EI698 (KhN77TYuR-VD) — Russian Equivalent of Inconel 718
EI698 (modern Russian designation KhN77TYuR-VD) is the Russian-grade precipitation-hardening nickel-iron-chromium superalloy that is equivalent to Inconel 718 (UNS N07718, Chinese GH4169). It is the world's most widely used superalloy for high-strength rotating and structural components in aerospace, thanks to its outstanding combination of strength, fatigue resistance and weldability up to about 650°C. This article covers its composition, properties, heat treatment and applications.
1. Chemical Composition
| Element | EI698 / Inconel 718 |
|---|---|
| Ni | 50.0–55.0 |
| Cr | 17.0–21.0 |
| Nb + Ta | 4.75–5.50 |
| Mo | 2.80–3.30 |
| Ti | 0.65–1.15 |
| Al | 0.30–0.70 |
| Fe | Balance |
| C | ≤0.08 |
The niobium (4.75–5.50%) is the key strengthening element: it forms the coherent gamma double-prime (γ'') phase that gives the alloy its very high strength.
2. Mechanical Properties (Precipitation-Hardened)
| Property | Typical Value |
|---|---|
| Yield strength σ₀.₂, MPa | ≥1035 |
| Tensile strength σᵦ, MPa | ≥1275 |
| Elongation, % | 12–15 |
| Service temperature | −253 to ~650°C |
3. Strengthening Mechanism
Inconel 718 / EI698 is strengthened by a dual precipitation of gamma double-prime (γ'') and gamma prime (γ'), both nucleated by niobium and titanium. Unlike some superalloys, it does not rely on coarse gamma prime, which makes it less prone to strain-age cracking during welding and heat treatment — a major reason for its excellent fabricability.
4. Heat Treatment
| Step | Typical Condition |
|---|---|
| Solution treatment | 950–980°C, air cool |
| First aging | ~720°C, hold, furnace cool |
| Second aging | ~620°C, hold, air cool |
The two-step aging develops the γ'' and γ' precipitates. The exact schedule is adjusted for product form and required strength.
5. Applications
| Industry | Typical Components |
|---|---|
| Aerospace engines | Turbine discs, shafts, blades, casings, fasteners |
| Oil & gas | Downhole hardware, wellhead components |
| Nuclear | Reactor internals, fasteners |
| General high-strength | Bolting, springs, cryogenic tanks |
6. Weldability
Inconel 718 / EI698 is among the most weldable precipitation-hardening superalloys. It is welded with Inconel 718 filler (ERNiFeCr-2) and is commonly used in the welded condition; post-weld aging is usually applied to restore full strength in the weld metal.
7. Standards and Equivalents
| System | Designation |
|---|---|
| UNS / Inconel | N07718 (Inconel 718) |
| Russian (GOST) | EI698, KhN77TYuR-VD |
| Chinese (GB) | GH4169 |
| ASTM | B637, B670, B983; AMS 5662/5663/5664 |
8. Conclusion
Need Inconel 718 / GH4169 Forgings or Bars?
Shanghai Hangbo Alloy Group supplies Inconel 718 (GH4169) forgings, discs, rings and bars equivalent to Russian EI698, with EN 10204 3.1/3.2 certification and full traceability.
📧 Email: serena@hangboalloy.com
📞 Tel: +86 166 2109 2936
💬 WhatsApp: +86 166 2109 2936
Summary: EI698 (KhN77TYuR-VD) and Inconel 718 are functionally equivalent precipitation-hardening superalloys. Their niobium-rich chemistry, dual γ''/γ' strengthening and excellent weldability make them the default choice for high-strength aerospace and energy components up to about 650°C.
9. Frequently Asked Questions (FAQ)
1. What is EI698 and how is it related to Inconel 718?
EI698 (KhN77TYuR-VD) is the Russian-grade equivalent of Inconel 718 (N07718, GH4169); they share essentially the same chemistry and strengthening system and are interchangeable for most purposes.
2. What is the chemical composition of EI698?
Ni 50-55, Cr 17-21, Nb+Ta 4.75-5.50, Mo 2.80-3.30, Ti 0.65-1.15, Al 0.30-0.70, Fe balance, C ≤0.08.
3. What are its mechanical properties?
In the precipitation-hardened condition: yield ~1035 MPa, tensile ~1275 MPa, elongation 12-15%, useful from cryogenic to ~650°C.
4. What heat treatment does it use?
Solution at 950-980°C followed by two-step aging at ~720°C and ~620°C to develop the γ''/γ' precipitates.
5. What are the main applications?
Aerospace turbine discs, shafts, blades, fasteners; oil & gas; nuclear; high-strength bolting.
6. Is it weldable?
Yes — one of the most weldable PH superalloys, welded with ERNiFeCr-2, often used in the welded condition with post-weld aging.
7. What standards cover it?
Inconel 718: ASTM B637/B670/B983, UNS N07718, AMS 5662-64. Russian EI698/KhN77TYuR-VD (GOST 5632). Chinese GH4169.
8. In what forms is it supplied?
Billet, bar, forged disc, ring, plate and sheet, supplied with EN 10204 3.1/3.2 certification.