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C55

C55 — high carbon structural steel between C45 and C60. Q+T gives Rm 750-900 MPa. For crankshafts, cams, high-strength bolts and cutting tools.

Carbon Steels High-Carbon Unalloyed Steel EN / ISOC55 / 1.0535 DINCk55 / 1.0535 AISI/SAE1055 ASTMA29 Grade 1055 +10
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Description

C55 per EN 10083-2 (1.0535). Carbon 0.52-0.60% provides good hardenability for moderate sections. Q+T achieves Rm 750-900 MPa. Intermediate between C45 (lower strength) and C60/C75 (more brittle). Used for crankshafts, medium-load springs, high-strength bolts and punching tools for soft materials.

Key Properties — Normalized
Rm (Tensile Strength)
650 – 800
MPa
Re / Rp0.2 (Yield)
380 – 530
MPa
A₅ (Elongation)
≥ 14.0
%
Hardness
185 – 240
HB
E (Young's Modulus)
210
GPa
Density
7.84
g/cm³
Main Designations (14)
Standard BodyDesignationCountry / RegionNote
EN / ISO C55 / 1.0535 EU
DIN Ck55 / 1.0535 Germany
AISI/SAE 1055 USA
ASTM A29 Grade 1055 USA
BS 070M55 UK
JIS S55C Japan
GOST 55 Russia
UNS G10550 USA (UNS)
GB 55 China
JUS C.1431 Yugoslavia Medium-high C steel; JUS B.B1.100
DIN W.Nr 1.0535 Germany
DIN (obsolete) Ck55 / 1.0535 Germany
GOST 55 (55 steel) Russia
JUS C.1531 Yugoslavia/BiH Srednje-visoki C mašinski celik C55; JUS B.B1.100
Standards (14)
#Standard BodyDesignationCountry / RegionNote
1 EN / ISO C55 / 1.0535 EU —
2 DIN Ck55 / 1.0535 Germany —
3 AISI/SAE 1055 USA —
4 ASTM A29 Grade 1055 USA —
5 BS 070M55 UK —
6 JIS S55C Japan —
7 GOST 55 Russia —
8 UNS G10550 USA (UNS) —
9 GB 55 China —
10 JUS C.1431 Yugoslavia Medium-high C steel; JUS B.B1.100
11 DIN W.Nr 1.0535 Germany —
12 DIN (obsolete) Ck55 / 1.0535 Germany —
13 GOST 55 (55 steel) Russia —
14 JUS C.1531 Yugoslavia/BiH Srednje-visoki C mašinski celik C55; JUS B.B1.100
All values in wt.%
C
Carbon
0.5200 – 0.6000
Si
Silicon
0.1700 – 0.3700
Mn
Manganese
0.6000 – 0.9000
P
Phosphorus
≤ 0.0300
ElementSymbolMin %Max %Typical %
Carbon C 0.5200 0.6000 0.5500
Silicon Si 0.1700 0.3700 0.2500
Manganese Mn 0.6000 0.9000 0.7500
Phosphorus P — 0.0300 —
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 650 800 380 530 14.0 35.0 — 185 240 — — 210.0
Q+T 600C +QT600 750 900 520 680 13.0 38.0 — 220 270 — — 210.0
Q+T 500C +QT500 900 1,100 700 900 10.0 33.0 — 265 320 — — 210.0
Physical Properties
Density
7.840
g/cm³
Melting Point
1425–1455
°C
Young's Modulus
210.0
GPa
Poisson's Ratio
0.295
—
Thermal Conductivity
47.0
W/m·K
Thermal Expansion
11.20
×10⁻⁶ /K
Specific Heat
490
J/kg·K
Electrical Resistivity
0.1800
µΩ·m
Magnetic
Yes
 
Heat Treatment
Spheroidising Anneal
Temperature:680°C – 720°C
Medium:Furnace
Duration:3-5 h
Cooling:<=20 C/h
Hardness After:<=HB 241
Before machining.
Austenitizing
Temperature:800°C – 840°C
Medium:Oil
Duration:20-30 min
Cooling:Oil quench
Hardness After:HRC 56-62
Oil only — never water.
Tempering
Temperature:450°C – 650°C
Medium:Oven
Duration:1-2 h
Cooling:Air cool
Hardness After:HRC 22-42
Select per application.
Machinability
Machinability Rating
relative to AISI B1112 = 100%
48.0%
Difficult
Turning Speed (HSS)
28
m/min
Turning Speed (Carbide)
140
m/min
Feed Rate (Turning)
0.160
mm/rev
Drilling Speed (HSS)
20
m/min
Milling Speed (Carbide)
145
m/min
CoolantSoluble oil 8-12%
Chip FormationShort-medium chips
Tool MaterialCarbide P20/P30; TiAlN
Surface FinishRa 0.8-1.6 um
Good in annealed. Difficult in hardened — grinding only.
Applications
Automotive
Crankshafts, camshafts, crank pins.
Fasteners
High-strength bolts class 10.9.
Springs
Flat springs and torsion bars for low-cycle applications.
Agricultural Tools
Cultivation tool shanks, disc blades, harrow tines and plough shares.
Railway
Rail clip bolts, fish-plate bolts and track fasteners.
Springs
Light-duty springs and spring washers where 51CrV4 is over-specified.
Technical Notes
🔥
Weldability
Poor. CE approx 0.70. Pre-heat 200-250 C; PWHT required. Avoid welding if possible.
✅
vs C60
C55 has slightly better toughness. C60 has higher fatigue strength. C55 preferred when impact resistance is needed alongside high strength.
✅
C55 position
C55 fills the gap between C45 (most common machine steel) and C60 (highest unalloyed). Use when C45 hardness is marginally insufficient but alloy steel is cost-prohibited.