Process for manufacturing a strip made of an Fe-Ni alloy

Process for manufacturing a strip made of a γ′ and/or γ″ structural hardenable Fe—Ni alloy, the thermal expansion coefficient between 20° C. and 150° C. of which is less than 7×10−6/K, in which:

• a hot strip is manufactured either by hot rolling a semi-finished product or by direct casting of a thin strip which is optionally lightly hot-rolled, and the hot strip is subjected to a softening annealing operation consisting of a soak between 950° C. and 1200° C. followed by rapid cooling and optionally to a pickling operation, in order to obtain a softened strip;
• a cold-worked strip is manufactured by cold rolling the said softened strip, with a reduction ratio of greater than 5%;
• and
• the cold-worked strip is subjected to a recrystallization annealing operation in an inert or reducing atmosphere, carried out either on the run at a temperature between 900° C. and 1200° C. with a residence time of between 30 s and 5 mm, or statically with a soak at a temperature of between 900° C. and 1050° C. for a time of between 15 mm to 5 h, followed by cooling down to a temperature below 500° C. at a cooling rate sufficient to prevent the formation of hardening precipitates,
• wherein the cooling time between each of the softening and the recrystallization annealing temperature and 500° C. is less than 5 minutes.

Process for manufacturing a strip made of a γ′ and/or γ″ structural hardenable Fe—Ni alloy, the thermal expansion coefficient between 20° C and 150° C. of which is less than 7×10−6/K, in which:

• a hot strip is manufactured either by hot rolling a semi-finished product or by direct casting of a thin strip which is optionally lightly hot-rolled, and the hot strip is subjected to a softening annealing operation consisting of a soak between 950° C. and 1200° C. followed by rapid cooling and optionally to a pickling operation, in order to obtain a softened strip;
• a cold-worked strip is manufactured by cold rolling the said softened strip, with a reduction ratio of greater than 5%;
• and
• the cold-worked strip is subjected to a recrystallization annealing operation in an inert or reducing atmosphere, carried out either on the run at a temperature between 900° C. and 1200° C. with a residence time of between 30 s and 5 mm, or statically with a soak at a temperature of between 900° C. and 1050° C. for a time of between 15 mm to 5 h, followed by cooling down to a temperature below 500° C. at a cooling rate sufficient to prevent the formation of hardening precipitates,
• wherein the inert or reducing atmosphere in which the recrystallization annealing is carried out consists of 20 to 30% nitrogen and 80% to 70% hydrogen and has a dew point below −40° C.

Process for manufacturing a strip made of a γ′ and/or γ″ structural hardenable Fe—Ni alloy, the thermal expansion coefficient between 20° C. and 150° C. of which is less than 7×10−6/K, in which:

• a hot strip is manufactured either by hot rolling a semi-finished product or by direct casting of a thin strip which is optionally lightly hot-rolled, and the hot strip is subjected to a softening annealing operation consisting of a soak between 950° C. and 1200° C. followed by rapid cooling and optionally to a pickling operation, in order to obtain a softened strip;
• a cold-worked strip is manufactured by cold rolling the said softened strip, with a reduction ratio of greater than 5%;
• and
• the cold-worked strip is subjected to a recrystallization annealing operation in an inert or reducing atmosphere, carried out either on the run at a temperature between 900° C. and 1200° C. with a residence time of between 30 s and 5 mm, or statically with a soak at a temperature of between 900° C. and 1050° C. for a time of between 15 mm to 5 h, followed by cooling down to a temperature below 500° C. at a cooling rate sufficient to prevent the formation of hardening precipitates,
• wherein a planishing operation is furthermore carried out, resulting in an equivalent cold-working ratio of less than 5%.

Process for manufacturing a strip made of a γ′ and/or γ″ structural hardenable Fe—Ni alloy, the thermal expansion coefficient between 20° C. and 150° C. of which is less than 7×10−6/K, in which:

• a hot strip is manufactured either by hot rolling a semi-finished product or by direct casting of a thin strip which is optionally lightly hot-rolled, and the hot strip is subjected to a softening annealing operation consisting of a soak between 950° C. and 1200° C. followed by rapid cooling and optionally to a pickling operation, in order to obtain a softened strip;
• a cold-worked strip is manufactured by cold rolling the said softened strip, with a reduction ratio of greater than 5%;
• and
• the cold-worked strip is subjected to a recrystallization annealing operation in an inert or reducing atmosphere, carried out either on the run at a temperature between 900° C. and 1200° C. with a residence time of between 30 s and 5 mm, or statically with a soak at a temperature of between 900° C. and 1050° C. for a time of between 15 mm to 5 h, followed by cooling down to a temperature below 500° C. at a cooling rate sufficient to prevent the formation of hardening precipitates,
• wherein before, during or after the cold rolling, at least one side of the strip is abraded, so as to obtain, after the recrystallization annealing, a uniform gold-coloured layer on said at least one side.