What Is S420M
S420M is a thermo-mechanically rolled, fine-grain high-strength structural steel specified in EN 10025-4. The "M" designation indicates thermo-mechanical rolling, a process that delivers consistent mechanical properties and better toughness than standard normalized grades. The grade provides a minimum yield strength of 420 MPa, excellent toughness and ductility, and good weldability and formability, which makes it suitable for bridges, offshore structures, cranes, heavy machinery, and structural engineering applications.
Tensile Strength by Thickness
The tensile strength of S420M varies with plate thickness. For thicknesses up to 16 mm, the tensile strength range is 520–680 MPa. The same range applies for thicknesses over 16 mm and up to 40 mm. For thicknesses over 40 mm and up to 63 mm, the range is 500–660 MPa, and for thicknesses over 63 mm and up to 80 mm, it is 480–640 MPa. Across the common supply range, the overall tensile strength therefore spans approximately 480 to 680 MPa depending on the plate thickness and processing.
Other Mechanical Properties
In addition to tensile strength, S420M provides a minimum yield strength of 420 MPa for plates up to 16 mm, with the minimum decreasing for thicker plates, and elongation (A5) of at least 20–22% depending on thickness. The Charpy impact requirement is at least 27 J at −20°C. Density is 7.85 g/cm³, consistent with structural steels. These properties make the grade suitable for dynamically loaded welded structures in cold environments.
Chemical Composition
The typical chemical composition of S420M is: carbon 0.22% maximum, silicon not more than 0.55%, manganese 1.00–1.60%, phosphorus 0.025% maximum, sulfur 0.020% maximum, with micro-alloying additions of niobium up to 0.06%, vanadium up to 0.12%, and titanium up to 0.03%. The fine-grain and micro-alloyed composition supports the high strength and good weldability of the grade, with carbon equivalent limits defined in EN 10025-4 for thicker plates.
Non-Destructive Testing and Certification
S420M does not inherently require ultrasonic (UT) or radiographic (RT) testing under the EN 10025-4 standard for general delivery. EN 10025-4 specifies mechanical and chemical properties, while non-destructive testing is only required if it is specified by the customer or the project. For critical structural applications such as offshore platforms, bridges, and pressure vessels, clients may require UT or RT to detect internal defects or inclusions. Standard S420M plates are typically supplied with mill test certificates per EN 10204 3.1 or 3.2, verifying chemical composition and mechanical properties.
Typical Applications
S420M combines high strength, toughness, and weldability, which makes it a preferred material for welded components in bridges, offshore structures, cranes, and heavy engineering. The thermo-mechanically rolled delivery condition gives consistent through-thickness properties, allowing designers to use thinner sections than would be required with lower-strength grades, reducing weight and fabrication cost.
Frequently Asked Questions
What is the tensile strength of S420M? The tensile strength is 520–680 MPa for plates up to 40 mm, 500–660 MPa for plates over 40 mm to 63 mm, and 480–640 MPa for plates over 63 mm to 80 mm.
What is the yield strength of S420M? The minimum yield strength is 420 MPa for plates up to 16 mm, decreasing stepwise for thicker plates according to EN 10025-4.
What does the M in S420M mean? M indicates thermo-mechanically rolled steel, a delivery condition that provides consistent mechanical properties and better toughness than normalized grades.
Does S420M require ultrasonic or radiographic testing? Not inherently. Under EN 10025-4, UT or RT is only required when specified by the customer or project, although it is common for critical structures such as offshore platforms and bridges.
What certificates are typically supplied with S420M plates? Standard plates are typically supplied with mill test certificates according to EN 10204 3.1 or 3.2, verifying chemical composition and mechanical properties.
Where is S420M used? S420M is used in bridges, offshore structures, cranes, heavy machinery, and general structural engineering where high strength, toughness, and weldability are required.
