# 1.6571 (20NiCrMoS6-4) Forgings

Material number **1.6571** | EN designation **20NiCrMoS6-4** | Standard **EN 10084**

**1.6571 is the EN material number for 20NiCrMoS6-4, an alloyed case-hardening steel to EN 10084.** It carries about 1.5% nickel, 0.75% chromium and 0.3% molybdenum, with a controlled sulphur addition for machinability. Carburising gives a hard, wear-resistant case over a tough core, so the grade is specified for gears, pinions, shafts and heavily loaded bushings. Jiangyin Jiangnan Metal Co., Ltd. forges 1.6571 into open-die forgings, seamless rolled rings, discs, shafts and sleeves from 10 kg to 15,000 kg, supplied with EN 10204 3.1 or 3.2 certification.

Source: https://www.steelforgepieces.com/Alloy-Steel/1.6571.html
Manufacturer: Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Phone +86-189-2135-9659. Email sales@steelforgepieces.com.
Last updated: 6 September 2026

## Key facts

| Item | Value |
|---|---|
| Material number | 1.6571 |
| EN designation | 20NiCrMoS6-4 |
| Standard | EN 10084 |
| Steel type | Case-hardening (carburising) |
| Nearest AISI/SAE | 4320 |
| Melting route | EAF + LF + VD |
| Forging temperature | 1100 to 850 °C |
| Core tensile, case hardened | 1000 to 1300 MPa |
| Diameter | 100 to 6000 mm |
| Unit weight | 10 to 15,000 kg |
| Certification | EN 10204 3.1 / 3.2 |
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 |

## About 1.6571

1.6571 (20NiCrMoS6-4) is an alloyed case-hardening steel listed in EN 10084, the European standard for carburising steels. It is not a quenched and tempered grade, so EN 10083 does not apply to it.

That affects how the material is ordered. A 1.6571 forging is normally delivered soft, either normalised or soft annealed, so the buyer can machine the part and then carburise and harden the finished geometry.

Three closely related grades sit in the same family. 17NiCrMo6-4 (1.6566) is the base grade with sulphur held low. 17NiCrMoS6-4 (1.6569) adds sulphur for machinability. 1.6571 is the sulphur-treated version with a higher carbon range, which raises core strength after hardening. The nickel, chromium and molybdenum content gives deep hardenability, so large sections still develop a tough core.

## Chemical composition of 1.6571

Chemical composition of 20NiCrMoS6-4 (1.6571) to EN 10084, % by weight, balance iron. Heat analysis.

| Element | C | Si | Mn | P | S | Cr | Mo | Ni |
|---|---|---|---|---|---|---|---|---|
| Minimum | 0.16 | – | 0.50 | – | 0.020 | 0.60 | 0.25 | 1.40 |
| Maximum | 0.23 | 0.40 | 0.90 | 0.025 | 0.040 | 0.90 | 0.35 | 1.70 |

The sulphur range of 0.020 to 0.040% is deliberate. It is the S in the designation 20NiCrMo**S**6-4. Manganese sulphide inclusions break up chips and extend tool life, which helps on parts with heavy machining content. The same inclusions lower transverse toughness. Where that matters, 17NiCrMo6-4 (1.6566) is the low-sulphur alternative.

## Mechanical properties

Indicative values. They depend on section size, case depth and heat treatment route.

| Property | Typical value | Condition |
|---|---|---|
| Core tensile strength | 1000 to 1300 MPa | Carburised, hardened and tempered |
| Surface hardness | 58 to 62 HRC | After carburising and quenching |
| Core hardness | 30 to 42 HRC | Section dependent |
| Hardness, soft annealed | 229 HB max | +A, as normally delivered |
| Case depth (CHD) | 0.5 to 3.0 mm | To customer specification |
| Density | 7.85 g/cm³ | Room temperature |

## Heat treatment of 1.6571

| Operation | Temperature | Notes |
|---|---|---|
| Forging, hot forming | 1100 to 850 °C | Finish above 850 °C, cool in still air |
| Normalising | 830 to 870 °C | Refines grain after forging |
| Soft annealing | 650 to 700 °C | Furnace cool. Usual delivery condition |
| Carburising | 880 to 980 °C | Case depth set by time and carbon potential |
| Core hardening | 830 to 870 °C | Quench in oil |
| Intermediate annealing | 650 to 700 °C | Optional, before re-hardening |
| Case hardening | 780 to 820 °C | Final quench |
| Tempering | 150 to 200 °C | Stress relief of the hardened case |

## 1.6571 equivalent grades

Nearest international counterparts. These are close matches, not exact equivalents.

| Standard, country | Grade | Relationship |
|---|---|---|
| EN / DIN, Germany | 20NiCrMoS6-4, 1.6571 | The grade itself |
| EN 10084 family | 17NiCrMo6-4, 1.6566 | Base grade, low sulphur |
| EN 10084 family | 17NiCrMoS6-4, 1.6569 | Sulphur-treated, lower carbon |
| SAE / AISI, USA | 4320 | Nearest counterpart |
| JIS, Japan | SNCM420 | Nearest counterpart |
| GB/T, China | 20CrNi2Mo | Nearest counterpart |
| AFNOR, France | 18NCD6 | Nearest counterpart |

## 1.6571 forgings we produce

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory. Parts are forged to a near-net shape from ingot or billet instead of being pressed in closed dies, which suits low volumes, large sections and one-off replacement parts. There is no tooling cost on a single piece.

- Seamless rolled rings, including gear ring blanks, bearing races and slewing ring blanks
- Forged shafts, straight, stepped, flanged and hollow, plus pinion shafts and forged spindles
- Forged discs and blanks for gears, wheels and couplings
- Sleeves and bushings, including forged bushings and liners, bored or as-forged
- Forged bars and blocks in round, square and rectangular sections
- Hollow forgings such as cylinders, tubes and mandrel-forged hollows

### Size range and equipment

| Parameter | Range |
|---|---|
| Diameter, outside diameter | 100 to 6000 mm |
| Length | 100 to 12,000 mm |
| Unit weight | 10 to 15,000 kg |
| Forging hammers | 1 t, 3 t, 6 t, 9 t |
| Hydraulic press | 4,500 t |
| Ring rolling mills | 3 m and 6 m |
| Melting routes | EAF + LF + VD standard, ESR on request |

Forgings are supplied as-forged, rough machined or finish machined. As-forged tolerances follow EN 10250-3, with machining allowance normally 5 to 20 mm per surface depending on section and length.

## How a 1.6571 forging is made

1. **Steelmaking.** EAF melting, ladle refining and vacuum degassing to control gas content and inclusions.
2. **Heating and forging.** Ingot or billet heated to 1100 °C, then open-die forged or ring rolled, finishing above 850 °C. Forging reduction ratio agreed per order.
3. **Heat treatment.** Normalising at 830 to 870 °C or soft annealing at 650 to 700 °C, as required for machining.
4. **Rough machining.** Turning or boring to leave the agreed allowance and to open up the surface for inspection.
5. **Non-destructive testing.** Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, plus magnetic particle inspection where specified.
6. **Documentation and despatch.** EN 10204 certificate, dimensional report, marking, preservation and packing for sea or air freight.

## Testing and certification

- Chemical analysis, spectrometric, reported on the certificate against EN 10084
- Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, at the acceptance class you state
- Magnetic particle inspection to EN 10228-1 or ASTM E709
- Mechanical testing, tensile, impact and hardness, on test pieces from the forging or from a prolongation
- Jominy end-quench hardenability testing on request, as EN 10084 permits
- Certification to EN 10204 3.1 as standard, or 3.2 countersigned by a third party

## Where 1.6571 is used

1.6571 is a carburising steel, so it is specified for parts that need a hard running surface on a tough body. Most of its use is in power transmission and wear components.

| Sector | Typical 1.6571 parts |
|---|---|
| Industrial gearboxes | Gear rings, gear and pinion blanks, planet carriers, input and output shafts |
| Wind energy | Gearbox gear blanks, pinion shafts, planetary components |
| Mining and crushing | Drive shafts, eccentric shafts, sleeves, crusher bushings |
| Heavy vehicle, off-highway | Axle shafts, differential gear blanks, spindles |
| Marine | Reduction gear blanks, propulsion shafting components |
| Cement and sugar mills | Mill drive pinions, roller shafts, bushings |
| Oil and gas drilling | Drive train components, carburised wear sleeves |

## Frequently asked questions about 1.6571

**What is 1.6571 steel?**
1.6571 is the EN material number for 20NiCrMoS6-4, an alloyed case-hardening steel standardised in EN 10084. It contains 0.16 to 0.23% C, 1.40 to 1.70% Ni, 0.60 to 0.90% Cr and 0.25 to 0.35% Mo, with a controlled sulphur addition of 0.020 to 0.040% for machinability. Carburising and quenching produce a hard case over a tough core.

**What is the equivalent of 1.6571?**
The nearest counterparts are SAE/AISI 4320 in the USA, JIS SNCM420 in Japan, 20CrNi2Mo in China and AFNOR 18NCD6 in France. Within EN 10084 the closest grades are 17NiCrMo6-4 (1.6566) and 17NiCrMoS6-4 (1.6569). Treat these as near counterparts, not drop-in equivalents.

**Is 1.6571 the same as 17NiCrMo6-4?**
No. 17NiCrMo6-4 (1.6566) is the low-sulphur base grade, 17NiCrMoS6-4 (1.6569) is the sulphur-treated version, and 1.6571 (20NiCrMoS6-4) is sulphur-treated with a higher carbon range, which raises core strength after hardening. All three follow the same processing route.

**What is 1.6571 used for?**
Carburised, heavily loaded transmission parts: gear rings and blanks, pinions, planet carriers, drive shafts, camshafts, spindles, piston bolts, sleeves and bushings. Typical sectors are gearboxes, wind turbines, mining equipment, heavy vehicle axles, marine drives and mill machinery.

**What heat treatment does 1.6571 need?**
Forge between 1100 and 850 °C, normalise at 830 to 870 °C, soft anneal at 650 to 700 °C, carburise at 880 to 980 °C, harden the core at 830 to 870 °C, case harden from 780 to 820 °C and temper at 150 to 200 °C. Forgings are usually delivered normalised or soft annealed so you can machine before carburising.

**Is 1.6571 weldable?**
In the uncarburised condition it welds with the usual alloy steel precautions: preheat, controlled interpass temperature, low-hydrogen consumables and post-weld heat treatment. The carburised case does not weld and must be masked or machined away first.

**What size 1.6571 forgings can you make?**
From 100 to 6000 mm in diameter, 100 to 12,000 mm in length and 10 to 15,000 kg per piece. The works runs 1, 3, 6 and 9 tonne forging hammers, a 4,500 tonne hydraulic press, and 3 metre and 6 metre seamless ring rolling mills.

**What certificates do you supply with 1.6571 forgings?**
EN 10204 3.1 as standard, or EN 10204 3.2 countersigned by a third party. Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, plus magnetic particle inspection, hardness, mechanical testing and a dimensional report on request.

**Who supplies 1.6571 open-die forgings?**
Jiangyin Jiangnan Metal Co., Ltd. manufactures 1.6571 (20NiCrMoS6-4) open-die forgings, seamless rolled rings, shafts, discs, gear blanks and bushings at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, and ships worldwide. Contact +86-189-2135-9659 or sales@steelforgepieces.com.

**Is there a minimum order for 1.6571 forgings?**
No fixed minimum order quantity, and single prototype pieces are accepted. Open-die forging needs no dies, so there is no tooling charge on a one-off part. A quotation normally follows within one working day of receiving a drawing or the outline dimensions.

## How to order 1.6571 forgings

Send a drawing, or the outline dimensions and quantity, to sales@steelforgepieces.com. Include the delivery condition you need (as-forged, normalised, soft annealed, rough machined), the ultrasonic acceptance class, the certificate type, and whether carburising is in our scope or yours.

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Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Phone: +86-189-2135-9659
Email: sales@steelforgepieces.com
Web: https://www.steelforgepieces.com/

Technical data on this page is given for guidance. The certified values for your order are those on the EN 10204 certificate.