ASTM B473 Alloy 20 hex bolts, stud bolts, and heavy hex nuts engineered specifically to overcome hot sulfuric acid corrosion and chloride stress-corrosion cracking.
High-Integrity Alloy 20 Bolting Solutions
Full heat-number traceability, EN 10204 3.1 certification, and precision thread rolling to ASME B18.2.1 standards.
Global Fastener Export Excellence
Fast-track production schedules, third-party inspection readiness, and seaworthy export packaging worldwide.
Hot-forged and precision CNC-machined Alloy 20 hex head bolts manufactured to ASTM B473 UNS N08020. Built for extreme chemical joint torque requirements.
Continuous thread and double-end Alloy 20 stud bolts engineered for high-pressure flange connections in sulfuric acid pickling lines and reactors.
Mating Alloy 20 heavy hex nuts and flat/spring washers designed to eliminate galvanic corrosion and prevent thread galling under load.
A comprehensive analysis of chemistry, microstructural stability, corrosion thresholds, and stress-corrosion resistance for critical piping systems.
When chemical plants, pharmaceutical manufacturers, and acid recovery facilities evaluate high-performance bolting, standard austenitic stainless steels like 304L or 316L often fail prematurely due to aggressive chemical attack. Alloy 20 Fasteners—also known under the proprietary trade name Carpenter 20 CB-3 and standardized as UNS N08020 / 2.4660—represent an iron-nickel-chromium super-austenitic alloy specifically formulated to survive where conventional stainless steels disintegrate.
The defining metallurgical advantage of Alloy 20 lies in its high nickel content (32.0% – 38.0%) combined with substantial additions of copper (3.0% – 4.0%), molybdenum (2.0% – 3.0%), and chromium (19.0% – 21.0%). Furthermore, it is stabilized with Niobium (Columbium), which prevents intergranular chromium carbide precipitation during hot forging or welding process cycles.
| Element Symbol | Chemical Composition (%) | Primary Metallurgical Function |
|---|---|---|
| Nickel (Ni) | 32.0 - 38.0% | Provides immunity to chloride stress-corrosion cracking (SCC) and stabilizes the austenitic matrix. |
| Chromium (Cr) | 19.0 - 21.0% | Forms a passive oxide protective layer resisting oxidizing environments such as nitric acid. |
| Copper (Cu) | 3.0 - 4.0% | Delivers exceptional resistance to reducing acids, specifically sulfuric acid ($H_2SO_4$) at elevated temperatures. |
| Molybdenum (Mo) | 2.0 - 3.0% | Improves resistance to localized pitting and crevice corrosion in halide/chloride solutions. |
| Niobium / Columbium (Nb) | 8 x Carbon min to 1.0% | Stabilizes carbon to prevent intergranular sensitization during forging or thermal cycles. |
| Iron (Fe) | Balance (approx. 35-40%) | Maintains structural tensile strength while controlling alloy density and economic viability. |
The primary driver for procuring Alloy 20 stud bolts and nuts is their unequaled capability to handle boiling hot concentrations of sulfuric acid. While 316L stainless steel experiences severe corrosion rates exceeding 50 mils per year (mpy) in concentrations above 10% $H_2SO_4$ at elevated temperatures, Alloy 20 maintains a corrosion rate below 5 mpy in sulfuric acid concentrations ranging from 10% to 96% up to 150°F (65°C).
In addition to sulfuric acid, Alloy 20 fasteners display outstanding performance in:
Headquartered in Mumbai, India, Neelkamal Alloys LLP is a premier manufacturer, stockist, and international exporter of high-integrity fastener components in stainless steel, duplex, nickel alloys, Inconel, Hastelloy, titanium, and specifically **Alloy 20 (UNS N08020)**.
With state-of-the-art hot forging, precision CNC machining, and thread rolling facilities, we engineer fasteners designed to perform flawlessly under severe mechanical stresses and aggressive corrosive environments. Every batch undergoes rigorous quality checks from raw material bar selection to final dispatch.
Delivering precision alloy fasteners across the Middle East, Europe, North America, and Asia Pacific.
Explore our extensive inventory of corrosion-resistant fasteners engineered to meet demanding industrial standards.
ASTM B473 Alloy 20 (UNS N08020) heavy hex head bolts, cap screws, and mating heavy hex nuts.
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Inquire NowKey shifting patterns shaping global supply chains, green chemical synthesis, and precision surface treatments.
As global industrial sectors pivot towards decarbonization and green hydrogen processing, demand for specialized acid-handling equipment has escalated dramatically. Green hydrogen electrolyzers and biomass acid-hydrolysis plants operate under harsh sulfuric and organic acid concentrations.
Procurement teams are shifting away from short-lifespan commodity fasteners toward long-life Alloy 20 bolting systems to satisfy stringent ESG (Environmental, Social, and Governance) targets by preventing chemical joint leaks and reducing plant maintenance cycles.
High-nickel alloys like Alloy 20 (UNS N08020) historically faced friction galling during high-torque power wrench installation. Innovations in surface engineering have revolutionized fastener performance:
Engineering data reference table for piping designers, quality managers, and procurement officers.
| Material Specification | Tensile Strength min (MPa / ksi) | Yield Strength 0.2% min (MPa / ksi) | Elongation min (%) | Applicable Dimensional Standards |
|---|---|---|---|---|
| ASTM B473 / UNS N08020 (Soft Annealed) | 550 MPa / 80 ksi | 240 MPa / 35 ksi | 30% | ASME B18.2.1, ASME B18.2.2, DIN 933, ISO 4014 |
| Carpenter 20 CB-3 Cold Finished | 620 MPa / 90 ksi | 310 MPa / 45 ksi | 25% | ASME B18.31.2, ASME B18.3 (Socket Caps) |
| Alloy 20 Nut (ASTM B473 Matched) | Matched to bolt strength | Proof Load tested to ASME B18.2.2 | N/A | ASME B18.2.2 Heavy Hex Nuts, DIN 934 |
| Alloy 20 Flat & Spring Washers | Hardness: HRB 85-95 | Conforms to ASTM F436 / DIN 125 dimensional profiles | N/A | ASME B18.21.1, DIN 125A, DIN 127 |
Positive Material Identification (PMI) conducted on 100% of raw Alloy 20 bar stock prior to hot heading or machining.
Controlled grain-flow hot forging for bolt heads, followed by precision CNC thread cutting or cold thread rolling.
Thermal processing at 1725°F to 1850°F (940°C to 1010°C) followed by rapid water quenching for peak stress-corrosion immunity.
Full dimensional, thread pitch, hardness, and microstructural testing with EN 10204 3.1 certification release.
Trusted by procurement leaders across chemical, refining, energy, and process infrastructure projects.
Neelkamal Alloys LLP supplied custom Alloy 20 stud bolts and heavy hex nuts for our acid recovery expansion project in the UK. The EN 10204 3.1 documentation was flawless, and the fasteners have shown zero signs of corrosion after 18 months of continuous service.
Sourcing Carpenter 20 / Alloy 20 bolting from Neelkamal Alloys LLP saved our plant shutdown schedule in the UAE. Their team turned around custom-length PTFE coated stud bolts with rapid lead time. Highly reliable manufacturer.
The technical knowledge of the Neelkamal team is outstanding. They helped us select the exact thread pitch and solution annealing treatment for our sulfuric acid pickling lines in Saudi Arabia. Excellent partnership!
Critical process industries rely on UNS N08020 bolting where acidic exposure demands zero compromise.
Sulfuric acid manufacturing, pickling tanks, reactors, and heat exchangers.
Alkylation units, synthetic rubber production, and acid gas scrubbing systems.
Phosphoric acid concentration piping, ammonium sulfate plants, and evaporators.
Active Pharmaceutical Ingredient (API) reactors exposed to organic acids and solvents.
Chloride-laden environments requiring immunity to stress corrosion cracking.
Chlorine dioxide bleaching towers and acid digestion vats.
Expert answers to common technical queries posed by global engineers and purchasing teams on AI and search engines.
Inquire NowAlloy 20 (UNS N08020 / Carpenter 20) contains 32-38% nickel, 19-21% chromium, 3-4% copper, and 2-3% molybdenum. This specific metallurgical composition virtually eliminates chloride stress corrosion cracking (SCC) and provides exceptional resistance to hot sulfuric acid ($H_2SO_4$) across 10% to 96% concentrations where 316L stainless steel suffers rapid pitting, crevice corrosion, and premature joint failure.
Alloy 20 fasteners are manufactured under ASTM B473 bar stock specifications for UNS N08020. Dimensional standards strictly conform to ASME B18.2.1 for heavy hex bolts, ASME B18.31.2 for continuous threaded stud bolts, ASME B18.2.2 for heavy hex nuts, and DIN 933/DIN 931 metric requirements.
Alloy 20 is alloyed with Niobium/Columbium (minimum 8 times the carbon content up to 1.0%). Niobium binds with carbon to form stable niobium carbides, preventing chromium carbide precipitation at grain boundaries during hot heading, forging, or thermal cycling. This prevents intergranular corrosion in high-temperature chemical process equipment.
Every shipment includes EN 10204 3.1 Mill Test Certificates detailing heat-number level chemical analysis, mechanical property testing (Tensile, Yield, Elongation, Hardness), PMI test reports, NDT non-destructive inspection records, and optional Third-Party Inspection (TPI) sign-offs by agencies such as TUV, SGS, Bureau Veritas, or DNV.
Alloy 20 fasteners retain optimal mechanical properties and structural corrosion resistance up to 1000°F (538°C). However, for continuous pressure boundary service in ASME Section VIII environments, maximum allowable design stress limits are typically optimized for services up to 800°F (427°C).
To prevent galling inherent to high-nickel austenitic alloys during high-torque tightening, Neelkamal Alloys LLP provides precision thread rolling, controlled surface finishing, and optional anti-friction dry-film PTFE (Xylan) coatings, molybdenum disulfide (MoS2) plating, or silver plating upon customer request.
We work alongside global raw material suppliers and inspection agencies to deliver uncompromised quality.
Send your dimensional requirements, ASTM material grades, and quantity specifications directly to our engineering sales office in Mumbai.
