JIS G 4053 nickel-chromium-molybdenum alloy structural steel. Former designation SNCM8.
SCNM439 does not appear in any published standard. It is a common misspelling of JIS SNCM439, the nickel-chromium-molybdenum alloy structural steel listed in JIS G 4053. The closest equivalent grade is AISI 4340.
SNCM439 contains 0.36 to 0.43 % carbon, 1.60 to 2.00 % nickel, 0.60 to 1.00 % chromium and 0.15 to 0.30 % molybdenum. Quenched and tempered it reaches at least 980 MPa tensile strength, 885 MPa yield strength and 293 to 352 HBW. It hardens deeply, which is why it is used for heavy sections above roughly 150 mm where 42CrMo4 will not harden through. Jiangyin Jiangnan Metal Co., Ltd. forges SNCM439 at its plant in Jiangyin, Jiangsu, China, in weights from 50 kg to 30,000 kg, with EN 10204 3.1 or 3.2 certificates.
SCNM439 is SNCM439 with the middle two letters swapped. The JIS prefix stands for Steel, Nickel, Chromium, Molybdenum, so the order is S-N-C-M. No standards body publishes a grade called SCNM439: not JIS, not ASTM, not EN, not GB, not GOST. When a drawing or an enquiry reaches us marked SCNM439, we read it as JIS G 4053 SNCM439 and quote on that basis.
SNCM439 itself is a medium-carbon, low-alloy steel meant to be quenched and tempered. The nickel content raises toughness and keeps impact energy usable at low temperature. Chromium and molybdenum carry hardenability into the middle of a thick section and stop the steel softening too fast during tempering. The practical result is that a 500 mm forged shaft can hold one strength band from surface to core. Plain carbon steels and Cr-Mo steels cannot do that at that size.
Ordering note. Write JIS G 4053 SNCM439 on the purchase order, the drawing and the test certificate. Mills and third-party inspectors will reject a certificate issued against a designation that does not exist in any standard. If your own system is locked to the SCNM439 spelling, we can issue the certificate as "SNCM439 (customer designation SCNM439)" so that both records reconcile.
Below are the ladle analysis limits of JIS G 4053 SNCM439 in weight percent, with AISI 4340 set alongside for comparison. Product analysis tolerances to JIS G 0321 apply to finished forgings.
| Grade | C | Si | Mn | P max | S max | Ni | Cr | Mo | Cu max |
|---|---|---|---|---|---|---|---|---|---|
| SNCM439 | 0.36–0.43 | 0.15–0.35 | 0.60–0.90 | 0.030 | 0.030 | 1.60–2.00 | 0.60–1.00 | 0.15–0.30 | 0.30 |
| AISI 4340 | 0.38–0.43 | 0.15–0.35 | 0.60–0.80 | 0.035 | 0.040 | 1.65–2.00 | 0.70–0.90 | 0.20–0.30 | — |
Balance iron and residual elements. On forgings above 1,000 kg we hold P and S to 0.020 % maximum each, and can work to 0.015 % if the order calls for it, to protect through-thickness toughness in heavy sections.
JIS G 4053 sets the following minima for SNCM439 in the quenched and tempered condition, measured on a standard test piece.
| Property | Requirement | Note |
|---|---|---|
| Tensile strength Rm | ≥ 980 MPa (100 kgf/mm²) | Longitudinal test piece |
| Yield strength Rp0.2 | ≥ 885 MPa (90 kgf/mm²) | — |
| Elongation A | ≥ 16 % | Proportional gauge length |
| Reduction of area Z | ≥ 45 % | — |
| Charpy impact | ≥ 69 J/cm² (U-notch) | Room temperature |
| Hardness | 293–352 HBW | Roughly 31 to 38 HRC |
| Density | 7.85 g/cm³ | — |
| Modulus of elasticity | ≈ 205 GPa | Room temperature |
These are the minima the standard sets on a test coupon. On heavy forgings we take properties from a prolongation that represents the thickest section of the part.
Strength drops as the ruling section grows, because the quench rate at the core falls. These are the bands we quote and guarantee on SNCM439 open-die forgings.
| Ruling section | Tensile Rm | Yield Rp0.2 | Elongation | Charpy KV₂ at −20 °C | Hardness |
|---|---|---|---|---|---|
| ≤ 100 mm | 980–1,180 MPa | ≥ 885 MPa | ≥ 12 % | ≥ 40 J | 293–352 HBW |
| 100–250 mm | 930–1,080 MPa | ≥ 785 MPa | ≥ 13 % | ≥ 35 J | 277–331 HBW |
| 250–500 mm | 880–1,030 MPa | ≥ 685 MPa | ≥ 14 % | ≥ 31 J | 255–311 HBW |
| 500–800 mm | 830–980 MPa | ≥ 635 MPa | ≥ 15 % | ≥ 27 J | 241–293 HBW |
Treat these as quoting figures. We confirm them against your drawing and acceptance criteria before we confirm the order. Tighter bands, sub-zero impact tests down to −60 °C, and mid-radius or core test positions are all available, but they need to be on the enquiry.
SNCM439 is supplied either annealed for machining or quenched and tempered to final properties. This is the practice we run on SNCM439 open-die forgings.
| Operation | Temperature | Cooling | Result |
|---|---|---|---|
| Forging | 1,180–850 °C | Slow cool, covered | Finish above 850 °C, minimum 4:1 forging ratio |
| Normalising | 850–880 °C | Still air | Refines the as-forged grain |
| Annealing | 800–830 °C | Furnace, ≤ 20 °C/h to 600 °C | ≤ 241 HBW, ready to machine |
| Austenitising | 840–870 °C | Hold 1 h per 25 mm | Carbides fully in solution |
| Quenching | — | Oil, agitated | Martensite through the section |
| Tempering | 550–650 °C | Air or forced air | Sets the final strength band |
| Stress relief | 30–50 °C below tempering | Furnace to 300 °C | After rough machining or welding |
Stay out of the 250 to 450 °C tempering range. SNCM439 suffers temper embrittlement there, as AISI 4340 and 34CrNiMo6 do. Impact energy collapses while hardness barely moves, so a hardness check will not catch it. If the part needs a surface above 40 HRC, nitride it or induction harden it over a core tempered at 550 °C rather than tempering the whole part low.
SNCM439 has counterparts in every major standard. AISI 4340 is the true equivalent: the composition ranges overlap almost completely and the two are routinely cross-certified. The rest are near equivalents and should be agreed in writing before anyone substitutes one for another.
| Country and standard | Grade | Match | Difference to note |
|---|---|---|---|
| Japan, JIS G 4053 | SNCM439, formerly SNCM8 | Reference | — |
| USA, ASTM A29 and SAE | AISI 4340, UNS G43400 | Equivalent | Composition ranges essentially identical |
| China, GB/T 3077 | 40CrNiMoA | Equivalent | Nickel slightly lower, 1.25 to 1.65 % |
| UK, BS 970 | 817M40, formerly EN24 | Equivalent | Supplied to T, U, V, W or X condition bands |
| France, AFNOR | 35NCD6, 40NCD7 | Near | Carbon band shifted slightly |
| Germany, EN 10083-3 | 34CrNiMo6, 1.6582 | Near | Chromium higher at 1.30 to 1.70 %, carbon lower at 0.30 to 0.38 % |
| Russia, GOST 4543 | 40KhN2MA | Near | Residual element limits differ |
| Italy, UNI | 38NiCrMo4 (KB), 40NiCrMo7 | Near | Nickel and molybdenum balance differs |
Under about 150 mm ruling section, 42CrMo4 or AISI 4140 gets you the same strength at a lower alloy cost, and that is the sensible default. Above 150 mm the answer flips. The 1.6 to 2.0 % nickel in SNCM439 keeps the core martensitic where 42CrMo4 has already started forming bainite and ferrite, so SNCM439 holds both strength and low-temperature impact energy in sections that 42CrMo4 cannot reach. Heavy shafts, thick-wall rings and drill collars working below 0 °C are the usual cases for SNCM439.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory, not a stockist. Every SNCM439 part is forged to your drawing from a traceable EAF + LF + VD heat, then heat treated, tested and machined in house. We do not cut lengths off rolled stock and call them forgings, which is why we can put a forging ratio and a grain-flow direction on the certificate.
| Parameter | Range |
|---|---|
| Single-piece forged weight | 50 kg to 30,000 kg |
| Forged bar diameter | 80 to 1,200 mm |
| Maximum forged length | 6,000 mm |
| Rolled ring outside diameter | 200 to 4,000 mm |
| Steel source | EAF + LF + VD, ESR on request |
| Minimum forging ratio | 4:1, higher on request |
| Delivery condition | As forged, normalised, annealed, normalised and tempered, or quenched and tempered |
| Surface | Black, shot blasted, rough turned, or finish machined to drawing |
| Machining | CNC turning, boring, milling, drilling, gear cutting |
| Lead time | 25 to 45 days depending on weight and test scope |
These figures cover the Zhouzhuang Town plant. Parts outside the envelope are quoted through partner presses in the Jiangyin cluster, and the quotation says so.
SNCM439 turns up wherever a large cross-section has to carry high cyclic load without going brittle. These are the jobs we forge it for most often.
Where the part also needs a hard running surface, we nitride or induction harden the SNCM439 forging after tempering. That gives a 55 to 60 HRC case on a tough 300 HBW core, without the embrittlement risk that comes with tempering the whole part low.
Every SNCM439 forging leaves the Jiangyin plant with a material certificate that traces the part back to its heat number. The standard scope is below. Anything beyond it goes on the order as a named test.
EN 10204 3.1 certificates are issued as standard. EN 10204 3.2 certificates witnessed by TUV, SGS, BV, Lloyd's Register or your own inspector are arranged on request, as are PED 2014/68/EU 4.3 material approvals and NACE MR0175 or ISO 15156 compliance statements for sour service.
SCNM439 does not appear in any published standard. It is a common misspelling of JIS SNCM439, the nickel-chromium-molybdenum alloy structural steel listed in JIS G 4053. Anyone searching for SCNM439 material, bars or forgings should write SNCM439 on the purchase order and the drawing. Jiangyin Jiangnan Metal Co., Ltd. supplies the grade under its correct designation, SNCM439.
AISI/SAE 4340, also listed as UNS G43400, is the true equivalent of JIS SNCM439. The carbon, nickel, chromium and molybdenum ranges of the two grades overlap almost completely. Near equivalents are GB/T 3077 40CrNiMoA in China, BS 970 817M40 or the old EN24 in the UK, AFNOR 35NCD6 in France and GOST 40KhN2MA in Russia. DIN 34CrNiMo6, material number 1.6582, is often accepted as a substitute, but it carries more chromium and less nickel, so agree the cross-certification in writing before ordering.
JIS G 4053 requires quenched and tempered SNCM439 to reach at least 980 MPa tensile strength, 885 MPa yield strength, 16 % elongation, 45 % reduction of area and a hardness of 293 to 352 HBW. Heavy forged sections are normally tempered down to a lower band, usually 850 to 1,000 MPa tensile, so that through-thickness toughness still meets the specification.
Jiangyin Jiangnan Metal Co., Ltd. open-die forges SNCM439 from 50 kg to 30,000 kg finished forged weight. Usual envelopes are forged round bars of 80 to 1,200 mm diameter, seamless rolled rings of 200 to 4,000 mm outside diameter, and forged blocks, discs and stepped shafts up to 6,000 mm long. Send the drawing to sales@steelforgepieces.com and we will check size and weight against the press.
SNCM439 forgings are normalised at 850 to 880 °C, then annealed near 820 °C with furnace cooling to soften them for machining. Final treatment is austenitising at 840 to 870 °C, oil quenching, and tempering between 550 and 650 °C to reach the required strength band. Tempering between 250 and 450 °C is avoided, because SNCM439 suffers temper embrittlement in that range, as AISI 4340 does.
Yes. Jiangyin Jiangnan Metal Co., Ltd. issues EN 10204 3.1 mill certificates as standard and arranges EN 10204 3.2 certification witnessed by TUV, SGS, BV or Lloyd's Register on request. Standard testing covers ladle and product chemical analysis, tensile and Charpy V-notch impact tests, a Brinell hardness survey and ultrasonic examination to SEP 1921 or ASTM A388.
SNCM439 goes into parts where a large cross-section carries high cyclic load: crankshafts and connecting rods, heavy drive and pinion shafts, gear blanks, landing-gear components, drill collars and downhole tools, press and extruder rams, high-tensile bolts and studs, and rock-drilling and mining equipment. It is chosen over 42CrMo4 above roughly 150 mm section because it hardens through.
Jiangyin Jiangnan Metal Co., Ltd. runs its open-die forging plant at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Jiangyin sits on the Yangtze River about 150 km from Shanghai, and forgings ship by sea from Shanghai or Zhangjiagang. Enquiries go to +86-189-2135-9659 or sales@steelforgepieces.com.
Email the drawing, or a sketch with dimensions, plus quantity, delivery condition and test requirements. We come back with forged weight, price, lead time and the certificate scope, usually within one working day.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China. The plant forges carbon steel, alloy steel, tool steel, stainless steel and nickel alloys into bars, seamless rolled rings, blocks, discs, shafts, sleeves and hollow forgings, from 50 kg to 30,000 kg per piece, and exports to OEMs and their machining partners. SNCM439, AISI 4340, 34CrNiMo6 and 42CrMo4 are among the grades that run most often.
Published 12 May 2016. Last reviewed 15 September 2026 by the technical sales team at Jiangyin Jiangnan Metal Co., Ltd. Property data quoted from JIS G 4053. Forging and testing figures describe the Zhouzhuang Town plant.
