4J29 Kovar (UNS K94610) - Glass-to-Metal Sealing Alloy Supplier of Strip, Wire & Bar | Shanghai Hangbo Alloy Group
Date: 2026年8月12日 Categories: News Views: 320
By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012
Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360
Quick Answer: What Is 4J29 Kovar?
4J29 Kovar (UNS K94610 / ASTM F15) is the classic Fe-29Ni-17Co controlled-expansion alloy engineered to match the thermal expansion of hard borosilicate glasses and alumina ceramics — enabling hermetic glass-to-metal seals that survive extreme thermal cycling without cracking. It is the most widely used sealing alloy in semiconductor packages, vacuum tubes, relays, and aerospace electrical feedthroughs. Shanghai Hangbo Alloy Group supplies 4J29 Kovar as cold-rolled strip, wire, and bar with GB/T 15018 / ASTM F15 certification.
Industry Pain Point: Hermetic package manufacturers chasing miniaturization face a CTE-matching challenge: mismatched expansion between the metal lead and glass bead cracks the seal during thermal shock (MIL-STD-883 testing), producing leak rates that fail helium leak detection. 4J29's tightly controlled CTE (4.6-5.2 x 10^-6/K from 30-400C) matches borosilicate glass within 0.5 x 10^-6/K — the precision required for reliable hermeticity across -65 to +300C cycling.
Key Properties at a Glance
| Property | Value |
|---|---|
| UNS Number | K94610 |
| W.Nr. | 1.3912 family |
| Alloy Family | Fe-Ni-Co Controlled Expansion |
| Density | 8.16 g/cm3 |
| Curie Temperature | ~435C |
| CTE (30-400C) | 4.6-5.2 x 10^-6/K |
| Tensile (Ann.) | >= 520 MPa (75 ksi) |
| Yield (Ann.) | >= 240 MPa (35 ksi) |
| Elongation (Ann.) | >= 25% |
| Key Standards | ASTM F15, GB/T 15018, MIL-I-23011 |
Product Overview
4J29 (Kovar, named after its inventor "Kovar" at Westinghouse) is the foundation material of the hermetic electronics industry. The Fe-29Ni-17Co composition produces a unique Invar-type low-expansion behavior: the alloy's thermal expansion matches hard glasses (borosilicate, 7052, 7056) and alumina ceramics across the sealing temperature range.
Why it works — the expansion match:
| Material | CTE (30-400C, x10^-6/K) |
|---|---|
| 4J29 Kovar | 4.6-5.2 |
| Borosilicate glass | 4.5-5.0 |
| Alumina ceramic | 6.0-7.0 (approximate) |
Key attributes:
- Pre-oxidation compatibility: Forms an adherent, thin oxide layer (Fe₂O₃ + CoO) that wets and chemically bonds glass during sealing — the essential mechanism for vacuum-tight joints.
- Weldability/brazeability: Compatible with gold plating, silver brazing, and resistance welding for lead attachment.
- Availability: Strip (0.05-2.0mm), wire (0.1-5mm), bar — the full range needed for headers, leads, and housings.
Shanghai Hangbo Alloy Group supplies 4J29 Kovar in all standard forms.
Executive Standards
| Product Form | ASTM | GB |
|---|---|---|
| Strip & Sheet | ASTM F15 | GB/T 15018 |
| Wire | ASTM F15 | GB/T 15018 |
| Bar & Rod | ASTM F15 | GB/T 15018 |
| Forgings | -- | -- |
Chemical Composition (wt.%)
| Element | Min | Max | Role |
|---|---|---|---|
| Ni | 28.5 | 29.5 | Low-expansion driver |
| Co | 16.5 | 17.5 | CTE tuning + glass wetting |
| Mn | 0.20 | 0.60 | Deoxidizer |
| Si | 0.10 | 0.30 | Oxide adhesion |
| C | -- | 0.03 | Control |
| Fe | Balance | -- | Matrix |
Mechanical & Physical Properties
Room-Temperature (Annealed)
| Property | Value |
|---|---|
| Tensile Strength | >= 520 MPa (75 ksi) |
| Yield Strength 0.2% | >= 240 MPa (35 ksi) |
| Elongation | >= 25% |
| Hardness | ~70-85 HRB |
Physical Properties
| Property | Value |
|---|---|
| Density | 8.16 g/cm3 |
| CTE (30-400C) | 4.6-5.2 x 10^-6/K |
| Thermal Conductivity | ~17 W/m-K |
| Curie Temperature | ~435C |
| Magnetic | Ferromagnetic |
Heat Treatment
Annealing: 850-900C (1560-1650F) in dry hydrogen, slow cool. This develops the controlled grain structure and surface condition essential for sealing.
Pre-oxidation (before glass sealing): 750-800C in controlled atmosphere (air/wet H₂) for 5-15 min to develop the oxide layer that bonds to glass.
Industry Applications
| Industry | Component | Why 4J29? |
|---|---|---|
| Semiconductor | Hermetic package headers, lead frames | Glass-to-metal seal reliability |
| Vacuum Tubes | Pin seals, envelope feedthroughs | Vacuum-tight glass seals |
| Aerospace | Electrical feedthroughs, sensors | Thermal cycle survival |
| Relays | Hermetic relay bases | Sealing + plating compatibility |
| Automotive | Pressure sensor housings | Cost-effective hermeticity |
Quality Assurance: 7-Stage
- Raw Material: Ni, Co, Fe verified by OES/ICP.
- Melt: Co +/-0.2%, Ni +/-0.3%, C <=0.02% internal.
- Hot Working: 1050-1150C, finishing >=900C.
- Annealing: 850-900C H₂ anneal verified.
- CTE Test: Dilatometer per ASTM E228 on each lot — 4.6-5.2 x 10^-6/K.
- NDE: Surface and dimensional verification. PMI per lot.
- Documentation: GB/T 15018 / ASTM F15 MTC. SGS witness available.
Frequently Asked Questions
Q1: What is 4J29 Kovar used for?
Hermetic glass-to-metal seals in semiconductor packages, vacuum tubes, relays, aerospace feedthroughs, and pressure sensors.
Q2: 4J29 vs 4J32?
4J29: Co 17%, CTE 4.6-5.2 — hard glass/ceramic seals. 4J32: Co 4%, CTE 5.5 — softer glass seals. Match to the glass.
Q3: Is it magnetic?
Yes — ferromagnetic (a disadvantage only where magnetic interference matters).
Q4: What is the price?
$35-60/kg EXW. Contact sales@hangboalloy.com.
Q5: Product forms?
Strip (0.05-2.0mm), wire (0.1-5mm), bar (6-50mm). SGS available.
Q6: Why pre-oxidation?
The oxide layer (Fe₂O₃/CoO) chemically bonds glass to metal — without it, seals leak.
Q7: What is the density?
8.16 g/cm3.
Q8: Does Shanghai Hangbo ship internationally?
Yes — FOB/CIF/DAP to 40+ countries.
Q9: What standards apply?
ASTM F15, GB/T 15018, MIL-I-23011.
Q10: Can it be plated?
Yes — nickel/gold plating standard for solderability and corrosion protection.
Q11: What is the CTE?
4.6-5.2 x 10^-6/K (30-400C).
Q12: What heat treatment?
850-900°C H₂ anneal; 750-800°C pre-oxidation before sealing.
Q13: Is it weldable?
Yes — resistance welding and laser welding for lead attachment.
Q14: What is the max service temperature?
~400C continuous (seal integrity maintained to ~425C).
Q15: Why cobalt?
Cobalt tunes the CTE to match hard glasses and improves glass wetting during sealing.
Contact Shanghai Hangbo Alloy Group
| Channel | Details |
|---|---|
| Company | Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier |
| Website | www.nickel-alloy.com |
| Email (Sales) | sales@hangboalloy.com |
| Email (Technical) | hangbo@nickel-alloy.com |
| WhatsApp (Lisa) | +86 13611656360 |
| Address | Room 1508, No. 288 Shiyi Road, Baoshan District, Shanghai 200940, China |
Shanghai Hangbo Alloy Group - Complete Product Range
| Family | Available Grades |
|---|---|
| Pure Nickel | NI200, NI201, N4, N5, N6 |
| Monel | 400, 401, 404, 502, K-500, R-405 |
| Inconel | 600, 601, 617, 625, 690, 693, 706, 718, X-750, 725 |
| Incoloy | 800, 800H, 800HT, 825, 925, 926, 945, A-286, 25-6HN, 27-7MO |
| Hastelloy | C-276, C-22, C-22HS, C-2000, C-4, G-30, G-35, G-50, X, B-2, B-3, B-4, HYBRID-BC1, N |
| Super Austenitic | 904L, Alloy 28, Alloy 31, 254SMO, 20Mo-6, AL-6XN |
| Chromium-Rich | Alloy 33 |
| High-Strength Stainless | Nitronic 50, Nitronic 60, PH13-8Mo |
| Chlorination-Resistant | Alloy 45 |
| Nimonic | 75, 80A, 90, 95, 105, 115, 263 |
| Haynes | 25, 188, 214, 230, 242, 282, 556, HR-120, HR-160 |
| RA Series | RA330, RA333 |
| Precision | 1J22, 1J46, 1J50, 1J79, 1J85, 3J21, 4J29, 4J32, 4J36, 4J45 |
| High-Strength | 18Ni250, 18Ni300, AerMet 100 |
| Heating | Cr20Ni80, Cr40Ni60 |
| Specialty | Alloy 20, Alloy 59, Inconel 686, 602CA |
Product Forms: Bars(6-500mm) | Tubes(OD 6-610mm) | Plates(0.1-100mm) | Forgings | Welded Pipes | Fittings | Wire(0.05-10mm) | Strip(0.02-4.0mm)
SGS/BV/TUV. Contact: sales@hangboalloy.com | WhatsApp (Lisa): +86 13611656360 | www.nickel-alloy.com
