ASTM F593
Alloy 20
Bolts & Fasteners
Why Copper Is the Key Addition Here
Alloy 20 starts from a nickel-iron-chromium base broadly similar in spirit to austenitic stainless steel, then adds molybdenum for general pitting and crevice corrosion resistance — the same mechanism that improves 316 stainless over 304. What makes Alloy 20 genuinely distinct is a deliberate copper addition, a choice most stainless and nickel alloys don’t make, and one made specifically because copper measurably improves resistance to sulfuric acid in a way molybdenum and chromium alone do not.
Sulfuric acid is a genuinely difficult corrosive to design against because its aggressiveness toward different materials varies dramatically with concentration and temperature — a material that resists dilute sulfuric acid well may fail rapidly in concentrated acid at elevated temperature, and vice versa. Alloy 20’s specific combination of nickel, chromium, molybdenum, and copper was engineered to provide genuinely useful resistance across a broad band of this concentration/temperature range, rather than excelling narrowly at one condition and failing elsewhere.
That makes Alloy 20 the correct, specific answer when sulfuric acid handling is the defining service condition — as distinct from chloride-driven pitting corrosion, where a molybdenum-focused alloy without copper (like standard 316 stainless) may already be sufficient and more economical. Confirming that sulfuric acid, specifically, is the governing corrosive is the key step before specifying this alloy.
Akbar Fasteners Pvt. Ltd. exports to over 50 countries, and our ASTM F593 Alloy 20 fastener range is manufactured and verified by chemical composition and mechanical testing under our ISO 9001:2015 quality system.
A Note on Standard Scope
ASTM F593 covers externally threaded stainless and corrosion-resistant alloy fasteners including bolts, hex cap screws, and studs. If your requirement is for matching nuts, ASTM F594 is the companion nut specification typically paired with F593 — please let us know if you’d like both quoted together for a matched Alloy 20 assembly.
Where This Material Genuinely Applies
Genuine Sulfuric Acid Resistance
Copper’s specific role provides resistance across a broad concentration and temperature range.
Genuine Pitting & Crevice Resistance
Molybdenum content provides the same general chloride-resistance mechanism found in 316 stainless.
The Standard Material for This Service
A globally established, well-proven choice specifically for sulfuric acid handling equipment.
Verified Mechanical Properties
Batch testing confirms genuine alloy content and mechanical properties for every lot.
Alloy 20 vs 316 Stainless — Quick Reference
Confirming whether sulfuric acid, specifically, is the governing corrosive before specifying the higher-cost Alloy 20 over standard 316 stainless. This table is the quick reference we use with buyers before quoting.
| Aspect | Alloy 20 (UNS N08020) | 316 Stainless Steel |
|---|---|---|
| Key Alloying Element | Copper (plus molybdenum) | Molybdenum only |
| Sulfuric Acid Resistance | Genuinely superior, broad range | Limited, concentration-dependent |
| Chloride Pitting Resistance | Good | Good, well-established |
| Best Suited For | Sulfuric acid handling equipment | General chloride/corrosive service |
Alloy 20 Specification Details
Nominal Composition
- Nickel ~32 – 38%
- Chromium ~19 – 21%
- Copper ~3.0 – 4.0%
- Molybdenum ~2.0 – 3.0%
Typical Mechanical Range
- Condition Solution Annealed
- Sulfuric Acid Resistance Genuinely Superior
- Pitting/Crevice Resistance Good, Mo-Enhanced
- Fastener Standard ASTM F593
Fastener Types We Manufacture
- Hex Bolts & Cap Screws Standard & Custom Sizes
- Studs Standard & Custom Sizes
- Matching Nuts ASTM F594, On Request
- Washers Matching Material
Application Areas
Wherever sulfuric acid handling, specifically, genuinely drives the material selection beyond what standard stainless can reliably handle.
Sulfuric Acid Process Equipment
piping, and flange bolting
Chemical Processing Plants
equipment fastening
Fertilizer & Chemical Manufacturing
and processing hardware
Pickling & Metal Treatment Equipment
equipment fastening
Standard Export Documentation
Prepared as standard practice for every ASTM F593 Alloy 20 fastener shipment.
Mill Test Certificate (MTC)
Heat number, chemical composition, and mechanical property verification for every lot.
Chemical Composition Report
Confirms actual nickel, chromium, copper, and molybdenum content fall within the specified UNS N08020 range.
Certificate of Conformance
Confirms the shipment matches the purchase order grade/size specification in full.
Certificate of Origin (COO)
Confirms India as country of manufacture for destination customs purposes.
NABL Accredited Test Reports
Independent mechanical and dimensional testing available on request.
Commercial Invoice & Packing List
Itemized value, Incoterm, and detailed carton/weight breakdown for customs clearance.
Internationally Recognised Standards Coverage
Related Fastener Grades & Materials
Hastelloy B3 Stud Bolts (UNS N10675)
Our nickel-molybdenum alloy for reducing acids like hydrochloric acid, distinct from Alloy 20’s sulfuric focus.
View Hastelloy B3 Studs →ASTM A194 Grade 8M Nuts
Our chloride-resistant 316 stainless grade, sufficient where sulfuric acid isn’t the governing corrosive.
View Grade 8M Nuts →UNS C71500 Cupro-Nickel 70/30
Our copper-nickel alloy for seawater erosion-corrosion, a different service environment from acid handling.
View UNS C71500 →Stainless Steel Fasteners Manufacturer India
Our broader fastener manufacturing capability across all major carbon, alloy, stainless, and non-ferrous grades.
View SS Manufacturer Guide →Sulfuric Acid
Handling Equipment?
Tell us your acid concentration and operating temperature — we’ll confirm whether Alloy 20 genuinely fits, and quote with full documentation, matched nuts included on request. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Sales: +91 724 0000 733 · Support: +91 800 9315 333 · sales@akbarfasteners.in