ISO 630-3:2021

Overview

ISO 630-3:2021 - "Structural steels - Part 3: Technical delivery conditions for fine-grain structural steels" defines the delivery requirements for hot‑rolled, weldable fine‑grain structural steels intended for heavily loaded parts of welded or bolted structures. It covers flat and long products (plates rolled on reversing mills, wide flats, hot‑rolled sections and bars) in specified delivery conditions: as‑rolled (SG grades only), normalized/normalized rolled, and thermomechanical processed. The standard is aimed at ensuring consistent chemical, mechanical and impact properties for fine‑grain steels used in structural applications.

Key topics and requirements

• Scope & product types: Applies to hot‑rolled plates, wide flats, sections and bars with nominal thicknesses from 3 mm up to specified maxima per grade (e.g., up to 250 mm for some N grades; see Annexes).
• Grades and qualities: 13 grades are specified across two normative annexes:
  • Annex A: S275, S355, S390, S420, S460, S500
  • Annex B: SG245, SG290, SG325, SG345, SG365, SG415, SG460
    Each grade is available in up to 6 qualities with different Charpy V‑notch impact requirements: A (no impact), C (0 °C), D (‑20 °C), E (‑40 °C), L (‑50 °C), F (‑60 °C).
• Chemical composition: Heat and product analyses are specified in the annex tables. Steels shall be fully killed, contain sufficient nitrogen‑binding elements and exhibit a fine‑grain microstructure.
• Mechanical properties: Tensile properties and Charpy V‑notch impact energy requirements are defined by grade/quality and thickness ranges.
• Carbon equivalent (CEV): Maximum CEV limits are specified to support weldability assessment.
• Inspection, sampling and test units: Verification is by heat. Typical test‑unit sizes: Annex A - 60 t (80 t for heavy sections >200 kg/m or certain cast masses); Annex B - 50 t. Specific test frequencies and methods reference ISO 630‑1.
• Delivery condition & marking: Delivery condition must be stated on inspection documents; marking and other delivery requirements refer to ISO 630‑1.

Applications

• Specification for materials used in bridges, cranes, heavy civil and structural steelwork, offshore platforms and other heavily loaded welded or bolted structures.
• Ensures weldability, required impact toughness at specified temperatures and predictable mechanical performance for design and fabrication.

Who should use this standard

• Steel producers and rolling mills for product specification and quality control
• Structural engineers and fabricators selecting steels for design and welding
• Procurement professionals specifying material delivery conditions
• Inspection bodies and testing laboratories performing conformity checks

Related standards

• ISO 630‑1 - General technical delivery conditions for hot‑rolled products (referenced for many procedures)
• ISO 643 - Grain size determination (used to define fine‑grain)
• ISO technical committees: ISO/TC 17/SC 12 (sheet & strip) and ISO/TC 5/SC 1 (tubular products) for excluded product families

Keywords: ISO 630-3:2021, structural steels, fine‑grain, technical delivery conditions, hot‑rolled, weldable steels, Charpy V‑notch, thermomechanical processed, normalized steel, steel grades.