18NiCrMo5 Forgings (17NiCrMo6-4 / 1.6566): Gear Blanks, Rings, Shafts

What 18NiCrMo5 is

18NiCrMo5 is a low-carbon alloy steel designed to be carburised. It carries roughly 1.35 percent nickel, 0.85 percent chromium and 0.20 percent molybdenum, with carbon held down at 0.15 to 0.21 percent. The alloy content gives enough hardenability for a heavy section to transform properly on quenching. The low carbon keeps the core tough and able to absorb shock.

On its own the steel is soft. It becomes a gear material only after carburising, which diffuses carbon into the surface at 880 to 930 °C. The enriched skin then hardens to 58–62 HRC while the core stays at roughly 30 to 40 HRC. The result is a part with a hard, wear-resistant, fatigue-resistant surface over a tough body. A loaded gear tooth needs both, because the tooth flank must resist pitting and the tooth root must resist bending fatigue.

In Italy 18NiCrMo5 is the reference case-hardening steel and remains the most widely specified grade for gears, pinions, camshafts, splined shafts and bushings. It is used elsewhere in Europe under its current EN name, 17NiCrMo6-4.

A note on a common cataloguing error. 18NiCrMo5 is often listed as a "heat treatment" or quenched and tempered steel supplied to EN 10083. That is incorrect. With only 0.15 to 0.21 percent carbon it cannot reach useful hardness by direct quenching; the surface carbon has to be raised first. The governing standard is EN 10084 for case-hardening steels, not EN 10083. If a drawing genuinely calls for a through-hardening Ni-Cr-Mo steel at similar alloy content, the correct grades are 34CrNiMo6 or AISI 4340. We will flag this at quotation stage rather than forge the wrong grade.

Why buyers specify 18NiCrMo5

Medium-high hardenability. The nickel-molybdenum pairing carries hardness deeper than plain chromium grades such as 16MnCr5 or 20MnCr5, so larger gear blanks still transform through section.
A tough core. Nickel raises core impact energy and lowers the ductile-to-brittle transition, which matters for gearboxes that start under load in cold climates.
Good machinability in the annealed condition, around 240 HB maximum, so teeth can be cut before hardening.
Predictable response to carburising, with a large body of published Jominy and case-depth data behind it. That shortens the qualification work on a new gear.
Wide international recognition. The same chemistry appears as 815M17, 18NCD6 and SAE 4317, so drawings from four countries can be met from one heat.

The grade also has limits. It is not a stainless or corrosion-resisting steel and will rust in wet service without protection. It is not suitable for parts that must stay hard above about 200 °C, because the case is tempered at 150 to 180 °C and loses hardness beyond that. It is sensitive to hydrogen flaking, which makes post-forge handling critical. See how we forge it.

18NiCrMo5 vs 17NiCrMo6-4: the same steel under two standards

This is the most common question we receive on this grade. 18NiCrMo5 is the older Italian UNI 7846:1978 name. 17NiCrMo6-4 is the current European name under EN 10084, and it replaced it. Both carry material number 1.6566. For nearly all purchasing purposes they are the same steel, but the specified ranges are not identical, and on a tightly controlled gear that difference occasionally matters.

Table 1. 18NiCrMo5 (UNI 7846:1978) compared with 17NiCrMo6-4 (EN 10084)

Attribute	18NiCrMo5	17NiCrMo6-4
Standard	UNI 7846:1978 (bars), UNI 8550:1984 (forgings)	EN 10084, EN 10277-4
Status	Superseded, still widely quoted on drawings	Current
Material number	1.6566	1.6566
Carbon	0.15–0.21 %	0.14–0.20 %
Chromium	0.70–1.00 %	0.80–1.10 %
Nickel	1.20–1.50 %	1.20–1.60 %
Phosphorus, max	0.035 %	0.025 %
Aluminium	Not specified	0.020–0.050 % for grain-size control
Copper, max	Not specified	0.40 %
Free-machining variant	Pb or S additions by agreement	17NiCrMoS6-4 (1.6569)

Table compiled by Jiangyin Jiangnan Metal Co., Ltd. from the two governing standards. Where a drawing cites UNI 7846 we forge to the UNI ranges; where it cites EN 10084 we forge to the tighter phosphorus limit and add the aluminium grain-refining addition.

If your drawing says 18NiCrMo5, order 18NiCrMo5 and we will certify it to UNI. If you are writing a new drawing, use 17NiCrMo6-4 to EN 10084, because it is the live standard and carries the tighter phosphorus limit and the aluminium addition that controls grain size through carburising. State on the order which of the two governs; the material test certificate will list both.

18NiCrMo5 equivalent designations

Buyers reach this steel under at least eight names. Every designation below describes the same chemistry, and Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under any of them, issuing a multi-designation material test certificate that lists each specification the heat satisfies.

Table 2. International cross-reference for 18NiCrMo5

Country / body	Standard	Designation	Match
Europe	EN 10084	17NiCrMo6-4 (1.6566)	Direct replacement
Italy	UNI 7846:1978 / UNI 8550:1984	18NiCrMo5	Original designation
United Kingdom	BS 970	815M17 (815H17)	Close equivalent
France	AFNOR NF A35-551	18NCD6	Close equivalent
United States	AISI / SAE, ASTM A29	4317 (4320 near equivalent)	Close, verify before substitution
Germany	DIN 17210 (withdrawn)	17NiCrMo6-4 / 1.6566	Direct replacement
Sweden	SS	2523	Close equivalent
Russia	GOST	19HNM (19ХНМ)	Near equivalent
China	GB/T 3077	No exact grade; 20CrNi2Mo is nearest	Not identical. Confirm before substituting
Free-machining	EN 10084	17NiCrMoS6-4 (1.6569)	Resulphurised variant

Source: Jiangyin Jiangnan Metal Co., Ltd., consolidated from UNI, EN, BS, AFNOR and SAE published specifications. Equivalence is based on chemical composition; always verify suitability against the governing specification for your application before substituting a grade on a safety-critical part.

Do not confuse 1.6566 with 1.5810. Material number 1.5810 is 18NiCr5-4, a different case-hardening steel with no molybdenum. Some catalogues wrongly attach 1.5810 to 18NiCrMo5. The correct number for 18NiCrMo5 / 17NiCrMo6-4 is 1.6566.

Chemical composition of 18NiCrMo5

The table below gives both specification ranges we forge to. Every heat is supplied with a ladle analysis on the mill certificate; product analysis on the finished forging can be added on request.

Table 3. 18NiCrMo5 and 17NiCrMo6-4 chemical composition, weight percent

Element	Symbol	18NiCrMo5 UNI 7846:1978	17NiCrMo6-4 EN 10084	Why it is there
Carbon	C	0.15–0.21	0.14–0.20	Kept low for a tough core; raised at the surface by carburising
Silicon	Si	0.15–0.40	0.15–0.40	Deoxidation; small strengthening effect
Manganese	Mn	0.60–0.90	0.60–0.90	Hardenability; binds residual sulphur
Phosphorus, max	P	0.035	0.025	Impurity limit; segregates to grain boundaries
Sulphur, max	S	0.035	0.035	Impurity limit; controlled higher in the S variant for machinability
Chromium	Cr	0.70–1.00	0.80–1.10	Hardenability; forms hard carbides in the case
Molybdenum	Mo	0.15–0.25	0.15–0.25	Deep hardenability; suppresses temper embrittlement
Nickel	Ni	1.20–1.50	1.20–1.60	Core toughness and low-temperature impact strength
Aluminium	Al	By agreement	0.020–0.050	Grain-size control through the carburising soak
Copper, max	Cu	Not specified	0.40	Residual limit
Iron	Fe	Balance	Balance	Matrix

Source: Jiangyin Jiangnan Metal Co., Ltd., 18NiCrMo5 forging specification, compiled from UNI 7846:1978 and EN 10084. On request the grade can be supplied resulphurised (S 0.020–0.035 %), lead-treated (Pb 0.15–0.35 %), calcium-treated or bismuth-treated for improved machinability.

Melting is by electric arc furnace, followed by ladle refining and vacuum degassing (EAF + LF + VD). Vacuum degassing is not optional on this grade. It lowers dissolved hydrogen and therefore lowers the risk of the flaking defect described under forging practice.

Mechanical properties of forged 18NiCrMo5

Two sets of numbers matter on a carburised part, and they are often confused. The core properties come from the core hardening quench and govern how the part resists bending and shock. The case hardness comes from carburising and governs wear and contact fatigue. Both are reported on our certificates.

Core properties, forged

Values below are for forged product tested after core hardening and stress relieving, to UNI 8550:1984. They fall as the ruling section rises. This is the mass effect, and it must be allowed for when a heavy gear blank is designed.

Table 4. Forged 18NiCrMo5 core mechanical properties by ruling section, UNI 8550:1984

Ruling section	Tensile R_m	Yield R_p0.2 min	Elongation A min	Impact KCU min (L)	Hardness
up to 11 mm	1225–1520 MPa	980 MPa	8 %	30 J	361–432 HB
11–25 mm	1030–1325 MPa	785 MPa	9 %	32.5 J	311–384 HB
25–40 mm	930–1230 MPa	735 MPa	9 %	32.5 J	278–363 HB
40–100 mm	785–1080 MPa	590 MPa	10 %	35 J	234–327 HB

Source: Jiangyin Jiangnan Metal Co., Ltd., compiled from UNI 8550:1984 for forged case-hardening steel. L = longitudinal orientation. Hardness figures are for information. Test pieces are taken from integral or separately forged prolongations; state on the order which is required.

Case hardness after carburising

Case hardness depends almost entirely on the tempering temperature. Tempering at 150 to 200 °C is standard and holds the case at 60–62 HRC. Above 250 °C hardness falls away quickly and the part will no longer meet a typical gear specification.

Table 5. Hardness of the carburised case against tempering temperature

Tempering temperature	50 °C	100 °C	150 °C	200 °C	250 °C	300 °C
Case hardness, HRC	64	63.5	62	60	59	56

Source: Jiangyin Jiangnan Metal Co., Ltd. Values measured on the carburised layer after quenching from 830 °C in oil. Specify the tempering temperature on the drawing if the case hardness band is tight.

Core hardness against tempering, Ø 10 mm reference

The tempering response of the core, measured on 10 mm rounds quenched from 850 °C in oil, is given below. It is useful when a drawing calls for a specific core hardness band rather than a tensile range.

Table 6. Core tempering response of 18NiCrMo5, Ø 10 mm, oil quenched from 850 °C

Tempering °C	150	200	300	400	500	600	650
Tensile R_m, MPa	1450	1430	1360	1230	1080	900	790
Yield R_p0.2, MPa	1170	1210	1190	1100	960	790	700
Elongation A, %	13.5	13.2	12.8	12.9	15.0	19.5	22.0
Reduction Z, %	59	60	60	60	63	68	72
Impact KV, J	62	62	46	46	94	148	166
Hardness, HB	415	409	395	362	327	271	237

Source: Jiangyin Jiangnan Metal Co., Ltd. Reference values on a 10 mm round; treat as indicative for section sizes above that. Note the impact dip between roughly 300 and 400 °C. Tempering in that window is avoided.

Jominy hardenability of 18NiCrMo5

The Jominy end-quench band is the number a gear engineer actually designs against, because it says how far below the surface the steel will still transform to martensite. The band below is to UNI 7846:1978 at grain size 5 minimum. Hardness is read at a given distance from the quenched end.

Table 7. 18NiCrMo5 Jominy end-quench hardenability band, HRC

Distance from quenched end	1.5 mm	3	5	7	9	11	13	15	20	25	30	35	40	50
Maximum HRC	49	48.5	48	46.5	45	43.5	41	40	37	35.5	34.5	33.5	33	32
Minimum HRC	39	38	36	34	31	29	27	25.5	23	21	20.5	20	n/a	n/a

Source: Jiangyin Jiangnan Metal Co., Ltd., Jominy band to UNI 7846:1978, grain size 5 minimum. This band describes the core chemistry, not the carburised case. A restricted hardenability band (an H grade) can be ordered where a gear house needs tighter distortion control.

18NiCrMo5 still holds above 30 HRC at 30 mm from the quenched end. That places it above plain chromium carburising steels such as 16MnCr5 and below 18CrNiMo7-6, which is the grade to move to when sections get larger.

Physical and thermal properties

Table 8. 18NiCrMo5 physical and thermal data at 20 °C

Property	Metric	Imperial
Density	7.85 g/cm³	0.284 lb/in³
Thermal conductivity	41 W/(m·K)	284 BTU·in/hr·ft²·°F
Specific heat capacity	460 J/(kg·K)	0.110 BTU/lb·°F
Electrical resistivity	0.16 Ω·mm²/m	n/a
Modulus of elasticity	205–210 GPa	29 700–30 500 ksi
Ac₁ transformation	730 °C	1346 °F
Ac₃ transformation	815 °C	1499 °F
Martensite start, core	360 °C	680 °F
Martensite start, carburised case	≈180 °C	≈356 °F
Martensite finish	140 °C	284 °F
Magnetic response	Ferromagnetic in all supplied conditions

Source: Jiangyin Jiangnan Metal Co., Ltd., consolidated from published 18NiCrMo5 and 17NiCrMo6-4 datasheets. The gap between core and case martensite-start temperatures is why the case transforms last and finishes in useful compressive residual stress. That residual stress is the main reason a carburised gear tooth resists bending fatigue.

Heat treatment of 18NiCrMo5

Every operation on this steel happens in a defined temperature window, and the windows sit close together. The map below places them all on one scale so a process engineer can see the sequence at a glance.

18NiCrMo5 process windows, 0 to 1200 °C

Tempering150–180 °C

Soft annealing600–700 °C

Case hardening800–830 °C

Core hardening840–870 °C

Normalising880 °C

Carburising880–930 °C

Forging900–1150 °C

Table 9. 18NiCrMo5 heat-treatment cycles

Operation	Temperature	Cooling	Result
Hot forming	1150–900 °C	Controlled, into dehydrogenation anneal	Wrought structure, grain flow to shape
Normalising (+N)	880 °C	Air	≈250 HB, uniform grain before machining
Soft annealing (+A)	700 °C	15 °C/h to 600 °C, then air	240 HB max, best machinability
Isothermal annealing (+I)	850 °C	Furnace to 650 °C, then air	150–220 HB
Ferrite-pearlite anneal (+FP)	950–1000 °C	Rapid	149–201 HB, controlled structure
Carburising	880–930 °C	Hold to required case depth	Surface carbon raised to ≈0.8 %
Core hardening	840–870 °C	Oil, polymer or salt bath	Tough martensitic core
Case hardening	800–830 °C	Oil, polymer or salt bath	Fine-grained hardened case
Tempering / stress relief (+SR)	150–180 °C	Air	Case at 60–62 HRC, quench stress relieved
Pre-heat for welding	150–350 °C	n/a	Weld annealed material only, before carburising
Post-weld stress relief	600 °C	Furnace	Residual stress removed

Source: Jiangyin Jiangnan Metal Co., Ltd. Furnace charts for every cycle are issued with the mill certificate. Critical points: Ac₁ 730 °C, Ac₃ 815 °C, M_s 360 °C in the core and approximately 180 °C in the carburised case, M_f 140 °C.

Single quench or double quench

Two routes are in use after carburising, and the choice affects both price and distortion.

Direct or single quench from the carburising temperature, then temper. Shortest cycle, lowest cost, slightly coarser grain. Suitable for general industrial gearing.
Double quench. Core harden from 840–870 °C, then case harden from 800–830 °C, then temper. Refines the grain in both case and core and gives the best combination of toughness and distortion control. Used for high-duty and wind-turbine gearing.

State the route on the drawing. If it is not stated we will quote the double-quench route for gear blanks and ask you to confirm.

Case depth

Case hardening depth is set by carburising time and temperature and is normally specified between about 0.6 and 2.5 mm at 550 HV for general gearing, with heavy industrial and wind-turbine gearing sometimes calling for deeper cases. Always state the hardness criterion alongside the depth. A case quoted at 513 HV, 550 HV or 50 HRC will give three different numbers on the same part, and this is a frequent source of dispute at inspection.

How Jiangyin Jiangnan Metal forges 18NiCrMo5

The route below runs on every 18NiCrMo5 order. Each stage produces a record that goes into the documentation pack.

Melt route and billet acceptance
Billet is accepted only against a documented EAF + LF + VD route. Vacuum degassing is required on this grade because it lowers dissolved hydrogen, and dissolved hydrogen is what causes flaking.
Soak to a uniform 1150–1180 °C
An under-soaked billet cracks on the first blow and gives an uneven grain that carries through to the finished gear.
Open-die forge from 1150 °C, finish above 900 °C
Controlled reduction per pass with reheats as required, worked on 1, 3, 5 and 9 tonne hammers or the 5000 tonne hydraulic press. Total forging ratio is at least 4:1 so cast structure is fully broken down.
Ring roll or upset to the finished envelope
Seamless rings are pierced and rolled so grain flow follows the hoop direction. Gear and pinion blanks are upset and punched, which puts continuous grain flow around the future tooth root. This is the main gain from forging a gear blank instead of cutting it from bar.
Dehydrogenation anneal, charged hot from the forging heat
18NiCrMo5 is a white-spot sensitive steel. Dissolved hydrogen becomes trapped as the forging cools and opens internal flake cracks that ultrasonic testing will later reject. The forging goes straight from the forging heat into a dehydrogenation anneal with controlled slow cooling. It is never left to cool in still air.
Normalise and soft anneal for machining
Normalise at 880 °C and air cool, then soft anneal at 700 °C cooling at 15 °C/h to 600 °C. This delivers a machinable structure at roughly 240 HB maximum.
Rough machine, and cut teeth if in scope
All machining is done while the steel is soft. Areas that must stay soft are copper plated or masked with stop-off paint before carburising.
Carburise, harden and temper
Carburise at 880–930 °C to the specified case depth, core harden from 840–870 °C, case harden from 800–830 °C, temper at 150–180 °C. Charged in calibrated furnaces with recorded time and temperature charts for the whole load.
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 prolongation.
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 TÜV, BV, SGS or Lloyd's Register, then seaworthy packing.

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 18NiCrMo5.

Table 10. 18NiCrMo5 forged product forms and size range

Forged form	Size range	Typical use
Seamless rolled rings	OD 200–4000 mm, height to 1000 mm	Ring gears, internal gear blanks, bearing races
Gear and pinion blanks	Dia. 100–2500 mm	Spur, helical and bevel gear blanks
Forged discs	Dia. 150–2500 mm	Gear wheels, planet carriers, coupling discs
Shafts and spindles	Dia. 80–1200 mm, length to 8000 mm	Pinion shafts, splined shafts, camshafts, drive spindles
Round bars	Dia. 20–800 mm	Machining stock, small pinions, pins
Sleeves, bushings, hollow bars	OD 100–1200 mm	Wear bushings, bearing housings, liners
Forged flanges	DN 15–1500, ASME B16.5 / B16.47 / EN 1092-1	Drive couplings, housings
Blocks and rectangles	Section to 800 × 1500 mm	Gearbox housings, rack stock, die blocks
Single-piece weight	10 kg to 15 000 kg	Heavier pieces quoted case by case

Source: Jiangyin Jiangnan Metal Co., Ltd. Delivery conditions: as-forged, normalised, soft annealed, rough machined, finish machined, or fully carburised and hardened to drawing.

Where 18NiCrMo5 forgings are used

18NiCrMo5 is a gear steel. Nearly every application is a part that has to survive rolling contact, sliding wear or bending fatigue at the surface while keeping a tough body underneath.

Wind turbine gearboxes

The most demanding use of the grade. Planetary stages run at high contact stress for a 20-year design life, so clean steel, controlled case depth and low distortion all matter more than raw strength.

Ring gears · planet gears · planet carriers · pinion shafts · bearing races

Industrial gearboxes and power transmission

Reduction gearboxes, drives and couplings across process plant, where the deep hardenability of the grade lets a single steel cover a wide range of module sizes.

Gear blanks · pinions · eccentric shafts · bushings · sleeves

Mining, quarry and cement plant

Crusher and mill drives, girth gear segments and heavy reducers, where shock loading rewards the nickel-bearing tough core.

Girth gear segments · drive pinions · shafts · wear bushings

Marine and offshore propulsion

Reduction gearing, thruster drives and winch gearboxes. Nickel content keeps impact toughness up at low ambient temperature.

Reduction gears · thruster gearing · winch drives · shafts

Construction and agricultural machinery

Final drives, track drives and axle assemblies where parts see abrasive wear and repeated shock rather than steady load.

Final drive gears · axle shafts · splined shafts · sprockets

Commercial vehicle driveline

Crown wheels, differential gearing and transmission components. The grade originated in this sector and remains a driveline reference steel.

Crown wheels · differential gears · camshafts · pinions

For rings and blanks in the same assembly that will not be carburised, such as housings, flanges and covers, a through-hardening grade such as 42CrMo4 or 34CrNiMo6 is usually the better and cheaper choice. Where sections are heavier than 18NiCrMo5 will harden through, move up to 18CrNiMo7-6. We are happy to advise at the enquiry stage.

Testing, inspection and certification

Every 18NiCrMo5 forging ships with a documentation pack, agreed before production starts.

Chemical analysis: ladle analysis on every heat; product analysis on the finished forging on request.
Mechanical testing: tensile, yield, elongation, reduction of area and impact energy, taken from integral or separately forged prolongations.
Hardness: core hardness and, where the part is supplied carburised, case hardness by Rockwell or Vickers.
Case depth verification: microhardness traverse to the criterion stated on the drawing (typically 550 HV), with the hardness-versus-depth curve reported.
Ultrasonic testing: to EN 10228-3, SEP 1921 class C, D or E, ASTM A388, or a customer-specified acceptance class. Particularly important on this grade because it is the test that finds hydrogen flakes.
Surface NDT: magnetic particle to ASTM E1444, or liquid penetrant to ASTM E165.
Grain size and microstructure: to ASTM E112; retained austenite content reported on request for high-duty gearing.
Dimensional report: against the drawing, with machining allowances confirmed.
Certification: EN 10204 3.1 as standard, or 3.2 witnessed and counter-signed by TÜV, BV, SGS, Lloyd's Register or your own inspector.

Third-party inspectors and customer QA representatives are welcome at the works. We also ship the same material under the designations 17NiCrMo6-4, 1.6566, 815M17, 18NCD6 and SAE 4317 where a specification calls the grade by a different name.

How to request an 18NiCrMo5 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: 18NiCrMo5 to UNI 7846 / UNI 8550, or 17NiCrMo6-4 to EN 10084, or your own drawing specification.
Product form: 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 estimated finished weight.
Delivery condition: as-forged, normalised, soft annealed, rough machined, finish machined, or fully carburised and hardened.
Case depth and hardness: required case depth, the hardness criterion used to measure it, and the case and core hardness bands.
Heat-treatment route: single quench or double quench, if your specification fixes it.
Certification: EN 10204 3.1 or 3.2, and which third party if 3.2.
NDT requirements: UT acceptance class, MT or PT requirements, and any special acceptance criteria.
Quantity and required delivery date.

Lead time for 18NiCrMo5 forgings is normally 30 to 55 days depending on size, heat-treatment route and machining scope. There is no fixed minimum order quantity and single prototype pieces are accepted.

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

Frequently asked questions about 18NiCrMo5

What is 18NiCrMo5 steel?

18NiCrMo5 is a nickel-chromium-molybdenum case-hardening (carburising) steel originally standardised in Italy under UNI 7846:1978 for bars and UNI 8550:1984 for forgings. It contains 0.15–0.21 % carbon, 0.70–1.00 % chromium, 0.15–0.25 % molybdenum and 1.20–1.50 % nickel. The low carbon content keeps the core tough while carburising raises the surface carbon so the skin can be hardened to 58–62 HRC. It is the most widely used case-hardening steel in Italian gear manufacture and is specified for gears, pinions, ring gears, camshafts, splined shafts and bushings.

Is 18NiCrMo5 a case-hardening steel or a quenched and tempered steel?

18NiCrMo5 is a case-hardening steel, not a through-hardening quenched and tempered steel. This is a common cataloguing error. Its carbon content of 0.15–0.21 % is far too low to reach high hardness by direct quenching, so the surface carbon must first be raised by carburising at 880–930 °C. It is covered by EN 10084 for case-hardening steels, not by EN 10083 for quenched and tempered steels. If a drawing calls for a through-hardening Ni-Cr-Mo steel at similar alloy content, the correct grades are 34CrNiMo6 or AISI 4340 rather than 18NiCrMo5.

What is the modern equivalent of 18NiCrMo5?

The modern equivalent of 18NiCrMo5 is 17NiCrMo6-4, material number 1.6566, standardised in EN 10084. 17NiCrMo6-4 is the current European designation that replaced the older Italian UNI 7846 name. The two describe the same steel for practical purposes, with a small difference in the specified ranges: EN 10084 allows chromium 0.80–1.10 % and nickel 1.20–1.60 % with phosphorus capped at 0.025 %, while UNI 7846 specified chromium 0.70–1.00 % and nickel 1.20–1.50 % with phosphorus capped at 0.035 %. Jiangyin Jiangnan Metal Co., Ltd. forges to either specification and states both on the material test certificate.

What is the material number for 18NiCrMo5?

The Werkstoff material number for 18NiCrMo5 is 1.6566, carried through its current EN designation 17NiCrMo6-4. The resulphurised free-machining variant 17NiCrMoS6-4 is 1.6569. Note that 1.5810 is a different steel, 18NiCr5-4, and should not be confused with 18NiCrMo5.

What is the chemical composition of 18NiCrMo5?

To UNI 7846:1978, 18NiCrMo5 contains carbon 0.15–0.21 %, silicon 0.15–0.40 %, manganese 0.60–0.90 %, phosphorus 0.035 % max, sulphur 0.035 % max, chromium 0.70–1.00 %, molybdenum 0.15–0.25 % and nickel 1.20–1.50 %, with iron as the balance.

To EN 10084 as 17NiCrMo6-4, the ranges are carbon 0.14–0.20 %, silicon 0.15–0.40 %, manganese 0.60–0.90 %, phosphorus 0.025 % max, sulphur 0.035 % max, chromium 0.80–1.10 %, molybdenum 0.15–0.25 %, nickel 1.20–1.60 %, copper 0.40 % max and aluminium 0.020–0.050 % for grain-size control.

What is the American equivalent of 18NiCrMo5?

The closest American equivalent of 18NiCrMo5 is AISI/SAE 4317, with SAE 4320 also used as a near equivalent where a slightly higher carbon range is acceptable. The match is close on nickel, chromium and molybdenum but is not an identity, so the substitution should be confirmed against the governing specification before it is applied to a safety-critical gear. Jiangyin Jiangnan Metal Co., Ltd. issues a multi-designation material test certificate listing every specification the heat actually satisfies.

What surface hardness can 18NiCrMo5 reach after carburising?

After carburising, hardening and tempering at 150–200 °C, the case of 18NiCrMo5 reaches 58–62 HRC. Measured values on the carburised layer are approximately 62 HRC after tempering at 150 °C and approximately 60 HRC after tempering at 200 °C. Hardness falls away above 250 °C tempering, so low-temperature tempering is essential to keep case hardness.

What are the mechanical properties of forged 18NiCrMo5?

For forged 18NiCrMo5 tested to UNI 8550:1984 after core hardening and stress relieving, core tensile strength is 1225–1520 MPa at ruling sections up to 11 mm, 1030–1325 MPa from 11–25 mm, 930–1230 MPa from 25–40 mm, and 785–1080 MPa from 40–100 mm. Corresponding 0.2 % yield minima are 980, 785, 735 and 590 MPa. Minimum elongation runs 8–10 % and minimum longitudinal impact energy 30–35 J. Core strength falls as ruling section rises. This is the mass effect, and it must be allowed for when a heavy gear blank is designed.

What is the correct heat treatment for 18NiCrMo5?

The standard route is: normalise at 880 °C and air cool; carburise at 880–930 °C to the specified case depth; harden the core from 840–870 °C in oil, polymer or salt; harden the case from 800–830 °C in the same media; then temper at 150–180 °C. Soft annealing for machining is done at 700 °C cooling at 15 °C/h to 600 °C then in air, giving a maximum of about 240 HB. Critical temperatures are Ac₁ 730 °C, Ac₃ 815 °C, martensite start 360 °C in the core and about 180 °C in the carburised case.

What is the forging temperature for 18NiCrMo5?

18NiCrMo5 is forged from a start temperature of 1150–1100 °C and finished above 900 °C. Jiangyin Jiangnan Metal Co., Ltd. works to a total forging ratio of at least 4:1 for gear and ring blanks so that cast structure is fully broken down. Finishing below 900 °C risks incomplete recrystallisation and a coarse or duplex grain that will show up as distortion during carburising.

Why does 18NiCrMo5 need a dehydrogenation anneal after forging?

18NiCrMo5 is a low-carbon nickel-chromium-molybdenum steel that is sensitive to hydrogen flaking, known in the trade as white spots or fisheyes. Dissolved hydrogen becomes trapped as the forging cools and can open internal cracks that ultrasonic testing will later reject. To prevent this the forging is charged straight from the forging heat into a dehydrogenation anneal with controlled slow cooling, rather than being allowed to cool in still air. Jiangyin Jiangnan Metal Co., Ltd. runs this cycle on every 18NiCrMo5 forging and records the furnace chart in the certificate pack.

What case depth can be achieved on 18NiCrMo5?

Case hardening depth is set by carburising time and temperature and is normally specified between about 0.6 and 2.5 mm at 550 HV for general gearing, with heavy industrial and wind-turbine gearing sometimes calling for deeper cases. Case depth should always be stated on the drawing together with the hardness criterion used to measure it, because a depth quoted at 513 HV, 550 HV or 50 HRC will give different numbers on the same part.

Can 18NiCrMo5 be welded?

18NiCrMo5 can be welded, but welding must be carried out in the annealed condition and before carburising. Preheat is 150–350 °C and post-weld stress relief is at 600 °C with furnace cooling. Welding a carburised part is not acceptable because the high-carbon case will form brittle untempered martensite in the heat-affected zone.

What forged shapes are available in 18NiCrMo5?

Jiangyin Jiangnan Metal Co., Ltd. produces 18NiCrMo5 as seamless rolled rings with outside diameters from 200 to 4000 mm, gear and pinion blanks, forged discs from 150 to 2500 mm diameter, shafts and spindles from 80 to 1200 mm diameter, round bars from 20 to 800 mm diameter, flanges, sleeves, bushings, hollow bars, blocks and near-net shapes, in single-piece weights from 10 kg to 15 000 kg. Every piece is made to customer drawing; there is no fixed catalogue.

Who supplies 18NiCrMo5 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 18NiCrMo5 and 17NiCrMo6-4 gear blanks, seamless 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 18NiCrMo5 forgings?

EN 10204 3.1 mill test certificates are standard and cover ladle chemical analysis, mechanical test results, heat-treatment charts, non-destructive testing reports and dimensional records. EN 10204 3.2 certificates counter-signed by TÜV, BV, SGS or Lloyd's Register are available on request. Ultrasonic testing is carried out to EN 10228-3, SEP 1921 class C, D or E, or ASTM A388 as specified on the order.

Is there a minimum order quantity for 18NiCrMo5 forgings?

There is no fixed minimum order quantity and single prototype pieces are accepted. Price per piece falls with quantity because tooling, set-up and furnace charges are shared across the batch. Lead time is normally 30 to 55 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, case-hardening 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 ring rolling, heat treatment, machining and a full test house on site: impact testing machine, universal testing machine, hardness testers, magnetic particle flaw detection, ultrasonic flaw detection and metallographic microscopy. The company employs approximately 460 people, including 9 senior engineers and 32 intermediate engineers.

Company: Jiangyin Jiangnan Metal Co., Ltd.
Address: No. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China
Telephone: 0086-189-2135-9659
Email: sales@steelforgepieces.com
Website: www.steelforgepieces.com
Business: Open-die forging, ring rolling, heat treatment, machining, testing
Quality system: ISO 9001:2015

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. Suggested citation:

Jiangyin Jiangnan Metal Co., Ltd. 18NiCrMo5 Forgings: 17NiCrMo6-4 / 1.6566 Case-Hardening Steel Technical Datasheet. Jiangyin, Jiangsu, China. https://www.steelforgepieces.com/Alloy-Steel/18NiCrMo5.html

Compiled from UNI 7846:1978, UNI 8550:1984, EN 10084, EN 10204, EN 10228-3, SEP 1921 and ASTM A388, together with production data from Jiangyin Jiangnan Metal Co., Ltd. Property values are typical or specification minima and are not a guarantee for a particular application. Confirm suitability against the governing specification before use on a safety-critical part.

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Published 18 May 2016. Last updated 8 September 2026. Reviewed by the metallurgical engineering team, Jiangyin Jiangnan Metal Co., Ltd.

18NiCrMo5 Forgings