WO2013125223A1 - 電磁鋼板の製造方法 - Google Patents
電磁鋼板の製造方法 Download PDFInfo
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- WO2013125223A1 WO2013125223A1 PCT/JP2013/000967 JP2013000967W WO2013125223A1 WO 2013125223 A1 WO2013125223 A1 WO 2013125223A1 JP 2013000967 W JP2013000967 W JP 2013000967W WO 2013125223 A1 WO2013125223 A1 WO 2013125223A1
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- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/147—Alloys characterised by their composition
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- H01F1/14775—Fe-Si based alloys in the form of sheets
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- 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
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- 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
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- 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
- C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
- C21D8/1261—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest following hot rolling
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- 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
- C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
- C21D8/1272—Final recrystallisation annealing
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/147—Alloys characterised by their composition
- H01F1/14766—Fe-Si based alloys
- H01F1/14791—Fe-Si-Al based alloys, e.g. Sendust
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/16—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
Definitions
- the present invention has a high strength suitable for use in components to which large stress is applied, such as a rotor of a high-speed rotating machine such as a turbine generator, a drive motor of an electric vehicle, a hybrid vehicle, or a motor for a machine tool.
- the present invention relates to a method for producing an electrical steel sheet having excellent fatigue properties and excellent magnetic properties.
- a magnet is embedded by providing a slit on the outer periphery of the rotor. For this reason, stress concentrates on a narrow bridge portion (such as a portion between the outer periphery of the rotor and the slit) due to the centrifugal force when the motor rotates at high speed.
- the core material used for the rotor requires high strength and high fatigue strength.
- Patent Document 1 the Si content is increased to 3.5 to 7.0%, and further elements such as Ti, W, Mo, Mn, Ni, Co, and Al are added to increase the strength for solid solution strengthening.
- Patent Document 2 proposes a method for improving magnetic properties by setting the grain size to 0.01 to 5.0 mm by devising finish annealing conditions in addition to the above-described strengthening method.
- troubles such as plate breakage are likely to occur in the continuous annealing process after hot rolling and the subsequent rolling process, resulting in problems such as a decrease in yield and line stoppage. there were.
- Patent Document 3 discloses a method of strengthening a solid solution with Mn or Ni in steel having a Si content of 2.0 to 3.5%
- Patent Document 4 discloses a method for steel having a Si content of 2.0 to 4.0%.
- solid solution strengthening is performed by adding Mn or Ni, and carbon nitrides such as Nb, Zr, Ti, and V are used to achieve both high strength and magnetic properties.
- these methods have a problem that a large amount of expensive elements such as Ni is added, and the yield is reduced due to an increase in defects such as baldness, resulting in high costs.
- the actual situation is that the fatigue characteristics of the materials obtained by these disclosed techniques have not been sufficiently studied.
- Patent Document 5 discloses a fatigue limit of 350 MPa or more by controlling the crystal grain size according to the steel composition of the electrical steel sheet having a Si content of 3.3% or less. Techniques to achieve are disclosed. However, this method has a low fatigue limit reaching level itself and does not satisfy the recent required level, for example, fatigue limit strength of 500 MPa or more.
- Patent Document 6 and Patent Document 7 propose a high-strength electrical steel sheet in which an unrecrystallized structure remains in the steel sheet. According to these methods, high strength can be obtained relatively easily while maintaining the productivity after hot rolling.
- the inventors have evaluated the stability of the mechanical properties of the material in which the non-recrystallized structure remains in this way, and it has been found that the variation tends to be large. That is, although it shows high mechanical properties on average, it has been found that because of large variations, it may break in a short time even with relatively small stress.
- the present invention has been developed in view of the above circumstances, and is advantageous as an electrical steel sheet that is suitable as a rotor material for a high-speed rotary motor, has stable high strength and fatigue properties, and is excellent in magnetic properties.
- the object is to propose a manufacturing method.
- the inventors have conducted a thorough examination on the mechanical strength and fatigue characteristics of a high-strength electrical steel sheet using an unrecrystallized recovery structure to reduce the variation in mechanical strength and fatigue strength.
- intensive research was conducted on manufacturing conditions for improving the manufacturability.
- precipitates that inhibit the growth of crystal grains, especially the structure after hot-rolled sheet annealing and post-annealing have a great influence on the variation in mechanical properties, and to improve manufacturability
- the addition of Ca is effective.
- the present invention is based on the above findings.
- the gist configuration of the present invention is as follows. 1. % By mass C: 0.0050% or less, Si: more than 3.5% and less than 5.0% Mn: 0.10% or less, Al: 0.0020% or less, P: 0.030% or less, N: 0.0040% or less, S: 0.0005% or more and 0.0030% or less and Ca: 0.0015% or more, Sn: 0.01% or more and 0.1% or less, and Sb: 0.01% or more and 0.1% or less.
- the annealing temperature 850 ° C to 1000 ° C
- annealing time 10 seconds to 10 minutes
- the annealing temperature 670 ° C or higher and 800 ° C or lower
- an electrical steel sheet having high strength and low iron loss and stably exhibiting high fatigue strength can be obtained with good manufacturability.
- the present invention will be specifically described below.
- the present inventors first examined the root cause of the variation in characteristics.
- the characteristic variation means that the characteristic fluctuates in the width direction or the length direction in the product steel plate, or that the characteristics of two products manufactured under similar manufacturing conditions are different.
- the finish annealing temperature is not strictly constant, but varies in the plate width direction or the length direction, and different coils do not have exactly the same temperature.
- the components in the slab also vary in the same way.
- the manufacturing method for reducing variation in product characteristics is a method in which the product characteristics do not vary even when the manufacturing conditions fluctuate as described above.
- the state of precipitates in the material has the most influence on the properties of the material in the intermediate process due to the fluctuation of the manufacturing conditions as described above.
- Precipitates affect the growth of crystal grains during hot-rolled sheet annealing and finish annealing. That is, it affects the crystal structure of the product plate. Therefore, in high-strength electrical steel sheets that utilize unrecrystallized recovery structure, it is extremely important to control the recrystallization rate, so reducing the fluctuations in the state of precipitates reduces the variation in product characteristics. It is considered effective.
- FIG. 1 shows the relationship between the reduction ratio of hot rough rolling and the tensile strength
- FIG. 2 shows the relationship between the hot-rolled sheet annealing temperature and the tensile strength.
- variation in tensile strength was evaluated by standard deviation (sigma), and the range of +/- 2 (sigma) was shown in FIG.1 and FIG.2. As shown in Fig. 1 and Fig.
- the average tensile strength was 650MPa or more in all conditions, which was very high compared to ordinary electromagnetic steel sheets, but the conditions for rough rolling and hot-rolled sheet annealing The degree of variation differs greatly depending on the condition 1 as shown in FIG. 1 where the cumulative rolling reduction ratio of the rough rolling is low, as shown in FIG. 2 the condition 4 where the hot-rolled sheet annealing temperature is low, and the hot-rolled sheet annealing temperature is high. Under condition 7, the variation in tensile strength was large.
- Condition 4 was a mixed structure of the rolled structure and the recrystallized structure expanded by hot rolling, and the average grain size of the recrystallized part was 27 ⁇ m.
- Conditions 1 to 3 and 5 to 7 are structures consisting only of a recrystallized structure, and the average crystal grain size is Condition 1: 270 ⁇ m, Condition 2: 275 ⁇ m, Condition 3: 280 ⁇ m, Condition 5: 100 ⁇ m, Condition 6: 280 ⁇ m, Condition 7: 480 ⁇ m.
- the cumulative reduction ratio in hot rolling rough rolling is increased, the recrystallization rate after hot-rolled sheet annealing is set to 100%, and the structure after hot-rolled sheet annealing is formed so as to keep the recrystallized grains fine. This is an important requirement for suppressing characteristic variation.
- appropriately controlling the cold rolling conditions is important for the structure control during the cold-rolled sheet annealing targeted in the present invention.
- C 0.0050% or less
- C has an effect of increasing strength by precipitation of carbides, but is harmful to variations in magnetic characteristics and mechanical characteristics of products. Since the strengthening of the present invention is achieved mainly by utilizing the solid solution strengthening of the substitutional element of Si and the unrecrystallized recovery structure, C is limited to 0.0050% or less.
- Si more than 3.5% and 5.0% or less Si is a main element constituting an electrical steel sheet because it is generally used as a deoxidizer for steel and has an effect of increasing electric resistance and reducing iron loss.
- Si is actively added in excess of 3.5% as an element that is a main component of solid solution strengthening.
- it is 3.6% or more.
- the productivity decreases as cracks occur during cold rolling, so the upper limit was made 5.0%. Desirably, it is 4.5% or less.
- Mn 0.10% or less Mn not only hinders domain wall movement when precipitated as MnS, but is also a harmful element that degrades magnetic properties by inhibiting crystal grain growth, in order to reduce variation in magnetic properties of products. To 0.10% or less.
- Al 0.0020% or less
- Al like Si, is generally used as a deoxidizer for steel, and has a large effect of increasing iron resistance by increasing electrical resistance. Typically used as an element.
- the amount of nitride needs to be extremely reduced in order to reduce the variation in the mechanical characteristics of the product, it is limited to 0.0020% or less.
- P 0.030% or less
- P is extremely effective for increasing the strength because a substantial solid solution strengthening ability can be obtained even in a relatively small amount. For that purpose, it is preferably 0.005% or more.
- excessive addition causes embrittlement due to segregation, resulting in intergranular cracking and reduced rollability, so the P content is limited to 0.030% or less.
- N 0.0040% or less N is limited to 0.0040% or less in order to increase the deterioration of the magnetic characteristics and the variation in the mechanical characteristics of the product in the same manner as C described above.
- S 0.0005% or more and 0.0030% or less
- the amount of sulfide needs to be extremely reduced, and is limited to 0.0030% or less.
- S is generally a harmful element that forms a sulfide such as MnS and not only hinders domain wall movement, but also deteriorates magnetic properties by inhibiting crystal grain growth. Reduction as much as possible contributes to improvement of magnetic properties.
- it was set to 0.0005% or more.
- Sn and Sb have the effect of improving the texture and enhancing the magnetic properties.
- Sn and Sb have the effect of improving the texture and enhancing the magnetic properties.
- Sn and Sb are added to each component at 0.1% or less in either case of single addition or composite addition.
- both components are 0.03% or more and 0.07% or less.
- Ca 0.0015% or more
- Mn is lower than that of a normal non-oriented electrical steel sheet
- Ca prevents the formation of liquid phase FeS by fixing S in the steel, during hot rolling.
- the upper limit is preferably about 0.01%.
- the fluctuation of the precipitate state that affects the growth of crystal grains can be reduced, so that the variation in the mechanical characteristics of the product can be reduced.
- other elements include O, V, Nb, and Ti, which are preferably reduced to 0.005% or less, 0.005% or less, 0.005% or less, and 0.003% or less, respectively.
- the high-strength electrical steel sheet of the present invention is composed of a mixed structure of recrystallized grains and non-recrystallized grains. It is important to appropriately control this structure and disperse the unrecrystallized grain group appropriately.
- the length of the connected non-recrystallized grain groups in the rolling direction in the steel sheet after finish annealing is 2.5 mm or less.
- the connected non-recrystallized grain group is a series of several structures in which crystal grains having different crystal orientations after hot rolling and / or crystal grains having different crystal orientations after hot-rolled sheet annealing are expanded by rolling. It means a lump of unrecrystallized grains forming a stretched structure, and a cross-sectional structure in the rolling direction is observed, and the length in the rolling direction of 10 or more unrecrystallized grain groups is defined by an average value.
- a more preferable non-recrystallized group length is 0.2 to 1.5 mm.
- this non-recrystallized grain group has a shape compressed in the plate thickness direction and expanded in the rolling direction and the direction perpendicular to the rolling direction. And mixed. Since the mechanical properties of unrecrystallized grains and recrystallized grains are significantly different, if a crack occurs due to a tensile stress, the crack propagates along the boundary between the unrecrystallized grains and the recrystallized grains, resulting in failure.
- the steel sheet produced by the present invention has almost no precipitate, it is closer to the boundary between the non-recrystallized grain group and the recrystallized grain than the high-strength electrical steel sheet utilizing the non-recrystallized recovery structure in which the normal precipitate exists. It is thought that cracks along the line are less likely to occur.
- the unrecrystallized grain group is coarse, the stress concentration at the tip of the non-recrystallized grain group becomes large, and the variation in mechanical characteristics is increased.
- the recrystallization ratio can be appropriately adjusted in the range of 30 to 95% according to the required strength level. That is, if the required strength level is high, the recrystallization rate can be lowered. On the other hand, when the magnetic properties are emphasized, the recrystallization rate can be increased. Thus, the strength level depends mainly on the proportion of unrecrystallized structure. On the other hand, in order to improve the magnetic properties, it is effective to increase the average crystal grain size of the recrystallized grains, and the average crystal grain size is preferably 15 ⁇ m or more. The upper limit of the average crystal grain size is preferably about 100 ⁇ m. A more preferable range of the average crystal grain size is 20 to 50 ⁇ m.
- the production of the high-strength electrical steel sheet according to the present invention can be carried out using processes and equipment applied to general non-oriented electrical steel sheets.
- steel that has been melted to a specified component composition in a converter or electric furnace is secondarily refined with a degassing facility, and then steel slab is obtained by continuous casting or ingot lump rolling, followed by hot rolling , Hot-rolled sheet annealing, pickling, cold rolling, finish annealing, and coating and baking of insulating coating.
- the slab heating temperature is preferably 1000 ° C. or more and 1200 ° C. or less. Especially when the slab heating temperature is high, not only is the energy loss large and uneconomical, but the high-temperature strength of the slab decreases and it is easy to cause manufacturing problems such as slab dripping. preferable.
- the cumulative rolling reduction ratio of rough rolling is set to 73.0% or more. At that time, it is preferable that the rolling reduction of the final pass of rough rolling is 25% or more. Furthermore, it is preferable that the rolling reduction of the final pass of rough rolling is less than 50%.
- the reason why the rolling reduction of rough rolling affects the variation in mechanical properties is not necessarily clear, but is considered as follows. Since the temperature at which rough rolling is performed on the slab heated to the above slab heating temperature is higher than the recrystallization temperature, if the rolling reduction ratio of rough rolling is 73% or more, rough rolling is performed in the time from rough rolling to before finishing rolling. The crystal grains extended by recrystallize. For this reason, the stretched grains of the hot-rolled sheet are reduced, and the size and shape of the crystal grains after finish annealing are made uniform, so that it is considered that the variation in mechanical characteristics is also reduced.
- hot rolling is usually rough rolling in which a hot slab of about 100 to 300 mm thickness is processed into an intermediate thickness called a rough bar of about 20 to 70 mm by rolling several passes, and this rough bar is tandem rolled.
- the finish rolling in the present invention refers to tandem rolling that is processed into the thickness of a hot-rolled sheet in a state where materials are connected between the first pass and the final pass of tandem rolling.
- the rough rolling may be tandem rolling or single rolling, or a combination thereof. In the case of single rolling, reverse rolling may be applied. It can be applied without any problem to roll down in the width direction by a roll after before or during rough rolling.
- the rolling reduction in the final pass of rough rolling is 25% or more. This is because, even if the cumulative rolling reduction ratio of rough rolling is the same, it is considered that a larger rolling reduction ratio in the final pass promotes recrystallization and reduces the stretched grains of the hot-rolled sheet, thereby reducing the variation in mechanical properties.
- the rolling reduction in the final pass of rough rolling is 50% or more, the biting angle becomes large and rolling becomes difficult. Therefore, the rolling reduction in the final pass of rough rolling is preferably less than 50%.
- the structure after hot-rolled sheet annealing needs to have a recrystallization rate of 100% and the average grain size of the recrystallized grains needs to be 80 ⁇ m or more and 300 ⁇ m or less.
- the annealing temperature exceeds 1000 ° C
- the precipitates dissolve and re-precipitate at the grain boundaries during cooling, which adversely affects the growth of crystal grains.
- the annealing time should be 10 seconds or more, while from the viewpoint of setting the average recrystallization grain size to 300 ⁇ m or less, the annealing time should be within 10 minutes. There is.
- the annealing conditions are selected so that the recrystallized grain size is not less than 80 ⁇ m and not more than 300 ⁇ m.
- the structure after hot-rolled sheet annealing has a recrystallization ratio of 100% because, if the processed structure remains after hot-rolled sheet annealing, it recrystallizes after the hot-rolled sheet annealing. This is because the recrystallization behavior at the time of finish annealing after cold rolling differs depending on the portion that is present, resulting in variations in crystal orientation, etc. after finish annealing, increasing the variation in mechanical properties of the product plate. .
- the rolling reduction at this time is preferably 80% or more. This is because if the rolling reduction is less than 80%, the amount of recrystallized nuclei necessary for subsequent finish annealing is insufficient, and it becomes difficult to properly control the dispersion state of the unrecrystallized structure. .
- the rolling reduction is less than 80%, the amount of recrystallized nuclei necessary for subsequent finish annealing is insufficient, and it becomes difficult to properly control the dispersion state of the unrecrystallized structure.
- the rolling reduction condition it is possible to appropriately control the dispersion state of the non-recrystallized structure in the subsequent finish annealing. This is presumably because the recrystallization nuclei in finish annealing are dispersed and increased by making the intermediate structure fine and introducing sufficient strain in the rolling process.
- the annealing temperature at this time needs to be 670 ° C. or higher and 800 ° C. or lower. This is because when the annealing temperature is less than 670 ° C., recrystallization does not proceed sufficiently and the magnetic properties may be significantly deteriorated, and the plate shape correction effect in continuous annealing is not fully exhibited, while 800 This is because when the temperature is higher than 0 ° C., the non-recrystallized structure disappears and the strength is reduced. From the viewpoint of setting the recrystallization rate to 30% or more, the annealing time should be 2 seconds or more. On the other hand, from the viewpoint of setting the recrystallization rate to 95% or less, the annealing time must be within 1 minute. There is.
- the area ratio of the recrystallized grains in the cross section in the rolling direction of the steel sheet after the finish annealing is 30 to 95% under the above-mentioned annealing temperature: 670 ° C. or more and 800 ° C. or less, annealing time: 2 seconds or more and 1 minute or less.
- the annealing conditions are selected so that the length of the connected unrecrystallized grain group in the rolling direction is 2.5 mm or less.
- an object of the present invention is to reduce iron loss as much as possible in a state where high strength is ensured by utilizing an unrecrystallized structure of a product plate.
- Mn precipitates that inhibit grain growth are minimized.
- addition of Ca is extremely effective.
- the present invention since the variation in mechanical characteristics is reduced, it is possible to reduce the iron loss as much as possible within the condition that sufficient mechanical characteristics can be obtained.
- a steel slab with a thickness of 200 mm having the composition shown in Table 2 is subjected to slab heating, hot rolling and hot-rolled sheet annealing under the conditions shown in Table 3, and after pickling, cold rolling to a sheet thickness of 0.35 mm After finishing, finish annealing was performed. However, since the steel type A cracked in the hot-rolled sheet, the steps after the hot-rolled sheet annealing were not performed. Steel types B and C were hot-rolled plates and no cracks occurred.
- the cross section in the rolling direction of the steel sheet was polished, etched, and observed with an optical microscope, and recrystallized.
- the average particle size (nominal particle size) of the recrystallized grains was determined by the rate (area ratio) and the quadrature method.
- the length in the rolling direction of the non-recrystallized group was measured for 10 groups or more, and the average value was calculated. Furthermore, the magnetic properties and mechanical properties of the product plates obtained were investigated.
- the magnetic properties were measured by cutting out Epstein test pieces in the rolling direction (L) and in the direction perpendicular to the rolling direction (C), and W 10/400 (magnetic flux density: 1.0) of L + C characteristics (measurement using the same number of samples in the L direction and the C direction). T, frequency: iron loss when excited at 400 Hz).
- the mechanical properties are 5 pieces in the rolling direction (L) and 5 pieces in the direction perpendicular to the rolling direction (C), and JIS No. 5 tensile test pieces are cut out and subjected to a tensile test to show the average value and variation of the tensile strength (TS). investigated. Table 4 shows the obtained results.
- Nos. 2 to 9 using steel type B are mainly those in which the hot-rolled sheet annealing temperature is changed, but the TS average value is 650 MPa or more, which is compared with that of ordinary electrical steel sheets. Very high strength.
- the variation in TS is large.
- No. 9 has a low cold rolling reduction rate, and it becomes difficult to properly control the dispersion state of the unrecrystallized structure.
- the finish annealing temperature is as low as 660 ° C.
- the recrystallization rate of the finish annealed plate is 28%
- the recrystallized grain size of the finish annealed plate is 13 ⁇ m, which is outside the scope of the present invention, and the iron loss is high.
- the finish annealing temperature is as high as 820 ° C.
- the recrystallization rate of the finish annealed plate is 96%, which is outside the scope of the present invention, and the average value of TS is low.
- the iron loss, the average value of TS, and the variation in TS are all good.
- the length of the non-recrystallized grain group is 2.5 mm or less. In this case, the variation is greatly reduced.
- Example 2 the average value of magnetic characteristics (L + C characteristics) and tensile strength (TS) and the variation thereof were investigated.
- the evaluation was performed in the same manner as in Example 1. Moreover, the measurement of the recrystallization rate after annealing and the average grain size of the recrystallized grains after the hot-rolled sheet annealing and after the finish annealing, and the measurement of the length in the rolling direction of the unrecrystallized group after the finish annealing, The same method as in Example 1 was used. The results obtained are shown in Table 6.
- the magnetic properties are excellent, and it is possible to stably obtain a high-strength non-oriented electrical steel sheet having excellent strength properties and small variations, such as a rotor material for a high-speed rotation motor. It can apply suitably for the use of.
Abstract
Description
加えて、高速回転モータでは、高周波磁束により渦電流が発生し、モータ効率が低下すると共に、発熱が生じる。この発熱量が多くなると、ロータ内に埋め込まれた磁石が減磁されることから、高周波域での鉄損が低いことも求められる。
従って、ロータ用素材として、磁気特性に優れ、かつ疲労特性にも優れた高強度の電磁鋼板が要望されている。
このような状況下にあって、高張力を有する電磁鋼板について幾つかの提案がなされている。
また、特許文献2には、上記強化法に加え、仕上焼鈍条件を工夫することにより結晶粒径を0.01~5.0 mmとして磁気特性を改善する方法が提案されている。
しかしながら、これらの方法を工場生産に適用した場合、熱延後の連続焼鈍工程や、その後の圧延工程などで板破断などのトラブルが生じやすく、歩留り低下やライン停止が余儀なくされるなどの問題があった。
この点、冷間圧延を、板温が数百℃の温間圧延とすれば、板破断は軽減されるものの、温間圧延のための設備対応が必要となるだけでなく、生産上の制約が大きくなるなど、工程管理上の問題も大きい。
しかしながら、これらの手法では、Niなどの高価な元素を多量に添加することや、ヘゲなどの欠陥増加による歩留りの低下で高コストになるという問題があった。また、これらの開示技術で得られた材料の疲労特性については十分な検討がなされていないのが実情である。
しかしながら、この方法では、疲労限の到達レベル自体が低く、昨今の要求レベル、例えば疲労限強度:500 MPa以上を満足するものではなかった。
しかしながら、発明者らが、このように未再結晶組織を残留させた材料について、機械的特性の安定性について評価したところ、ばらつきが大きい傾向にあることが判明した。すなわち、平均的には高い機械的特性を示すものの、ばらつきが大きいため、比較的小さい応力でも短時間で破断する場合があることが判明した。
しかしながら、仕上焼鈍を低温化して未再結晶組織を増加させた場合、鉄損が増加するという問題があった。
すなわち、機械的特性のばらつきが大きくなると、鉄損の増加を余儀なくされる。
従って、機械的特性のばらつき自体を小さくすることは、鉄損の低減にも有効となる。
その結果、結晶粒の成長を阻害する析出物、特に熱延板焼鈍後および仕上焼鈍後の組織が機械的特性のばらつきに大きな影響を及ぼしていることおよび、製造性を良好なものにするためには、Caの添加が有効であることを見出した。さらに、熱間圧延での粗圧延における累積圧下率、特に粗圧延での最終パスの圧下率を制御することが有効であることを見出した。
本発明は、上記の知見に立脚するものである。
1.質量%で、
C:0.0050%以下、
Si:3.5%超 5.0%以下、
Mn:0.10%以下、
Al:0.0020%以下、
P:0.030%以下、
N:0.0040%以下、
S:0.0005%以上 0.0030%以下および
Ca:0.0015%以上
を含み、さらに
Sn:0.01%以上 0.1%以下および
Sb:0.01%以上 0.1%以下
のうちから選んだ1種または2種を含有し、残部はFeおよび不可避的不純物の成分組成からなるスラブを、スラブ加熱後、粗圧延および仕上圧延からなる熱間圧延を施し、ついで熱延板焼鈍を施し、酸洗後、1回の冷間圧延によって最終板厚としたのち、仕上焼鈍を施す一連の工程によって高強度電磁鋼板を製造するに際し、
上記熱間圧延における粗圧延の累積圧下率を73.0%以上とし、
上記熱延板焼鈍工程において、焼鈍温度:850℃以上1000℃以下、焼鈍時間:10秒以上 10分以下の条件下で、熱延板焼鈍後の鋼板圧延方向断面における再結晶粒の面積率が100%で、かつ再結晶粒径が80μm以上300μm以下となる焼鈍条件を選定すると共に、
上記仕上焼鈍工程において、焼鈍温度:670℃以上 800℃以下、焼鈍時間:2秒以上1分以内の条件下で、仕上焼鈍後の鋼板圧延方向断面における再結晶粒の面積率が30%以上 95%以下で、かつ連結した未再結晶粒群の圧延方向の長さが2.5mm以下となる焼鈍条件を選定する
ことを特徴とする電磁鋼板の製造方法。
さて、本発明者らはまず、特性のばらつきの根本的な原因について検討を加えた。特性がばらつくとは、製品鋼板内において板幅方向または長さ方向で特性が変動すること、または同様な製造条件で製造した2つの製品の特性が異なることを意味する。製造条件として、例えば仕上焼鈍温度などは厳密には一定の温度ではなく、板幅方向または長さ方向で変動し、また異なるコイルでは厳密に同じ温度とはならない。また、スラブ内の成分も同様に変動する。
発明者らは、製品の特性のばらつきを小さくする製造方法とは、製造条件が上述のように変動しても製品の特性がばらつかないような方法であると考えた。
析出物は、熱延板焼鈍や仕上焼鈍での結晶粒の成長に影響を与える。すなわち、製品板の結晶組織に影響を与える。従って、未再結晶回復組織を活用した高強度電磁鋼板では、再結晶率を制御することが極めて重要であるから、析出物の状態の変動を小さくすることが製品の特性のばらつきを小さくするのに有効と考えられる。
ここで、発明者らは、析出物がほとんどない状態にすることを選択した。というのは、析出物がほとんどない方が鉄損に有利なだけでなく、製品板の粒成長性が良いのでセミプロセス材への流用が可能であると考えたからである。
具体的な組成は、3.65%Si-0.03%Mn-0.0005%Al-0.02%P-0.0019%S-0.0018%C-0.0019%N-0.04%Snである。なお、成分に関する「%」表示は特に断らない限り質量%を意味するものとする。
かような破断防止のためには、Sを低減すればよいが、製造上Sを下げるには限界があり、脱硫によるコストが増加する。一方、Mnを増加してSをMnSとして固定することが考えられるが、析出したMnSは、方向性電磁鋼板でインヒビターとして用いられているように、結晶粒成長の抑制力が強い析出物である。
3.71%Si-0.03%Mn-0.0004%Al-0.02%P-0.0021%S-0.0018%C-0.0020%N-0.04%Sn-0.0030%Caからなる鋼スラブを、1100℃で加熱した後、2.0mm厚までの熱間圧延における粗圧延を表1に示す種々の条件にて行い、得られた熱延板に表1に示す種々の条件にて熱延板焼鈍を施し、ついで、酸洗後、板厚:0.35mmに冷間圧延したのち、表1に示す温度で仕上焼鈍した。なお、この実験の過程で熱延板の外観を調査したが、割れの発生は認められなかった。
その結果について、熱間粗圧延の圧下率と引張強度との関係を図1に、そして熱延板焼鈍温度と引張強度との関係を図2に、それぞれ示す。なお、引張強度のばらつきは標準偏差σで評価し、図1及び図2中には±2σの範囲を示した。
図1及び図2に示したとおり、いずれの条件とも引張強度は平均値で650MPa以上と、通常の電磁鋼板と比較して非常に高い強度を示したが、粗圧延や熱延板焼鈍の条件によってばらつきの程度は大きく異なっており、図1に示すように粗圧延の累積圧下率の低い条件1、図2に示すように熱延板焼鈍温度が低い条件4および熱延板焼鈍温度が高い条件7では、引張強度のばらつきが大きくなった。
その結果、いずれも再結晶率:60~80%で、残部は未再結晶組織との混合組織であった。未再結晶部は、正確な判別は困難であるが、元々の熱延板焼鈍後の結晶粒が冷間圧延により展伸した組織がいくつか連なって展伸組織群を形成しているものと思われる。
条件1,4および7の鋼板は、この未再結晶粒群の圧延方向長さが他の製造条件の鋼板より長い傾向にあることが判明したので、この組織形態の違いが特性ばらつきを大きくする要因ではないかと推察した。
従って、熱間圧延の粗圧延における累積圧下率を高くし、熱延板焼鈍後の再結晶率を100%とし、かつ再結晶粒を微細に留めるように熱延板焼鈍後の組織を作り込むことが、特性ばらつきを抑制する重要な要件であると考えた。
また、この熱延板焼鈍後組織の制御に加えて、冷間圧延条件も適正に制御することが、本発明で目標とする冷延板焼鈍時における組織制御に重要であることも併せて見出し、かかる知見に基づいて、磁気特性、機械的特性および疲労特性に優れ、しかもかような特性ばらつきの抑制効果が高い未再結晶回復組織を含む高強度電磁鋼板の開発に成功し、本発明を完成させるに至ったのである。
C:0.0050%以下
Cは、炭化物の析出により強度を高める効果を有するが、磁気特性および製品の機械的特性のばらつきには有害となる。本発明の高強度化は主としてSiの置換型元素の固溶強化と未再結晶回復組織を利用することによって達成するので、Cは0.0050%以下に限定する。
Siは、鋼の脱酸剤として一般的に用いられる他、電気抵抗を高めて鉄損を低減する効果を有するため、電磁鋼板を構成する主要元素である。本発明では、Mn,Al,Niなど他の固溶強化元素を用いないため、Siを固溶強化の主体となる元素として、3.5%を超えて積極的に添加する。好ましくは、3.6%以上とする。しかしながら、Si量が5.0%を超えると冷間圧延中に亀裂を生じるほど製造性が低下するため、その上限を5.0%とした。望ましくは4.5%以下である。
Mnは、MnSとして析出すると磁壁移動の妨げになるだけでなく、結晶粒成長を阻害することで磁気特性を劣化させる有害元素であり、製品の磁気特性のばらつきを小さくするために、0.10%以下に制限する。
Alは、Siと同様、鋼の脱酸剤として一般的に用いられており、電気抵抗を増加して鉄損を低減する効果が大きいため、無方向性電磁鋼板の主要構成元素として用いるのが通例である。しかしながら、本発明では製品の機械的特性のばらつきを小さくするため窒化物量を極めて少なくする必要があることから、0.0020%以下に制限する。
Pは、比較的少量の添加でも大幅な固溶強化能が得られるため、高強度化に極めて有効である。そのためには、好ましくは0.005%以上とする。一方、過剰な添加は偏析による脆化で粒界割れや圧延性の低下をもたらすので、P量は0.030%以下に制限する。
Nは、前述したCと同様、磁気特性劣化および製品の機械的特性のばらつきを大きくするので、0.0040%以下に制限する。
本発明では製品の機械的特性のばらつきを小さくするため、硫化物量を極めて少なくする必要があり、0.0030%以下に制限する。無方向性電磁鋼板においてSは、一般的に、MnSなどの硫化物を形成し磁壁移動の妨げになるだけでなく、結晶粒成長を阻害することで磁気特性を劣化する有害元素であるので、極力低減することは磁気特性の向上に寄与する。とはいえ、脱硫によるコスト増を抑えるため、0.0005%以上とした。
Sn,Sbはいずれも、集合組織を改善し磁気特性を高める効果を有するが、その効果を得るには、Sb,Snを単独添加または複合添加するいずれの場合にも各成分を0.01%以上添加する必要がある。一方、過剰に添加すると鋼が脆化し、鋼板製造中の板破断やヘゲが増加するため、Sn,Sbは単独添加または複合添加いずれの場合も各成分を0.1%以下とする。好ましくは、両成分ともに、0.03%以上0.07%以下である。
本発明では、Mnが通常の無方向性電磁鋼板に比較して低いため、Caは鋼中でSを固定することで液相のFeSの生成を防止し、熱間圧延時の製造性を良好にする。その効果を得るには、0.0015%以上添加する必要がある。しかしながら、あまりに多量の添加はコストが増加するため、上限は0.01%程度とすることが好ましい。
なお、本発明では、その他の元素は製品の機械的特性のばらつきを大きくするため、製造上問題のないレベルで低減することが望ましい。ここに、その他の元素としては、O、V、NbおよびTi等が挙げられ、それぞれ0.005%以下、0.005%以下、0.005%以下および0.003%以下に低減することが好ましい。
本発明の高強度電磁鋼板は、再結晶粒と未再結晶粒の混合組織で構成されるが、この組織を適正に制御し、未再結晶粒群を適度に分散させることが重要である。
まず、仕上焼鈍後の鋼板の再結晶粒の面積率を、鋼板圧延方向断面(板幅方向に垂直な断面)組織において30%以上95%以下の範囲に制御する必要がある。再結晶面積率が30%未満では、鉄損が増加し、一方再結晶率が95%を超えると、従来の無方向性電磁鋼板と比較して十分に優位な強度が得られなくなる。より好ましい再結晶率は65~85%である。
ここで、連結した未再結晶粒群とは、熱延後の結晶方位が異なる結晶粒および/または熱延板焼鈍後の結晶方位が異なる結晶粒が圧延により展伸した組織が幾つか連なって展伸組織を形成している未再結晶粒の固まりを意味し、圧延方向断面組織を観察し、10群以上の未再結晶粒群の圧延方向長さを測定した平均値で規定する。この未再結晶群長さを2.5mm以下に抑制することによって、製品の機械的特性のばらつきを低減し、安定的に高強度・高疲労特性を有する材料を製造することが可能となる。より好ましい未再結晶群長さは0.2~1.5mmである。
すなわち、この未再結晶粒群は、板厚方向に圧縮、圧延方向と圧延直角方向に展伸した形状であるが、本発明で製造される鋼板は、この未再結晶粒群が再結晶粒と混在している。未再結晶粒群と再結晶粒は機械的特性が大幅に異なるため、引張応力により亀裂が発生した場合、この未再結晶粒群と再結晶粒の境界に沿って亀裂が伝播し、破壊に至るものと考えられる。本発明で製造される鋼板は析出物がほとんど存在しないため、通常の析出物が存在する未再結晶回復組織を活用した高強度電磁鋼板よりも、未再結晶粒群と再結晶粒の境界に沿っての亀裂は発生しにくくなっていると考えられる。しかしながら、本発明においても未再結晶粒群が粗大であると、未再結晶粒群の先端への応力集中が大きくなり、機械的特性のばらつきを大きくする。
この点、連結した未再結晶粒群の圧延方向長さが上記の範囲であれば、必要とする強度レベルに応じて再結晶比率は30~95%の範囲で適宜調整することができる。すなわち、必要な強度レベルが高ければ再結晶率を低くし、一方磁気特性が重視される場合には、再結晶率を高めるように調整することができる。かように、強度レベルは主として未再結晶組織の比率に依存する。一方、磁気特性を改善するには再結晶粒の平均結晶粒径を大きくすることが有効であり、平均結晶粒径は15μm以上とすることが好ましい。なお、平均結晶粒径の上限値は100μm 程度とすることが好ましい。平均結晶粒径のより好ましい範囲は20~50μmである。
本発明の高強度電磁鋼板の製造は、一般の無方向性電磁鋼板に適用されている工程および設備を用いて実施することができる。
例えば、転炉あるいは電気炉などで所定の成分組成に溶製された鋼を、脱ガス設備で二次精錬し、連続鋳造または造塊後の分塊圧延により鋼スラブとしたのち、熱間圧延、熱延板焼鈍、酸洗、冷間圧延、仕上焼鈍および絶縁被膜の塗布焼き付けといった工程である。
ここで、所望の鋼組織を得るためには、製造条件を以下に述べるように制御することが重要である。
粗圧延の圧下率が、機械特性のばらつきに影響する理由は必ずしも明らかではないが、以下のように考えている。上記のスラブ加熱温度まで加熱されたスラブに粗圧延を施す際の温度は再結晶温度より高いため、粗圧延の圧下率を73%以上にすると粗圧延後から仕上圧延前までの時間に粗圧延で伸展した結晶粒が再結晶する。そのため、熱延板の伸展粒が減少し、仕上焼鈍後の結晶粒の大きさや形状が均一になるため、機械特性もばらつきが小さくなるものと考えられる。
そして、粗圧延は、タンデム圧延またはシングル圧延でよく、これらの組み合わせでもよい。シングル圧延の場合は、リバース圧延を適用してもよい。粗圧延の前後または途中で、竪ロールにより幅方向に圧下することも問題なく適用できる。
上記の鋼組織とするには、熱延板焼鈍の温度を850℃以上、1000℃以下とする必要がある。
というのは、焼鈍温度が850℃未満では、熱延板焼鈍後に再結晶率を安定して100%とすることが難しく、一方焼鈍温度が1000℃超になると、熱延板焼鈍後の平均再結晶粒径が300μm を超える場合が生じるようになるからである。また、本発明で所期する、析出物量が少ない鋼では、焼鈍温度が1000℃を超えると析出物が固溶し冷却時に粒界に再析出するため、結晶粒の成長性に悪影響を及ぼすことが考えられる。
また、再結晶率を安定的に100%とする観点からは、焼鈍時間を10秒以上とし、一方平均再結晶粒径を300μm以下とする観点からは、焼鈍時間を10分以内とする、必要がある。
ここで、熱延板焼鈍後の組織を再結晶率:100%とするのは、熱延板焼鈍後に加工組織が残存していると、この加工組織部分と熱延板焼鈍後に再結晶している部分とで、冷間圧延後の仕上焼鈍時の再結晶挙動が異なってしまうために、仕上焼鈍後の結晶方位等にばらつきが生じ、製品板の機械的特性のばらつきを大きくするからである。
これらの焼鈍後組織と圧下率の条件を共に満たすことにより、引き続く仕上焼鈍での未再結晶組織の分散状態を適正に制御することが可能となる。これは、中間組織を微細化し、圧延加工で十分な歪みを導入することにより、仕上焼鈍における再結晶核が分散、増加するためであると推定される。
また、再結晶率を30%以上とする観点からは、焼鈍時間は2秒以上とすることが、一方、再結晶率を95%以下とする観点からは、焼鈍時間は1分以内とする必要がある。
さらに、得られた製品板の磁気特性および機械的特性を調査した。磁気特性は圧延方向(L)および圧延直角方向(C)にエプスタイン試験片を切り出し測定し、L+C特性(L方向とC方向の試料を同数用いた測定)のW10/400(磁束密度:1.0T、周波数:400Hzで励磁したときの鉄損) で評価した。機械的特性は、圧延方向(L)に5枚ずつ、圧延直角方向(C)に5枚ずつJIS 5号引張試験片を切り出し、引張試験を行って引張強度(TS)の平均値とばらつきを調査した。
得られた結果を表4に示す。
これに対し、仕上焼鈍板の未再結晶粒連結群の長さが2.5mm以下と本発明の範囲内のNo.3,5,6,8ではTSのばらつきが2σで35MPa以内と極めて小さい。
また、鋼種Cを用いたNo.10~14は、主として仕上焼鈍温度を変化させたものであるが、No.10では粗圧延の累積圧下率が70%と低く、本発明の範囲外であり、TSのばらつきが大きい。No.11では仕上焼鈍温度が660℃と低く、仕上焼鈍板の再結晶率が28%、仕上焼鈍板の再結晶粒径が13μmと本発明の範囲外であり、鉄損が高い。また、No.14では仕上焼鈍温度が820℃と高く、仕上焼鈍板の再結晶率が96%と本発明の範囲外であり、TSの平均値が低い。
これに対し、本発明の範囲内であるNo.12、13、15では、鉄損、TSの平均値、TSのばらつきいずれもが良好である。
その他の電磁鋼板について、磁気特性(L+C特性)と引張強度(TS)の平均値およびそのばらつきについて調査した。なお、評価は実施例1と同様の方法で行った。また、熱延板焼鈍後および仕上焼鈍後の試料についての焼鈍後の再結晶率および再結晶粒の平均粒径の測定、並びに仕上焼鈍後の未再結晶群の圧延方向長さの測定は、実施例1と同様の方法で行った。
得られた結果を表6に示す。
Claims (4)
- 質量%で、
C:0.0050%以下、
Si:3.5%超 5.0%以下、
Mn:0.10%以下、
Al:0.0020%以下、
P:0.030%以下、
N:0.0040%以下、
S:0.0005%以上 0.0030%以下および
Ca:0.0015%以上
を含み、さらに
Sn:0.01%以上 0.1%以下および
Sb:0.01%以上 0.1%以下
のうちから選んだ1種または2種を含有し、残部はFeおよび不可避的不純物の成分組成からなるスラブを、スラブ加熱後、粗圧延および仕上圧延からなる熱間圧延を施し、ついで熱延板焼鈍を施し、酸洗後、1回の冷間圧延によって最終板厚としたのち、仕上焼鈍を施す一連の工程によって電磁鋼板を製造するに際し、
上記粗圧延における累積圧下率を73.0%以上とし、
上記熱延板焼鈍工程において、焼鈍温度:850℃以上1000℃以下、焼鈍時間:10秒以上 10分以下の条件下で、熱延板焼鈍後の鋼板圧延方向断面における再結晶粒の面積率が100%で、かつ再結晶粒径が80μm以上300μm以下となる焼鈍条件を選定すると共に、
上記仕上焼鈍工程において、焼鈍温度:670℃以上 800℃以下、焼鈍時間:2秒以上1分以内の条件下で、仕上焼鈍後の鋼板圧延方向断面における再結晶粒の面積率が30%以上 95%以下で、かつ連結した未再結晶粒群の圧延方向の長さが2.5mm以下となる焼鈍条件を選定する
ことを特徴とする電磁鋼板の製造方法。 - 前記粗圧延における最終パスの圧下率が25%以上であることを特徴とする請求項1に記載の電磁鋼板の製造方法。
- 前記仕上焼鈍後の鋼板圧延方向断面における再結晶粒の平均結晶粒径が15μm 以上であることを特徴とする請求項1または2に記載の電磁鋼板の製造方法。
- 請求項1から3のいずれかに記載の電磁鋼板の製造方法において、冷間圧延における圧下率を80%以上とすることを特徴とする電磁鋼板の製造方法。
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