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

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.