Alloy steel · Case-hardening (carburising) grade · W.Nr. 1.6587 · EN 10084 / EN ISO 683-3
18CrNiMo7-6 Forgings (1.6587)
Gear and ring-gear blanks, seamless rolled rings, pinion and shaft blanks, discs, sleeves, bushings and round bars, open-die forged to your drawing in 18CrNiMo7-6 and delivered soft and ready for your carburising cycle, with an EN 10204 3.1 or 3.2 certificate.
18CrNiMo7-6 (Werkstoff 1.6587) is a chromium-nickel-molybdenum case-hardening steel to EN 10084 and EN ISO 683-3, containing 0.15–0.21% carbon, 1.50–1.80% chromium, 1.40–1.70% nickel and 0.25–0.35% molybdenum. Carburised, hardened and tempered at 150–200 °C it develops a wear-resistant case of about 58–62 HRC over a core that stays tough at a tensile strength of roughly 1,050–1,350 N/mm². The nickel and molybdenum give it the hardenability to harden right through the section under a deep case. It is therefore the standard grade for heavy gearing, in sections where 16MnCr5 and 20MnCr5 no longer harden through.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The company forges 18CrNiMo7-6 to customer drawings: gear blanks, seamless rolled rings to 6,000 mm outside diameter, pinion and shaft blanks to 8,000 mm long, discs, sleeves and bars, up to 15,000 kg single-piece weight. Forgings are normalised and annealed to a machinable structure, ultrasonically tested to EN 10228-3 and certified to EN 10204 3.1 or 3.2. For a quotation, send a drawing to sales@steelforgepieces.com or call +86 189 2135 9659.
18CrNiMo7-6 at a glance
- Grade
- 18CrNiMo7-6 (also written 18CrNiMo76, 18 CrNiMo 7-6)
- Material number
- 1.6587
- Former designation
- 17CrNiMo6, under the withdrawn DIN 17210
- Steel family
- Low-carbon Cr-Ni-Mo case-hardening (carburising) steel
- Governing standards
- EN 10084 (case hardening steels); EN ISO 683-3. Not EN 10083, which covers quenched and tempered steels
- Delivery condition
- Soft, for machining and gear cutting: +A ≤229 HBW, +FP 159–207 HBW, +TH 179–229 HBW, +S ≤255 HBW or +QT ≤229 HBW
- Case hardness
- 58–62 HRC (≈650–750 HV) after carburising, hardening and tempering at 150–200 °C
- Core strength
- 1,050–1,350 N/mm² tensile in the case-hardened condition
- Defining strength
- Deep hardenability with high core toughness in heavy sections; high bending fatigue strength at the tooth root
- Density
- 7.85 g/cm³ (0.284 lb/in³)
- Certification
- EN 10204 3.1 standard; 3.2 third-party witnessed on request
- Forged by
- Jiangyin Jiangnan Metal Co., Ltd., Jiangyin, Jiangsu, China
What 18CrNiMo7-6 is, and when to specify it
18CrNiMo7-6 is supplied soft, at 159 to 229 HBW. In that condition it machines and hobs like a mild alloy steel. It develops its working properties only in the carburising and hardening cycle that follows gear cutting, which is normally carried out by the gear manufacturer rather than by the forge.
Hardenability is the main difference between this grade and the cheaper carburising steels. 16MnCr5 and 20MnCr5 contain manganese and chromium but no nickel and no molybdenum, so in sections much thicker than about 30 mm the core will not transform to a strong, uniform structure during the quench. 18CrNiMo7-6 contains 1.40 to 1.70% nickel and 0.25 to 0.35% molybdenum in addition to 1.50 to 1.80% chromium. Nickel lowers the critical cooling rate and toughens the ferrite. Molybdenum suppresses the ferrite-pearlite transformation and resists temper embrittlement. In combination they allow a 300 mm gear blank to harden through to a strong core beneath a 4 mm case.
Specify 18CrNiMo7-6 when
- The part is a gear, pinion or ring gear that will be carburised after cutting.
- The section is heavy, a gear blank over about 150 mm or a case depth over about 2 mm, and a plain Mn-Cr grade will not harden through.
- Tooth-root bending fatigue governs the design as much as flank wear.
- The drive sees shock loading: mill drives, crusher gearing, marine reversing duty.
- The customer specification already calls for 1.6587, 17CrNiMo6 or 18NCD6.
Specify another grade when
- The part needs strength through the whole section rather than a hard skin. Use 42CrMo4 or AISI 4140, which are quenched and tempered.
- The gear is small and the section is thin. 16MnCr5 or 20MnCr5 will do the same job for less money.
- The component is a pressure-retaining part in a vessel, valve or heat exchanger. Case-hardening steel is not a pressure-vessel material; use a carbon or Cr-Mo pressure grade.
- Corrosion resistance is required. Use a stainless steel or nickel alloy.
Chemical composition of 18CrNiMo7-6
The limits below are the EN 10084 ranges for 18CrNiMo7-6 / 1.6587, in weight percent. The highlighted rows are the nickel and molybdenum additions that separate this grade from the Mn-Cr carburising steels and give it its hardenability in heavy sections.
| Element | Min % | Max % | Role in the steel |
|---|---|---|---|
| Carbon (C) | 0.15 | 0.21 | Kept low so the core stays tough. Surface carbon is raised to about 0.8% by the carburising cycle, not by the melt. |
| Silicon (Si) | – | 0.40 | Deoxidiser. Held low to limit oxide inclusions that shorten gear fatigue life. |
| Manganese (Mn) | 0.50 | 0.90 | Hardenability and deoxidation. Combines with sulfur. |
| Chromium (Cr) | 1.50 | 1.80 | Raises hardenability and forms the carbides that give the case its hardness and wear resistance. |
| Nickel (Ni) | 1.40 | 1.70 | Toughens the core and lowers the critical cooling rate, so heavy sections harden through. |
| Molybdenum (Mo) | 0.25 | 0.35 | Suppresses the ferrite-pearlite transformation, refines the structure and resists temper embrittlement. |
| Phosphorus (P) | – | 0.025 | Residual. Segregates to grain boundaries and embrittles; held tight. |
| Sulfur (S) | – | 0.035 | Residual. Controlled-sulfur variants of 0.020–0.040% are made for machinability. |
| Copper (Cu) | – | 0.40 | Residual from scrap; normally capped by agreement. |
Source: EN 10084, Case hardening steels: technical delivery conditions. Where sulfur is raised for machinability the manganese upper limit may be increased by 0.15%. Every heat forged by Jiangyin Jiangnan Metal Co., Ltd. is supplied with a ladle analysis on the mill certificate; a product analysis on the finished forging can be added on request.
Note on two figures that are often quoted incorrectly. A number of supplier listings, including the earlier version of this page, give the manganese range of 18CrNiMo7-6 as 0.40–0.60% and the standard as EN 10083-1. Both are wrong. EN 10084 sets manganese at 0.50–0.90%, and EN 10083 is the standard for quenched and tempered steels such as 42CrMo4, not for case-hardening steels. Order to EN 10084 or EN ISO 683-3.
Mechanical properties of 18CrNiMo7-6
Delivery condition, before carburising
18CrNiMo7-6 forgings are shipped soft so the customer can machine and gear cut them. The condition is stated on the order with the symbol below.
| Symbol | Condition | Hardness | Used for |
|---|---|---|---|
| +A | Soft annealed | max 229 HBW | General machining; the default for open-die forgings |
| +FP | Treated to ferrite-pearlite structure and hardness range | 159–207 HBW | Gear cutting. Preferred by gear makers: uniform structure machines and distorts predictably |
| +TH | Treated to hardness range | 179–229 HBW | Where a defined hardness band is specified but structure is not |
| +S | Treated for cold shearability | max 255 HBW | Bar stock for cold shearing; rarely relevant to forgings |
| +QT | Pre-quenched and tempered | max 229 HBW | Improved machined surface finish on some geometries |
Source: EN 10084 delivery conditions. State the symbol on the purchase order. The difference between +A and +FP affects both machining behaviour and distortion in the carburising cycle.
Case-hardened condition
These are reference values for blank-hardened test pieces. They give the strength of the core beneath the case, which is what carries the tooth bending load.
| Section | Yield Rp0.2 | Tensile Rm | Elongation A5 | Reduction Z | Impact KV, 20 °C |
|---|---|---|---|---|---|
| ≤ 160 mm | ≥785 N/mm² | ≥1,080 N/mm² | ≥8% | ≥35% | ≥40 J |
| > 160 mm | ≥785 N/mm² | ≥1,080 N/mm² | ≥8% | ≥25% | ≥25 J |
Reference values for blank-hardened samples. Dimension-dependent mechanical values are no longer specified in EN ISO 683-3; the figures above derive from the withdrawn DIN 17210 and remain in general use as design guidance. In the fully case-hardened condition the core tensile strength of 18CrNiMo7-6 is normally quoted as 1,050–1,350 N/mm², depending on section size and quench severity. Acceptance values for a given order are agreed on the purchase order and the mill test certificate governs.
Hardenability
18CrNiMo7-6 is available with restricted hardenability, ordered as +H, or to the narrowed upper and lower Jominy scatter bands +HH and +HL under EN ISO 683-3. Where gear distortion has to be repeatable from batch to batch, which is normal in series gear production, specify the restricted band rather than the plain grade. State it on the enquiry so the steel can be sourced accordingly.
Physical properties of 18CrNiMo7-6
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Modulus of elasticity | ≈210 GPa | ≈30.5 × 10⁶ psi |
| Coefficient of thermal expansion, 20–200 °C | ≈11.5 × 10⁻⁶ /K | ≈6.4 × 10⁻⁶ /°F |
| Thermal conductivity | ≈44 W/m·K | ≈25 Btu/h·ft·°F |
| Specific heat capacity | ≈460 J/kg·K | ≈0.11 Btu/lb·°F |
| Ac1 / Ac3 transformation temperatures | ≈690 °C / ≈774 °C | ≈1,274 °F / ≈1,425 °F |
| Magnetic response | Ferromagnetic | Ferromagnetic |
Nominal values for a low-alloy steel of this composition, for design screening. Ac1 and Ac3 are thermodynamically calculated values reported for 18CrNiMo7-6 gear steel in the published literature and vary with actual heat chemistry. Where a physical property enters a design calculation, request the figure in writing against the specific condition.
Heat treatment and carburising of 18CrNiMo7-6
The cycle below is the standard route. Carburising, hardening and tempering are normally carried out by the gear manufacturer after machining, not by the forge. Jiangyin Jiangnan Metal Co., Ltd. carries out the forging, normalising and annealing stages and can arrange the hardening cycle where a customer wants a finished part.
| Operation | Temperature | Cooling | Result |
|---|---|---|---|
| Hot forging | 1,150 → 850 °C | Slow cool in sand or furnace | Wrought grain flow following the part contour; forging must finish above 850 °C |
| Normalising | 850–880 °C | Air | Refines the as-forged structure and evens out grain size before carburising |
| Soft annealing | 650–700 °C | Slow, in furnace | Machinable structure at max 229 HBW |
| Carburising | 880–980 °C | Air, then reheat to harden | Raises surface carbon to about 0.8%; time at temperature sets the case depth |
| Direct hardening | 810–850 °C | Oil, polymer or warm bath | Quench straight from the carburising heat; least distortion-tolerant but quickest |
| Double hardening, core stage | 830–870 °C | Oil, polymer or warm bath | Refines the core structure of heavy sections |
| Double hardening, case stage | 780–820 °C | Oil, polymer or warm bath | Refines the carburised case; best combination of case and core properties |
| Tempering | 150–200 °C, min 1 h | Air | Relieves quench stress with minimal loss of case hardness; result 58–62 HRC |
Source: EN ISO 683-3 typical values, with forging temperatures from established mill practice for 1.6587. Older data sheets to DIN 17210 quote water quenching; oil, polymer or warm-bath quenching is now normal practice on gear parts and gives less distortion. Confirm the cycle against your own furnace and part geometry.
Case hardening depth
Case hardening depth (CHD) is set by the carburising time and temperature, not by the steel grade. It is measured to the 550 HV limiting hardness under ISO 2639 and EN ISO 18203, It must be stated on the drawing, because a case that is too shallow will spall under contact stress and a case that is too deep leaves the tooth root brittle.
- A common design rule of thumb for gears is CHD ≈ 0.15 to 0.25 × module. A module 20 gear therefore calls for roughly 3–5 mm.
- Practical case depths in 18CrNiMo7-6 run from about 0.8 mm on small components to 6 mm and beyond on large mill and wind turbine gearing.
- Case depth grows roughly with the square root of carburising time, so doubling the depth costs about four times the furnace hours.
- In heavy sections the nickel and molybdenum content is what keeps the core hardening properly under a deep case. That is the usual reason for choosing this grade over 20MnCr5.
18CrNiMo7-6 compared with other case-hardening and gear steels
These are the grades that compete for the same drawing. The choice is driven by section size and required case depth first, and by cost second.
| Criterion | 18CrNiMo7-6 | 20MnCr5 | 16MnCr5 | 17NiCrMo6-4 | 42CrMo4 |
|---|---|---|---|---|---|
| Material number | 1.6587 | 1.7147 | 1.7131 | 1.6566 | 1.7225 |
| Type | Case hardening | Case hardening | Case hardening | Case hardening | Quenched & tempered |
| Nominal C | 0.15–0.21% | 0.17–0.22% | 0.14–0.19% | 0.14–0.20% | 0.38–0.45% |
| Nominal Cr | 1.50–1.80% | 1.00–1.30% | 0.80–1.10% | 0.80–1.10% | 0.90–1.20% |
| Nickel | 1.40–1.70% | – | – | 1.20–1.50% | – |
| Molybdenum | 0.25–0.35% | – | – | 0.15–0.25% | 0.15–0.30% |
| Hardenability | Highest of the group | Moderate | Low | High | High (through-hardening) |
| Practical section limit | Heavy: gear blanks well over 300 mm | To roughly 60 mm | To roughly 30 mm | Medium to heavy | Heavy, but no hard case |
| Core toughness | Highest | Moderate | Moderate | High | High |
| Surface hardness achievable | 58–62 HRC | 58–62 HRC | 58–62 HRC | 58–62 HRC | Nitrided or induction only |
| Relative cost | Highest | Low | Lowest | Medium-high | Low |
| Choose it for | Wind, mill, marine and mining gearing; heavy sections with deep case | Automotive and general industrial gears | Small gears, pins, shafts | Mid-size gearing where 20MnCr5 is marginal | Shafts and gears needing through strength, not a hard skin |
Comparison compiled by Jiangyin Jiangnan Metal Co., Ltd. from EN 10084, EN ISO 683-3 and EN 10083-3. Section limits are practical guidance, not standard values; the real limit depends on quench severity, geometry and the required core strength. See also our pages on 42CrMo4 and 17CrNiMo6.
18CrNiMo7-6 equivalent designations and standards
18CrNiMo7-6 is a European grade with no exact counterpart in the American, Chinese or Japanese systems. The grades below are the usual cross-references, but every one of them differs in chromium or nickel, so hardenability and case behaviour differ too. Where case depth or core strength governs the design, order to 18CrNiMo7-6 or 1.6587 rather than to a national cross-reference.
| System | Designation | How close is it? |
|---|---|---|
| EN / ISO | 18CrNiMo7-6 (EN 10084, EN ISO 683-3) | The grade itself |
| Werkstoff Nr. (Germany) | 1.6587 | Identical. The material number for this grade |
| DIN 17210 (withdrawn) | 17CrNiMo6 | Same steel, earlier designation. Carbon and manganese ranges were widened slightly when it moved into EN 10084 |
| AFNOR (France) | 18NCD6 / 18CND6 | Closest true equivalent |
| AISI / SAE (USA) | 4820, sometimes 4320 | No exact equivalent. 4820 carries roughly twice the nickel and only residual chromium; 4320 carries far less chromium |
| GB/T 3077 (China) | 20CrNi2Mo | Nearest GB grade, but with about a third of the chromium. Chinese mills also produce 18CrNiMo7-6 directly to EN 10084 |
| JIS G4053 (Japan) | SNCM 420 | Nearest JIS grade; chromium is much lower |
Cross-references compiled by Jiangyin Jiangnan Metal Co., Ltd. for identification only. They are not statements of interchangeability. Jiangyin Jiangnan Metal accepts orders under any of these names and lists every designation the heat satisfies on the material test certificate.
| Standard | Covers |
|---|---|
| EN 10084 | Case hardening steels: technical delivery conditions. The chemistry and delivery condition of 18CrNiMo7-6 |
| EN ISO 683-3 | Heat-treatable steels, alloy steels and free-cutting steels, Part 3: case-hardening steels. Heat treatment and hardenability bands |
| EN 10204 | Inspection documents: 3.1 mill certificate, 3.2 third-party witnessed certificate |
| EN 10228-3 | Ultrasonic testing of ferritic and martensitic steel forgings |
| SEP 1921 / ASTM A388 | Alternative ultrasonic acceptance classes commonly specified on gear forgings |
| ISO 2639 / EN ISO 18203 | Determination of case hardening depth to the 550 HV limit |
| ASTM E112 | Grain size. A fine austenitic grain size is required for a predictable carburising response |
| ISO 6336 / AGMA 2001 | Gear rating standards that the case depth and core strength feed into |
EN 10083 does not apply to this grade. It covers quenched and tempered steels and appears on many 18CrNiMo7-6 listings in error.
18CrNiMo7-6 forgings we produce
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory. Every item below is forged to the customer's drawing or dimensional sketch. Open-die forging and seamless ring rolling need no dies, so there is no tooling charge, no fixed catalogue and no minimum order quantity by piece. A single prototype gear blank is quoted the same way as a production batch.
Size and weight capability in 18CrNiMo7-6
| Product form | Dimensional range | Unit weight |
|---|---|---|
| Seamless rolled rings | OD 200–6,000 mm, height to 1,000 mm | 20–15,000 kg |
| Gear blanks and discs | Ø200–2,500 mm, thickness to 800 mm | 30–15,000 kg |
| Shafts and pinion blanks | Ø80–1,000 mm, length to 8,000 mm | to 15,000 kg |
| Round bars and billets | Ø80–800 mm, length to 6,000 mm | 20–8,000 kg |
| Sleeves and bushings | OD to 2,000 mm, bored or trepanned | to 10,000 kg |
Machining allowance is normally 6–20 mm per surface depending on section size, unless the drawing states otherwise; rough-machined and finish-machined parts are also supplied. Plant equipment: 1 t, 3 t, 5 t and 9 t open-die forging hammers, a 5,000 t hydraulic press, and 3 m and 6 m seamless ring rolling mills.
How we make 18CrNiMo7-6 forgings
- Melting 18CrNiMo7-6 is melted by electric arc furnace with ladle furnace refining and vacuum degassing (EAF + LF + VD). Vacuum degassing brings hydrogen down to the low single-digit ppm range that gear-steel practice requires, and holds oxygen and inclusion content low. Inclusions are the usual origin of gear fatigue cracks.
- Billet verification Heat chemistry is confirmed by spectrometer against the EN 10084 limits, in particular the 1.50–1.80% chromium, 1.40–1.70% nickel and 0.25–0.35% molybdenum, before any material is heated.
- Open-die forging Forged on hammers and the hydraulic press from 1,150 °C, finishing above 850 °C, with a controlled reduction ratio to close porosity and develop wrought grain flow that follows the part contour. Rings are ring-rolled seamless so there is no weld and the grain runs circumferentially.
- Normalising and annealing Normalised at 850–880 °C in air to refine the as-forged structure, then annealed to the ordered delivery condition: +A at max 229 HBW, or +FP at 159–207 HBW where a uniform ferrite-pearlite structure is wanted for gear cutting.
- Rough or finish machining Turned, bored, drilled and faced to your drawing with the agreed machining allowance, or finish machined to final dimensions.
- Non-destructive testing Ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388 to your nominated class, plus magnetic particle and dimensional inspection where required.
- Certification and despatch EN 10204 3.1 mill certificate as standard, 3.2 with third-party witness (TÜV, BV, LR, SGS, DNV) on request. Hard stamped, preserved and packed for sea or air freight.
Where 18CrNiMo7-6 forgings are used
18CrNiMo7-6 is a gear steel. Most applications are components that transmit torque through a hardened contact surface, with the body beneath carrying the shock load.
| Industry | Components forged in 18CrNiMo7-6 |
|---|---|
| Wind energy | Planetary and helical gearbox gears, internal ring gears, planet carriers, sun and pinion shafts, main shaft gearing |
| Mining and cement | Girth gear segments, mill and kiln drive pinions, crusher gearing and shafts, conveyor drive gears |
| Marine and offshore | Propulsion reduction gearing, thrust and intermediate shafts, azimuth and thruster drive gears, winch and windlass gearing |
| Rail | Traction gears and pinions, axle drive gearing, gearbox shafts |
| Construction and earthmoving | Final drive and travel gears, swing drive pinions, track drive components, excavator slewing gears |
| Cranes and lifting | Slewing ring gears, hoist gearbox gears and pinions, luffing drive components |
| Heavy machinery | Rolling mill drive pinions and pinion stands, press gearing, extruder and mixer gearboxes, paper and sugar mill drives |
| Oil and gas drilling | Drawworks and rotary table gearing, top drive gears, mud pump gear ends |
| Bearings and wear parts | Heavy-duty bearing rings and races, cam followers, wear pins, sprockets, clutch dogs, tappets |
These positions are governed by contact stress at the surface and bending fatigue at the tooth root. 18CrNiMo7-6 is not a pressure-vessel, valve-body or corrosion-service material, and it should not be specified for those duties.
Welding and machining 18CrNiMo7-6
Welding
18CrNiMo7-6 is weldable with a controlled procedure, but it is not a structural welding steel. Calculated from the mid-range composition with the IIW carbon equivalent formula, CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15, the value is approximately 0.79. At that level hydrogen cracking in the heat-affected zone is the governing risk.
- Preheat to 200–250 °C and hold the interpass temperature in that range.
- Use low-hydrogen consumables, dried and stored to the maker's instructions.
- Post-weld heat treatment immediately after welding, before the part cools to room temperature.
- Weld the soft blank. Complete all welding before carburising, stress relieve, then machine and case harden.
- Do not weld a carburised surface at 58–62 HRC; it will crack.
Machining
- Machine in the delivery condition, before carburising. The +FP condition at 159–207 HBW gives the most consistent chip formation and the most predictable distortion afterwards.
- The annealed +A condition at up to 229 HBW is harder work and gives a poorer finish on fine features.
- After case hardening the surface is 58–62 HRC and only grinding, honing or hard turning with CBN will touch it. Allow grinding stock on all cased surfaces.
- Order the forging close to net shape. Removing a large allowance from a Cr-Ni-Mo steel usually costs more than the extra forging work.
Testing, inspection and certification
- Chemical analysis. Spectrometric ladle analysis on every heat and, on request, product analysis on the finished forging.
- Mechanical testing. Tensile, yield, elongation, reduction of area and Charpy V-notch impact, on test pieces from the forging or from a prolongation as specified.
- Hardness. Brinell in the delivery condition; Rockwell C and Vickers hardness traverses on case-hardened parts.
- Case hardening depth. Measured to the 550 HV limit per ISO 2639 and EN ISO 18203 where the hardening cycle is in our scope.
- Grain size. Determined to ASTM E112. A fine, uniform austenitic grain size is what makes the carburising response repeatable.
- Ultrasonic testing. EN 10228-3, SEP 1921 class C/D/E, ASTM A388 or your nominated class.
- Surface NDT. Magnetic particle inspection to EN 10228-1 or ASTM E1444; liquid penetrant where specified.
- Certification. EN 10204 3.1 as standard; EN 10204 3.2 witnessed by TÜV, BV, LR, SGS or DNV on request. Full heat traceability and hard stamping.
Customers retain the right to witness any production stage: chemistry analysis, forging, heat treatment cycles, mechanical testing and final NDE. Witnessing is arranged with our QA team at no charge.
Frequently asked questions about 18CrNiMo7-6
What is 18CrNiMo7-6 steel?
18CrNiMo7-6 is a chromium-nickel-molybdenum case-hardening (carburising) steel covered by EN 10084 and EN ISO 683-3, with the material number 1.6587. It contains 0.15–0.21% carbon, 1.50–1.80% chromium, 1.40–1.70% nickel and 0.25–0.35% molybdenum. Carburised, hardened and tempered at 150–200 °C it develops a wear-resistant surface of about 58–62 HRC over a tough core with a tensile strength of roughly 1,050–1,350 N/mm². The combination of deep hardenability and high core toughness makes it the standard grade for heavy gearing in wind turbine gearboxes, mining and cement mill drives, marine propulsion and rail traction.
Which standard covers 18CrNiMo7-6?
18CrNiMo7-6 is specified in EN 10084, Case hardening steels: technical delivery conditions, and in EN ISO 683-3, which now covers the same family internationally. It is not covered by EN 10083. EN 10083 applies to quenched and tempered steels such as 42CrMo4, and the reference to EN 10083-1 that appears on many supplier listings for this grade is incorrect. Order 18CrNiMo7-6 to EN 10084 or EN ISO 683-3 chemistry and state the required delivery condition, hardenability class and case depth on the purchase order.
What is the chemical composition of 18CrNiMo7-6?
To EN 10084, in weight percent: carbon 0.15–0.21, silicon max 0.40, manganese 0.50–0.90, phosphorus max 0.025, sulfur max 0.035, chromium 1.50–1.80, nickel 1.40–1.70 and molybdenum 0.25–0.35, with copper normally held to 0.40 max. Free-cutting variants with controlled sulfur between 0.020 and 0.040% are available, in which case the manganese upper limit may be raised by 0.15%. Jiangyin Jiangnan Metal Co., Ltd. supplies a ladle analysis on every mill certificate and can add a product analysis on the finished forging on request.
Is 18CrNiMo7-6 the same as 17CrNiMo6?
They are the same steel family and the two names are used interchangeably in the market, but they are not identical specifications. 17CrNiMo6 was the designation under the withdrawn DIN 17210. When the grade moved into EN 10084 the carbon and manganese ranges were widened slightly and it was renamed 18CrNiMo7-6. Both share the material number 1.6587. New enquiries should be placed as 18CrNiMo7-6 to EN 10084 or EN ISO 683-3, which is the current designation. Jiangyin Jiangnan Metal Co., Ltd. accepts orders under either name and states both on the material test certificate.
What is the AISI, GB or JIS equivalent of 18CrNiMo7-6?
There is no exact equivalent in the American, Chinese or Japanese systems. The grades most often cross-referenced are AISI/SAE 4820 and 4320 in the United States, 20CrNi2Mo to GB/T 3077 in China and SNCM 420 to JIS G4053 in Japan, but all of them carry markedly less chromium than the 1.50–1.80% of 18CrNiMo7-6, and AISI 4820 carries roughly twice the nickel. Hardenability and case behaviour therefore differ. The French AFNOR designation 18NCD6 is the closest true equivalent. Where the design depends on case depth or core strength, specify 18CrNiMo7-6 or 1.6587 to EN 10084 and not a national cross-reference.
What hardness does 18CrNiMo7-6 reach after case hardening?
After carburising at 880–980 °C, hardening and tempering at 150–200 °C, the case typically reaches 58–62 HRC, equivalent to roughly 650–750 HV. Surface hardness depends on the carbon potential of the carburising atmosphere, the quench severity and the tempering temperature. The core is much softer and much tougher, at roughly 30–45 HRC with a tensile strength of 1,050–1,350 N/mm². In the annealed delivery condition, before any carburising, the steel is soft at a maximum of 229 HBW so that it can be machined and gear cut.
What case hardening depth can be achieved in 18CrNiMo7-6?
Case hardening depth is set by the carburising time and temperature, not by the steel, and is measured to the 550 HV limiting hardness per ISO 2639 and EN ISO 18203. Practical case depths run from about 0.8 mm on small components to 6 mm or more on large mill and wind turbine gearing. A common design rule of thumb for gears is a case depth of 0.15 to 0.25 times the module, so a module 20 gear normally calls for 3–5 mm. In a heavy section with a deep case, the nickel and molybdenum content is what keeps the core hardening through. That is the usual reason for specifying 18CrNiMo7-6 in place of 16MnCr5 or 20MnCr5 on large gears.
In what condition are 18CrNiMo7-6 forgings delivered?
Soft, not hardened, because the customer carburises after machining and gear cutting. The usual conditions are annealed (+A) at max 229 HBW, treated to a ferrite-pearlite structure and hardness range (+FP) at 159–207 HBW, or treated to a hardness range (+TH) at 179–229 HBW. Gear manufacturers generally ask for +FP, because a uniform ferrite-pearlite structure machines predictably and distorts predictably in the subsequent carburising cycle. Jiangyin Jiangnan Metal Co., Ltd. normalises and anneals every 18CrNiMo7-6 forging before despatch and supplies to whichever delivery condition is stated on the order.
Can 18CrNiMo7-6 be quenched and tempered instead of carburised?
It can be supplied pre-quenched and tempered (+QT) at max 229 HBW, but that is a machining condition rather than a service condition. With only 0.15–0.21% carbon the steel cannot reach the through-hardened strength of a quenched and tempered grade. If a part needs high strength through the whole section rather than a hard surface over a tough core, specify 42CrMo4, 34CrNiMo6 or AISI 4140 instead. Choose 18CrNiMo7-6 where surface wear resistance and bending fatigue strength at the tooth root govern the design.
Can 18CrNiMo7-6 be welded?
It can be welded, but it is not a structural welding steel and the procedure must be controlled. The carbon equivalent calculated from the mid-range composition using the IIW formula is approximately 0.79, which is high, so preheat of 200–250 °C, low-hydrogen consumables, controlled interpass temperature and post-weld heat treatment are needed to avoid hydrogen cracking in the heat-affected zone. Welding should be completed before carburising. A carburised surface at 58–62 HRC must never be welded. Where a joint is unavoidable in a gear assembly, weld the soft blank, stress relieve, then machine and carburise.
What sizes of 18CrNiMo7-6 forgings can you supply?
Jiangyin Jiangnan Metal Co., Ltd. forges 18CrNiMo7-6 seamless rolled rings from 200 to 6,000 mm outside diameter, gear and pinion shafts up to 8,000 mm long, discs and gear blanks from 200 to 2,500 mm diameter, round bars and billets from 80 to 800 mm diameter, and sleeves and bushings up to 2,000 mm outside diameter, with single-piece weights up to 15,000 kg. Plant equipment includes 1 t, 3 t, 5 t and 9 t open-die forging hammers, a 5,000 t hydraulic press and 3 m and 6 m seamless ring rolling mills. Open-die forging needs no dies, so one-off and prototype quantities are economic: there is no tooling charge and no minimum order quantity by piece.
Do you supply a material certificate with 18CrNiMo7-6 forgings?
Yes. Every 18CrNiMo7-6 forging ships with an EN 10204 3.1 mill test certificate as standard, showing the heat number, ladle chemical analysis, mechanical test results, heat treatment record, hardness and ultrasonic test results. EN 10204 3.2 certification witnessed by a third party such as TÜV, BV, LR, SGS or DNV is available on request at the time of order. Ultrasonic testing is carried out to EN 10228-3, SEP 1921 or ASTM A388 to the class stated on the purchase order, and grain size to ASTM E112 is reported where the carburising response requires it.
How long does an 18CrNiMo7-6 forging take to produce?
Lead time depends on whether billet stock in the grade is on hand and on the size of the forging. Rings, discs and shafts from stock material typically run 30–45 days. Parts needing a new melt, restricted hardenability (+HH or +HL), heavy machining or third-party witnessed inspection take longer. Send your drawing and a firm date will be confirmed with the quotation.
Who supplies open-die forged 18CrNiMo7-6 parts in China?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It forges 18CrNiMo7-6 (W.Nr. 1.6587) and other alloy steels, carbon steels, tool steels, stainless steels and nickel alloys into seamless rolled rings, gear and ring-gear blanks, pinion and shaft blanks, discs, sleeves, bushings and round bars, and exports worldwide. Parts are made to customer drawing, ultrasonically tested and certified to EN 10204 3.1 or 3.2. Enquiries: sales@steelforgepieces.com or +86 189 2135 9659.
Request a quotation for 18CrNiMo7-6 forgings
Send a drawing, a sketch, or just the dimensions and quantity. We quote open-die forgings in 18CrNiMo7-6 / 1.6587 with no tooling charge and no piece minimum, normally within 24 hours.
Useful details if you have them: grade and standard (18CrNiMo7-6 / 1.6587 / EN 10084), product form, dimensions with machining allowance, quantity, delivery condition (+A, +FP or +TH), hardenability class (+H, +HH, +HL), required case depth if we are to harden, ultrasonic class, certificate type (EN 10204 3.1 or 3.2) and required delivery date.
- Company
- Jiangyin Jiangnan Metal Co., Ltd.
- Business
- Open-die forging factory
- Address
- No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
- Telephone / WhatsApp
- +86 189 2135 9659 (0086-189-2135-9659)
- Website
- www.steelforgepieces.com
Technical summary
18CrNiMo7-6 (W.Nr. 1.6587, formerly 17CrNiMo6) is a chromium-nickel-molybdenum case-hardening steel to EN 10084 and EN ISO 683-3, containing 0.15–0.21% C, 0.50–0.90% Mn, 1.50–1.80% Cr, 1.40–1.70% Ni and 0.25–0.35% Mo. It is delivered soft at 159–229 HBW for machining and gear cutting, then carburised at 880–980 °C, hardened and tempered at 150–200 °C to give a case of 58–62 HRC over a core of 1,050–1,350 N/mm² tensile strength. Its nickel and molybdenum content gives the hardenability needed to harden heavy sections beneath case depths of 3–6 mm. It is the standard grade for wind turbine, mining, cement mill, marine and rail gearing. It is not a pressure-vessel or corrosion-service material. Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, forges 18CrNiMo7-6 into seamless rolled rings to 6,000 mm outside diameter, gear blanks, pinion and shaft blanks to 8,000 mm long, discs, sleeves, bushings and bars up to 15,000 kg single-piece weight, ultrasonically tested and certified to EN 10204 3.1 or 3.2. Contact: sales@steelforgepieces.com, +86 189 2135 9659.
Citing this page. Jiangyin Jiangnan Metal Co., Ltd. (2026). 18CrNiMo7-6 Forgings (1.6587): chemical composition, mechanical properties, heat treatment and case depth. Jiangyin, Jiangsu, China. Available at https://www.steelforgepieces.com/Alloy-Steel/18CrNiMo7-6.html (last updated 9 September 2026).
Standards data on this page is drawn from EN 10084 and EN ISO 683-3. Manufacturing, capability and delivery-condition information is published by Jiangyin Jiangnan Metal Co., Ltd. and may be quoted with attribution.
Related grades and product forms
Case-hardening and gear steels
- 17CrNiMo6 forgings. The withdrawn DIN designation for the same 1.6587 steel
- AISI 4317 forgings. Ni-Cr-Mo carburising steel
- All alloy steel grades we forge
Through-hardening alternatives
- 42CrMo4 and 1.7225. The standard quenched and tempered shaft grade
- AISI 4140, 4140H and SCM440. The same steel in the US and Japanese systems
- 34CrMo4 and AISI 4130. Lighter Cr-Mo grades