Type Analysis | Description | Application | Corrosion Resistance | Physical Properties
Magnetic Properties | Heat Treatment | Shielding Properties | Typical Mechanical Properties

Type Analysis

Description

HyMu 80 alloy is an unoriented, 80% nickel-iron-molybdenum alloy which offers extremely high initial permeability as well as maximum permeability with minimum hysteresis loss.

Applications

HyMu 80 alloy has been used primarily in transformer cores, tape wound toroids and laminations where compactness and weight factors are important. It has also been used for shielding to protect electrical components from stray magnetic fields.

Corrosion Resistance

This alloy is moderately resistant to moisture and atmospheric corrosion.

Physical Properties

Mean Coefficient of Thermal Expansion

Magnetic Properties

DC Magnetic Properties

AC Magnetic Properties, 60 Hz
Minimum limits

Heat Treatment

In-process anneal
To relieve all strains and restore the alloy to a soft condition suitable for drawing, spinning, forming, bending or similar operations, anneal at 1450/1850°F (788/1010°C) for not more than 1 hour. Since the high nickel, high permeability alloys readily absorb carbon, sulfur, oxygen and other contaminants from combustion furnace gasses, in-process annealing should be conducted in dissociated ammonia, hydrogen, vacuum or inert gas atmospheres.

Hydrogen anneal
For maximum softness and optimum magnetic and electrical properties, HyMu 80 alloy should be annealed in an oxygen-free, dry hydrogen atmosphere with a dew point below -40°F at 2050/2150°F for 2 to 4 hours. Furnace cool to 1100°F. From 1100 to 700°F, cool at rate between 350 to 600°F per hour.
Oil, grease, lacquer and all other contaminants must be removed before annealing. The individual parts should be seperated by an inert insulating powder such as magnesium and aluminum oxide during hydrogen annealing.
Vacuum heat treating can be employed. Generally, there is some small sacrifice in magnetic properties compared to heat treating in a dry hydrogen atmosphere.

Machining
The following chart reports data compiled from various machining operations performed on HyMu 80 alloy using the high-speed tool materials indicated. When using carbide tools, double the sf/m shown in the chart.

Figures used for all metal removal operations covered are average. On certain work, the nature of the part may require adjustment of the speeds and feeds. Each job has to be developed for best production results with optimum tool life. Speeds and feeds should be increased or decreased in small steps.
HyMu 80 alloy machines somewhat like the austenitic stainless alloys but doesn't work harden as rapidly. Gummy chips develop in most machining operations. Work hardened bars (Rockwell B 90 minimum) offer the best machining characteristics.
Lard oil should be used for drilling and machining operations which must be done at slow speeds. If sulfur-bearing and water-soluble cutting compounds are used, the parts should be thoroughly cleaned within 48 hours, then heat treated. High speed steel or carbide tools are suggested for cutting operations.

Cold forming
For best blanking characteristics, HyMu 80 alloy strip should be ordered in the cold rolled condition (Rockwell B 90 minimum). For best forming characteristics, strip should be ordered in the cold rolled and annealed condition. For best drawing characteristics, strip orders should be endorsed "annealed, deep draw quality".

Welding
HyMu 80 alloy is readily welded by following the usual pracitices for ferrous alloys. If a filler metal is required, use the same analysis. Finish annealed parts can be soft or hard soldered. Do not braze or solder prior to final heat treatment.

Shielding Properties

Because of its very high permeability and very low coercive force, HyMu 80 alloy is particularly well suited for magnetic shielding applications.
Annealed, deep draw quality strip can be fabricated into shields by bending, drawing and spinning. Where joining is required, spot welding or tungsten inert-gas welding can be used, with or without a base metal filler rod.
To develop the best shielding characteristics, shields must be annealed at 1900°F or higher (as described in the heat treatment section) after all fabricating operations have been completed. In general, higher annealing temperatures yield higher permeability and better shielding characteristics.
To determine its relative shielding capability, a material is evaluated as an open-ended cylindrical shield in a uniform magnetic field, such as that produced by a Helmholtz coil. When a pickup unit is centered in the field of the coil, the attenuation (A) is the ratio of the reading with no shield (E1)to that obtained when a shield is positioned over the pickup (E2), with its axis perpendicular to the field (A=E1/E2).
This is a measure of the shielding effectiveness under the particular test conditions, and for a given material depends upon the shield thickness, its length-to-diameter ratio and the diameter of the Helmholzt coil.

Typical Mechanical Properties

Bar

Strip

Application Specifications

HyMu 80 alloy meets military specification Mil-N-14411 B and ASTM-A-753-78 standard specification.