What is EN10028-6 P355QH Steel ?

P355QH is a high-strength carbon steel for pressure vessels and high-temperature use. “P” stands for pressure, “355” indicates a 355 MPa yield strength, and “QH” refers to quenching and tempering. Equivalent grades include P355NH and A516 Grade 70. It offers toughness, weldability, and heat resistance and is used in boilers, pressure vessels, and heat exchangers in the oil, gas, power, and chemical industries.

• Normalizing (Optional):
  • Heat to 890-950°C (1634-1742°F).
  • Hold until fully austenitized, then air cool.
  • Effect: Refines grain structure and improves toughness.
• Quenching:
  • Heat to 900-950°C (1652-1742°F).
  • Hold until fully austenitized, then rapidly cool in water or oil.
  • Effect: Increases strength and hardness while refining grain structure.
• Tempering:
  • Reheat to 600-680°C (1112-1256°F).
  • Hold for a sufficient time, then air cool.
  • Effect: Reduces brittleness and improves toughness and ductility.
• Stress Relieving (Optional):
  • • Heat to 550-650°C (1022-1202°F).
    • Hold for 1-2 hours, then cool in air.
    • Effect: Relieves internal stresses from quenching or forming.

1. Pickling: Removes surface impurities and oxidation for a clean metal surface.
2. Galvanizing: Coats the steel with zinc to enhance corrosion resistance.
3. Painting: Adds a protective layer to resist corrosion and wear.
4. Shot Blasting: Cleans the surface and improves coating adhesion.
5. Polishing: Provides a smooth, reflective finish for aesthetic or functional purposes.
6. Passivation: Enhances corrosion resistance by forming a protective oxide layer.