EN 10025-3 S460NL Welding and Heat Treatment

EN 10025-3 S460NL Welding and Heat Treatment

S460NLis a high-strength structural steel grade specified in EN 10025-3, known for its fine grain structure, normalized delivery condition, and excellent toughness at low temperatures (tested at –50 °C). It is widely used in heavy welded structures, bridges, offshore platforms, wind towers, and crane components.
To ensure safe performance in service, understanding the welding behavior and heat treatment process of S460NL is essential.

1. Welding Characteristics of S460NL

S460NL has good weldability mainly due to its controlled chemical composition and low carbon equivalent (CEV). However, because of its high strength, special attention must be given to heat input, preheating, and post-weld stress control.

1.1 Typical Chemical Limits for Weldability

CE ≤ 0.50 ensures good weldability, but thicker plates may still need preheating.

2. Welding Guidelines

2.1 Preheating Recommendations

Purpose:
✔Prevent cold cracking
✔Reduce hydrogen-induced cracking
✔Improve weld penetration and quality

2.2 Recommended Welding Methods

2.3 Post-Weld Heat Treatment (PWHT)

• Not always requiredfor general structural applications
• Used when:
  ✅Plate thickness is > 50 mm
  ✅Welded structures are under high residual stress
  ✅Code/standard requires stress relief (EN, Eurocode 3, ASME)

Stress Relief Temperature:

• 530 °C – 580 °C for 1–2 hours (depending on thickness)

3. Heat Treatment of S460NL

S460NL is supplied in the Normalized or Normalized-Rolled (N/NL) condition.

3.1 Normalizing (as-delivered state)

• Temperature: 850 °C to 950 °C
• Air cooling
• Produces fine ferrite–pearlite structure
• Enhances toughness at low temperatures

3.2 Annealing

• Rarely necessary unless repairing excessive hardness or distortion
• Full annealing: 650–700 °C, slow cooling

3.3 Quenching & Tempering

• Not typical for standard S460NL
• If higher strength is needed, consider S460Q / S460QL (EN 10025-6) instead of heat-treating S460NL

4. Selection of Welding Consumables

✔Choose low-hydrogen electrodes
✔Ensure impact toughness ≥ 27J at –50 °C
✔Pre-dry electrodes at 350–400 °C for 1–2 hours to avoid hydrogen cracking

5. Welding Defects & Prevention

6. Conclusion

• S460NL offers excellent weldability and toughness, but proper welding parameters are essential.
• Preheating and controlled heat inputare critical for thick plates.
• PWHT (stress relieving)is optional but beneficial for thick or stress-sensitive structures.
• The steel is delivered in normalized (N/NL) condition, making additional heat treatment usually unnecessary.
• Choosing the correct filler material, preheat, and welding procedure ensures safe performance in service.