Q355C High Strength Low Alloy Structural Steel
Compliant with GB/T 1591-2018 | Replaces Q345C | Hot Rolled (AR) Delivery
4.1 Designation System
Format: Q + Minimum Upper Yield Strength + Delivery Condition Code + Quality Grade (B, C, D, E, F)
Example Q355C: Q = Yield strength, 355 = Minimum yield value (MPa), C = Quality grade C
Note 1: Hot rolled condition (AR/WAR) code can be omitted. Q355C is hot rolled state.
Note 2: Q + minimum upper yield strength + delivery condition code = "Steel grade".
For Z-direction property: Add suffix like Q355CZ25
7.3 Delivery Condition
Q355C steel is supplied in Hot Rolled (AR) condition.
Note: Hot rolled condition includes hot rolled without special rolling and/or heat treatment. Normalized condition includes normalized + tempering; TMCP condition includes TMCP + tempering.
Table 1 Chemical Composition (Ladle Analysis) — Hot Rolled Q355C
| Grade | Quality | C max | Si max | Mn | P max | S max | N max | Alt min | Microalloy |
|---|---|---|---|---|---|---|---|---|---|
| Q355 | C | 0.20 | 0.50 | 0.90-1.65 | 0.030 | 0.030 | 0.012 | 0.015 | Nb/V/Tia |
a To improve steel properties, alloying elements (Nb, V, Ti) may be added by agreement. Total microalloy content ≤0.22%.
b For normalized/normalized rolled steel: Al ≥0.015%, Nb+V+Ti ≤0.22%.
c For TMCP steel: Nb ≤0.09%, V ≤0.10%, Ti ≤0.06%.
d Nitrogen content analysis may be omitted if guaranteed by supplier.
e Product analysis tolerance according to GB/T 222.
f For supply of commercial steel billets, lower limit of chemical composition may be agreed upon.
g When thickness direction performance (Z-direction) is required, sulfur content shall comply with GB/T 5313.
Table 2 Carbon Equivalent CEV (max) — Hot Rolled Q355C
| Grade | Quality | ≤30mm | >30-63mm | >63-150mm | >150-250mm | >250-400mm |
|---|---|---|---|---|---|---|
| Q355 | C | 0.45 | 0.47 | 0.47 | 0.49 | — |
a When Si is controlled (e.g., hot dip galvanizing): for Si ≤0.030%, CEV may increase by 0.02%; for Si ≤0.25%, CEV may increase by 0.01%.
b For sections and bars, max CEV can be 0.54%.
Table 7 Tensile Properties — Hot Rolled Q355C
| Thickness (mm) | Upper Yield Strength (MPa) min | Tensile Strength (MPa) |
|---|---|---|
| ≤16 | 355 | 470-630 |
| >16-40 | 345 | |
| >40-63 | 335 | |
| >63-80 | 325 | |
| >80-100 | 315 | 470-630 |
| >100-150 | 295 | 470-630 |
| >150-200 | 285 | 450-600 |
| >200-250 | 275 |
* When yield point is not obvious, Rp0.2 may be used instead of upper yield strength.
* For plates and coils with nominal width ≥600mm, transverse specimens; for other steel products, longitudinal specimens.
* For nominal width ≥600mm plates and strips, transverse specimens for tensile test; for other steel products, longitudinal specimens.
Table 8 Elongation — Hot Rolled Q355C
| Direction | ≤40mm | >40-63 | >63-100 | >100-150 | >150-250 |
|---|---|---|---|---|---|
| Longitudinal | 22 | 21 | 20 | 18 | 17 |
| Transverse | 20 | 19 | 18 | 18 | 17 |
Table 11 Charpy V-Notch Impact Test — Q355C
| Quality Grade | Test Temperature | Longitudinal KV2 (J) min | Transverse KV2 (J) min |
|---|---|---|---|
| C | 0°C | 34 | 27 |
* For nominal thickness ≥6mm or diameter ≥12mm, impact test shall be performed.
* Standard specimen: 10×10×55mm. For smaller sizes: 10×7.5×55mm (75% of specified value) or 10×5×55mm (50% of specified value).
* Impact test takes longitudinal specimens by default. Transverse specimens may be taken by agreement.
* When the supplier does not specify the test temperature, grades C shall be tested at 0°C.
Table 12 Bending Test (180°) — Q355C
| Thickness (mm) | Bending Diameter D |
|---|---|
| ≤16 | D = 2a (a = specimen thickness) |
| >16-100 | D = 3a |
* For plates and coils with nominal width ≥600mm, transverse specimens; for other steel products, longitudinal specimens.
* If the supplier can guarantee bending test qualification, the test may be omitted.
Appendix A International Grade Comparison — Q355C
| GB/T 1591-2018 | ISO 630-2 | EN 10025-2 | EN 10025-3 | EN 10025-4 | Previous GB/T 1591-2008 |
|---|---|---|---|---|---|
| Q355C (Hot Rolled) | S355C | S355J0 | — | — | Q345C (Hot Rolled) |
* Q355C replaces Q345C with improved mechanical properties (increased by 10-15 MPa).
* For normalized grade Q355NC, refer to EN 10025-3 S355N; for TMCP grade Q355MC, refer to EN 10025-4 S355M.
CEV formula: CEV(%) = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
Pcm formula: Pcm(%) = C + Si/30 + Mn/20 + Cu/20 + Ni/60 + Cr/20 + Mo/15 + V/10 + 5B
Note: Carbon equivalent (CEV) based on ladle analysis. When C ≤0.12% in TMCP steel, Pcm may be used instead of CEV.