WO2021167063A1 - 無方向性電磁鋼板用熱延鋼板 - Google Patents
無方向性電磁鋼板用熱延鋼板 Download PDFInfo
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- C22C—ALLOYS
- 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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- 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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- 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
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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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
- C21D8/1222—Hot 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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- 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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- 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
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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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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- C22C38/00—Ferrous alloys, e.g. steel alloys
- 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
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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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
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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
- H01F1/14775—Fe-Si based alloys in the form of sheets
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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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- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/76—Adjusting the composition of the atmosphere
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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
- C21D2241/00—Treatments in a special environment
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C2202/00—Physical properties
- C22C2202/02—Magnetic
Definitions
- the present invention relates to a hot-rolled steel sheet for non-oriented electrical steel sheets having excellent magnetic properties, which is mainly used as an iron core material for electrical equipment.
- the present application claims priority based on Japanese Patent Application No. 2020-0247497 filed in Japan on February 20, 2020, the contents of which are incorporated herein by reference.
- Iron loss and magnetic flux density are the characteristics required for non-oriented electrical steel sheets for improving motor characteristics. So far, the texture of the product board has been controlled and improved by recrystallizing the region of 60% or more by high-temperature winding of hot rolling.
- Patent Document 1 discloses that by causing recrystallization and grain growth at the stage of hot rolling, the crystal grains and texture at the product stage after annealing are affected and the magnetic properties are improved. ing.
- the present invention can suppress breakage due to bending-bending back in the subsequent pickling step even if annealing after hot rolling is omitted, and further has excellent magnetic properties when made into an electromagnetic steel sheet.
- An object of the present invention is to provide a hot-rolled steel sheet for a non-directional electromagnetic steel sheet having improved toughness.
- the present inventors have sufficient hot-rolled sheet toughness to omit annealing in the hot-rolling process and to suppress the occurrence of fracture of the steel sheet end during pickling. , We have conducted extensive research on methods for achieving both magnetic properties in electromagnetic steel sheets.
- the hardness at the center of the plate thickness (1 / 2t portion) is Hv220 or less.
- the present inventors have found that the area of the processed structure can be increased. As a result, even if the recrystallization rate is about 60% or more and about 80% or less, the toughness of the hot-rolled steel sheet is improved, fracture due to bending-bending back can be prevented, and excellent magnetic properties when made into a non-oriented electrical steel sheet. The present inventors have found that the above can be realized.
- the present invention has been made based on the above findings, and the gist thereof is as follows.
- a hot-rolled steel sheet for non-directional electromagnetic steel sheets which is characterized by the following.
- the hardness of the hardness H U of recrystallization texture of the plate thickness surface layer portion in the plate width direction end portion of the non-oriented electrical steel sheet for hot-rolled steel sheets (1 / 8t position) the difference H S H D -H U is a non-oriented electrical steel sheet for hot-rolled steel sheet of the above (1), characterized in that within HV20.
- thermoforming in the hot-rolling process even when annealing in the hot-rolling process is omitted, sufficient hot-rolled plate toughness is provided, and when a non-oriented electrical steel sheet is used, both low iron loss and high magnetic flux density are achieved.
- a hot-rolled steel sheet for non-oriented electrical steel sheets can be provided.
- the hot-rolled steel sheet for non-oriented electrical steel sheet is a material for non-oriented electrical steel sheet, and may be simply referred to as "hot-rolled steel sheet" below.
- a non-oriented electrical steel sheet can be obtained by cold rolling and finish annealing on a hot-rolled steel sheet.
- the mechanical properties and metallographic structure of non-oriented electrical steel sheets that have undergone the above steps are completely different from those of hot-rolled steel sheets.
- non-oriented electrical steel sheets are softer than hot-rolled steel sheets.
- the processed structure of the hot-rolled steel sheet according to the present embodiment means a structure stretched by hot rolling.
- the recrystallized structure of the hot-rolled steel sheet according to the present embodiment means a structure that is once stretched by hot rolling and then recrystallized by self-annealing. Those skilled in the art can easily distinguish between the processed structure and the recrystallized structure.
- one of the problems of the hot-rolled steel sheet according to the present embodiment is to exhibit excellent magnetic characteristics at the stage of becoming an electromagnetic steel sheet through the above-mentioned steps, but regarding the magnetic characteristics of the hot-rolled steel sheet itself. No need to consider.
- the magnetic property is not the magnetic property of the hot-rolled steel sheet itself, but the magnetic property of the non-oriented electrical steel sheet obtained by subjecting the hot-rolled steel sheet to the above-mentioned step. means.
- C 0.0010 to 0.0050% C is preferably contained in an amount of 0.0010% or more because it segregates at the grain boundaries and enhances toughness. On the other hand, it is a harmful component that deteriorates iron loss and causes magnetic aging, so the C content is set to 0.0050% or less.
- the C content is more preferably 0.0015% or more, 0.0020% or more, or 0.0025% or more.
- the C content is preferably 0.0040% or less, 0.0035% or less, or 0.0030% or less.
- Si 1.90% to 3.50%
- Si is a component that has the effect of reducing iron loss by increasing electrical resistance and reducing eddy current loss, and has the effect of improving punching workability to the iron core by increasing the yield ratio. Also has. In order to exert these effects, it is necessary to contain 1.90% or more of Si.
- the Si content is 3. .50% or less.
- the Si content is preferably 2.00% or more, 2.20% or more, or 2.50% or more.
- the Si content is preferably 3.20% or less, 3.00% or less, or 2.80% or less.
- Al 0.10% to 3.00%
- Al is also a component having an effect of reducing iron loss by increasing electrical resistance and reducing eddy current loss.
- the amount of increase in hardness due to Al is smaller than that of Si. Therefore, it is necessary to contain 0.10% or more of Al.
- the Al content is 3.00. % Or less. It is preferably 2.50% or less.
- Mn 0.05 to 2.00%
- Mn has the effect of increasing the electrical resistance to reduce the eddy current loss and improving the primary recrystallization texture to develop the ⁇ 110 ⁇ ⁇ 001> crystal orientation which is desirable for improving the magnetic characteristics in the rolling direction.
- Mn has an effect of lowering the solubility of MnS contained in the slab.
- the amount of MnS that dissolves when the slab is heated decreases, and the amount of fine MnS that reappears when the slab is cooled decreases. That is, the addition of Mn suppresses the precipitation of fine sulfides such as MnS, which are harmful to crystal grain growth. For these purposes, it is necessary to contain Mn of 0.05% or more.
- the Mn content is set to 2.00% or less.
- the Mn content is preferably 0.20% or more, 0.40% or more, or 0.80% or more.
- the Mn content is preferably 1.50% or less, 1.20% or less, or 1.00% or less.
- P 0.100% or less
- P has an effect of improving punching accuracy and may be contained in a hot-rolled steel sheet.
- the steel sheet containing 2% or more of Si becomes very brittle. Therefore, the P content is 0.100% or less, preferably 0.10% or less, 0.080% or less, 0.05% or less, 0.050% or less, or 0.030% or less.
- the P content may be 0%, but may be, for example, 0.001% or more, 0.002% or more, or 0.003% or more in order to avoid an increase in refining cost.
- S 0.005% or less S inhibits recrystallization and grain growth during finish annealing and the like due to fine precipitation of sulfides such as MnS. Therefore, the S content is 0.005% or less, preferably 0.004% or less, 0.003% or less, or 0.002% or less.
- the S content may be 0%, but may be, for example, 0.0001% or more, 0.0002% or more, or 0.0003% or more in order to avoid an increase in refining cost.
- N 0.0040% or less N reduces the coverage of the internal oxide layer on the surface of the hot-rolled plate by fine precipitation of nitrides such as AlN generated during hot-rolled sheet annealing and finish annealing, and further during finish annealing. Inhibits recrystallization and grain growth. Therefore, the N content is 0.0040% or less, preferably 0.0030% or less, 0.0020% or less, or 0.0010% or less. The N content may be 0%, but may be, for example, 0.0001% or more, 0.0002% or more, or 0.0003% or more in order to avoid an increase in refining cost.
- B 0.0060% or less B inhibits recrystallization and grain growth during finish annealing and the like due to fine precipitation of nitrides such as BN. Therefore, the B content is 0.0060% or less, preferably 0.0040% or less, 0.0030% or less, or 0.0020% or less.
- the B content may be 0%, but may be, for example, 0.0001% or more, 0.0002% or more, or 0.0003% or more in order to avoid an increase in refining cost.
- Sn and Sb are not essential elements, but they improve the primary recrystallization texture of the steel sheet to develop into a ⁇ 110 ⁇ ⁇ 001> texture that is desirable for improving the magnetic properties in the rolling direction, and also to make the magnetic properties. It has the effect of suppressing the undesired ⁇ 111 ⁇ ⁇ 112> texture. Therefore, Sn and Sb may be contained in the hot-rolled steel sheet as needed. For these purposes, it is preferable to contain one or both of Sn and Sb in an amount of 0.01% or more, respectively. On the other hand, even if the contents of Sn and Sb are increased, the action is saturated, and rather, the toughness of the hot-rolled plate may be lowered.
- the contents of Sn and Sb are set to 0.50% or less, respectively.
- the lower limit of the Sn content and the lower limit of the Sb content may be 0.02%, 0.03%, or 0.05%, respectively.
- the upper limit of the Sn content and the upper limit of the Sb content may be 0.45%, 0.40%, or 0.20%, respectively.
- Cu 0 to 0.50%
- Cu is not an essential element, it may be contained in a hot-rolled steel sheet if necessary because it precipitates in steel and exhibits an action of improving strength. In order to obtain this effect, it is preferable that 0.01% or more of Cu is contained.
- the Cu content is preferably 0.50% or less.
- the Cu content may be 0.02% or more, 0.03% or more, or 0.05% or more.
- the Cu content may be 0.40% or less, 0.30% or less, or 0.20% or less.
- REM 0 to 0.0400% or less Ca: 0 to 0.0400% or less Mg: 0 to 0.0400% or less REM, Ca, Mg are not essential elements, but they are elements that promote grain growth and are necessary. It may be contained in the hot-rolled steel sheet according to the above.
- the content of each of one or more elements selected from the group consisting of REM, Ca, and Mg is preferably 0.0005% or more, more preferably 0.0010% or more. More preferably, it is 0.0050% or more or 0.0100% or more.
- the contents of each of REM, Ca, and Mg exceed 0.0400%, the magnetic characteristics deteriorate, so the content is set to 0.0040% or less.
- the content of any element is 0.0300% or less, more preferably 0.0200% or less or 0.0150% or less.
- REM refers to a total of 17 elements composed of Sc, Y and lanthanoids, and the above-mentioned “content of REM” means the total content of these 17 elements.
- lanthanoids are used as REMs, industrially, REMs are added in the form of mischmetal.
- the rest of the components of the hot-rolled steel sheet of the present embodiment are Fe and impurity elements.
- Impurities are components that are mixed in by raw materials such as ore or scrap, or various factors in the manufacturing process, for example, when steel materials are industrially manufactured, and adversely affect the hot-rolled steel sheet of the present embodiment. Means something that is acceptable to the extent that it does not exist.
- a non-oriented electrical steel sheet having excellent magnetic characteristics can be obtained when the hot-rolled steel sheet is made into an electromagnetic steel sheet.
- the hot rolled steel sheet of the present embodiment is characterized in hardness H D of the working tissue thickness center portion (1 / 2t position) is Hv220 or less.
- H D hardness of the working tissue thickness center portion (1 / 2t position) is Hv220 or less.
- t means a plate thickness.
- the hardness H D of the working tissue thickness center portion of the hot-rolled steel sheet (1 / 2t position) is Hv220 than, after cold-rolled and the processed structure, emerge therefrom at annealing, deteriorates the magnetic properties ⁇ 111 ⁇
- the recrystallization driving force of the grain is increased. Therefore, the magnetic characteristics of the non-oriented electrical steel sheet deteriorate.
- the hardness H D of the working tissue thickness center portion of the hot-rolled steel sheet (1 / 2t position) is desirably Hv220 or less.
- the processed structure is harder than the recrystallized structure.
- the proportion of the processed structure in the hot-rolled plate is large, the hardness of the hot-rolled plate becomes high.
- the degree of integration of ⁇ 211 ⁇ ⁇ 011> of the cold-rolled plate is increased. Then, the annealing improves the degree of integration of the ⁇ 111 ⁇ orientation that appears from the place where the degree of integration of ⁇ 211 ⁇ ⁇ 011> is high, so that the magnetic characteristics deteriorate.
- the hot-rolled plate is annealed so as to reduce the processed structure of the hot-rolled plate as much as possible, and the recrystallized region of the hot-rolled plate is increased to about 80% or more, and then cold-rolled. And was annealed.
- the recrystallized structure is softer than the processed structure, there are few dislocations that affect toughness. Therefore, if the recrystallization region is increased to about 80% or more, the toughness of the hot-rolled steel sheet becomes low, and the possibility that the steel sheet will break due to the next pickling and bending-bending back in the cold-rolled line increases.
- recrystallization of the hot-rolled steel sheet is suppressed to the extent possible (for example, hot-rolled steel sheet).
- recrystallization rate of the steel sheet is about 60% to about 80% or less), leaving the worked structure in hot-rolled steel sheet, and the hardness H D of the working tissue thickness center portion (1 / 2t position) Hv220 It is desirable to do the following. That is, in the hot-rolled steel sheet according to the present embodiment, the hardness of the hot-rolled steel sheet is lowered by softening the processed structure while setting the amount of the processed structure to a predetermined value or more.
- the Vickers hardness is measured in a cross section parallel to the rolling direction and perpendicular to the plate surface at a position 10 mm from the end surface in the plate width direction of the hot-rolled steel sheet to the center in the plate width direction (hereinafter referred to as the end portion in the plate width direction). do.
- hardness H D of the working tissue thickness center portion of the cross section (1 / 2t position), sheet thickness surface layer portion hardness H U of recrystallized structure of (1 / 8t position), in a direction parallel to the rolling direction Measure at 10 points at 10 ⁇ m intervals.
- the reason is that the higher the Hv of the hot-rolled plate, the easier it is to cause recrystallization in annealing after cold rolling, but the difference in hardness between the central portion and the surface layer portion of the hot-rolled plate is small, so that it is cold.
- Hardness H U of recrystallization texture having a thickness of the surface layer portion (1 / 8t position) can also be measured by the hardness H D a manner similar to processed structure of the center of plate thickness (1 / 2t position).
- the surface layer is usually harder than the central portion. This is because the amount of recrystallized structure in the surface layer of the hot-rolled steel sheet is larger than that in the central portion.
- the hardness of the central portion which is expected to be the hardest, is controlled to a predetermined value or less.
- the hardness difference between the surface layer and the central portion is usually small or almost nonexistent.
- the method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets according to this embodiment is A process of continuously casting molten steel having the above components to obtain a slab, and The process of heating the slab within the temperature range of 1080 to 1200 ° C. A process of hot-rolling a slab in the temperature range of 1080 to 1200 ° C. at a finishing temperature of 850 to 1000 ° C. to obtain a hot-rolled plate. The process of winding the hot-rolled sheet at a winding temperature of 700 to 850 ° C.
- the process of cooling the hot-rolled sheet that caused Have is 30 to 120 ° C./hr.
- molten steel having the above-mentioned components is made into a slab by continuous casting, and further hot-rolled to make a hot-rolled sheet, and the heat of a coil wound after hot-rolling is used.
- Manufactured by self-annealing The method for producing the slab may be a conventional method.
- the slab is then heated to preferably 1080-1200 ° C. and subjected to hot rolling.
- the heating temperature is preferably 1080 ° C. or higher because the finishing temperature is 850 ° C. or higher and annealing by reheating after winding is omitted as described later.
- the heating temperature is preferably 1200 ° C. or lower in order to prevent solid solution and fine precipitation of impurities such as sulfide and not to increase iron loss.
- the finishing temperature in hot rolling is preferably 850 to 1000 ° C. As will be described later, this is because the recrystallization rate is increased by self-annealing with the heat of the coil at a winding temperature of 700 to 850 ° C., and further, annealing due to reheating is omitted. Further, if the finishing temperature is low, the hot workability is lowered, and the uniformity of the plate thickness along the width direction of the steel plate, that is, the plate thickness accuracy may be lowered. On the other hand, the finishing temperature is preferably 1000 ° C. or lower in order to prevent a decrease in toughness due to coarsening of the ferrite particle size.
- the hot-rolled steel sheet after finishing rolling is wound at 700 to 850 ° C.
- self-annealing can be performed by the heat accumulated in the wound coil. According to this self-annealing, it is possible to increase the recrystallization rate of the hot-rolled steel sheet, and even if annealing by reheating is omitted, it is possible to suppress the development of crystal grains in the ⁇ 111 ⁇ orientation, which adversely affects the magnetic properties. It becomes.
- the winding temperature is preferably 850 ° C. or lower.
- the coil after winding is covered with a heat-retaining cover to retain heat.
- the heat retention temperature is 670 ° C. or higher, and the holding time is 1 minute or longer.
- the holding time is preferably 2 hours or less.
- the holding time is the time during which the heat retaining cover is put on the coil.
- the heat retention step may be carried out without using the heat retention cover.
- the heat retention step means from the time when the hot-rolled steel sheet is wound and the coil is formed to the time when the temperature of the coil starts to drop.
- the time when the coil is formed is the time when one winding of the coil is completed from the hot-rolled steel plate in one band.
- the time when the temperature of the coil starts to drop is the time when the cooling rate of the coil changes, in other words, the inflection point on the cooling rate curve.
- the temperature change of the coil may be extremely small for a predetermined time from the time when the coil is wound, and after the predetermined time, the temperature of the coil starts to drop rapidly.
- the average cooling rate CR1 from the winding temperature after hot rolling to 400 ° C. and / or the average cooling rate CR2 in the temperature range of 600 to 400 ° C. after holding in the heat retention step is 30 to 120.
- the temperature is preferably ° C./hr.
- the average cooling rate CR1 from the winding temperature after hot rolling to 400 ° C means the period from winding to the start of heat retention and from the end of heat retention to the coil temperature reaching 400 ° C. It is the average value of the cooling rate during the period.
- the "average cooling rate CR1 from the winding temperature after hot rolling to 400 ° C.” is a value calculated by the following formula.
- CR1 (winding temperature-400 ° C) / (time from winding temperature to 400 ° C-time with heat insulating cover)
- the "average cooling rate CR2 in the temperature range of 600 to 400 ° C. after holding in the heat retention step” is an average value of the cooling rates during the period from the coil temperature to 600 ° C. to 400 ° C.
- the "average cooling rate CR2 in the temperature range of 600 to 400 ° C. after holding in the heat retention step” is a value calculated by the following formula.
- the cooling after holding in the heat retaining step is started immediately after the above-mentioned cover is removed.
- the cooling step is preferably started by the time the coil temperature begins to drop.
- the average cooling rate applied in the production of the hot-rolled steel sheet according to the present embodiment is considerably slower than usual.
- the coil after winding is water-cooled, and its average cooling rate is much higher than 120 ° C./hr.
- the average cooling rate is considered to be at least 150 ° C./hr.
- the reason for cooling the coil with water is to shorten the time required for manufacturing the non-oriented electrical steel sheet.
- the average cooling rate CR1 and / or CR2 is preferably 30 ° C./hr or more and 120 ° C./hr or less.
- Cooling after heat retention is performed in a state where the steel plate is wound into a coil.
- the above cooling rate is at the outer peripheral portion of the coil. Further, as described above, since it is the end portion of the steel plate that cracks and leads to the breakage of the steel plate, the above cooling rate is at the end portion of the steel plate (that is, both ends in the winding core direction of the coil).
- the average cooling rate CR1 from the winding temperature to 400 ° C. can be further preferably controlled.
- the toughness of the hot-rolled steel sheet can be further improved.
- the hot-rolled steel sheet for non-oriented electrical steel sheet of the present embodiment obtained as described above is subjected to pickling, cold rolling, and finish annealing by a conventional method, so that the non-oriented electrical steel sheet having excellent magnetic characteristics is obtained.
- a steel plate can be obtained.
- the conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is described in this one condition example. It is not limited. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.
- Example 1 Steel was cast with the components shown in Table 1 and hot-rolled to prepare a hot-rolled plate having a plate thickness of 2.0 mm. Then, under the conditions shown in Table 2, it was wound around a coil, kept warm, and then cooled.
- Reference numeral B0 is a reference example in which the coil is wound, cooled, and then annealed with a hot-rolled plate in a 100% nitrogen atmosphere.
- Table 3 shows the measurement results of the fracture surface transition temperature in the Charpy test conducted to evaluate the hardness and toughness of the hot-rolled plate processed structure at the end of the prepared hot-rolled plate.
- the hardness of the end of the steel plate is 10 mm from the end face in the width direction of the steel plate to the center in the width direction (end in the width direction), and in the cross section parallel to the rolling direction, the center of the plate thickness (1 / 2t position).
- hardness H D and the plate thickness surface layer portion of the processed tissue hardness H U of recrystallized structure of (1 / 8t position) in a direction parallel to the rolling direction of) at 10 ⁇ m intervals were measured 10 points.
- the fracture surface transition temperature was measured by performing a Charpy test in accordance with JIS Z 2242. In this example, when the fracture surface transition temperature is less than 0 ° C., it is judged that the toughness is good.
- the hot-rolled steel sheet for non-directional electromagnetic steel sheet of the present invention By using the hot-rolled steel sheet for non-directional electromagnetic steel sheet of the present invention, the hot-rolled steel sheet for non-directional electromagnetic steel sheet which has been subjected to the conventional hot-rolled sheet annealing is not used without causing breakage of the steel sheet in pickling. It was confirmed that a non-directional electromagnetic steel sheet having excellent characteristics similar to that of the directional electromagnetic steel sheet can be obtained.
- Example 2 Using the steels shown in Table 1 and the manufacturing methods shown in Table 2, hot-rolled steel sheets for non-oriented electrical steel sheets were similarly produced, and then non-oriented electrical steel sheets were obtained.
- the magnetic characteristics of the non-oriented electrical steel sheet were measured in the same manner as in Example 1. The results are shown in Table 4.
- Example 3 In Invention Example C1 and Comparative Example c16 disclosed in Table 3, cold rolling and finish annealing were carried out under cold rolling conditions of 75% reduction and soaking conditions under finish annealing conditions of 1000 ° C. ⁇ 30 seconds. It was a non-oriented electrical steel sheet. The hardness of the central portion (1 / 2t position) of the plate thickness at the end portion in the plate width direction of these non-oriented electrical steel sheets was measured. The hardness of the edge of the non-oriented electrical steel sheet was measured by the following procedure. The measurement surface was a cross section at a position (end in the plate width direction) of 10 mm from the end surface in the plate width direction of the steel plate to the center in the plate width direction and parallel to the rolling direction.
- the hardness of the central portion (1 / 2t position) of the plate thickness was measured at 10 points in a direction parallel to the rolling direction at intervals of 10 ⁇ m.
- C1 and c16 have the same chemical composition, and the hardness at the stage of making non-oriented electrical steel sheet is almost the same level, but the processed structure hardness at the stage of hot-rolled steel sheet is significantly different. In other words, it is difficult to estimate the hardness at the stage of hot-rolled steel sheet from the hardness measured at the stage of non-oriented electrical steel sheet.
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Abstract
Description
本願は、2020年2月20日に、日本に出願された特願2020-027497に基づき優先権を主張し、その内容をここに援用する。
なお、無方向性電磁鋼板用熱延鋼板とは、無方向性電磁鋼板の材料であり、以下、単に「熱延鋼板」と称される場合がある。熱延鋼板に冷間圧延、及び仕上焼鈍を施すことにより、無方向性電磁鋼板を得ることができる。上述の工程を経た無方向性電磁鋼板の機械特性及び金属組織は、熱延鋼板のそれらとは全く相違している。一般に、無方向性電磁鋼板の方が、熱延鋼板よりも軟質である。加工組織よりも再結晶組織の方が軟質であり、且つ、無方向性電磁鋼板においては仕上焼鈍によって再結晶組織の量が増大しているからである。
本実施形態に係る熱延鋼板の加工組織とは、熱間圧延によって延伸された組織を意味する。また、本実施形態に係る熱延鋼板の再結晶組織とは、熱間圧延によって一旦延伸された後、自己焼鈍によって再結晶した組織を意味する。なお、加工組織と再結晶組織との判別は、当業者であれば容易にすることができる。例えば「鉄鋼の組織制御」(牧正志著、2015年、内田老鶴圃)第30頁の図2.22「冷間加工材の焼なまし(焼鈍)による組織と性質の変化(回復→再結晶→粒成長)」には、加工組織と再結晶組織との視覚的な相違点が模式的に説明されている。本実施形態に係る熱延鋼板は冷間加工材ではないが、本実施形態に係る熱延鋼板における加工組織及び再結晶組織は、上記文献に説明される加工組織及び再結晶組織と同様の様相を呈する。
また、本実施形態に係る熱延鋼板の課題の一つは、上述の工程を経て電磁鋼板となった段階で優れた磁気特性を発揮することであるが、熱延鋼板自体の磁気特性については考慮する必要がない。以下、本実施形態に係る熱延鋼板の説明において、磁気特性とは、熱延鋼板自体の磁気特性ではなく、熱延鋼板を上述の工程に供して得られる無方向性電磁鋼板の磁気特性を意味する。
まず、本実施形態に係る無方向性電磁鋼板用熱延鋼板の成分の限定理由について述べる。以下、熱延鋼板の成分についての「%」は「質量%」を意味する。
Cは、粒界に偏析して靱性を強化させるため、0.0010%以上含有させることが好ましい。一方で、鉄損を劣化させる有害な成分で、磁気時効の原因ともなるので、C含有量は0.0050%以下とする。C含有量は、さらに好ましくは0.0015%以上、0.0020%以上、又は0.0025%以上である。C含有量は、好ましくは0.0040%以下、0.0035%以下、又は0.0030%以下である。
Siは、電気抵抗を増大させて渦電流損を減少させることにより、鉄損を低減する作用のある成分であり、また、降伏比を増大させることにより、鉄心への打ち抜き加工性を向上させる作用も有する。これらの作用を奏するためには、1.90%以上のSiを含有させる必要がある。一方、Siの含有量が増えると、磁束密度が低下し、かつ、無方向性電磁鋼板の製造工程そのものにおいても、冷延等の作業性の低下、コスト高ともなるので、Si含有量は3.50%以下とする。Si含有量は、好ましくは2.00%以上、2.20%以上、又は2.50%以上とする。Si含有量は、好ましくは3.20%以下、3.00%以下、又は2.80%以下である。
Alも、Siと同様に電気抵抗を増大させて渦電流損を減少させることにより、鉄損を低減する作用のある成分である。しかし、Siに比較し、Alによる硬度の上昇量は少ない。そのため、0.10%以上のAlを含有させる必要がある。一方、Alの含有量が増えると、飽和磁束密度が低下し、磁束密度の低下を招き、さらには、降伏比の減少を招いて、打ち抜き精度をも劣化させるので、Al含有量は3.00%以下とする。好ましくは2.50%以下とする。
Mnは、電気抵抗を増大させて渦電流損を減少させるとともに、一次再結晶集合組織を改善して圧延方向磁気特性の向上に望ましい{110}<001>結晶方位を発達させる効果を有する。さらに、Mnは、スラブ中に含まれるMnSの溶解度を下げる効果を有する。これにより、スラブ加熱の際に溶解するMnS量が減少し、スラブの冷却の際に再度現れる微細なMnSの析出量が減少する。すなわち、Mn添加により、結晶粒成長に有害なMnS等の微細硫化物の析出を抑制する。
これらの目的のためには、0.05%以上のMnを含有させる必要がある。しかし、Mnの含有量が増えると、焼鈍時の結晶粒成長性そのものが低下し、鉄損が増大するので、Mn含有量は2.00%以下とする。Mn含有量は、好ましくは0.20%以上、0.40%以上、又は0.80%以上である。Mn含有量は、好ましくは1.50%以下、1.20%以下、又は1.00%以下である。
Pは、打ち抜き精度を上げる効果があり、熱延鋼板に含有させてもよい。しかし、Pの含有量が増えると、2%以上のSiを含有する鋼板は非常に脆くなる。そのため、P含有量は0.100%以下、好ましくは0.10%以下、0.080%以下、0.05%以下、0.050%以下、又は0.030%以下とする。P含有量は0%であってもよいが、精錬コストの高騰を回避するために、例えば0.001%以上、0.002%以上、又は0.003%以上としてもよい。
Sは、MnS等の硫化物の微細析出により、仕上焼鈍時等における再結晶及び結晶粒成長を阻害する。そのため、S含有量は0.005%以下、好ましくは0.004%以下、0.003%以下、又は0.002%以下とする。S含有量は0%であってもよいが、精錬コストの高騰を回避するために、例えば0.0001%以上、0.0002%以上、又は0.0003%以上としてもよい。
Nは、熱延板焼鈍や仕上焼鈍時に生成するAlN等の窒化物の微細析出により、熱延板表面の内部酸化層の被覆率を下げ、さらに仕上焼鈍時等における再結晶及び結晶粒成長を阻害する。そのため、N含有量は0.0040%以下、好ましくは0.0030%以下、0.0020%以下、又は0.0010%以下とする。N含有量は0%であってもよいが、精錬コストの高騰を回避するために、例えば0.0001%以上、0.0002%以上、又は0.0003%以上としてもよい。
Bは、BN等の窒化物の微細析出により、仕上焼鈍時等における再結晶及び結晶粒成長を阻害する。そのため、B含有量は0.0060%以下、好ましくは0.0040%以下、0.0030%以下、又は0.0020%以下とする。B含有量は0%であってもよいが、精錬コストの高騰を回避するために、例えば0.0001%以上、0.0002%以上、又は0.0003%以上としてもよい。
Sb:0~0.50%
Sn、及びSbは、必須の元素ではないが、鋼板の一次再結晶集合組織を改善して、圧延方向磁気特性の向上に望ましい{110}<001>集合組織に発達させ、かつ、磁気特性に望ましくない{111}<112>集合組織等を抑制する効果を有する。そのため、Sn、及びSbを必要に応じて熱延鋼板に含有させてもよい。これらの目的のためには、Sn及びSbの一方又は両方を、それぞれ0.01%以上含有させるのが好ましい。一方、Sn及びSbの含有量が増えても作用は飽和し、むしろ、熱延板の靱性を低下させることがある。そのため、Sn及びSbを含有させる場合も、Sn及びSbの含有量は、それぞれ0.50%以下とする。Sn含有量の下限値、及びSb含有量の下限値は、それぞれ0.02%、0.03%、又は0.05%であってもよい。Sn含有量の上限値、及びSb含有量の上限値は、それぞれ0.45%、0.40%、又は0.20%であってもよい。
Cuは必須の元素ではないが、鋼中に析出して強度を向上させる作用を呈するので、必要に応じて熱延鋼板に含有させてもよい。この作用を得るためには、0.01%以上のCuが含まれることが好ましい。その一方で、Cuが0.50%を超えて含有されると、圧延時に割れおよび疵が生じたりすることがある。したがって、Cuの含有量は0.50%以下が好ましい。Cu含有量は0.02%以上、0.03%以上、又は0.05%以上であってもよい。Cu含有量は0.40%以下、0.30%以下、又は0.20%以下であってもよい。
Ca:0~0.0400%以下
Mg:0~0.0400%以下
REM、Ca、Mgは必須の元素ではないが、粒成長を促進する元素であり、必要に応じて熱延鋼板に含有させてもよい。この効果を得るためには、REM、Ca、及びMgからなる群から選択される一種以上の元素それぞれの含有量を0.0005%以上とすることが好ましく、さらに好ましくは0.0010%以上、一層好ましくは0.0050%以上又は0.0100%以上である。一方、REM、Ca、Mgそれぞれの含有量が0.0400%を超えると、磁気特性が劣化するので、0.0040%以下とする。好ましくは、いずれの元素の含有量も0.0300%以下、より好ましくは0.0200%以下又は0.0150%以下である。
なお「REM」との用語は、Sc、Yおよびランタノイドからなる合計17元素を指し、上記「REMの含有量」とは、これらの17元素の合計含有量を意味する。ランタノイドをREMとして用いる場合、工業的には、REMはミッシュメタルの形で添加される。
次に、本実施形態の熱延鋼板は、板厚中心部(1/2t位置)の加工組織の硬度HDがHv220以下であることが特徴である。ここで「t」は板厚を意味する。
圧子=対面角136°のビッカース四角錐ダイヤモンド圧子、
押し込み荷重=10gf、
押し込み時間=20sec
である。
なお、熱延鋼板においては、表層の方が中心部よりも硬いことが通常である。熱延鋼板においては、表層における再結晶組織の量の方が、中心部よりも多いからである。以上の事情を考慮し、本実施形態に係る熱延鋼板では、最も硬質であると予想される中心部の硬さを所定値以下に制御している。一方、熱延鋼板に冷間圧延及び仕上焼鈍をして得られる無方向性電磁鋼板においては、表層と中心部との間の硬度差は小さいか、又はほとんど存在しないことが通常である。
次に、本実施形態の無方向性電磁鋼板用熱延鋼板の製造方法について説明する。本実施形態の無方向性電磁鋼板用熱延鋼板の製造方法は、
前記の成分を有する溶鋼を連続鋳造してスラブを得る工程と、
スラブを1080~1200℃の温度範囲内に加熱する工程と、
1080~1200℃の温度範囲内にあるスラブを、仕上温度850~1000℃で熱間圧延して熱延板を得る工程と、
巻取り温度700~850℃で、熱延板を巻取る工程と、
保熱温度670℃以上、及び保持時間1分以上2時間以下で、熱延板に自己焼鈍を生じさせる工程と、
熱間圧延後の巻取り温度から400℃までの平均冷却速度CR1、および/または、自己焼鈍の後の600~400℃の温度範囲の平均冷却速度CR2を30~120℃/hrとして、自己焼鈍を生じさせた熱延板を冷却する工程と、
を有する。
次いで、スラブを、好ましくは1080~1200℃に加熱し、熱間圧延に供する。加熱温度を1080℃以上とするのが好ましいのは、仕上温度を850℃以上とし、後述するように、巻取り後の再加熱による焼鈍を省略するためである。加熱温度を1200℃以下とするのが好ましいのは、硫化物等の不純物の固溶及び微細析出を防ぎ、鉄損を増大させないためである。
次いで、仕上圧延終了後の熱延鋼板を700~850℃で巻取る。700~850℃で巻取ることにより、巻取ったコイルが蓄積している熱により自己焼鈍を行うことが可能となる。この自己焼鈍によれば、熱延鋼板において再結晶率を高め、さらに、再加熱による焼鈍を省略しても、磁気特性に悪影響を及ぼす{111}方位の結晶粒の発達を抑制することが可能となる。磁気特性、特に磁束密度を向上させるために、冷間圧延前の熱延鋼板の組織の再結晶領域を増やすことが好ましいが、焼鈍温度が高いと再結晶率が60%を超え、加工組織が少なくなり、靱性向上の効果が得られない。そのため、巻取り温度は850℃以下とすることが好ましい。
冷間圧延前の熱延鋼板の結晶粒径を粗大化させるために、巻取り後のコイルに保熱カバーをかぶせて保熱する。熱延板の加工組織の硬度を下げる観点から、保熱の温度は670℃以上、保持時間は1分以上とする。一方、再結晶率が高くなりすぎると、酸洗工程及び冷延工程で、破断が生じやすくなるので、保持時間は2時間以下が好ましい。なお、保持時間とは、保熱カバーをコイルにかぶせている時間のことである。
なお、保熱カバーを用いることなく保熱工程を実施してもよい。この場合、保熱工程とは、熱延鋼板を巻き取り、コイルを形成した時点から、コイルの温度が下がり始める時点までを意味する。コイルを形成した時点とは、一帯の熱延鋼板から一巻きのコイルを巻き終えた時点である。また、コイルの温度が下がり始める時点とは、コイルの冷却速度が変化する時点であり、換言すれば冷却速度曲線上の変曲点である。保熱温度によっては、コイルを巻き終えた時点から所定の時間は、コイルの温度変化が極めて小さい場合があり、所定の時間を過ぎるとコイルの温度が急速に下がり始める。
本実施形態においては、加工組織の硬度を下げるため、冷却速度を制御することが重要である。具体的には、熱間圧延後の巻取り温度から400℃までの平均冷却速度CR1、および/または、保熱工程における保持後の600~400℃の温度範囲の平均冷却速度CR2を30~120℃/hrとするのが好ましい。
ここで、「熱間圧延後の巻取り温度から400℃までの平均冷却速度CR1」とは、巻取から保熱開始までの期間、及び、保熱終了からコイル温度が400℃になるまでの期間の冷却速度の平均値である。換言すると、「熱間圧延後の巻取り温度から400℃までの平均冷却速度CR1」は、下記式によって算出される値である。
CR1=(巻取り温度-400℃)/(巻取温度から400℃に至るまでの時間-保熱カバーをかぶせている時間)
また、「保熱工程における保持後の600~400℃の温度範囲の平均冷却速度CR2」とは、コイル温度が600℃から400℃になるまでの期間の冷却速度の平均値である。換言すると、「保熱工程における保持後の600~400℃の温度範囲の平均冷却速度CR2」とは、下記式によって算出される値である。
CR2=(600℃-400℃)/(600℃から400℃に至るまでの時間)
なお、保熱工程における保持後の冷却は、上述したカバーを取り外した直後に開始することが好ましい。あるいは、冷却工程は、コイルの温度が下がり始める時点までの間に開始することが好ましい。
しかし本発明者らは、熱延鋼板の加工組織の硬さを小さくするためには、保熱後のコイルを徐冷する必要があると知見した。平均冷却速度CR1および/またはCR2が大きすぎると、十分に加工組織の硬度を下げることができない。また、平均冷却速度が小さすぎると、自己焼鈍の時間が長くなり、加工組織が失われ靱性が劣化する。したがって、平均冷却速度CR1および/またはCR2は30℃/hr以上、120℃/hr以下とするのが好ましい。
なお、鋼板にSn、Sbを添加した場合には、これらの元素は、低鉄損、高磁束密度化に寄与するので、保熱温度を低くすることができ、結果的に、靭性向上させることができる。このとき、保熱の温度を850℃以下、好ましくは800℃以下、より好ましくは750℃以下とすることにより、適切な靭性と、低鉄損化、高磁束密度化を高度に両立させることができる。
表1に示す成分で鋼を鋳造し、熱延し、板厚2.0mmの熱延板を作製した。その後、表2に記載の条件で、コイルに巻取り、保熱した後、冷却した。なお、製造符号B0は、コイル巻取り、冷却後に、窒素100%雰囲気で熱延板焼鈍を施した参考例である。作成した熱延板の端部における熱延板加工組織の硬度、靱性評価のため行ったシャルピー試験における破面遷移温度の測定結果を表3に示す。
表1に示す鋼、表2に示す製造方法を用いて、同様に、無方向性電磁鋼板用熱延鋼板を作製し、その後、無方向性電磁鋼板を得た。
表3に開示された発明例C1及び比較例c16に、冷間圧延条件を圧下率75%、仕上焼鈍条件における均熱条件を1000℃×30秒として、冷間圧延及び仕上焼鈍を実施し、無方向性電磁鋼板とした。これら無方向性電磁鋼板の、板幅方向端部における板厚中心部(1/2t位置)の硬さを測定した。
無方向性電磁鋼板の端部の硬度測定は以下の手順で行った。鋼板の板幅方向端面から板幅方向中心部へ10mmの位置(板幅方向端部)、かつ、圧延方向に平行な断面を測定面とした。この測定面において、板厚中心部(1/2t位置)の硬度を、圧延方向と平行な方向に、10μm間隔で、10点測定した。ビッカース硬さは、JIS Z 2244(2009年)に準拠してHV10を測定した。具体的な測定条件は、圧子=対面角136°のビッカース四角錐ダイヤモンド圧子、押し込み荷重=10gf、押し込み時間=20secである。測定結果を表5に示す。
Claims (3)
- 質量%で、
C :0.0010~0.0050%、
Si:1.90%~3.50%、
Al:0.10%~3.00%、
Mn:0.05~2.00%、
P :0.100%以下、
S :0.005%以下、
N :0.0040%以下、
B :0.0060%以下、
Sn:0~0.50%、
Sb:0~0.50%、
Cu:0~0.50%、
REM:0~0.0400%、
Ca:0~0.0400%、及び
Mg:0~0.0400%
を含有し、残部がFeおよび不純物である無方向性電磁鋼板用熱延鋼板であって、
前記無方向性電磁鋼板用熱延鋼板の板幅方向端部において、板厚中心部(1/2t位置)の加工組織の硬度HDがHv220以下であることを特徴とする無方向性電磁鋼板用熱延鋼板。 - 前記加工組織の硬度HDと、前記無方向性電磁鋼板用熱延鋼板の板幅方向端部における板厚表層部(1/8t位置)の再結晶組織の硬度HUとの硬度差HS=HD-HUがHv20以内であることを特徴とする請求項1に記載の無方向性電磁鋼板用熱延鋼板。
- 質量%で、Sn:0.01%以上0.50%以下、Sb:0.01%以上0.50%以下、Cu:0.01以上0.50%以下、REM:0.0005%以上、0.0400%以下、Ca:0.0005%以上、0.0400%以下、Mg:0.0005%以上、0.0400%以下の1種又は2種以上を含有することを特徴とする請求項1又は2に記載の無方向性電磁鋼板用熱延鋼板。
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