SIST EN 3491:2009

Overview

SIST EN 3491:2009 is a European standard developed by CEN that specifies the requirements for Steel FE-PM3901 (X15CrNi17-3) used in aerospace applications. This standard covers air melted, hardened and tempered forgings with a diameter equal to or less than 100 mm and a tensile strength between 900 MPa and 1,100 MPa. Designed specifically for the aerospace industry, these high-performance steel forgings are critical for manufacturing durable and reliable components subject to rigorous mechanical demands.

The standard provides clear guidelines on chemical composition, mechanical properties, heat treatment processes, and quality assurance for these steel forgings, ensuring that they meet the stringent safety and performance criteria necessary for aerospace manufacturing.

Key Topics

• Material Specification
  Steel FE-PM3901, also known as X15CrNi17-3, is an austenitic stainless steel characterized by:

  • Carbon (C): max 0.20%
  • Chromium (Cr): 15.0% min, 17.0% max
  • Nickel (Ni): 2.00% min, 3.00% max
  • Other elements including Silicon (Si), Manganese (Mn), Phosphorus (P), Sulfur (S), and Molybdenum (Mo) within controlled limits.

• Form and Dimensions
  The standard governs forgings with a maximum diameter of 100 mm to guarantee uniform properties and performance.

• Heat Treatment
  Key for achieving specified mechanical properties, the steel is hardened and tempered using:

  • Quenching between 950°C and 1,040°C
  • Tempering between 585°C and 685°C
    These treatments ensure strength (Rm between 900 MPa and 1,100 MPa) and ductility (minimum elongation of 12%).

• Mechanical Properties
  SIST EN 3491:2009 mandates:

  • Tensile strength (Rm): 900 MPa to 1,100 MPa
  • Proof stress (Rp0.2): minimum 700 MPa
  • Hardness: 262 HB to 331 HB
  • Impact strength: minimum 20 J at ambient temperature
  • Chemical and mechanical uniformity in line with aerospace quality standards.

• Quality Control and Testing
  In line with aerospace industry demands, the standard requires:

  • Microstructure analysis with δ-ferrite content less than 5%
  • Dimensional, external and internal defect inspections according to EN 2157-3
  • Batch uniformity and product qualification agreements between supplier and purchaser.

Applications

SIST EN 3491:2009 steel forgings are primarily intended for aerospace structural components and critical parts where high strength and corrosion resistance are essential. Typical use cases include:

• Aircraft engine components
• Landing gear assemblies
• Structural supports
• High-stress mechanical parts in aerospace vehicles

The strict control on dimensions, heat treatment, and mechanical properties ensures these steel forgings can withstand the demanding environments typical in the aerospace sector, including high mechanical loads and exposure to corrosive conditions.

Related Standards

Users of SIST EN 3491:2009 should consider these additional standards for comprehensive compliance in aerospace material applications:

• EN 2157-3: Technical specifications for aerospace steel forgings – pre-production and production forgings
• EN 3365: Steel FE-PM3901 – Air melted, softened forging stock
• EN 4436: Test methods for determination of δ-ferrite content in steel
• EN 4258: General organization of aerospace metallic materials standards
• EN 4500-5: Rules for drafting and presentation of aerospace steels standards

These interconnected standards provide guidance on material testing, stock preparation, and standardization frameworks, facilitating full compliance and quality assurance in aerospace manufacturing processes.

Keywords: SIST EN 3491:2009, steel forgings, aerospace steel standards, FE-PM3901, X15CrNi17-3, air melted steel, hardened and tempered steel, aerospace forgings, tensile strength 900 MPa, 1100 MPa steel, aerospace materials standards, CEN aerospace steel.