The strongest bolting alloy we make: 185 ksi tensile after double ageing, stable from cryogenic temperatures to 1300°F, and supplied with full EN 10204 3.1 traceability from our Mumbai works.
Most nickel superalloys trade strength for corrosion resistance. Inconel 718 fasteners refuse that trade-off. Known as Alloy 718, UNS N07718, Werkstoff Nr. 2.4668 and by trade names such as Nicrofer 5219 and Superimphy 718, this precipitation-hardening nickel-chromium alloy develops roughly 185 ksi (1275 MPa) tensile and 150 ksi (1034 MPa) yield after solution treatment and double ageing — comparable to a quenched-and-tempered alloy steel bolt, but with that strength retained at 1200°F and full ductility retained down to cryogenic temperatures. At Unifit Fastener, we manufacture the complete bolting family in Alloy 718 — hex bolts, heavy hex nuts, stud bolts, threaded rods, washers, screws and anchor fasteners — from M3 to M100 and 3/16" to 4", to ASTM B637, ASME SB637, AMS 5662/5663 and ASTM F467/F468. Every lot is PMI-verified, hardness-surveyed after ageing and released with an EN 10204 3.1 mill test certificate. Whether you are bolting a gas turbine casing, a downhole tool, a sour-service wellhead or an LNG transfer line, you get certified heat treatment and documented traceability — not just a bag of nickel-coloured hardware.
Inconel 718 fasteners are threaded components manufactured from a precipitation-hardenable nickel-chromium-iron alloy containing niobium, molybdenum, titanium and aluminium. Unlike solid-solution alloys such as Inconel 600 or Inconel 625, Alloy 718 gains most of its strength from a controlled heat treatment that precipitates fine gamma double-prime (Ni₃Nb) particles through the matrix. That single metallurgical difference is why a 718 bolt is roughly twice as strong as a 625 bolt at room temperature.
This is the point most supplier pages miss, and it causes real procurement errors. Alloy 718 is sold in two very different conditions, and the mechanical values differ by nearly a factor of two:
If a quotation does not state the condition, it is not a quotation for a load-bearing fastener. Every Unifit Fastener 718 item is supplied solution treated and double aged unless you specifically instruct otherwise, and the certificate states the cycle used.
Unifit Fastener manufactures more than 40 fastener forms in Alloy 718, all produced in-house or from our own certified bar stock — we do not re-badge trading material.
Condition |
Tensile (min) |
Yield 0.2% (min) |
Elongation |
Hardness |
When to Specify |
|---|---|---|---|---|---|
Solution annealed (as-supplied bar) |
~965 MPa / 140 ksi |
~550 MPa / 80 ksi |
30% min |
≤ 100 HRB |
Only where further forming or customer-side ageing is planned |
Solution treated + double aged (AMS 5663 / B637) |
1275 MPa / 185 ksi |
1034 MPa / 150 ksi |
12% min |
331 HBW min |
Virtually all finished fasteners — this is what you should be buying |
Parameter | Specification |
|---|---|
Material Grade | Inconel 718 / Alloy 718 / Nickel Alloy 718 |
UNS Designation | UNS N07718 |
Werkstoff Number | 2.4668 |
Common Trade Names | Nicrofer 5219 Nb, Superimphy 718, Haynes 718, Pyromet 718 |
Governing Standards | ASTM B637, ASME SB637, AMS 5662 (solution treated), AMS 5663 (solution treated + aged), AMS 5664, ASTM F467, ASTM F468, ASTM F2281, API 6A718 |
Dimensional Standards | ASME B18.2.1, ASME B18.2.2, ASME B18.3, ASME B18.21.1, DIN 931, DIN 933, DIN 934, DIN 125, DIN 976, DIN 7991, ISO, JIS, BS, GB, IS |
Supply Condition | Solution treated and double aged (standard) or solution annealed (on request) |
Size Range (Bolts) | M3 – M100 | 3/16" to 4" | custom sizes on request |
Size Range (Nuts) | M3 – M56 | 3/16" to 2" |
Size Range (Washers) | M3 – M56 | 3/16" to 2" |
Length Range | 3 mm to 200 mm and above (custom lengths available) |
Thread Types | UNC, UNF, UN, 8UN, BSW, BSF, metric coarse, metric fine, left or right hand |
Thread Configuration | ASME B1.1 2A/3A – 2B/3B inch unified; ASME B1.13M 6g–6H metric coarse |
Head Styles | Hex, heavy hex, square, round, flange, countersunk, socket, T-head, triangular, knurled |
Point / End Styles | Chamfered, cone, cup, flat, dog point, rolled thread end |
Manufacturing Route | Hot forging, cold heading, CNC turning, thread rolling, solution treatment, double ageing |
Surface Finish | Bright / self-colour, passivated, pickled, black oxide, Xylan, PTFE, phosphate, zinc-nickel |
Tolerance | OEM / ODM to drawing; ±0.03 mm achievable on machined features |
Test Certificate | EN 10204 / 3.1 mill test certificate; PED 2014/68/EU and AD 2000 W2 on request |
Certification | Dual certified to ASTM and ASME codes |
HS Code | 7318 (threaded fasteners of nickel alloy); 7505 applies to bar and rod stock — confirm with your customs broker by product form |
Delivery | Standard products 7–15 days; custom products 2–4 weeks |
Country of Origin | India (Mumbai, Maharashtra) |
Composition limits per ASTM B637 / ASME SB637, expressed as weight percentage.
Element | Symbol | Weight % | Metallurgical Role |
|---|---|---|---|
Nickel (+ cobalt) | Ni | 50.00 – 55.00 | Austenitic matrix; corrosion backbone |
Chromium | Cr | 17.00 – 21.00 | Oxidation and general corrosion resistance |
Iron | Fe | Balance | Matrix constituent; keeps cost workable |
Niobium (+ tantalum) | Nb | 4.75 – 5.50 | Forms gamma double-prime — the primary strengthener |
Molybdenum | Mo | 2.80 – 3.30 | Solid-solution strength; pitting resistance |
Titanium | Ti | 0.65 – 1.15 | Secondary gamma-prime precipitate |
Aluminium | Al | 0.20 – 0.80 | Supports gamma-prime; deoxidiser |
Cobalt | Co | 1.00 max | Residual limit |
Carbon | C | 0.08 max | Controlled to limit carbide networks |
Manganese | Mn | 0.35 max | Deoxidiser |
Silicon | Si | 0.35 max | Deoxidiser |
Copper | Cu | 0.30 max | Residual limit |
Boron | B | 0.006 max | Grain-boundary strengthening in trace amounts |
Phosphorus | P | 0.015 max | Restricted impurity |
Sulphur | S | 0.015 max | Restricted to protect hot workability |
Property | Metric Value | Imperial Value |
|---|---|---|
Tensile Strength (min) | 1275 MPa | 185,000 psi |
Yield Strength (0.2% offset, min) | 1034 MPa | 150,000 psi |
Elongation in 2" (min) | 12% | 12% |
Reduction of Area (min) | 15% | 15% |
Hardness (min) | 331 HBW / ~36 HRC | 331 HBW / ~36 HRC |
Typical Tensile at 649°C (1200°F) | ~1000 MPa | ~145,000 psi |
*Values are minima for the aged condition per ASTM B637 Grade 718 / AMS 5663. Certified results for your specific heat appear on the accompanying mill test certificate.*
Property | Value |
|---|---|
Density | 8.19 g/cm³ (0.296 lb/in³) |
Melting Range | 1260 – 1336 °C (2300 – 2437 °F) |
Modulus of Elasticity (RT) | ~200 GPa (29 × 10⁶ psi) |
Poisson's Ratio | 0.284 – 0.30 |
Thermal Conductivity (RT) | 11.4 W/m·K |
Specific Heat | 435 J/kg·K |
Electrical Resistivity (RT) | ~1.25 µΩ·m (125 µΩ·cm) |
Mean Coefficient of Thermal Expansion (25–100°C) | 12.8 µm/m·°C |
Maximum Continuous Service Temperature | ~704 °C (1300 °F) |
Magnetic Response | Non-magnetic in the aged condition |
Standard | Werkstoff Nr. | UNS | JIS | EN | AMS | Trade Names |
|---|---|---|---|---|---|---|
Inconel 718 | 2.4668 | N07718 | NCF 718 | NiCr19Fe19Nb5Mo3 | 5662 / 5663 / 5664 | Nicrofer 5219 Nb, Superimphy 718 |
Bolt / Screw Type | Common Standard | Typical Use Case |
|---|---|---|
Hex bolts / hex head bolts | ASME B18.2.1, DIN 931/933 | General high-strength structural and flange bolting |
Heavy hex bolts | ASME B18.2.1 | High-pressure and high-preload flanged joints |
Socket head cap screws | ASME B18.3, DIN 912 | Turbine casings, valve internals, compact assemblies |
12-point flange bolts | OEM drawing | Maximum torque in restricted-access aerospace assemblies |
Flange head bolts | DIN 6921 | Vibration-prone joints without a separate washer |
Countersunk / flat head screws | DIN 7991, ISO 10642 | Flush-mounted liners and covers |
Shoulder bolts | ISO 7379 | Precision location under load |
Hanger bolts, J bolts, U bolts, eye bolts | DIN 580 / custom | Pipe support, lifting and tube clamping |
Anchor bolts and expansion anchors | ASTM B637 / drawing | Equipment and foundation anchoring |
Set screws and grub screws | DIN 913–916 | Shaft and collar location at temperature |
Self-drilling and self-tapping screws | DIN 7504 / 7981 | Sheet, duct and cladding fixings |
Torx and machine screws | ISO 14579 | Tamper-resistant and precision assemblies |
Nut Type | Common Standard | Typical Use Case |
|---|---|---|
Hex nuts | ASTM F467, DIN 934 | Standard mating nut for Alloy 718 bolting |
Heavy hex nuts | ASTM F467, ASME B18.2.2 | Pressure-boundary and high-preload joints |
Hex jam / thin nuts | DIN 439 | Locking and clearance-limited joints |
Castle and slotted nuts | DIN 935 | Cotter-pin retention on rotating hardware |
All-metal prevailing torque lock nuts | DIN 980 | High-temperature vibration locking |
Keps-K lock nuts | DIN 6923 style | Captive washer for fast assembly |
Coupling nuts | DIN 6334 | Threaded rod extension |
Cap / acorn / dome nuts | DIN 1587 | Thread protection and finished appearance |
Wing nuts, stove nuts, T-nuts | DIN 315 / custom | Hand-adjusted access hardware |
Square nuts and 12-point nuts | DIN 557 / OEM | Channel fixing and high-torque assemblies |
Weld nuts, rivet nuts, insert nuts | DIN 928 / custom | Blind and sheet-metal fastening |
Stud / Rod Type | Description |
|---|---|
Fully threaded stud bolts | Continuous thread both ends — the standard ASME B16.5 flange stud |
Double-ended studs (tap-end / nut-end) | Plain centre body with threaded ends for tapped-hole assemblies |
Reduced-shank stud bolts | Waisted body for controlled elongation and improved fatigue performance |
Half-threaded and partial-thread studs | Where a plain grip length passes through the joint |
Threaded rods / all-thread rod | DIN 976 in cut-to-length or standard bar lengths |
Tie rods and tie bars | Turbine casing and duct restraint hardware |
Dowel pins and precision studs | Location hardware machined to h6 tolerance |
See our dedicated Inconel stud bolts page and the general stud bolts range, or the guide to types of stud bolts.
Washer Type | Standard | Function |
|---|---|---|
Plain / flat washers | DIN 125, DIN 126, ASME B18.21.1 | Load distribution under head or nut |
Structural and fender washers | F436 style / custom | Large bearing area on soft or oversized holes |
Spring / split lock washers | DIN 127 | Vibration resistance in cycled joints |
Belleville / conical spring washers | DIN 6796 | Preload maintenance through thermal cycling |
Tab washers and lock plates | DIN 93 / 463 | Positive mechanical locking |
Star / serrated tooth lock washers | DIN 6797 / 6798 | Anti-rotation on coated surfaces |
Square and ogee washers | Custom | Heavy plate and structural work |
Related pages: Inconel washers, nickel alloy washers and the reference article on types of washers.
This is the question engineers actually search for, and generic fastener torque charts get it badly wrong for Alloy 718 — most published tables assume a 30–90 ksi proof stress and will leave a 718 joint under-clamped by more than half.
The Method. Torque is derived, not looked up. Use T = K × D × F, where T is torque, K is the nut factor (typically 0.20 dry, 0.15 lubricated, 0.10–0.12 with a PTFE or Xylan coating), D is nominal diameter, and F is the target preload. For aged 718 at a target preload of 65% of the 150 ksi yield strength (97.5 ksi on the tensile stress area), the figures work out as follows.
Size (UNC / 8UN) | Tensile Stress Area (in²) | Target Preload (lbf) | Torque, Dry K=0.20 (ft-lb) | Torque, Lubricated K=0.15 (ft-lb) |
|---|---|---|---|---|
3/8"–16 | 0.0775 | 7,556 | 47 | 35 |
1/2"–13 | 0.1419 | 13,835 | 115 | 86 |
5/8"–11 | 0.2260 | 22,035 | 230 | 172 |
3/4"–10 | 0.3340 | 32,565 | 407 | 305 |
7/8"–9 | 0.4620 | 45,045 | 657 | 493 |
1"–8 | 0.6060 | 59,085 | 985 | 739 |
1-1/4"–8 | 1.0000 | 97,500 | 2,031 | 1,523 |
Alloy 718 is one of the few fastener materials where the heat treatment matters as much as the chemistry. Two bolts with identical certified analysis can differ by 80 ksi in tensile strength purely because of the ageing cycle.
Stage | Typical Cycle | Purpose |
|---|---|---|
Solution treatment | 1725 – 1850 °F (940 – 1010 °C), then rapid cool | Dissolves precipitates and delta phase; sets grain size (AMS 5662 route) |
High-temperature solution (creep-rupture route) | 1900 – 1950 °F (1040 – 1065 °C) | Coarser grain for optimum stress-rupture life at temperature (AMS 5664) |
First age | 1325 °F (718 °C) for 8 hours | Nucleates the gamma double-prime precipitate |
Furnace cool | To 1150 °F (621 °C) at ~100 °F/hour | Controlled transition between ageing steps |
Second age | 1150 °F (621 °C) for 8 hours, then air cool | Completes precipitation and develops full 185 ksi strength |
Total cycle time is around 18 hours, which is precisely why under-aged material exists in the market — skipping the second stage saves a day of furnace time and is invisible without a hardness check. Ask for the hardness result on the finished fastener, not the billet. Anything below 331 HBW in the aged condition has not been fully processed.
Alloy 718 bolting is specified where high strength, elevated temperature and corrosive or cyclic conditions occur together — a combination no single conventional material handles.
Industry | Where Inconel 718 Fasteners Are Used | Why This Alloy Wins |
|---|---|---|
Aerospace & gas turbine | Engine casings, turbine discs, exhaust hardware, airframe fittings, lockwire | Highest strength-to-temperature ratio in the nickel family |
Oil & gas — downhole | Wellhead components, packers, downhole tool joints, drilling hardware | Strength plus H₂S and CO₂ resistance in sour service |
Subsea & offshore | Connector bolting, riser hardware, ROV-serviced joints | Corrosion resistance with high preload capacity |
Power generation | Steam and gas turbine bolting, generator retaining hardware | Creep resistance and preload retention over long hot holds |
Nuclear engineering | Reactor internals, pressurised water reactor hardware, fuel handling | High strength with controlled magnetic permeability |
Cryogenic & space | Liquid oxygen and LNG hardware, rocket motor fasteners, cryogenic tanks | Retains ductility to −253 °C with no transition temperature |
Turbomachinery | Turbochargers, compressor casings, high-speed rotating assemblies | Fatigue strength under vibration and thermal cycling |
Chemical processing | High-pressure reactors, heat exchangers, exhaust systems | Combined pressure and corrosion duty |
Mining & tunnel boring | Cutter head hardware, high-load structural fixings | Impact and fatigue resistance at high preload |
Further reading: why Inconel 718 bolts are preferred for high-temperature environments and the broader guide to the applications and uses of Inconel fasteners.
Over-specifying wastes money; under-specifying costs a shutdown. Use this grid to confirm 718 is the right call before releasing the order.
Grade | Min Yield | Min Tensile | Max Service Temp | Best Suited To |
|---|---|---|---|---|
Inconel 718 | 150 ksi (1034 MPa) | 185 ksi (1275 MPa) | ~1300°F (704°C) | High-strength hot bolting, downhole, aerospace, cryogenic |
Inconel X-750 | ~115 ksi (795 MPa) | ~165 ksi (1140 MPa) | ~1300°F (704°C) | Springs, retaining hardware, moderate-strength hot service |
Inconel 625 | 60 ksi (414 MPa) | 120 ksi (827 MPa) | ~1800°F (982°C) | Seawater, acids, subsea — corrosion-led duty |
Inconel 600 | 35 ksi (240 MPa) | 80 ksi (550 MPa) | ~2000°F (1093°C) | Furnaces and heat exchangers — temperature-led duty |
ASTM A453 Gr 660 (A286) | 85 ksi (585 MPa) | 130 ksi (896 MPa) | ~1200°F (649°C) | Cost-effective alternative below 650°C and mild corrosion |
Compare directly with Inconel 600 fasteners, Inconel 601 fasteners, Inconel 625 fasteners, Inconel X-750 fasteners, Incoloy 925 fasteners and ASTM A453 Gr 660 fasteners.
Criterion | Inconel 718 | A286 (A453 Gr 660) | 17-4 PH Stainless |
|---|---|---|---|
Nominal nickel content | 50 – 55% | 24 – 27% | 3 – 5% |
Minimum tensile | 185 ksi | 130 ksi | 135 – 190 ksi (by condition) |
Practical temperature ceiling | ~704°C | ~649°C | ~315°C |
Cryogenic capability | Excellent to −253°C | Good | Limited — embrittles |
Sour service (H₂S) | Qualified under API 6A718 | Limited | Not suitable |
Relative cost index | Highest | Medium-high | Low-medium |
Best-fit duty | Extreme strength + heat + corrosion | Hot bolting on a budget | Ambient high-strength corrosion service |
Also consider Hastelloy fasteners, titanium grade 5 fasteners, super duplex fasteners and high tensile fasteners where the balance of duty is different.
Test | Purpose | Availability |
|---|---|---|
Positive Material Identification (PMI) | Confirms alloy grade before dispatch | 100% of lots |
Chemical analysis (spectro) | Verifies composition against ASTM B637 | Per heat |
Hardness survey (Brinell / Rockwell) | Confirms complete ageing — the critical 718 check | Per lot, on finished parts |
Tensile, yield, elongation and RA | Confirms mechanical class | Per lot / per heat |
Stress-rupture testing | Validates creep performance for AMS 5664 material | On request / per spec |
Ultrasonic testing (UT) | Internal flaw detection in billets and large studs | On request / per spec |
Dye penetrant (DP) testing | Surface crack detection after ageing | On request |
Micro and macro examination | Grain size, delta phase and forging flow verification | On request |
Flattening and flaring tests | Ductility verification where specified | On request |
Third-party inspection | TÜV, BV, SGS, Lloyd's witness inspection | On request |
Standard | Scope for Inconel 718 Fasteners |
|---|---|
ASTM B637 / ASME SB637 | Precipitation-hardening nickel alloy bars, forgings and forging stock for high-temperature service — the primary standard for 718 fasteners |
AMS 5662 | Solution treated condition — used where the customer will age after forming |
AMS 5663 | Solution treated and double aged — the standard finished-fastener condition |
AMS 5664 | High-temperature solution treatment for optimum stress-rupture performance |
ASTM F467 / F468 | Nonferrous nuts, bolts, hex cap screws and studs for general use |
ASTM F2281 | Nickel alloy fasteners for high-temperature service |
API 6A718 / NACE MR0175 (ISO 15156) | Sour service qualification for oilfield equipment — specify explicitly at enquiry stage |
ASME B18.2.1 / B18.2.2 / B18.3 | Dimensional standards for inch bolts, nuts and socket screws |
ASME B1.1 / B1.13M | Unified inch and metric thread tolerance classes |
DIN 931 / 933 / 934 / 125 / 976 | Metric bolt, nut, washer and threaded rod dimensions |
EN 10204 3.1 | Mill test certificate issued by the manufacturer's independent inspection function |
PED 97/23/EC, AD 2000 W2 | Pressure equipment conformity documentation (on request) |
More context in our fasteners standards reference and the guide to ISO fastener standards.
718 punishes process shortcuts more than any other alloy we work. Our route is built around the two things that go wrong most often: incomplete ageing, and threads produced in the wrong sequence.
We supply Inconel 718 fasteners across India — Mumbai, Pune, Ahmedabad, Chennai, Hyderabad, Bangalore, Coimbatore, Jamnagar, Vadodara, Kolkata, Vizag and Pimpri-Chinchwad — and export to the UAE, Saudi Arabia, Qatar, Oman, Kuwait, Jordan, Singapore, Malaysia, Thailand, Indonesia, Vietnam, South Korea, Japan, Australia, the United States, Canada, Mexico, Brazil, the United Kingdom, Germany, Netherlands, Italy, Turkey, Egypt, Nigeria and South Africa.
Alloy 718 is rated for continuous service up to approximately 1300°F (704°C). It retains most of its strength to about 1200°F and can survive brief excursions higher, though the strengthening precipitate begins to coarsen and over-age above roughly 1350°F. For sustained service above 800°C, choose Inconel 600 or Inconel 601 instead.
No. Stainless steel is an iron-based alloy with a minimum of about 10.5% chromium. Inconel 718 is a nickel-based superalloy with 50–55% nickel and iron as the balance. The nickel base is what gives it strength retention at temperature and resistance to chloride and sulphide attack that no stainless grade can match.
718 is precipitation-hardened and 625 is solid-solution strengthened. That makes 718 roughly twice as strong (185 ksi versus 120 ksi tensile) but limits it to about 704°C, while 625 works to about 982°C and offers superior pitting and crevice resistance in seawater and acids. Choose 718 for strength, 625 for corrosion.
Solution treatment at roughly 940–1010°C followed by a two-stage age: 8 hours at 718°C, furnace cool to 621°C, then a further 8 hours before air cooling. Skipping the second stage leaves the fastener significantly under-strength, and the only reliable field check is hardness — aged material should read 331 HBW or higher.
Yes. Alloy 718 retains excellent toughness and ductility down to approximately −253°C (−423°F) with no ductile-to-brittle transition, which is why it is standard for liquid oxygen, LNG and rocket propellant hardware.
Bolts and screws from M3 to M100 (3/16" to 4"), nuts and washers from M3 to M56 (3/16" to 2"), and lengths from 3 mm to 200 mm as standard. Larger diameters and non-standard lengths are produced to drawing.
Send us your drawing, condition, standard and quantity — our engineering team will confirm grade suitability, ageing route, thread sequence and lead time before quoting. No obligation, no generic price lists, no guesswork.
Speak to a Materials Engineer — call or WhatsApp us today.
Not sure which grade you need? Compare Inconel 600, 625 and X-750, or contact our team for a recommendation.