S355NL Z-Grades for Toughness

S355NL Z-Grades for Toughness

S355NL Z35, S355NL Z25, S355NL-Z35, and S355NL Z15 are enhanced quality variants of S355NL, a high-strength, low-alloy structural steel under EN 10025-3. These Z-grades indicate through-thickness ductility per EN 10164, reducing the risk of lamellar tearing in heavy welded structures. Z15 (≥15% reduction of area), Z25 (≥25%), and Z35 (≥35%) ensure superior toughness for demanding applications like offshore platforms and bridges. This article details the Z-grades, chemical composition, mechanical properties, and applications, addressing core keywords s355nl z35, s355nl z25, s355nl-z35, and s355nl z15. For more details, visit our EN 10025-3 S355NL normalized structural steel plate.

What are S355NL Z-Grades?

S355NL is a fine-grain structural steel under EN 10025-3, with:

• S: Structural steel.
• 355: Minimum yield strength of 355 MPa (≤16 mm).
• NL: Normalized, with impact toughness tested at -50°C.

Z-grades per EN 10164 add through-thickness quality:

• S355NL Z15: ≥15% reduction of area in through-thickness tensile testing.
• S355NL Z25: ≥25% reduction of area, for moderate welds.
• S355NL Z35and S355NL-Z35: ≥35% reduction of area, the highest Z-quality for heavy welds, preventing lamellar tearing.

The Z-test measures ductility through the plate thickness, ensuring weld reliability in thick sections.

Chemical Composition of S355NL Z-Grades

The composition of S355NL Z35, S355NL Z25, and S355NL Z15 is identical to standard S355NL, with low impurities for Z-quality:

Carbon Equivalent (CEV): ≤0.43% (≤63 mm), calculated as CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15, ensures weldability. Low sulfur (≤0.015%) minimizes inclusions, critical for Z-grades.

Mechanical Properties of S355NL Z-Grades

The mechanical properties of S355NL Z35, S355NL Z25, and S355NL Z15 match standard S355NL, with added through-thickness ductility:

• Z-Quality: S355NL-Z35 ensures ≥35% reduction of area through thickness (EN 10164), preventing lamellar tearing in heavy welds; Z25 ≥25%, Z15 ≥15%.
• Yield Strength: ≥355 MPa (≤16 mm) for load-bearing.
• Tensile Strength: 470-630 MPa for durability.
• Impact Toughness: ≥27 J at -50°C for cold climates.

Z-Test for Through-Thickness Toughness

The Z-test per EN 10164 measures ductility through the plate thickness to prevent lamellar tearing in thick welds:

• Z15: ≥15% reduction of area, basic quality.
• Z25: ≥25% reduction of area, moderate welds.
• Z35: ≥35% reduction of area, highest quality for heavy welds.
• Testing: Tensile test on cylindrical samples from the plate thickness, ensuring no internal defects.

Z-grades are optional but recommended for thick plates (>40 mm) in welded structures.

Welding and Heat Treatment

S355NL Z35, S355NL Z25, and S355NL Z15 are weldable:

• Welding: GMAW or SAW per EN 1011-2. Preheating (100-150°C) for >20 mm; Z-quality reduces cracking risk.
• PWHT: Optional at 550-650°C for critical welds.
• Consumables: ER70S-6 (GMAW), EM12K flux with EH14 wire (SAW).

Z-grades ensure weld reliability in heavy joints.

Applications of S355NL Z-Grades

S355NL Z35, S355NL Z25, and S355NL Z15 are used in:

• Offshore Platforms: Z35 for thick welded joints in cold marine environments.
• Wind Turbine Towers: Z25/Z35 for heavy structural welds in sub-zero climates.
• Bridges: Z35 for critical load-bearing welds in northern regions.
• Pressure Vessels: Z25/Z35 for low-temperature storage with robust welds.

S355NL Z15 is suitable for less demanding welds.

Why Choose Gangsteel?

Gangsteel supplies S355NL-Z35:

• Inventory: Extensive stock in China.
• Sizes: Thickness 6–250 mm, widths 2000/2500/3000 mm, lengths up to 12,000 mm.
• Delivery: 7-30 days globally.
• Certifications: EN 10204 3.1/3.2, Z-test (EN 10164), UT testing (EN 10160), ABS/LR/BV/DNV approvals.
• Processing: Cutting, welding, bending.

Contact us for EN 10025-3 S355NL normalized structural steel plate.

FAQ

What is S355NL Z35?
S355NL Z35 is S355NL steel with Z35 quality per EN 10164, ensuring ≥35% reduction of area through thickness, preventing lamellar tearing in heavy welded structures like offshore platforms.

How does S355NL Z25 differ from Z35?
S355NL Z25 requires ≥25% reduction of area, suitable for moderate welds, while Z35 (≥35%) is for critical heavy welds in bridges and wind towers, both maintaining -50°C toughness.

What is S355NL-Z35?
S355NL-Z35 is synonymous with S355NL Z35, denoting high through-thickness ductility (≥35% reduction) per EN 10164, ideal for thick plates in welded structures with low lamellar tearing risk.

What is S355NL Z15?
S355NL Z15 is the basic Z-quality with ≥15% reduction of area, suitable for less demanding welds in moderate-thickness plates, while Z25/Z35 offer higher ductility for heavy welds.

Are S355NL Z35 grades weldable?
Yes, S355NL Z35 grades are weldable with CEV ≤0.43%, using GMAW/SAW with preheating (100-150°C for >20 mm); Z-quality reduces lamellar tearing risks in thick welded joints.

What applications use S355NL Z25?
S355NL Z25 is used in moderate welded structures like wind towers and bridges in cold climates, with ≥25% through-thickness ductility ensuring weld reliability.