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 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
  • C21D8/1205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular fabrication or treatment of ingot or slab
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/008—Heat treatment of ferrous alloys containing Si
• • 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
  • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
  • C21D8/1233—Cold rolling
• • 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
  • C21D8/1272—Final recrystallisation annealing
• • 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
  • 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
  • C21D8/1227—Warm 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
  • C21D8/1266—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 between cold rolling steps
• • 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

Definitions

• the present invention relates to a method of manufacturing an electric steel sheet with oriented grains for the production in particular of magnetic circuits of transformers comprising, successively: a continuous casting of steel in the form of a slab or a strip of steel containing in particular in its composition less than 0.1% carbon, from 0 2.5 to 4% silicon and at least the elements aluminum, nitrogen, manganese, sulfur, copper, intended to form compounds which inhibit normal growth ,
• the texture of a grain-oriented electric steel sheet is a so-called Goss texture symbolized by the MILLER indices, ⁇ 1 10 ⁇ ⁇ 001>, according to which the axis ⁇ 001>, which is an axis of easy magnetization , is substantially parallel to the rolling direction and the plane ⁇ 1 10 ⁇ is a plane 0 substantially parallel to the surface of the sheet.
• This texture gives the grain oriented electrical steel sheet good magnetic properties in the rolling direction which is substantially the direction of easy magnetization.
• Measurements of the B800 induction acquired under a magnetic field of 800 A / m and of the energy losses W (1, 7/50) of the steel sheet for a working induction 5 of 1.7 Tesia (T ) at a frequency of 50 Hertz are used in practice to evaluate the magnetic quality of samples taken parallel to the direction of rolling of the sheet.
• the so-called conventional sheets are characterized by a B800 induction of less than 1.86 Tesia; they are obtained by a process which notably comprises two cold rolling operations separated by an intermediate annealing, the reduction rate of the second rolling being generally less than 70%.
• the so-called high permeability sheets are characterized by a B800 induction greater than 1.88 Tesia; they are obtained by a process which notably comprises a single cold rolling operation or two cold rolling operations with intermediate annealing, the reduction rate of cold rolling in one operation or of the second cold rolling generally being greater than 80% .
• the conventional sheet steel contains, before hot rolling, manganese, sulfur and copper.
• High permeability sheet steel contains aluminum, manganese, copper, sulfur and nitrogen before hot rolling.
• the heating of the steel slab before hot rolling is carried out at a temperature above 1300 ° C., of the order of 1350 to 1400 ° C. to completely re-dissolve the precipitates AIN, MnS and CuS alone or in combination.
• Their size in the raw casting state generally greater than 1 micrometer, is too coarse to allow the development of secondary recrystallization.
• the compounds AIN, MnS and CuS re-precipitate alone or in combination in the form of fine particles, of average size less than 150 nanometers (nm) during hot rolling and annealing before cold rolling carried out in a single operation.
• the main drawback of reheating the slab or strip of grain-oriented steel to a temperature above 1300 ° C. is the formation of liquid oxides which necessitates the periodic shutdown of the furnace specially adapted for this production in order to scouring. To obtain a magnetic quality equivalent to that of products from the reheating of slabs in the temperature range 1350-
• nitriding is used which has as its object the formation of fine precipitates of silicon nitride and aluminum (Si, Al) N before the start of secondary recrystallization.
• Nitriding is carried out either by an additional heat treatment in a gaseous atmosphere containing ammonia NH3, or by addition of a compound containing nitrogen, such as manganese nitrides MnN, ferro-manganese FeMnN, chromium CrN, to the annealing separator consisting mainly of MgO magnesia.
• the slabs generally contain aluminum, and optionally titanium Ti, chromium Cr, boron B, elements known for their ability to form nitrides TiN, CrN, BN. Since this process aims at precipitating fine particles (Si, Al) N at the stage of secondary recrystallization annealing, the previous presence of fine precipitates MnS and AIN is not necessary. Consequently, the re-solution of the coarse particles MnS and AIN is incomplete during the reheating of the slabs, preceding the hot rolling. In addition, an incomplete re-solution of the aluminum is essential for the precipitation of the silicon nitride.
• German patents DE 43 1 1 1 51 and European EP 0 619 376 describe a process which comprises: - A reheating of the slabs to a temperature which is lower than the solubility temperature of the manganese sulphide and which is higher than the solubility temperature copper sulfide.
• the copper sulfide precipitates are dissolved.
• the manganese sulfide precipitates are not redissolved and, being in the form of coarse particles, no longer play the role of inhibitor.
• the strip is decarbonized so that the oxygen content of the oxide film formed is less than 800 10 ⁇ 4 %, the composition also contains up to 0.15% tin,
• the product resulting from the multiplication of the nitrogen content by the aluminum content is less than 240.10 "6
• the steel is hot rolled so as to precipitate the nitrogen in the form of fine particles containing in particular nitrogen and aluminum with an average diameter of less than 100 nanometers, the percentage of precipitated nitrogen being less than 40%
• the hot rolled steel is annealed so as to precipitate the nitrogen in the form of fine particles containing in particular nitrogen and aluminum with an average diameter of less than 100 nanometers, the percentage of nitrogen precipitated being greater than 60%,
• the steel is hot rolled so as to precipitate the sulfur in the form of particles whose average diameter is less than 100 nanometers, - after annealing of the hot rolled sheet at a temperature between 850 ° C and 1150 ° C for 1 to 10 minutes and cooling, at a speed greater than 10 ° C per second from 800 ° C, cold rolling to a final thickness of less than 0.5 mm is carried out, in a single operation comprising several passes rolling, with an overall reduction rate greater than 70%, the temperature of the sheet being between 100 ° C and 300 ° C for at least one rolling pass,
• - cold rolling to a final thickness of less than 0.5 mm, is carried out in two operations with intermediate annealing, at a temperature between 850 ° C and 1150 ° C for 1 to 10 minutes, followed by a cooling, at a speed greater than 10 ° C per second from 800 ° C, the reduction rate of the second cold rolling being greater than 40%, the temperature of the sheet being between 100 ° C and 300 ° C for at least one cold rolling pass when the reduction rate of the second frpid rolling is greater than 70%,
• the sheet is subjected to annealing at a temperature between 850 ° C and 1150 ° C for 1 to 10 minutes, in particular if the final thickness of the sheet is less than 0, 27 mm, - magnesia contains, in addition to optional additions of titanium dioxide, boron or a boron compound, at least one sulfur compound and / or a sulfur and nitrogen compound and / or a compound of antimony taken alone or in combination.
• Magnesia contains, in addition to optional additions of titanium dioxide, boron or a compound containing boron, sulfur or one or more sulfur or nitrogen compounds chosen from magnesium sulfate, manganese sulfate, urea, sodium thiosulfate.
• Magnesia contains, in addition to optional additions of titanium dioxide, boron or a boron compound, at least one sulfur and nitrogen compound chosen from ammonium sulfate, amidosulfuric acid (sulphamic acid), thiosulfate ammonium.
• - magnesia contains, in addition to optional additions of titanium dioxide, boron or a boron compound, antimony chloride,
• FIG. 1 is a curve showing the loss of mass as a function of the heating temperature of the slab and illustrating the formation of fusible oxides above 1300 ° C.
• Figure 2 shows, after hot rolling, the relationship between the average diameter of the precipitates and the percentage of sulfur in the steel.
• FIG. 3 shows, after decarburization, the precipitate densities as a function of the stopping temperature of the secondary recrystallization annealing.
• FIG. 4 shows the magnetic characteristics obtained according to the invention, in the case of a cold rolling operation comprising several passes, the final thickness being 0.285 mm and corresponding to an overall reduction rate of 87%.
• FIGS. 5A and 5B show the magnetic characteristics, obtained according to the invention, as a function of the mass oxygen content of the surface film formed during the decarburization of a sheet of thickness 0.285 mm, having undergone cold rolling with a rate 87% reduction, 1% sulfur in the form of amidosulfuric acid having been added to the magnesia deposited on the sheet before the annealing of secondary recrystallization.
• the present invention relates to the use of a steel of determined composition by weight as follows: carbon comprised between 0.02 and 0.09%, silicon comprised between 2.5 and 4%, copper comprised between 0.06 and 0.50% and a selection, manganese between 0.027 and 0.17%, sulfur between 0.007 and 0.020%, aluminum between 0.010 and
• the contents of manganese, sulfur, aluminum and nitrogen are chosen in very narrow ranges, which allows the almost complete solution and sufficient quantity of the precipitates AIN, MnS and CuS taken alone or in combination, during the reheating of the slabs, before hot rolling, at a temperature equal to or less than 1300 ° C. which avoids the surface formation of fusible oxides.
• the precipitates containing sulfur and or nitrogen are mainly re-dissolved during the reheating of the slabs as a result of the adaptation of the chemical composition to the lower reheating temperature.
• the main inhibitor is aluminum nitride, which does not precipitate much during hot rolling and essentially during the annealing of hot-rolled sheet in the form of fine particles with an average diameter of less than 100 nanometers.
• Manganese sulfide is a complementary inhibitor. Copper in particular has a refining effect of the size of these AIN and MnS precipitates with which it can be associated.
• the CuS precipitates which trap part of the sulfur in the steel at the hot rolling stage contributes to the reduction in the average diameter of the precipitates as shown in FIG. 2.
• the grain-oriented steel sheets according to the invention are produced from the following successive stages:
• an optional short-term annealing from 1 to 10 minutes, between 850 ° C and 1150 ° C before the first cold rolling is likely to stabilize the secondary recrystallization in particular if the final thickness of the sheet is less than 0.27 mm; the cooling rate may be slower.
• - primary recrystallization and decarburization annealing in a humid atmosphere containing hydrogen and nitrogen at the final thickness
• the oriented grain steel according to the invention having undergone the manufacturing steps described above, contains from 0.02 to 0.09% of carbon, from 2.5 to 4% of silicon, from 0.027 to 0.17 % manganese, 0.007 to 0.020% sulfur, 0.010 to 0.030% aluminum, 0.004 to 0.01 2% nitrogen, 0.06% to 0.50% copper, and optionally up to 0.15% tin, the rest being iron and impurities.
• the product resulting from the multiplication of the sulfur content by the manganese content is less than or equal to 1 60.10-5; (% S) x (% Mn) ⁇ 1 60.10- 5
• the product resulting from the multiplication of the nitrogen content by the aluminum content is less than 240.10 "6: (% N) x (% Al) ⁇ 240.10- 6
• the percentage of nitrogen precipitated after hot rolling, in the form of fine particles with an average diameter of less than 100 nanometers, is less than 40%.
• the percentage of nitrogen precipitated, after hot rolling and annealing, in the form of fine particles with an average diameter of less than 100 nanometers, is greater than 60%.
• the magnesia used as a separator during the annealing of secondary recrystallization and of purification at high temperature may contain, alone or as a mixture, sulfur or one or more sulfur or nitrogen compounds chosen from magnesium sulfate and / or manganese sulfate and / or sodium thiosulfate, and / or urea, one or more sulfur and nitrogen compounds chosen from, amidosulfuric acid, (sulphamic acid) and / or ammonium sulfate and / or ammonium thiosulfate, antimony chloride, boron or a compound of boron and titanium dioxide.
• FIG. 2 shows, after hot rolling, the relation existing between the average diameter of the precipitates and the percentage of sulfur in the steel, in the case of almost complete re-solution of all the precipitates during reheating slab.
• the sulfur content according to the present invention is limited to 0.020%.
• the fine MnS precipitates playing an active role as secondary inhibitor during the secondary recrystallization annealing, the sulfur content must be at least equal to 0.007% to obtain a sufficient quantity of these precipitates.
• the manganese content according to the present invention must be greater than 0.027% in order to obtain the precipitation of a sufficient quantity of fine MnS precipitates exerting an inhibiting effect and to have an availability of free manganese in the case of supply of sulfur by the d-channel. additive to magnesia for strengthening the inhibitory power of MnS precipitates.
• compliance with the condition [% S] x [% Mn] ⁇ 160.10 * 5 promotes the presence of fine MnS precipitates in the slabs and their redissolution between 1200 ° C and 1300 ° C before hot rolling .
• the nitrogen content must be greater than 0.004% in order to obtain sufficient precipitation of fine precipitates AIN, main inhibitor, during the annealing of the hot-rolled sheet.
• the nitrogen content is limited to 0.012% to avoid the formation of blistering on the surface of the steel.
• the condition (% N) x (% Al) ⁇ 240.10 ' G allows almost complete dissolution of the AIN precipitates when reheating the slabs between 1200 ° C and 1300 ° C before hot rolling.
• the aluminum content must be equal to or greater than 0.010% on the one hand, so that the quantity of precipitates AIN formed during the annealing of the hot-rolled sheet is sufficient, AIN being the main inhibitor and on the other hand, to have a free aluminum availability, in the case of nitrogen supply via the magnesia additive channel with a view to strengthening the inhibitory power of the AIN precipitates.
• the aluminum content is less than 0.030% to avoid precipitation of coarse AIN particles during the final phase of hot rolling.
• the steel can contain up to 0.15% tin which exerts a beneficial effect on inhibition.
• the density of the inhibitory precipitates containing either sulfur and manganese or nitrogen and aluminum may prove to be insufficient to obtain complete secondary recrystallization and homogeneity of the magnetic quality.
• it is preferably added to the magnesia one or more compounds containing sulfur and or nitrogen or antimony which allow the formation of a complement of inhibitors, either based on sulfur and manganese, either based on nitrogen and aluminum, or based on antimony during the temperature rise preceding the start of the secondary recrystallization.
• the present invention is illustrated from the following observations and examples, Table 1 giving the chemical composition of the steels tested.
• Steels 2 to 5 and 7 to 9 are steels described by the present invention.
• the content of phosphorus, a residual element, according to the present invention, is less than 0.01 5%.
• Steel No. 1 is a reference steel containing 0.021% sulfur and 0.030% aluminum (Steel No. 1, Table 1), a slab of which has been reheated to 1400 ° C before hot rolling, so as to dissolve the majority of AIN, MnS, CuS precipitates of coarse size.
• the cold rolling was carried out according to the invention, in a single operation after annealing the hot rolled sheet at 1 1 20 ° C.
• the hot finish rolling in 7 passes up to the thickness of 2.3 mm, the temperature of the start of the hot finish rolling being between 1070 ° C. and 1000 ° C., the final temperature of the hot rolling being between 965 ° C and 91 5 ° C,
• Milk of magnesia consists of 150 g of MgO per liter of water. To this milk are added the additives.
• the percentage of an element of magnesia additive (Ti, B, S, Sb, N) is the quotient of the mass of the element by the mass of dry magnesia multiplied by 100.
• the coating is composed of silica, aluminum phosphate and chromic acid
• the steel No. 2 was cold rolled to the intermediate thickness of 0.74 mm, underwent annealing for 90 seconds at 1050 ° C. followed by cooling, very rapid from 800 ° C. with a passage time between 700 ° C. and 300 ° C. of less than 15 seconds, and was then rolled to the final thickness of 0.285 mm, which corresponds to a rate of second cold reduction of 61%.
• the magnetic characteristics obtained are as follows:
• Example 2 After reheating the slab to 1280 ° C, hot rolling and coiling to 530 ° C, annealing the hot rolled sheet at 950 ° C for 1 60 seconds, cooling, very fast from 800 ° C, cold rolling to the final thickness of 0.285 mm, which corresponds to a cold reduction rate of 87%, and further processing as indicated previously, the magnetic characteristics obtained for steel No. 3 are as follows:
• the annealing separator consisted of magnesia containing 0.080% boron and 1.2% of the titanium element. in the form of titanium dioxide Ti ⁇ 2- Example 3
• Example 6 Under the conditions of Example 2, 0.026% of the antimony element in the form of antimony chloride is added to the magnesia.
• the magnetic characteristics obtained for steel No. 2 are as follows:
• Example 7 Under the conditions of Example 2 with an annealing temperature of the hot-rolled strip of 1050 ° C., 0.93% of nitrogen in the urea state is added to the magnesia.
• Example 8 Under the conditions of Example 2, but with an annealing temperature of the hot-rolled strip of 1080 ° C. and a magnesia containing 3.6% of the titanium element in the state of titanium dioxide, 0 , 10% boron and free from sulfur and / or nitrogen additives and antimony chloride, the characteristics obtained for steel No. 8 are as follows:
• Example 2 Under the conditions of Example 2, but with a heating temperature of the slab of 1240 ° C., an annealing temperature of the hot-rolled strip equal to 1050 ° C., and a magnesia containing 1.5% of sulfur at the state of amidosulfuric acid, the magnetic characteristics obtained for steel No. 9 were as follows:
• magnesium sulfate, manganese, sodium thiosulfate is added to magnesia.
• magnesia of a nitrogenous compound makes it possible to introduce nitrogen into the steel which reinforces the inhibition by the precipitates containing nitrogen and aluminum.
• magnesia of a sulfur and nitrogen compound (ammonium thiosulfate, amidosulfuric acid which contains both 33% sulfur and 14% nitrogen) allows sulfur to be introduced into the steel and nitrogen to reinforce the inhibition by the precipitates containing, on the one hand, manganese and sulfur and, on the other hand, nitrogen and aluminum.
• the beneficial effect of nitrogen associated with sulfur is illustrated by the fact that the percentage of sulfur used in example 5 is lower than that used in example 4.
• ammonium sulfate to magnesia also allows a simultaneous supply of sulfur and nitrogen.
• antimony chloride to magnesia allows the introduction into the steel of the antimony element, which by segregating at the grain boundaries, acts as an inhibitor.
• the addition of a water-soluble sulfur compound is preferred to the possible addition of insoluble elemental sulfur since the dispersion in milk of magnesia is more homogeneous.
• the addition, to magnesia, of compounds containing sulfur, nitrogen and antimony promotes the obtaining of a homogeneous magnetic quality over the length of the strip of coiled sheet.
• Table 2 shows that according to the invention, the percentage of nitrogen precipitated from the hot-rolled sheet is less than 40%. Lowering the winding temperature makes it possible to significantly reduce the percentage of nitrogen precipitated, up to less than 5% in the case of steel No. 3 reheated to 1280 ° C, hot rolled and coiled to 530 ° C. At this winding temperature, the percentage of precipitated nitrogen remains very low when the slab reheating temperature decreases from 1,280 ° C to 1,240 ° C, the usual reheating temperature for carbon steels.
• the amount of nitrogen combined with aluminum was determined from the assay of precipitated aluminum.
• Table No. 3 shows that according to the invention, the percentage of precipitated nitrogen is greater than 60% after annealing the hot-rolled sheet at 950 ° C.
• Table No. 4 shows that, according to the invention, the average diameter of the precipitates containing nitrogen and aluminum, obtained by annealing 160 seconds from the hot-rolled sheet of steel No. 2, wound at 530 ° C, is less than 50 nanometers in a wide range of annealing temperature.
• the precipitates containing nitrogen and aluminum can therefore play an active role as an inhibitor.
• the effect of copper has been analyzed in the context of the present invention.
• Table No. 5 gives the average diameter and the density of the precipitates after reheating to 1280 ° C of the steel slab No. 2 at 0.15% copper, hot rolling to the thickness 2.3 mm and winding at 640 ° C.
• the characteristics of the precipitates of the hot-rolled sheet to the thickness 2.3 mm and wound at 640 ° C of the reference steel No. 1 with 0.09% copper are presented. It appears from Table 5 that the increase in the copper content results in an increase in the density of the CuS and AINCuS precipitates and a decrease in their mean diameter.
• the combinations of precipitated compounds are designated by the nature of the constituent elements without taking account of the proportions.
• FIG. 3 indicates the evolution of the density of the CuS and MnCuS precipitates after decarburization and during the secondary recrystallization annealing of steel No. 6 which does not contain aluminum, a composition chosen in order to facilitate the counting of the precipitates by transmission electron microscopy.
• This steel the slabs of which were reheated to 1400 ° C, underwent two cold rolling operations with intermediate annealing at 950 ° C, the reduction rate of the second cold rolling being 60%.
• the fine CuS precipitates gradually dissolve before the secondary recrystallization which occurs around 950 ° C, the release of sulfur accompanied by a fine precipitation of MnS particles.
• the particles identified under the electron microscope are MnCuS because copper precipitates on the MnS particles during cooling. According to the present invention, the fine CuS particles do not play a decisive inhibitory role for the development of secondary recrystallization.
• the percentage of CuS precipitates with an average diameter of less than 100 nm is less than 3% of the total population, after annealing of hot rolled sheet.
• MnS precipitates formed after decarburization and before secondary recrystallization which reinforce the inhibition by the precipitates containing nitrogen and aluminum.
• the copper content must be greater than 0.06% to obtain fine precipitation at the hot rolled and hot rolled and annealed stages.
• the increase in the copper content promotes refinement of precipitation.
• the copper content is limited to 0.50% to avoid the problems of pickling the sheet obtained.
• the method of the present invention described for continuous casting slabs of thickness between 150 and 300 mm can be applied to thinner slabs, of thickness between approximately 15 and 100 mm.
• the process of the present invention can also be applied to thin strips obtained by casting liquid steel between two rollers, thicker than 2 mm, the strips being heated between 1200 ° C and 1300 ° C, before undergoing hot rolling.
• the number of passes of the preliminary hot rolling and the finishing hot rolling is a function of the thickness of the continuously cast product and of the thickness referred to in the hot rolled state. If the thickness of the continuously cast product is sufficiently small, the preliminary hot rolling can be omitted.
• the total duration of the heating cycle for the continuously cast product is a function of its thickness. The smaller this thickness, the faster the reheating temperature is reached at heart.
• Table 2 Percentage of nitrogen precipitated after hot rolling Reference Temperature temperature of% N precipitated Steel reheating of the slabs winding (° C) (° C)
• Table 3 Percentage of nitrogen precipitated after annealing the hot rolled sheet.
• Table No. 4 Influence of the annealing temperature of hot-rolled sheet on the average diameter, density and nature of the precipitates containing aluminum.

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Citations (7)

• 1995
  • 1995-03-14 FR FR9502916A patent/FR2731713B1/fr not_active Expired - Fee Related
• 1996
  • 1996-03-08 CN CN96190188A patent/CN1148411A/zh active Pending
  • 1996-03-08 AT AT96400486T patent/ATE206171T1/de not_active IP Right Cessation
  • 1996-03-08 JP JP8527325A patent/JPH10500454A/ja active Pending
  • 1996-03-08 BR BR9605937A patent/BR9605937A/pt not_active Application Discontinuation
  • 1996-03-08 DE DE69615429T patent/DE69615429T2/de not_active Expired - Lifetime
  • 1996-03-08 ES ES96400486T patent/ES2161988T3/es not_active Expired - Lifetime
  • 1996-03-08 WO PCT/FR1996/000364 patent/WO1996028576A1/fr active IP Right Grant
  • 1996-03-08 PL PL96317155A patent/PL317155A1/xx unknown
  • 1996-03-08 CZ CZ963684A patent/CZ284873B6/cs not_active IP Right Cessation
  • 1996-03-08 PT PT96400486T patent/PT732413E/pt unknown
  • 1996-03-08 EP EP96400486A patent/EP0732413B1/fr not_active Expired - Lifetime
  • 1996-11-11 KR KR1019960706379A patent/KR970702932A/ko not_active Application Discontinuation

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