Premium Controlled‑Expansion Alloy – Equivalent to 4J29, Nilo K, 1.3981 – Available in Bar, Tube, Wire, Sheet & Plate
We are a direct China‑based manufacturer for Glass‑Sealing Alloy of Kovar Alloy 4J29 (UNS K94610, ASTM F15) , which is known worldwide under various equivalent designations – 4J29 (China), Nilo K (UK), W.Nr. 1.3981 (Germany), 29HK (Russia), and Dilver P0 (France). Whichever standard you work with, we supply the same high‑quality material in all product forms – round bars, precision tubes, fine wires, strips, sheets, and heavy plates – with custom diameters, lengths, thicknesses, and widths, all at factory‑direct best prices and rapid lead times.
Our Kovar alloy Kovar Alloy 4J29 (UNS K94610, ASTM F15) is engineered to match the thermal expansion of borosilicate glass and alumina ceramics (CTE: 4.6–5.2 × 10⁻⁶/K at 30–400°C), ensuring reliable hermetic seals in aerospace, semiconductor, vacuum electronics, and medical devices. No matter whether you call it ASTM F15, 4J29, or Nilo K, the performance and certification are fully compliant with the latest revisions of ASTM F15, AMS 7727, and MIL‑I‑23011 Class 1.
Important Note: 4J29 is the standard equivalent for ASTM F15 Kovar alloy. Other glass‑sealing grades such as 4J33, 4J45 belong to the Kovar‑type alloy family but have different thermal‑expansion properties, which cannot be substituted for ASTM F15‑K94610. Please confirm your required grade before ordering.
Available Forms & Custom‑Size Service
We do not limit you to one shape. Choose the form that fits your production – all are manufactured to the same composition and properties as ASTM F15 / UNS K94610 / 4J29:
| Form | Available Sizes |
|---|---|
| Round Bar / Rod (also supplied as 4J29 bar, Nilo K bar) | Diameter 0.5 mm – 600 mm, length up to 6,000 mm |
| Precision‑Ground Bar (tolerance ±0.003 mm, surface finish 32 µin Ra) | Same as above |
| Tube / Pipe (equivalent to 1.3981 tube, 29HK pipe) | OD 6 mm – 630 mm, wall thickness 0.5 – 100 mm |
| Wire (also known as 4J29 wire, Nilo K wire) | Diameter 0.02 mm – 8 mm (coils or straight lengths) |
| Sheet / Strip / Coil (compliant with ASTM F15, UNS K94610) | Thickness 0.1 – 150 mm, width up to 1,200 mm |
| Plate (heavy sections) | Thickness ≥ 150 mm, custom dimensions |
| Flat Bar / Rectangular Bar | Custom width × thickness |
Custom tolerances, special surface finishes and dedicated heat‑treatment services are available for trial‑sample and bulk‑volume orders.All sizes can be tailored to your drawings. We also offer cutting, grinding, polishing, and heat treatment services – all for the same material, whether you order it as ASTM F15, 4J29, or Nilo K.
Technical Specifications – Kovar Alloy 4J29 (UNS K94610, ASTM F15)
Chemical Composition (wt%) – Common to All Equivalent Grades
| Element | ASTM F15 / UNS K94610 | 4J29 (GB) | Nilo K (UK) | 1.3981 (DIN) |
|---|---|---|---|---|
| Nickel (Ni) | 28.5 – 29.5% | 28.5 – 29.5% | ~29% | 28.5 – 29.5% |
| Cobalt (Co) | 16.8 – 17.8% | 16.8 – 17.8% | ~17% | 16.8 – 17.8% |
| Iron (Fe) | Balance | Balance | Balance | Balance |
| Manganese (Mn) | ≤ 0.50% | ≤ 0.50% | ≤ 0.50% | ≤ 0.50% |
| Silicon (Si) | ≤ 0.20% | ≤ 0.20% | ≤ 0.20% | ≤ 0.20% |
| Carbon (C) | ≤ 0.04% | ≤ 0.04% | ≤ 0.04% | ≤ 0.04% |
Physical & Mechanical Properties (Annealed) – Identical Across All Standards
| Property | Value |
|---|---|
| Density | 8.16 – 8.36 g/cm³ |
| CTE (30–400°C) | 4.6 – 5.2 × 10⁻⁶/K |
| Tensile Strength | ≥ 520 MPa |
| Yield Strength (0.2%) | ≥ 240 MPa |
| Elongation | ≥ 25% |
| Hardness (Rockwell B) | ~75 |
Why Choose Our Kovar Alloy Products Kovar Alloy 4J29 (UNS K94610, ASTM F15) ?
Full Certification & Traceability
Every shipment includes a mill test certificate (MTC) confirming compliance with ASTM F15, AMS 7727, and MIL‑I‑23011 Class 1. We explicitly state the equivalent grade (e.g., 4J29 or Nilo K) on the certificate, so your quality team can verify against your local standard.
Factory‑Direct Pricing
By manufacturing in‑house, we eliminate intermediaries. Our prices are consistently 15–30% lower than US and European suppliers for the same certified material – whether you call it UNS K94610 or 4J29.
Fast Custom Production – 5 to 7 Days
Standard sizes ship within 48 hours. Custom sizes are typically ready in 5‑7 business days – far quicker than the 60‑90 days quoted by many Western mills. We can even mark the packaging with your preferred grade name (e.g., "4J29") for easy identification.
Stringent Quality Control
Each batch undergoes spectrochemical analysis, ultrasonic inspection, dimensional verification, and surface finish testing – ensuring that our ASTM F15 material meets the exact requirements of its equivalents like 4J29 and 1.3981.
Available Forms & Customization
We supply Kovar Alloy 4J29 (UNS K94610, ASTM F15) in a wide range of forms and custom sizes:
| Form | Options |
|---|---|
| Round Bars | Diameter 2.0 mm – 100 mm, length up to 6,000 mm |
| Rods & Wires | Custom diameters and lengths |
| Strips & Sheets | Custom thickness and width |
| Tubes & Pipes | Custom OD, ID, wall thickness |
| Custom Components | Machined parts per customer drawings |
| Other Forms | Hexagonal bars, square bars, flanges, forgings |
International Equivalents
Kovar Alloy 4J29 is recognized globally under multiple designations:
| Country / Region | Designation |
|---|---|
| China (GB) | 4J29 |
| USA (UNS / ASTM) | UNS K94610 / ASTM F15 |
| UK | Nilo K |
| Germany (DIN) | 1.3981 / Vacon 12 |
| Japan | KV-1 |
| France | Dilvar P0 / Ni29Co17 |
| Russia | 29HK, 29HK-ВИ |
| International | FeNi29Co18 |
Case Study: Custom‑Size Kovar Bar Supplied to a US Aerospace Customer – Ordered as 4J29 Equivalent
Project Background
- Customer: A leading AS9100‑certified aerospace component manufacturer in the United States
- Requirement: They needed ASTM F15 Kovar round bars (equivalent to 4J29 and Nilo K) in a non‑standard diameter of 38.10 mm (1.500″) with a tolerance of ±0.025 mm, for machining hermetic connector housings used in satellite communication systems. Their engineering team was familiar with the 4J29 designation from previous Chinese suppliers, so we confirmed that our material is 100% interchangeable with 4J29, meeting both ASTM F15 and GB/T 15018 standards.
- Their existing US suppliers quoted 12‑week lead times and prices above $85/kg.
Our Solution
- Form: Precision‑ground round bar (we also offered the same material in tube or wire if needed, but bar was their choice)
- Diameter: 38.10 mm, ground to ±0.025 mm
- Length: 3,000 mm per piece (cut to blanks on request)
- Condition: Annealed (Temper A) for optimal machinability
- Certification: Full MTC confirming ASTM F15 / UNS K94610 and cross‑referencing 4J29 and Nilo K standards – with chemical and mechanical test reports.
- Surface Finish: 32 µin Ra maximum for consistent machining
Products And Package
Results
- Lead time: 6 business days from order confirmation to shipment (vs. 12 weeks)
- Cost savings: 28% below their current US supplier pricing
- Quality outcome: 100% passed incoming inspection; the customer reported zero dimensional rejects across the entire 500 kg order.
- Repeat business: The customer has since placed three additional orders totaling over 2,000 kg, now also inquiring about Kovar tubes (1.3981 equivalent) for their next project.
| Item | Details | |
|---|---|---|
| MOQ | 5 kg for strips, sheets & bars; 2 kg for wire; small trial orders acceptable | |
| Lead Time | Stock items: 7‑10 working days; Custom‑cut / special dimensions: 15‑25 working days | |
| FOB Port | FOB Shanghai / FOB Tianjin (China); CIF & CFR available upon request | |
| Payment Terms |
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| Packaging | Anti‑rust paper + waterproof plastic film + wooden case / plywood pallet; export‑grade packing for sea & air shipment | |
| Certificates | EN 10204 3.1 Material Test Report (MTR), chemical & mechanical test report; ISO certification; third‑party inspection support |
Key Applications
| Industry | Applications |
|---|---|
| Aerospace & Defense | High-vacuum and high-pressure hermetic seals, space optoelectronic devices |
| Electronics & Semiconductors | Integrated circuit packages, transistor and diode housings, power tubes, microwave tubes |
| Optoelectronics | Fiber optic components, laser packages, optical devices |
| Automotive | Sensors, electronic control units, hermetic packaging |
| Telecommunications | RF and microwave components, hermetic enclosures |
| Medical Devices | Implantable device housings requiring hermetic seals |
For more details about the industry applications of our UNS K94610 ASTM F15‑Kovar Alloy 4J29, please visit our Product Applications Module.
Selection Guide
Most Kovar alloys cannot be strengthened by heat treatment and can only restore corrosion resistance and relieve stress through solution treatment. Strict control of heat input, thorough cleaning, and sufficient argon protection are required during welding, and stress relief annealing must be performed after welding. The slow cooling process of 4J34 (≤ 5 ℃/min) and the strain rate control of 4J33 are their respective process "red lines" that cannot be crossed.
- The sealing object is hard glass (such as DM-308), with a working temperature of 20-450 ℃ - choose 4J29, which is the most mature, economical, and largest usage solution.
- The sealing object is 95% Al₂O₃ ceramic, with a working temperature of -60~400 ℃ and high requirements for magnetic stability (such as precision instruments and magnetic sensors) - choose 4J33, whose low magnetostrictive properties are the core advantage.
- The sealing object is 95% Al₂O₃ ceramic, with a working temperature of 400-600 ℃, and requires high-temperature creep resistance (such as magnetron, traveling wave tube, IGBT module) - choose 4J34, whose high-temperature expansion matching ability and high-temperature stability brought by high cobalt are irreplaceable.
Selection Decision Tree
Are you sealing to hard borosilicate glass (e.g., DM-305, DM-308)?
Yes → Choose 4J29 (Kovar) – the industry standard for this application
No → Go to step 2
Are you sealing to soft glass or ceramics with a higher CTE?
Yes → Consider 4J42 (Alloy 42) – lower cost, no cobalt
No → Go to step 3
Do you need extremely low thermal expansion for dimensional stability?
Yes → Consider 4J36 (Invar) – ultra-low CTE, not for glass sealing
No → Choose 4J29 – the most versatile and widely used precision alloy
To dive deeper into real‑world deployment of this material, read our technical article:4J29 Kovar Alloy Applications in Semiconductor Hermetic Packaging, where we cover material characteristics, typical components and critical purchasing considerations for semiconductor‑grade Kovar.
About Us
HSMetal is a specialized manufacturer and global exporter of precision controlled‑expansion and glass‑to‑metal hermetic sealing alloys. Our core portfolio covers ASTM F15 Kovar Alloy (UNS K94610 / 4J29), alongside a full range of kovar grades including 4J34, 4J33, 4J36 and 4J32. We supply custom‑size Kovar bar, sheet, forging and other semi‑finished products for semiconductor packaging, optoelectronic devices, vacuum electronic sealing components, aerospace, petrochemical and high‑end precision‑manufacturing industries.
We strictly follow ASTM, UNS and GB international material standards. Our in‑house laboratory supports full‑range inspection including chemical composition analysis, PMI verification, mechanical performance testing, thermal expansion coefficient testing, hardness examination and non‑destructive testing. Solution‑annealing and age‑hardening heat‑treatment services are available per‑customer drawings. Full‑batch Mill Test Reports (MTR) are provided, and third‑party spectroscopic re‑inspection is acceptable, to meet strict quality audit requirements for industrial and precision sealing applications.
With rich worldwide export experience delivering custom‑sized Kovar alloy products to industrial manufacturers across the United States, Germany, the United Kingdom, South Korea, Saudi Arabia, UAE and Southeast‑Asian markets, we provide complete material certification and professional technical support. Whether you require standard‑size stock or custom‑processed Kovar alloy parts, we deliver traceable, dimensionally stable and high‑reliability materials for global hermetic sealing projects
Our Factory
Automatic Cold Drawing Line For Precision Superalloy Bars
Seamless Pipe Production Line
Alloy Welding Wire Drawing Production Line for High Performance Alloy
Metal Strip Continuous Annealing Production Line
Aging Treatment Equipment
Headstand Wire Drawing Machine
FAQ
Q1: What is Kovar alloy? What are its equivalent grades?
A:Kovar is a nickel‑iron‑cobalt controlled‑expansion alloy (Fe‑29Ni‑17Co) designed to match the thermal expansion of borosilicate glass and alumina ceramics, enabling reliable hermetic glass‑to‑metal and ceramic‑to‑metal sealing. Our ASTM F15 UNS K94610 material is fully equivalent to 4J29 (China GB/T 15018), Nilo K (UK), W.Nr. 1.3981 (Germany DIN 17745), 29HK (Russia), and Dilver P0 (France).
Q2: What are the chemical composition and key physical/mechanical properties of 4J29?
A: Chemical composition (wt%): Ni 28.5–29.5, Co 16.8–17.8, C ≤0.03, Mn ≤0.50, Si ≤0.30, Cu ≤0.20, Fe balance.
Typical properties (annealed): Tensile strength ≥515 MPa, yield strength ≥340 MPa, elongation ≥30%; density 8.17 g/cm³; average coefficient of thermal expansion (20–450°C) of 4.6–5.2×10⁻⁶/℃, which precisely matches borosilicate hard glass (DM305/DM308); Curie point ~430°C, with stable low‑temperature structure and minimal phase transformation risk.
Q3: What product forms and custom sizes do you offer?
A:We supply ASTM F15 Kovar alloy in all forms: round bars (0.5 – 600 mm dia.), precision‑ground bars (±0.003 mm tolerance), tubes/pipes (6 – 630 mm OD), wire (0.02 – 8 mm dia.), sheets/strips/coils (0.1 – 150 mm thick), plates (≥150 mm thick), and flat bars. All sizes can be customized to your drawings, with lengths up to 6,000 mm.
Q4: What are the core characteristics of 4J29, and how do you distinguish it from 4J36 (Invar) and 4J33 for material selection?
A:Selection rule of thumb: For glass‑to‑metal hermetic sealing, choose 4J29; for dimensional stability without sealing requirements, choose 4J36.
- 4J29 (Kovar): Fe‑Ni‑Co system, designed for hard glass hermetic sealing. Delivers reliable airtightness after sealing – the top choice for vacuum electronics and semiconductor lead‑outs
- 4J36 (Invar): Low‑expansion Fe‑Ni alloy without cobalt, focusing on extremely low expansion near room temperature – not suitable for glass sealing.
- 4J33: Matches ceramic and some soft glass. Its CTE range differs from 4J29 – primarily used for ceramic packaging.
Q5: What are the typical applications of 4J29?
A: Vacuum electronic devices, transmitting tubes, magnetrons, relay sealed pins; semiconductor IC packaging bases and lead frames; aerospace hermetic connectors; optoelectronic components, vacuum instruments, medical hermetic devices, and microwave device glass‑to‑metal sealing assemblies.
Q6: What are the common risks when purchasing 4J29, and what inspection documents do you provide?
A: Common risks: Impurity content exceeding limits, inconsistent CTE values, missing hydrogen annealing, insufficient surface cleanliness – leading to post‑sealing leakage or thermal cycle cracking; substitution with ordinary Fe‑Ni alloy counterfeit materials.
Delivery documentation: Original mill MTC (Material Test Certificate), spectral analysis report, CTE test report, metallographic examination – all with full lot traceability. We can also supply pre‑cleaned blanks upon request, suitable for OEM packagers and vacuum electronics project qualifications.
Q7: Is your material certified? What documentation do you provide?
A:Yes. Every batch is supplied with an official Mill Test Certificate (MTR) confirming compliance with ASTM F15, AMS 7727, and MIL‑I‑23011 Class 1. The certificate includes chemical composition analysis, mechanical properties, and dimensional inspection results. We also provide commercial invoice, packing list, Bill of Lading, Certificate of Origin, and preferential origin documents where applicable.
Q8: What is the lead time for custom sizes?
A:Standard sizes ship within 10-15 days. Custom diameters, lengths, and thicknesses are typically ready in 15‑25 business days – significantly faster than the 60‑90 days quoted by many US and European mills.
Q9: Can Kovar be welded, brazed, or plated?
A:Yes. Kovar can be welded, brazed, and plated when appropriate processes are used. Nickel and gold plating are commonly applied for additional oxidation protection, solderability, or specific sealing requirements. For welding, precautions against oxidation are recommended – the alloy oxidizes easily at high temperatures in air.
Q10: Can I request samples before placing a bulk order?
A: Absolutely. We offer sample quantities for customer evaluation. Please let us know your required specifications (diameter, wall thickness, length, and surface condition), and we will arrange shipment promptly. For new customer we need you pay for the sample costs, as old customer sample costs are typically credited against your next bulk order.
Q11: What is the Minimum Order Quantity (MOQ)?
A: Normally MOQ is 50kg, We always expect more opportunities with you. But for some special material or special size let's communicate the actual status.
Q12: What payment terms do you accept?
A: We accept T/T, L/C, and other common methods. For new customers, we usually require 50% deposit and 50% balance before shipment. Flexible terms can be negotiated for long-term partners
Q13:Does HSMetal perform NDT on Kovar products?
A:Yes. To meet aerospace and semiconductor standards, our ASTM F15 (4J29) bars, tubes, and precision parts undergo strict Dye Penetrant Flaw Testing (PT) per ASTM E165. This ensures zero surface cracks, porosity, or laps that could compromise hermetic glass-to-metal sealing.
Q14: What if I find quality issues after receiving the goods?
A: We provide a 100% quality guarantee. If any non-conformity is found, please provide photos and test data within 7 working days of receipt. We will respond within 48 hours and agree on replacement, return, or compensation terms.
Hot Tags: Kovar Alloy 4J29 (UNS K94610, ASTM F15) glass‑sealing Fe‑Ni‑Co alloy from China. Available in bar, strip, sheet & wire, custom‑cut sizes for glass‑to‑metal hermetic sealing applications. Fast lead time, factory‑direct supply.
