SNCM439 or SCM440 for a big shaft?

SNCM439’s ~1.8% nickel keeps through-hardness and low-temperature toughness in sections where SCM440 (4140 class) falls off — above roughly 100 mm ruling section the Ni-Cr-Mo grade is the safe choice.

Grades · Alloy & Engineering Steel · SNCM439

SNCM439

Data verified

SNCM439 is the JIS designation of the 4340 Ni-Cr-Mo through-hardening steel — deep hardenability and high fatigue strength for large shafts, gears and high-strength fasteners on Japanese and Asian certificates.

Hardness33–45 HRC typical

DIN1.6511 (36CrNiMo4)

AISI4340

JISSNCM439 (JIS G4053)

CategoryAlloy & Engineering Steel

Chemical composition

Element	Content (%)
C	0.36–0.43
Si	0.15–0.35
Mn	0.60–0.90
P	≤0.030
S	≤0.030
Cr	0.60–1.00
Ni	1.60–2.00
Mo	0.15–0.30

Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.

Properties

Hardness (Q&T)	33–45 HRC typical
Tensile strength	≥980 MPa (Q&T reference)
Yield strength	≥835 MPa (Q&T reference)
Density	7.85 g/cm³
Hardenability	Very high (large sections)

Heat treatment

Quench ≈850 °C oil; temper 550–650 °C — avoid the 250–350 °C tempered-martensite embrittlement range.

Equivalent grades

Standard	Designation
din	1.6511 (36CrNiMo4)
aisi	4340
jis	SNCM439 (JIS G4053)
gb	40CrNiMo

Compare side by side: SNCM439 vs 4340

Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.

Applications & Processing

Applications: Large shafts and gears, high-strength bolts, heavy-vehicle and press components, downhole tools.

Processing: As 4340: machine annealed; weld only with strict preheat and post-weld heat treatment; grind after hardening.

FAQ

SNCM439 or SCM440 for a big shaft?: SNCM439’s ~1.8% nickel keeps through-hardness and low-temperature toughness in sections where SCM440 (4140 class) falls off — above roughly 100 mm ruling section the Ni-Cr-Mo grade is the safe choice.

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Source: JIS G4053 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.