What Steel Is CT3? An Honest Answer

It isn't, not automatically. And when you need a specific number to calculate bending force, the answer is more complicated than it looks.

Why it's hard

"CT3" comes from an older grade system and is used loosely in the Vietnamese market — sometimes just to mean "ordinary steel plate". Under the same name, two deliveries can differ in:

• the specific grade within TCVN (CT31 / CT33 / CT34 / CT38 / CT42)
• deoxidation state
• thickness range, which in turn changes yield strength

For that reason we do not publish an "official" yield or tensile figure for CT3. In NKAM's material lookup, those fields say plainly not reliably confirmed.

Grades with clearer data

CT38 (TCVN 1765:1975)
 Yield strength 250 MPa at thickness ≤ 20 mm
 Tensile strength 380 – 490 MPa

SS400 (JIS G3101)
 Yield strength ≥ 245 MPa (t ≤ 16 mm)
 ≥ 235 MPa (16 < t ≤ 40 mm)
 Tensile strength 400 – 510 MPa

Worth stressing: CT38 is not automatically SS400, nor automatically Q235 or A36. The standards differ in test conditions and thickness ranges. Direct equivalence is an assumption, not a fact.

On the shop floor

• Calculating bending force for ordinary parts: estimating CT3 as SS400 is acceptable; the error will not change the machine class.
• Load-bearing parts, structural work, or anything subject to inspection: request the material certificate. Don't calculate from a name.
• Supplier cannot produce a certificate: that itself is important information, and worth weighing before the material goes into a critical part.