C-103 Niobium Fasteners – Nb-10Hf-1Ti (UNS R04295) Bolts, Nuts & Studs
ASC LLP, Mumbai, supplies C-103 niobium fasteners – bolts, nuts, studs, screws and washers in C-103 (C103, Nb-10Hf-1Ti, UNS R04295). They are machined to drawing from ASTM B655 / AMS 7852 bar and come with EN 10204 3.1 certificates. C-103 keeps useful strength up to about 1,370 °C (2,500 °F), so C-103 fasteners are used to join hot structures in rocket and satellite thrusters and in vacuum furnaces. See our full niobium fasteners range.
What is C-103 Niobium Alloy?
C-103 is a niobium alloy containing about 10% hafnium and 1% titanium, balance niobium (≈ 89%). It is not a steel. Hafnium and titanium give C-103 roughly twice the strength of pure niobium at high temperature, while it stays ductile, formable and weldable at room temperature. C-103 is supplied annealed and is not hardened by heat treatment. For bar, sheet, plate and wire, see our C-103 niobium alloy page.
C-103 Fasteners – Quick Facts
- Alloy: C-103 / C103, Nb-10Hf-1Ti, UNS R04295
- Raw material: ASTM B655 bar / AMS 7852, annealed (recrystallized)
- Fastener standard: none specific to C-103 – supplied to customer drawing (ISO / UNC / UNF / UNJ threads)
- Types: hex and socket-head bolts, studs, nuts, screws, washers, pins and special parts
- Service: vacuum, inert gas or with an oxidation-resistant silicide coating
- Certificate: EN 10204 3.1 including interstitial (C, O, N, H) analysis
Properties of C-103 Fasteners
- High-temperature strength: retains useful strength to about 1,370 °C (2,500 °F) – far beyond nickel superalloy fasteners.
- Ductility and toughness: ductile at room temperature, with a low ductile-to-brittle transition, so fasteners can be torqued and reused.
- Matching expansion: C-103 bolts expand at the same rate as C-103 flanges, nozzles and brackets, so joints stay tight when hot.
- Weldable and machinable: can be machined, thread-rolled and welded in vacuum or high-purity argon.
- Density: about 8.85 g/cm³ – similar to steel and about twice titanium, so C-103 is chosen for temperature capability, not light weight.
Oxidation & Coatings
Like all niobium alloys, C-103 oxidises rapidly in air above about 400 °C. Hot C-103 fasteners are therefore used either:
- in vacuum or inert gas (space, vacuum furnaces, test chambers), or
- with an oxidation-resistant silicide coating (for example R512E-type Si-Cr-Fe coatings) for service in air or combustion gases.
Specify coating requirements, thread allowances for coating thickness, and any anti-galling lubricant when ordering.
C-103 Fastener Types & Sizes
| Fastener type | Typical size range | Notes |
| Hex bolts & socket-head screws | M3 – M24 (#4 – 1″) | Metric or UNC / UNF / UNJ; rolled or cut threads |
| Studs & threaded rod | M3 – M24 | Full or partial thread |
| Nuts & washers | M3 – M24 | Hex, flange and lock nuts; flat washers |
| Pins, rivets & special parts | To drawing | Dowel pins, clevis pins, thruster brackets |
Typical ranges – other sizes, lengths and special parts to drawing.
Mechanical Properties of C-103 Fasteners
| Property | Room temperature (annealed, min.) | At 1,095 °C / 2,000 °F (typical) |
| Ultimate tensile strength | 370 MPa (54 ksi) | 145 MPa (21 ksi) |
| Yield strength (0.2% offset) | 260 MPa (38 ksi) | 110 MPa (16 ksi) |
| Elongation | 20% | ≈ 20% |
Room-temperature values are ASTM B655 minimums for annealed bar; elevated-temperature values are typical.
C-103 Fastener Specifications
| Item | Details |
| Material | C-103 niobium alloy, UNS R04295 (Nb-10Hf-1Ti) |
| Bar standards | ASTM B655, AMS 7852 |
| Sheet / plate (washers, brackets) | ASTM B654, AMS 7857 |
| Fastener standard | None for C-103 – to customer drawing |
| Threads | ISO metric, UNC, UNF, UNJ or special |
| Condition | Annealed (recrystallized) |
| Testing | Chemistry incl. interstitials, tensile on bar, dimensional and thread gauging, PMI |
| Certificate | EN 10204 3.1; third-party inspection on request |
We also supply unfinished C-103 niobium alloy bar for in-house machining.
C-103 Chemical Composition (UNS R04295)
| Element | Composition (wt %) |
| Hafnium (Hf) | 9.0 – 11.0 |
| Titanium (Ti) | 0.7 – 1.3 |
| Zirconium (Zr) | 0.70 max |
| Tantalum (Ta) | 0.50 max |
| Tungsten (W) | 0.50 max |
| Carbon (C) | 0.015 max |
| Oxygen (O) | 0.0225 max |
| Nitrogen (N) | 0.015 max |
| Hydrogen (H) | 0.0010 max |
| Niobium (Nb) | Balance (≈ 89%) |
Physical Properties of C-103
| Property | Value (approx.) |
| Density | 8.85 g/cm³ (0.319 lb/in³) |
| Melting point | ≈ 2,350 °C (4,260 °F) |
| Crystal structure | Body-centred cubic (single phase) |
| Magnetic | Non-magnetic |
Applications of C-103 Fasteners
| Industry | Applications for C-103 fasteners |
| Space propulsion | Bolting for thruster and rocket-engine nozzles, chambers and injectors |
| Aerospace & defence | Hot-structure joints, hypersonic and missile test hardware |
| Test facilities | High-temperature test rigs and engine test stands |
| Vacuum furnaces | Hot-zone fixtures, heat-shield and element supports |
| Research & energy | High-temperature and liquid-metal experimental systems |
C-103 is not used for jet-engine turbine blades or nuclear reactor pressure parts.
C-103 vs Pure Niobium & Nb-1Zr Fasteners
| Grade | Type | Strength (bar, annealed min.) | Best for |
| C-103 (this page) | Nb-10Hf-1Ti, R04295 | 370 / 260 MPa | Load-bearing joints at high temperature |
| R04200 / R04210 | Pure niobium | 125 / 73 MPa | Corrosion service and low-load hardware |
| R04251 / R04261 | Nb-1Zr | 195 / 125 MPa | Liquid-metal and nuclear-type service |
Why Buy C-103 Fasteners from ASC LLP?
- Correct material: genuine C-103 (UNS R04295) bar to ASTM B655 / AMS 7852, with 3.1 certificates including interstitial analysis.
- Supplied to drawing: bolts, studs, nuts and special parts in small or production quantities.
- Matching hardware: C-103 flanges, C-103 fittings and C-103 bar, sheet and plate.
- Clean, protected export packing and worldwide shipment.
Send drawing, size, quantity and coating requirements to sales@amardeepsteel.com or call 022-67439130.
Frequently Asked Questions – C-103 Niobium Fasteners
What is C-103 niobium alloy?
C-103 (UNS R04295) is a niobium alloy containing about 10% hafnium and 1% titanium, balance niobium. It keeps useful strength up to about 1,370 °C and is the standard material for rocket and satellite thruster hardware.
Which standard covers C-103 fasteners?
There is no fastener standard specific to C-103. C-103 fasteners are machined to the customer drawing from bar to ASTM B655 or AMS 7852, with threads to ISO, UNC, UNF or UNJ as required.
What is the strength of C-103?
Annealed C-103 bar to ASTM B655 has minimum room-temperature properties of 370 MPa tensile, 260 MPa yield and 20% elongation. At 1,095 °C (2,000 °F) typical tensile strength is about 145 MPa.
Can C-103 fasteners be used in air at high temperature?
Not uncoated. C-103 oxidises rapidly in air above about 400 °C, so hot C-103 fasteners are used in vacuum or inert gas, or with an oxidation-resistant silicide coating such as R512E.
Is C-103 lightweight?
No. C-103 has a density of about 8.85 g/cm³, similar to steel and about twice that of titanium. It is chosen for its high-temperature strength, not for low weight.
Is C-103 the same as R04295?
Yes. UNS R04295 is the unified numbering designation for C-103 (Nb-10Hf-1Ti) niobium alloy.
Global Reach
ASC LLP supplies niobium, C-103, tantalum and other refractory-metal products to aerospace, research and industrial customers worldwide, with secure packing and full documentation. Buyers in the USA, Europe, the Middle East and Asia rely on our C-103 niobium fasteners for certified material and traceability.
Countries We Export To
UNITED STATES, EUROPE, UK, UAE, SAUDI ARABIA, OMAN, KUWAIT, JORDAN, QATAR, INDONESIA, MALAYSIA, BRAZIL, SPAIN, ITALY, FRANCE, GERMANY, BAHRAIN, SRI LANKA, AZERBAIJAN, AUSTRALIA, AUSTRIA, PHILIPPINES, TURKEY, RUSSIA, IRAN, IRAQ, CANADA, KOREA, JAPAN, YEMEN, FINLAND, ZIMBABWE, HUNGARY, PORTUGAL, VIETNAM, MOROCCO, THAILAND, SOUTH AFRICA, MEXICO, SINGAPORE, GREECE, KUWAIT, POLAND, NEW ZEALAND, SWEDEN, SWITZERLAND, BELGIUM, BHUTAN, BANGLADESH, TAIWAN, ROMANIA, CAMBODIA, KAZAKHSTAN, AFGHANISTAN.
