C35 Steel vs C40 Steel, Which One is More Suitable For Your Needs?

C35 steel and C40 steel, two medium-carbon steels that are only distinguished by slight differences in carbon content, show completely different characteristics in mechanical properties, processing technology and application scenarios.

How does carbon content affect them? Should we choose C40 steel that pursues higher strength and hardness, or C35 steel that emphasizes plasticity and toughness? This article will deeply analyze the essential differences between the two to help you choose the optimal solution.

Chemical Composition:C35 Steel vs C40 Steel

Grade	C	Si	Mn	P	S
C35	0.32-0.39	0.10-0.40	0.50-0.80	≤0.035	≤0.035
C40	0.37-0.44	0.10-0.40	0.50-0.80	≤0.035	≤0.035

As can be seen from the table above, both C35 and C45 are medium carbon structural steels, with the core difference being the carbon content, which directly leads to differences in mechanical properties and applications.

Mechanical Properties:C35 Steel vs C40 Steel

Grade	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)	Hardness (HB)
C35	530-680	≥310	≥18	170-210
C40	620-800	≥340	≥16	190-230

The table above shows the changes caused by differences in carbon content. In terms of strength and hardness, C40 steel is slightly higher than C35 steel, but its toughness is relatively lower.

Processing Performance:C35 Steel vs C40 Steel

The difference in carbon content is also reflected in its processing performance.

Machinability:Compared to C35 steel, C40 steel has a slightly higher hardness, making it relatively more difficult to process and exhibiting a significant tendency for work hardening.
Weldability:The carbon equivalent of C40 steel is approximately 0.6, which is higher than that of C35 steel (approximately 0.5).Neither has very good weldability, so both require strict welding procedures. Relatively speaking, C35 is better.
Heat treatment:C40 steel has slightly better hardenability than C35 steel, but its risk of deformation and cracking is increased. Therefore, the cooling rate of C40 needs to be more strictly controlled.
Cold forming:C35 has better plasticity,making it suitable for bending and stamping.While C40 requires greater forming force, easy to rebound.

Typical Application:C35 Steel vs C40 Steel

C35 steel-Balanced overall performance, suitable for medium stress and high processability requirements.

Typical Application:Shafts, gears, connecting rods, bolts (medium load); cold forgings;welded structural parts; hydraulic cylinders.

C40 steel-Biased towards high strength and wear resistance, but some processing convenience needs to be sacrificed.

Typical Application:High-strength gears, spindles, crankshafts, high-stress bolts;wear-resistant parts (such as guide rails); non-critical tool parts; heavy machinery parts.

Which One is More Suitable For Your Needs?

If we choose based on cost, the difference between the two is actually not significant and can be almost ignored.Specific considerations need to be made based on the strength,toughness and process requirements of the working conditions.

Choose C35: Need to balance strength and formability/weldability, or cost-sensitive and medium load.
Choose C40: High wear resistance, high strength demand scenario, and processing conditions allow.