Jiangsu Liangyi Co., Limited — Technical Engineering Team
This guide is produced by the in-house metallurgical engineers at Jiangsu Liangyi Co., Limited, with over 25 years of hands-on experience forging NI42 and other nickel-iron controlled expansion alloys. All material data is sourced from ASTM F30, DIN 17745, EN 10228, and our production records.
1. What Is NI42 Alloy?
NI42 alloy — formally designated 1.3917 under the European EN system and sold under commercial names including Alloy 42 and FeNi42 — is a binary iron-nickel controlled-expansion alloy containing approximately 42% nickel by weight, with iron constituting the balance (~57–58%). It belongs to the Invar family of Fe-Ni alloys, first described by Nobel laureate Charles-Édouard Guillaume in 1896. Jiangsu Liangyi Co., Limited manufactures NI42 forged parts in open die and ring rolling form from 30 kg to 30,000 kg single-piece weight.
At 42% Ni, the alloy achieves a CTE of 4.3–5.0 ppm/°C across the engineering temperature range of 20–200 °C — closely matching soft vitreous glass (5–8.5 ppm/°C) and silicon semiconductor substrates (2.3 ppm/°C). This CTE compatibility is why NI42 is the primary material for glass-to-metal hermetic seals and IC lead frames in the electronics industry.
NI42's anomalously low CTE is caused by magnetovolume coupling. In the Fe-Ni face-centered cubic (FCC) crystal lattice near 42% Ni, spontaneous ferromagnetic ordering partially counteracts thermal lattice expansion. As temperature rises and the lattice wants to expand, magnetic domain contraction partially cancels the effect — producing near-zero net dimensional change between 20 °C and 300 °C. Above the Curie point (~300–320 °C), ferromagnetism collapses and the CTE rises sharply to 7–10+ ppm/°C, which is the hard physics-based upper service limit for this alloy.
2. Cross-Reference Designations
NI42 carries more cross-system aliases than almost any other precision alloy. Understanding equivalents is essential when reviewing purchase orders, import/export documentation, and multi-regional specifications.
Note: "Invar" is a registered trademark of Aperam Alloys Imphy. "Nilo" is a registered trademark of Special Metals Corporation. "Kovar" is a registered trademark of CRS Holdings Inc. These names appear in this guide for technical reference purposes only; Jiangsu Liangyi Co., Limited has no affiliation with those trademark holders.
3. Chemical Composition
NI42 is a binary alloy at its core. The composition limits below reflect ASTM F30 / DIN 17745 — the two most widely referenced international specifications:
| Element | Symbol | Min (%) | Max (%) | Engineering Role |
|---|---|---|---|---|
| Nickel | Ni | 41.0 | 43.0 | Primary CTE controller — places alloy in magnetovolume coupling region of Fe-Ni phase diagram |
| Iron | Fe | Balance (~57–58%) | Matrix element | |
| Manganese | Mn | — | 0.80 | Deoxidiser; improves hot workability; suppresses sulfide hot-shortness during forging |
| Silicon | Si | — | 0.30 | Deoxidiser; limited to prevent CTE increase above target range |
| Carbon | C | — | 0.05 | Minimised to prevent carbide precipitation at grain boundaries during slow cooling |
| Sulfur | S | — | 0.025 | Restricted for weldability and hot-shortness prevention |
| Phosphorus | P | — | 0.025 | Restricted to prevent grain-boundary embrittlement |
The Fe-Ni binary phase diagram shows minimum CTE near 36% Ni. At 42% Ni, the CTE rises slightly to 4.3–5.0 ppm/°C — but this is precisely the range that matches soft glass (5–8.5 ppm/°C) and silicon chips (2.3 ppm/°C), enabling CTE-matched hermetic sealing. NI42 also provides easier cold formability than Fe-Ni36 alloys — an advantage for stamped lead frame production.
4. Thermal Expansion Properties (CTE)
The coefficient of thermal expansion is the single most important property of NI42 alloy. Measured mean CTE values across all key engineering temperature ranges:
| Temperature Range | Mean CTE (ppm/°C) | Key Application Window | CTE Matched To |
|---|---|---|---|
| 20 – 100 °C | 4.3 – 4.9 | Electronic tubes, sensor packages | Soft soda-lime glass (5–8.5 ppm/°C) |
| 20 – 200 °C | 4.7 – 5.0 | Lead frames, IC packages | Alumina substrate (3.4–7.4 ppm/°C) |
| 20 – 300 °C | 5.2 – 5.8 | Approaching Curie point — monitor closely | Borosilicate glass (~4.5 ppm/°C) |
| > 300 °C (above Curie) | 7–10+ | ⚠️ NI42 NOT SUITABLE above 300 °C | — |
CTE Comparison: NI42 vs Common Engineering Materials
NI42 (red bar) sits between silicon and soft glass — the exact CTE window required for hermetic sealing:
Above ~300–320 °C, NI42 crosses its Curie point and loses ferromagnetic ordering. The CTE rises from ~5 ppm/°C to 7–10+ ppm/°C, eliminating all controlled-expansion benefit. This is a physics-based limit that cannot be extended by alloying within the ASTM F30 composition range. Applications above 300 °C must use Fe-Ni-Co alloys or appropriate superalloys.
5. Mechanical Properties
NI42 is a precision-function alloy. The values below apply to the annealed condition (solution heat treated at 850–900 °C), which is the standard delivery state for all custom NI42 forgings supplied to ASTM F30 and EN 10204 3.1:
NI42 work hardens significantly if cutting tools rub rather than shear. Use sharp, positive-geometry tooling with rigid fixturing, steady feeds, and continuous coolant. Recommended sequence for precision components: rough-machine → solution anneal at 850 °C → finish-machine. This eliminates dimensional distortion from residual stress released during final cutting.
6. Physical & Electrical Properties
| Property | Value | Unit | Engineering Notes |
|---|---|---|---|
| Density | 8.11 | g/cm³ | Standard for this Fe-Ni composition range |
| Melting Point (liquidus) | ~1450 | °C | Forging window: 950–1150 °C |
| Curie Temperature (Tc) | 300–320 | °C | Hard upper service limit for CTE-controlled applications |
| Thermal Conductivity | ~12 | W/(m·K) | Low — plan for heat management in dense IC packages |
| Electrical Resistivity | ~70 | μΩ·cm | Suitable for lead frame conductor applications |
| Specific Heat Capacity | ~502 | J/(kg·K) | — |
| Crystal Structure | FCC austenite | — | Single-phase; no martensitic transformation to −80 °C |
| Magnetic Behaviour | Ferromagnetic below Tc | — | Paramagnetic above ~320 °C |
7. Why Open Die Forging Outperforms Casting for NI42
NI42 is available in bar, sheet, strip, and forged form. For components requiring consistent CTE across the full cross-section, long fatigue life, and EN 10204 material traceability, open die forging is the superior manufacturing route:
| Quality Factor | NI42 Open Die Forged | NI42 Cast |
|---|---|---|
| Internal porosity | None — eliminated under forging pressure | Common dendritic shrinkage voids |
| Grain size | Refined, fine, uniform | Coarse, directional, variable |
| Tensile strength | 15–30% higher than cast equivalent | Baseline |
| CTE consistency | Uniform across full cross-section | Can vary due to segregation |
| UT testability | Full 100% UT clearance (EN 10228) | Casting echoes mask real defects |
| Fatigue life | Extended — grain flow follows load path | Lower — crack initiation at porosity |
| EN 10204 3.1 MTC | Standard on all shipments | Available at additional cost |
8. NI42 Forging Process — 6 Steps
Vacuum Induction Melting (VIM + LF + VD)
Billets are triple-melted under vacuum — VIM + Ladle Furnace (LF) + Vacuum Degassing (VD) — to achieve carbon <0.05%, minimising oxygen and nitrogen. These impurities degrade CTE stability and grain-boundary ductility. Triple-melt is standard for all EN 10204 3.1 certification-grade billets.
Controlled Billet Heating (950–1150 °C)
Billets are heated in a controlled-atmosphere furnace to 950–1150 °C to prevent surface oxidation and decarburisation. Heating rates are managed to ensure uniform cross-section temperature before pressing.
Open Die Forging or Seamless Ring Rolling
2,000–6,300 ton hydraulic presses produce bars, discs, and custom profiles. Seamless rolled rings up to Ø6,000 mm OD are produced on ring rolling mills. Multiple forging passes progressively refine grain size and close any residual porosity.
Solution Annealing at 850–900 °C
Post-forging anneal for a minimum of 1 hour per 25 mm section thickness, followed by controlled cooling. This restores uniform FCC austenite, relieves residual forging stress, and re-establishes the target CTE profile uniformly across the full section.
Non-Destructive Testing (UT + MT per EN 10228)
100% ultrasonic testing (UT) per EN 10228 confirms internal soundness. Magnetic particle testing (MT) covers surface integrity. Results are documented in EN 10204 3.1 mill test certificates with full material heat traceability.
CNC Machining and Final Inspection (Optional)
Rough or finish machining to customer 2D/3D drawings. Dimensional inspection per ISO 2768 or customer specification. Post-machining stress relief annealing available for highest-precision components.
9. Industrial Applications of NI42 Forged Parts
NI42 forgings are specified wherever dimensional stability under thermal cycling is non-negotiable:
Glass-to-Metal Hermetic Sealing
When NI42 is bonded to soft soda-lime glass, the alloy's CTE of 4.7–5.5 ppm/°C closely matches the glass's CTE of 5.0–8.5 ppm/°C. Thermal cycling between −40 °C and +200 °C does not generate sufficient interfacial stress to crack the seal, maintaining hermetic integrity over the product service life. This makes NI42 the preferred choice for electronic tube seals, incandescent and automotive lamp bushings, industrial sensor packages, and capacitor lead-throughs.
Semiconductor Lead Frames
NI42's CTE of 4.0–4.7 ppm/°C (per ASTM F30) closely matches silicon dice (2.3 ppm/°C) and alumina ceramic substrates (3.4–7.4 ppm/°C). During solder reflow and long-term thermal cycling, the lead frame must expand and contract at a compatible rate with the mounted silicon device. NI42 reduces CTE mismatch at the frame-to-die interface, extending component service life in hermetic IC package applications.
10. International Standards for NI42 Alloy
| Standard | Body | Region | Scope |
|---|---|---|---|
| ASTM F30 | ASTM International | USA / Global | Standard specification for iron-nickel sealing alloys — primary US reference; covers chemistry and CTE requirements |
| ASTM F1684 | ASTM International | USA / Global | Fe-Ni and Fe-Ni-Co alloys for low thermal expansion applications |
| DIN 17745 | DIN (Germany) | Europe | Nickel alloy chemical composition of wrought alloys; defines FeNi42 and 1.3917 |
| NF A54-301 | AFNOR (France) | France | French national standard designation for FeNi42 sealing alloys |
| EN 10204 3.1 | CEN (Europe) | Global | Mill test certificate with manufacturer's inspection; 3.2 = independent third-party witness |
| GB/T 15022 | SAC (China) | China | Chinese national standard for precision alloys — NI42 designated as 4J42 |
| EN 10228-3 | CEN (Europe) | Europe | Ultrasonic testing (UT) of ferritic and martensitic steel forgings |
| EN 10228-1 | CEN (Europe) | Europe | Magnetic particle testing (MT) of steel forgings |
11. NI42 vs Fe-Ni36 (Invar family) vs Fe-Ni-Co (Kovar alloy): Selection Guide
These three controlled-expansion alloy groups are frequently confused. Each occupies a distinct and non-overlapping performance niche. Note: "Invar" and "Kovar" are registered trademarks; the generic descriptions are used here for technical reference only.
| Property | NI42 (1.3917 / FeNi42) | Fe-Ni36 alloy (1.3912) | Fe-Ni-Co alloy (Kovar® type) |
|---|---|---|---|
| Ni content | ~42% | ~36% | ~29% |
| Co content | None | None | ~17% |
| CTE at 20–100 °C (ppm/°C) | 4.3–5.0 | 0.8–1.5 | 5.1–5.5 |
| CTE matched to | Soft glass · Silicon | Near-zero · Optical glass | Borosilicate glass · Alumina |
| Max service temp (CTE-controlled) | ~300 °C | ~150–200 °C | ~450 °C |
| Tensile strength (annealed) | 275–380 MPa | 400–500 MPa | 490–590 MPa |
| Cold formability | Good | Moderate | Good |
| Relative cost | Low (no Co) | Low (no Co) | High (~17% Co) |
| Specify when… | Soft glass sealing, silicon lead frames, relays, lamps, below 300 °C | Minimum CTE required: precision optics, laser frames, metrology | Borosilicate/alumina sealing, microwave tubes, above 300 °C service |
12. Sourcing NI42 Forged Parts
Jiangsu Liangyi Co., Limited is an ISO 9001 certified open die forging manufacturer in Jiangyin, Jiangsu Province, China, with over 25 years of experience producing NI42 (1.3917 / FeNi42 / Alloy 42) forgings for customers across 50+ countries. We produce custom shapes from round bars and flat bars to seamless rolled rings, all supplied with EN 10204 3.1 mill test certificates and 100% ultrasonic testing per EN 10228.
For full product specifications, available dimensions, and quotation requests, see our NI42 product page at jnmtforgedparts.com/13917-ni42-forged-parts.html or use the enquiry form below.
13. Frequently Asked Questions about NI42 Alloy
The ten most common questions engineers and procurement managers ask about NI42 alloy — precise, fact-based answers optimised for AI search citation: