Why aluminium in a nitriding steel?

Aluminium forms very hard aluminium nitrides in the case during nitriding, giving the highest case hardness of the common nitriding steels — that is the whole point of the 38CrMoAlA chemistry.

Grades · Alloy & Engineering Steel · 38CrMoAlA

38CrMoAlA

Data verified

38CrMoAlA is China’s standard nitriding steel (GB/T 3077): the 0.70–1.10% aluminium addition gives an exceptionally hard, wear-resistant nitrided case over a strong Q&T core — the counterpart of JIS SACM645 and the European 41CrAlMo7 family.

DIN1.8509 (41CrAlMo7-10, near)

AISI— (nitriding grade)

JISSACM645

CategoryAlloy & Engineering Steel

Chemical composition

Element	Content (%)
C	0.35–0.42
Si	0.20–0.45
Mn	0.30–0.60
P	≤0.035
S	≤0.035
Cr	1.35–1.65
Mo	0.15–0.25
Al	0.70–1.10

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

Properties

Tensile strength	≥980 MPa (GB/T 3077 reference Q&T)
Yield strength	≥835 MPa (reference)
Nitriding response	Excellent — 0.70–1.10% Al forms a hard, stable nitrided case
Density	7.85 g/cm³

Heat treatment

Q&T first (quench ~930 °C oil, temper ~600 °C class), finish-machine, then gas/plasma nitride at ~500–540 °C.

Equivalent grades

Standard	Designation
din	1.8509 (41CrAlMo7-10, near)
aisi	— (nitriding grade)
jis	SACM645
gb	38CrMoAlA (GB/T 3077)

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

Applications & Processing

Applications: Precision gears, worm shafts, pump plungers, injection-machine screws and barrels, gauges.

Processing: Machine in the Q&T condition; nitriding adds almost no distortion, so finish dimensions are held easily. Remove the brittle white layer where fatigue is critical.

FAQ

Why aluminium in a nitriding steel?: Aluminium forms very hard aluminium nitrides in the case during nitriding, giving the highest case hardness of the common nitriding steels — that is the whole point of the 38CrMoAlA chemistry.

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Source: GB/T 3077 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.