Method for fabricating a substantially equiatomic FeCo-alloy cold-rolled strip or sheet, and magnetic part cut from same

1 . A method for manufacturing of a cold-rolled strip or sheet of substantially equiatomic FeCo-alloy, wherein:

a hot-rolled strip or sheet with a thickness comprised between 1.5 mm and 2.5 mm is prepared, the hot-rolled strip or sheet having a composition consisting of, in percentages by weight,

47.0%≤Co≤51.0%;

0%≤V+W≤3.0%;

0%≤Ta+Zr≤0.5%;

0%≤Nb≤0.5%;

0%≤B≤0.05%;

0%≤Si≤3.0%;

0%≤Cr≤3.0%;

0%≤Ni≤5.0%;

0%≤Mn≤2.0%;

0%≤C≤0.02%;

0%≤O≤0.03%;

0%≤N≤0.03%;

0%≤S≤0.005%;

0%≤P≤0.015;

0%≤Mo≤0.3%;

0%≤Cu≤0.5%;

0%≤Al≤0.01%;

0%≤Ti≤0.01%;

0%≤Ca+Mg≤0.05%;

0%≤rare earths≤500 ppm;

a remainder being iron and impurities resulting from melting;

said hot-rolled strip or sheet having a recrystallization start temperature Trc and a 100% recrystallized microstructure;

then a first cold-rolling step of the hot-rolled strip or sheet is carried out in one or a plurality of passes, with an overall reduction ratio TR1 of 70% to 90%, to bring the strip or sheet to a thickness e1 less than or equal to 1 mm;

an intermediate annealing R1 is then carried out as the strip or sheet passes through an annealing furnace, leading to a partial recrystallization of the strip or sheet, a degree of partial recrystallization being from 10% to 50%, and the temperature of the strip or sheet, in an effective zone of the annealing furnace having an effective length Lu, is comprised between Trc and 900° C., the strip or sheet remaining in the effective zone Lu for 15 s to 5 min at a temperature T such that 26° C. min≤(T−Trc)×Lu/V≤160° C. min, with T and Trc in ° C., Lu in meter, V being a travelling speed of the strip or sheet through the annealing furnace, in meter/min, and the strip or sheet being cooled at an exit of the annealing furnace at a rate of at least 600° C./hour, down to a temperature less than or equal to 200° C., thereby obtaining an annealed steel sheet or strip;

a second cold-rolling step of the annealed sheet or strip being then carried out, in one or a plurality of passes, with an overall reduction ratio of 60% to 80%, bringing the cold-rolled strip or sheet to a thickness of 0.05 to 0.25 mm;

the cold-rolled strip or sheet, having been subjected to the second cold-rolling then undergoing a static final annealing for at least 30 minutes, at a temperature of 750 to 900° C., in an atmosphere consisting of argon and/or nitrogen, in a reducing atmosphere or under vacuum, in order to obtain a complete recrystallization of the cold-rolled strip or sheet, followed by cooling at a rate of 100 to 500° C./hour.

2 . The method according to claim 1 , wherein (V+W)/2+ (Ta+Zr)/0.2≥0.8%.

3 . The method according to claim 1 wherein 0%≤Si≤0.1%.

4 . The method according to claim 1 wherein 0%≤Cr≤0.1%.

5 . The method according to claim 1 , wherein

before said first cold-rolling step, at least one additional cycle of additional cold-rolling and additional intermediate annealing is carried out to bring the cold-rolled strip or sheet to a thickness comprised between a thickness of the strip or sheet after hot-rolling and an input thickness of the first cold-rolling step,

during each additional intermediate annealing, a passage time of the strip or sheet in the effective zone of the furnace, between Trc and 900° C., leading to a total recrystallization of the strip or of the sheet,

each additional intermediate annealing Ri having a passage time in the effective zone of effective length Lu of the annealing furnace, where the temperature of the strip or sheet is between Trc and 900° C., of 10 s to 10 min,

followed by a cooling of the strip or of the sheet at the exit of the annealing furnace at a rate of at least 600° C./hour, down to a temperature less than or equal to 200° C., the strip or sheet having a 100% recrystallized microstructure after the last of said additional intermediate annealings.

6 . The method according to claim 5 wherein the additional intermediate annealing is a continuous annealing of the strip or sheet and the additional cold-rolling is performed in one or a plurality of passes, with an overall reduction rate of at least 40%.

7 . The method according to claim 1 wherein after hot-rolling and before the first cold-rolling step, the hot rolled strip or sheet undergoes hyper-quenching, by cooling the hot-rolled strip or sheet from a temperature comprised between 80° and 1000° C. at a rate of at least 600° C./s, down to room temperature.

8 . The method according to claim 7 , wherein said hyper-quenching takes place directly after the hot-rolling, without any intermediate reheating.

9 . The method according to claim 1 , wherein the atmospheres of the annealing furnace and in the static final annealing are reducing.

10 . The method according to claim 1 , wherein after the static final annealing, an additional continuous annealing of the cold-rolled strip or sheet having been subjected to the static final annealing is carried out, so that the alloy reaches at least 700° C. and at most 900° C., for at least 10 seconds and at most 1 h, followed by cooling at a rate of at least 1000° C./hour.

11 . A method for manufacturing of a cold-rolled strip or sheet of substantially equiatomic FeCo-alloy, wherein:

a hot-rolled strip or sheet with a thickness comprised between 1.5 and 2.5 mm is prepared, the hot-rolled strip or sheet having a composition consisting of, in percentages by weight

47.0%≤Co≤51.0%;

0%≤V+W≤3.0%;

0%≤Ta+Zr≤0.5%;

0%≤Nb≤0.5%;

0%≤B≤0.05%;

0%≤Si≤3.0%;

0%≤Cr≤3.0%;

0%≤Ni≤5.0%;

0%≤Mn≤2.0%;

0%≤C≤0.02%;

0%≤O≤0.03%;

0%≤N≤0.03%;

0%≤S≤0.005%;

0%≤P≤0.015;

0%≤Mo≤0.3%;

0%≤Cu≤0.5%;

0%≤Al≤0.01%;

0%≤Ti≤0.01%;

0%≤Ca+Mg≤0.05%;

0%≤rare earths≤500 ppm;

a remainder being iron and impurities resulting from melting;

said hot-rolled strip or sheet having a recrystallization start temperature Trc and a 100% recrystallized microstructure;

then a first cold-rolling step of the hot-rolled strip or sheet is carried out in one or a plurality of passes, with an overall reduction ratio TR1 of 70% to 90%, to bring the strip or sheet to a thickness e1 less than or equal to 1 mm;

an intermediate annealing R1 is then carried out as the strip or sheet passes through an annealing furnace, leading to a partial recrystallization of the strip or sheet, a degree of partial recrystallization being from 10% to 50%, and the temperature of the strip or sheet, in an effective zone of the annealing furnace having an effective length Lu, is comprised between Trc and 900° C., the strip or sheet remaining in the effective zone Lu for 15 s to 5 min at a temperature T such that 26° C. min≤(T−Trc)×Lu/V≤160° C. min, with T and Tre in ° C., Lu in meter, V being a travelling speed of the strip or sheet through the annealing furnace, in meter/min, and the strip or sheet being cooled at an exit of the annealing furnace at a rate of at least 600° C./hour, down to a temperature less than or equal to 200° C., to obtain an annealed steel sheet or strip;

a second cold-rolling step of the annealed sheet or strip being then carried out, in one or a plurality of passes, with an overall reduction ratio of 60% to 80%, bringing the cold-rolled strip or sheet to a thickness of 0.05 to 0.25 mm;

cutting the cold-rolled strip or sheet having been subjected to the second cold-rolling, thereby obtaining a part;

the part then undergoing a static final annealing for at least 30 minutes, at a temperature of 750 to 900° C., in an atmosphere consisting of argon and/or nitrogen, in a reducing atmosphere or under vacuum, in order to obtain a complete recrystallization of the part, followed by cooling at a rate of 100 to 500° C./hour.