ISO 9327-4:1999

ISO 9327-4:1999 - Overview

ISO 9327-4:1999 specifies technical delivery conditions for weldable fine grain steels with high proof strength used for steel forgings and rolled or forged bars for pressure purposes. It applies to products up to 250 mm thickness and is intended to be used together with ISO 9327-1 (General requirements). The standard classifies steels into room‑temperature (P...), elevated‑temperature (PH...), low‑temperature (PL...) and combined low/elevated‑temperature (PLH...) grades. “Fine grain” is defined as grain size 6 or finer per ISO 643.

Key topics and requirements

• Chemical composition and product analysis: Limits for cast analysis and permissible product analysis tolerances are given (see Table 1 and Table 2).
• Mechanical properties: Tensile properties at room temperature and minimum 0.2% proof strength at elevated temperatures are defined (Table 4).
• Toughness / impact energy: Minimum Charpy V‑notch impact energy requirements are specified (Table 3). Tests use standard 10 mm × 10 mm specimens per ISO 148; the average of three tests is required, with one value allowed down to 70% of the specified average.
• Heat treatment and delivery condition: Typical delivery conditions (e.g., normalized, quenched & tempered) are indicated for each grade.
• Inspection, testing and conformity: Conformity assessment, sampling and testing frequency reference ISO 9327-1 and ISO/TR 15461. Marking and ordering follow ISO 9327-1.

Practical applications

ISO 9327-4 is tailored for components where a combination of high proof strength, good weldability, and fine‑grain toughness is critical. Typical applications include:

• Pressure vessels and boilers
• Piping flanges, forged fittings and connectors for high‑pressure systems
• Valve and pump components subjected to elevated or low temperatures
• Critical structural forgings in petrochemical and power industries

Using this standard helps ensure material traceability, consistent mechanical performance (strength and toughness), and suitability for welding in pressure‑rated applications.

Who should use this standard

• Material and metallurgical engineers specifying steel grades for pressure equipment
• Forging houses, steel mills and foundries producing forgings and bars
• Quality and inspection teams performing chemical, tensile and impact testing
• Design engineers, procurement and compliance personnel working to pressure‑equipment regulations

Related standards

• ISO 9327-1 - General requirements (ordering, inspection, marking)
• ISO 148 - Charpy impact test (V‑notch)
• ISO 643 - Grain‑size determination
• ISO/TR 15461 - Testing frequency and sampling for forgings

Keywords: ISO 9327-4:1999, weldable fine grain steels, steel forgings, rolled bars, pressure purposes, technical delivery conditions, proof strength, Charpy V‑notch, chemical composition, heat treatment.