A method of production of cold rolled Fe-Si steel sheet comprising the successive steps consisting in: - melting a steel composition that contains in weight percentage: 2.8 ≤ Si ≤ 4 0.4 ≤ Cu ≤ 0.6, 0.05 ≤ Mn ≤ 0.4, 0.001 ≤ Al ≤ 0.04, 0.025 ≤ C ≤ 0.05 0.005 ≤ N ≤ 0.02, 0.005 ≤ Sn ≤ 0.03 S < 0.015 And optionally Ti, Nb, V or B in a cumulated amount below 0.02, the following relationships being respected: Mn / Sn ≤ 40, 2.0 ≤ C / N ≤ 5.0 Al / N ≥ 1.20 and the balance being Fe and other inevitable impurities - and producing a slab having thickness not higher than 80 millimeters, so that, after the solidification, said slab surface does not cool below 850°C for longer than 5 minutes, - reheating of said slab up to a temperature between 1080°C to 1200°C for 20 minutes at least, - subsequently, hot rolling said slab with a first thickness reduction taking place while said slab temperature is above 1060°C and last thickness reduction taking place above a finish rolling temperature of 950°C in order to obtain a hot band, - cooling down said hot band to a temperature ranging between 500°C and 600°C within less than 10 seconds, then - coiling the hot band wherein hot band Fe-Si contains less than 60% of acid soluble Al in precipitated form, said precipitate does not contain AlN precipitates in the size range between 5nm and 150nm at all then, - cleaning its surface, then - carrying out a first cold rolling step of the hot band with a cold rolling ratio of at least 60% without having previously annealed said hot band, then - performing a primary recrystallization annealing step at a temperature T 1 between 780°C and 920°C, the steel being held at T 1 for a minimum time t 1 of 2 minutes in an atmosphere composed of a mixture of hydrogen, nitrogen and water vapor, then cooling to room temperature so as to obtain a steel carbon content below 0.004% and a primary average grain size below 16 micrometers after the cooling, then - carrying out a second cold rolling step with a cold rolling ratio of at least 50% to, obtain the cold rolled steel sheet final thickness, then - depositing a layer of an isolating separator on the surface of said cold rolled steel sheet, then - the isolated cold rolled steel sheet goes through a secondary annealing in an atmosphere containing hydrogen and nitrogen, the steel heating rate V1 being below 15°C per hour between 600°C and 1150°C, the sheet temperature being held at a minimum temperature T 2 of 1150°C for a minimum time t 2 of 600 minutes, the annealing total time being above 120 hours so as reduce the content for each of sulfur and nitrogen below 0.001 % and to have a secondary average grain size below 15 millimeters, then - Performing a slow cooling down to room temperature. - melting a steel composition that contains in weight percentage: 2.8 ≤ Si ≤ 4 0.4 ≤ Cu ≤ 0.6, 0.05 ≤ Mn ≤ 0.4, 0.001 ≤ Al ≤ 0.04, 0.025 ≤ C ≤ 0.05 0.005 ≤ N ≤ 0.02, 0.005 ≤ Sn ≤ 0.03 S < 0.015 And optionally Ti, Nb, V or B in a cumulated amount below 0.02, the following relationships being respected: Mn / Sn ≤ 40, 2.0 ≤ C / N ≤ 5.0 Al / N ≥ 1.20 and the balance being Fe and other inevitable impurities - and producing a slab having thickness not higher than 80 millimeters, so that, after the solidification, said slab surface does not cool below 850°C for longer than 5 minutes, - reheating of said slab up to a temperature between 1080°C to 1200°C for 20 minutes at least, - subsequently, hot rolling said slab with a first thickness reduction taking place while said slab temperature is above 1060°C and last thickness reduction taking place above a finish rolling temperature of 950°C in order to obtain a hot band, - cooling down said hot band to a temperature ranging between 500°C and 600°C within less than 10 seconds, then - coiling the hot band wherein hot band Fe-Si contains less than 60% of acid soluble Al in precipitated form, said precipitate does not contain AlN precipitates in the size range between 5nm and 150nm at all then, - cleaning its surface, then - carrying out a first cold rolling step of the hot band with a cold rolling ratio of at least 60% without having previously annealed said hot band, then - performing a primary recrystallization annealing step at a temperature T 1 between 780°C and 920°C, the steel being held at T 1 for a minimum time t 1 of 2 minutes in an atmosphere composed of a mixture of hydrogen, nitrogen and water vapor, then cooling to room temperature so as to obtain a steel carbon content below 0.004% and a primary average grain size below 16 micrometers after the cooling, then - carrying out a second cold rolling step with a cold rolling ratio of at least 50% to, obtain the cold rolled steel sheet final thickness, then - depositing a layer of an isolating separator on the surface of said cold rolled steel sheet, then - the isolated cold rolled steel sheet goes through a secondary annealing in an atmosphere containing hydrogen and nitrogen, the steel heating rate V1 being below 15°C per hour between 600°C and 1150°C, the sheet temperature being held at a minimum temperature T 2 of 1150°C for a minimum time t 2 of 600 minutes, the annealing total time being above 120 hours so as reduce the content for each of sulfur and nitrogen below 0.001 % and to have a secondary average grain size below 15 millimeters, then - Performing a slow cooling down to room temperature.