Matching Chinese Carbon Steels to Strength Classes

Can Q235 be used for 8.8-grade bolts? What about 45# for Class 10.9? Here’s a clear breakdown of which Chinese carbon steels belong in each strength class—and where to draw the line.

Class 4.8 (Low Strength)

• Typical grades: Q195, Q215, Q235, ML08Al, ML10

• Heat treatment: None (as-formed or as-rolled)

• Max diameter: No practical limit

• Typical use: Furniture, light construction, non-critical assemblies

Class 8.8 (Medium Strength)

• Typical grades: 35#, 45#, ML35, ML40, ML45

• Heat treatment: Quench + temper (tempering)

• Important: For larger diameters, consider 40Cr (alloy steel) for better through-hardening

• Typical use: Automotive assemblies, machinery, structural connections

Class 10.9 (High Strength)

• Note: Carbon steels cannot reliably achieve Class 10.9 in larger diameters

• Exception: Small diameters in 45# may reach 10.9, but alloy steels (35CrMo, SCM435) are preferred

• Typical use: Critical joints, high-load applications