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
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • 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
• • 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
• • 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

Definitions

• the invention relates to a method for the production of high-quality grain-oriented electrical steel, in particular for the production of so-called HGO material (Highly Grain O ⁇ ented - material) based on thin slab continuous casting.
• HGO material Highly Grain O ⁇ ented - material
• JP 2002212639 A describes a process for the production of grain-oriented electrical steel in which a melt which contains (in% by mass) in addition to 2.5-4.0% Si and 0.02-0.20% Mn significant inhibitor components 0.0010 - 0.0050% C, 0.002 - 0.010% Al and levels of S and Se and other optional alloying constituents, such as Cu, Sn, Sb, P, Cr, Ni, Mo and Cd, balance iron and unavoidable impurities, comprises, thin slabs having a thickness of 30 mm to 140 mm are produced.
• the thin slabs are annealed prior to hot rolling at a temperature of 1000 0 C to 1250 0 C, in order to achieve optimum magnetic properties of the finished electrical steel.
• the known method provides that the hot rolled 1.0 mm to 4.5 mm thick strip is annealed after hot rolling at temperatures of 950 0 C to 1150 0 C for 30 sec to 600 sec before it at degrees of deformation of 50% to 85% is rolled to cold strip.
• CGO material Conventional Grain Oriented - material
• JP 56-158816 A Another method for the production of grain-oriented electrical steel, which, however, relates only to the production of standard grades, so-called CGO material (Conventional Grain Oriented - material), is known from JP 56-158816 A.
• the hot rolling of these thin slabs is started before their temperature drops below 700 0 C. In the course of the hot rolling, the thin slabs are rolled to a hot strip with a thickness of 1.5 - 3 mm.
• the thin slabs are rolled to hot strip with a thickness of 1.5 - 3.5 mm.
• This hot strip thickness has the disadvantage here that the commercial for grain-oriented electrical sheet standard end thicknesses below 0.35 mm only by Kaltwalzgrade above 76% in single-stage cold rolling or conventional multi-stage cold rolling can be produced with intermediate annealing, which is disadvantageous in this operation that the high degree of cold work is not matched to the relatively weak inhibition by MnS and MnSe. This leads to unstable and unsatisfactory magnetic properties of the finished product.
• a complex and expensive multi-stage cold rolling process with intermediate annealing must be accepted.
• the hot rolling parameters must be selected such that the material always remains enough ductile remains.
• ductility for bulk material for grain-oriented electrical sheet the ductility is greatest when the strand is cooled after solidification to about 800 0 C, then only a relatively short time to compensation temperature, eg. B. 1150 0 C, dwells while being thoroughly heated through.
• An optimal hot rollability of such a material is therefore given when the first forming pass at temperatures below 1150 0 C and with a degree of deformation of at least 20% and the rolling stock from an intermediate thickness of 40 mm to 8 mm by means of high-pressure inter-frame cooling devices within of not more than two successive Umststichen is brought to rolling temperatures of below 1000 0 C. This avoids that the rolling stock in the critical temperature range for ductility around 1000 0 C is formed.
• the hot strip thus obtained is then cold rolled one or more stages with recrystallizing intermediate annealing to a final thickness in the range of 0.15 to 0.50 mm.
• This cold strip is finally recrystallized and decarburizing annealed, provided with a predominantly MgO containing Glühseparator and then final annealing to the expression of a Gosstextur.
• the tape is coated with electrical insulation and annealed stress-free.
• the ladle furnace In this unit, the molten steel for the thin slab caster is provided and set by heating the desired dispensing temperature for potting. In addition, in the ladle furnace, the final adjustment of the chemical composition of the steel in question can be made by adding alloying elements. In addition, the slag is usually conditioned in the ladle furnace. In the processing of aluminum-killed steels, additional small amounts of Ca are added to the molten steel in the ladle furnace in order to ensure the castability of these steels.
• the preparation of grain oriented electrical steel also requires a high accuracy adjustment of the chemical target analysis, i. the setting of the contents of the individual elements must be very closely matched, so that depending on the selected absolute content, the boundaries of some elements are very narrow.
• the treatment in the ladle furnace reaches its limits.
• the invention therefore an object of the invention to provide a method that allows the economical production of high-quality grain-oriented electrical steel sheet (especially HGO) using thin slab continuous casting plants.
• m) optionally: coating the final annealed cold-rolled strip with electrical insulation and then stress-relieving the coated cold-rolled strip.
• the predetermined by the invention sequence of operations is tuned so that, using conventional aggregates, an electrical sheet can be produced which has optimized electro-magnetic properties.
• a molten steel is melted with known composition in the first step.
• This melt is then treated by secondary metallurgy.
• This treatment is preferably first carried out in a vacuum plant to adjust the chemical composition of the steel to the required narrow analytical margins and to achieve low hydrogen contents of at most 10 ppm in order to minimize the risk of strand breakage during casting of molten steel.
• the use of a ladle furnace for slag conditioning would also first be followed by treatment in a vacuum system for adjusting the chemical composition of the molten steel within narrow analytical limits.
• this combination has the disadvantage that, in the case of casting delays, the temperature of the melt drops to such an extent that the molten steel can no longer be cast.
• this has the disadvantage that the analysis accuracy is not as good as in the treatment in a vacuum system and also high hydrogen contents in the casting melt can occur with the risk of strand breakthroughs.
• the invention further, only use the vacuum system. On the one hand, however, this involves the risk that, in the case of casting delays, the temperature of the melt drops to such an extent that the molten steel can no longer be cast. On the other hand, there is a risk that the immersion spouts clog in the sequence and thus the sequence must be canceled.
• both systems are thus used in combination with the availability of ladle furnace and vacuum system depending on the respective melting metallurgical and casting requirements.
• a strand is then poured, which preferably has a thickness of 25 mm to 150 mm.
• the molten steel is poured in a continuous casting mold, which is equipped with an electromagnetic brake, such errors can be largely avoided.
• a brake causes a calming and homogenization of the flow in the mold, in particular in Badador Kunststoff by generating a magnetic field, which, in interaction with the casting molds entering the mold reduces their speed due to the effect of the so-called "Lorenzkraft".
• the formation of a microstructure of the cast steel strand which is favorable with regard to the electromagnetic properties can also be assisted by casting at a low superheating temperature.
• the latter are preferably at most 25 K above the liquidus temperature of the cast melt. If this advantageous variant of the invention is taken into account, a freezing of the molten steel cast at low superheat at the bath level and hence casting disturbances up to the casting break can likewise be avoided by using an electromagnetic brake on the casting mold.
• the force exerted by the electromagnetic brake directs the hot melt to the bath level and there causes a temperature increase sufficient to ensure a smooth casting process.
• the homogeneous and fine-grained solidification structure of the cast strand achieved in this way has a favorable effect on the magnetic properties of the grain-oriented electrical steel produced according to the invention.
• the aim is to avoid the formation of nitridic precipitates prior to hot rolling and during hot rolling as much as possible in order to make extensive use of the possibility of a controlled production of such precipitates during the cooling of the hot strip.
• it is provided according to an advantageous embodiment of the invention to make an inline thickness reduction of cast from the melt, but still core liquid strand.
• LCR Liquid Core Reduction
• SR Soft Reduction
• the reduction in the number of stitches and the rolling forces in the rolling mills of the hot strip mill can be reduced with the result that the work roll wear of the rolling mills and the slumpiness of the hot strip can be reduced and the strip run can be improved.
• the thickness reduction achieved by LCR according to the invention is preferably in the range of 5 mm to 30 mm.
• SR Under SR is meant the targeted reduction in thickness of the strand in the swamp tip near Enderstarrung.
• the SR aims to reduce mitigation and core porosity. This method has hitherto been used predominantly in billet and slab continuous casting plants.
• the invention now proposes to apply the SR also in the production of grain-oriented electrical steel on thin slab continuous casting or casting rolling.
• the achievable in this way in particular the silicon Mitsenigerung in the subsequently hot-rolled precursors can be a homogenization of the chemical composition across the strip thickness reach, which is beneficial for the magnetic values.
• Good SR results are obtained when the reduction in thickness achieved using SR is 0.5-5 mm.
• the casting mold strand In thin slab continuous casting the usually emerging from the casting mold strand is bent at lower points and guided in a horizontal direction.
• the casting cast from the melt strand at 700 0 C. Bending and directed at 1000 0 C temperature (preferably 850 to 950 0 C) can be avoided, cracks on the surface of the separated from the strand thin slabs can be avoided, which may otherwise occur, in particular, as a result of edge cracks of the strand.
• the steel used according to the invention has a good ductility at the strand surface or in the edge region, so that it can follow well the deformations occurring during bending and straightening.
• the cast strand thin slabs are divided in a conventional manner, which are then heated in an oven to the appropriate hot rolling start temperature and then fed to hot rolling.
• the temperature at which the thin slab arriving in the furnace is preferably above 650 0 C.
• the residence time in the oven should be below 60 minutes in order to avoid Klebzunder.
• An aspect of the invention which is essential in view of the desired production of HGO material is that the hot rolling is carried out following the first forming pass in the two-phase region ( ⁇ / ⁇ ). Also, this measure has the goal of reducing the formation of nitridic precipitates in the course of hot rolling as far as possible in order to be able to control these precipitates specifically via the cooling conditions on the outlet roller table behind the last mill stand of the hot strip mill.
• hot rolled at temperatures where mixed in the structure of the hot strip austenitic and ferritic shares are above about 800 ° C., in particular in the range from 850 ° C. to 1150 ° C.
• the AIN In the ⁇ phase, the AIN is kept in solution at these temperatures.
• Another positive aspect of hot rolling in the two-phase mixing area is the grain-separating effect.
• austenite By converting the austenite into ferrite following the hot whale passes, a finer-grained and more homogeneous hot-band structure is achieved, which has a positive effect on the magnetic properties of the end product.
• the prevention of nitridic precipitations during hot rolling is further supported by the fact that already in the first forming pass a degree of deformation of at least 40% is achieved in order to have only relatively small Stichab changes in the last frameworks for achieving the desired Endbanddicke necessary.
• the use of high reduction rates (degrees of deformation) in the first two stands causes the required conversion of the coarse-grained solidification microstructure into a fine rolling structure, which is the prerequisite for good magnetic properties of the final product to be produced. Accordingly, the reduction in stitching in the last stand should be limited to a maximum of 30%, preferably less than 20%, and it is also favorable for an optimum in terms of the desired properties warm rolling result, if the reduction in the penultimate stand of the finishing mill is less than 25% , A pass plan tested in practice on a seven-stand finished hot rolling mill, which has led to optimum properties of the finished electrical sheet, provides that with a pre-strip thickness of 63 mm and a hot strip thickness of 2 mm, the degree of deformation achieved on the first stand is 62%, that on the second stand achieved 54%, the third scaffold 47%, the fourth scaffold 35%, the fifth scaffold 28%, the sixth scaffold 17% and the seventh scaffold 11%.
• an early onset of cooling of the hot strip behind the last rolling stand of the finishing train is advantageous. According to a practical embodiment of the invention, it is therefore provided within a maximum of five seconds after leaving the last Rolling mill to start with the water cooling.
• the aim is to have the shortest possible break times, for example, of one second and less.
• the cooling of the hot strip can also be controlled so that it is cooled in two stages with water. For this purpose, first after the last rolling mill to a temperature close to the alpha / gamma transformation temperature can be cooled to then, preferably after to equalize the temperature over the tape thickness inserted cooling pause of one to five seconds, a further cooling by water until to perform the required reel temperature.
• the first phase of the cooling can take place as a so-called "compact cooling", in which the hot strip is cooled rapidly over a short conveyor line with high intensity and cooling rate (at least 200 K / s) while discharging large amounts of water, while in the second phase of the Water cooling is cooled over a longer conveyor line with reduced intensity in order to achieve the most uniform possible cooling over the belt cross-section.
• the reel temperature should preferably be in the temperature range of 500-780 0 C. Overlying temperatures would on the one hand lead to undesirably coarse precipitates and on the other hand worsen the treatability.
• a so-called short distance reel is used, which is located directly after the compact cooling zone.
• the inventive method in the production of the hot strip is preferably carried out so that the hot strip obtained sulfidic and / or nitridic precipitates having a mean particle diameter below 150 nm and an average density of at least 0.05 microns 2 is achieved .
• This type of hot strip has optimal conditions for the effective control of grain growth during the subsequent process steps.
• the hot strip thus produced can optionally be annealed after reeling or before cold rolling.
• the strip obtained is annealed recrystallizing and decarburizing.
• the cold rolled strip may be annealed during or after decarburization annealing in an NH 3 -containing atmosphere.
• N-containing antacid additives such as manganese nitride or chromium nitride
• a molten steel of composition 3, 15% Si, 0.047% C, 0.154% Mn, 0.006% S, 0.030% Al, 0.0080% N, 0.22% Cu and 0.06% Cr became after the secondary metallurgical treatment
• a ladle furnace and a vacuum system continuously poured into a 63 mm thick strand Before entering the in-line equalization furnace, the strand was split into thin slabs. After a residence time of 20 minutes in the equalizing furnace at 1150 ° C., the thin slabs were then descaled and hot-rolled in various ways:
• the first pass was made at 1090 0 C with a degree of deformation of 61% and the second pass at 1050 0 C with a degree of deformation of 50%.
• the rolling temperatures in the Stitches 3 to 7 were 1010 ° C., 980 ° C., 950 ° C., 930 ° C. and 900 ° C.
• the degrees of deformation were 17% and 11%, respectively.
• the following austenite proportions were obtained in Stitches 1 to 7: 30% / 25% / 20% / 18% / 15% / 14% and 12%.
• the cooling was identical for both hot rolling variants with the use of water spraying within 7 s after leaving the last mill stand and a coiler temperature of 650 0 C.
• samples for metallographic examinations were also produced by hot rolling after the second pass was stopped by rapid cooling.
• the strips were first annealed in a continuous furnace and then cold rolled in 1 step without intermediate annealing to a final thickness of 0.30 mm.
• annealing 2 different variants were chosen:
• the different magnetic results depending on the selected hot rolling conditions can be explained by the different microstructures.
• the high austenite contents in the individual forming passes form a finer and, above all, significantly more homogeneous structure (FIG. 1).

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• Chemical & Material Sciences (AREA)
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• Mechanical Engineering (AREA)
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• Crystallography & Structural Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Electromagnetism (AREA)
• Manufacturing Of Steel Electrode Plates (AREA)
• Soft Magnetic Materials (AREA)
• Metal Rolling (AREA)
• Continuous Casting (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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