EN 4720:2014

Overview

EN 4720:2014 is a European standard developed by CEN that specifies the technical requirements for Aerospace series steel grade X4CrNiMo16-5-1 (1.4418). This high-performance stainless steel is air melted and electroslag remelted (ESR), hardened and tempered, offered as bars with an external diameter (De) of up to 200 mm. The steel exhibits a tensile strength range of 1150 MPa to 1300 MPa, making it ideal for critical aerospace applications.

This standard ensures consistent chemical composition, mechanical properties, and material quality, catering specifically to the demanding safety and performance criteria of the aerospace industry. The document supports the use of this steel under precise heat treatment and manufacturing conditions, ensuring optimal strength, durability, and cleanliness.

Key Topics

• Material Specification: Steel grade X4CrNiMo16-5-1 (1.4418), also known as AIR: Z 8 CND 17-04, characterized by a controlled chemical composition including carbon (C), silicon (Si), manganese (Mn), chromium (Cr), molybdenum (Mo), and nickel (Ni).

• Manufacturing Process: Bars are produced through air melting followed by electroslag remelting (ESR) to improve cleanliness and reduce inclusions, crucial for aerospace reliability.

• Mechanical Properties:

  • Tensile strength (Rm): 1150 MPa to 1300 MPa
  • Proof stress (Rp0.2): ≥ 900 MPa
  • Elongation and impact strength requirements, ensuring toughness at ambient and subzero temperatures
  • Hardness range specified between 350 and 401 HBW in the hardened and tempered condition

• Heat Treatment: Standardized procedures include hardening by quenching (oil or water quench) and subsequent tempering within defined temperature ranges to achieve desired mechanical characteristics.

• Dimensions and Forms: Bars with external diameters of up to 200 mm, adhering strictly to dimensional tolerances to maintain consistency during assembly.

• Quality Assurance:

  • Microstructure requirements: Grain size G = 5 or finer
  • Cleanliness class and limits on non-metallic inclusions to prevent compromising performance
  • Inspection methods including ultrasonic testing and visual inspection

• Standard References: EN 4700-002 for technical specifications on bars, EN 2043 for product qualification, EN 2951 for micrographic testing, and AMS 2315 for delta ferrite content determination.

Applications

EN 4720:2014 steel bars are designed specifically for aerospace industry applications where high strength, toughness, and corrosion resistance are critical. Typical aerospace uses include:

• Structural components subject to high mechanical stress
• Fasteners and precision-engineered parts requiring durability and fatigue resistance
• Aircraft engine and landing gear components where material performance is vital
• Components exposed to varying temperatures and demanding service environments

The steel’s high tensile strength and refined microstructure enhance fatigue life and reliability, making it suitable for safety-critical aerospace systems.

Related Standards

• EN 4700-002: Details technical specifications for bar and section forms of steels and heat-resisting alloys.
• EN 2043: Provides general requirements for qualification of semi-finished metallic aerospace products.
• EN 2951: Specifies micrographic methods for determining non-metallic inclusion content in metallic materials.
• EN 4050-4: Establishes ultrasonic inspection protocols for bars and forgings, setting acceptance criteria for aerospace-grade materials.
• EN 4258: Describes the organization of Aerospace metallic material standards, linking EN 4720 to broader aerospace material standardization.
• AMS 2315: A widely recognized US standard for measuring delta ferrite content in aerospace steels.

EN 4720:2014 sets a robust benchmark for aerospace-grade stainless steel bars, ensuring high performance through stringent control of composition, mechanical properties, and quality inspection. Adhering to this standard guarantees material integrity vital for aerospace safety and reliability.