Alloy Steel Forgings · Technical Datasheet

18NiCrMo6-4 Forgings

Werkstoff 1.6566 · 17NiCrMo6-4 · 18NiCrMo5 · 18NCD6 · 817M17 · SAE 4317. Case hardening steel gear blanks, rolled rings, shafts, discs and bars

18NiCrMo6-4 is a nickel-chromium-molybdenum case hardening steel, material number 1.6566, listed in EN 10084 under its current designation 17NiCrMo6-4. It is carburised and quenched to give a wear-resistant surface of 58 to 62 HRC over a tough core, which is why it is specified for gears, pinions, shafts and bearing components rather than for pressure-retaining parts. Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, forges 18NiCrMo6-4 into gear blanks, seamless rolled rings, pinion shafts, discs, flanges, sleeves and round bars to customer drawing, supplied with EN 10204 3.1 or 3.2 mill test certificates.

W.Nr.1.6566
StandardEN 10084
Surface58–62 HRC
Core Rm900–1200 MPa
Carburise880–980 °C
Forge1100–850 °C

Send drawing for a quote Call 0086-189-2135-9659

Case hardening depth on 18NiCrMo6-4 is measured to EN ISO 2639 at the 550 HV1 limiting hardness. The carbon-enriched case carries contact and bending fatigue load; the low-carbon core keeps the part from failing in a brittle way under shock.

0.14–0.20 %Carbon
1.20–1.50 %Nickel
≥1200 MPaRm, d ≤ 16 mm
149–201 HB+FP for gear cutting
15 000 kgMax single piece

What is 18NiCrMo6-4?

18NiCrMo6-4 is a low-carbon alloy case hardening steel containing nickel, chromium and molybdenum, catalogued under material number 1.6566 and listed in the current EN 10084 standard as 17NiCrMo6-4.

The grade carries only 0.14 to 0.20 percent carbon, so in the as-supplied condition it is soft, tough and easy to cut. Its working properties are created afterwards, in the furnace. The part is carburised at 880 to 980 °C so that carbon diffuses into the outer skin, then quenched. The carbon-enriched surface transforms to hard martensite while the low-carbon core does not, and the result is a component with a wear-resistant case on a shock-tolerant core.

Nickel at 1.20 to 1.50 percent is the element that distinguishes this grade from cheaper carburising steels such as 16MnCr5. Nickel raises core toughness and lowers the ductile-to-brittle transition temperature, which matters for gearing that starts under load in cold weather. Chromium at 0.80 to 1.10 percent increases hardenability and forms the fine carbides that give the case its wear resistance. Molybdenum at 0.15 to 0.25 percent suppresses temper embrittlement and helps the core harden through in heavier sections.

Because the carbon content is low and the grade is not supplied in a quenched and tempered condition, 18NiCrMo6-4 is not a pressure-vessel or valve-body material. Buyers who need a through-hardening alloy steel for those duties should look at 42CrMo4, 34CrNiMo6 or AISI 4140 instead.

We supply 18NiCrMo6-4 as forged product only: open-die forgings and seamless rolled rings. Forging closes porosity from the ingot, refines grain, and aligns grain flow with the direction of principal stress, which raises bending fatigue strength at the tooth root of a gear compared with a part cut from plate or bar stock.

18NiCrMo6-4 designations and equivalent grades

18NiCrMo6-4 is the former designation of the steel now written 17NiCrMo6-4; both refer to material number 1.6566. Buyers reach this one chemistry through at least six national names.

Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under any of the designations below and issues a material test certificate listing every specification the heat satisfies. Equivalence between national standards is close but never exact, so state on the order which specification governs acceptance.

Table 1. 18NiCrMo6-4 cross-reference to national standards
Standard or country	Designation	Note
EN 10084 (current)	17NiCrMo6-4	Current European designation for this chemistry
EN / DIN (former)	18NiCrMo6-4	Earlier name, still used on drawings and in tender documents
Werkstoffnummer	1.6566	German material number
Italy, UNI 7846	18NiCrMo5	Superseded by 17NiCrMo6-4
France, AFNOR	18NCD6	Near equivalent
United Kingdom, BS 970	817M17	Near equivalent; see also 820M17 and 822M17
United States, SAE / AISI	4317	Near equivalent, Ni-Cr-Mo carburising grade

Source: Jiangyin Jiangnan Metal Co., Ltd., compiled from EN 10084 and published producer datasheets.

Free-cutting variants of the same base chemistry

Where machining volume rather than fatigue life sets the cost, the sulphur-bearing versions of this grade cut faster at some loss of transverse ductility:

17NiCrMoS6-4, material number 1.6569. Controlled sulphur addition for improved machinability.
20NiCrMoS6-4, material number 1.6571. Higher carbon plus controlled sulphur, for higher core strength.

A note on the naming. Producer datasheets, including Saarstahl's, publish this steel as “17NiCrMo6-4 (18NiCrMo6-4)”, with the older number shown in brackets. If your drawing says 18NiCrMo6-4 and a mill offers 17NiCrMo6-4, or the reverse, they are quoting the same material. Ask for both designations to be printed on the certificate so that incoming inspection does not reject the delivery.

Why 18NiCrMo6-4 is specified

Hard case, tough core in one part. Carburising and quenching produce 58 to 62 HRC at the surface for contact and wear resistance while the core stays at 30 to 42 HRC and absorbs shock. No through-hardened steel gives both.
Nickel keeps the core tough when cold. The 1.20 to 1.50 percent nickel content lowers the transition temperature, so gearing that starts under load at low ambient temperature is less likely to fail by brittle fracture. This is the main reason the grade is chosen over 16MnCr5 or 20MnCr5.
Medium-high hardenability. Chromium and molybdenum let the core harden through in sections that would stay soft in a plain carburising steel, so it covers ruling sections up to roughly 100 mm without moving to a more expensive grade.
Good machinability before hardening. Supplied at 149 to 201 HB in the +FP condition, teeth can be hobbed or shaped at commercial feed rates, and the geometry only has to survive the distortion of the hardening cycle.
Compressive residual stress at the surface. The volume expansion of the martensitic case leaves the tooth flank in compression, which raises bending fatigue strength at the root and resists pitting.
Cheaper than the heavy-section grade. Where the section allows it, 18NiCrMo6-4 does the job of 18CrNiMo7-6 at a lower alloy cost.

The grade has real limits. It has no corrosion resistance, so parts in wet or chemical service need coating or a different material. It should not be used above about 200 °C in service, because the tempering temperature of the case is itself 150 to 200 °C and the case will soften. And it is not a candidate for pressure-retaining or welded structural parts.

18NiCrMo6-4 vs 18CrNiMo7-6 vs 20NiCrMo2-2

These three EN 10084 carburising steels sit at three price and hardenability levels. Choose by ruling section and core strength requirement, not by surface hardness, because all three reach a similar case hardness.

Table 2. The three common Ni-Cr-Mo carburising grades compared
Attribute	18NiCrMo6-4	18CrNiMo7-6	20NiCrMo2-2
Material number	1.6566	1.6587	1.6523
Also known as	17NiCrMo6-4, 18NiCrMo5, SAE 4317	17CrNiMo6	SAE 8620
Carbon	0.14–0.20 %	0.15–0.21 %	0.17–0.23 %
Chromium	0.80–1.10 %	1.50–1.80 %	0.35–0.65 %
Nickel	1.20–1.50 %	1.40–1.70 %	0.40–0.70 %
Molybdenum	0.15–0.25 %	0.25–0.35 %	0.15–0.25 %
Hardenability	Medium-high	High	Low to medium
Practical ruling section	Up to about 100 mm	Heavy sections, 100 mm and above	Up to about 40 mm
Core Rm, quenched, tempered 200 °C	900–1200 N/mm²	1000–1200 N/mm²	700–1000 N/mm²
Relative alloy cost	Medium	High	Low
Typical use	Industrial and vehicle gearing, pinion shafts, bushings	Wind turbine gear rings, large planetary gears, mining drives	Small gears, bushings, high-volume automotive parts

Source: Jiangyin Jiangnan Metal Co., Ltd., compiled from EN 10084 composition limits. See also our pages on 18CrNiMo7-6, 1.6587 and 1.6523.

How to choose in practice. Work out the ruling section of the finished part, which for a gear is roughly the rim thickness below the root. Below about 40 mm, 20NiCrMo2-2 will usually meet the core requirement and costs least. Between 40 and 100 mm, 18NiCrMo6-4 is normally the right answer. Above 100 mm, or where the core has to reach 1000 N/mm² through a heavy rim, move to 18CrNiMo7-6.

Chemical composition of 18NiCrMo6-4

The table below is the specification range we forge to. Every heat is supplied with a ladle analysis on the mill certificate; product analysis can be added on request. Iron makes up the balance.

Table 3. 18NiCrMo6-4 / 1.6566 chemical composition, percent by mass
Element	Symbol	Specified range	Permissible deviation on product analysis	Function in the steel
Carbon	C	0.14–0.20	± 0.02	Sets core strength; kept low so the core stays tough
Silicon	Si	0.40 max	+ 0.03	Deoxidation; held low to avoid retarding carbon diffusion
Manganese	Mn	0.60–0.90	± 0.04	Hardenability; ties up residual sulphur
Phosphorus	P	0.035 max	+ 0.005	Impurity limit; segregates to grain boundaries
Sulphur	S	0.035 max	+ 0.005	Impurity limit; controlled additions in the S variants
Chromium	Cr	0.80–1.10	± 0.05	Hardenability and case wear resistance through fine carbides
Molybdenum	Mo	0.15–0.25	± 0.03	Core hardenability; suppresses temper embrittlement
Nickel	Ni	1.20–1.50	± 0.05	Core toughness and low-temperature impact resistance
Iron	Fe	Balance	—	Matrix

Source: Jiangyin Jiangnan Metal Co., Ltd., 18NiCrMo6-4 forging specification, in agreement with the published analysis for 17NiCrMo6-4 / 1.6566 in EN 10084.

Melting route is EAF plus ladle furnace plus vacuum degassing (EAF + LF + VD). Vacuum degassing matters on this grade because hydrogen left in a heavy forged section causes flaking, and because low oxygen content reduces the oxide inclusions that start pitting on a loaded tooth flank. Where a customer specification calls for it, we source electroslag remelted (ESR) stock for critical rotating parts.

Mechanical properties of 18NiCrMo6-4

After hardening and tempering at 200 °C, 18NiCrMo6-4 reaches a minimum tensile strength of 1200 N/mm² in sections up to 16 mm, 1000 N/mm² from 16 to 40 mm, and 900 N/mm² from 40 to 100 mm.

Core strength falls as section size rises, because the cooling rate at the centre of a heavy section during quench is lower and less of the core transforms to martensite. This is why ruling section, not surface hardness, drives grade selection.

Table 4. Core tensile strength after hardening and tempering at 200 °C
Diameter d	Tensile strength R_m, metric	Tensile strength R_m, imperial
d ≤ 16 mm	min. 1200 N/mm²	min. 174 ksi
16 < d ≤ 40 mm	min. 1000 N/mm²	min. 145 ksi
40 < d ≤ 100 mm	min. 900 N/mm²	min. 131 ksi

Source: published property table for 17NiCrMo6-4 / 1.6566, reproduced by Jiangyin Jiangnan Metal Co., Ltd. Sections above 100 mm are agreed case by case against the drawing.

Delivery hardness before machining

State the treatment condition on the order. It decides how the material cuts and how much distortion the hardening cycle will produce. For gear cutting, ask for +FP.

Table 5. 18NiCrMo6-4 hardness by delivery condition
Condition	Symbol	Brinell hardness	When to specify it
Treated for cold shearability	+S	max. 255 HB	Bar to be cropped or cold sheared into blanks
Soft annealed	+A	max. 229 HB	Heavy stock removal, deep drilling, boring
Treated for strength	+TH	179–229 HB	General machining where some strength is wanted in the blank
Ferrite and pearlite structure, defined hardness	+FP	149–201 HB	Gear hobbing, shaping and broaching; the usual gear-blank condition

Source: published delivery conditions for 17NiCrMo6-4 / 1.6566, reproduced by Jiangyin Jiangnan Metal Co., Ltd.

Typical properties after carburising and hardening

The figures below are what we record on prolongation test pieces from our own 18NiCrMo6-4 heats. They are typical results, not standard minima, and they vary with case depth, section size and quench severity. Acceptance values are agreed against your drawing before production starts.

Table 6. Typical case-hardened properties recorded by Jiangyin Jiangnan Metal
Property	Typical value	Test method
Surface hardness, case	58–62 HRC (660–750 HV)	ISO 6508 / ASTM E18
Core hardness	30–42 HRC (300–400 HV)	ISO 6508 / ASTM E18
Core 0.2 % proof strength	700–950 N/mm²	ISO 6892-1 / ASTM E8
Core elongation A₅	9–13 %	ISO 6892-1 / ASTM E8
Core impact energy KV, room temperature	35–60 J	ISO 148-1 / ASTM E23
Retained austenite in case	≤ 25 % typical, lower on request	X-ray diffraction
Grain size	ASTM 5 or finer	ASTM E112

Source: Jiangyin Jiangnan Metal Co., Ltd. internal test records for 18NiCrMo6-4 forgings. Values are indicative and are confirmed per order.

Physical and thermal properties

18NiCrMo6-4 is a low-alloy steel, so its physical constants sit close to those of plain steel. They are given here because they are needed for heat-transfer and shrink-fit calculations on gear rims and bushings.

Table 7. Typical physical and thermal data for 18NiCrMo6-4
Property	Metric	Imperial
Density	7.85 g/cm³	0.284 lb/in³
Modulus of elasticity, 20 °C	210 GPa	30 500 ksi
Poisson's ratio	0.29	0.29
Thermal conductivity, 20 °C	44 W/m·K	305 BTU·in/hr·ft²·°F
Specific heat capacity, 20 °C	460 J/kg·K	0.110 BTU/lb·°F
Thermal expansion, 20–200 °C	11.5 µm/m·K	6.4 µin/in·°F
Thermal expansion, 20–400 °C	12.5 µm/m·K	6.9 µin/in·°F
Electrical resistivity, 20 °C	0.20 µΩ·m	—
Melting range	1420–1480 °C	2590–2700 °F
Magnetic response	Ferromagnetic in all conditions

Source: Jiangyin Jiangnan Metal Co., Ltd., consolidated typical values for low-alloy case hardening steel. Use them for design estimation, not as certified acceptance values.

Heat treatment of 18NiCrMo6-4

The published cycles for 18NiCrMo6-4 are: forge or hot roll between 1100 and 850 °C, normalise at 830 to 870 °C, soft anneal at 650 to 700 °C, carburise at 880 to 980 °C, core harden at 830 to 870 °C, quench for case hardening from 780 to 820 °C, and temper at 150 to 200 °C.

Every furnace cycle we run on 18NiCrMo6-4 is recorded on a calibrated chart and the chart is issued with the mill certificate.

Table 8. 18NiCrMo6-4 heat-treatment cycles
Operation	Temperature	Cooling	Purpose
Forging or hot rolling	1100–850 °C	Slow cool in furnace or sand	Shape the part; close porosity; direct grain flow
Normalising	830–870 °C	Air	Refine grain after forging; even out structure before machining
Soft annealing	650–700 °C	Slow, in furnace	Drop hardness to max. 229 HB for heavy stock removal
Carburising	880–980 °C	Per route below	Diffuse carbon into the surface to form the case
Intermediate annealing	650–700 °C	Slow	Soften carburised parts for intermediate machining
Core hardening	830–870 °C	Oil quench	Harden the core when core strength governs
Case hardening quench	780–820 °C	Oil quench	Transform the carbon-rich case to martensite
Tempering	150–200 °C	Air	Relieve quench stress without softening the case

Source: published heat-treatment data for 17NiCrMo6-4 / 1.6566, reproduced by Jiangyin Jiangnan Metal Co., Ltd.

Which hardening route to specify

Direct quench. Quench straight from the carburising temperature. Shortest cycle and lowest cost, but coarser grain and more retained austenite. Suitable for bushings, sleeves and low-duty gearing.
Single quench from 780 to 820 °C. Cool from carburising, reheat into the case-hardening range and quench. Refines the case, gives the best combination of case hardness and dimensional stability. This is our default for gears.
Double quench. Core harden at 830 to 870 °C first, then case harden at 780 to 820 °C. Used where both a fine case and a fully hardened core are required. Longest cycle and the most distortion, so allow more grinding stock.
Sub-zero treatment. Optional soak at about −70 °C after quench to convert retained austenite before tempering, where dimensional stability over service life is critical.

Leave grinding stock. Every carburising route moves the part. Tell us the finished tolerance and we will agree a machining allowance, typically 0.3 to 0.8 mm per flank on gear teeth depending on size and case depth, so that the ground surface stays inside the effective case.

Case depth and surface hardness

Case hardening depth on 18NiCrMo6-4 is normally specified between 0.4 and 2.5 mm, measured to EN ISO 2639 at the 550 HV1 limiting hardness.

Case depth is set by carburising time and temperature, not by the steel. Time rises with roughly the square of required depth: doubling the case depth takes about four times as long in the furnace, which is why over-specifying case depth is expensive. Specify the depth the contact stress needs and no more.

Table 9. Case-depth ranges we run on 18NiCrMo6-4
CHD at 550 HV1	Typical parts	Notes
0.4–0.8 mm	Small pinions, bushings, sleeves, splined ends	Short cycle; least distortion
0.8–1.5 mm	General industrial gearing, module 4 to 10, pinion shafts	The most commonly ordered range
1.5–2.5 mm	Large module gear rings, heavy planetary gears, drive pinions	Long cycle; agree grinding stock in advance
Above 2.5 mm	Special cases	Quoted individually; consider 18CrNiMo7-6 instead

Source: Jiangyin Jiangnan Metal Co., Ltd. A common rule of thumb for gearing is a case depth of roughly 0.15 to 0.25 times the normal module; confirm against your own gear rating calculation.

State three things on the drawing and the heat treatment can be planned without further correspondence: the case hardening depth and the limiting hardness it is measured to, the required surface hardness in HRC or HV, and the core hardness or core tensile strength. If the limiting hardness is not stated we assume 550 HV1 in line with EN ISO 2639.

How Jiangyin Jiangnan Metal forges 18NiCrMo6-4

The route below is what we run for every 18NiCrMo6-4 order. Each stage produces a record that goes into the documentation pack.

Melting and ingot supply

Electric arc furnace, ladle furnace and vacuum degassing (EAF + LF + VD). Vacuum degassing removes the hydrogen that causes flaking in heavy sections and lowers oxide inclusion count, which matters for tooth-flank fatigue life. ESR stock is sourced where the specification demands it.
Billet preparation and soaking

Surfaces are conditioned and the billet is soaked to a uniform through-temperature before the first blow. An under-soaked billet cracks at the centre where the section is still cold.
Open-die forging, 1100 to 850 °C

Forged on 1, 3, 5 and 9 tonne hammers and a 5000 tonne hydraulic press, with controlled reduction ratio and reheats. Forging is finished above 850 °C; below that the steel work-hardens and surface tearing starts.
Ring rolling or upsetting to shape

Gear ring blanks are pierced and rolled to the finished envelope so grain flow follows the hoop direction. Discs are upset and punched. Both give continuous grain flow around the eventual tooth root, which is where bending fatigue cracks start.
Controlled cooling and normalising

Slow cooling in furnace or sand straight after forging, then normalising at 830 to 870 °C to refine grain, followed by the delivery-condition treatment: +A, +TH or +FP.
Rough or finish machining

Supplied as-forged, rough machined with an agreed allowance, or finish machined to drawing tolerance. Gear blanks are normally supplied rough turned and bored, ready for tooth cutting.
Carburising, hardening and tempering

Carried out in calibrated furnaces to the agreed route, with recorded time and temperature charts for the whole load, and case depth verified on a coupon carburised alongside the parts.
Non-destructive and mechanical testing

Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. Magnetic particle or penetrant inspection as specified. Tensile, impact, hardness, case depth and grain size from prolongations.
Marking, certification and packing

Hard-stamped heat number and part identification, EN 10204 3.1 certificate, or 3.2 counter-signed by a third party such as TUV, BV, SGS or Lloyd's Register, then seaworthy packing.

18NiCrMo6-4 forged forms and size capability

All parts are made to your drawing or dimensional sketch. There is no fixed catalogue. The range below covers what we forge regularly in 18NiCrMo6-4.

Table 10. 18NiCrMo6-4 product forms and size range
Forged form	Size range	Common uses
Seamless rolled rings and gear ring blanks	OD 200–5000 mm, height up to 1000 mm	Gear rings, slewing ring blanks, spacer rings
Forged discs and gear blanks	Dia. 150–3000 mm	Gear blanks, sprocket blanks, coupling discs
Forged shafts, pinion shafts, spindles	Dia. 80–1200 mm, length up to 8000 mm	Pinion shafts, drive spindles, splined shafts
Round bars	Dia. 20–800 mm	Machining stock, pinion stock, small gear blanks
Forged rings and flanges	DN 15–1500	Bearing carriers, housings, mounting flanges
Sleeves, bushings, hollow bars	OD 100–1200 mm	Wear sleeves, bearing bushes, liners
Forged blocks and rectangles	Up to 800 × 1500 mm section	Rack stock, housings, machine components
Eccentric shafts and crankshafts	To drawing	Press drives, crushers, heavy machinery
Overall plant envelope	Dia. 80–6000 mm; single-piece weight 10–15 000 kg	Heavier pieces quoted case by case

Source: Jiangyin Jiangnan Metal Co., Ltd. Delivery conditions: as-forged, normalised, annealed to +A, treated to +FP, rough machined or finish machined. Carburising and hardening are available in house or the part is supplied ready to harden.

Where 18NiCrMo6-4 forgings are used

18NiCrMo6-4 is used for parts that must resist surface wear and contact fatigue while surviving shock loads through the section: gears, gear rings, pinions, pinion shafts, camshafts, spindles, bushings and bearing races.

Industrial gearboxes and drives

The main application. Carburised teeth carry high contact stress while the nickel-bearing core absorbs start-up and reversal shock.

Gear rings · pinions · pinion shafts · gear blanks · sprockets · couplings

Automotive and commercial vehicle drivelines

Transmission and axle components where a hard flank and a tough core have to coexist in a small, light part.

Transmission gears · differential gears · camshafts · splined shafts · piston bolts

Earthmoving, mining and agriculture

Drive trains that run in dust and grit with impact loading, where abrasion resistance decides overhaul interval.

Final drive gears · track drive components · crusher shafts · PTO shafts

Marine and heavy machinery

Reduction gearing, winch and deck machinery drives, and press and mill drive trains in continuous duty.

Reduction gears · drive pinions · eccentric shafts · forged rolls

Bearings and wear components

Races, sleeves and liners where a deep, hard case gives rolling-contact fatigue life and the core stops the part shattering.

Bearing races · bushings · wear sleeves · cam followers · rollers

Machine tool and power transmission

Precision spindles, worm and rack components, and slewing ring blanks that need dimensional stability after hardening.

Spindles · worm shafts · racks · slewing ring blanks · keyed shafts

What this grade is not for. 18NiCrMo6-4 is a carburising steel with 0.14 to 0.20 percent carbon. It is not used for pressure vessels, valve bodies, tube sheets or flanges in pressure service, and it has no corrosion resistance. For those duties see 42CrMo4, 34CrNiMo6, AISI 8630 or our stainless steel and nickel alloy ranges.

Machining, grinding and welding 18NiCrMo6-4

Machining before hardening

All cutting is done before carburising. In the +FP condition at 149 to 201 HB the steel hobs and shapes at rates close to a plain carbon steel. In the +A condition at up to 229 HB it takes heavy roughing cuts without tool breakdown. Where machining volume dominates cost, consider the free-cutting variant 17NiCrMoS6-4 (1.6569), accepting some loss of transverse ductility.

Grinding after hardening

Only grinding is practical once the case is at 58 to 62 HRC. Keep wheel speed and infeed low enough to avoid grinding burn: a re-tempered or re-hardened layer at the tooth flank ruins the compressive residual stress that the carburising cycle was carried out to create. Nital etch inspection to ISO 14104 is available on request to verify that no grinding burn is present.

Welding

18NiCrMo6-4 can be welded in the annealed or normalised condition with low-hydrogen consumables, preheat of roughly 200 to 250 °C and post-weld stress relief. It is not welded after carburising and hardening, because the hard martensitic case cracks. Where a weld is unavoidable on a part that will be carburised, mask the area with copper plating or stop-off paint and complete the weld before the hardening cycle.

Distortion control

Normalise after forging and before rough machining, so that forging stresses are released before the part takes its shape.
Rough machine, stress relieve, then finish machine on parts with thin rims or large diameter-to-thickness ratios.
Support large rings on fixtures during quench, or use press quenching where roundness and flatness are tight.
Agree grinding stock in advance: normally 0.3 to 0.8 mm per flank depending on size and case depth.

Testing, inspection and certification

Every 18NiCrMo6-4 forging ships with a documentation pack. Its content is agreed before production starts.

Chemical analysis: ladle analysis on every heat, product analysis on request.
Mechanical testing: tensile, yield, elongation, reduction of area, impact energy and hardness, taken from integral or separately forged prolongations.
Case verification: case hardening depth to EN ISO 2639 at 550 HV1, surface hardness in HRC or HV, core hardness, and a microhardness traverse where the drawing calls for one.
Ultrasonic testing: EN 10228-3, SEP 1921 class C, D or E, ASTM A388, or a customer acceptance class.
Surface NDT: magnetic particle to ASTM E1444 or liquid penetrant to ASTM E165.
Microstructure: grain size to ASTM E112, case microstructure, retained austenite and, on request, nital etch grinding-burn inspection to ISO 14104.
Dimensional report against the drawing.
Certification: EN 10204 3.1 as standard, or 3.2 witnessed and counter-signed by TUV, BV, SGS, Lloyd's Register or your own inspector.

In-house equipment includes a universal testing machine, impact testing machine, hardness testers, magnetic particle flaw detection and a metallographic microscope. Third-party inspectors and customer QA representatives are welcome at the works. Material is shipped under whichever designation your specification uses, with every equivalent listed on the certificate.

How to request an 18NiCrMo6-4 quotation

Send a drawing or a dimensional sketch to sales@steelforgepieces.com. Quotations are normally returned within one working day when the following are supplied.

Grade and standard. 18NiCrMo6-4, 17NiCrMo6-4, 1.6566, 18NiCrMo5, 18NCD6, 817M17 or SAE 4317, and which specification governs acceptance.
Product form. Rolled ring, gear blank, disc, shaft, bar, flange, sleeve or custom shape.
Dimensions. OD, ID and height for rings; diameter and length for bars and shafts; plus an estimated finished weight.
Delivery condition. As-forged, normalised, +A, +TH, +FP, rough machined or finish machined.
Case-hardening requirement. Case depth and the limiting hardness it is measured to, surface hardness, and core hardness or core tensile strength. Say whether we carburise or you do.
Certification and NDT. EN 10204 3.1 or 3.2, which third party if 3.2, ultrasonic acceptance class, and any MT or PT requirement.
Quantity and required date.

Lead time for 18NiCrMo6-4 forgings is normally 30 to 60 days depending on size, heat-treatment route and machining scope.

Email your drawing to sales@steelforgepieces.com 0086-189-2135-9659

Frequently asked questions about 18NiCrMo6-4

What is 18NiCrMo6-4 steel?

18NiCrMo6-4 is a nickel-chromium-molybdenum case hardening steel, also called a carburising steel, catalogued as Werkstoff number 1.6566. It contains 0.14 to 0.20 percent carbon, 0.80 to 1.10 percent chromium, 1.20 to 1.50 percent nickel and 0.15 to 0.25 percent molybdenum. It is carburised and hardened to give a wear-resistant surface of 58 to 62 HRC over a tough, impact-resistant core, which is why it is used for gears, pinions, shafts and bearing components.

Is 18NiCrMo6-4 the same as 17NiCrMo6-4?

Yes. 18NiCrMo6-4 is the former designation for the steel now listed in EN 10084 as 17NiCrMo6-4, and both names refer to material number 1.6566. Steel producers such as Saarstahl publish the grade as 17NiCrMo6-4 with 18NiCrMo6-4 shown in brackets as the earlier name. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under either designation and issues a material test certificate that lists both.

What is the material number for 18NiCrMo6-4?

The material number, or Werkstoffnummer, for 18NiCrMo6-4 is 1.6566. The related free-cutting variants are 17NiCrMoS6-4 with material number 1.6569 and 20NiCrMoS6-4 with material number 1.6571.

What is the chemical composition of 18NiCrMo6-4?

18NiCrMo6-4 contains carbon 0.14 to 0.20 percent, silicon 0.40 percent maximum, manganese 0.60 to 0.90 percent, phosphorus 0.035 percent maximum, sulphur 0.035 percent maximum, chromium 0.80 to 1.10 percent, molybdenum 0.15 to 0.25 percent and nickel 1.20 to 1.50 percent, with iron as the balance.

Which standard covers 18NiCrMo6-4?

18NiCrMo6-4, as 17NiCrMo6-4 and material number 1.6566, is covered by EN 10084, the European standard for case hardening steels. Open-die forgings and rolled rings in this grade are supplied to EN 10250-3, the standard for open die steel forgings in alloy special steels. Case depth is verified to EN ISO 2639 and certification follows EN 10204.

What are the equivalent grades to 18NiCrMo6-4?

The nearest equivalents to 18NiCrMo6-4 are 17NiCrMo6-4 and material number 1.6566 in EN 10084, 18NiCrMo5 in the Italian UNI 7846 standard, 18NCD6 in the French AFNOR standard, 817M17 in British Standard BS 970, and SAE or AISI 4317 in the United States. Equivalence is close but not exact, so the governing specification should always be stated on the order.

What surface hardness can 18NiCrMo6-4 reach?

After carburising, hardening and low-temperature tempering, 18NiCrMo6-4 typically reaches a surface hardness of 58 to 62 HRC, equivalent to roughly 660 to 750 HV. The core, which is not carburised, stays at about 30 to 42 HRC so that the part keeps its toughness and resistance to shock loading.

What case depth is achievable on 18NiCrMo6-4 forgings?

Case hardening depth on 18NiCrMo6-4 is normally specified between 0.4 and 2.5 mm, measured to EN ISO 2639 at the 550 HV1 limiting hardness. Depths near 0.4 to 0.8 mm suit small pinions and bushings, 0.8 to 1.5 mm suits general industrial gearing, and 1.5 to 2.5 mm is used on large module gear rings. Deeper cases are possible but carburising time rises roughly with the square of the required depth.

What is the correct heat treatment for 18NiCrMo6-4?

The published cycles for 18NiCrMo6-4 are: forging or hot rolling between 1100 and 850 degrees Celsius; normalising at 830 to 870 degrees Celsius; soft annealing at 650 to 700 degrees Celsius; carburising at 880 to 980 degrees Celsius; core hardening at 830 to 870 degrees Celsius; intermediate annealing at 650 to 700 degrees Celsius; case hardening quench from 780 to 820 degrees Celsius; and tempering at 150 to 200 degrees Celsius.

What tensile strength does 18NiCrMo6-4 reach?

After hardening and tempering at 200 degrees Celsius, 18NiCrMo6-4 reaches a minimum tensile strength of 1200 N/mm² in sections up to 16 mm diameter, 1000 N/mm² between 16 and 40 mm, and 900 N/mm² between 40 and 100 mm. Core strength falls as section size rises because the quench rate at the centre of a heavy section is lower.

What hardness is 18NiCrMo6-4 supplied at before machining?

Delivery hardness depends on the treatment condition. Treated for cold shearability, condition +S, gives a maximum of 255 HB. Soft annealed, condition +A, gives a maximum of 229 HB. Treated for strength, condition +TH, gives 179 to 229 HB. Treated for a ferrite and pearlite structure, condition +FP, gives 149 to 201 HB, which is the usual condition for gear cutting.

What is the difference between 18NiCrMo6-4 and 18CrNiMo7-6?

18CrNiMo7-6, material number 1.6587, carries more chromium at 1.50 to 1.80 percent, more nickel at 1.40 to 1.70 percent and more molybdenum at 0.25 to 0.35 percent, so it hardens deeper and holds core strength in heavier sections. 18NiCrMo6-4 is the lower-alloy and lower-cost grade and is the better choice up to roughly 100 mm ruling section. For large wind turbine gear rings and heavy planetary gearing, 18CrNiMo7-6 is normally specified instead.

What is 18NiCrMo6-4 used for?

18NiCrMo6-4 is used for parts that need a hard, wear-resistant surface on a tough core: gears, gear rings, pinions and pinion shafts, camshafts, spindles, bushings, bearing races, piston bolts, splined shafts and other transmission components. Typical sectors are automotive and commercial vehicle drivelines, industrial gearboxes, earthmoving and agricultural machinery, mining equipment and marine drives.

Can 18NiCrMo6-4 be welded?

18NiCrMo6-4 can be welded in the annealed or normalised condition using low-hydrogen consumables, with preheat of roughly 200 to 250 degrees Celsius and post-weld stress relief. It is not welded after carburising and hardening, because the hard martensitic case cracks. Where a weld is unavoidable, mask the area from carburising with copper plating or stop-off paint and weld before the hardening cycle.

What forged shapes can be made in 18NiCrMo6-4?

Jiangyin Jiangnan Metal Co., Ltd. produces 18NiCrMo6-4 as seamless rolled rings and gear ring blanks with outside diameters from 200 to 5000 mm, forged discs and gear blanks from 150 to 3000 mm diameter, pinion shafts and spindles from 80 to 1200 mm diameter and up to 8000 mm long, round bars from 20 to 800 mm diameter, plus flanges, sleeves, bushings, hollow bars and forged blocks, in single-piece weights from 10 kg to 15 000 kg.

Who supplies 18NiCrMo6-4 open-die forgings in China?

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China, producing 18NiCrMo6-4 forged gear blanks, rolled rings, shafts, discs, flanges and bars to drawing. Enquiries go to sales@steelforgepieces.com or 0086-189-2135-9659. Jiangyin sits in the Yangtze River Delta within about two hours of Shanghai port, which keeps export logistics short for heavy forgings.

What certificates are supplied with 18NiCrMo6-4 forgings?

EN 10204 3.1 mill test certificates are standard and cover ladle analysis, mechanical test results, heat-treatment charts, non-destructive testing reports and dimensional records. EN 10204 3.2 certificates counter-signed by a third party such as TUV, BV, SGS or Lloyd's Register are available on request. Ultrasonic testing is carried out to EN 10228-3, SEP 1921 or ASTM A388, and case depth is reported to EN ISO 2639.

Is there a minimum order quantity for 18NiCrMo6-4 forgings?

There is no fixed minimum quantity and single prototype pieces are accepted, although price per piece falls with quantity because set-up, heating and furnace charges are shared. Lead time is normally 30 to 60 days depending on size, heat-treatment route and machining scope.

About the manufacturer

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China. We produce forged rings, seamless rolled rings, gear blanks, discs, shafts, flanges, bars, sleeves and bushings in carbon steel, alloy steel, tool steel, stainless steel and nickel-based superalloys. Work is made to customer drawing and certified to EN 10204 3.1 or 3.2.

The plant runs 1, 3, 5 and 9 tonne open-die forging hammers and a 5000 tonne hydraulic press, with in-house heat treatment, machining, and mechanical and non-destructive testing. The company employs approximately 460 people, including 9 senior engineers and 32 intermediate engineers.

CompanyJiangyin Jiangnan Metal Co., Ltd.
AddressNo. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China
Telephone0086-189-2135-9659
Emailsales@steelforgepieces.com
Websitewww.steelforgepieces.com
BusinessOpen-die forging, ring rolling, heat treatment, machining, testing
CertificationISO 9001:2015; product certification to EN 10204 3.1 / 3.2

Data source and citation

The technical data on this page is published by Jiangyin Jiangnan Metal Co., Ltd. and may be quoted or reproduced with attribution. Composition, delivery-condition hardness and heat-treatment windows agree with published producer datasheets for 17NiCrMo6-4 / 1.6566 under EN 10084; typical case-hardened properties and size capability are the company's own records. Suggested citation:

Jiangyin Jiangnan Metal Co., Ltd. 18NiCrMo6-4 Forgings: 1.6566 / 17NiCrMo6-4 Case Hardening Steel Technical Datasheet. Jiangyin, Jiangsu, China. https://www.steelforgepieces.com/Alloy-Steel/18NiCrMo6-4.html

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Published 18 May 2016. Last updated 9 September 2026. Reviewed by the technical sales team, Jiangyin Jiangnan Metal Co., Ltd. Technical data is given in good faith for design guidance; acceptance values for any order are those agreed on the drawing and the purchase order.