Classifications

• • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • 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
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• a thin slab refers to a slab with a thickness of 30 mm or more and 180 mm or less.
• Example 1 The inventors of the present invention considered whether it would be possible to fix S present in steel as CaS, which has a high precipitation temperature, and conducted a study by measuring iron loss.
• Figure 1 shows the relationship between the amount of Ca added to molten steel and iron loss W 10/400 .
• Figure 1 makes clear that iron loss can be reduced by controlling the amount of Ca added to molten steel to a range of 0.0010% or more. Furthermore, in the range where iron loss was reduced, the crystal grain size of the steel sheet observed with an optical microscope was coarsened, and when the steel sheet was observed with an SEM, the number of MnS particles was reduced.
• the cast thin slab was transported to the hot rolling mill without heating and hot rolled to obtain a hot-rolled steel sheet with a thickness of 1.6 mm.
• the hot rolling entry temperature was 980°C.
• the hot rolling was performed in five passes, with the strain rate of the first pass being 3.0/sec.
• the steel sheet was heated to 980°C using a bar heater only between the first and second passes.
• the obtained hot-rolled steel sheet was subjected to the same procedure as in Experiment 1, and the iron loss was measured.
• Figure 3 shows the relationship between the time from the addition of Ca until casting and iron loss W10 /400 .
• Figure 3 shows that when the time from the addition of Ca until casting is less than 150 seconds, iron loss increases. The inventors presumed that this was because, if the time until casting was short, CaS could not be sufficiently coarsened in the molten steel, increasing iron loss.
• FIG. 1 is a diagram showing the relationship between the amount of Ca added to molten steel and iron loss W 10/400 .
• FIG. 1 is a diagram showing the relationship between the entry temperature of hot rolling and iron loss W 10/400 .
• FIG. 1 is a diagram showing the relationship between the time from the addition of Ca until casting and the iron loss W 10/400 .
• C 0.010% or less
• C is a harmful element that causes magnetic aging in the finished steel sheet, forming carbides and degrading iron loss. Therefore, in the present invention, in order to suppress the magnetic aging, the C content is set to 0.005% or less.
• the lower limit is not particularly limited and may be 0%, but from the viewpoint of suppressing decarburization costs, it is preferable to set the lower limit to about 0.0001%.
• S 0.0050% or less
• S is an element that forms sulfides and increases iron loss. Therefore, when S is contained, the S content is set to 0.0050% or less, preferably 0.0020% or less.
• the lower the S content the better, so the lower limit of the S content is not limited and may be 0%.
• S is an element that is inevitably mixed into steel as an impurity, and excessive reduction leads to an increase in manufacturing costs. Therefore, from the viewpoint of cost, it is preferable to set the lower limit to about 0.0005%.
• Zn 0.010% or less Zn reacts with S to form coarse sulfides, suppressing the precipitation of fine sulfides such as MnS and reducing iron loss. However, if the Zn content exceeds 0.010%, the amount of the sulfides increases, which in turn inhibits grain growth and increases iron loss. Therefore, when Zn is added, the Zn content is set to 0.010% or less.
• the lower limit of the Zn content is not particularly limited and may be 0%, but from the viewpoint of reducing iron loss, it is preferable to set the lower limit to about 0.001%.
• Sb 0.20% or less
• Sb is an element that has the effect of suppressing nitriding and oxidation of the surface layer and reducing iron loss. However, even if added in an amount exceeding 0.20%, the effect saturates. Therefore, when Sb is added, the Sb content is set to 0.20% or less, preferably 0.10% or less.
• the lower limit of the Sb content is not particularly limited and may be 0%, but from the viewpoint of strength, it is preferable to set the lower limit to about 0.005%.
• the molten steel further optionally contains at least one selected from Group A: Mg: 0.0001% or more and 0.10% or less and REM: 0.0001% or more and 0.10% or less; Group B: B: 0.002% or more and 0.01% or less; Group C: at least one selected from V: 0.001% or more and 0.050% or less, Nb: 0.001% or more and 0.005% or less, Ta: 0.0001% or more and 0.0020% or less, W: 0.001% or more and 0.050% or less, and Pb: 0.0001% or more and 0.0020% or less; Group D: Co: 0.001% or more and 0.100% or less; Group E: one or two selected from Ga: 0.0005% or more and 0.0300% or less and Ge: 0.0005% or more and 0.0300% or less; and Group F: As: 0.001% or more and 0.020% or less; It may contain at least one group selected from the following:
• Mg at least one selected from 0.0001% to 0.10% and REM: 0.0001% to 0.10%
• Mg 0.0001% to 0.10%
• Mg is an element that fixes S as sulfides and contributes to reducing iron loss. To achieve this effect, the Mg content should be 0.0001% or more. On the other hand, if the Mg content exceeds 0.10%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.10%. Therefore, it is preferable that Mg be contained in the range of 0.0001% to 0.10%.
• REM 0.0001% or more and 0.10% or less REM (rare earth metal elements) are a group of elements that fix S as sulfides and contribute to reducing iron loss. To obtain this effect, the REM content should be 0.0001% or more. On the other hand, if the REM content exceeds 0.10%, the effect saturates and costs increase unnecessarily, so the upper limit is set to 0.10%. Therefore, the REM content is preferably in the range of 0.0001% or more and 0.10% or less.
• Ta 0.0001% or more and 0.0020% or less Ta is an element that has the effect of increasing the strength of the steel sheet and can be added as needed. To obtain this effect, the Ta content should be 0.0001% or more. However, if the Ta content exceeds 0.0020%, fine precipitates will form in the steel sheet, increasing iron loss, so the upper limit of the Ta content is set to 0.0020%.
• Pb 0.0001% or more and 0.0020% or less
• Pb is an element that has the effect of increasing the strength of steel sheet and can be added as needed. To obtain this effect, the Pb content should be 0.0001% or more. However, if the Pb content exceeds 0.0020%, fine precipitates will form in the steel sheet, increasing iron loss, so the upper limit of the Pb content is set to 0.0020%.
• Co 0.001% or more and 0.100% or less
• Co is an element that has the effect of increasing the magnetic flux density of the steel sheet and can be added as needed. To achieve this effect, the Co content should be 0.001% or more. However, since a large amount of Co increases the alloy cost, the upper limit of the Co content is set to 0.100%.
• Ge 0.0005% or more and 0.0300% or less Ge is an element that has the effect of improving the texture of the steel sheet and increasing the magnetic flux density, and can be added as needed. To obtain such effects, the Ge content should be 0.0005% or more. However, adding a large amount of Ge saturates the effect and increases the alloy cost, so the upper limit of the Ge content is set to 0.0300%.
• Group F As: 0.001% or more and 0.020% or less As is an element that has the effect of increasing the strength of steel sheets and can be added appropriately. To obtain this effect, the As content should be 0.001% or more. However, if the As content exceeds 0.020%, the risk of fracture during cold rolling increases. Therefore, the upper limit of the As content is set to 0.020%.
• the remainder other than the above-mentioned components consists of Fe and unavoidable impurities.
• the Ca added to the molten steel may be simple Ca or a Ca alloy such as CaSi.
• the surface temperature of the thin slab is maintained at 850°C or higher, and the surface temperature of the thin slab at the inlet side of the hot rolling mill is set to 950°C or higher.
• Hot rolling including two or more passes is carried out under the condition that the strain rate in the first pass is 5.0/sec or less, and the steel sheet is heated to 950°C or more by a bar heater between the first and second passes.
• the method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet of the present invention includes the following two methods.
• a thin slab is produced by a continuous casting method, and the obtained thin slab is transported to the inlet side of a hot rolling mill without being heated (for example, without passing through a heating furnace) while being kept at a high temperature, and the surface temperature of the thin slab at the inlet side of the hot rolling mill is set to 950°C or higher.
• a thin slab is produced by a continuous casting method, and the resulting thin slab is transported to a tunnel furnace while maintaining its surface temperature at 850°C or higher.
• the slab is then kept at a temperature such that the surface temperature of the slab at the exit of the tunnel furnace is 950°C or higher and 1250°C or lower, and then transported to the entry side of a hot rolling mill, where the surface temperature of the thin slab at the entry side of the hot rolling mill is 950°C or higher.
• the chemical composition of the thin slab obtained in this invention is substantially the same as the chemical composition of the molten steel.
• the surface temperature of the thin slab obtained in the casting process is maintained at 850°C or higher until it reaches the inlet side of the hot rolling mill.
• the thin slab after the casting process is at a high temperature, typically 1000 to 1400°C.
• the surface temperature of the thin slab is preferably maintained at 1250°C or lower. It is desirable not to actively cool the thin slab in the transporting process.
• the thin slab obtained in the continuous casting process is transported to the inlet of the hot rolling mill without heating (e.g., without passing through a heating furnace) while maintaining a high temperature.
• the temperature of the thin slab decreases after the continuous casting process.
• the surface temperature of the thin slab at the inlet of the hot rolling mill is set to 950°C or higher. Therefore, under the conditions of (A), the thin slab is transported to the inlet of the hot rolling mill while it is still at 950°C or higher. In this transport process, it is desirable to transport the thin slab as quickly as possible to avoid a decrease in its temperature.
• the thin slab may be cut before being transported to the inlet of the hot rolling mill.
• the temperature at the exit of the tunnel furnace should be set to 950°C or higher, preferably 1100°C or higher.
• the temperature at the exit of the tunnel furnace should be set to 1250°C or lower, preferably 1200°C or lower, in order to effectively prevent precipitates in the steel from dissolving and precipitating finely in subsequent processes, which would increase iron loss.
• the heating method in the heat retention treatment is not particularly limited, and any method can be used, such as induction heating, a gas furnace, an electric furnace, etc. However, from the viewpoint of reducing CO2 emissions, it is preferable to use induction heating or an electric furnace, which are heating methods that use electrical energy.
• the entry side temperature of hot rolling is set to 950°C or higher.
• the upper limit of the temperature can be set to 1250°C or lower, preferably 1200°C or lower, and a higher temperature within this range is more desirable.
• the number of passes in hot rolling is not particularly limited and can be any number of passes equal to or greater than two, for example, 10 or less, or even 6 or less.
• strain rate in the first pass of hot rolling 5.0/sec or less
• the strain rate in the first pass of hot rolling exceeds 5.0/sec
• the rate at which dislocations, which are the driving force for precipitation, are introduced exceeds the rate at which the dislocations recover, resulting in the precipitation of fine precipitates such as nitrides during hot rolling. Therefore, the strain rate in the first pass of hot rolling is set to 5.0/sec or less.
• a strain rate of 1.0/sec or more is preferable because productivity decreases when the strain rate is less than 1.0/sec.
• the strain rate ⁇ ′ is calculated using the following equations (1) and (2).
• ⁇ ' is the strain rate in the first pass of hot rolling
• h1 is the slab thickness before hot rolling
• h 0 is the slab thickness after one pass of hot rolling
• tc is the time required for the first pass of hot rolling
• R is the roll diameter in the first pass of hot rolling
• v 0 is the threading speed of the steel slab.
• the bar heater may be one that heats the entire width of the steel material (or rough bar), or it may be one that heats only the widthwise ends (edge heater). However, from the perspective of uniform temperature distribution across the plate width, it is preferable to use a heater that can heat the entire width of the steel material.
• a heater that can heat the entire width of the steel material it is preferable to use, for example, a solenoid-type induction heating device in which a heating coil is wound in a cylindrical shape and the steel material is induction-heated by passing through it. When a solenoid-type induction heating device is used, both the surface layer and the widthwise ends of the steel plate are heated.
• the temperature of the steel sheet at the delivery side of the hot rolling mill is not particularly limited, but is preferably 800° C. or higher.
• the steel sheet can be wound into a coil at the delivery side of the hot rolling mill.
• the thickness of the steel sheet at the exit side in hot rolling is not particularly limited and may be any thickness. However, if the exit side thickness is less than 0.4 mm, the overall length of the steel sheet will be excessively long, reducing productivity. Therefore, from the perspective of productivity, it is preferable that the exit side thickness in hot rolling be 0.4 mm or more. On the other hand, if the exit side thickness exceeds 2.0 mm, the load on cold rolling will increase. Therefore, from the perspective of reducing the load on cold rolling, it is preferable that the exit side thickness in hot rolling be 2.0 mm or less.
• a method for producing a non-oriented electrical steel sheet in an embodiment of the present invention includes a hot-rolled steel sheet production step of producing a hot-rolled steel sheet by the above-mentioned production method, a hot-rolled sheet annealing step of subjecting the hot-rolled steel sheet to hot-rolled sheet annealing, a cold-rolling step of cold-rolling the hot-rolled steel sheet that has been subject to the hot-rolled sheet annealing to form a cold-rolled steel sheet, and a finish annealing step of subjecting the cold-rolled steel sheet to finish annealing.
• Example 1 A 60 mm thick slab having the chemical composition shown in Table 1 was produced by continuous casting.
• the time from the addition of Ca until the molten steel was cast was set to 300 seconds.
• the slab was transported to the inlet side of a hot rolling mill without heating and subjected to five passes of hot rolling to obtain a hot-rolled steel sheet.
• the surface temperature of the slab at the inlet side of the hot rolling mill was set to 1000°C, and the strain rate in the first pass of hot rolling was set to 3.0/sec. Only between the first and second passes, the steel sheet was heated to the bar heater heating temperature shown in Table 2 using a bar heater.
• the obtained hot-rolled steel sheet was subjected to hot-rolled annealing at 1000°C for 30 seconds to obtain a hot-rolled annealed sheet.
• the hot-rolled annealed sheet was then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.20 mm.
• the cold-rolled steel sheet was then finish-annealed at 1000°C for 10 seconds to obtain a non-oriented electrical steel sheet.
• Epstein samples with a width of 30 mm and a length of 280 mm were cut out from the rolling direction and the width direction of the obtained non-oriented electrical steel sheet, and the iron loss W10/ 400 was measured using an Epstein tester.
• an iron loss W10 /400 of 12.5 W/kg or less is considered to be good.
• Table 1 show that non-oriented electrical steel sheets with good core loss properties can be obtained using molten steel with a chemical composition that meets the conditions of this invention. Note that Nos. 7, 13, 19, and 23 in Table 1 are examples that could not be evaluated because they fractured during cold rolling.
• Example 2 A steel having a component composition containing, in mass%, C: 0.002%, Si: 3.00%, Mn: 0.50%, P: 0.01%, S: 0.0030%, Al: 0.50%, N: 0.0020%, Cu: 0.01%, Mo: 0.010%, Zn: 0.001%, Ti: 0.002%, and Ca: 0.002%, with the balance being Fe and unavoidable impurities, was melted, and a hot-rolled steel sheet for non-oriented electrical steel sheet was produced under the conditions shown in Table 2.
• the obtained hot-rolled steel sheets were subjected to hot-rolled sheet annealing at 1000°C for 30 seconds to obtain hot-rolled annealed sheets.
• the hot-rolled and annealed steel sheets were then cold-rolled to obtain cold-rolled steel sheets having a thickness of 0.30 mm, which were then subjected to finish annealing at 1000°C for 10 seconds to obtain non-oriented electrical steel sheets.
• Epstein samples with a width of 30 mm and a length of 280 mm were cut out from the rolling direction and the width direction of the obtained non-oriented electrical steel sheet, and the iron loss W10/ 400 was measured using an Epstein tester.
• an iron loss W10 /400 of 12.5 W/kg or less is considered to be good.

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