
  • the Si content is at least 2.5%, preferably at least 3.2%.
  • Al should be contained in an amount of at least 0.01% as acid-soluble Al, to ensure the AlN or (Al, Si) nitride content necessary for a stabilization of the secondary recrystallization. If the acid-soluble Al content exceeds 0.060%, the content of AlN in the hot-rolled sheet is not correct, and the secondary recrystallization becomes unstable. Accordingly, the upper limit of the acid-soluble Al content is set as 0.060%.
  • the lower limit of the N content is set as 0.0030%. If the N content exceeds 0.0130%, blistering of the surface of the steel sheet occurs, and therefore, the upper limit of the N content is set as 0.0130%.
  • the lower limit of the Mn content is 0.05%. If the Mn content is lower than 0.05%, the shape (flatness) of the hot-rolled sheet obtained by the hot rolling, especially the side edge of the strip, becomes wavy, and the problem of a reduction of the yield of the product arises. To obtain a good forsterite film, preferably the Mn content is not lower than [0.05 + 7(S + 0.405Se)]%.
  • MnO exerts a catalytic function, and therefore, to secure the necessary quantity of the activity of Mn in the steel, Mn must be present in an amount larger than the amount necessary for trapping S or Se in the form of MnS or MnSe. If the Mn content is lower than [0.05 + 7(S + 0.405Se)]%, the crystal grain diameter of forsterite becomes large and the adhesion of the film becomes poor. Therefore, the lower limit of the Mn content is pref­erably [0.05 + 7(S + 0.405Se)]%. If the Mn content exceeds 0.8%, the magnetic flux density of the product is reduced.
  • the slab-heating temperature is limited to a level lower than 1280°C, preferably 1200°C or less.
  • the heated slab is then hot-rolled to obtain a hot-rolled steel sheet.
  • the characteristic features of the present invention reside in the hot rolling step. Namely, in the present invention, the hot rolling-­terminating temperature is adjusted to 700 to 1150°C and the cumulative reduction ratio at final three passes is adjusted to at least 40%. Furthermore, to obtain better magnetic properties, preferably the reduction ratio at the final pass is at least 20%.
  • the hot rolling finish temperature is adjusted to 750 to 1150°C
  • the hot-rolled sheet is maintained at a temperature not lower than 700°C for at least 1 second after termination of the hot rolling and the winding temperature is adjusted to a level lower than 700°C.
  • the above-mentioned rolling conditions is satisfied as well as this condition of the adjustment of the cooling step, i.e., the cumulative reduction ratio at final three passes of the finish hot rolling is adjusted to at least 40%.
  • the reduction ratio at the final pass is at least 20%.
  • the hot rolling step comprises, in general, rough rolling of a heated slab having a thickness of 100 to 400 mm through a plurality of passes and finish rolling through a plurality of passes.
  • the rough rolling method is not particularly critical and can be performed according to customary procedures.
  • the present invention is characterized by the finish rolling conducted after the rough rolling.
  • the finish rolling is generally carried out by a high-speed continuous rolling of 4 to 10 passes.
  • the reduction ratio is distributed so that the reduction ratio is high at the former stage and the reduction ratio is gradually decreased at the latter stage, whereby a good shape is obtained.
  • the rolling speed is usually 100 to 3000 m/min and the time between two adjacent passes is 0.01 to 100 seconds.
  • the hot rolling-terminating tempera­ture, the cumulative reduction ratio at the final three passes and the reduction ratio at the final pass are restricted as the rolling conditions, and other conditions are not particularly critical, but if the time between two passes at the final three passes is extraordinarily long and exceeds 1000 seconds, the strain is relieved by a recovery and recrystallization between passes, and the effect of accumulation of the strain is not substantially obtained. Therefore, too long a time between two passes at the final three passes is not preferred.
  • the reduction ratio at several passes of the former stage of the finish hot rolling is not particularly specified because it is not expected that the strain applied at these passes will be left at the final pass, and it is sufficient if only the reduction ratio at the final three passes is taken into consideration.
  • the reasons for limiting the hot rolling-finish temperature 700 to 1150°C and the cumulative reduction ratio at the final three passes to 40% are as described below. As apparent from Fig. 1, if these conditions are satisfied, a product having a good magnetic flux density B8 of B8 ⁇ 1.90T can be obtained.
  • the upper limit of the cumulative reduction ratio at the final three passes is not particularly critical, but it is industrially difficult to apply a cumulative reduction ratio higher than 99.9%. In the present invention, most preferably the reduction ratio at the final pass is at least 20%. As seen from Fig. 2, if this requirement is satisfied, a product having a better magnetic flux density B8 of B8 ⁇ 1.92T can be obtained.
  • the upper limit of the reduction ratio at the final pass is not particularly critical, but it is industrially difficult to apply a reduction ratio exceeding 90%.
  • the upper limit of the time of maintenance of the sheet at a temperature not lower than 700°C is not particularly critical, but since the time between the point of termination of the hot rolling and the point of initiation of the winding is usually about 0.1 to about 1000 seconds, in view of the equipment, it is difficult to maintain the steel sheet in the form of a strip at a temperature not lower than 700°C for at least 1000 seconds.
  • the winding temperature after the hot rolling is not lower than 700°C, because of the difference of the heat history in the coil at the cooling step, the state of precipitation of AlN or the like, the state of surface decarburization and the microstructure become irregular in the coil, resulting in a dispersion of the magnetic properties in the product. Therefore, the winding temperature must be lower than 700°C.
  • the upper limit of the cumulative reduction ratio at the final three passes in the cooling step-adjusting method is not particularly critical, but it is industrially difficult to apply a cumulative reduction ratio higher than 99.9%.
  • the reason why the reduction ratio at the final pass is preferably adjusted to at least 20% is that, as seen from Fig. 8, a product having a much better magnetic flux density of B8 ⁇ 1.94T is obtained.
  • the upper limit of the reduction ratio at the final pass is not particularly critical, but it is industrially difficult to apply a reduction ratio not lower than 90%.
  • the hot-rolled steel sheet prepared according to the above-mentioned process is subjected to the hot-­rolled sheet annealing according to need, and at least one cold rolling including intermediate annealing, according to need, is carried out.
  • the reason why the reduction ratio at the final cold rolling is adjusted to at least 80% is that, if this requirement is satisfied, appropriate amounts of sharp ⁇ 110 ⁇ 001> oriented grains and coincidence oriented grains [ ⁇ 111 ⁇ 112> oriented grains, etc.] which is easily corroded by the above grains can be obtained, and the magnetic flux density is greatly improved.
  • the steel sheet After the cold rolling, the steel sheet is subjected to decarburization annealing, coating with an anneal separating agent, and finish annealing according to customary procedures to obtain a final product.
  • the inhibitor intensity necessary for a secondary recrystallization is insufficient in the state after decarburization annealing, it is necessary to carry out an inhibitor-reinforcing treatment at the finish annealing or the like.
  • the inhibitor-­reinforcing method there is known, for example, a method in which, for an Al-containing steel, the partial pressure of nitrogen in the gas of the finish annealing atmosphere is set at a relatively high level.
  • a slab having a thickness of 40 mm which comprised 0.056% by weight of C, 3.28% by weight of Si, 0.14% by weight of Mn, 0.005% by weight of S, 0.029% by weight of acid-soluble Al and 0.0078% by weight of N, with the balance consisting of Fe and unavoidable impurities, was heated at 1150°C, the hot rolling was started at 1050°C, and the slab was hot-rolled through 6 passes to obtain a hot-rolled sheet having a thickness of 2.3 mm.
  • the reduction ratio distribution adopted was (1) 40 mm ⁇ 15 mm ⁇ 7 mm ⁇ 3.5 mm ⁇ 3 mm ⁇ 2.6 mm ⁇ 2.3 mm, (2) 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 10 mm ⁇ 5 mm ⁇ 2.8 mm ⁇ 2.3 mm, or (3) 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 10 mm ⁇ 5 mm ⁇ 3 mm ⁇ 2.3 mm.
  • the hot-rolled sheet was subjected to a winding simulation where the sheet was air-cooled for 1 second, water-cooled to 550°C, maintained at 550°C for 1 hour, and subjected to furnace cooling.
  • the hot-rolled sheet was subject to hot-rolled sheet annealing where the sheet was maintained at 1120°C for 30 seconds and at 900°C for 30 seconds, and then rapidly cooled. Thereafter, the sheet was then rolled at a reduction ratio of about 88%, to obtain a cold-rolled sheet having a thickness of 0.285 mm, the cold-rolled sheet was maintained at 830°C for 150 seconds to effect decarburization annealing, the obtained decarburized and annealed sheet was coated with an anneal separating agent composed mainly of MgO, and was subjected to final finish annealing wherein the temperature was elevated to 1200°C at a rate of 10°C/hr in an atmosphere gas comprising 75% of N2 and 25% of H2 , and the sheet was maintained at 1200°C for 20 hours in an atmosphere gas comprising 100% of H2.
  • a slab having a thickness of 26 mm which comprised 0.053% by weight of C, 3.28% by weight of Si, 0.15% by weight of Mn, 0.006% by weight of S, 0.030% by weight of acid-soluble Al and 0.0081% by weight of N, with the balance consisting of Fe and unavoidable impurities, was heated at 1150°C and the slab was hot-rolled through six passes to obtain a hot-rolled sheet having a thickness of 2.3 mm.
  • the reduction ratio distribution adopted was 26 mm ⁇ 15 mm ⁇ 10 mm ⁇ 7 mm ⁇ 5 mm ⁇ 2.8 mm ⁇ 2.3 mm.
  • the hot-rolling-starting temperature was (1) 1000°C, (2) 900°C, (3) 800°C or (4) 700°C.
  • the conditions of the cooling after the hot rolling and the step of up to the final finish annealing were the same as those of Example 1.
  • Table 2 Hot Rolling Condition Hot Rolling-Finish Temperature (°C) Cumulative Reduction Ratio (%) at Final Three Passes Reduction Ratio (%) at Final Pass B8 (T) Remarks (1) 904 67 18 1.91 present invention (2) 832 67 18 1.91 present invention (3) 743 67 18 1.90 present invention (4) 665 67 18 1.88 comparison
  • a slab having a thickness of 40 mm which comprised 0.051% by weight of C, 3.30% by weight of Si, 0.14% by weight of Mn, 0.006% by weight of S, 0.031% by weight of acid-soluble Al and 0.0082% by weight of N, with the balance consisting of Fe and unavoidable impurities, was heated at 1250°C and the slab was hot-rolled through 6 passes to obtain a hot-rolled sheet having a thickness of 2.0 mm.
  • the reduction ratio distribution adopted was 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 10 mm ⁇ 5 mm ⁇ 3 mm ⁇ 2 mm, and the hot rolling-initiating temperature was (1) 1250°C, (2) 1100°C or (3) 1000°C.
  • the hot-rolled sheet was cooled under the same conditions as adopted in Example 1.
  • the hot-rolled sheet was main­tained at 1120°C for 30 seconds and at 900°C for 30 minutes, and rapidly cooled to effect the hot-rolled sheet annealing.
  • the sheet was then rolled at a reduction ratio of 89% to obtain a cold-rolled sheet having a thickness of 0.220 mm, maintained at 830°C for 120 seconds and at 910°C for 20 seconds to effect the decarburization annealing, and the obtained decarburized sheet was coated with an anneal separating agent composed mainly of MgO.
  • the temperature was elevated to 880°C at a rate of 10°C/hr in an atmosphere gas comprising 25% of N2 and 75% of H2 , the temperature was elevated to 1200°C at a rate of 15°C/hr in an atmosphere gas comprising 75% of N2 and 25% of H2 , and the sheet was maintained at 1200°C for 20 hours in an atmosphere gas comprising 100% of H2 to effect the final finish annealing.
  • the hot rolling condition, the hot rolling-termi­nating temperature, and the magnetic properties of the product are shown in Table 3.
  • a slab having a thickness of 40 mm which comprised 0.052% by weight of C, 3.21% by weight of Si, 0.14% by weight of Mn, 0.006% by weight of S, 0.030% by weight of acid-soluble Al and 0.0080% by weight of N, with the balance consisting of Fe and unavoidable impurities, was heated at 1150°C, and the hot rolling was started at 1050°C and the slab was hot-rolled through 6 passes to obtain a hot-rolled sheet having a thickness of 1.6 mm.
  • the reduction ratio distribution adopted was (1) 40 mm ⁇ 16 mm ⁇ 7 mm ⁇ 2.6 mm ⁇ 2.0 mm ⁇ 1.8 mm ⁇ 1.6 mm, (2) 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 10 mm ⁇ 5 mm ⁇ 2.5 mm ⁇ 1.6 mm, (3) 40 mm ⁇ 30 mm ⁇ 22 mm ⁇ 12 mm ⁇ 6 mm ⁇ 3.1 mm ⁇ 1.6 mm or (4) 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 11 mm ⁇ 4.5 mm ⁇ 2.9 mm ⁇ 1.6 mm.
  • the cooling after the hot rolling was carried out under the same conditions as described in Example 1.
  • the hot-rolled sheet was maintained at 1120°C for 30 seconds and at 900°C for 30 seconds to effect the hot-rolled sheet annealing, and the sheet was then rolled at a reduction ratio of 89% to obtain a cold-rolled sheet having a thickness of 0.170 mm.
  • the operations up to the final finish annealing were carried out under the same conditions as described in Example 1.
  • Table 4 Hot Rolling Condition Hot Rolling-Finish Temperature (°C) Cumulative Reduction Ratio (%) at Final Three Passes Reduction Ratio (%) at Final Pass B8 (T) Remarks (1) 886 38 11 1.89 comparison (2) 904 84 36 1.93 present invention (3) 920 87 48 1.95 present invention (4) 954 85 45 1.94 present invention
  • the hot rolling-terminating tempera­ture was 854°C.
  • the sheet was then subjected to (1) a winding simulation wherein the sheet was air-cooled (852°C), water-cooled to 550°C at a rate of 250°C/sec, maintained at 550°C for 1 hour, and subjected to furnace cooling, or (2) a winding simulation where the sheet was air-cooled (804°C), water-cooled to 550°C at a rate of 100°C/sec, maintained at 550°C for 1 hour, and subjected to furnace cooling.
  • the hot-rolled sheet was maintained at 1050°C for 30 seconds and at 900°C for 30 seconds and then rapidly cooled to effect the hot-rolled sheet annealing.
  • the sheet was then rolled at a reduction ratio of 88% to obtain a cold-rolled sheet having a thickness of 0.285 mm, was maintained at 830°C for 150 seconds to effect the decarburization annealing, the decarburized sheet was coated with an anneal separating agent composed mainly of MgO, the temperature was elevated to 1200°C at a rate of 10°C/hr in an atmosphere gas comprising 75% of N2 and 25% of H2 , and the sheet was maintained at 1200°C for 20 hours in an atmosphere gas comprising 100% of H2 to effect the final finish annealing.
  • an anneal separating agent composed mainly of MgO
  • Table 5 Hot Rolling Condition Hot Rolling-Finish Temperature (°C) Time (sec) of Maintenance not lower than 700°C after Hot Rolling Winding Temperature (°C) Cumulative Reduction Ratio (%) at Final Three Passes Reduction Ratio (%) at Final Pass B8 (T) Remarks (1) 854 0.8 550 34 12 1.89 comparison (2) 854 6 550 34 12 1.91 present invention
  • a slab having a thickness of 26 mm which comprised 0.053% by weight of C, 3.26% by weight of Si, 0.15% by weight of Mn, 0.007% by weight of S, 0.030% by weight of acid-soluble Al and 0.0081% by weight of N, with the balance consisting of Fe and unavoidable impurities, was heated at 1150°C, and the slab was hot-rolled through 6 passes to obtain a hot-rolled sheet having a thickness of 2.3 mm.
  • the reduction ratio distribution adopted was 26 mm ⁇ 15 mm ⁇ 10 mm ⁇ 7 mm ⁇ 5 mm ⁇ 2.8 mm ⁇ 2.3 mm.
  • the hot rolling-starting temperature was adjusted to (1) 1000°C, (2) 900°C, (3) 800°C or (4) 700°C.
  • the sheet was subjected to a winding simulation where the sheet was air-cooled for 3 seconds, water-cooled to 550°C at a rate of 100°C/sec, maintained at 550°C for 1 hour, and subjected to the furnace cooling. Then the operations up to the final finish annealing were carried out under the same conditions as described in Example 5.
  • a slab having a thickness of 40 mm which comprised 0.054% by weight of C, 3.27% by weight of Si, 0.14% by weight of Mn, 0.006% by weight of S, 0.029% by weight of acid-soluble Al and 0.0080% by weight of N, with the balance consisting of Fe and unavoidable impurities, was heated at 1150°C, and the hot rolling was started at 1000°C and the slab was hot-rolled through a pass schedule of 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 10 mm ⁇ 5 mm ⁇ 3 mm ⁇ 2 mm.
  • the sheet was subjected to cooling under such conditions that (1) the sheet was air-cooled for 2 seconds, water-cooled to 550°C at a rate of 100°C/sec, maintained at 550°C for 1 hour and subjected to the furnace cooling or (2) the sheet was air-cooled for 2 seconds, water-cooled to 750°C at a rate of 50°C/sec, maintained at 750°C for 1 hour, and subjected to the furnace cooling. Then the hot-rolled sheet was maintained at 1120°C for 30 seconds and at 900°C for 30 seconds and was rapidly cooled to effect the hot-rolled sheet annealing. The subsequent operations up to the final finish annealing were carried out in the same manner as described in Example 5.
  • a slab having a thickness of 40 mm which comprised 0.053% by weight of C, 3.40% by weight of Si, 0.14% by weight of Mn, 0.006% by weight of S, 0.030% by weight of acid-soluble Al and 0.0080% by weight of N, with the balance consisting of Fe and unavoidable impurities, was heated at 1250°C and hot-rolled through 6 passes to obtain a hot-rolled sheet having a thickness of 40 mm.
  • the reduction ratio distribution adopted was 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 10 mm ⁇ 5 mm ⁇ 3mm ⁇ 2 mm, and the hot rolling-initiating temperature was (1) 1250°C, (2) 1100°C or (3) 1000°C.
  • the sheet was cooled under the same conditions as described in Example 6.
  • the hot-rolled sheet was maintained at 1120°C for 30 seconds and at 900°C for 30 seconds and was rapidly cooled to effect the hot-rolled sheet annealing.
  • the sheet was cold-rolled at a reduc­tion ratio of 89% to obtain a cold-rolled sheet having a thickness of 0.220 mm, the sheet was maintained at 830°C for 120 seconds and at 900°C for 20 seconds to effect the decarburization annealing, and the obtained decarburized sheet was coated with an anneal separating agent composed mainly of MgO.
  • the temperature was elevated to 880°C at a rate of 10°C/hr in an atmosphere gas comprising 25% of N2 and 75% of H2
  • the temperature was elevated to 1200°C at a rate of 15°C/hr in an atmosphere gas comprising 75% of N2 and 25% of H2
  • the sheet was maintained at 1200°C for 20 hours in an atmosphere gas comprising 100% of H2.
  • a slab having a thickness of 40 mm which comprised 0.052% by weight of C, 3.21% by weight of Si, 0.14% by weight of Mn, 0.006% by weight of S, 0.030% by weight of acid-soluble Al and 0.0080% by weight of N, with the balance consisting of Fe and unavoidable impurities, were heated at 1150°C, the hot rolling was started at 1050°C, and the sheet was hot-rolled through 6 passes to obtain a hot-rolled sheet having a thickness of 1.6 mm.
  • the reduction ratio distribution adopted was (1) 40 mm ⁇ 16 mm ⁇ 7 mm ⁇ 2.6 mm ⁇ 2.0 mm ⁇ 1.8 mm ⁇ 1.6 mm, (2) 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 10 mm ⁇ 5 mm ⁇ 2.5 mm ⁇ 1.6 mm, (3) 40 mm ⁇ 30 mm ⁇ 22 mm ⁇ 12 mm ⁇ 6 mm ⁇ 3.1 mm ⁇ 1.6 mm or (4) 40 mm ⁇ 30 mm ⁇ 20 mm ⁇ 11 mm ⁇ 4.5 mm ⁇ 2.9 mm ⁇ 1.6 mm.
  • the cooling after the hot rolling was carried out under the same conditions as described in Example 6.
  • the hor-rolled sheet was maintained at 1120°C for 30 seconds and at 900°C for 30 seconds to effect the hot-rolled sheet annealing.
  • the sheet was rolled at a reduction ratio of about 89% to obtain a cold-rolled sheet having a thickness of 0.170 mm, and the subsequent operations up to the final finish annealing were carried o t under the same condi­tions as described in Example 5

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EP19900107030 1989-04-14 1990-04-12 Procédé pour produire de tôle d'acier électrique à grain orienté possédant des caractéristiques magnétiques améliorées Expired - Lifetime EP0392535B2 (fr)

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JP1094412A JPH0788531B2 (ja) 1989-04-14 1989-04-14 磁気特性の優れた一方向性電磁鋼板の製造方法
JP9441289 1989-04-14
JP1094413A JP2787776B2 (ja) 1989-04-14 1989-04-14 磁気特性の優れた一方向性電磁鋼板の製造方法
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998048062A1 (fr) * 1997-04-24 1998-10-29 Acciai Speciali Terni S.P.A. Nouveau procede de production d'acier electrique extremement permeable a partir de plaquettes
WO2008000396A1 (fr) 2006-06-26 2008-01-03 Sms Demag Ag Procédé et dispositif de production de matériau de laminage de feuillards à chaud en acier au silicium à base de brames fines

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2016987A (en) * 1978-03-11 1979-10-03 Nippon Steel Corp Process for producing grainoriented silicon steel sheet
GB2095287A (en) * 1981-03-19 1982-09-29 Allegheny Ludlum Steel Method for producing grain- oriented silicon steel
EP0098324A1 (fr) * 1982-07-08 1984-01-18 Nippon Steel Corporation Procédé de production d'un feuillard d'acier au silicium à grain orienté contenant de l'aluminium
GB2130241A (en) * 1982-09-24 1984-05-31 Nippon Steel Corp Method for producing a grain- oriented electrical steel sheet having a high magnetic flux density
EP0219611B1 (fr) * 1985-08-15 1990-05-16 Nippon Steel Corporation Procédé de fabrication d'une tôle en acier électrique à grain orienté

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2016987A (en) * 1978-03-11 1979-10-03 Nippon Steel Corp Process for producing grainoriented silicon steel sheet
GB2095287A (en) * 1981-03-19 1982-09-29 Allegheny Ludlum Steel Method for producing grain- oriented silicon steel
EP0098324A1 (fr) * 1982-07-08 1984-01-18 Nippon Steel Corporation Procédé de production d'un feuillard d'acier au silicium à grain orienté contenant de l'aluminium
GB2130241A (en) * 1982-09-24 1984-05-31 Nippon Steel Corp Method for producing a grain- oriented electrical steel sheet having a high magnetic flux density
EP0219611B1 (fr) * 1985-08-15 1990-05-16 Nippon Steel Corporation Procédé de fabrication d'une tôle en acier électrique à grain orienté

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998048062A1 (fr) * 1997-04-24 1998-10-29 Acciai Speciali Terni S.P.A. Nouveau procede de production d'acier electrique extremement permeable a partir de plaquettes
WO2008000396A1 (fr) 2006-06-26 2008-01-03 Sms Demag Ag Procédé et dispositif de production de matériau de laminage de feuillards à chaud en acier au silicium à base de brames fines

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EP0392535A3 (fr) 1992-09-30
DE69022617T3 (de) 2003-04-03
DE69022617D1 (de) 1995-11-02
EP0392535B1 (fr) 1995-09-27
DE69022617T2 (de) 1996-03-21

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