Steel Alloy 79
UNS K94100 · also Permalloy 80, Mu-metal
Alloy 79 is a very high-permeability 79% nickel-iron alloy, usually molybdenum-modified (the Mu-metal / Permalloy 80 type), covered by ASTM A753 Type 4 as UNS K94100.
Reference datasheet — Alloy 79 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the Annealed condition
Alloy 79 tempers and conditions
Alloy 79 is supplied in 4 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
final dry-hydrogen anneal ~1100–1180 °C with controlled slow cool (magnetic properties developed) | Choose for finished shields/cores where maximum permeability and lowest coercivity are needed; parts must not be bent or machined afterwards. | 230 | 500 | 42 | 105 HB | 3 % IACS |
Hot Rolled + Annealed | Heavy-section form for machined cores, pole pieces and thick shield housings. | 260 | 560 | 38 | 130 HB | 3 % IACS |
AnnealedDefault mill (strand/bright) annealed strip, sheet and bar, soft and formable | Standard stock condition: soft enough to stamp, draw and machine, with final hydrogen anneal done after fabrication. | 270 | 550 | 40 | 120 HB | 3 % IACS |
Cold rolled | Use when springiness, flatness or thin gauge matters and the part will be magnetically annealed later; magnetic properties in this state are poor. | 700 | 830 | 3 | 22 HRC | 3 % IACS |
Supply forms, finishes and certifications
Ways Alloy 79 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
CD-WIRE | Cold Drawn Wire | Supply form |
What is Alloy 79?
Alloy 79 is a very high-permeability 79% nickel-iron alloy, usually molybdenum-modified (the Mu-metal / Permalloy 80 type), covered by ASTM A753 Type 4 as UNS K94100. Engineers specify it where extreme sensitivity to low magnetic fields and maximum shielding effectiveness are required; it is available as annealed and hydrogen-annealed sheet and strip, cold-rolled and hot-rolled annealed plate, and cold-drawn wire. Typical values are 270 MPa yield, 550 MPa tensile, 40% elongation, 120 HB (65 HRB) and service to 400 °C. It is not stainless, machines poorly (rating 32) and loses permeability with any cold work, so parts must be hydrogen-annealed last; Alloy 48 is the choice when higher saturation flux density is needed. Alloy 79 has a density of 8.74 g/cm³ (0.316 lb/in³), heavier than 100% of steel grades. It melts at 1,425°C (2,597 °F). Alloy 79 has a yield strength of 270 MPa (39.2 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 91% of steel grades. Elongation at break is 40% and the elastic modulus is 205 GPa (29.7 Msi).
What is Alloy 79 used for?
- precision magnetic shielding
- audio transformer cores
- recording heads
- sensitive relays
- fluxgate sensors
Advantages
- Ductile — tolerates forming and impact — 40%, better than 99% of steel grades
- Good corrosion resistance — 50/100, better than 99% of steel grades
- Forms and bends easily — 85/100, better than 96% of steel grades
- Polishes to a fine finish — 75/100, better than 94% of steel grades
Limitations
- High embodied carbon — 11 kg CO₂/kg, worse than 100% of steel grades
- Low strength — 270 MPa (39.2 ksi), worse than 91% of steel grades
- Low electrical conductivity — 3 % IACS, worse than 91% of steel grades
- Difficult to machine — 32/100, worse than 87% of steel grades
- Poor heat conductor — 30 W/m·K (17.3 BTU/hr·ft·°F), worse than 83% of steel grades
Alloy 79 properties
Typical room-temperature values for Alloy 79-Annealed; bars are the position among steel grades.
Physical3
Alloy 79 has a density of 8.74 g/cm³ (0.316 lb/in³), heavier than 100% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical14
Alloy 79 has a yield strength of 270 MPa (39.2 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 91% of steel grades. Elongation at break is 40% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
Alloy 79 is rated for continuous service to 400°C (752 °F). It conducts heat at 30 W/m·K (17.3 BTU/hr·ft·°F), worse than 83% of steel grades. Thermal expansion is 12.7 µm/m·K (7.06 µin/in·°F).
Electrical3
Alloy 79 conducts electricity at 3 % IACS, worse than 91% of steel grades.
Chemical & Environmental3
Corrosion resistance is fair (50/100), better than 99% of steel grades.
Sustainability4
Producing a kilogram of Alloy 79 takes about 115 MJ of energy and emits 11 kg of CO₂ — more than 100% of steel grades. Typical recycled content is 25%.
Manufacturability6
Alloy 79's machinability is poor (32/100, worse than 87% of steel grades); weldability good (60/100); formability excellent (85/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. Alloy 79 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Alloy 79
Is Alloy 79 easy to machine?
Gummy and work-hardening: use sharp positive-rake carbide, rigid setup, heavy coolant, slow speeds and avoid dwell; finish light to limit strained surface layer before the magnetic anneal.
Can Alloy 79 be welded?
TIG, micro-plasma, laser and resistance welding all work with matching or Ni filler, but any weld or heat-affected zone must be re-annealed in dry hydrogen to recover permeability.
Can Alloy 79 be formed, bent or molded?
Excellent deep-drawing and bending in the annealed condition (shield cans, cylinders); all cold work degrades permeability, so form first and hydrogen-anneal last with minimal handling.
Alloy 79 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| NiASTM A753 Type 4 / 1J79 nominal 79–80 % | 79 – 82 | 80 |
| MoMu-metal / HyMu 80 modification | 3.8 – 5.5 | 4.3 |
| Mn | 0.3 – 0.8 | 0.5 |
| Si | 0.1 – 0.5 | 0.3 |
| Clow C essential for permeability | ≤ 0.03 | 0.02 |
| S | ≤ 0.02 | |
| P | ≤ 0.02 | |
| Curesidual | ≤ 0.2 | |
| Crresidual | ≤ 0.3 | |
| Febalance ≈14–16 % | balance |
What surface finishes work on Alloy 79?
Not stainless — protect finished shields with electroless nickel, tin plate, chromate or clear lacquer; polishes well, and avoid abrasive blasting or mechanical straightening after the final anneal.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel Alloy 79 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- K94100
- Trade names
- Permalloy 80Mu-metal
- Similar grades
- A753 Type 4
How much does Alloy 79 cost?
Alloy 79 is a high-cost steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Alloy 79 — frequently asked
What is Alloy 79 used for?
Alloy 79 is typically used for precision magnetic shielding, audio transformer cores, recording heads, sensitive relays and fluxgate sensors. In short: highest permeability Ni-Fe; best low-field shielding alloy; anneal after all forming.
What is the yield strength of Alloy 79?
Alloy 79 has a typical yield strength of 270 MPa (39.2 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 91% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is Alloy 79 easy to machine?
Not especially — machinability is rated poor (32/100, worse than 87% of steel grades). Gummy and work-hardening: use sharp positive-rake carbide, rigid setup, heavy coolant, slow speeds and avoid dwell; finish light to limit strained surface layer before the magnetic anneal.
Can Alloy 79 be welded?
Yes — weldability is rated good (60/100). TIG, micro-plasma, laser and resistance welding all work with matching or Ni filler, but any weld or heat-affected zone must be re-annealed in dry hydrogen to recover permeability.
What surface finishes work on Alloy 79?
Not stainless — protect finished shields with electroless nickel, tin plate, chromate or clear lacquer; polishes well, and avoid abrasive blasting or mechanical straightening after the final anneal.
Can Alloy 79 be formed, bent or molded?
Excellent deep-drawing and bending in the annealed condition (shield cans, cylinders); all cold work degrades permeability, so form first and hydrogen-anneal last with minimal handling.
What is the maximum service temperature of Alloy 79?
Alloy 79 is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Alloy 79 Annealed and Alloy 79-CR?
Annealed is the default condition — standard stock condition: soft enough to stamp, draw and machine, with final hydrogen anneal done after fabrication. CR: use when springiness, flatness or thin gauge matters and the part will be magnetically annealed later; magnetic properties in this state are poor. Yield strength is 270 MPa in Annealed versus 700 MPa in CR.
How much does Alloy 79 cost?
Alloy 79 is a high-cost steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM A753 — Standard Specification for Wrought Nickel-Iron Soft Magnetic Alloys (Type 4) — ASTM International (2018)
- GB/T 15018 / YB/T 5235 1J79 (2018)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (Soft Magnetic Alloys) — ASM International (1990)
- HyMu 80 Alloy technical datasheet — Carpenter Technology (2020)
- MAGNIFER 7904 soft magnetic alloy datasheet — VAC / VDM Metals (2019)
- MuMETAL shielding alloy data — Magnetic Shield Corporation (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.