What Is an Iron Nickel Alloy?

1. Introduction

Iron-nickel alloy, often referred to as nickel iron alloy or alloy of iron and nickel, is a family of materials primarily composed of iron (Fe) and nickel (Ni). By adjusting the nickel content, engineers can precisely control magnetic behavior, thermal expansion, corrosion resistance, and mechanical strength.

Think of iron-nickel alloys as a “tunable material system.” Low-nickel grades focus on strength and cost efficiency, while high-nickel grades deliver exceptional dimensional stability and magnetic performance.

2. Iron Nickel Alloy Properties

2.1 Mechanical Properties

Iron-nickel alloys generally offer:

Good tensile strength
Excellent toughness
Reliable fatigue resistance

Compared with plain carbon steel, they provide better consistency. Compared with stainless steel, they offer superior magnetic or thermal stability in specific compositions.

2.2 Thermal Properties and Dimensional Stability

Thermal behavior is one of the strongest reasons to choose iron-nickel alloys. Certain grades, such as FeNi36 (Invar alloy), are famous for their ultra-low coefficient of thermal expansion (CTE), making them indispensable for precision components exposed to temperature fluctuations.

2.3 Electrical and Thermal Conductivity

While not designed as high-conductivity materials, iron-nickel alloys maintain stable electrical and thermal behavior, which is critical in electronic packaging and functional metal parts.

3. Corrosion of Iron Nickel Alloys

3.1 Corrosion Mechanism

Corrosion resistance improves as nickel content increases. Nickel enhances passivation and reduces oxidation rates, especially in mild or controlled environments.

3.2 Performance in Different Environments

Iron-nickel alloys perform well in dry, indoor, or mildly corrosive conditions. For harsh environments such as salt spray or acidic exposure, surface treatments or coatings are recommended to extend service life.

4. Magnetic Properties of Iron-Nickel Alloys

4.1 Magnetic Permeability and Hysteresis

Low-carbon iron-nickel alloys exhibit high magnetic permeability and low coercivity, making them ideal for electromagnetic and sensing applications.

4.2 Magnetic Losses

One key advantage is low magnetic loss at higher frequencies. This explains why iron-nickel alloys are widely used in precision electronics, transformers, and sensor housings.

5. Nickel Iron Alloy vs Cobalt Iron Alloy

5.1 Performance Comparison

Cobalt iron alloys deliver superior magnetic saturation but at a significantly higher cost. Iron nickel alloys offer a more balanced combination of performance, processability, and affordability.

5.2 Cost and Application Differences

For mass production and MIM applications, iron-nickel alloys are often the preferred choice due to lower raw material costs and better availability.

6. Iron Nickel Alloy in Metal Injection Molding

6.1 MIM 4605

A low-alloy steel with small nickel additions, commonly used for structural MIM parts requiring strength and cost control.

Normal chemical composition of MIM 4605

MIM 4605	Iron	Nickel	Molybdenum	Silicon	Carbon	Sulphur	Phosphorus
Percent by Weight	Bal.	1.50-2.50	0.20-0.60	1.00	0.40-0.60	0.03	0.035

Mechanical Properties (After Heat Treatment)
Tensile Strength	860 – 1080 MPa (125 – 157 ksi)
Yield Strength	690 – 860 MPa (100 – 125 ksi)
Elongation	4 – 8%
Hardness (HRC)	30 – 35 HRC (after quenching and tempering)
Density	7.7 – 7.8 g/cm³
Physical Properties
Melting Point	1430 – 1500°C
Thermal Conductivity	30 – 35 W/m·K
Coefficient of Thermal Expansion	~12 x 10⁻⁶ /°C (20 – 300°C)
Heat Treatment Process
Austenitizing	840 – 870°C (1544 – 1598°F)
Quenching	Rapid cooling (oil or water)
Tempering	150 – 200°C (302 – 392°F)
Applications
Gears and Pinions	High-strength, wear-resistant components
Structural Components	Parts in automotive and aerospace industries
Tools and Dies	Components requiring moderate wear resistance
Firearm Components	Manufacturing various firearm parts

6.2 Fe2Ni

Low nickel content, suitable for structural components with minimal magnetic requirements.

Normal chemical composition of Fe2Ni (Fe02Ni)

MIM Fe2Ni	Iron	Carbon	Nickel	Sulfur	Phosphorus
Percent by Weight	BaL.	0.40-0.60	1.50-2.50	0.00-0.03	0.00-0.035

Mechanical Properties (Typical)
Tensile Strength	400 – 550 MPa (58 – 80 ksi)
Yield Strength	250 – 350 MPa (36 – 51 ksi)
Elongation	20 – 30%
Hardness	140 – 180 HB
Density	~7.85 g/cm³
Physical Properties
Melting Point	1480 – 1520°C
Thermal Conductivity	30 – 35 W/m·K
Coefficient of Thermal Expansion	~12 x 10⁻⁶ /°C (20 – 300°C)
Electrical Resistivity	~0.1 µΩ·m
Magnetic Properties
Saturation Magnetization	1.5 – 1.7 T
Coercivity	≤ 10 A/m
Permeability (µ)	1000 – 5000
Curie Temperature	~770°C
Heat Treatment
Annealing	600 – 700°C (slow cooling)
Stress Relieving	400 – 500°C
Applications
Magnetic Cores	Transformers, inductors
Structural Components	Low-stress structural parts
Tooling	Simple tools and dies
Electrical Contacts	Electrical and electronic components

6.3 Fe4Ni

Improved toughness and consistency, often used in precision mechanical parts.

Normal chemical composition of Fe4Ni (Fe04Ni)

MIM Fe4Ni	Iron	Carbon	Nickel	Sulfur	Phosphorus
Percent by Weight	BaL.	0.40-0.60	3.00-5.00	0.00-0.03	0.00-0.035

Mechanical Properties (Typical)
Tensile Strength	450 – 600 MPa (65 – 87 ksi)
Yield Strength	300 – 400 MPa (43 – 58 ksi)
Elongation	18 – 28%
Hardness	150 – 200 HB
Density	~7.85 g/cm³
Physical Properties
Melting Point	1470 – 1500°C
Thermal Conductivity	30 – 34 W/m·K
Coefficient of Thermal Expansion	~11 x 10⁻⁶ /°C (20 – 300°C)
Electrical Resistivity	~0.09 µΩ·m
Magnetic Properties
Saturation Magnetization	1.4 – 1.6 T
Coercivity	≤ 8 A/m
Permeability (µ)	2000 – 6000
Curie Temperature	~770°C
Heat Treatment
Annealing	650 – 750°C (slow cooling)
Stress Relieving	450 – 550°C
Applications
Magnetic Components	Magnetic circuits, cores
Structural Parts	General-purpose structural components
Tooling	Simple tools, dies, fixtures
Electrical Applications	Electrical components, connectors

6.4 Fe08Ni

Balances strength and dimensional stability, widely applied in powder metallurgy and MIM.

Normal chemical composition of Fe8Ni (Fe08Ni)

MIM Fe8Ni	Iron	Carbon	Nickel	Sulfur	Phosphorus
Percent by Weight	BaL.	0.40-0.60	7.0-9.0	0.00-0.03	0.00-0.035

Mechanical Properties (Typical)
Tensile Strength	450 – 600 MPa (65 – 87 ksi)
Yield Strength	300 – 400 MPa (43 – 58 ksi)
Elongation	18 – 28%
Hardness	150 – 200 HB
Density	~7.85 g/cm³
Physical Properties
Melting Point	1470 – 1500°C
Thermal Conductivity	30 – 34 W/m·K
Coefficient of Thermal Expansion	~11 x 10⁻⁶ /°C (20 – 300°C)
Electrical Resistivity	~0.09 µΩ·m
Magnetic Properties
Saturation Magnetization	1.4 – 1.6 T
Coercivity	≤ 8 A/m
Permeability (µ)	2000 – 6000
Curie Temperature	~770°C
Heat Treatment
Annealing	650 – 750°C (slow cooling)
Stress Relieving	450 – 550°C
Applications
Magnetic Components	Magnetic circuits, cores
Structural Parts	General-purpose structural components
Tooling	Simple tools, dies, fixtures
Electrical Applications	Electrical components, connectors

6.5 Fe50Ni

Medium-to-high nickel alloy offering excellent magnetic and thermal stability.

Normal chemical composition of Fe50Ni (FeNi50)

Fe50Ni	Iron	Nickel	Silicon	Carbon	RoHS Compliant
Percent by Weight	Bal.	49.0-51.0	1.00	0.05	Yes

Mechanical Properties (Typical)
Tensile Strength	450 – 550 MPa (65 – 80 ksi)
Yield Strength	300 – 400 MPa (43 – 58 ksi)
Elongation	25 – 35%
Hardness	130 – 160 HB
Density	~8.25 g/cm³
Physical Properties
Melting Point	1425 – 1450°C
Thermal Conductivity	22 – 25 W/m·K
Coefficient of Thermal Expansion	~8 x 10⁻⁶ /°C (20 – 300°C)
Electrical Resistivity	~0.12 µΩ·m
Magnetic Properties
Saturation Magnetization	0.8 – 1.0 T
Coercivity	≤ 5 A/m
Permeability (µ)	5000 – 8000
Curie Temperature	~550°C
Heat Treatment
Annealing	800 – 900°C (slow cooling)
Stress Relieving	400 – 500°C
Applications
Magnetic Shielding	Devices requiring protection from magnetic fields
Magnetic Components	Core material in transformers, inductors
Electronic Applications	Stable magnetic properties in electronic devices
Precision Instruments	Precision components requiring low thermal expansion

7. Ni-Rich Iron Nickel Alloys

7.1 FeNi80

Known for extremely high magnetic permeability, commonly used in electronic and magnetic shielding components.

Normal chemical composition of FeNi80

FeNi80	Iron	Nickel	Chromium	Silicon	Manganese	Copper	Carbon
Percent by Weight	Bal.	79.0-81.5	2.60-3.00	1.10-1.50	0.60-1.10	0.20	0.03

Mechanical Properties (Typical)
Tensile Strength	550 – 700 MPa (80 – 102 ksi)
Yield Strength	300 – 400 MPa (43 – 58 ksi)
Elongation	20 – 30%
Hardness	160 – 200 HB
Density	~8.5 g/cm³
Physical Properties
Melting Point	1435 – 1455°C
Thermal Conductivity	13 – 15 W/m·K
Coefficient of Thermal Expansion	~7 x 10⁻⁶ /°C (20 – 300°C)
Electrical Resistivity	~0.10 µΩ·m
Magnetic Properties
Saturation Magnetization	0.6 – 0.8 T
Coercivity	≤ 2 A/m
Permeability (µ)	10,000 – 30,000
Curie Temperature	~400°C
Heat Treatment
Annealing	800 – 900°C (slow cooling)
Stress Relieving	400 – 500°C
Applications
Magnetic Shielding	Sensitive electronic devices
Magnetic Cores	Transformers, inductors, magnetic amplifiers
Telecommunications	Communication device components
Precision Instruments	Low thermal expansion, stable magnetic performance

7.2 Fe35Ni65

A versatile alloy with balanced magnetic and mechanical performance.

Normal chemical composition of Fe35Ni65(FeNi65)

Fe35Ni65	Iron	Nickel	Silicon	Carbon
Percent by Weight	34.0-35.0	62.0-65.0	1.00-1.50	0.03

Mechanical Properties (Typical)
Tensile Strength	450 – 600 MPa (65 – 87 ksi)
Yield Strength	250 – 400 MPa (36 – 58 ksi)
Elongation	20 – 30%
Hardness	150 – 180 HB
Density	~8.4 g/cm³
Physical Properties
Melting Point	1420 – 1450°C
Thermal Conductivity	15 – 18 W/m·K
Coefficient of Thermal Expansion	~8 x 10⁻⁶ /°C (20 – 300°C)
Electrical Resistivity	~0.11 µΩ·m
Magnetic Properties
Saturation Magnetization	0.7 – 0.9 T
Coercivity	≤ 3 A/m
Permeability (µ)	8000 – 12000
Curie Temperature	~500°C
Heat Treatment
Annealing	800 – 900°C (slow cooling)
Stress Relieving	400 – 500°C
Applications
Magnetic Shielding	Electronic devices
Magnetic Cores	Transformers, inductors
Precision Instruments	Low thermal expansion, stable magnetic performance
Telecommunications	Communication device components

7.3 FeNi36 (Invar Alloy)

Invar alloy composition nickel iron is typically around 36% Ni. It is famous for near-zero thermal expansion and is critical in high-precision assemblies.

Normal chemical composition of FeNi36 (64FeNi)

FeNi36 (64FeNi)	Iron	Nickel	Manganese	Silicon	Carbon	Sulphur	Phosphorus
Percent by Weight	Bal.	35.0-37.0	0.20-0.60	0.30	0.05	0.02	0.02

Mechanical Properties (Typical)
Tensile Strength	490 – 620 MPa (71 – 90 ksi)
Yield Strength	240 – 410 MPa (35 – 59 ksi)
Elongation	30 – 50%
Hardness	120 – 160 HB
Density	~8.1 g/cm³
Physical Properties
Melting Point	1430°C
Thermal Conductivity	~10 W/m·K
Coefficient of Thermal Expansion	~1.2 x 10⁻⁶ /°C (20 – 100°C)
Electrical Resistivity	~0.78 µΩ·m
Magnetic Properties
Saturation Magnetization	0.8 – 1.2 T
Coercivity	≤ 4 A/m
Permeability (µ)	2000 – 10000
Curie Temperature	~230°C
Heat Treatment
Annealing	830 – 900°C (slow cooling)
Stress Relieving	400 – 500°C
Applications
Precision Instruments	Laser systems, optical devices, measuring equipment
Aerospace and Satellites	Spacecraft components
Cryogenic Applications	Liquefied gas storage, low-temperature environments
Electronics and Telecommunications	Consistent dimensions in varying thermal conditions

7.4 IN718 in MIM Applications

Although primarily a nickel-based superalloy, IN718 is increasingly explored in advanced MIM applications for high-temperature and high-strength requirements.

Normal chemical composition of IN718 (Inconel 718)

MIM IN718

Iron

Nickel

Chromium

Niobium

Molybdenum

Cobalt

Titanium

Aluminum

Manganese

Copper

Silicon

Carbon

Percent by Weight

BaL.

50.0-55.0

17.0-21.0

4.75-5.50

2.80-3.30

1.00max

0.65-1.15

0.20-0.80

0.35max

0.30max

0.35max

0.08max

Mechanical Properties (Typical)
Tensile Strength	965 MPa (140 ksi)
Yield Strength	550 MPa (80 ksi)
Elongation	12 – 15%
Hardness	200 – 250 HB
Density	~8.19 g/cm³
Physical Properties
Melting Point	1260 – 1336°C
Thermal Conductivity	~11.4 W/m·K (at 100°C)
Coefficient of Thermal Expansion	13.0 x 10⁻⁶ /°C (20 – 1000°C)
Electrical Resistivity	~1.29 µΩ·m
High-Temperature Properties
Maximum Service Temperature	~700°C
Oxidation Resistance	Excellent up to 980°C
Creep Resistance	High
Fatigue Resistance	High
Heat Treatment
Solution Treatment	925°C for 1 hour, air cool
Aging Treatment	First stage: 720°C for 8 hours, cool to 620°C; hold for 8 hours; air cool
Applications
Aerospace	Gas turbine engines, rocket motors, spacecraft components
Power Generation	Gas turbines, nuclear reactors, heat exchangers
Oil & Gas	Downhole tools, fasteners
Automotive	Turbocharger rotors
Marine	Seawater-resistant components

8. Advantages of Iron Nickel Alloys in the MIM Process

8.1 Complex Geometry in One Step

Metal injection molding allows iron nickel alloys to form complex geometries that are difficult or impossible with traditional machining.

8.2 Excellent Dimensional Consistency

MIM iron nickel alloy parts show excellent batch-to-batch consistency, a critical factor for global OEMs and precision component suppliers.

9. How to Choose Iron Nickel Alloy for the MIM Process

9.1 Understand the Application Requirements

Is the part structural, magnetic, or thermally sensitive? Defining the function is the first step.

9.2 Evaluate Compatibility with the MIM Process

Not all iron nickel alloys sinter equally well. Powder size distribution, binder compatibility, and sintering window must be considered.

9.3 Consider the Material Properties

Balance strength, magnetic performance, thermal expansion, and corrosion resistance based on real application needs.

9.4 Assess Environmental and Regulatory Compliance

For export markets, compliance with RoHS, REACH, and other regulations is essential.

9.5 Review Case Studies and Industry Usage

Proven industry applications reduce risk and shorten development cycles.

Conclusion

Iron-nickel alloys offer a rare combination of dimensional stability, magnetic performance, and MIM process compatibility. For precision manufacturing companies seeking reliable, scalable, and cost-effective solutions, iron-nickel alloys remain one of the most practical material choices.

1. Are iron-nickel alloys suitable for all MIM parts?

No. Selection depends on application requirements and performance priorities.

2. Why is Invar alloy more expensive than other iron-nickel alloys?

Because its ultra-low thermal expansion is difficult to replicate with other materials.

3. Do iron-nickel MIM parts require surface treatment?

It depends on the operating environment and corrosion requirements.

4. How stable is dimensional control in MIM iron-nickel alloys?

Very stable, especially for high-volume production.

5. How can manufacturers reduce iron-nickel alloy part costs?

By optimizing design, selecting appropriate alloy grades, and scaling production volumes.