Classifications

• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
  • C21D8/1222—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—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
  • C21D8/1255—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 with diffusion of elements, e.g. decarburising, nitriding
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—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
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—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
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1277—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular surface treatment
  • C21D8/1283—Application of a separating or insulating coating
• • 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
• • 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
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • 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
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • 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
• • 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
  • C21D2201/00—Treatment for obtaining particular effects
  • C21D2201/05—Grain orientation

Definitions

• the present invention relates to a method for producing a grain-oriented electrical steel strip, to a grain-oriented electrical steel strip, to a laminated stack of at least two grain-oriented electrical steel strips of the invention and to the use of such a grain-oriented electrical steel strip or laminated stack thereof as material for the production of parts for electric motors, for electric transformers or for other electric devices.
• the present invention relates to a grain-oriented electrical steel strip with improved mechanical properties, in particular improved yield strength, and excellent electromagnetic properties.
• sheet or “strip” are used in the present text synonymously to indicate a flat steel product which is obtained by a rolling process and which length and width is much greater than its thickness.
• sheet or “strip” are used in the present text synonymously to indicate a flat steel product which is obtained by a rolling process and which length and width is much greater than its thickness.
• Grain-oriented electrical steel is a soft magnetic material, which typically exhibits high silicon contents.
• GOES has a high permeability to the magnetic field and can be magnetized and demagnetized easily.
• the casting and the high temperature slab reheating is performed at temperatures of up to 1400 °C.
• Such high temperature casting and reheating results in a well-developed inhibition system which comprises particles of AlN, MnS and other compounds in the iron matrix even before the cold process. The presence of said particles promotes an abnormal grain growth in the steel structure, which has a positive effect on the magnetic properties of the GOES sheet.
• the primary recrystallization (PRX) occurring during the decarburization annealing prepares and controls the secondary grain growth.
• PRX The primary recrystallization
• this process step is unstable due to the large number of metallurgical phenomena that compete with each other during the decarburization annealing. These phenomena are in particular carbon removal, formation of the oxide layer, primary grain growth.
• decarburization annealing is essential to obtain efficient nitriding, a high-quality insulating forsterite film, and a sufficient number of Goss nuclei in the matrix.
• a dense oxide layer which occurs during the beginning of decarburization annealing, can promote surface quality but can also act as a barrier to decarburization and nitriding.
• the steel strip runs through a high temperature annealing cycle either in a batch annealing furnace or a rotary batch annealing furnace.
• secondary recrystallization SRX
• an abnormal grain growth takes place which leads to the Goss texture controlled by the inhibitors previously formed.
• disturbing elements such as sulfur or nitrogen are removed and a forsterite layer, also often called “glass film” is formed on the surface of the strip.
• This forsterite layer acts as an electric insulation coating layer and applies an additional tension on the surface of the strip, which contributes to the magnetic properties of the strip.
• a solution based on magnesium phosphate or aluminum phosphate or mixtures of both with various additives, such as chromium compounds and Si oxide, can be applied to the forsterite layer and baked at temperatures above 350 °C.
• the layer system thus formed on the electrical steel forms an insulating layer, which transfers additional tensile stresses to the steel material that have a favorable effect on the electromagnetic properties of the electrical steel or sheet.
• the cores of stators and rotors of conventional radial-flux electric motors are usually made of the same materials.
• the standard core material used is non-grain-oriented electrical steel sheet ("NGO").
• NGO non-grain-oriented electrical steel sheet
• grain-oriented electrical steel characterized by better mechanical properties than grain-oriented electrical steel.
• magnetic properties of GOES are significantly better in the rolling direction than those of NGO.
• the object of the present invention is to provide a method of producing a grain-oriented electrical steel strip, in particular for use in stator and rotor teeth in electric motors, in particular in radial flux motors, with improved mechanical properties, in particular improved yield strength in the rolling direction, without compromising its polarization.
• the invention solved this problem by means of a method of producing a grain-oriented electrical steel sheet with at least the features specified in claim 1, a grain-oriented electrical steel sheet with at least the features specified in claim 10, a stack thereof with the features specified in claim 13 and the use of the grain-oriented electrical steel sheet or the stack with at least the features specified in claim 15.
• the method of producing the grain-oriented electrical steel sheet according to the present invention comprises at least the following working steps:
• the method of the invention may comprise further steps that are known to the skilled person and that are usually performed when producing grain-oriented electrical steel sheets.
• the invention is based here on the realization that good mechanical properties, namely an increased yield strength, and ideal polarizations of a grain-oriented electrical steel strip according to the invention can be ensured by carefully controlling the temperatures in steps b) and e) of the process. It was found that depending on the content of the grain boundary segregating elements Cu, P and Mg in the steel slab different temperatures T1 to T3 for step b) and a different temperature CT for step e) should be selected.
• the invention makes use of the fact that by controlling the furnace temperature in step b) and the coiling temperature in step e) specific intermetallic phases can be eliminated and specific intermetallic phases can be deliberately avoided so that they are not deposited at grain boundaries.
• specific intermetallic phases can be deliberately avoided so that they are not deposited at grain boundaries.
• the inventors can strike a balance between Zener pinning and grain growth during final annealing in step j), which in turn allows the yield strength to be manipulated without negatively affecting the polarization.
• the individual content of S, Se, Sb, Bi, Ni, Co, Mo, if present in the grain-oriented electrical steel sheet may amount to 0.01 to 0.1 wt.-% and the individual content of Sn and Cr, if present in the grain-oriented electrical steel sheet, may amount to 0.01 to 0.15 wt.-%.
• the steel slab is hot rolled into a hot strip, wherein between the end of rough rolling and the start of final hot rolling coiling and/or intermediate annealing of the rough rolled hot strip is carried out.
• an intermediate annealing is performed, the time between the end of rough rolling and the start of hot rolling is above 15 s.
• the time between end of intermediate annealing and start of final hot rolling is below 15 s to securely avoid a decrease in temperature and the problems resulting therefrom. In case coiling of the hot strip is carried out this serves to minimize the temperature difference across its length, i.e.
• step d) of the method of the invention the hot strip obtained in step c) is cooled by vapor and/or liquid spray cooling, wherein the cooling starts at most 5 s after the end of the last final hot rolling step, preferably within 2 s after the final hot rolling step.
• An immediate cooling after final hot rolling is needed to prevent grain growth and recovery, which would negatively impact the primary recrystallization during step h).
• vapor and/or liquid spray cooling cooling rates higher than 50 K/s can be achieved, which are needed for the same reasons as mentioned above, i.e. to prevent grain growth and recovery.
• the cooling rate from the end of final hot rolling to the end of vapor and/or liquid spray cooling is higher than 40 K/s, more preferably between 60 K/s and 100 K/s. Higher cooling rates are not preferred as these increase the risk for edge cracks of the hot rolled coils.
• multi-stage rolling is cold rolling in at least three passes, wherein the hot-rolled strip is cold rolled to an intermediate thickness, an intermediate annealing takes place, and after the intermediate annealing the strip is further cold-rolled to the final thickness.
• Methods for cold rolling a grain-oriented steel strip are generally known to the skilled expert as well and, for example, described in WO 2007/014868 A1 and WO 99/19521 A1 .
• an intermediate annealing is performed in a temperature range of 700 to 1150 °C, preferably 800 to 1100 °C, under an atmosphere which dew point is set to 10 to 80 °C. Typical annealing times are 30s to 900 s.
• decarburization annealing of the cold rolled strip obtained in step g) takes place.
• This decarburization annealing may optionally include a nitriding treatment.
• the decarburization annealing is preferably carried out at temperatures in the range of 600 to 950°C, more preferably of 600 to 900 °C.
• the duration t A of the decarburization annealing is preferably 30 to 300 s.
• the decarburization annealing is typically carried out using a high dew point atmosphere with a dew point between 40 and 80°C, preferably between 40 and 65°C.
• an annealing separator is applied onto at least one surface of the cold strip obtained in step b).
• the annealing separator comprises MgO and optionally oxides and mixed oxides of iron, aluminum, titanium, magnesium and/or silica.
• step j) of the process according to the invention the cold rolled strip obtained in step h) and coated with the annealing separator in step i) undergoes a final annealing during which the forsterite layer is formed and secondary recrystallization occurs.
• the final annealing of the cold strip in step j) according to the method of the invention takes place at a maximum soaking temperature of at least 1076°C but less than 1247 °C. Temperatures below 1076 °C are insufficient for dissolving residual elements such as N or S, which would otherwise deteriorate the final magnetic properties of the GOES. Final annealing temperatures above 1247 °C lead to unwanted physical deformations of the steel strip due to decreased hardness of the steel.
• the steel strip After the final annealing the steel strip is cooled down in a common manner, e.g. by natural cooling, to room temperature.
• step j) of the process according to the invention the secondary recrystallization takes place, which ensures that the grain-oriented steel sheet processed in this way is prepared to reliably develop the optimized properties of a grain-oriented steel sheet according to the invention as outlined above.
• the steel strip is cleaned, and optionally pickled.
• Methods with which the steel strip is pickled are known to the skilled expert.
• the steel strip can be treated with an aqueous acidic solution. Suitable acids are for example phosphoric acid, sulfuric acid and/or hydrochloric acid.
• step k) of the method of the invention the annealed cold strip obtained in step j) of the method of the invention is coated with an electric insulation coating and the insulation coated cold strip is annealed.
• the insulating layer is preferably applied on at least one side of the GOES.
• the method for applying the insulating layer is known to the artisan and can be found in e.g. EP 2 902 509 B1 and EP2 954 095 A1 .
• An insulation coating applied to a grain oriented electrical steel product has a positive effect on minimization of the hysteresis losses.
• the insulation coating can transfer tensile stresses to the base material, which not only improves the magnetic loss values of the grain oriented electrical steel product but also reduces the magnetostriction, thereby having in turn a positive effect on the noise behavior of the finished transformer.
• Formation of the insulation coating involves applying an aqueous solution of metallic phosphate containing colloidal silica and optional chromium compounds onto the surface of the steel sheet and baking the same at temperatures in the range of 800 °C to 950 °C for 10 to 600 s.
• the grain-oriented electrical steel has a yield strength in the rolling direction of at least 340 MPa determined according to DIN EN ISO 6892-1, a polarization J500 of at least 1.85 and preferably a polarization J2500 of at least 1.93.
• the chemical composition of the grain-oriented electrical steel is preferably as follows: Si: 2.0 to 4.0, Mn: 0.01 to 0.5, at least one element selected from the group consisting of P, Cu, Mg, with the following contents, in wt.%,P: 0.005 to 0.10, Mg: 0.0003 to 0.0020, Cu: 0.001 to 0.50; optionally one or more elements selected from the group consisting of Se, Sn, Sb, Bi, Ni, Cr, Co, Mo, wherein the individual content of each of these elements is 0.005 to 0.2 wt.-%; optionally one or more elements selected from the group consisting of As, B, V, Nb, Te, Ti, wherein the individual content of each of these elements is 0.0003 to 0.1 wt.-%; the remainder of the composition being Fe and unavoidable impurities.
• the composition of the resulting grain-oriented electrical steel does contain Al sl , C, N and S only as unavoidable impurities as these elements are dissolved out of the steel during steps h) and j) of the method of the invention.
• the grain oriented electrical steel sheet may also be characterized by a coarse grain structure, which shows a medium grain size, which can be measured by any known method such as line intersection method or other methods according to DIN EN ISO 643, of several mm, preferably a medium grain size of at least 10 mm and less than 50 mm.
• the grain-oriented electrical steel sheets can be prepared in any format, like steel strips that are provided as coils, or cut steel pieces that are provided by cutting these steel pieces from the steel strips. Methods to provide coils or cut steel pieces are known to the skilled expert.
• the grain-oriented electrical steel sheet produced according to the method of the present invention shows improved mechanical properties, in particular improved yield strength in the rolling direction, and at the same time excellent magnetic properties, in particular excellent polarization, in comparison to grain-oriented electrical steel sheets according to the prior art.
• the grain-oriented electrical steel sheet according to the invention is in particular useful for the manufacture of parts for electric motors.
• a preferred use of the grain-oriented electrical steel sheet of the present invention is as material for the manufacture of stator or rotor core for radial or axial flux motors.
• stator or rotor core stacks of the grain-oriented electrical steel sheet are typically formed by laminating the GOES sheets together with a resin, for example, a coating as described in DE 10 2015 012172 A1 or a backlack type resin.
• a resin for example, a coating as described in DE 10 2015 012172 A1 or a backlack type resin.
• the lamination of the GOES sheets temperatures below 230°C are usually used.
• the optimal duration of the lamination depends on the lamination temperature used and on the thickness of the stack to be laminated and is typically adapted depending on the stack geometry and the type of heating used.
• the exact conditions for the manufacturing of the resin coating depend on the resin type used and can be found in the respective data sheets of the resin manufacturer.
• the optimal duration for the lamination increases with decreasing lamination temperature and/or increasing laminated stack thickness.
• lamination of a thin stack of GOES at a lamination temperature of 200°C using a lamination time of 2 minutes may be sufficient, while for laminating a thicker stack of GOES a lower temperature of 180°C for a duration of 1 hour or at 140°C for a duration of 2 hours may be preferable.
• the temperatures mentioned for the lamination are not the furnace temperatures, but the core temperatures of the stack and the holding time is the time that elapses between reaching the core temperature and removal from the furnace.
• the lamination is usually carried out using a pressure between 150 to 300 N/cm 3 .
• Another aspect of the present invention is a laminated stack of grain-oriented electrical steel sheets, wherein the stack comprises at least two grain-oriented electrical steel sheets according to the invention laminated together with a resin.
• a laminated stack of grain-oriented electrical steel sheets comprises at least 2 or at least 3 grain-oriented electrical steel sheets according to the invention laminated together with a resin.
• the resin for laminating the grain-oriented electrical steel sheets together is not particularly limited. Any resin known to the skilled person for this purpose can be used. Preferably, the resin for laminating the grain-oriented electrical steel sheets together is selected from a backlack type resin or a coating as described in DE 10 2015 012172 A1 . These resin types are known to the skilled person and are described, e.g., in DE 10 2015 012172 A1 .
• FIG. 1 shows a schematic illustration of four differently decorated grain boundaries A to D.
• Grain boundary A corresponds to a GOES produced according to the prior art.
• the grain boundary between grain 1 and grain 2 is not decorated with any intermetallic phases. This results in good polarization but poor mechanical properties.
• Grain boundary B corresponds to a GOES produced according to the invention, wherein the boundary between grain 1 and grain 2 is partially decorated with specific intermetallic phases. This results in high polarization and good mechanical properties.
• the excessively decorated grain boundary C exhibits high polarization but leads to poor mechanical properties.
• the intermetallic phases are agglomerated below the surface, which impedes Bloch wall movement and leads to poor polarization due to deformation of the hysteresis curve.
• step e) of the method of the invention leads to a fully decorated grain boundary C due to excessive diffusion of the segregating elements.
• the inventors have found that in case the slab temperature to which the slab is heated prior to hot rolling in step b) of the method of the invention is too low, i.e. below the minimum temperatures T1, T2 or T3 specified in step b) of the method of the invention, this leads to grain boundary D, wherein the intermetallic phases are agglomerated below the surface. It appears that in such a case non-dissolved agglomerations accumulate on the grain boundary. A similar situation is also observed in case the hot strip annealing temperature in step f) of the method of the invention is too low.
• the cold strips underwent decarburization annealing including a nitriding treatment at an annealing temperature of 850°C.
• decarburization annealing including a nitriding treatment at an annealing temperature of 850°C.
• an annealing separator mainly comprising MgO onto the strip surface
• final annealing of the coated decarburization annealed cold strips with a temperature of 1210°C to form a Goss texture was carried out.
• the final annealed cold strips were coated with an electric insulation coating containing a metal phosphate, colloidal silica and a chromium compound, and subsequently annealed for relieving stresses. Domain refinement of the coated cold strips was carried out.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Electromagnetism (AREA)
• Manufacturing & Machinery (AREA)
• Manufacturing Of Steel Electrode Plates (AREA)

Priority Applications (1)

Applications Claiming Priority (1)

Publications (1)

Family

ID=89661069

Family Applications (1)

Country Status (1)

Citations (10)

• 2025
  • 2025-01-17 EP EP25152487.2A patent/EP4589028A1/fr active Pending

Patent Citations (10)

Non-Patent Citations (3)

Similar Documents

Legal Events