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C25 (Medium-Low Carbon Machine Steel)

C25 -- unalloyed machine steel between C20 and C35. Rm 470-620 MPa normalized. For lightly-loaded shafts, bolts and machine parts requiring more strength than C20 without alloy steel cost.

Carbon Steels Carbon Steel EN 10083-2C25 / 1.0406 DIN W.Nr1.0406 AISI/SAE1025 JISS25C +3
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Description

C25 (EN 1.0406) per EN 10083-2. Carbon 0.22-0.29% sits between C20 (case-hardening focus) and C35 (through-hardening focus) -- often used simply as a normalized machine steel without further heat treatment. Standard for lightly loaded shafts, machine bolts and general components where C20 strength is marginal but full C35 hardenability is not required.

Key Properties — Normalized
Rm (Tensile Strength)
470 – 620
MPa
Re / Rp0.2 (Yield)
295
MPa
A₅ (Elongation)
≥ 21.0
%
Hardness
135 – 190
HB
E (Young's Modulus)
210
GPa
Density
7.85
g/cm³
Main Designations (7)
Standard BodyDesignationCountry / RegionNote
EN 10083-2 C25 / 1.0406 EU
DIN W.Nr 1.0406 Germany
AISI/SAE 1025 USA
JIS S25C Japan
GOST 25 (25 steel) Russia
UNS G10250 USA (UNS)
JUS C.1330 Yugoslavia/BiH Srednje-niski C celik C25; JUS B.B1.100
Standards (7)
#Standard BodyDesignationCountry / RegionNote
1 EN 10083-2 C25 / 1.0406 EU —
2 DIN W.Nr 1.0406 Germany —
3 AISI/SAE 1025 USA —
4 JIS S25C Japan —
5 GOST 25 (25 steel) Russia —
6 UNS G10250 USA (UNS) —
7 JUS C.1330 Yugoslavia/BiH Srednje-niski C celik C25; JUS B.B1.100
All values in wt.%
C
Carbon
0.2200 – 0.2900
Si
Silicon
0.1500 – 0.4000
Mn
Manganese
0.4000 – 0.7000
ElementSymbolMin %Max %Typical %
Carbon C 0.2200 0.2900 0.2550
Silicon Si 0.1500 0.4000 0.2500
Manganese Mn 0.4000 0.7000 0.5500
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
Normalized +N 470 620 295 — 21.0 55.0 — 135 190 — — 210.0
Q+T (light hardening) +QT 550 700 370 — 17.0 50.0 — 160 210 — — 210.0
Physical Properties
Density
7.850
g/cm³
Melting Point
1465–1500
°C
Young's Modulus
210.0
GPa
Poisson's Ratio
0.301
—
Thermal Conductivity
50.0
W/m·K
Thermal Expansion
11.60
×10⁻⁶ /K
Specific Heat
490
J/kg·K
Electrical Resistivity
0.1780
µΩ·m
Magnetic
Yes
 
Heat Treatment
Normalizing
Temperature:860°C – 900°C
Medium:Still Air
Duration:-
Cooling:Air cool
Hardness After:Standard delivery
Austenitizing (light Q+T)
Temperature:840°C – 870°C
Medium:Water or oil quench
Duration:15-20 min
Cooling:Quench
Hardness After:HRC 40-48
Limited hardenability -- effective mainly in thin sections.
Tempering
Temperature:500°C – 650°C
Medium:Oven
Duration:1-2 h
Cooling:Air cool
Hardness After:HRC 22-38
NOT case-hardening focused
Medium:Intermediate C content -- used mainly as-normalized rather than for carburising
Duration:N/A
Cooling:N/A
Hardness After:N/A
Machinability
Machinability Rating
relative to AISI B1112 = 100%
70.0%
Moderate
Turning Speed (HSS)
42
m/min
Turning Speed (Carbide)
180
m/min
Feed Rate (Turning)
0.230
mm/rev
Drilling Speed (HSS)
29
m/min
Milling Speed (Carbide)
183
m/min
CoolantSoluble oil 5-8%
Chip FormationMedium ductile chips
Tool MaterialCarbide P20; HSS M2
Surface FinishRa 0.8-3.2 um
Good machinability.
Applications
Machine Shafts
Lightly loaded machine shafts and spindles.
Bolts
General machine bolts and fasteners.
General Components
Machine parts requiring moderate strength without alloy steel cost.
Technical Notes
✅
C25 position
C25 fills the narrow gap between C20 (case-hardening) and C35 (through-hardening focus). In practice many designers simply specify C20 or C35 directly, making C25 a less commonly stocked intermediate grade -- useful where a specific normalized-strength target between the two is genuinely required.