The thickness has a direct, significant effect on the mechanical properties of S355J0WP, especially yield strength, tensile strength, toughness, and weldability.
1. Yield & Tensile Strength
Thinner plate (≤ 16 mm)Strength is highest; yield strength easily reaches ≥ 355 MPa, often higher.
Thicker plate (> 16 mm, up to 40 mm, 60 mm, 80 mm)Strength gradually decreases with increasing thickness.
Standard allows lower minimum yield for thicker sections:
≤ 16 mm: ≥ 355 MPa
16–40 mm: ≥ 345 MPa
40–63 mm: ≥ 335 MPa
63–80 mm: ≥ 325 MPa
2. Toughness (impact resistance)
Thin plates: better toughness, more stable impact energy.
Thick plates:Core material cools slower during production → coarser grain → lower toughness in the center.S355J0WP requires impact test at 0°C; thick plates may show lower absorbed energy.
3. Weldability
Thin plates (< 16 mm):Low cold-crack tendency; usually no preheat needed.
Thick plates (> 20–30 mm):Higher carbon equivalent effect; slower heat dissipation →Higher risk of hardening in HAZ; may need preheat (80–150°C).
4. Hardness & Uniformity
Thin plates: more uniform structure and hardness.
Thick plates:Surface and core structure differ → hardness less consistent.
5. Stability & Deformation resistance
Thinner plates: easier to warp, bend, or deform under load or heat.
Thicker plates: higher rigidity, better dimensional stability.
