AM350values describe: AM350 SCT850
Vacuum equipment & componentsBig science (accelerators, light sources, public fusion)Space test
Why it wins
Edge-welded and hydroformed bellows live on fatigue: precipitation-hardening steels give the cycle life plain 316L cannot.
Why not the alternative
316L bellows are fine for static offsets; motion feedthroughs and thermal cycling eat them.
Watch out
PH grades are magnetic: check the permeability budget near beams.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated.
Provisional provenance: ASM Handbook: properties, corrosion, heat treatment; Electron tube and ceramic-to-metal sealing practice.
Wet cleaning
| Recipe | degrease and DI rinse; convolutions trap fluid, so long drain and hot dry |
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| Forbidden | high-power ultrasonics: thin convolutions crack |
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| Limit | the convolution root, not the surface |
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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 | negligible |
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Temperature
| Bake, assembled | 450 °C |
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| Vacuum degas | 950 °C |
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| Braze / H2 firing | 1000 °C |
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| Metallurgical limit | anneal 930 °C, age 850 °C |
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Thermal
| CTE | 11.9 ppm/K |
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| Thermal conductivity | 15 W/m·K |
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| Specific heat | 480 J/kg·K |
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| Emissivity | 0.2 |
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| Melting / softening | 1400 °C |
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Mechanical
| Strength | 1000+ ys MPa |
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| Tensile | 1200 MPa |
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| Elongation | 12 % |
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| Young's modulus | 200 GPa |
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| Hardness | ~400 HV |
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| Density | 7.91 g/cm3 |
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Electrical and magnetic
| Relative permeability | ferromagnetic after ageing |
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| Resistivity | 80 µΩ·cm |
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Engineering
| Corrosion | good |
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| Joining | welded then aged |
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| Process notes | formed soft, hardened after |
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| Availability and cost | bellows makers stock it |
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Grades
| AM 350 (S35000) | the edge-welded diaphragm standard |
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| 17-7 PH (S17700) | hydroformed convolutions |
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| 316L | non-magnetic choice when cycles are few |
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Sources · 1
- O Hanlon, A Users Guide to Vacuum Technology
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