Exotic alloy grades compared: A-286, Inconel 718, Inconel X-750, Monel K-500 and titanium
These five grades cover the service conditions carbon and stainless steels walk away from — cryogenic flight, 1200 °F exhaust-side hardware, high-velocity seawater, corrosion-critical weight-limited joints. This table compares the five grades we publish individual specification pages for, using only fields that mean the same thing across the columns. Where the collected sources are silent — most of the Monel K-500 column, for example — the cell says so and asks you to confirm it at RFQ; nothing is filled in with an assumption, and no cell implies a grade cannot be supplied.
Comparison table
Temperature windows and strength ceilings are quoted from the collected NASA fastener-material table in °F and ksi verbatim; strength figures carry their own production caveats per column and are marked where the bases differ.
| Field | A-286 | Inconel 718 | Inconel X-750 | Monel K-500 | Titanium |
|---|---|---|---|---|---|
| Alloy class | Precipitation-hardened austenitic stainless steel | Nickel-chromium superalloy | Nickel-chromium alloy, precipitation hardenable | Precipitation-hardened nickel-copper alloy (K-Monel) | Titanium, fastener grade — the collected table lists no grade split, so the required grade is named at quotation Conditional — confirm configuration |
| Useful design temperature window All figures from the collected NASA fastener-material table, °F verbatim per column — one table, one basis, so the windows compare directly. | -423 to 1200 °F — the widest collected window on the page | -423 to 900 °F — or the cadmium-plate limit when cadmium plated | -320 to 1200 °F | No tabulated design window — cryogenic-suitable (bulletin: strengths increase as temperature drops, NASA data to -423 °F, no ductile-to-brittle transformation at liquid-hydrogen temperature); hot hardness tabulated to 1100 °F Conditional — confirm configuration | -350 to 500 °F — a corrosion-and-weight ceiling, not a high-temperature one |
| Ultimate tensile strength, room temperature (as published) Same meaning (room-temperature UTS) and one source table for four of the five columns; the A-286 column additionally carries the collected prose on how high it is actually produced. | Up to 220 ksi — usually produced only to 160 ksi; 220-ksi fasteners are a special order per the collected prose | Up to 220 ksi (table verbatim); a collected bolt-grade chart additionally quotes 1,240 MPa specialty fasteners beyond Class 12.9 | Up to 180 ksi (table verbatim) | Rod hot-finished aged: 140–190 ksi (965–1310 MPa nominal range); fastener samples (bulletin Table 7, cold-drawn & aged): threaded stud 165.0 ksi smooth tensile / 232.0 ksi notched | Up to 160 ksi (table verbatim) |
| Strength at temperature | Not tabulated in the collected sources Unverified — confirm at RFQ | Short-time tensile 164.5 ksi at 1200 °F / 145.5 ksi at 1300 °F (Special Metals bulletin Table 20, 5/8-in. aged round) — tabulated to 1300 °F even though the design window stops at 900 °F | 136 ksi at 1200 °F — the only column with a printed hot-strength value | Hot tensile is figure-only, not tabulated; the bulletin tabulates hot hardness instead (aged rod: Brinell 293 at 900 °F, 255 at 1000 °F, 179 at 1100 °F) | Not tabulated in the collected sources — the window itself ends at 500 °F Unverified — confirm at RFQ |
| Surface treatment (per the collected table) | Passivated per MIL-S-5002 | Passivated per QQ-P-35, or cadmium plated (temperature limit then reads "or cadmium plate limit") | None listed | Not tabulated in the collected sources Unverified — confirm at RFQ | None listed |
| Corrosion & environment evidence | Not susceptible to stress corrosion — the wider -423 to 1200 °F window traded against the stress-corrosion-sensitive 17-7PH / 17-4PH space | High-strength bolting in critical subsea service; pitting and crevice corrosion resistance in chloride-rich waters | No environment narrative in the collected sources — the column is positioned by its 1200 °F window and printed hot strength Unverified — confirm at RFQ | Exceptional seawater corrosion resistance in high-velocity flow; resists biofouling — the flowing-seawater column | Ultimate corrosion immunity and strength-to-weight ratio in critical marine applications |
| Hydrogen caution (as documented) | Not established by the collected sources — state any hydrogen exposure at RFQ Unverified — confirm at RFQ | Susceptible at high hydrogen pressure; documented ductility loss under high-pressure gaseous hydrogen | Not established by the collected sources — state any hydrogen exposure at RFQ Unverified — confirm at RFQ | K-Monel has been embrittled by hydrogen at high pressure; solid-solution Monel 400 is generally resistant | Not established by the collected sources — state any hydrogen exposure at RFQ Unverified — confirm at RFQ |
| Best for | Aerospace and space-flight joints needing stainless corrosion behaviour across the full -423 to 1200 °F window without the PH-martensitic stress-corrosion sensitivity | The strength-ceiling column — highest collected UTS with temperature headroom to 900 °F, for critical subsea and high-load joints | Joints that must still carry load at temperature — a printed hot-strength value (136 ksi at 1200 °F) across the widest tabulated window, now joined by Inconel 718's bulletin ladder | Shafts, valves and fasteners in flowing seawater, where high-velocity corrosion resistance and biofouling behaviour decide | Corrosion-critical, weight-critical joints up to 500 °F — immunity first, with the lowest strength ceiling of the five |
- Verified
- Differs
- Unverified — confirm at RFQ
- Conditional — confirm configuration
How to choose
By what the joint must survive first
Decide whether temperature or environment is the controlling constraint, because the grades order differently on each. On temperature, A-286 and Inconel X-750 share the 1200 °F ceiling and X-750 alone prints a strength value at that temperature; on environment, the corrosion evidence splits by medium — flowing seawater points to Monel K-500, chloride-rich subsea at high load points to Inconel 718, weight-critical corrosion immunity points to titanium, and stress-corrosion-sensitive designs move from the 17-4PH / 17-7PH space to A-286. A joint that is both hot and wet is the case to specify in full rather than resolve from one row.
By the strength ceiling you actually need
The "up to" figures position the grades, they are not deliverable schedules: A-286 and Inconel 718 both reach 220 ksi in the collected table, but the A-286 prose notes the alloy is usually produced only to 160 ksi, with 220-ksi fasteners on special order — and titanium tops out at 160 ksi by design intent, chosen for corrosion and weight rather than raw load. Name your working load, temperature and size on the RFQ and confirm the delivered strength class at quotation.
By the documented cautions
Two columns carry hydrogen cautions — Inconel 718 under high-pressure gaseous hydrogen, and Monel K-500 at high hydrogen pressure (with solid-solution Monel 400 as the generally resistant sibling). The other three columns are silent in the collected sources, and silence is not clearance: if your service exposes fasteners to hydrogen, say so explicitly at RFQ regardless of grade so the selection is reviewed against the exposure case.
Frequently asked questions
Which of these alloys for a high-temperature joint, and which for a corrosive one?
Read the temperature row and the corrosion row as separate filters. On temperature, A-286 runs -423 to 1200 °F and Inconel X-750 -320 to 1200 °F with a printed 136 ksi at 1200 °F, while Inconel 718's design window stops at 900 °F even though its bulletin tabulates short-time tensile strength to 1300 °F (164.5 ksi at 1200 °F); titanium stops at 500 °F. On corrosion, the collected evidence splits by environment: Monel K-500 for flowing seawater, titanium for ultimate corrosion immunity at low weight, Inconel 718 for chloride-rich subsea service at high strength, and A-286 where stress-corrosion susceptibility rules out the 17-4PH / 17-7PH space. A joint that is both hot and wet is exactly the case to describe fully on the RFQ rather than pick from a single column.
The strength figures all say "up to" — how should I use them?
They are ceiling values from the collected NASA fastener-material table, quoted verbatim, and the production reality sits under them: the A-286 page's collected prose notes the alloy is usually produced only to 160 ksi, with 220-ksi fasteners a special order. Treat "up to 220 ksi" as what the alloy system can reach, name your actual load and size at quotation, and confirm the delivered strength class — the figure is a positioning marker between columns, not a design allowable for a specific fastener.
Do I need to worry about hydrogen for these alloys?
Only two of the five columns carry documented cautions: Inconel 718 (measurable ductility loss under high-pressure gaseous hydrogen) and Monel K-500 (embrittled by hydrogen at high pressure, while solid-solution Monel 400 is generally resistant). The remaining columns say nothing either way in the collected sources — silence is not clearance. If your service exposes fasteners to high-pressure hydrogen, say so explicitly at RFQ regardless of the grade, so the selection and any testing are confirmed against the exposure case.
Individual alloy specification pages
Each grade has its own page — designation detail, collected table values and RFQ guidance.
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