# US 6,296,719 B1 · Process for the production of grain oriented electrical steel strip having high magnetic characteristics, starting from thin slabs > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,296,719 B1 - Document ID: US6296719B1 - Status: Granted - Kind: B1 - Application number: 09/243,000 - Filed: 1999-02-26 - Granted: 2001-10-02 - Earliest claimed: 1996-08-30 - Assignees: Acciai Speciali Terni S.p.A. - Inventors: Stefano Fortunati; Stefano Cicale'; Giuseppe Abbruzzese - Web page: https://patentgrep.com/patent/US6296719B1 ## CPC - C22C 38/02: containing silicon - B22D 11/00: Continuous casting of metals, i.e. casting in indefinite lengths (metal drawing, metal extruding B21C) - C21D 8/1211: {Rapid solidification; Thin strip casting} - C21D 8/1222: {Hot rolling} - C21D 8/1255: {with diffusion of elements, e.g. decarburising, nitriding} - C21D 8/1261: {following hot rolling} - C21D 8/1272: {Final recrystallisation annealing} - C22C: ALLOYS (treatment of alloys C21D, C22F) - B22D: CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES (shaping of plastics or substances in a plastic state B29C; metallurgical processing, selection of substances to be added to metal C21, C22) - 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 (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) ## Abstract In the production of high permeability electrical steel, the control of condition of thin slab continuous casting allows to obtain advantageous solidification structures and precipitates. This, in turn, allows to decritize the process for controlling the grain dimensions and to add nitrogen to the cold rolled sheet, such as to immediately form aluminum nitride. ## Claims ### Claim 1 Process for the production of high characteristics silicon steel strip, in which a steel containing in weight percent, 2.5-5 Si, 0.002-0.075 C, 0.05-0.4 Mn, <0.015% S or <0.015% (S+(0.503×Se)), 0.010-0.045 Al, 0.003-0.0130 N, up to 0.2 Sn, 0.040-0.03 Cu, remaining being iron and minor impurities, is continuously cast, high temperature annealed, hot rolled, cold rolled in a single step or in a plurality of steps with intermediate annealing, the cold rolled strip so obtained is annealed to perform primary annealing and decarburization, coated with annealing separator and box annealed to obtain final secondary recrystallization treatment, said process being characterized by the combination in cooperation relationship of: (i) continuously casting a thin slab having a thickness of between 20 and 80 mm utilizing a) a casting speed of 3 to 5 m/min, b) a steel temperature during the casting of between 20 and 40° C., higher than the liquids temperature of steel, c) such a cooling speed as to obtain a complete solidification within 30 to 100 s, d) a mold oscillation amplitude of between 1 and 10 mm, and e) an oscillation frequency of between 200 and 400 cycles per minute; (ii) equalizing the thus obtained slabs at a temperature comprised between 1150 and 1300° C.; (iii) hot rolling the equalized slabs with a starting rolling temperature of between 1000 and 1200° C. and a finishing rolling temperature of between 850 and 1050° C.; (iv) continuously annealing the hot rolled strips for 30 to 300 s at a temperature no less than 850° C. and maintaining said temperature for 30 to 300 s, and then cooling them; (v) cold rolling the strip in a single step or in a plurality of steps with intermediate annealing, the last step being performed with a reduction ratio of at least 80%; (vi) continuously treating the cold rolled strip to obtain primary annealing and decarburization for a total time of 100 to 350s, at a temperature comprised between 850 and 1050° C. in a wet nitrogen/hydrogen atmosphere, with a ratio between partial pressures of water vapor and hydrogen according (pH2O/pH2) comprised between 0.3 and 0.7; (vii) coating the strip with annealing separator, coiling it and box annealing the coils in an atmosphere having the following compositions during the heating-up: hydrogen mixed with at least 30% vol nitrogen up to 900° C., hydrogen mixed with at least 40% vol nitrogen up to 1100-1200°, then, maintaining the coils at this temperature in pure hydrogen. ### Claim 2 (depends on 1) Process according to claim 1, in which the slab thickness is comprised between 50 and 60 mm. ### Claim 3 (depends on 1) Process according to claim 1, in which the steel carbon content is comprised between 20 and 100 ppm. ### Claim 4 (depends on 1) Process according to claim 1, in which the copper content is between 700 and 2000 ppm. ### Claim 5 (depends on 1) Process according to claim 1, in which the tin content is comprised between 1000 and 1700 ppm. ### Claim 6 (depends on 1) Process according to claim 1, in which during the continuous casting the casting parameters are so chosen as to obtain a number of equiaxed grains to the number of columnar grains of between 35 and 75% with equiaxed grain dimensions comprised between 0.7 and 2.5 mm. ### Claim 7 (depends on 6) Process according to claim 6, in which the number of equiaxed grains to the number of columnar grains is higher than 50%. ### Claim 8 (depends on 1) Process according to claim 1, in which after the cold rolled strip is continuously annealed, a nitriding treatment is performed at a temperature between 900 and 1050° C. in a nitriding atmosphere with a water vapor quantity of between 0.5 and 100 gm3. ### Claim 9 (depends on 1) Process according to claim 1, in which during the decarburization annealing the temperature is kept under 950° C., and the nitrogen content in the atmosphere of the subsequent box-annealing is chosen as to allow the diffusion into the strip of nitrogen up to 50 ppm. ### Claim 10 (depends on 1) Process according to claim 1, in which during the last cold rolling step the strip temperature is maintained at a value of at least 200° C. in at least two rolling passes. ### Claim 11 (depends on 1) Process according to claim 1, wherein in step (iv), cooling is carried out with boiling water.