1.6566 Forgings, 17NiCrMo6-4 Case-Hardening Steel
Also written as DIN 1.6566, W.Nr. 1.6566, EN 1.6566, 17NiCrMo6-4. Standard: EN 10084. Type: Ni-Cr-Mo case-hardening steel
1.6566 is the European material number for 17NiCrMo6-4, a nickel-chromium-molybdenum case-hardening steel specified in EN 10084. It contains 0.14 to 0.20 % carbon, 1.20 to 1.50 % nickel, 0.80 to 1.10 % chromium and 0.15 to 0.25 % molybdenum. Parts are machined in the soft-annealed condition and then carburised and hardened, which gives a surface hardness of about 58 to 62 HRC over a tough core. The grade is widely used for heavy-duty gears, pinions, ring gears and drive shafts.
Jiangyin Jiangnan Metal Co., Ltd. forges 1.6566 into seamless rolled rings, flanges, shafts, discs, sleeves, bars and hollow forgings from 100 mm to 6,000 mm in diameter, 10 kg to 15,000 kg in weight and up to 12,000 mm in length. The steel is melted by EAF + LF + VD, ultrasonically tested to EN 10228-3 and supplied with EN 10204 3.1 or 3.2 certification.
1.6566 summary data
- Material number
- 1.6566
- Steel name
- 17NiCrMo6-4
- Standard
- EN 10084 (case-hardening steels), also ISO 683-11
- Steel group
- Alloyed case-hardening steel
- Melting practice
- EAF + LF + VD (vacuum degassed)
- Delivery condition
- Soft annealed (+A), normalised (+N) or treated to hardness (+TH)
- Typical case hardness
- 58 to 62 HRC after carburising and tempering
- Forged forms supplied
- Seamless rolled rings, gear ring blanks, flanges, shafts, discs, sleeves, bushings, round bars, blocks, hollow forgings
- Size range
- 100 to 6,000 mm diameter, 10 to 15,000 kg, length to 12,000 mm
- NDT
- Ultrasonic to EN 10228-3, SEP 1921 or ASTM A388. MT and PT on request
- Certification
- EN 10204 3.1 as standard, 3.2 with third-party witness on request
- Supplier
- Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin, Jiangsu, China
Chemical composition of 1.6566
The table below gives the specification range for 17NiCrMo6-4 to EN 10084. Every heat is checked by optical emission spectrometry and the actual ladle analysis is printed on the mill certificate.
| C | Si max | Mn | P max | S max | Cr | Mo | Ni | Al |
|---|---|---|---|---|---|---|---|---|
| 0.14-0.20 | 0.40 | 0.60-0.90 | 0.035 | 0.035 | 0.80-1.10 | 0.15-0.25 | 1.20-1.50 | 0.020-0.050 |
Source: EN 10084 specification limits for 17NiCrMo6-4. Balance iron. Aluminium is added to control grain size during carburising. A sulphur-controlled version for better machinability can be supplied on request.
Mechanical properties
1.6566 is a case-hardening steel, so two sets of properties apply: the core properties after hardening, and the case properties produced by carburising. Core strength drops as the section gets larger, which is why heavier gears are often specified in 18CrNiMo7-6 instead.
| Ruling section | Yield Rp0.2 min | Tensile Rm | Elongation A min |
|---|---|---|---|
| 11 to 30 mm | 685 MPa (99 ksi) | 980 to 1,270 MPa | 8 % |
| 30 to 63 mm | 590 MPa (86 ksi) | 880 to 1,180 MPa | 9 % |
| 63 to 100 mm | 540 MPa (78 ksi) | 780 to 1,080 MPa | 10 % |
| Condition | Typical hardness |
|---|---|
| Soft annealed (+A), as delivered for machining | 229 HB max |
| Treated to hardness (+TH) | 152 to 201 HB |
| Carburised case, after hardening and tempering | 58 to 62 HRC |
| Case depth (CHD at 550 HV1) | 0.6 to 2.5 mm, to customer specification |
These values are indicative. Actual results depend on section size, quenchant and the heat treatment cycle used. The guaranteed values for a supplied part are those recorded on its EN 10204 certificate. Test pieces are taken at the section size stated on the order.
Heat treatment and forging temperatures
| Operation | Temperature | Cooling |
|---|---|---|
| Forging | Start 1,100 to 1,150 °C, finish above 850 °C | Slow cool in still air or in furnace |
| Normalising | 870 to 900 °C | Air |
| Soft annealing | 650 to 700 °C | Furnace cool to 550 °C, then air |
| Carburising | 900 to 940 °C | According to case depth required |
| Core hardening | 830 to 870 °C | Oil |
| Case hardening | 810 to 840 °C | Oil |
| Tempering | 150 to 200 °C | Air |
Typical values for the 17NiCrMo6-4 grade. Direct quenching from the carburising temperature is possible, but it produces coarser grain and lower core toughness than reheating and quenching. Reheat quenching is recommended for gear components.
1.6566 equivalent grades
There is no exact replacement for 17NiCrMo6-4 outside Europe. The grades listed below are the closest ones in common use, but each differs in nickel or chromium content, which changes hardenability. Compare the actual mill certificate before substituting.
| Standard and country | Designation | How close |
|---|---|---|
| EN 10084, Europe | 17NiCrMo6-4 (1.6566) | Base grade |
| ISO 683-11 | 17NiCrMo6-4 | Identical |
| UNI, Italy | 18NiCrMo5 | Very close |
| AFNOR, France | 18NCD6 | Very close |
| BS 970, UK | 820M17 | Close, wider nickel band |
| SAE / AISI, USA | 4320, 4317 | Nearest only, higher Ni and lower Cr |
| JIS, Japan | SNCM420 | Nearest only, higher Ni and lower Cr |
| GB, China | 20CrNi2Mo | Nearest only |
1.6566 or 1.6587? These two grades are often confused. Both are EN 10084 case-hardening steels. 1.6587, or 18CrNiMo7-6, contains more chromium (1.50 to 1.80 %) and more nickel (1.40 to 1.70 %), so it hardens deeper. 1.6587 is the usual choice for large-module gears and heavy sections. 1.6566 costs less and is suitable for small and medium sections.
1.6566 cannot be through-hardened. With 0.14 to 0.20 % carbon it will not reach high hardness through the full section. Where a part needs uniform strength rather than a hard surface layer, 42CrMo4 (1.7225) and 34CrNiMo6 (1.6582) are the normal alternatives.
1.6566 forged products and sizes
All of the following are produced in 1.6566 to customer drawing, as rough forgings, semi-machined blanks or finish-machined parts.
- Seamless rolled rings and gear ring blanks. Rolled on 3 m and 6 m ring mills. This is our highest-volume 1.6566 product.
- Forged shafts. Gear shafts, pinion shafts, drive shafts, spindles, stepped shafts and eccentric shafts.
- Forged flanges, tube sheets and discs.
- Forged sleeves, bushings and hollow forgings. Bored or trepanned.
- Forged round bars, flat bars and blocks.
- Contoured rolled rings and near-net-shape blanks that reduce machining time on gear rims.
| Parameter | Range |
|---|---|
| Outside diameter | 100 mm to 6,000 mm (4 in to 236 in) |
| Piece weight | 10 kg to 15,000 kg (22 lb to 33,000 lb) |
| Length | up to 12,000 mm (39 ft) |
| Forging hammers | 1 t, 3 t, 6 t and 9 t |
| Hydraulic press | 4,500 t |
| Ring rolling mills | 3 m and 6 m |
| Machining | Rough, semi-finish or finish machined to drawing |
Applications of 1.6566 forgings
1.6566 combines a hard carburised surface with a tough core, so it is used mainly for parts that carry load through rolling or sliding contact, such as gear teeth, splines and bearing races. These are the applications our customers order 1.6566 forgings for.
- Wind turbine gearboxesPlanet gears, sun gears, internal ring gears, planet carriers and gearbox shafts.
- Industrial and marine gearboxesBull gears, pinions, gear blanks and couplings for propulsion and drive trains.
- Mining and cement millsGirth gear segments, drive pinions and ring gears for ball mills and SAG mills.
- Off-highway drivetrainsCrown wheels, differential gears, axle shafts and final drive components.
- Slewing and large bearingsCarburised raceway rings for slewing bearings on cranes and excavators.
- Rolling mill and paper machine drivesGear spindles, drive couplings and pinion stand components.
- Oil and gas surface equipmentMud pump gears, drawworks gearing and rotary table components.
- Heavy machineryWinch drums, hoist gearing and general power transmission parts.
Manufacturing, testing and certification
1.6566 is melted by EAF + LF + VD: electric arc furnace, ladle refining, then vacuum degassing. Vacuum degassing lowers hydrogen content and reduces non-metallic inclusions, both of which affect gear fatigue life. Every 1.6566 order goes through the following before release.
- Chemical analysis by optical emission spectrometer, ladle analysis and product analysis.
- Mechanical testing: tensile, Charpy V-notch impact and hardness, taken from a test block heat treated together with the parts.
- Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, to the class specified on the order.
- Magnetic particle or dye penetrant inspection to EN 10228-1 or ASTM E709 on request.
- Metallography: grain size to ISO 643, inclusion rating to ISO 4967, and case depth measurement to ISO 2639 or DIN 50190 where carburising is in our scope of supply.
- Dimensional inspection against the drawing, with a report issued for machined parts.
- Certification: EN 10204 3.1 as standard, EN 10204 3.2 witnessed by TUV, BV, SGS or Lloyd's Register on request.
The plant employs 460 people, including 9 senior engineers and 32 intermediate engineers, and works to an ISO 9001 quality system.
How to order 1.6566 forgings
Send the following to sales@steelforgepieces.com. Quotations are normally returned within 24 hours.
- Grade: write 1.6566 or 17NiCrMo6-4. Both are understood.
- Drawing, or rough dimensions. For rings give OD, ID and height. For shafts and bars give diameter and length.
- Quantity, and whether this is a one-off, a prototype or an annual requirement.
- Delivery condition: as forged, normalised, soft annealed, or heat treated and machined.
- Certificate level: EN 10204 3.1 or 3.2.
- NDT requirement, for example EN 10228-3 Class 3.
- Destination port and Incoterm.
If you are not certain that 1.6566 is the correct grade, send the drawing together with the working conditions of the part. Our engineers will confirm the grade or propose an alternative.
1.6566 frequently asked questions
What is 1.6566 steel?
1.6566 is the European material number for 17NiCrMo6-4, a nickel-chromium-molybdenum case-hardening steel specified in EN 10084. It contains 0.14 to 0.20 % carbon, 1.20 to 1.50 % nickel, 0.80 to 1.10 % chromium and 0.15 to 0.25 % molybdenum. It is supplied soft annealed or normalised, machined to shape, then carburised and hardened so that the surface reaches about 58 to 62 HRC while the core stays tough.
Which standard covers 1.6566?
EN 10084, the European standard for case-hardening steels, and ISO 683-11 under the same name 17NiCrMo6-4. It is not covered by EN 10083, which applies to quenched and tempered steels such as 42CrMo4. This is a common error on supplier datasheets.
What is the AISI or SAE equivalent of 1.6566?
The closest American grades are SAE 4320 and SAE 4317. Neither is an exact match, because both contain more nickel (1.65 to 2.00 %) and less chromium (0.40 to 0.60 %) than 17NiCrMo6-4. Other close grades are 18NCD6 (AFNOR), 820M17 (BS 970), 18NiCrMo5 (UNI), SNCM420 (JIS) and 20CrNi2Mo (GB). Confirm the actual analysis on the mill certificate before substituting.
Is 1.6566 the same as 1.6587 or 18CrNiMo7-6?
No. Both are EN 10084 case-hardening steels, but 1.6587 contains more chromium (1.50 to 1.80 %) and more nickel (1.40 to 1.70 %), so it hardens deeper. 1.6587 is normally used for larger sections and heavier gear teeth, while 1.6566 is used for small and medium sections at lower cost.
What hardness does 1.6566 reach after carburising?
After carburising at 900 to 940 °C, oil quenching and tempering at 150 to 200 °C, the case normally reaches 58 to 62 HRC. Case depth is controlled by carburising time and is usually specified by the customer between 0.6 mm and 2.5 mm.
Can 1.6566 be through-hardened?
No. With only 0.14 to 0.20 % carbon there is not enough carbon to reach high hardness through the full section. For a through-hardened forging, use 42CrMo4 (1.7225) or 34CrNiMo6 (1.6582).
What is the largest 1.6566 forging you can supply?
We forge 1.6566 from 100 mm to 6,000 mm in diameter, from 10 kg to 15,000 kg in weight and up to 12,000 mm in length, using 1, 3, 6 and 9 tonne forging hammers, a 4,500 tonne hydraulic press and 3 m and 6 m seamless ring rolling mills.
Is 1.6566 weldable?
Weldability is limited. Welding should be carried out before carburising, with preheat of about 200 to 250 °C, low-hydrogen consumables and post-weld stress relief. Carburised surfaces should not be welded.
What certificate is supplied with 1.6566 forgings?
An EN 10204 3.1 mill certificate as standard, covering heat number, chemical analysis, heat treatment condition, mechanical test results and NDT results. EN 10204 3.2 witnessed by a third party such as TUV, BV, SGS or Lloyd's Register is available on request.
What information do you need in order to quote?
Grade, drawing or rough dimensions, quantity, delivery condition, certificate level, NDT class and destination port. Send these to sales@steelforgepieces.com and you will normally have a price within 24 hours.
Request a price for 1.6566 forgings
Send a drawing, or just the dimensions. We quote rough forgings, semi-machined blanks and finish-machined parts, and we ship worldwide from Shanghai and Zhangjiagang.
Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Phone, WhatsApp and WeChat: +86 189-2135-9659. Email: sales@steelforgepieces.com
Related grades
- 1.6587 (18CrNiMo7-6), higher hardenability case-hardening steel for heavy sections
- 18CrNiMo7-6, 17CrNiMo6, 17NiCrMo6-4
- AISI 4320, AISI 4317, 18NCD6, 820M17
- 42CrMo4 (1.7225) and 34CrNiMo6 (1.6582), through-hardening alternatives
- 1.6565, 1.6580, AISI 4340
Data source and revision
Composition and property limits on this page follow EN 10084 for 17NiCrMo6-4. Processing temperatures, size ranges and equipment data reflect production practice at the Jiangyin Jiangnan open-die forging plant, Jiangyin, Jiangsu, China. Page last revised 6 September 2026. For the mill certificate covering a specific heat, contact sales@steelforgepieces.com or +86 189-2135-9659.