SNCM 21 (SNCM220) forgings, JIS nickel-chromium-molybdenum case-hardening steel
Datasheet and forging capability for JIS SNCM 21, the pre-1979 designation now standardised as SNCM220: chemical composition, mechanical minimums, carburizing and tempering practice, international equivalents, and the forged shapes we make to drawing.
Grade summary
SNCM 21 is the former JIS designation for SNCM220, a nickel-chromium-molybdenum case-hardening steel. The grade was renumbered from SNCM 21 to SNCM220 when JIS G 4103 was revised in 1979. SNCM220 now sits in JIS G 4053, and the hardenability-guaranteed version, SNCM220H, in JIS G 4052.
Composition runs 0.17–0.23 % C with 0.40–0.70 % Ni, 0.40–0.65 % Cr and 0.15–0.30 % Mo, which puts the grade alongside AISI/SAE 8620, EN 21NiCrMo2 (1.6523), BS 805M20 and GB 20CrNiMo.
Carbon is too low for through hardening, so SNCM 21 is used carburized. The case comes out at roughly 58–62 HRC and the core stays at 248–341 HBW. It is a gear, shaft and bearing-race steel, not a pressure-retaining grade.
Jiangyin Jiangnan Metal Co., Ltd. forges SNCM 21 / SNCM220 to drawing: rings, flanges, discs, shafts, gear blanks, sleeves and bushings, melted by EAF + LF + VD, ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388, and certified to EN 10204 3.1 or 3.2.
- Current name
- SNCM220, of which SNCM 21 is the old name
- Standards
- JIS G 4053; JIS G 4052 for SNCM220H; formerly JIS G 4103
- Steel type
- Low-carbon Ni-Cr-Mo case-hardening (carburizing) steel
- Close equivalents
- AISI 8620, EN 21NiCrMo2 / 1.6523, BS 805M20, GB 20CrNiMo
- Density
- 7.85 g/cm³
- Supplied as
- Open-die forgings and rolled rings, 20 to 8,000 kg per piece
What is SNCM 21?
SNCM 21 is a Japanese Industrial Standards grade of nickel-chromium-molybdenum steel meant for case hardening. The letters stand for Steel, Nickel, Chromium and Molybdenum. The original two-digit numbers (SNCM 21, SNCM 22, SNCM 23 and so on) were sequential grade numbers and said nothing about composition.
JIS G 4103 was revised in 1979 and the SNCM family was renumbered so that the number reflects composition and strength class. SNCM 21 became SNCM220 and SNCM 22 became SNCM415. JIS G 4103 was later folded into JIS G 4053, Low-alloyed steels for machine structural use, which is the standard to quote on an order today.
An old drawing calling for SNCM 21 is satisfied by material certified to SNCM220. We accept either designation on an enquiry and certify against the current standard, adding the legacy name to the certificate where the drawing requires it.
Grades this one gets confused with. SNCM 21 (SNCM220) is not SNCM420 or SNCM439; those are higher-alloy grades at different carbon levels. It is also unrelated to SCM 21 / SCM420, the chromium-molybdenum steels in JIS G 4105. An earlier version of this page cited JIS G 4105 for SNCM 21. That was wrong, and the standards referenced here are JIS G 4103 and JIS G 4053.
Chemical composition of SNCM 21 / SNCM220
| Element | Symbol | Specified range | Role in the grade |
|---|---|---|---|
| Carbon | C | 0.17 to 0.23 | Kept low so the core stays tough; case carbon comes from carburizing |
| Silicon | Si | 0.15 to 0.35 | Deoxidation, modest strengthening |
| Manganese | Mn | 0.60 to 0.90 | Hardenability, sulphur control |
| Phosphorus | P | 0.030 max | Impurity, limited for toughness |
| Sulphur | S | 0.030 max | Impurity, limited for transverse properties |
| Nickel | Ni | 0.40 to 0.70 | Core toughness, low-temperature impact |
| Chromium | Cr | 0.40 to 0.65 | Hardenability, case hardness and wear resistance |
| Molybdenum | Mo | 0.15 to 0.30 | Hardenability in heavy sections, resists temper embrittlement |
| Copper | Cu | 0.30 max | Residual limit |
| Iron | Fe | Balance |
Ranges are the JIS specified limits for SNCM220. Some editions and secondary databases give narrower chromium and molybdenum bands, Cr 0.40 to 0.60 % and Mo 0.15 to 0.25 %. Where a project is chemistry-critical, state the edition on the enquiry and the heat will be selected accordingly. The mill certificate for the actual heat governs.
Nickel, chromium and molybdenum are added together in modest amounts. Nickel and molybdenum working together are what let a forging of this grade harden through a substantial section, and the molybdenum holds off the high-temperature temper brittleness that limits plain nickel-chromium steels.
Mechanical properties
JIS specifies the following minimums for SNCM220 on a test piece given the standard double quench and low-temperature temper. They describe the core of a case-hardened part. The carburized surface is far harder.
| Property | Requirement | Imperial |
|---|---|---|
| Tensile strength, Rm | 830 N/mm² min | 120 ksi min |
| Yield strength, Re | Not specified by JIS for this grade | |
| Elongation, A | 17 % min | 17 % min |
| Reduction of area, Z | 40 % min | 40 % min |
| Charpy impact value | 59 J/cm² min | 281 ft·lb/in² min |
| Hardness | 248 to 341 HBW | 24 to 37 HRC approx. |
| Case hardness after carburizing | 58 to 62 HRC | 653 to 746 HV |
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Modulus of elasticity | 200 to 215 GPa | 29 to 31 × 10³ ksi |
Case hardness and case depth are not fixed by the grade. They follow the carburizing cycle you specify. Annealed delivery hardness for machining is normally 200 to 250 HBW.
Why a case-hardening steel behaves differently
A finished SNCM 21 part is two materials in one body. Carbon diffuses into the surface at 900 to 930 °C, so after quenching the outer layer is high-carbon martensite at 58 to 62 HRC while the low-carbon core below it stays at 248 to 341 HBW. The skin carries contact stress and wear. The core absorbs shock and stops cracks running. One hardness figure therefore never describes the part, which is why drawings for this grade call out surface hardness, core hardness and effective case depth separately.
Heat treatment of SNCM 21 forgings
| Operation | Temperature | Cooling | Purpose |
|---|---|---|---|
| Forging | 1,150 to 1,200 °C start 850 °C finish min | Slow cool or into furnace | Break down the cast structure; minimum 3:1 forging ratio on our shop |
| Annealing | 830 to 870 °C | Furnace cool | Machinable delivery condition, 200 to 250 HBW |
| Normalizing | 850 to 900 °C | Air | Uniform grain size before machining or carburizing |
| Carburizing | 900 to 930 °C | Held to depth | Raise surface carbon to about 0.8 % |
| First quench | 850 to 900 °C | Oil | Refine the core structure |
| Second quench | 800 to 850 °C | Oil | Harden the case |
| Tempering | 150 to 200 °C | Air | Relieve quench stress, keep case hardness |
| Stress relief | 550 to 650 °C | Slow cool | After heavy machining or welding, before final grinding |
The double quench above is the practice given for SNCM220 in JIS. Single quench and temper direct from the carburizing furnace is also common and is used where distortion control matters more than maximum core refinement. Tell us which route the drawing requires.
Most customers order SNCM 21 forgings in the annealed or normalized condition and carburize after machining, since carburizing a rough forging wastes the case. Where a finished part is wanted, we can arrange carburizing, hardening and tempering to a specified effective case depth and supply the hardness traverse with the certificate.
SNCM 21 equivalent grades and cross-reference
| Standard and region | Grade | Number | Relationship |
|---|---|---|---|
| JIS G 4053, Japan | SNCM220 | Current designation of SNCM 21 | |
| JIS G 4052, Japan | SNCM220H | Same chemistry, hardenability guaranteed | |
| AISI / SAE, USA | 8620, 8620H | UNS G86200 | Closest widely traded equivalent |
| EN 10084, Europe | 20NiCrMo2-2, 21NiCrMo2 | 1.6523 | European case-hardening counterpart |
| BS 970, UK | 805M20, 805H20 | Equivalent British grade | |
| AFNOR, France | 20NCD2 | Equivalent French grade | |
| GB/T 3077, China | 20CrNiMo, 20CrNiMoH | Chinese counterpart, most economical route | |
| ISO 683-11 | 20NiCrMo2 | ISO case-hardening grade | |
| Near grades | SAE 8615, 8617, 8622 | Same family, different carbon; substitute only with engineering approval |
Cross-references are for selection guidance. National standards differ in residual-element limits, hardenability bands and test conditions, so an equivalent grade is not automatically an acceptable substitute on a qualified drawing. Where a substitution is under consideration we send both chemistries side by side before any material is committed.
SNCM 21 forged products and size range
We forge SNCM 21 / SNCM220 to customer drawing rather than holding it as stock sizes, which suits the gearbox, bearing and machinery work where the grade is normally specified.
| Product | Size range | Typical use |
|---|---|---|
| Seamless rolled rings | OD 200 to 3,000 mm, height 800 mm max | Gear rims, bearing races, slewing rings |
| Gear and pinion blanks | OD 100 to 2,000 mm | Spur, helical and bevel gear blanks |
| Shafts and spindles | Ø 80 to 800 mm, length 6,000 mm max | Transmission and pinion shafts |
| Discs and hubs | Ø 150 to 2,500 mm | Coupling hubs, gear discs |
| Sleeves and bushings | OD 100 to 1,200 mm | Wear sleeves, bearing housings |
| Flanges and rings | OD 150 to 2,000 mm | Machinery connections |
| Round bars and blocks | Ø 60 to 700 mm | Machining stock |
| Piece weight | 20 to 8,000 kg |
Surface condition: as-forged, shot-blasted, rough-turned or proof-machined. Machining allowance and tolerances to your drawing, or to ISO 8062-3 and our standard allowance table where the drawing gives none.
Grade selection. SNCM 21 is a carburizing steel. For a pressure-retaining flange, valve body, tube sheet or vessel shell it is the wrong grade; those parts call for a through-hardening or pressure-vessel steel such as 42CrMo4, AISI 4140 or AISI 8630. Send the drawing and the duty and we will say which grade fits before you order.
How we make and verify SNCM 21 forgings
- Melting. EAF + LF + VD as standard, which gives low hydrogen and tight residuals. ESR is available where inclusion cleanliness is critical.
- Ingot inspection and cropping. Ingot ends are removed to clear shrinkage and segregation before forging.
- Open-die forging or ring rolling. Upsetting and drawing on hydraulic presses to a minimum 3:1 forging ratio, finishing above 850 °C so the grain structure is worked throughout the section.
- Heat treatment. Annealing, normalizing, or carburize, harden and temper, in furnaces with calibrated recording charts supplied with the order.
- Non-destructive testing. Ultrasonic inspection to EN 10228-3, SEP 1921 or ASTM A388 at the acceptance class you nominate. MPI to ASTM E709 and dimensional inspection on request.
- Mechanical and chemical testing. Tensile, impact and hardness on a representative test block, chemistry by spectrometer, grain size and microstructure where specified.
- Certification. EN 10204 3.1 as standard, or 3.2 with third-party witness by SGS, TÜV, BV or your own inspector.
Test specimens are taken in the direction and location your specification requires. We hold retained samples so a certificate can be reissued years later if your end client asks for it.
Where SNCM 21 forgings are used
Power transmission
- Gear and pinion blanks
- Ring gears and gear rims
- Pinion and output shafts
- Industrial and marine gearbox parts
Bearings and rolling contact
- Bearing inner and outer races
- Roller and cam followers
- Slewing-ring raceways
Heavy machinery
- Wear sleeves and bushings
- Mill and conveyor rolls
- Pins, links and couplings
Automotive and off-highway
- Drive and axle shafts
- Differential and transmission gears
- Splined hubs
What these have in common is rolling or sliding contact combined with shock loading, which is the duty a hard case over a tough core was developed for. Where a part instead needs uniform strength through a heavy section, a quenched and tempered grade such as 34CrNiMo6 or 18CrNiMo7-6 is usually the better choice.
How to request a quotation
Send the items below to sales@steelforgepieces.com and you will normally have a price and lead time within one working day.
- Drawing or dimensions. A PDF or STEP file, or simply OD by ID by height for a ring and diameter by length for a shaft.
- Grade and standard edition. SNCM 21, SNCM220 or an equivalent, and the standard the drawing calls up.
- Quantity and delivery date, including whether this is a prototype or a repeat order.
- Delivery condition. As-forged, annealed, normalized, or fully heat treated with a required case depth and hardness.
- Testing and certification. UT class, mechanical test requirements, EN 10204 3.1 or 3.2, and any third-party witness.
- Destination port, for an FOB Shanghai, CIF or DAP price.
Frequently asked questions about SNCM 21
Is SNCM 21 the same as SNCM220?
Yes. SNCM 21 is the pre-1979 JIS designation and SNCM220 is the current name for the same nickel-chromium-molybdenum case-hardening steel. The grade was renumbered when JIS G 4103 was revised in 1979, and material certified to SNCM220 satisfies a drawing calling for SNCM 21.
Which standard covers SNCM 21 today?
JIS G 4053, Low-alloyed steels for machine structural use, which absorbed the former JIS G 4103. The hardenability-guaranteed version, SNCM220H, is covered by JIS G 4052. SNCM 21 is not part of JIS G 4105, which covers the chromium-molybdenum SCM grades.
What is the American equivalent of SNCM 21?
AISI/SAE 8620 (UNS G86200) is the closest widely traded equivalent, with 8620H where hardenability must be guaranteed. European drawings usually specify 21NiCrMo2 or 20NiCrMo2-2, material number 1.6523; British drawings 805M20; Chinese drawings 20CrNiMo.
What hardness can SNCM 21 reach?
After carburizing, quenching and low-temperature tempering the case normally reaches 58 to 62 HRC, while the core stays in the JIS range of 248 to 341 HBW. In the annealed condition for machining the hardness is usually 200 to 250 HBW. A single hardness number does not describe a case-hardened part, so specify surface hardness, core hardness and effective case depth separately.
Can SNCM 21 be welded?
Yes, with care, and before carburizing. The low carbon content gives reasonable weldability, but the alloy content means preheat of about 200 to 300 °C, low-hydrogen consumables and post-weld stress relief at 550 to 650 °C are advisable. Welding on or through a carburized case is not recommended, because the high-carbon surface layer cracks readily.
Is SNCM 21 suitable for pressure vessels or valve bodies?
No. It is a carburizing gear and shaft steel with no pressure-vessel approval, and the mechanical properties in the standard describe the core of a case-hardened part. For pressure-retaining forgings use a through-hardening grade such as 42CrMo4, AISI 4140 or AISI 8630, or a dedicated pressure-vessel specification such as ASTM A182 or A350.
What is the minimum order quantity for SNCM 21 forgings?
One piece. Because SNCM 21 forgings are made to drawing rather than pulled from stock, we quote single prototypes as well as production batches. The piece price reflects tooling and set-up spread over the quantity.
What lead time should I allow?
As a guide, 25 to 35 days for forging in the annealed or normalized condition, and 40 to 55 days where carburizing, hardening, third-party witnessed testing or proof machining is included. Firm dates are confirmed with the quotation against current press loading.
About the supplier of this data
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, producing forged rings, flanges, shafts, discs, sleeves and seamless rolled rings in carbon, alloy, tool and stainless steels and nickel alloys. SNCM 21 / SNCM220 is one of the case-hardening grades we forge to customer drawing, melted by EAF + LF + VD and certified to EN 10204 3.1 or 3.2.
Contact
Jiangyin Jiangnan Metal Co., Ltd.No.1 Chengxiqiao Road, Zhouzhuang Town,
Jiangyin City, Jiangsu Province, China
Tel and WhatsApp: +86 189 2135 9659
Email: sales@steelforgepieces.com
Web: www.steelforgepieces.com
Capability
- Open-die forging and ring rolling
- Piece weight 20 to 8,000 kg
- In-house heat treatment and UT
- Exporting to Europe, North America, the Middle East and Southeast Asia
Reference
Data on this page is compiled from the JIS specifications for SNCM220 and from our own production practice. Reviewed by the Jiangnan Metal technical department. Cite as: SNCM 21 (SNCM220) forgings, Jiangyin Jiangnan Metal Co., Ltd., updated 18 September 2026.