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31CrMoV9 (Nitriding Steel)

Standard nitriding steel per EN 10085. After gas nitriding achieves HV 900-1100 surface hardness. For crankshafts, camshafts and precision gear shafts.

Alloy Steels Nitriding Steel EN 1008531CrMoV9 / 1.8519 DIN31CrMoV9 / 1.8519 ASTMNo direct equivalent BS EN31CrMoV9 +7
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Description

31CrMoV9 per EN 10085 (1.8519). Cr-Mo-V composition designed specifically for gas nitriding after Q+T. V addition promotes very hard carbonitride surface layer. After gas nitriding at 500-530 C for 20-80 h achieves HV 900-1100 case (HRC 66-70) without quenching. Minimal distortion — parts remain dimensionally stable. Standard for automotive crankshafts, camshafts, precision spindles and injection mould pins.

Key Properties — Q+T (pre-nitriding base)
Rm (Tensile Strength)
900 – 1,100
MPa
Re / Rp0.2 (Yield)
700 – 900
MPa
A₅ (Elongation)
≥ 12.0
%
Hardness
270 – 330
HB
E (Young's Modulus)
210
GPa
Density
7.85
g/cm³
Main Designations (11)
Standard BodyDesignationCountry / RegionNote
EN 10085 31CrMoV9 / 1.8519 EU
DIN 31CrMoV9 / 1.8519 Germany
ASTM No direct equivalent USA
BS EN 31CrMoV9 UK
JIS SACM645 (nearest) Japan
GOST 38H2MYuA (38Kh2MYuA) Russia
UNS K24070 (nearest) USA (UNS)
GB 38CrMoAl China
JUS C.4763 Yugoslavia Cr-Mo-V nitriding steel; JUS C.B1.042
DIN W.Nr 1.8519 Germany
JUS C.4834 Yugoslavia/BiH Cr-Mo-V nitrirajuci celik 31; JUS C.B1.055
Standards (11)
#Standard BodyDesignationCountry / RegionNote
1 EN 10085 31CrMoV9 / 1.8519 EU —
2 DIN 31CrMoV9 / 1.8519 Germany —
3 ASTM No direct equivalent USA —
4 BS EN 31CrMoV9 UK —
5 JIS SACM645 (nearest) Japan —
6 GOST 38H2MYuA (38Kh2MYuA) Russia —
7 UNS K24070 (nearest) USA (UNS) —
8 GB 38CrMoAl China —
9 JUS C.4763 Yugoslavia Cr-Mo-V nitriding steel; JUS C.B1.042
10 DIN W.Nr 1.8519 Germany —
11 JUS C.4834 Yugoslavia/BiH Cr-Mo-V nitrirajuci celik 31; JUS C.B1.055
All values in wt.%
C
Carbon
0.2700 – 0.3400
Si
Silicon
0.1000 – 0.4000
Mn
Manganese
0.4000 – 0.7000
Cr
Chromium
2.3000 – 2.7000
Mo
Molybdenum
0.1500 – 0.2500
V
Vanadium
0.1000 – 0.2000
ElementSymbolMin %Max %Typical %
Carbon C 0.2700 0.3400 0.3100
Silicon Si 0.1000 0.4000 0.2500
Manganese Mn 0.4000 0.7000 0.5500
Chromium Cr 2.3000 2.7000 2.5000
Molybdenum Mo 0.1500 0.2500 0.2000
Vanadium V 0.1000 0.2000 0.1500
Mechanical Properties
ConditionCode Rm min
MPa		Rm max
MPa		 Re min
MPa		Re max
MPa		 A₅ min
%		 Z
%		 KV
J		 HB minHB max HRC minHRC max E
GPa
Q+T (pre-nitriding base) +QT 900 1,100 700 900 12.0 45.0 — 270 330 — — 210.0
Nitrided surface (typical) GN — — — — — — — — — 66.0 70.0 210.0
Physical Properties
Density
7.850
g/cm³
Melting Point
1445–1480
°C
Young's Modulus
210.0
GPa
Poisson's Ratio
0.290
—
Thermal Conductivity
38.0
W/m·K
Thermal Expansion
12.20
×10⁻⁶ /K
Specific Heat
480
J/kg·K
Electrical Resistivity
0.2400
µΩ·m
Magnetic
Yes
 
Heat Treatment
Quench + Temper (before nitriding)
Temperature:880°C – 920°C
Medium:Oil
Duration:20-30 min
Cooling:Oil quench
Hardness After:HRC 28-36
Q+T to this hardness range before nitriding. Core provides toughness.
Gas Nitriding
Temperature:500°C – 530°C
Medium:NH3 atmosphere
Duration:20-80 h
Cooling:Furnace cool to 200 C then air
Hardness After:HV 900-1100 surface; core unchanged
White layer (compound layer) 5-20 um forms. Can be lapped off for precision parts.
Plasma Nitriding
Temperature:450°C – 520°C
Medium:N2/H2 plasma (vacuum)
Duration:8-30 h
Cooling:Furnace cool
Hardness After:HV 900-1100 surface; no white layer
Preferred for precision parts — no white layer, tighter dimensional control, 50% shorter cycle.
Machinability
Machinability Rating
relative to AISI B1112 = 100%
55.0%
Difficult
Turning Speed (HSS)
32
m/min
Turning Speed (Carbide)
155
m/min
Feed Rate (Turning)
0.170
mm/rev
Drilling Speed (HSS)
22
m/min
Milling Speed (Carbide)
158
m/min
CoolantSoluble oil 8-10%
Chip FormationMedium chips (Q+T condition)
Tool MaterialCarbide P20/P30; TiAlN
Surface FinishRa 0.4-1.6 um
Machine in Q+T condition before nitriding. After nitriding: only grinding possible.
Applications
Automotive
Crankshafts, camshafts, cam followers, injection pump shafts and precision spindles.
Machine Tools
Ball-screw shafts, spindle journals, precision guide rails.
Moulds
Injection mould core pins, ejector pins and wear-resistant guide bushings.
Crankshafts
Automotive and industrial engine crankshafts -- classic application.
Gears
Precision gears for machine tools and instrumentation.
Hydraulic Cylinders
Hydraulic piston rods and cylinder bores.
Technical Notes
✅
Nitriding vs Case Hardening
Nitriding: no quench needed (zero distortion), HV 900-1100, case depth 0.1-0.7 mm. Case hardening: deeper case (0.5-2 mm), lower surface hardness (HRC 58-64), quench distortion. Choose nitriding for precision-ground components; case hardening for deeper case depth needs.
💡
Al-bearing nitriding steels
38CrMoAl (Nitralloy 135) with Al addition achieves even higher hardness (HV 1000-1200) via AlN precipitation. 31CrMoV9 is preferred where better toughness is needed.
✅
31CrMoV9 vs 32CrMoV12-10
31CrMoV9: slightly less Cr (2.5% vs 3.0%), similar nitriding result (HV 800-1000 vs 1000-1100). Both excellent. 32CrMoV12-10 gives marginally higher surface hardness; 31CrMoV9 is equally popular in European specifications. Use either interchangeably for standard nitriding applications.