Case hardening steel for open-die forgings and seamless rolled rings

20NiCrMo2-2 Forgings (1.6523, SAE 8620, 805M20, SNCM220)

• 20NiCrMo2-2
• 1.6523
• 21NiCrMo2
• SAE / AISI 8620
• UNS G86200
• 805M20
• SNCM220
• 20NCD2
• 20CrNiMo
• 20HGNM
• SS 2506
• EN 10084

Published 18 May 2016. Last updated 10 September 2026, reviewed by the Jiangyin Jiangnan Metal metallurgical engineering team.

Material number

1.6523EN 10084:2008

Steel type

Ni-Cr-Mocase hardening / carburising

Carbon

0.17–0.23% by mass

Case hardness

58–64HRC after carburising

Core yield, 30 mm

590MPa min

Core tensile, 30 mm

830–1130MPa

Carburising

880–980°C

Forge from

1100°C, finish above 900

Density

7.86g/cm³

Delivered

≤230HB, ready to machine

What 20NiCrMo2-2 forged products can you buy?

Almost everything we make in this grade ends up carburised, so the geometry decides the forging route. Seamless ring rolling is the right answer for gear blanks, bearing races and any part where a continuous circumferential grain flow matters. Open-die forging covers shafts, pinion blanks, discs and blocks. Upset forging handles short heavy hubs and flange forms. On a carburised part the forging route is not just a cost decision: grain flow that follows the tooth or race profile is what keeps a bending fatigue crack from running straight through the root.

Size ranges are the plant envelope across all grades. Because hardenability limits useful core strength above roughly 60–75 mm ruling section, most 20NiCrMo2-2 orders sit well inside these figures. Send the pre-carburising drawing rather than a billet size. On a gear blank the forging route usually saves more than any other decision on the order.

What is 20NiCrMo2-2, and why is it used?

A gear tooth has to satisfy two contradictory requirements. The flank has to be hard enough to resist pitting and wear under contact stress, and the root has to be tough enough to absorb shock without cracking. No single homogeneous steel does both well. Carburising solves it by making the part out of two materials: a high-carbon martensitic skin and a low-carbon tough core, produced from one billet in one heat-treatment cycle.

20NiCrMo2-2 is the alloy that made this cheap. At 0.17–0.23% carbon it machines easily and normalises to a uniform ferrite–pearlite structure. The three alloying additions each do one job:

• Nickel, 0.40–0.70%. Toughens both case and core, and keeps the core ductile at high strength. It is the reason this grade survives shock loading where a plain chromium carburising steel would crack.
• Chromium, 0.35–0.70%. Raises hardenability and forms the carbides that give the case its hardness and wear resistance.
• Molybdenum, 0.15–0.25%. Suppresses temper embrittlement, improves hardenability through the section and helps keep the case hard at slightly elevated running temperatures.

Compared with the plain chromium grades 16MnCr5 and 20MnCr5, the nickel and molybdenum buy toughness and a more forgiving quench. Compared with the heavy-duty grade 18CrNiMo7-6, 20NiCrMo2-2 has roughly a third of the nickel and half the chromium, so it costs less and hardens less deeply. That trade sets its whole application range: light to medium sections, high volume, moderate to high load.

What are the equivalent grades of 20NiCrMo2-2?

This one chemistry is bought under more than a dozen names, because it was standardised independently in the United States, Britain, France, Germany, Italy, Japan, China, Russia and Scandinavia. All of the designations in Table 2 describe the same nominal 0.20C–0.5Ni–0.5Cr–0.2Mo composition, and we accept purchase orders under any of them. They are not automatically interchangeable in acceptance testing: the bands differ at the edges, and the product-form standard decides the test regime.

Table compiled by Jiangyin Jiangnan Metal Co., Ltd. from EN 10084:2008 and the corresponding national standards. Standards are cited by number only; always work to the revision in force at your contract date. Matching a name here does not by itself prove equivalence for a specific acceptance requirement.

What is the chemical composition of 20NiCrMo2-2?

The table below is the EN 10084:2008 ladle-analysis requirement for material number 1.6523. Every heat we forge is supplied with the ladle analysis on the mill certificate; product analysis on the finished forging can be added on request, in which case the permissible deviations in the third row apply.

Source: EN 10084:2008, case hardening steels, technical delivery conditions. Balance iron. Lead 0.15–0.35% can be added by agreement for improved machinability, which changes the designation. Grain size 5 or finer is required.

What each element does

What are the mechanical properties of 20NiCrMo2-2?

Two sets of numbers matter on a carburised part, and confusing them is the commonest source of argument at inspection. Case properties are surface hardness and case depth, measured on the finished part. Core properties are tensile, yield, elongation and core hardness, measured on a test blank of a stated diameter that has been core hardened and stress relieved. A certificate quoting 62 HRC and one quoting 590 MPa yield are describing the same part in different places.

Core properties by ruling section

Values per UNI 7846:1978 for reference, consistent with EN 10084 practice. Hardness figures at 30 and 63 mm are for information. Note the pattern: core strength roughly halves between an 11 mm and a 63 mm section. That fall, not any metallurgical failure, is what limits this grade to light and medium sections.

Forged-condition core properties

Source: UNI 8550:1984, forged 20NiCrMo2, given for reference. Above 50 mm section, state on the order whether tensile tests are to be taken longitudinally or transversely: transverse values run lower, and an unqualified requirement is the usual cause of a rejected certificate.

As-delivered condition

We supply forgings in whichever pre-carburising condition your process needs. The hardness bands below are what you machine against.

If your drawing does not name a delivery condition, we supply normalised. For a precision gear that will be ground after carburising, isothermal annealing is usually the better choice: it buys the most consistent distortion behaviour and pays for itself in grinding stock.

Case hardness, case depth and carburising

Case depth is the specification, and it is set by furnace time. Carbon diffuses according to Fick's law, so case depth grows with the square root of time: doubling the depth costs roughly four times the hours. That single relationship governs the cost of a carburised part more than anything else on the drawing.

Published reference figures for gas carburising at normal carbon potential. Actual depth depends on temperature, carbon potential, furnace type, atmosphere control and part geometry. Qualify the cycle on a coupon from the same heat before releasing production parts, and verify to ISO 2639.

If the drawing calls for 58 HRC minimum at the surface, temper at 150–200 °C and do not let a subsequent stress-relief or plating bake exceed it. This is a common route to a rejected batch.

Transformation temperatures

How deeply does 20NiCrMo2-2 harden?

Hardenability is measured by the Jominy end-quench test: one end of a standard bar is water quenched and hardness is read at intervals along its length. The EN 10084 band for 20NiCrMo2-2 with grain size 5 or finer is below.

Test conducted from 870 °C, water quenched. Read this as the practical section limit: hardness has fallen to about 20–33 HRC only 11 mm from a directly water-quenched surface. That is why core strength collapses on heavy sections and why the grade should be replaced above roughly 60–75 mm ruling section. If your drawing demands guaranteed hardenability, order to 8620H (UNS H86200) and require the Jominy curve on the certificate.

What are the physical properties of 20NiCrMo2-2?

20NiCrMo2-2 vs 16MnCr5, 20MnCr5 and 18CrNiMo7-6: which gear steel?

Almost every carburising enquiry comes down to a choice between four grades. The deciding variable is not strength, it is ruling section: how thick the part is where it has to be strong. Pick the cheapest grade that still hardens through that section, and no cheaper.

Compositions from EN 10084:2008. 17CrNiMo6 is the older DIN designation for material number 1.6587 and is functionally the same choice as 18CrNiMo7-6. Full data for that grade is on the 18CrNiMo7-6 page.

Three questions that settle it

1. What is the ruling section where the part must be strong? Not the outside size, but the thickness the core hardening has to reach. Above about 60–75 mm, move to 18CrNiMo7-6 and stop arguing about price.
2. Does the part see shock, or only steady contact load? Shock is where nickel earns its cost. A plain chromium grade like 20MnCr5 is perfectly adequate for a steady-load gear and a poor choice for a mining drivetrain.
3. Where will the part be re-ordered and repaired? If spares will be sourced in North America or Asia, 20NiCrMo2-2 / 8620 is the safest specification on the list: every mill in the world makes it, under one name or another.

How is 20NiCrMo2-2 forged and heat treated?

The forging itself is undemanding. This is a low-carbon low-alloy steel with a wide hot-working window. What is demanding is everything that prepares the part for carburising. Grain size, structural uniformity and residual stress in the blank all show up later as distortion on the finished gear, and by then it is expensive.

1. Melt and verifyEAF + LF + VD. Ladle analysis checked against EN 10084 limits, heat number recorded and carried through to the certificate. Vacuum degassing controls hydrogen and keeps the inclusion rating down, which matters for bending fatigue at the tooth root.
2. Heat for forgingSoak through section into the 900–1100 °C hot-forming range. On heavy sections, soak through. Do not surface-heat and start hammering.
3. Forge or ring rollTotal reduction of at least 3:1 to close cast porosity and refine the structure. On rings and gear blanks, roll so the grain flow follows the circumference. Finish above about 900 °C; deformation below that raises loads and risks surface cracking.
4. Controlled coolingCool in still air or under a hood as the section requires. Uncontrolled cooling of a heavy forging leaves bainite in the structure, which raises hardness, ruins machinability and drives distortion in carburising.
5. Pre-carburising heat treatmentNormalise at 860–880 °C in air for most work. For precision gears, use isothermal annealing at 850 °C with a furnace cool to 650 °C then air, which gives 161–212 HB and the most repeatable distortion behaviour. Ferrite-pearlite annealing at 950–1000 °C with a quick cool gives 149–194 HB where the drawing calls for it.
6. Rough machineTo the pre-carburising drawing, leaving grinding stock on functional surfaces. Mask or copper-plate anything that must stay soft: threads, bores that will be welded, areas to be drilled after treatment.
7. Carburise880–980 °C, held for the time that gives the specified case depth (see the calculator). Low-pressure vacuum carburising with gas quenching is the route for minimum distortion on precision work.
8. HardenQuench from 800–830 °C in oil, polymer or salt. Where core toughness governs, add a separate core-refining step at 860–900 °C between carburising and the case hardening quench. It refines the grain coarsened by the long carburising hold, at the cost of a cycle.
9. Temper150–200 °C. Relieves quenching stress and leaves case hardness at about 62–64 HRC. Sub-zero treatment before tempering is worth considering where retained austenite must be minimised for dimensional stability.
10. Finish and inspectGrind or hard-turn to the final drawing. Verify case depth to ISO 2639, surface and core hardness, microstructure, grain size, magnetic particle examination and ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388. Issue the EN 10204 certificate.

Machining, grinding and surface treatment

Machining before carburising

This is the easy part of the job and the reason the grade exists. At 149–230 HB in the delivered condition, 20NiCrMo2-2 machines like a mild alloy steel: carbide tooling at conventional speeds, no special handling. Two points worth planning for:

• Leave the right grinding stock. A carburised gear moves. Typical allowance is 0.1–0.3 mm per flank for a ground tooth, more on long thin parts. Too little and the case grinds through; too much and the ground surface never reaches full case hardness.
• Consider the S grade for volume work. If the part is machined in the tens of thousands and is not loaded across the grain, 20NiCrMoS2-2 (1.6526) with 0.020–0.040% sulphur cuts cycle time noticeably. Do not use it for a highly stressed gear.

Grinding after carburising

Grinding a 62 HRC case is where good parts get destroyed. Grinding burn re-tempers the surface locally, replaces the useful compressive residual stress with tensile stress, and produces exactly the surface condition that starts a bending fatigue crack. Use free-cutting wheels, generous coolant directed into the cut, light final passes, and specify a nital etch inspection to ISO 14104 on critical gear teeth. A burnt tooth flank looks perfect until it fails.

Surface treatment

20NiCrMo2-2 has no corrosion resistance. Forgings ship oiled for transit; for service, specify phosphating, black oxide, zinc plating or paint. If plating, control hydrogen embrittlement: bake within four hours of plating, at 190–220 °C, and check that the bake does not exceed the tempering temperature you used.

How do 20NiCrMo2-2 parts fail, and how do you stop it?

What can Jiangyin Jiangnan Metal forge in 20NiCrMo2-2?

20NiCrMo2-2 is a stock grade for us rather than a made-to-order melt, which is the main practical difference between this page and our specialty-alloy pages. Billet is normally available without waiting for a dedicated heat, so lead time is driven by the forging and heat-treatment queue rather than by the mill.

Rolled ring OD

200–2,500mm, radial-axial mills

Forging diameter

80–6,000mm plant envelope

Single piece weight

10–15,000kg

Shaft length

≤8,000mm

Bar diameter

25–500mm

Ring wall, minimum

30mm

Employees

460incl. 41 engineers

Lead time

8–12weeks typical

Which standards and certificates apply to 20NiCrMo2-2 forgings?

Quality management is certified to ISO 9001:2015. Third-party witness certificates are issued through the inspection body you nominate: Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or SGS. Customers keep an unrestricted right to witness any production stage, including chemistry, forging, heat treatment and mechanical testing.

How do you specify a 20NiCrMo2-2 forging order?

1. Name the grade and the standard together. Write 20NiCrMo2-2 / 1.6523 to EN 10084 or SAE 8620 to ASTM A29. The material number 1.6523 is the least ambiguous identifier on the page.
2. State the delivery condition. Normalised, isothermally annealed, soft annealed or ferrite-pearlite annealed, with the hardness band you will machine against. If you leave this out you will get normalised.
3. Give the pre-carburising drawing, not the billet size. Tell us the grinding and distortion stock you want left on. We can advise, but only you know your heat-treatment line's behaviour.
4. Specify case requirements even if we are not doing the carburising. Effective case depth at flank and root, surface hardness range, core hardness range and the measurement standard. It affects how we forge the grain flow and how much stock we leave.
5. Say whether you need guaranteed hardenability. If yes, order to 8620H / UNS H86200 and require the Jominy curve on the certificate. A standard 1.6523 heat is not hardenability-guaranteed.
6. Define non-destructive examination and its acceptance class. “UT per EN 10228-3, quality class 3” is a specification; “ultrasonic test” is not.
7. State test direction and position above 50 mm section. Longitudinal or transverse, mid-radius or surface. Unqualified tensile requirements are the usual cause of a rejected certificate.
8. Give quantity, date, Incoterm and destination. And the certificate type, 3.1 or 3.2, because witnessed release adds one to two weeks.

Drawing callout you can copy

MATERIAL:      20NiCrMo2-2 / W.Nr. 1.6523 per EN 10084
               (equivalent SAE 8620 / 805M20 / SNCM220 / 20CrNiMo acceptable,
                cross-certification to be shown on the certificate)
MELT ROUTE:    EAF + LF + VD, fully killed, fine grain, ASTM E112 grain size 5 or finer
FORM:          Seamless rolled ring / open-die forging to drawing no. ______
               Forged reduction 3:1 minimum, circumferential grain flow
DELIVERY
CONDITION:     Isothermally annealed, 161-212 HB
               (or normalised 860-880 deg C air cool, state which)
CHEMISTRY:     Ladle analysis reported for C, Si, Mn, P, S, Cr, Mo, Ni
               P 0.025% max, S 0.035% max
CLEANLINESS:   Inclusion rating to ASTM E45 method A or DIN 50602, limits ______
CASE (by customer, after machining):
               Effective case depth ______ mm at 550 HV, flank and root
               Surface hardness 58-62 HRC, core hardness ______ HRC
               Carburise 880-980 deg C, harden 800-830 deg C, temper 150-200 deg C
               Case depth verified to ISO 2639
NDE:           UT per EN 10228-3 quality class 3 (or SEP 1921 / ASTM A388)
               MT per EN 10228-1 on machined surfaces
MECHANICAL:    Core tensile per EN 10084 for ______ mm ruling section,
               test direction ______ , test position ______
CERTIFICATE:   EN 10204 3.1 (3.2 with third-party witness if stated on the PO)
MARKING:       Heat number, grade, condition and drawing number,
               low-stress stamped or vibro-etched

Seven mistakes buyers make with 20NiCrMo2-2

1. Citing EN 10083 instead of EN 10084. EN 10083 is for quenched and tempered steels and does not contain this grade. The order cannot be certified as written.
2. Specifying it for pressure-boundary parts. Valve bodies, flanges on pressure joints, tube sheets and vessel components need A105, A182, A350 or a stainless grade. A carburising steel has no business in that role, whatever an old catalogue page says.
3. Using it above its hardenability limit. Core yield at 63 mm is 490 MPa minimum. Specifying 20NiCrMo2-2 for a 150 mm pinion shaft and expecting 18CrNiMo7-6 performance is the single most common technical error on this grade.
4. Quoting a surface hardness with no case depth. 62 HRC over a 0.2 mm case will crush under contact load. Depth is the specification; hardness alone is not.
5. Assuming 8620 and 1.6523 are certified identically. They are commercially interchangeable and technically near-identical, but the acceptance standards differ. Ask for cross-certification rather than assuming.
6. Ordering the S grade for a loaded gear. 20NiCrMoS2-2 machines better and is weaker across the grain. Fine for a bushing, wrong for a tooth root.
7. Machining a gear blank from plate or solid bar. It cuts the grain flow across the tooth root and throws away the fatigue benefit you paid a forging price for. Ring roll it.

Where is 20NiCrMo2-2 used?

It is a power-transmission steel. Everywhere it appears, the part has a surface that must resist contact and wear and a body that must not crack. That is the whole application space, and it is a large one.

Two worked examples

Example 1: choosing between 20NiCrMo2-2 and 18CrNiMo7-6 for a pinion shaft

Given. A gearbox pinion shaft, 95 mm diameter at the toothed section, driven by a reversing mill drive with substantial shock loading, tooth module 8, required surface hardness 58 HRC minimum.

Assessment. Surface hardness is not the discriminator: both grades reach 58–62 HRC in the case. The ruling section is. At 95 mm, 20NiCrMo2-2 cannot core harden usefully. The Jominy band shows hardness down to 20–33 HRC only 11 mm from a quenched surface, and the published core yield of 490 MPa minimum at 63 mm is already falling away. With a module of 8, the required effective case depth is roughly 1.2–2.0 mm, and beneath that the core has to hold the tooth up. A soft core under a deep case is how case crushing starts.

Decision. Specify 18CrNiMo7-6 / 1.6587. The extra nickel and chromium buy the hardenability the section needs, and the shock duty justifies the toughness. If the drawing were 45 mm rather than 95 mm, 20NiCrMo2-2 would be the correct and cheaper answer.

Example 2: why a rolled ring beats a machined disc on a gear blank

Given. A finished ring gear blank, 620 mm OD × 480 mm ID × 210 mm high, in 20NiCrMo2-2.

Method. Net volume = π/4 × (0.620² − 0.480²) × 0.210 = 0.0254 m³. At 7,860 kg/m³ that is about 200 kg finished. Ring rolled with 25% stock, the forging is roughly 250 kg. Machined from a solid forged disc of the same outside diameter and height, the input is about 498 kg, so you buy, forge and then cut away nearly 300 kg.

Result. Ring rolling roughly halves the purchased weight. On a low-alloy steel the raw-material saving alone is smaller than it would be on a superalloy, but the second effect matters more: the rolled ring has continuous circumferential grain flow. Teeth cut into it have grain running along the root fillet rather than across it. On a bending-fatigue-limited gear that is worth considerably more than the material saved, and it is not something you can add back later.

Glossary

20NiCrMo2-2 frequently asked questions

References

1. CEN, EN 10084:2008, Case hardening steels: technical delivery conditions. The governing standard for 20NiCrMo2-2 / 1.6523: chemical composition, permissible deviations, hardenability bands and delivery conditions.
2. CEN, EN 10204, Metallic products: types of inspection documents. Defines the 3.1 and 3.2 certificates referred to throughout this page.
3. CEN, EN 10250-3, Open die steel forgings for general engineering purposes: alloy special steels.
4. ISO, ISO 2639, Steels: determination and verification of the depth of carburized and hardened cases, and ISO 18203 for case-depth determination.
5. ASTM International, ASTM A29/A29M and ASTM A322 for SAE 8620 bar; SAE J404 chemistry and SAE J1268 hardenability for 8620H.
6. Lucefin Group, 20NiCrMo2-2 technical card to EN 10084:2008. Source of the transformation temperatures, heat-treatment temperature ranges, core property tables, case-depth-against-time data and physical constants reproduced here.
7. Saarstahl, 20NiCrMo2-2 (21NiCrMo2) / 20NiCrMoS2-2 material specification sheet. Application guidance and core tensile ranges.
8. UNI, UNI 7846:1978 and UNI 8550:1984. Core property tables for hot-rolled and forged material, reproduced for reference.
9. CEN, EN 10228-1 and EN 10228-3; SEP 1921; ASTM A388, covering magnetic particle and ultrasonic examination of steel forgings.
10. ISO, ISO 6336, and AGMA, AGMA 2001, load capacity calculation for spur and helical gears, including the material quality grades that a change of steel can affect.

Standards are cited by number; always work to the revision in force at your contract date. Property values on this page are published typical and specification figures for screening and are not design allowables. Test results on our certificates are independent and traceable to calibrated equipment.

About the manufacturer, and how to cite this page

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, with 460 employees including 9 senior and 32 intermediate engineers. The plant runs 1 t to 9 t open-die hammers, 4,500 t and 5,000 t hydraulic presses and radial-axial ring rolling mills to 2,500 mm outside diameter, with in-house heat treatment, machining, mechanical testing and non-destructive examination. Alongside 20NiCrMo2-2 / 1.6523 we forge the carbon, alloy and tool steels, the precipitation-hardening and duplex stainless families, and the nickel and cobalt high-temperature alloys. Quality management is certified to ISO 9001:2015; material is supplied with EN 10204 3.1 certification as standard and 3.2 with third-party witness on request.

Related grades and forged products

Other case hardening and alloy steel grades

18CrNiMo7-6 · AISI 4317 · AISI 4820 · 18NiCrMo5 · 17NiCrMo6-4 · 18NiCrMo6-4 · AISI 4140 · 34CrNiMo6 · All alloy steel grades

Product forms we forge in this grade

Forged rings · Forged discs · Forged gears · Forged shafts · Forged eccentric shafts · Forged cylinders · Forged rolls · All forged products