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US 6,471,787 B2Granted
Process for the production of oriented-grain electrical steel sheet with high magnetic characteristics
AssigneeAcciai Speciali Terni S.p.A.
InventorsStefano Cicale', Stefano Fortunati, Giuseppe Abbruzzese
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Abstract
A process for the production of oriented-grain electrical steel sheet with high magnetic characteristics, and more precisely a process in which the slab obtained from continuous casting is continuously nitrided by a reaction between aluminium and nitrogen is described. Amount, size and distribution of precipitates are controlled, enabling a high-temperature continuous heat treatment during which the primary-recrystallization and a high-temperature nitriding are realized.
Claims14
In a process for production of silicon steel sheet having the high magnetic characteristics, in which said silicon steel consists of from 2.5% to 4.5% by weight of silicon;
- from 150 to 750 ppm, of C;
- from 300 to 4000 ppm, of Mn;
- less than 120 ppm of S;
- from 100 to 400 ppm of Alsol;
- from 30 to 130 ppm, of N;
- and less than 50 ppm, of Ti;
- the remainder consisting of iron and minor impurities, undergoes continuous casting to form slabs, high-temperature annealing, hot-rolling to obtain a hot-rolled strip, coiling the hot-rolled strip and allowing said hot-rolled strip to cool, heat-treating, pickling, and cold rolling in a single stage or in more than one stage, the cold rolled-strip thus obtained being continuously annealed to carry out primary re-crystallization and decarburization, then coated with annealing separator, and box-annealed for a secondary-recrystallization final treatment, the improvement which comprises the combination of the following steps:
- carrying out on the continuously cast slabs a high temperature annealing comprising an equalization heat treatment at a temperature of between 1200° C. and 1320° C.;
- hot rolling the slabs thus obtained, and coiling the resultant hot rolled strip at a temperature of less than 700° C.;
- heating the hot rolled strip to a temperature of between 1000° C. and 1150° C., with subsequent cooling down to and stopping at a temperature of between 800° C. and 950° C., followed by quenching;
- carrying out a continuous decarburization annealing of the cold-rolled strip for a total time of between 50 and 350 sec, at a temperature of between 800° C. and 950° C. in a wet nitrogen-hydrogen atmosphere, with pH2O/pH2 ranging between 0.3 and 0.7;
- carrying out a continuous nitriding annealing at a temperature of between 850° C. and 1050° C., for a period of time of between 15 and 120 sec, feeding into the furnace a nitrogen-hydrogen based gas containing NH3 in quantities of between 1 and 35 standard liters per kg of strip, with a water-vapor content of between 0.5 and 100 g/m3 wherein the box annealing for secondary-recrystallization is carried out for 2 to 20 hours at a temperature of between 700° C. and 1200° C.
9 more elements
In a process for the production of silicon steel sheet having high magnetic characteristics, in which said silicon steel containing from 2.5% to 4.5% by weight of silicon;
- from 250 to 500 ppm, of C;
- from 300 to 4000 ppm, of Mn;
- from 50 to 70 ppm, of S;
- from 200 to 350 ppm, of Alsol;
- from 60 to 100 ppm, of N;
- and less than 30 ppm, of Ti;
- the remainder consisting of iron and mirror impurities, undergoes continuous casting to form slabs, high-temperature annealing to obtain a hot-rolled strip, cooling the hot-rolled strip and allowing said hot-rolled strip to cool, uncoiling the hot rolled strip, heat-treating, pickling, hot-rolling, and cold rolling in a single stage or in more than one stage, the cold rolled-strip thus obtained being continuously annealed to carry out primary re-crystallization and decarburization, then coated with annealing separator, and box-annealed for a secondary-recrystallization final treatment, wherein the improvement comprises the following steps in a cooperative relationship:
- carrying out on the continuously cast slabs a high temperature annealing comprising an equalization heat treatment at a temperature of between 1200° C. and 1320° C.;
- hot rolling the slabs thus obtained, and coiling the resultant hot rolled strip at a temperature of less than 700° C.;
- heating said hot-rolled strip to a temperature of between 1000° C. and 1150° C., with subsequent cooling down to and stopping at a temperature of between 800° C. and 950° C., followed by quenching;
- carrying out a continuous decarburization annealing of the cold-rolled strip for a total time of between 50 and 350 sec., at a temperature of between 800° C. and 950° C. in a wet nitrogen-hydrogen atmosphere, with pH2O/pH2 ranging between 0.3 and 0.7;
- carrying out a continuous decarburization annealing of the cold-rolled strip for a total time of between 50 and 350 sec., at a temperature of between 800° C. and 950° C. in a wet nitrogen-hydrogen atmosphere, with pH2O/pH2 ranging between 0.3 and 0.7;
- carrying out a continuous nitriding annealing at a temperature of between 850° C. and 1050° C., for a period of time of between 15 and 120 sec., feeding into the furnace a nitrogen-hydrogen based gas containing NH3 in quantitites of between 1 and 35 standard liters per kg of strip, with a water vapor content of between 0.5 and 100 g/M3 wherein the box annealing for secondary-recrystallization is carried out for 2 to 20 hours at a temperature of between 700° C. and 1200° C.
10 more elements
Dependencies are inferred from the claim text.