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Alloy 20 Hex Cap Screws

Alloy 20 Hex Cap Screws, also known as Carpenter 20 and 20CB-3, offers a combination of nickel, chromium, molybdenum, and copper which provides good general corrosion resistance. Alloy 20 (2.4660) Hex Cap Screws are best suited for mid-range corrosion use – better than steel alloys but not at the level of high performance nickel based alloys like Hastelloy C276. Alloy 20 is a nickel alloy that was specifically designed to withstand the harsh environment of hot sulfuric acid but also performs well in a variety of other acids. Alloy 20 Hex Cap Screws are an ideal choice when you don’t need the corrosion resistance power and price-tag of high performance nickel alloys like Hastelloy C276; but you need something that will give you more protection than 316 stainless steel or even a Super Duplex 2507 stainless steel.

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Mid-range corrosion resistant alloy
Decent mechanical strength to 1000°F
Good sulfuric acid protection at 20% - 40%
Decent stress corrosion cracking, pitting and crevice corrosion resistance in chloride
Resonable general corrosion protection
Good intergranular corrosion resistance in the as-welded condition

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RAYCHIN LIMITED

Name: Alloy 20 Hex Cap Screws
SKU: 0

Specialist in Alloy 20 Hex Cap Screws · Hex Head · Heavy Hex · Custom

Alloy 20 Hex Cap Screws: Corrosion-Resistant Hex Head Screws for Critical Applications

UNS N08020 / W. Nr. 2.4660 / 20Cb-3 / Carpenter 20 / Incoloy 20

RAYCHIN LIMITED is a recognized expert in Alloy 20 hex cap screws — from Alloy 20 hex head cap screws, Alloy 20 heavy hex cap screws, Alloy 20 hexagon head screws to custom non-standard configurations. Alloy 20 (UNS N08020) is a nickel-iron-chromium superalloy with additions of copper and molybdenum, stabilized with niobium. Also designated as 20Cb-3, Carpenter 20, and Incoloy 20, it maintains exceptional corrosion resistance in aggressive chemical environments up to 538°C (1000°F). This makes it the preferred material for hex cap screws in sulfuric acid service, phosphoric acid handling, heat exchangers, chemical processing, oil & gas (sour service), pharmaceuticals, and food processing equipment requiring reliable external drive fastening. Hex cap screws, also known as hex head cap screws or hexagon head bolts, feature a six-sided head designed for wrenching and are available in both partial thread (DIN 931, ISO 4014) and full thread (DIN 933, ISO 4017) configurations. The alloy's high nickel content (32-38%) provides immunity to chloride stress corrosion cracking, while copper and molybdenum additions enhance resistance to reducing acids. Our portfolio includes hex cap screws manufactured to NAS, AN, MS, ANSI, ASTM, ASME, SAE, API, NACE, ISO, DIN and KS standards. Engineered for extreme environments where corrosion resistance and reliable wrenching are critical. Alloy 20 hex cap screws are supplied in solution annealed condition with full traceability and third-party certifications.

Alloy 20 Hex Cap ScrewsAlloy 20 Hex Head Cap ScrewsAlloy 20 Heavy Hex Cap ScrewsAlloy 20 Hexagon Head ScrewsUNS N08020 Hex Cap Screws2.4660 Hex Cap Screws20Cb-3 Hex Cap ScrewsCarpenter 20 Hex Head ScrewsIncoloy 20 Hex Cap ScrewsASTM B473 Hex Cap ScrewsNACE MR0175 Hex Cap ScrewsDIN 931 Alloy 20 ScrewsDIN 933 Alloy 20 ScrewsISO 4014 Alloy 20 ScrewsISO 4017 Alloy 20 ScrewsASME B18.2.1 Alloy 20 Screwssulfuric acid resistant hex head screwscorrosion resistant hex cap screwschemical processing hex screwssour service hex cap screws

Complete Range of Alloy 20 Hex Cap Screws – Configurations

Hex Cap Screws – Partial Thread (DIN 931 / ISO 4014)

Alloy 20 hex cap screws with partial thread manufactured to DIN 931, ISO 4014, and ASME B18.2.1 standards. Features a hex head with a partially threaded shank, providing unthreaded length for shear strength and alignment. Ideal for high-temperature corrosive applications up to 538°C where the unthreaded portion passes through clearance holes. Precision rolled threads for superior strength and corrosion resistance. Available in sizes from M6 to M36 (metric) and 1/4" to 1-1/2" (inch) in various lengths. Supplied in solution annealed condition per ASTM B473.

Hex Cap Screws – Full Thread (DIN 933 / ISO 4017)

Alloy 20 hex cap screws with full thread manufactured to DIN 933, ISO 4017, and ASME B18.2.1 standards. Features a hex head with threads extending the entire shank length, providing maximum thread engagement. Ideal for applications where the full length of the screw must be threaded or where grip length adjustment is required. Precision rolled UNC, UNF, and metric threads for superior fatigue resistance. Available in sizes from M6 to M36 (metric) and 1/4" to 1-1/2" (inch) in various lengths. Supplied with passivated finish per ASTM A967.

Heavy Hex Cap Screws (DIN 6914 / ASME B18.2.1)

Alloy 20 heavy hex cap screws manufactured to DIN 6914, ASME B18.2.1 (heavy hex series), and ASTM A325/A490 dimensional standards. Features a larger head configuration providing increased bearing area for high-pressure flange connections and pressure vessel applications. Essential for API 6A and ASME B16.5 bolting assemblies in corrosive environments. The heavier head distributes load more effectively and resists dilation at elevated temperatures. Available with controlled hardness ≤ 35 HRC for NACE MR0175 sour service compliance. Supplied with matching Alloy 20 heavy hex nuts.

Hex Cap Screw Design & Standards

Dimensional Standards

Our Alloy 20 hex cap screws meet or exceed the following specifications:

Metric Partial Thread	DIN 931, ISO 4014
Metric Full Thread	DIN 933, ISO 4017
Inch Partial Thread	ASME B18.2.1, SAE J429
Inch Full Thread	ASME B18.2.1, SAE J429
Heavy Hex	DIN 6914, ASME B18.2.1 (heavy series)
Aerospace	NAS1802, MS16995, MS16996

Available in UNC, UNF, UNJF-3A, and metric coarse/fine thread configurations.

Head Styles & Configurations

Standard Hex: Regular hex head for general applications.
Heavy Hex: Larger head for increased bearing area.
Finished Hex: Precision-formed with underhead fillet.
Hex Flange: Integrated flange for washer elimination.

Surface Finish Options

Passivated: Per ASTM A967 for maximum corrosion resistance.
Electropolished: For clean room and pharmaceutical applications.
PTFE Coated: For anti-galling and lubricity.
Silver Plating: Per AMS 2410 for high-temperature anti-seize.

Key Benefits of Alloy 20 Hex Cap Screws

Exceptional Sulfuric Acid Resistance

Alloy 20 was specifically designed to withstand hot sulfuric acid environments. Offers good resistance to stress-corrosion cracking in boiling sulfuric acid at 20-40% concentration, as well as general sulfuric acid resistance. Corrosion rates typically below 0.5 mm/year across most concentrations.

External Drive Design

Hex head design allows for high torque application with standard wrenches and sockets. Suitable for applications requiring frequent assembly and disassembly. Available in both standard and heavy hex configurations for increased wrenching area.

Chloride SCC Immunity

With 32-38% nickel content, Alloy 20 offers practical immunity to chloride stress corrosion cracking, making it ideal for marine and brackish water applications where 304/316 hex cap screws would fail.

Sour Service Approved

NACE MR0175 / ISO 15156 qualified for H₂S environments. Suitable for wellhead equipment, valve assemblies, and subsea connections in oil and gas applications requiring corrosion-resistant hex cap screws.

Partial & Full Thread Options

Available in both partial thread (for shear applications) and full thread (for maximum thread engagement) configurations to suit specific application requirements.

Temperature Versatility

Maintains useful mechanical properties up to 538°C (1000°F), suitable for heat exchanger and process equipment applications at elevated temperatures.

Manufacturing Standards for Alloy 20 Hex Cap Screws

RAYCHIN LIMITED manufactures Alloy 20 hex cap screws to the following national and international standards, ensuring full compliance for projects worldwide. Both standard and non-standard custom configurations are available.

NASANMSANSIASTMASMESAEAPINACEISODINKSJISGB

International Standards & Global Designations for Alloy 20 Hex Cap Screws

To serve clients worldwide, RAYCHIN LIMITED manufactures Alloy 20 hex cap screws from material conforming to the following national and international specifications. This ensures full compliance for projects in the Americas, Europe, Asia, and the Middle East.

Country / Region	Standard / Specification	Designation / Grade
USA	ASTM B473 / ASME SB473, ASTM B462, ASTM B463, ASTM F2281, UNS N08020	Alloy 20 · 20Cb-3 · Carpenter 20 · Incoloy 20
Germany (DIN)	W. Nr. 2.4660, DIN 17744, DIN 931 (partial thread), DIN 933 (full thread), DIN 6914 (heavy hex)	2.4660 · NiCr20CuMo
Europe (CEN)	EN 10269 (for fasteners), EN 10095	1.4500 (similar designation)
France (NF)	NF A35-572/573	Z2NCDU25-20
UK (BS)	BS 3076, BS 3692 (hex bolts)	NA 20
China (GB)	GB/T 15007, GB/T 1220, GB/T 5782 (partial thread), GB/T 5783 (full thread)	NS1403 · 0Cr20Ni35Mo3Cu4Nb
Japan (JIS)	JIS G4903, JIS G4904, JIS B1180 (hex bolts)	NCF 20
ISO	ISO 15156-3 (NACE MR0175), ISO 4014 (partial thread), ISO 4017 (full thread)	UNS N08020
NACE	NACE MR0175 / ISO 15156	Alloy 20 (qualified for sour service)
API	API 20F	Alloy 20

UNS N08020 2.4660 ASTM B473 ASME SB473 NACE MR0175 20Cb-3 Carpenter 20 Incoloy 20 DIN 931 DIN 933 ISO 4014 ISO 4017 ASME B18.2.1 NAS1802

Chemical Composition (Weight %) – Alloy 20 (UNS N08020 / 2.4660)

Our Alloy 20 hex cap screws are produced from melts that strictly conform to the limits below per ASTM B473 / ASME SB473. The high nickel content provides immunity to chloride stress corrosion cracking, while chromium ensures resistance to oxidizing media. Copper and molybdenum provide exceptional resistance to reducing acids such as sulfuric and phosphoric acids. Niobium stabilization prevents intergranular corrosion.

Element	ASTM B473 / ASME SB473 (Range %)	Typical (analysis)
Nickel (Ni)	32.0 – 38.0	34.0
Chromium (Cr)	19.0 – 21.0	20.0
Copper (Cu)	3.0 – 4.0	3.5
Molybdenum (Mo)	2.0 – 3.0	2.5
Niobium + Tantalum (Nb+Ta)	8 x C min – 1.0 max	0.5
Carbon (C)	≤ 0.07	0.03
Manganese (Mn)	≤ 2.00	1.2
Phosphorus (P)	≤ 0.045	0.020
Sulfur (S)	≤ 0.035	0.010
Silicon (Si)	≤ 1.00	0.5
Iron (Fe)	Balance	Balance

Expert note: The nickel content (32-38%) places Alloy 20 in the austenitic superalloy category, providing exceptional resistance to chloride stress corrosion cracking. Copper (3-4%) is the key element for sulfuric acid resistance, while molybdenum (2-3%) enhances pitting resistance. Niobium stabilization prevents chromium carbide precipitation at grain boundaries, maintaining corrosion resistance after welding or thermal processing. Columbium stabilization ensures intergranular corrosion resistance in the as-welded condition.

Complete Mechanical Properties of Alloy 20 Hex Cap Screws (per ASTM B473)

Alloy 20 hex cap screws are supplied in the solution annealed condition (1030-1120°C followed by rapid quenching). The data below represent minimum requirements per ASTM B473 / ASME SB473 unless otherwise noted.

Tensile Requirements – ASTM B473 (Bar & Fastener Stock)

Size Range	Tensile Strength (min)	Yield Strength 0.2% Offset (min)	Elongation (min)	Reduction of Area (min)
All sizes	550 MPa (80 ksi)	240 MPa (35 ksi)	30%	50%

Typical Mechanical Properties (Solution Annealed)

Property	Typical Value	Notes
Ultimate Tensile Strength	620 MPa (90 ksi)	Exceeds minimum requirements
Yield Strength (0.2% Offset)	300 MPa (43.5 ksi)	Exceeds minimum requirements
Elongation	40%	Excellent ductility
Hardness (Brinell)	217 HB max	Typically 150-190 HB
Hardness (Rockwell C)	19 HRC max	Typically 10-15 HRC
Modulus of Elasticity	193 GPa (28,000 ksi)	At room temperature
Poisson's Ratio	0.31	—
Electrical Resistivity (RT)	651 ohm-cir mil/ft	—

For NACE MR0175 / API 20F sour service applications, maximum hardness of 35 HRC is easily met (Alloy 20 typically below 20 HRC in annealed condition).

Elevated Temperature Mechanical Properties

Alloy 20 maintains useful mechanical properties at elevated temperatures up to approximately 538°C (1000°F), suitable for heat exchanger and process equipment applications.

Temperature	Yield Strength (typical)	Tensile Strength (typical)	Retention (%)
Room Temperature (20°C)	300 MPa	620 MPa	100%
100°C (212°F)	275 MPa	590 MPa	90-95%
200°C (392°F)	260 MPa	570 MPa	85-90%
300°C (572°F)	250 MPa	550 MPa	80-85%
400°C (752°F)	240 MPa	530 MPa	75-80%
500°C (932°F)	230 MPa	500 MPa	70-75%
538°C (1000°F)	220 MPa	480 MPa	65-70%

Note: For service above 538°C, nickel-based alloys such as Inconel 625 or 718 are recommended.

Physical Properties

Property	Value
Density	8.08 g/cm³ (0.292 lb/in³)
Melting Point	1357 – 1430°C (2475 – 2606°F)
Thermal Expansion Coefficient (20-100°C)	14.7 x 10⁻⁶ /°C (8.2 µin/in-°F)
Thermal Conductivity (20°C)	12.3 W/m·K (85 Btu-in/ft²-hr-°F)
Specific Heat Capacity	0.45 J/g·°C
Electrical Resistivity (RT)	135.9 × 10⁻⁶ ohm-cm (53.5 µohm-in)
Magnetic Permeability	≤ 1.02 (non-magnetic)

Exceptional Corrosion Resistance of Alloy 20 Hex Cap Screws

Alloy 20 was originally developed for sulfuric acid service and has become the industry standard for fasteners in aggressive chemical environments. The combination of nickel, chromium, copper, and molybdenum provides outstanding resistance to both oxidizing and reducing acids.

Sulfuric Acid Resistance

Alloy 20 hex cap screws offer exceptional resistance to sulfuric acid across a wide range of concentrations and temperatures. The copper addition (3-4%) is particularly beneficial for sulfuric acid environments. Alloy 20 offers good resistance to stress-corrosion cracking in boiling sulfuric acid at 20-40% concentration, as well as general sulfuric acid resistance.

Concentration	Temperature	Corrosion Rate
Up to 50% H₂SO₄	Up to 80°C	< 0.5 mm/year (excellent)
50-80% H₂SO₄	Up to 50°C	< 0.5 mm/year (good)
80-95% H₂SO₄	Room temperature	< 0.5 mm/year (excellent)
All concentrations	Up to 50°C	< 0.5 mm/year (good)

Phosphoric & Nitric Acid Resistance

Excellent resistance to phosphoric acid, including wet process phosphoric acid containing fluoride impurities. Also shows useful resistance to nitric acid. Widely used in fertilizer industry applications where hex cap screws secure agitator blades and mixing equipment.

Chloride Stress Corrosion Cracking (SCC) Resistance

With 32-38% nickel content, Alloy 20 hex cap screws have practical immunity to chloride stress corrosion cracking. This makes them ideal for marine environments, brackish water, and applications where chloride SCC is a concern with 300-series stainless steels.

Pitting and Crevice Corrosion Resistance

The molybdenum addition (2-3%) provides enhanced resistance to pitting and crevice corrosion in chloride-containing media. The Pitting Resistance Equivalent (PRE) is approximately 26-28, providing moderate resistance to localized corrosion in seawater and brine solutions.

Intergranular Corrosion Resistance

Alloy 20 is stabilized with columbium (niobium) to minimize carbide precipitation during welding. This provides excellent intergranular corrosion resistance in the as-welded condition, maintaining corrosion resistance at grain boundaries.

Resistance to Other Media

Environment	Resistance Level	Notes
Nitric Acid	Good	Chromium provides resistance to oxidizing acids
Hydrochloric Acid	Moderate	Limited resistance at higher concentrations/temperatures
Hydrofluoric Acid	Good	Resistant to all concentrations at room temperature, up to 10% HF at 70°C
Mixed Acids (H₂SO₄ + HNO₃)	Excellent	Widely used in nitration processes
Caustic Solutions	Good	Resistant to caustic soda and potash
Seawater	Good	Moderate resistance to pitting and crevice corrosion
Sour Service (H₂S)	Excellent	Qualified per NACE MR0175/ISO 15156

Special focus: Alloy 20 Hex Cap Screws for Critical Applications

For critical applications requiring exceptional corrosion resistance and reliable wrenching, RAYCHIN offers Alloy 20 hex cap screws manufactured to ASTM, ASME, NACE, and customer-specific specifications. Our capabilities include:

Chemical Processing: Reactor manway covers, distillation column access ports, heat exchanger heads, agitator blade screws, mixing tanks, pickling tanks and racks, piping flanges.
Sulfuric Acid Plants: Acid coolers, pump housings, agitator blade retention, piping flanges, acid circulation systems, heat exchanger covers.
Phosphoric Acid Production: Reactor access covers, evaporator inspection ports, heat exchanger heads, mixer blade attachments, piping systems.
Oil & Gas / Sour Service: NACE MR0175 compliant hex cap screws for wellhead equipment, valve assemblies, subsea control modules, offshore platform equipment.
Power Generation: Flue-gas desulfurization (FGD) systems, heat exchanger connections, turbine components, boiler access panels.
Pharmaceutical Manufacturing: Reactor ports, clean room equipment, process piping clamps, sanitary fittings, mixing vessels.
Food Processing: Mixer access covers, tank manways, process equipment guards, sanitary piping systems, conveyor components.
Marine Applications: Instrument enclosures, panel fasteners, offshore platform equipment covers, seawater handling systems.
Aerospace: Ground support equipment, chemical handling systems, test stand components.
Standards: DIN 931/933 (metric), ISO 4014/4017 (metric), ASME B18.2.1 (inch), NAS1802 (aerospace).
Thread Configurations: Partial thread (DIN 931, ISO 4014) and full thread (DIN 933, ISO 4017).
Thread Classes: 2A, 3A, UNJF-3A, 6g, 6H.
Sizes: M6 through M36, 1/4" through 1-1/2".
Certifications: EN 10204 3.1/3.2 material certifications, NACE MR0175, API 20F, PED 2014/68/EU.

All Alloy 20 hex cap screws are supplied with full traceability and third-party NDT upon request. Material certifications included.

Why RAYCHIN LIMITED – The Alloy 20 Hex Cap Screw Authority

Metallurgical competence

Engineers on staff with deep expertise in nickel-based superalloys. We ensure proper solution annealing (1030-1120°C) for optimal corrosion resistance across all Alloy 20 hex cap screws. Every heat is verified by in-house PMI testing to confirm chemistry. With 32-38% nickel and copper-molybdenum additions, our hex cap screws provide exceptional resistance to sulfuric acid, phosphoric acid, and chloride stress corrosion cracking while maintaining reliable wrenching capability.

Global approvals & traceability

Our quality system is ISO 9001:2015 and AS9100D certified; we also comply with NAS, AN, MS, ANSI, ASTM, ASME, SAE, API, NACE, ISO, DIN and KS. Full material traceability from melt to final packaging (EN 10204 3.1/3.2). Third-party inspections (ABS, DNV, Lloyds) available. All Alloy 20 hex cap screws meet applicable ASTM B473, ASME SB473, NACE MR0175, and screw standards including DIN 931, DIN 933, ISO 4014, ISO 4017, ASME B18.2.1.

Precision head forming & thread rolling

In-house CNC cold heading, hot forging, and precision thread rolling capabilities ensure consistent head dimensions and thread geometry. Precision rolled threads provide superior fatigue life and dimensional accuracy. Accurate hex heads for positive wrench engagement. 100% thread and dimensional inspection available. Controlled underhead fillet for improved fatigue resistance.

Custom solutions

Need a special head configuration, unusual thread size, or custom length for your corrosive application? Our engineering team works with you to produce custom Alloy 20 hex cap screws to your drawing. We provide specialized surface treatments, passivation, and NACE MR0175 compliant processing per customer requirements.

Contact the Alloy 20 hex cap screw experts today

Request a quote for Alloy 20 hex cap screws, hex head cap screws, heavy hex cap screws & custom configurations – any global standard (NAS, AN, MS, ANSI, ASTM, ASME, SAE, API, NACE, ISO, DIN, KS), any quantity. Inquire about sulfuric acid resistant hex head screws, NACE MR0175 sour service requirements, or high-temperature applications.

sales@ray-chin.com | +86 534 2166 566

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