AISI 1055 / DIN C55 1.0535 / S55C / BS 070M55 Carbon Steel

C55 / 1.0535 is a widely used carbon structural steel compliant with the European standard EN10250-2 and EN 10083-2. With a carbon content of 0.52–0.60%, this medium-high carbon steel offers excellent strength, hardness, and a certain degree of wear resistance after normalizing or quenching and tempering heat treatment.

Although it has moderate hardenability, C55 provides good machinability and heat treatability, making it an economical choice for manufacturing high-strength components. It is commonly used in the automotive industry, machinery manufacturing, and general engineering for producing shafts, gears, connecting rods, and other parts subjected to medium stress, ensuring reliable performance in various industrial environments.

1: Steel equivalent

2: Chemical composition

3: Mechanical properties .

Mechanical properties for C55 quenching and tempering carbon steel according to EN10083-2.

Mechanical properties for C55 normalizing carbon steel according to EN10083-2 and ISO683-1.

Sampling and preparation of test pieces for C55 quenching and tempering steel.

1): According to EN10083-1, all samples shall be taken at a distance of 12.5mm below the heat treated surface

2): As stipulated in the contract between buyer and seller.

Mechanical properties for C55 open die forgings steel in the normalized and normalized and tempered conditions according to EN10250-2.

Remark: L= Longitudinal    Tr = Transverse

Sampling and preparation of test pieces for steel forging.

1: According to EN10250-1, all samples shall be taken at a distance of 4/T below the heat treated surface (with a minimum of 20mm and a maximum of 80mm), and t/2 from the end (where t is the equivalent thickness of the thickness of the ruling section of the forging at the time of heat treatment.

2: As stipulated in the contract between buyer and seller.

4: Surface hardness and hardenability.

Where the steel is ordered by using the symbols for normal (+H) or restricted (+HL, +HH) hardenability requirements, the hardenability values should apply below:

Scatter bands for the Rockwell - C hardness in the end quench hardenability test.

5: Supply size & Tolerance & Stock size

Qilu steel stock hot rolled bar and forged bars more than ten thousands tons every month, below our our stock size.

1): Stock diameter for hot rolled bar

2) : Stock diameter for hot forged bar

Since the stocks change everyday, if you want to know our stock available information, please contact our salesman.

6：Forging processing

Put the C55 ingot into the furnace and heat to 1150-1200℃

Forge the ingot, forging temperature should be not less than 800-850℃

Cooling in the furnace after forged

7: Heat treatment

Soft annealed:

Heat C55 steel to 780-820℃ in the furnace

Soak at this temperature in the furnace

Cooling in the furnace (≤30°C/h) to 550°C followed by air cooling

Normalized:

Heat C55 steel to 825-885℃ in the furnace

Soak at this temperature in the furnace

Cooling in the air

Quenching and tempering:

Heat C55 steel to 810-850℃ in the furnace

Soak at this temperature in the furnace

Quench in water or oil

Temper steel at 550-660℃ in the furnace

Take out of C55 steel from furnace and cool in the air.

Remark: The conditions given above are for guidance, at the temperatures at the lower end of the range are generally applicable to hardening in water and those at the upper end for hardening in oil.

8: Weldability

C55 steel has relatively poor weldability. For steel materials, weldability is strongly influenced by the carbon content—when the carbon content exceeds 0.25%, weldability begins to deteriorate significantly. The carbon content of C55 is typically between 0.52% and 0.60%, classifying it as a high-carbon steel with limited weldability. Welding such material requires strict preheating, controlled interpass temperature, and post-weld heat treatment to avoid cracking and achieve acceptable joint properties.

9：Application

C55 steel, as a medium-to-high carbon steel, finds extensive application across multiple industrial sectors due to its excellent strength, wear resistance, and moderate cost. Its primary uses include:

• Shaft components: Commonly used for manufacturing drive shafts, mandrels, and rotating shafts subjected to moderate loads and rotational speeds.

• Gears: Suitable for producing transmission components such as gears and gear rings for medium-sized machinery; heat treatment yields superior wear resistance.

• Connecting rods and cranks: Employed in connecting rods and crank components for internal combustion engines, compressors, and similar equipment.

• Guide rails and friction parts: Suitable for machine tool guide rails, pins, and other friction components requiring wear resistance and adequate strength.

• Spring collets and tool components: Also used for manufacturing spring collets (requiring appropriate heat treatment) and certain uncomplicated small tool parts.