Incoloy 925 (UNS N09925) is an age-hardenable nickel-iron-chromium superalloy manufactured by Special Metals Corporation with deliberate additions of molybdenum, copper, titanium and aluminum. Nominal composition is 42-46% Ni, 19.5-22.5% Cr, 22% min Fe, 2.5-3.5% Mo, 1.5-3% Cu and 1.9-2.4% Ti. The alloy precipitates a gamma-prime Ni3(Al,Ti) phase during age-hardening, delivering yield strength of 110 ksi minimum while retaining the corrosion resistance of solution-annealed nickel alloys. Primary applications include sour-service oil and gas down-hole tools, wellhead bolting, tubing and casing hangers, surface safety valves, Christmas tree components, drill string tool joints, marine bolting and pump-shafting in chloride-bearing environments. Incoloy 925 sees heavy use in NACE MR0175 / ISO 15156-3 sour-service projects where 304/316 stainless cannot survive H2S exposure.

What is the difference between Inconel and Incoloy 925?

INCOLOY and INCONEL are both registered trademarks of Special Metals Corporation that designate two different alloy families. Incoloy denotes iron-based superalloys with substantial nickel and chromium content — Incoloy 925 carries 22% minimum iron alongside its 42-46% nickel and 19.5-22.5% chromium. Inconel denotes nickel-base superalloys with 50% nickel minimum and lower iron — examples include Inconel 625, 718 and 725. The choice between families depends on cost and service: Inconel grades typically deliver higher yield strength (Inconel 718 reaches 180 ksi+) at roughly two to three times the price, while Incoloy 925 offers a balanced cost-performance position for NACE MR0175 sour-service applications. 'Inconel 925' is a common industry misnomer — the correct registered trademark for UNS N09925 is INCOLOY 925.

Is Incoloy 925 NACE MR0175 / ISO 15156 compliant for sour service?

Yes. Incoloy 925 is explicitly listed under ISO 15156-3 Annex B for sour-service H2S environments up to 0.2 bar partial pressure H2S. Hardness must be controlled to 35 HRC maximum in the age-hardened condition; TorqBolt verifies each heat lot with calibrated Rockwell testing per ASTM E18. Sulfide stress cracking resistance has been validated by independent C-ring test programs at 100% yield strength for 720 hours in NACE TM0177 Solution A with zero observed crack initiation. For each NACE MR0175 order, TorqBolt supplies stamped MTC certificates per EN 10204 3.1 (manufacturer-witnessed) or 3.2 (third-party witnessed by Lloyd's Register, DNV, Bureau Veritas or TUV) and product marking compliant with API 6A PSL-1 through PSL-4 traceability requirements.

What are the mechanical properties of Incoloy 925 in the age-hardened condition?

Per Special Metals SMC internal specification HA 46 and ASTM B805, age-hardened Incoloy 925 delivers minimum Yield Strength of 110 ksi (758 MPa) at 0.2% offset, minimum Tensile Strength of 140 ksi (965 MPa), Elongation of 18% in 4D, Reduction of Area 25% minimum, Charpy V-notch Impact Energy of 35 J minimum at room temperature, and Hardness in the 26-38 HRC range. Density is 8.08 g/cm3, Young's modulus 200 GPa, mean coefficient of thermal expansion 13.0 x 10^-6 /K from 20-100°C. At elevated service temperatures, yield strength retention is excellent — Incoloy 925 retains 80% of room-temperature yield at 540°C. All mechanical values comply with NACE MR0175 / ISO 15156-3 hardness limits for sour H2S service.

What standards apply to Incoloy 925 fasteners?

ASTM B805 is the primary specification for Incoloy 925 bar and forgings, covering chemistry, mechanical property requirements, heat treatment and hardness limits. ASTM B983 covers UNS N09925 sheet, plate and strip. ASTM A193 and A194 cover bolting and nuts where Incoloy 925 is supplied as the equivalent grade — typically as an upgrade from B8M or B7M in sour service. NACE MR0175 / ISO 15156-3 governs sour-service compliance (35 HRC max, 0.2 bar pH2S). API 6A applies to wellhead and Christmas tree bolting across PSL-1, PSL-2, PSL-3 and PSL-4 levels. NORSOK M-630 covers the material data sheet for North Sea oil and gas projects, and NORSOK M-650 covers the manufacturer qualification of suppliers — TorqBolt maintains active M-650 QTR documentation.

What is the heat treatment for Incoloy 925?

The two-step heat treatment per Special Metals SMC HA 46 begins with solution anneal at 1900°F (1040°C) for 1 hour followed by air cool — this dissolves carbides and homogenizes alloying elements. Aging follows at 1365°F (740°C) for 6 to 9 hours then furnace cool at a controlled rate to 1150°F (621°C) plus or minus 15°F (8°C) for a total aging time of 18 hours, finally air cool to ambient. Aging precipitates the coherent gamma-prime Ni3(Al,Ti) phase that increases hardness to 26-38 HRC and yield strength to a minimum of 110 ksi while preserving the corrosion resistance of the solution-annealed matrix. For welded structures, full post-weld solution anneal plus age is required to restore mechanical properties in the heat-affected zone.

What welding filler metal is recommended for Incoloy 925?

Per the Special Metals welding datasheet (Tables 12 and Figures 7 through 12), the recommended filler metal for Incoloy 925 is INCO-WELD Filler Metal 725NDUR for both Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW). For GTAW, use direct current straight polarity with argon shielding at 15-20 cubic feet per hour, slight stringer beads, low heat input below 25 kJ/inch and interpass temperature kept under 300°F to prevent grain coarsening. Preheat is not required for fully solution-annealed base metal. After welding, the joint must receive a full post-weld solution anneal at 1900°F (1040°C) followed by aging at 1365°F (740°C) to achieve specification mechanical properties — yield strength of 110 ksi minimum — in the weld and heat-affected zone.

Incoloy 925 (UNS N09925) | Bolts, Studs, Nuts

INCOLOY® alloy 925 (UNS N09925) is an agehardenable nickel-iron-chromium alloy with additions of molybdenum, copper, titanium and aluminum. The alloy’s chemical composition, is designed to provide a combination of high strength and excellent corrosion resistance. The nickel content is sufficient for protection against chloride-ion stresscorrosion cracking. The nickel, in conjunction with the molybdenum and copper, also gives outstanding resistance to reducing chemicals. The molybdenum aids resistance to pitting and crevice corrosion. The alloy’s chromium content provides resistance to oxidizing environments. The titanium and aluminum additions cause a strengthening reaction during heat treatment.
INCOLOY alloy 925 is used in various applications requiring a combination of high strength and corrosion resistance. Because of the alloy’s resistance to sulfide stress cracking and stress-corrosion cracking in “sour” (H2S containing) crude oil and natural gas, it is used for down-hole and surface gaswell components including tubular products, valves, hangers, landing nipples, tool joints and packers. The alloy is also useful for fasteners, marine and pump shafting and high-strength piping systems.
At TorqBolt we stock a huge variety of Studs, Heavy Hex Nuts, washers and headed bolts along with their corresponding forgings, pipe fittings, flanges, pipes, plates, sheets and bar stock, wire, wirelines, welding wire and covered electrodes.

Incoloy 925 Equivalents

Incoloy 925 Specifications

Incoloy 925 Applications

Incoloy 925 Basecoats & Top Coats

Typical performance for Incoloy 925

General Corrosion

Incoloy 925 is highly resistant to corrosion in a wide range of organic and inorganic acids. The copper content gives excellent resistance to corrosion in many oxidising acids. Commercial acid applications often contain chlorides and other impurities which can cause corrosion of some stainless steels. Incoloy 925 offers much improved corrosion performance in these environments.

Incoloy 925 is also highly resistant to strong alkalis. The production of caustic soda results in hot, strong solutions and even in 60 wt% caustic soda, Incoloy 925 has very low corrosion rates (<0.004 ipy). Caustic soda is often found with chlorides in extraction processes and even with 10g/L chloride, Incoloy 925 has excellent corrosion resistance. Three years service experience of fabricated Incoloy 925 pipework in 2M caustic soda with chlorides at 446°F (230°C) has been excellent.

Pitting Corrosion

UNS	N09925
WerkStoff	2.4858
JIS	NCF 925

Category	Description	Typical Applications for Incoloy 925
Plates and Sheets	Flat rolled products used for fabrication, machining, or cladding.	Pressure vessels, heat exchangers, chemical plant linings.
Forged Flanges, Fittings, Rings, Forged Pipes	Components produced by forging for superior mechanical integrity.	High-pressure flanges, connectors, downhole oilfield tools.
Bars and Shapes	Solid long products, round/square/hex bars, or custom extruded profiles.	Shafts, fasteners, pump shafts, and machined parts.
Fasteners, Stud Bolts, Heavy Hex Nuts	Precision-machined threaded fasteners for corrosive and high-stress environments.	Offshore equipment, chemical process units, sour gas wells.
HIP Flanges and Fittings	Hot-Isostatically-Pressed components with uniform density and strength.	Subsea and petrochemical equipment needing defect-free materials.
Forgings	Shaped metal components produced via hot or cold deformation.	Valves, couplings, and mechanical connectors.
Pipes, Tubes and Tubings	Seamless or welded hollow sections used for fluid transport.	Oil & gas production tubing, flowlines, marine service.
Pipe Fittings	Connectors and joints (elbows, tees, reducers, etc.) for pipe systems.	Chemical and offshore pipeline installations.
Castings	Components shaped by molten metal pouring, useful for complex geometries.	Valve bodies, pump casings, compressor components.

Oil & Gas Applications	Industrial & Chemical Applications
Downhole tubing and casing components	Heat exchangers
Wellhead and packer components	Chemical processing equipment
Tubing hangers and valve parts	Pollution control equipment
Fasteners and shafts in sour gas service	Desalination plant components
Marine and offshore platform hardware	Acid and alkali handling systems
Subsea connectors and fittings	Pulp and paper industry equipment
Pumps and shafts for seawater service	Power generation (steam and gas turbine hardware)
Oilfield tools and couplings	Pharmaceutical and food processing equipment
Sour gas and crude oil pipelines	Geothermal and mining systems
Flowlines and riser systems	Fuel gas desulfurization units

Exposure to 6% FeCl3 for 24 hours in accordance with ASTM G48 method A to determine the maximum temperature at which no pitting occurs (the critical pitting temperature, CPT), has given the following results:
Solution annealed wrought and cast Incoloy 925: 158 - 176°F (70-80°C) depending on product form and manufacturing route.
Incoloy 925 welded with AWS A5.14 ERNiCrMo-3 (Inconel 625) filler metal: 95-140°F (35 - 60°C), depending on the welding variables, i.e. process, joint geometry, procedure etc.
These values are for single exposure testing; testing a single specimen at a series of increasing temperatures gives a higher CPT value.

Crevice Corrosion

The resistance to localized corrosion is often assessed by use of the PREN number (%Cr + 3.3 x %Mo + 16 x %N). Incoloy 925 is made to a minimum PREN of 40, ensuring a guaranteed and high resistance to pitting and crevice corrosion. Incoloy 925 has been in service in seawater since 1986 as castings, and since 1989 as wrought pipes and fittings giving satisfactory performance.
At sea water temperatures above ambient, 68°F (20°C), the risk of crevice corrosion increases. Incoloy 925 resists crevice corrosion up to 131°F (55°C) but is limited by the pitting resistance of the welds to about 104°F (40°C). With the application of post weld surface treatments, seawater temperatures up to 149°F (65°C) have been handled successfully.

Repassivation

Short-term elevated-temperature upsets are common in cooling water circuits. Laboratory tests and field experience show that Incoloy 925 does not suffer crevice corrosion easily during short upsets; when corrosion does initiate, repassivation occurs readily on cooling at temperatures above the normal operating temperature of 104°F (40°C). The alloy's molybdenum (2.5–3.5%) and copper (1.5–3%) additions hold its repassivation temperature above typical service ranges, so transient upsets do not propagate corrosion under normal operating conditions.

Stress Corrosion Cracking

Incoloy 925 has excellent resistance to stress corrosion cracking (SCC) in both chloride environments, and process environments containing H₂S and CO₂. Incoloy 925 is listed in ISO 15156 / NACE MR0175 part 3 as being suitable in sour service at 0.2 bar partial pressure of H₂S. In brines with lower chloride contents Incoloy 925 can tolerate much higher pressures of H2S, as shown in Figure 4. As the pH, at temperature and pressure, increases, so does the resistance to sulfide SCC (Figure 4).

For sour-service envelopes by chloride content, partial pressure H₂S, in-situ pH and temperature, refer to NACE MR0175 Annex B (Nickel Alloys). Incoloy 925 is qualified to 0.2 bar partial pressure H₂S with pH ≥ 3.5 and chloride ≤ 175,000 mg/L. TorqBolt supplies a project-specific sour-service compliance datasheet on RFQ.

Hydrogen Embrittlement & Sulfide Stress Cracking

Incoloy 925's age-hardened nickel-iron-chromium-molybdenum microstructure (44–46% Ni) provides intrinsic resistance to hydrogen-induced cracking and sulfide stress cracking. The alloy is qualified under NACE MR0175 / ISO 15156-3 for sour-service oil & gas downhole and subsea use to 0.2 bar partial pressure H₂S, with hardness controlled to 35 HRC max in the age-hardened condition. Subsea cathodic-protection projects using Incoloy 925 fasteners require standard design stress criteria with no special coating beyond manufacturer-recommended thread lubricants.

Incoloy 925 Manufacturing

Heat Treatment

Per Special Metals SMC internal specification HA 46: Incoloy 925 is solution annealed at 1900°F (1040°C) for 1 hour, air cooled, then aged at 1365°F (740°C) for 6–9 hours, furnace cooled to 1150°F (621°C) ±15°F (8°C) for a total aging time of 18 hours. Age hardening precipitates the gamma prime Ni₃(Al, Ti) phase, raising hardness to 26–38 HRC and yield strength to ≥110 ksi (758 MPa).

Hot Forming

Per Special Metals: hot working range is 1600–2150°F (870–1175°C). At temperatures up to 2000°F (1095°C), Incoloy 925 has hot-working characteristics similar to Incoloy alloy 825. For maximum corrosion resistance and highest strength after direct aging, final hot working is followed by solution annealing and water quenching, then aging.

Cold Forming

Incoloy 925 can be adequately cold formed by various processes but the high mechanical properties should be taken into account. It is recommended that any cold work in excess of 10% -15% is removed by solution annealing and water quenching.
It should be noted that cold working above these limits can result in hardness levels above those specified in ISO 15156 / NACE MR0175 for sour-service nickel-iron-chromium alloys (35 HRC max for Incoloy 925 in the age-hardened condition).

Welding

Incoloy 925 is readily weldable using INCO-WELD Filler Metal 725NDUR for GTAW (Gas Tungsten Arc Welding) and GMAW (Gas Metal Arc Welding), as documented in Special Metals' datasheet (Figures 7–12). Recommended pre-weld condition is solution annealed; post-weld treatment is solution anneal at 1900°F (1040°C) for 1 hour air cool, plus age at 1365°F (740°C) for 6–9 hours furnace cool to achieve full mechanical properties in the weld zone. TorqBolt issues weld procedure qualification records (WPQR) per ASME IX on request.

Machining

Incoloy 925 requires a little more care in machining than the 300 series austenitics. If heavy or uneven machining to tight tolerances is to be carried out on wrought Incoloy 925 components, machining should be carried out in stages. As a last resort, a stress relieving heat treatment can be applied but this can result in a reduction of toughness and corrosion resistance.

Incoloy 925 Standards & Specifications

TorqBolt manufactures Incoloy 925 (UNS N09925) bolting, fasteners, bars, forgings, and rings to the following internationally recognised standards. Mill test certificates per NACE MR0175 / ISO 15156-2 sour-service compliance and EN 10204 3.1 (manufacturer) or 3.2 (third-party witnessed) supplied with every order.

ASTM B805, Standard Specification for Incoloy 925 (UNS N09925) Bar and Forgings
ASTM B983, Specification for Precipitation Hardened Nickel-Iron-Chromium-Molybdenum-Copper Alloy (UNS N09925, N09945) Sheet, Plate & Strip
ASTM A193 / A193M, Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure Service (B7M, B16, B7 grades; Incoloy 925 supplied as equivalent)
ASTM A194 / A194M, Specification for Carbon Steel, Alloy Steel, and Stainless Steel Nuts for Bolts for High-Pressure or High-Temperature Service
NACE MR0175 / ISO 15156-2 / -3 , Sour-service compliance for H₂S-bearing oil & gas environments; Incoloy 925 listed in Table A.20 / A.30 to 0.2 bar partial pressure H₂S
API 6A, Specification for Wellhead and Christmas Tree Equipment, including PSL-1/2/3/4 bolting
NORSOK M-630, Material Data Sheets for piping, equipment and bolting (MDS R12 lists Incoloy 925)
NORSOK M-650, Qualification of manufacturers of special materials

Mill Test Certificates: EN 10204 3.1 vs 3.2

EN 10204 3.1 is a manufacturer's certificate inspected and signed by an authorised TorqBolt QA representative, included as standard with every Incoloy 925 order. EN 10204 3.2 adds independent third-party witness inspection (TÜV, Lloyd's, BV, SGS or buyer-nominated TPI) of chemistry, mechanical testing, NDT and dimensional inspection, typical lead-time addition is 5–7 days. NACE-stamped MTCs are also available on request for sour-service projects.