s420nl vs s420ml

As a premier exporter and manufacturer of high-quality structural steel plates, Gangsteel specializes in producing EN 10025-compliant materials, including the S420NL and S420ML steel grades.

S420NL (EN 10025-3) and S420ML (EN 10025-4) are both high-strength low-alloy (HSLA) fine-grain structural steels with a minimum yield strength of 420 MPa, designed for welded constructions in demanding environments.

The primary difference lies in their delivery conditions: S420NL is normalized (+N), while S420ML is thermomechanically rolled (+M). This affects their microstructure, with S420ML often providing better formability and potentially lower production costs due to the TM process. Both grades offer excellent toughness at low temperatures (-50°C), making them ideal for bridges, cranes, offshore structures, and heavy machinery in cold climates.

Our S420NL and S420ML plates are delivered in their respective conditions to ensure superior weldability and impact resistance. For a comprehensive overview of our en 10025 3 normalized steel plate offerings, explore our full range.

What is S420NL Steel?

S420NL, designated as 1.8912 under EN 10025-3, is a normalized fine-grain structural steel optimized for low-temperature toughness (down to -50°C) and weldability. The normalization process involves heating to austenitizing temperature and air cooling, resulting in a refined grain structure that enhances ductility and resistance to brittle fracture. It is commonly used in applications where consistent mechanical properties and high impact resistance are critical, such as arctic infrastructure.

Gangsteel produces S420NL plates in thicknesses up to 250 mm, with precise control over chemical composition to meet CEV limits for optimal weldability.

What is S420ML Steel?

S420ML, designated as 1.8836 under EN 10025-4, is a thermomechanically rolled fine-grain structural steel with similar strength and low-temperature toughness as S420NL. The TM process combines controlled rolling with accelerated cooling, producing a finer grain structure without full normalization, which can reduce energy costs and improve formability. This makes S420ML suitable for applications requiring bending or shaping, like offshore components or heavy machinery frames.

Gangsteel supplies S420ML plates in thicknesses up to 100 mm, ensuring compliance with EN 10025-4 for projects demanding high strength in cold environments.

Chemical Composition Comparison

Both grades have similar low-carbon profiles for weldability, with S420NL having slightly tighter limits on some elements for enhanced toughness. Below is the ladle analysis for nominal thicknesses ≤ 100 mm, with a maximum Carbon Equivalent Value (CEV) of 0.48.

*Note: S420ML's slightly lower C and V may improve formability, while both maintain low CEV for welding without preheating in thin sections.

Mechanical Properties Comparison

Both grades have identical strength profiles but differ in delivery, affecting microstructure. All values are for their respective conditions (+N for S420NL, +M for S420ML). The table below consolidates yield strength, tensile strength, elongation, and Charpy V-Notch impact energy (longitudinal and transverse at -50°C minimums).

*Notes: Elongation based on Lo = 5.65 √So. Impact values are minimums; higher at warmer temperatures. S420ML's TM rolling may provide better formability, while S420NL's normalization ensures consistent toughness in thicker sections.

Heat Treatment Guide for S420NL and S420ML Steel

S420NL is supplied in normalized (+N) condition, while S420ML is thermomechanically rolled (+M), both refining grain structure for improved properties.

Normalization for S420NL

• Heating Temperature: Austenitize at 880–920°C (uniform throughout the thickness).
• Soaking Time: Hold for approximately 1 hour per 25 mm of thickness, minimum 30 minutes.
• Cooling: Air cool to room temperature at a controlled rate to avoid excessive hardening.
• Purpose: Refines ferrite-pearlite structure, enhances ductility, and ensures compliance with mechanical properties post-delivery.

Thermomechanical Rolling for S420ML

• Rolling Temperature: Controlled hot rolling followed by accelerated cooling.
• Purpose: Achieves fine-grain structure without full normalization, improving formability and reducing energy costs.

If post-delivery heat treatment is needed, re-normalize to maintain properties. Avoid quenching unless specified.

Welding Heat Treatment Guidelines (Both Grades)

• Preheating: Not required for ≤ 50 mm; recommend 100–150°C for thicker sections to prevent cold cracking, based on CEV ≤ 0.48.
• Interpass Temperature: Maximum 200°C to preserve fine grain.
• Post-Weld Heat Treatment (PWHT): Optional stress-relief at 550–650°C for 1 hour per 25 mm thickness, followed by slow cooling. Not typically needed due to low hardenability.
• Hot Forming: Perform above 850°C; re-normalize if forming temperature drops below 720°C.

Always consult EN 1011-2 for welding recommendations. Gangsteel provides plates optimized for these processes to minimize heat treatment needs.

Applications of S420NL and S420ML Steel

Both grades are used in:

• Heavy Engineering: Cranes, earthmoving equipment, and load-bearing frameworks.
• Infrastructure: Bridges, viaducts, and offshore platforms where low-temperature ductility is critical.
• Construction: Welded structures in shipbuilding and pressure vessels.

S420ML is preferred for applications requiring better formability, while S420NL is suited for thicker sections needing consistent normalization.

For higher strength needs, consider upgrading to en 10025 3 s460n normalized structural steel plate or en 10025 3 s460nl normalized structural steel plate.

Equivalent Grades to S420NL and S420ML

Why Choose Gangsteel for S420NL and S420ML Steel?

With state-of-the-art mills and a commitment to ISO-certified quality, Gangsteel delivers S420NL and S420ML plates tailored to your specifications. Stocked in various sizes and ready for immediate export worldwide. For detailed pricing and availability, visit our en 10025 3 s420nl normalized structural steel plate product page or contact our sales team today.

Summary

S420NL (EN 10025-3, normalized) and S420ML (EN 10025-4, thermomechanically rolled) are high-strength fine-grain steels with 420 MPa yield and -50°C toughness (27 J), differing mainly in processing: normalization for consistent properties in thick sections vs TM rolling for better formability and cost efficiency. Both excel in cold welded structures like bridges and offshore platforms. S420NL and S420ML from Gangsteel ensure reliability for global projects.

FAQ

What is the main difference between S420NL and S420ML?

S420NL is normalized (+N) for consistent toughness in thicker plates, while S420ML is thermomechanically rolled (+M) for improved formability and potentially lower costs; both have identical strength and -50°C impact.

Are the chemical compositions of S420NL and S420ML identical?

Nearly — S420ML has slightly lower max C (0.16% vs 0.20%) and V (0.12% vs 0.20%), with CEV ≤0.45 vs 0.48, for better formability.

Do S420NL and S420ML have the same mechanical properties?

Yes, identical yield (420 MPa ≤16 mm), tensile (520–680 MPa), elongation (18–19%), and -50°C impact (27 J longitudinal), but S420ML's TM process may enhance bendability.

When should I choose S420NL over S420ML?

Opt for S420NL in thicker sections (>100 mm) or when normalization is specified for consistent properties; S420ML for formable, thinner plates.

Are S420NL and S420ML weldable without preheating?

Yes, both have low CEV (≤0.48/0.45), so no preheat for ≤50 mm; 100–150°C for thicker, per EN 1011-2.