Q355NC High Strength Low Alloy Structural Steel
Compliant with GB/T 1591-2018 | Normalized / Normalized Rolled (N) Delivery
4.1 Designation System
Format: Q + Minimum Upper Yield Strength + Delivery Condition Code + Quality Grade (B, C, D, E, F)
Example Q355NC: Q = Yield strength, 355 = Minimum yield value (MPa), N = Normalized/Normalized rolling, C = Quality grade C
Note 1: Normalized condition includes normalized + tempering. N code represents both normalized and normalized rolling.
Note 2: Q + minimum upper yield strength + delivery condition code = "Steel grade".
For Z-direction property: Add suffix like Q355NCZ25
7.3 Delivery Condition
Q355NC steel is supplied in Normalized (N) or Normalized Rolling (N) condition.
Note: Normalized condition includes normalized + tempering. Normalized rolling is a rolling process where final deformation is carried out in a certain temperature range to achieve a condition equivalent to normalized.
Table 3 Chemical Composition (Ladle Analysis) — Normalized Q355NC
| Grade | Quality | C max | Si max | Mn | P max | S max | N max | Alt min | Microalloy | Additional |
|---|---|---|---|---|---|---|---|---|---|---|
| Q355N | C | 0.20 | 0.50 | 0.90-1.65 | 0.030 | 0.025 | 0.012 | 0.015 | Nb+V+Ti≤0.22b | — |
a For normalized/normalized rolled steel: Al ≥0.015%, Nb+V+Ti ≤0.22% (fine grain elements).
b For normalized steel (Q355NC), the total content of Nb, V, Ti shall not exceed 0.22%.
c Nitrogen content analysis may be omitted if guaranteed by supplier.
d Product analysis tolerance according to GB/T 222.
e For supply of commercial steel billets, lower limit of chemical composition may be agreed upon.
f When thickness direction performance (Z-direction) is required, sulfur content shall comply with GB/T 5313.
Table 4 Carbon Equivalent CEV (max) — Normalized Q355NC
| Grade | Quality | ≤63mm | >63-100mm | >100-250mm | >250-400mm | Note |
|---|---|---|---|---|---|---|
| Q355N | C | 0.43 | 0.45 | 0.45 | Agreement | a |
a For thickness >250-400mm, CEV value shall be agreed upon between supplier and purchaser.
Table 9 Tensile Properties — Normalized Q355NC
| Thickness (mm) | Upper Yield Strength (MPa) min | Tensile Strength (MPa) | Elongation A% min | Note |
|---|---|---|---|---|
| ≤16 | 355 | 470-630 | 22 | a |
| >16-40 | 345 | |||
| >40-63 | 335 | |||
| >63-80 | 325 | |||
| >80-100 | 315 | 470-630 | ||
| >100-150 | 295 | |||
| >150-250 | 285 | 450-600 | 22 | b |
| >250-400 | 275 |
* When yield point is not obvious, Rp0.2 may be used instead of upper yield strength.
a For plates and coils with nominal width ≥600mm, transverse specimens; for other steel products, longitudinal specimens.
b For thickness >150-400mm, only applicable for quality grade D and higher (not for Grade C).
Table 11 Charpy V-Notch Impact Test — Q355NC
| Quality Grade | Test Temperature | Longitudinal KV2 (J) min | Transverse KV2 (J) min | Note |
|---|---|---|---|---|
| C | 0°C | 34 | 27 | a |
a 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, grade C shall be tested at 0°C.
Table 12 Bending Test (180°) — Q355NC
| Thickness (mm) | Bending Diameter D | Note |
|---|---|---|
| ≤16 | D = 2a (a = specimen thickness) | a |
| >16-100 | D = 3a |
a 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 — Q355NC
| GB/T 1591-2018 | EN 10025-3 | ISO 630-3 | Previous GB/T 1591-2008 | Note |
|---|---|---|---|---|
| Q355NC (Normalized) | S355N | — | Q345C (Normalized) | a |
a Q355NC replaces Q345C normalized grade with improved mechanical properties (increased by 10-15 MPa). EN 10025-3 S355N is the European equivalent for normalized fine grain structural steel. For low temperature impact (-20°C), Q355ND corresponds to EN 10025-3 S355NL.
CEV formula: CEV(%) = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
Note: Carbon equivalent (CEV) based on ladle analysis.