Incoloy Fasteners: Understanding the Complete Family of Nickel-Iron-Chromium Alloy Bolts

When applications demand high-temperature strength, oxidation resistance, and resistance to chloride stress corrosion cracking, the Incoloy family of alloys frequently becomes the material of choice. These nickel-iron-chromium alloys—commonly specified as Incoloy 800, 800H, 800HT, 825, 925, 945, and 25-6Mo—offer engineers a versatile palette of mechanical and corrosion properties. RAYCHIN LIMITED, a specialist global manufacturer and supplier of high-performance alloy fasteners with decades of in-house experience, produces the full spectrum of Incoloy fasteners, from UNS N08825 bolts to high-strength UNS N09925 studs. This guide provides a comprehensive overview of the Incoloy family, clarifying the differences between grades and helping you select the right alloy for your specific environment.

1. What Is Incoloy Alloy?

What is Incoloy alloy? Incoloy is a family of nickel-iron-chromium alloys developed by Special Metals Corporation. Unlike Inconel, which is primarily nickel-based (typically >50% Ni), Incoloy alloys have a lower nickel content (usually 30–45%) and a higher iron content, making them a more economical alternative while still providing excellent high-temperature and corrosion performance. They are specifically formulated to resist oxidation, carburization, and chloride stress corrosion cracking in a wide range of environments. Incoloy nickel iron chromium alloy bolts are used extensively in chemical processing, oil & gas, power generation, and marine engineering.

2. The Incoloy Family at a Glance

The table below summarizes the key Incoloy grades that RAYCHIN manufactures, along with their typical UNS numbers and primary characteristics.

3. Incoloy 800 vs 800H vs 800HT — Understanding the High-Temperature Trio

Incoloy 800 vs 800H vs 800HT is a frequent source of confusion. All three alloys share the same basic nickel (32%), chromium (21%), and iron (balance) composition. The critical difference lies in carbon content and high-temperature strength.

• Incoloy 800 (UNS N08800): Carbon ≤0.10%. Basic grade with good oxidation resistance up to 1100°C but limited creep strength. Used for general furnace hardware and heat exchangers.
• Incoloy 800H (UNS N08810): Carbon restricted to 0.05–0.10% and solution-annealed at higher temperature to produce a coarser grain size. This provides significantly improved creep and stress-rupture strength at temperatures above 600°C. Widely used for steam methane reformer tubes and ethylene pyrolysis coils.
• Incoloy 800HT (UNS N08811): Carbon 0.06–0.10%, with additional restrictions on Al and Ti content. It is essentially 800H with even tighter control to maximize high-temperature strength. Recommended for service above 700°C where creep resistance is critical.

For fastener applications, RAYCHIN typically supplies 800H and 800HT for bolting in high-temperature furnaces, reformers, and power plants where the fastener must maintain preload and resist relaxation at elevated temperatures.

4. Incoloy 825 Fasteners: Chemical Composition and Properties

Incoloy 825 (UNS N08825) is a nickel-iron-chromium alloy with added molybdenum, copper, and titanium. It was developed for exceptional resistance to reducing and oxidizing acids, and it remains a top choice for sulfuric and phosphoric acid service. The alloy also resists chloride stress corrosion cracking and offers excellent weldability. Below is the typical Incoloy 825 chemical composition.

In the annealed condition, Incoloy 825 has a minimum tensile strength of 586 MPa (85 ksi) and a yield strength of 241 MPa (35 ksi). It is used in chemical processing equipment, pickling tanks, oil and gas wellhead components, and marine exhaust systems. RAYCHIN supplies UNS N08825 fasteners in hex bolts, studs, nuts, and washers, with full traceability and PMI testing.

5. Incoloy 925 and 945: High-Strength Age-Hardenable Grades

Incoloy 925 (UNS N09925) is a precipitation-hardenable nickel-iron-chromium alloy with additions of molybdenum, copper, titanium, and aluminum. Through a solution anneal and aging heat treatment, it achieves yield strengths of 758 MPa (110 ksi) or higher while retaining excellent corrosion resistance, including NACE MR0175 compliance for sour gas service. Incoloy 925 properties make it a preferred choice for high-pressure oilfield fasteners such as wellhead studs, downhole tools, and valve components.

Incoloy 945 (UNS N09945) is an advanced age-hardenable grade with even higher strength and corrosion resistance, designed for the most demanding HPHT completions and subsea fastener applications. RAYCHIN manufactures both UNS N09925 fasteners and Incoloy 945 bolts with controlled heat treatment and full mechanical testing.

6. Incoloy 25-6Mo: The Chloride Fighter

Incoloy 25-6Mo (UNS N08926) is a super austenitic stainless steel with 6% molybdenum, often referred to in the same family due to its similar nickel-iron-chromium base. It offers a PREN of 43–47, providing outstanding pitting and crevice corrosion resistance in warm seawater, FGD systems, and chemical environments. While sometimes classified separately as Alloy 926, it is frequently grouped with Incoloy grades for procurement purposes. RAYCHIN supplies Incoloy 25-6Mo fasteners for the most demanding chloride service.

7. Incoloy Equivalent Grades and International Designations

The table below lists common Incoloy equivalent grades and their international designations to aid in specification and cross-referencing.

8. RAYCHIN's Incoloy Fastener Manufacturing Capabilities

As a true manufacturer, RAYCHIN LIMITED produces the complete line of Incoloy nickel iron chromium alloy bolts for global markets:

• Hex bolts – ASME B18.2.1, DIN 931/933, M6–M48, 1/4″–2″
• Stud bolts and threaded rod – ASME B16.5, DIN 976, M6–M64, 1/4″–2‑1/2″
• Socket head cap screws – ASME B18.3
• Heavy hex nuts and washers – ASME B18.2.2 / B18.22.1
• Custom parts – per your drawings; flanged bolts, stepped studs

All products are solution-annealed (or age-hardened where applicable), with full material certification, PMI testing, and EN 10204 3.1/3.2 certificates. Our inventory covers a wide range of diameters for rapid delivery.