Why aluminium in a steel for nitriding?

Aluminium forms ultra-hard AlN in the diffusion zone — Al-bearing grades reach the highest nitrided case hardness (~1100 HV) of any nitriding steel family.

1.8550 vs 31CrMoV9 (1.8519)?

1.8519 is the Cr-Mo-V nitriding grade without aluminium: slightly lower case hardness but deeper, tougher case and easier grinding. 1.8550 wins on peak surface hardness and wear.

Grades · Alloy & Engineering Steel · 1.8550 / 34CrAlNi7-10

1.8550 / 34CrAlNi7-10

Data verified

1.8550 (34CrAlNi7-10) is the premium European nitriding steel: its aluminium is the nitride former that builds the extremely hard, wear-resistant case, while the nickel keeps the quenched-and-tempered core tough. It is the reference grade for large nitrided gears and plasticising screws.

DIN1.8550

AISI— (Nitralloy type, near)

JIS— (SACM645 family, near)

CategoryAlloy & Engineering Steel

Chemical composition

Element	Content (%)
C	0.30–0.37
Si	≤0.40
Mn	0.40–0.70
P	≤0.025
S	≤0.035
Cr	1.50–1.80
Al	0.80–1.20
Ni	0.85–1.15

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

Properties

Delivery condition	Quenched & tempered
Core tensile	900–1100 MPa (typical sections)
Nitrided case	~950–1100 HV, 0.4–0.6 mm deep
Density	7.85 g/cm³

Heat treatment

Quench and temper to core strength first, machine, then gas or plasma nitride at 500–530 °C — no further hardening after nitriding, so distortion stays minimal.

Equivalent grades

Standard	Designation
din	1.8550
aisi	— (Nitralloy type, near)
jis	— (SACM645 family, near)
gb	38CrMoAl (near)

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

Applications & Processing

Applications: Large nitrided gears and pinions, extruder and injection-molding screws and barrels, crankshafts, hydraulic components, precision worm shafts.

Processing: Machine in the Q&T condition leaving a small grinding allowance; nitride as the last step. The white layer is controlled or removed per application — specify case depth (NHD) on the order.

FAQ

Why aluminium in a steel for nitriding?: Aluminium forms ultra-hard AlN in the diffusion zone — Al-bearing grades reach the highest nitrided case hardness (~1100 HV) of any nitriding steel family.
1.8550 vs 31CrMoV9 (1.8519)?: 1.8519 is the Cr-Mo-V nitriding grade without aluminium: slightly lower case hardness but deeper, tougher case and easier grinding. 1.8550 wins on peak surface hardness and wear.

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Source: EN 10085 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.