Project Description

C55 steel is an unalloyed medium carbon engineering steel which has 0.52%-0.6% Carbon as per EN10083 standard.It will obtain high hardness and high strength  after hardening due to the relatively high carbon content,and also can be flame or induction hardened to surface hardness Min 58HRC.C55 steel is generally supplied in an untreated or normalised condition.C55 steel

1.Supply Form & Size & Tolerance

Hot Forged round bar:Φ130-Φ1000mm,Length:3000-10000mm

Flat bar/Blcoks:Thickness :120-800mm xWidth:120-1500mm,Length:2000-6000mm

Surface FinishBlack-Forged Black-Rolled Turned   GrindingPolishedPeeledCold Drawn
Tolerance(0,+5mm)(0,+1mm)(0,+3mm)Best h9Best h11Best H11Best H11

2.Chemical Composition

C55/1.05350.52-0.60.60-0.90≤ 0.045≤ 0.045≤ 0.4≤ 0.4≤ 0.1≤ 0.4≤ 0.63
C55E/1.12030.52-0.60.60-0.90≤ 0.03≤ 0.035≤ 0.4≤ 0.4≤ 0.1≤ 0.4≤ 0.63
C55R/1.12090.52-0.60.60-0.90≤ 0.030.02-0.04≤ 0.4≤ 0.4≤ 0.1≤ 0.4≤ 0.63

3.Relevant Standards

1055070M55 / EN955#S55C1055

4. Mechanical Property

Mechanical properties a at room temperature in the quenched and tempered condition (+QT)
Diameter d mm≤ 1616-4040-100
Thickness t mm< 88-2020-60
Yield Strength Mpa≥550≥490≥420
Tensile Strength Mpa800-950750-900700-850
Elongation, %≥12≥14≥15
Reduction of area ,%≥30≥45≥40
Mechanical properties a at room temperature in the normalized condition (+N)
Diameter d mm≤ 1616-100100-250
Thickness t mm≤ 1616-100100-160
Yield Strength Mpa≥370≥330≥300
Tensile Strength Mpa≥680≥640≥620
Elongation, %≥11≥12≥12


C55 steel forging temperature:900 – 1050°C ,cooling as slowly as possible in still air or in sand after forged.

6.Heat Treatment

  • Normalizing:  825 – 885°C,Cooling in air
  • Soft Annealing:650 – 700°C,Cooling in furnace
  • Hardening:810 – 850°C,water or oil quench
  • Tempering:550 – 660°C,Cooling in air

Guideline value Curve for C55 Steel Mechanical Property

C55 steel Mechanical property reference curve

X:Tempering temperature,oC

Y:Tensile and Yield Strength,Mpa

Z:Elongation and Reduction in  area,%

7.Surface Hardness

  • Treated to improve shearability (+S):Max 255HB
  • Soft annealed (+A):Max 229HB
  • Flame or induction hardening:Min 58HRC
NORMAL HARDENABILITY +H (Hardness HRC – distance mm)
HRC - mm12345678910111315202530


C55 is a medium carbon steel suitable for various type of applications where high strength is needed.It is used for components of small cross section requiring low tensile strength, and heavy forgings in the normalized condition for automotive and general engineering such as axles, clutch members, shafts, pressed and punched parts, piston rods and gear racks.

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