Steel Overview & Material Identity
17NiCrMo6-4 (1.6566) is a Ni-Cr-Mo case-hardening steel per EN 10084:2008. Its designation encodes the composition: 0.17% nominal carbon, with alloying additions of nickel, chromium, and molybdenum at ~1.5%, ~1.0%, and ~0.20% respectively.
This grade evolved from the older Italian designation 18NiCrMo5 (UNI 7846) and is functionally equivalent to the French 18 NCD 6 (NF A 35-551) and the British 815M17 (BS 970 Part 1). In North American practice, the closest US equivalent is AISI/SAE 4317, though exact chemical windows differ slightly between standards.
Why engineers specify it: 17NiCrMo6-4 delivers carburized surface hardness ≥ 58 HRC, a tough fatigue-resistant core, and acceptable machinability — simultaneously. This combination is difficult to achieve with simpler Cr or Cr-Mn grades. The Ni-Mo system also lowers the ductile-to-brittle transition temperature, making it viable in cold-climate and sub-zero applications.
The steel is produced as forged billets, seamless rolled rings, and near-net-shape open-die forgings from a few kilograms to 30-tonne shafts. When consistent grain flow, tight dimensional tolerances, and EN 10204 / 3.1 or 3.2 material traceability are required, forging is the preferred manufacturing route over bar machining.
For procurement teams and design engineers ready to specify this grade, Jiangsu Liangyi Co., Limited manufactures custom open-die forgings and seamless rolled rings in 17NiCrMo6-4 (1.6566) across a wide size range, from 30 kg gear blanks to 30-tonne shafts, with EN 10204/3.1 material certification as standard.
Chemical Composition per EN 10084 : 2008
EN 10084:2008 specifies 17NiCrMo6-4 (1.6566) with C 0.14–0.20%, Si max 0.40%, Mn 0.60–0.90%, Cr 0.80–1.10%, Mo 0.15–0.25%, Ni 1.20–1.60%, P max 0.025%, S max 0.035%, and Al 0.020–0.050%.
| Element | Symbol | Min (%) | Max (%) | Metallurgical Role |
|---|---|---|---|---|
| Carbon | C | 0.14 | 0.20 | Core hardness and surface carbon uptake during carburizing |
| Silicon | Si | 0.15 | 0.40 | Deoxidizer; moderate solid-solution strengthening |
| Manganese | Mn | 0.60 | 0.90 | Hardenability and impact toughness |
| Chromium | Cr | 0.80 | 1.10 | Primary hardenability; promotes dense carbide layer in carburizing |
| Molybdenum | Mo | 0.15 | 0.25 | Deepens hardenability in thick sections; resists temper brittleness |
| Nickel | Ni | 1.20 | 1.60 | Core toughness, sub-zero impact resistance, improved fatigue life |
| Phosphorus | P | — | 0.025 max | Minimized to preserve toughness and ductility |
| Sulfur | S | — | 0.035 max | Low for maximum fatigue resistance; raised in 1.6569 for machinability |
| Aluminum | Al | 0.020 | 0.050 | Grain refinement; controls austenite grain coarsening during carburizing |
| Copper | Cu | — | 0.40 max | Residual element; corrosion benefit at low levels |
| Source: EN 10084:2008 heat analysis. Product analysis deviations allowed per standard. Free-cutting variant 17NiCrMoS6-4 (1.6569, S 0.020–0.040%) on request. | ||||
Table 1 — Chemical composition of 17NiCrMo6-4 (1.6566) per EN 10084:2008
Why the Ni-Cr-Mo Triplet Matters
Nickel (1.2–1.6%) is the key toughening element. It lowers the ductile-to-brittle transition temperature below −20°C and significantly raises impact energy in the core. Chromium (0.8–1.1%) increases hardenability and promotes a dense, adherent carbide layer during gas or vacuum carburizing — directly governing surface wear resistance. Molybdenum (0.15–0.25%) suppresses temper embrittlement and extends hardenability to thicker cross-sections; critical for large-diameter forged shafts where quench cooling rates are slower at the core.
Mechanical Properties by Reference Diameter
Core mechanical properties of 17NiCrMo6-4 are tested in the quenched and tempered condition. Tensile strength ranges from 750–1,000 MPa for large sections (>160 mm) to 1,100–1,350 MPa for small sections (≤16 mm). Surface hardness reaches 58–64 HRC after the full carburizing and hardening sequence.
| Reference Dia. | Tensile Rm (MPa) | Yield Rp0.2 (MPa) min | Elongation A5 (%) min | Impact KV (J) min | Hardness (HB) |
|---|---|---|---|---|---|
| ≤ 16 mm | 1100–1350 | 900 | 9 | 55 | 331–401 |
| 16–40 mm | 1000–1250 | 800 | 10 | 55 | 302–375 |
| 40–100 mm | 900–1150 | 700 | 11 | 55 | 270–346 |
| 100–160 mm | 800–1050 | 600 | 12 | 50 | 241–314 |
| 160–250 mm | 750–1000 | 550 | 13 | 45 | 224–300 |
| Condition: +QT (quenched and tempered) per EN 10084:2008. For open-die forgings >250 mm, agree values with the forging manufacturer at order stage. Test location (¼T, ½T) must be specified. | |||||
Table 2 — Core mechanical properties by reference diameter (EN 10084:2008, +QT condition)
Key Performance Indicators
Large forgings: Open-die forgings commonly exceed 160 mm in ruling section. Expect core properties toward the lower end of Table 2. Always specify test location (¼T or ½T) and minimum property requirements at enquiry stage, not at delivery. Request a dedicated mechanical property guarantee clause in your purchase order.
7-Step Heat Treatment Process for 17NiCrMo6-4 Forgings
The complete heat treatment sequence for 17NiCrMo6-4 consists of 7 stages: hot forming at 900–1,100°C → normalizing at 880°C → optional soft annealing at 700°C → carburizing at 880–930°C → core hardening quench at 830–870°C → case hardening quench at 780–820°C → low tempering at 150–180°C to achieve ≥ 58 HRC surface hardness.
All forging operations are performed in this temperature window. Working below 900°C risks internal forging cracks and creates residual stresses that compromise subsequent ultrasonic inspection quality. Parts must not be air-cooled directly from forging temperature without controlled cooling procedures.
Hold for a minimum of 1 hour per 25 mm of ruling section, then cool in still air. This refines the as-forged austenite grain structure (targeting ASTM grain size 5 or finer), eliminates banded segregation from the hot working process, and establishes a uniform, machineable microstructure ready for rough machining.
Specified when extensive rough machining or cold forming is required before case hardening. The furnace-cooled condition achieves maximum 229 Brinell hardness, enabling free cutting with standard carbide tooling. This step is not necessary if normalizing hardness already permits efficient machining.
The surface layer is enriched to a target carbon content of approximately 0.75–0.85%. Carburizing time controls case depth: at 920°C in a standard endothermic gas atmosphere, a nominal CHD (case hardening depth) of 1.0 mm requires approximately 4–8 hours of diffusion time. The aluminum addition (0.020–0.050% Al) suppresses austenite grain coarsening at carburizing temperatures.
The forging is reheated to this temperature range and quenched to achieve the specified core hardness. For large forgings, polymer quenching provides more controlled and uniform cooling than straight oil quench, reducing thermal gradients and distortion risk. Salt bath quenching is specified for complex geometries requiring dimensional stability.
A second, lower-temperature quench refines the case microstructure and locks in the hardened surface layer at 58–64 HRC. This double-quench sequence is standard for high-duty gear forgings requiring both fine austenite grain and maximum surface hardness simultaneously.
Relieves residual quench stresses and eliminates the risk of grinding cracks during subsequent machining — while fully preserving surface hardness at ≥ 58 HRC. Critical: never exceed 200°C without re-qualifying surface hardness. Tempering above this threshold progressively softens the carburized layer; at 250°C, surface hardness may drop below the 58 HRC minimum.
Forging Characteristics of 17NiCrMo6-4
17NiCrMo6-4 exhibits excellent hot workability between 900–1,100°C with no hot shortness. Open-die forging aligns grain flow with part geometry, improving fatigue life compared to machined bar stock components. Standard open-die capability: 30 kg to 30,000 kg per piece; seamless rings to OD 5,000 mm.
Clean forging at 900–1,100°C with no hot shortness. Mo and Ni maintain austenite ductility throughout the working range. Suitable for heavy open-die operations on ingots up to 30+ tonnes without forging defects.
Forging aligns grain flow with part geometry. In gear shafts, aligned grain flow improves fatigue life and impact resistance compared to machined bar-stock components — an advantage that machining alone cannot replicate.
30 kg to 30,000 kg per piece. Shaft length to 10,000 mm. Bar diameters Ø100–1,200 mm. Seamless rolled rings to OD 5,000 mm. Multiple form factors in one grade from one qualified source.
Proper normalizing achieves ASTM grain size 5 or finer, enabling reliable ultrasonic testing per EN 10228-3 — the standard commonly required by wind turbine gearbox OEMs and mining equipment customers.
In the soft-annealed condition (≤229 HB), 17NiCrMo6-4 machines freely with carbide tooling. Rough machining is done before case hardening; final geometry is achieved by precision grinding post-heat-treatment to prevent re-softening.
Every forging is traceable to its original heat/melt. EN 10204/3.1 MTR (chemical analysis, mechanical test, heat treatment record, UT/MT report) supplied as standard. 3.2 third-party co-sign available on request.
Forged Product Forms Available in 17NiCrMo6-4
| Product Form | Weight Range | Typical End Applications |
|---|---|---|
| Round / Square Billets | 50–5,000 kg | Feed stock for gear blanks, pinion forgings |
| Forged Shafts & Spindles | 100–15,000 kg | Gearbox output shafts, crusher drive shafts |
| Seamless Rolled Rings | 30–20,000 kg | Ring gears, bearing housings, large flanges |
| Gear Blanks (Disk / Cup) | 50–8,000 kg | Planetary gears, bevel wheels, sun gears |
| Bushings & Sleeves | 20–3,000 kg | Eccentric bushings, bearing sleeves, liners |
Table 3 — Standard forged product forms in 17NiCrMo6-4
All five product forms are available from a single qualified source. To obtain dimensional drawings, weight estimates, or a commercial quotation for custom 17NiCrMo6-4 forgings, submit your specification to Jiangsu Liangyi's engineering team.
Global Grade Equivalents for 17NiCrMo6-4
17NiCrMo6-4 (1.6566) equivalents include AISI/SAE 4317 (USA), 18NiCrMo5 (Italy/UNI 7846), 18 NCD 6 (France/NF A35-551), and 815M17 (UK/BS 970). Chemical windows differ between standards; verify composition compliance before substituting on critical applications.
| Standard | Region | Equivalent Grade | Key Difference vs. EN 10084 |
|---|---|---|---|
| EN 10084 : 2008 | Europe | 17NiCrMo6-4 / 1.6566 | Primary reference — specify this for EU procurement |
| AISI / SAE | USA | 4317 | Ni range 1.65–2.00% (slightly higher than EN) |
| UNI 7846 | Italy | 18NiCrMo5 | Legacy designation; superseded by EN 10084 |
| NF A 35-551 | France | 18 NCD 6 | S limit and heat treatment slightly differ |
| BS 970 Part 1 | UK | 815M17 | Equivalent for bar and billet; forging spec varies |
| DIN 17210 | Germany | 18NiCrMo5 | Former DIN designation, replaced by EN system |
| GOST 4543 | Russia | No direct equivalent | Nearest: 20KhN2M (lower Mo content) |
| JIS G 4103 | Japan | No direct equivalent | Nearest: SNCM220H (lower Cr content) |
| Equivalents for cross-reference only. Always verify chemical composition and mechanical property compliance independently before specifying on critical applications. | |||
Table 4 — International grade equivalents for 17NiCrMo6-4 / 1.6566
Industrial Applications of 17NiCrMo6-4 Forgings
17NiCrMo6-4 forgings are used wherever components must simultaneously resist contact stress, bending fatigue, and impact loading across long service intervals — particularly in wind energy gearboxes, mining and cement drives, marine propulsion, and heavy industrial machinery.
Planet carrier shafts, ring gear forgings, sun gears, and high-speed output shafts in multi-MW wind turbine drivetrains. The Ni content supports sub-zero impact toughness (KV ≥ 45 J) required for Arctic and offshore installations.
Pinion shafts, bull gear rings, and eccentric bushings for ball mills, rotary kilns, vertical roller mills, and cone crushers. Components routinely weigh 1–15 tonnes and require UT Class 3 inspection as standard.
High-torque marine gearbox shafts and pinions. The Ni-Mo combination resists fatigue crack initiation under the cyclic torsional loading profiles of propulsion shafts in long-service marine environments.
Gear shafts and coupling flanges for steel mill rolling drives, paper mill main drives, and petrochemical compressor trains — where planned maintenance intervals exceed 3–5 years.
Case-hardened differential gear blanks, camshafts, and transmission shaft forgings. For high-volume machining, the free-cutting variant 17NiCrMoS6-4 (1.6569) with raised sulfur is preferred to increase cycle throughput.
Wear-resistant bushings, heavy-duty spindles, structural pins, and eccentric shafts — wherever a hard surface and impact-resistant core are required and the cost premium of higher-alloy grades cannot be justified.
If your application matches one of the above categories, the next step is confirming material specification, forging dimensions, and inspection requirements. See the 17NiCrMo6-4 forging parts product page for full supply scope and to submit a technical enquiry.
17NiCrMo6-4 vs. 18CrNiMo7-6: Which Grade to Specify?
For ruling sections below 160 mm in standard environments, 17NiCrMo6-4 (1.6566) costs 12–20% less than 18CrNiMo7-6 (1.6587) and meets virtually all fatigue, hardness, and impact requirements. Upgrade to 1.6587 only for sections >160 mm, sub-zero applications below −20°C, or case depth requirements >2.5 mm CHD.
| Comparison Factor | 17NiCrMo6-4 (1.6566) | 18CrNiMo7-6 (1.6587) | Preferred Grade |
|---|---|---|---|
| Chromium content | 0.8–1.1% | 1.5–1.8% | 1.6587 (higher Cr) |
| Molybdenum content | 0.15–0.25% | 0.25–0.35% | 1.6587 (higher Mo) |
| Hardenability (sections >160 mm) | Medium-high | High | 1.6587 |
| Max case depth (CHD) | ~2.5 mm | ~3.5 mm | 1.6587 for deep case |
| Sub-zero impact toughness | Very good (>−20°C) | Excellent (>−40°C) | 1.6587 for Arctic duty |
| Surface hardness achievable | 58–62 HRC | 60–64 HRC | 1.6587 marginally |
| Machinability (annealed) | Good (≤229 HB) | Good (≤229 HB) | Equal |
| Material cost vs. base | Base reference ✓ Lower cost | +12–20% typical | 1.6566 |
| Availability, large forgings | Excellent ✓ Better stock | Very good | 1.6566 |
| EN 10084 compliance | Yes (1.6566) | Yes (1.6587) | Equal |
| Cost premium is indicative and varies by market conditions. Verify current pricing with your forging supplier at enquiry stage. | |||
Table 5 — Technical and commercial comparison: 17NiCrMo6-4 vs. 18CrNiMo7-6
Specification decision rule: For ruling sections ≤160 mm in standard industrial service (ambient temperature, standard fatigue loadings), 17NiCrMo6-4 (1.6566) is the cost-optimal choice — 12–20% lower material cost, equivalent mechanical properties, and superior availability in large-section forgings. Upgrade to 18CrNiMo7-6 (1.6587) only when the section exceeds 160 mm, service temperature drops below −20°C, or case depth specification exceeds 2.5 mm CHD.
Ordering 17NiCrMo6-4 Forgings from Jiangsu Liangyi
Jiangsu Liangyi Co., Limited is an ISO 9001:2015 certified manufacturer of 17NiCrMo6-4 (1.6566) forgings for global industrial customers. Capability: 30 kg to 30,000 kg per piece, Ø100–1,200 mm bars, seamless rings to OD 5,000 mm, EN 10204/3.1 material certification supplied as standard.
| Parameter | Our Capability |
|---|---|
| Weight range per piece | 30 kg – 30,000 kg |
| Round bar diameter | Ø 100 – 1,200 mm |
| Shaft length | 100 – 10,000 mm |
| Seamless ring OD | Up to Ø 5,000 mm |
| Delivery condition | Hot forged / Normalized / Q+T / Carburized & Hardened |
| Machining | Rough-machined (black) or finish-machined to customer drawing |
| NDE inspection | UT per EN 10228-3 · MT per EN 10228-1 · PT (as agreed per order) |
| Material certification | EN 10204 / 3.1 standard · 3.2 third-party on request |
| Quality system | ISO 9001 : 2015 certified |
| Quotation turnaround | 24 hours from receipt of technical enquiry |
Table 6 — Jiangsu Liangyi manufacturing capability for 17NiCrMo6-4 forgings
All forgings are produced under ISO 9001:2015 with full documentation — chemical analysis, mechanical test results, heat treatment records, and NDE certificates. To request a 17NiCrMo6-4 forging quotation, submit your drawing or specification using the contact details below; the engineering team responds within 24 hours.
Frequently Asked Questions
They are close functional equivalents but not identical. AISI 4317 specifies a nickel range of 1.65–2.00%, which is slightly higher than EN 10084:2008's 1.20–1.60% for 17NiCrMo6-4. For European-standard procurement, always use the EN designation (1.6566). For US or dual-standard projects, confirm chemistry window compliance with your metallurgist before substituting on fatigue-critical applications such as wind gearbox shafts.
The "S" free-cutting variant (1.6569) contains controlled sulfur at 0.020–0.040%. This improves chip breakability and enables higher machining feed rates in CNC production environments — a significant advantage for high-volume automotive gear manufacturing. However, the sulfur inclusions marginally reduce transverse ductility and fatigue life. For large-section industrial forgings (wind, mining, marine) where core toughness is the primary performance driver, always specify the standard 1.6566 grade without elevated sulfur.
Welding of case-hardened 17NiCrMo6-4 is not recommended — the heat-affected zone loses surface hardness irreversibly. In the normalized or soft-annealed condition, welding is technically possible with pre-heat of 150–200°C and appropriate post-weld heat treatment (PWHT), but this scenario is uncommon in forging applications. Consult your welding engineer and forging supplier before specifying weld repairs on any heat-treated 1.6566 component.
In standard gas carburizing at 900–920°C, case depths of 0.5–2.5 mm CHD (measured at 550 HV) are routinely achievable. Vacuum carburizing or extended cycle times can push this toward 3.0 mm, but at increased distortion risk and process cost. Always specify CHD at enquiry stage — it directly determines the forging machining allowance, final grinding stock, and overall forging dimensions. Typical gas carburizing cycle time for 1.0 mm CHD: 4–8 hours depending on temperature, atmosphere carbon potential, and steel cross-section.
Yes. EN 10204 / 3.2 inspection — where an independent third-party inspector or client-nominated inspector witnesses testing and co-signs the material test report — is available on request. This service is commonly required by wind energy gearbox OEMs, marine classification society projects, and high-integrity industrial applications. Specify 3.2 inspection at purchase order stage to allow sufficient scheduling lead time for inspector coordination.
Choose 17NiCrMo6-4 (1.6566) when: the ruling section is below 160 mm; the operating temperature remains above −20°C; CHD requirements are 2.5 mm or less; and cost optimization is a factor (1.6566 is typically 12–20% cheaper than 18CrNiMo7-6). Choose 18CrNiMo7-6 (1.6587) when: ruling sections exceed 160 mm and deep-section hardenability is critical; operating temperatures drop below −20°C (Arctic or offshore); CHD requirements exceed 2.5 mm; or maximum surface hardness above 62 HRC is required.
Request a Quote for Custom 17NiCrMo6-4 Forgings
Send us your drawing, weight, quantity, delivery condition, and inspection requirements. ISO 9001:2015 certified. EN 10204/3.1 standard. Response within 24 hours.