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.
Standards
| Standard Body |
Designation |
Country |
| 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 |
| GB |
55 |
China |
| JUS |
C.1431 |
Yugoslavia |
| DIN W.Nr |
1.0535 |
Germany |
| DIN (obsolete) |
Ck55 / 1.0535 |
Germany |
| GOST |
55 (55 steel) |
Russia |
| JUS |
C.1531 |
Yugoslavia/BiH |
Composition (wt.%)
| Element |
Symbol |
Min % |
Max % |
Typical % |
| Carbon |
C |
0.520 |
0.600 |
0.550 |
| Silicon |
Si |
0.170 |
0.370 |
0.250 |
| Manganese |
Mn |
0.600 |
0.900 |
0.750 |
| Phosphorus |
P |
— |
0.030 |
— |
Physical
Melting Range
1425 – 1455
°C
Thermal Conductivity
47
W/mK
Thermal Expansion
11.2
×10⁻⁶/K
Machinability
| Rating |
48.0% (B1112=100%) |
| Turning HSS |
28.0 m/min |
| Turning Carbide |
140.0 m/min |
| Surface Finish |
Ra 0.8-1.6 um |
| Coolant |
Soluble oil 8-12% |
Mechanical
| Condition |
Rm (MPa) | Re (MPa) | A (%) |
HB | HRC | KV (J) | E (GPa) |
| Normalized (+N) |
650 – 800 |
380 – 530 |
14 – 18 |
185 – 240 |
— |
— |
210 |
| Q+T 600C (+QT600) |
750 – 900 |
520 – 680 |
13 – 17 |
220 – 270 |
— |
— |
210 |
| Q+T 500C (+QT500) |
900 – 1100 |
700 – 900 |
10 – 13 |
265 – 320 |
— |
— |
210 |
Heat Treatment
| Process |
Temperature |
Medium |
Duration |
Hardness After |
| Spheroidising Anneal |
680 – 720°C |
Furnace |
3-5 h |
<=HB 241 |
| Austenitizing |
800 – 840°C |
Oil |
20-30 min |
HRC 56-62 |
| Tempering |
450 – 650°C |
Oven |
1-2 h |
HRC 22-42 |
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.
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.