A286values describe: A286
Big science (accelerators, light sources, public fusion)Quantum hardwareSpace testVacuum equipment & components
Why it wins
Bolting is where UHV builds actually fail: galling, seized threads, trapped volumes. The doctrine: anti-galling alloys, plated threads, vented screws.
Why not the alternative
Standard A2 stainless on stainless galls cold-welded; lubricants are banned or rationed inside.
Watch out
Every blind tapped hole needs a vented screw or a relief: virtual leaks are fastener physics.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated.
Provisional provenance: ASM Handbook: properties, corrosion, heat treatment; CERN Accelerator School, vacuum and materials proceedings; Electron tube and ceramic-to-metal sealing practice.
Wet cleaning
| Recipe | degrease only; plated bolts are used as delivered |
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| Forbidden | stripping the anti-galling plating |
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| Limit | the plating is the wear surface, cleaning must not touch it |
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Vacuum and outgassing
| Outgassing, unbaked (10 h) | 2e-9 mbar·L/s/cm² |
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| Outgassing, baked | 1e-11 mbar·L/s/cm² |
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| Vapour pressure | silver plating evaporates above ~600 °C |
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Temperature
| Bake, assembled | 450 °C |
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| Vacuum degas | 1000 °C |
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| Braze / H2 firing | 1100 °C |
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| Metallurgical limit | solution 900 °C then age 720 °C |
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Thermal
| CTE | 16.5 ppm/K |
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| Thermal conductivity | 12.6 W/m·K |
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| Specific heat | 460 J/kg·K |
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| Emissivity | 0.2–0.3 |
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| Melting / softening | 1370–1400 °C |
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Mechanical
| Strength | 590–725 ys MPa |
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| Tensile | 900–1000 MPa |
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| Elongation | 15 % |
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| Young's modulus | 201 GPa |
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| Hardness | ~300 HV |
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| Density | 7.94 g/cm3 |
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Electrical and magnetic
| Relative permeability | <1.01 |
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| Resistivity | 91 µΩ·cm |
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Engineering
| Corrosion | good |
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| Joining | not welded; used as fasteners |
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| Process notes | silver or MoS₂ coated against galling |
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| Availability and cost | stock as UHV bolt sets |
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Grades
| A4-80 (316 class), silver plated | the default UHV bolt: Ag stops galling and survives bake |
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| A286 (S66286) | non-magnetic high strength, cryo rated: flanges under load |
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| Nitronic 60 (S21800) | inherently anti-galling: nuts and wear pairs without plating |
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| MoS2-coated hardware | where silver is forbidden (some plasma and optics contexts) |
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Sources · 2
- CERN Accelerator School, vacuum proceedings
- O Hanlon, A Users Guide to Vacuum Technology
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