UNS N06625 / W.Nr. 2.4856 | ASTM B443 / ASME SB443 Certified | DIN 125, ISO 7089, DIN 9021, DIN 127
Inconel 625 washers are precision-made fasteners made from a nickel-chromium-molybdenum-niobium superalloy (UNS N06625 / W.Nr. 2.4856) with a unique property profile of high mechanical strength, high oxidation resistance, and resistance to aqueous corrosion. These washers are manufactured with dimensional tolerances of ± 0.001" to ± 0.030" by cold forging, hot forging, and bar stock machining processes at Unifit Fastener, ensuring that they will perform structurally in the harshest service conditions, from cryogenic pipelines at −320°F (−196°C) to furnace components at 1800°F (982°C).
Inconel 625's high yield strength is derived primarily from solid-solution strengthening by molybdenum and niobium, which means that there is no need for precipitation heat treatment in most service applications. This makes them particularly appropriate for welded assemblies in chemical processing plants, subsea umbilicals, bolting of jet engines, heat exchanger flanges, and nuclear waste containment systems. All washers we supply at Unifit Fastener come with complete material traceability documentation and third-party inspection certificates, upon request, conforming to international standards, including ASTM B443, DIN 125, ISO 7089, DIN 9021, and ASME B18.22.1.
Request a QuoteThe standard workhorse of our washer range. Designed for general fastening applications, these provide a clean bearing surface that distributes clamp load uniformly, protecting flange faces from galling and embedding. Available in metric sizes M6 through M24.
| Nominal Size | Inside Dia. (mm) | Outside Dia. (mm) | Thickness (mm) |
| M6 | 6.4 | 12.0 | 1.6 |
| M8 | 8.4 | 16.0 | 1.6 |
| M10 | 10.5 | 20.0 | 2.0 |
| M12 | 13.0 | 24.0 | 2.5 |
| M16 | 17.0 | 30.0 | 3.0 |
| M20 | 21.0 | 37.0 | 3.0 |
| M24 | 25.0 | 44.0 | 4.0 |
Engineered with a significantly larger outer diameter, fender washers spread fastener loads across a wider bearing area. This is critical when bolting into soft or composite flange materials, oversized clearance holes, or slotted mounting slots common in offshore structural assemblies.
| Nominal Size | Inside Dia. (mm) | Outside Dia. (mm) | Thickness (mm) |
| M6 | 6.4 | 18.0 | 1.6 |
| M8 | 8.4 | 24.0 | 2.0 |
| M10 | 10.5 | 30.0 | 2.5 |
| M12 | 13.0 | 37.0 | 3.0 |
| M16 | 17.0 | 50.0 | 3.0 |
| M20 | 22.0 | 60.0 | 4.0 |
| M24 | 26.0 | 72.0 | 5.0 |
These split-ring washers are specifically designed to resist self-loosening under vibration and thermal cycling — a critical requirement in turbine casing assemblies, compressor covers, and any bolted joint exposed to pulsating loads. The helical cut provides a resilient spring effect that maintains continuous clamp-load compensation.
| Nominal Size | Inner Dia. Min (mm) | Outer Dia. Max (mm) | Thickness (mm) |
| M6 | 6.1 | 11.8 | 1.6 |
| M8 | 8.1 | 14.8 | 2.0 |
| M10 | 10.2 | 18.1 | 2.2 |
| M12 | 12.2 | 21.1 | 2.5 |
| M16 | 16.2 | 27.4 | 3.5 |
| M20 | 20.2 | 33.6 | 4.0 |
| Property | Inconel 625 Washer Features |
| Alloy Grade | Inconel 625 (UNS N06625), a nickel-based alloy strengthened by molybdenum and niobium additions for superior mechanical performance. |
| Temperature Capability | Maintains strength and toughness from cryogenic conditions up to approximately 982°C (1800°F). |
| Hardness | Typical annealed hardness ranges around 220 HB (approx. 22 HRC). |
| Corrosion Resistance | Excellent resistance to chloride-induced stress corrosion cracking, pitting, and crevice corrosion. |
| Age Hardening Behavior | Gradual strengthening may occur after prolonged exposure to temperatures between 650°C and 870°C (1200°F-1600°F). |
| USS Washer Standard (ASME B18.22.1) | Larger OD profile optimised for heavy structural fastening; hole diameter referenced to nominal bolt diameter per ASME B18.22.1 tables. |
| SAE Washer Standard | Designed with a more compact profile where space limitations are critical. |
| Functional Benefits | Reduces friction under bolt heads, improves load distribution, supports thermal stability, and minimizes galvanic corrosion when used with Alloy 625 fasteners. |
| Element | Ni | Cr | Mo | Nb | Fe | Al | Ti | C | Mn | Si |
| wt % | 58.0 min | 20.0-23.0 | 8.0-10.0 | 3.15-4.15 | 5.0 max | 0.40 max | 0.40 max | 0.10 max | 0.50 max | 0.50 max |
| Property | Value |
| Density | 8.4 g/cm³ |
| Melting Range | 1290-1350°C (2354-2460°F) |
| Tensile Strength | ≥ 830 MPa (≥ 120 ksi) |
| Yield Strength (0.2% offset) | ≥ 414 MPa (≥ 60 ksi) |
| Elongation in 2" | ≥ 30% |
| Hardness (Annealed) | ~207-220 HB (approx. 20-22 HRC) |
| Modulus of Elasticity | 207 GPa |
| Thermal Expansion (20-100°C) | 12.8 micrometer/m.°C |
| Parameter | Detail |
| Nominal Size Range | M2 to M64 (DIN metric); 1/4" to 2 1/2" (ASME inch) |
| Length / Thickness Range | 0.5 mm to 20 mm |
| Manufacturing Methods | Cold Forged, Hot Forged, Bar Stock Machined, Bar Stock Milled |
| Surface Finish | Pickled & Annealed / Bright Annealed / Polished on request |
| Dimensional Standards | DIN 125 / 127 / 9021, ISO 7089 / 7090 / 7093, ASME B18.22.1 |
| Testing Standards | ASTM E8, ASTM E18, ASTM A751, ASTM E112 |
| Application Environment | Temperature Range |
| Cryogenic (LNG, liquid nitrogen pipelines) | -196°C to -320°F |
| Ambient Industrial Service | Up to 400°C |
| Elevated Temperature (Oxidizing Atmosphere) | Up to 816°C (1500°F) |
| High Temperature (Non-cyclic, Controlled Exposure) | Up to 982°C (1800°F) |
The combination of high strength, broad temperature tolerance, and unmatched corrosion resistance makes Inconel 625 washers the preferred choice across several critical industries:
| Industry | Specific Application | Why Alloy 625? |
| Aerospace & Defence | Jet engine nacelle bolting, exhaust fasteners, aircraft structural joints | Extreme temp cycling, vibration resistance, low creep |
| Oil & Gas (Upstream) | Subsea wellhead connectors, Christmas tree assemblies, riser pipe flanges | Seawater + H2S resistance, pressure retention |
| Chemical Processing | Reactor vessel flanges, heat exchanger tube sheets, acid-service piping | Resists HCl, H2SO4, HF acids, SCC immunity |
| Marine & Offshore | Platform structural bolting, hull fitting fasteners, offshore desalination plants | Full chloride corrosion immunity, long service life |
| Nuclear Power | Waste containment, reactor pressure vessel fasteners, cooling loop joints | Radiation stability, high purity, ASME compliance |
| Power Generation | Steam turbine casing bolts, gas turbine combustion section, heat recovery units | Creep resistance at sustained high temperatures |
| Cryogenic & LNG | LNG storage tank flanges, cryogenic valve seats, cold box assemblies | No ductile-to-brittle transition, retains toughness |
| Pharmaceutical & Food | Autoclave and sterilization vessel bolting, high-purity process equipment | Non-contaminating, resists aggressive cleaning agents |
Alloy 625 demonstrates complete immunity to chloride-ion stress corrosion cracking (SCC) — the primary failure mechanism responsible for over 40% of stainless steel fastener failures in marine and chemical environments. The high molybdenum and chromium content provides a stable passive film across pH levels from highly acidic to caustic conditions.
Unlike carbon and low-alloy steels that suffer rapid strength degradation above 500°C, Inconel 625 maintains structural integrity up to 982°C. Gradual precipitation hardening between 650°C-870°C actually increases yield strength over extended service, making it ideal for maintenance-free high-temperature joints.
The alloy's high fatigue strength — combined with the spring-back characteristics of our DIN 127 lock washer profile — ensures reliable bolt pre-load retention in applications subject to mechanical vibration, thermal cycling, and dynamic loading.
When used with matching Alloy 625 bolts and nuts, our washers eliminate galvanic couples entirely. Where mixed alloy assemblies are required, the noble electrochemical potential of Inconel 625 minimizes galvanic attack on adjacent components.
Austenitic nickel alloys do not undergo the ductile-to-brittle transition seen in ferritic steels. Inconel 625 washers retain excellent impact toughness at temperatures as low as -196°C, meeting the demanding requirements of LNG facilities and cryogenic storage systems.
Our precision-machined flat and fender washer profiles provide a hardened, dimensionally stable bearing surface that prevents under-head friction from consuming applied torque, ensuring that virtually all bolt tension converts directly into clamp force — critical for pressure-boundary joints.
| Property | Inconel 625 | SS 316L | SS 317L | Hastelloy C276 | Monel 400 |
| Ni Content | 58% min | 10-14% | 11-15% | 57% min | 63-70% |
| Max Service Temp | 982°C | 870°C | 870°C | 1038°C | 480°C |
| Chloride SCC Immunity | Excellent | Poor | Moderate | Excellent | Good |
| Tensile Strength | 830 MPa+ | 485 MPa | 515 MPa | 760 MPa | 550 MPa |
| Seawater Resistance | Excellent | Moderate | Good | Excellent | Very Good |
| HF Acid Resistance | Good | Poor | Poor | Excellent | Excellent |
| Cryogenic Performance | Excellent | Good | Good | Good | Good |
| Relative Cost Index | High | Low | Medium | Very High | Medium-High |
| Best For | Universal high-perf | General purpose | Mild chemical | Reducing acids | Seawater only |
Every Inconel 625 washer we produce follows a rigorous 8-step manufacturing and quality assurance process:
| Step | Process | Quality Control |
| 1 | Raw Material Sourcing — ASTM B443 certified billets from approved mills | Incoming PMI test + MTC verification |
| 2 | Cutting & Blanking — Precision plasma/saw cutting to washer blanks | Dimensional check per lot |
| 3 | Hot / Cold Forging or Bar Machining — Profile formation to DIN/ISO spec | First-article dimensional inspection |
| 4 | Annealing / Solution Treatment — 1080°C water quench for optimal ductility | Hardness test post-anneal |
| 5 | Pickling & Surface Finishing — Acid passivation for oxide-free surface | Visual + surface roughness check |
| 6 | Final Machining — CNC turning/milling for tight ID/OD/thickness tolerances | CMM dimensional report |
| 7 | Testing & Inspection — Chemical, mechanical, hardness, and PMI per ASTM | Third-party lab reports available |
| 8 | Packaging & Dispatch — Corrosion-inhibited packaging with MTC and CoC | Pre-shipment inspection on request |
Inconel 625 is widely used in industries that require exceptional strength, corrosion resistance, and high-temperature performance. Common applications include aerospace components, marine equipment, chemical processing plants, offshore oil and gas systems, heat exchangers, and power generation facilities.
Inconel 625 has moderate to difficult machinability due to its high strength and tendency to work-harden during machining. For best results, manufacturers use rigid tooling, slower cutting speeds, and adequate cooling methods. Despite machining challenges, the alloy is preferred for critical applications because of its outstanding mechanical and corrosion-resistant properties.
Absolutely. Unifit Fastener operates CNC turning and milling centres capable of producing Inconel 625 washers to any custom ID, OD, and thickness specification. Minimum order quantities apply for fully custom dimensions; please contact us with your engineering drawing or dimensional requirements for a prompt quotation.
Both offer excellent corrosion resistance, but they serve different optimum conditions. Super Duplex is cost-effective for seawater service up to ~300°C with very high strength. Inconel 625 outperforms in: (a) temperatures above 300°C, (b) reducing acid environments (HCl, HF), (c) applications requiring total SCC immunity, and (d) cryogenic service. For mixed acid/seawater high-temperature environments, Inconel 625 is the safer engineering choice.