RAYCHIN LIMITED

Complete Range of Alloy 20 Fasteners – Types & Configurations

Manufacturing Standards for Alloy 20 Fasteners

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

Fastener Dimensional Standards

All dimensional standards available in UNC, UNF, and metric thread configurations. Standard sizes from 1/4" to 4" (M6 to M100). Custom sizes available upon request.

International Standards & Global Designations for Alloy 20 Fasteners

To serve clients worldwide, RAYCHIN LIMITED manufactures Alloy 20 fasteners 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.

UNS N08020 2.4660 ASTM B473 ASME SB473 NACE MR0175 20Cb-3 Carpenter 20 Incoloy 20 NS1403 NCF 20

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

Our Alloy 20 fasteners 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 after welding.

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 in the as-welded condition.

Complete Mechanical Properties of Alloy 20 Fasteners (per ASTM B473)

Alloy 20 fasteners are supplied in the solution annealed condition (typically 1030-1120°C followed by rapid quenching). The data below represent minimum requirements per ASTM B473 / ASME SB473 unless otherwise noted. Proof load testing ensures compatibility with mating nuts.

Tensile Requirements – ASTM B473 (Bar & Fastener Stock)

Typical Mechanical Properties (Solution Annealed)

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, suitable for heat exchanger and process equipment applications.

Note: Alloy 20 is not typically used for high-strength applications above 600°C. For service above 600°C, nickel-based alloys such as Inconel 625 or 718 are recommended.

Physical Properties

Exceptional Corrosion Resistance of Alloy 20 Fasteners

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 fasteners 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 is resistant to sulfuric acid of all concentrations up to at least 50°C with corrosion rates below 0.13 mm/year.

Phosphoric Acid Resistance

Excellent resistance to phosphoric acid, including wet process phosphoric acid containing fluoride impurities. Widely used in fertilizer industry applications.

Chloride Stress Corrosion Cracking (SCC) Resistance

With 32-38% nickel content, Alloy 20 fasteners 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 calculated as:

PRE = Cr + 3.3Mo + 30N (nitrogen content low in Alloy 20)

Alloy 20 PRE is approximately 26-28, providing moderate resistance to localized corrosion in seawater and brine solutions.

Resistance to Other Media

Critical Corrosion Considerations for Fasteners

• Sulfuric Acid Applications: Alloy 20 is the preferred material for fasteners in sulfuric acid environments up to moderately elevated temperatures. Copper content is critical for performance.
• Phosphoric Acid Service: Excellent resistance in wet process phosphoric acid, even with fluoride impurities. Widely used in fertilizer plant fasteners.
• Chloride Environments: Immunity to chloride SCC makes Alloy 20 ideal for marine and brackish water applications where 304/316 stainless steels may fail.
• NACE MR0175 Compliance: Qualified for sour service (sulfide stress cracking resistance) in oilfield equipment per NACE MR0175/ISO 15156.
• Temperature Limitations: Maximum service temperature for continuous service is 600°C (1112°F). Above this temperature, strength decreases and oxidation may become significant.
• Galvanic Corrosion: When paired with carbon steel or less noble materials, galvanic corrosion should be considered. Alloy 20 is cathodic to most steels.
• Non-Magnetic Property: Alloy 20 is essentially non-magnetic (permeability ≤ 1.02), suitable for applications requiring non-magnetic components.
• Weldability: Niobium stabilization prevents intergranular corrosion in the heat-affected zone, allowing welding without post-weld heat treatment.

Heat Treatment & Microstructural Stability of Alloy 20 Fasteners

Optimal corrosion resistance in Alloy 20 fasteners is achieved through solution annealing:

• Solution Annealing: Heat to 1030-1120°C (1885-2050°F) followed by rapid quenching (water or air). This dissolves any precipitated carbides and ensures homogeneous distribution of alloying elements for maximum corrosion resistance.
• Stabilization: Niobium (columbium) addition (8 x C min) ties up carbon as stable NbC carbides, preventing chromium carbide precipitation at grain boundaries during welding or slow cooling. This ensures resistance to intergranular corrosion in the as-welded condition.

All fasteners are supplied in the solution annealed condition to ensure optimum corrosion resistance. Cold worked fasteners are available for higher strength applications but may have slightly reduced corrosion resistance in severe environments.

Why RAYCHIN LIMITED – The Alloy 20 Fastener Authority