SIST EN 4721:2015

Overview

EN 4721:2014 (CEN) is a European aerospace material standard that defines requirements for steel X4CrNiMo16-5-1 (1.4418) supplied as bars (De ≤ 200 mm). The standard covers both air melted and electroslag remelted (ESR) production routes and specifies the hardened-and-tempered delivery condition with a tensile strength range of 900 MPa to 1 050 MPa. Common alternate designation: AIR / Z 8 CND 17-04.

Key topics and technical requirements

• Material designation and chemistry: Chemical composition limits for C, Si, Mn, P, S, N, Cr, Mo, Ni and balance Fe are given to ensure consistent corrosion resistance and mechanical performance (see standard for exact limits).
• Melting and product form: Permitted melting methods: air melted and electroslag remelted (ESR). Product form: bars with external diameter De ≤ 200 mm.
• Heat treatment: Austenitizing at 1 010 °C to 1 060 °C followed by quenching (oil or water quench; air quenching allowed for De ≤ 20 mm by agreement) and tempering at 580 °C to 610 °C.
• Mechanical properties: Specified tensile strength Rm = 900–1 050 MPa and proof stress Rp0.2 (minimum around 700 MPa depending on diameter/condition). Brinell hardness and elongation limits are specified by diameter and delivery/use condition. Charpy impact energy requirements are defined for specified test orientations and temperatures.
• Microstructure and cleanliness: δ‑ferrite content limited to ≤5%; grain size G ≥ 5 or finer (EN ISO 643); inclusion cleanliness and micro-cleanness requirements (category 4 per EN 2951); ultrasonic acceptance levels for internal defects (class 5 per EN 4050-4).
• Inspection and qualification: Dimensional, marking and inspection rules reference EN 4700-002. Product qualification and test-programme requirements are aligned with EN 2043 and related aerospace-series rules.

Applications and users

EN 4721:2014 is intended for high-strength aerospace applications where a corrosion-resistant, martensitic stainless-steel bar is required in a hardened-and-tempered condition. Typical users include:

• Aerospace OEMs and tiered suppliers specifying material for structural and mechanical components
• Materials and metallurgical engineers responsible for procurement and qualification
• Quality, inspection and testing laboratories performing acceptance tests
• Manufacturers of semi-finished bars requiring compliance with aerospace material standards

Related standards

Key normative references and linked aerospace-series standards: EN 4700-002, EN 4258, EN 2043, EN 2951, EN 4050-4, EN 4500-005 and EN ISO 643. These provide test methods, microstructure, cleanliness, ultrasonic acceptance and general organization rules for aerospace metallic materials.

Keywords: EN 4721:2014, X4CrNiMo16-5-1, 1.4418, aerospace steel, ESR, hardened and tempered, bar, 900 MPa, CEN.