Patent GB-831129-A (GB)
Title: Improved nickel-iron magnetic alloy and method of making the same
IPC: C22F1/10
Filed: 1956-06-14
Abstract: A method for preparing face-centred cubic-crystalline sheet metal having magnetic properties, comprises providing a casting having at least two parallel planar faces and consisting of 55 to 70% nickel, 1 to 3% molybdenum, the balance substantially all iron, having a plurality of elongated columnar grains extending between the planar faces and having their longitudinal axes substantially perpendicular to the planar faces, reducing the casting into sheet metal in a plurality of rolling passes, the direction of rolling being maintained substantially perpendicular to the longitudinal axes of the columnar grains, heat treating the material and subjecting the resulting recrystallized sheet metal to a magnetic anneal.  An alloy of 64.45% nickel, 2.01% molybdenum, 0.22% manganese, 0.06% silicon, 0.01 aluminium, balance iron, melted in an induction furnace is cast, in split graphite moulds in 1 1/2 by 4 by 12 inch slabs with their largest dimensions vertical.  The slab is ground to remove surface defects, heated in a hydrogen atmosphere at from 1000 DEG C. to 1150 DEG C., hot rolled from approximately 1 3/8 to 1/2 inch thickness, reheated to 900 DEG C. to 1000 DEG C. and hot rolled to 1/4 inch thickness.  The material is then heated for one hour in a hydrogen atmosphere at from 900 DEG C. to 1000 DEG C. then rapidly cooled in a hydrogen atmosphere, then cold rolled to about 0.1 inch thickness, then annealed for 4 1/2 to 5 hours at 700 DEG C. in hydrogen then rapidly cooled in hydrogen.  The material is then cold rolled to 0.002 inch thickness.  The material in the form of a tape is then recrystallized by annealing for 10 to 30 minutes in hydrogen at a temperature between 500 DEG C. and 900 DEG C. The tape is wound on a core and annealed for 2 to 4 hours at 1050 DEG C. to 1250 DEG C. in hydrogen and then magnetically annealed for one hour at 650 DEG C. in hydrogen in a magnetic field of 10 oersteds. The strip may then be reannealed for 4 hours at 1200 DEG C. in hydrogen and then magnetically annealed.  A further 4 hour anneal at 1300 DEG C. followed by a magnetic anneal worsens the properties of the material. It is desirable that 0.01 to 0.05% oxygen be present in the ascast alloy.  A cast slab 2 1/2 inches thick, of 63.4% nickel, 1.9% molybdenum, 0.16% manganese, trace of silicon, 0.02% aluminium, balance iron, was heated to 1150 DEG C., hot rolled to 1/2 inch thick, heated to 1000 DEG C. hot rolled to 1/4 inch thick, annealed for 1 hour at 1000 DEG C. in hydrogen, rapidly cooled, cold rolled to 0.1 inch thick, annealed in hydrogen for 5 hours at 700 DEG C., cooled, cold rolled to 0.002 inch thick, recrystallized by annealing at 900 DEG C. for 10 minutes, annealed for 4 hours at 1100 DEG C., then magnetically annealed at 650 DEG C. for 1 hour in a field of 10 oersteds.  Another slab first hot forged at 1100 DEG C. to 1150 DEG C. then treated as above had poor magnetic qualities.  A cast ingot of square-cross-section of an alloy of 64.5% nickel, 1.88% molybdenum, 0.30% manganese, 0.04% silicon, trace of aluminium and balance iron, hot forged at 1150 DEG C. to reduce its thickness from 5 inches to 1 1/4 inch then treated somewhat as above had poorer magnetic properties.  Strips of "65 Permalloy" - 65% nickel balance iron-"Deltamax"-50% nickel, 50% iron-"Supermalloy"-79% nickel, 5% molybdenum, balance iron are stated to have been similarly prepared. An alloy of 65.1% nickel, 2.0% molybdenum, 0.21% manganese, less than 0.01% silicon, 0.0372% oxygen, balance iron, and a similar alloy with 0.0432% oxygen may be somewhat similarly treated to form the strip. The strip may be used for the core of a magnetic amplifier.  Alloys which may be used comprise preferably 58-68% Ni, 1.75-2.25% Mo, 0.2-0.4% Mn over 0.01% oxygen and the balance substantially all iron. Alloys with 65% Ni, 1, 2.16 or 2.9% Mo and the balance iron may be used.