S355N Z35, Z25, Z15 Through-Thickness Grades

S355N Z35, Z25, Z15 Through-Thickness Grades

At Gangsteel, we’re excited to delve into the S355N Z35, Z25, Z15 through-thickness grades, essential features of this high-strength, low-alloy structural steel under EN 10025-3, enhanced for superior ductility in heavy welded structures. S355N with Z-quality (Z15, Z25, Z35 per EN 10164) is designed to prevent lamellar tearing in thick plates, making it ideal for demanding applications like bridges, cranes, and offshore platforms in moderate climates.

As part of the en 10025 3 normalized steel plate family, S355N Z-grades offer a minimum yield strength of 355 MPa and -20°C toughness, with varying levels of through-thickness ductility. Gangsteel explores S355N Z35, Z25, Z15 through-thickness grades, their chemical composition, mechanical properties, and applications, comparing them to grades like en 10025 3 s420n normalized structural steel plate and en 10025 3 s460n normalized structural steel plate. For more details, visit our en 10025 3 s355n normalized structural steel plate page.

What are S355N Z-Grades?

S355N is a high-strength structural steel with a minimum yield strength of 355 MPa for plates up to 16 mm thick. The Z-grades, per EN 10164, add through-thickness quality for enhanced ductility:

• S355N Z15: ≥15% reduction of area, basic quality for moderate welds.
• S355N Z25: ≥25% reduction of area, for standard heavy welds.
• S355N Z35: ≥35% reduction of area, the highest quality for critical heavy welds, preventing lamellar tearing.

These grades ensure ductility through the plate thickness, vital for thick sections in welded structures. Compared to en 10025 3 s460n normalized structural steel plate, S355N Z35 offers lower strength (355 MPa vs 460 MPa) but superior weld reliability for moderate-load applications.

Chemical Composition of S355N Z-Grades

The chemical composition of S355N Z35, Z25, and Z15 is the same as standard S355N, 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, ensuring weldability. Low sulfur (≤0.025%) and phosphorus (≤0.030%) minimize inclusions, critical for Z-grades.

Mechanical Properties of S355N Z-Grades

The mechanical properties of S355N Z35, Z25, and Z15 match standard S355N, with added through-thickness ductility:

• Yield Strength: Starts at 355 MPa for thin plates, ideal for moderate loads.
• Tensile Strength: 470-630 MPa ensures durability.
• Elongation: ≥22% supports complex designs.
• Impact Toughness: ≥27 J at -20°C ensures reliability in moderate climates.
• Z-Quality: S355N Z35 ensures ≥35% reduction of area through thickness (EN 10164), preventing lamellar tearing; Z25 ≥25%, Z15 ≥15%.
• Hardness: Typically 150-190 HB (Brinell), balancing machinability and durability.

Z-Test for Through-Thickness Toughness

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

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

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

Welding and Heat Treatment

S355N Z35, Z25, and 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 S355N Z-Grades

S355N Z35, Z25, and Z15 are used in:

• Bridges: Z35 for thick welded girders in moderate climates.
• Cranes: Z25/Z35 for heavy structural welds.
• Building Frameworks: Z35 for critical load-bearing welds.
• Heavy Machinery: Z25/Z35 for robust welds.

S355N Z15 suits less demanding welds.

Why Choose Gangsteel?

Gangsteel supplies S355N Z-grades:

• Inventory: Extensive stock in China.
• Sizes: Thickness 6–200 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 normalized steel plate.

FAQ

What is S355N Z35?
S355N Z35 is S355N with Z35 quality per EN 10164, ensuring ≥35% reduction of area through thickness, preventing lamellar tearing in heavy welded structures like bridges.

How does S355N Z25 differ from Z35?
S355N Z25 requires ≥25% reduction of area for moderate welds, while Z35 (≥35%) is for critical heavy welds in cranes, both with -20°C toughness.

What is S355N-Z35?
S355N-Z35 is synonymous with S355N Z35, denoting high through-thickness ductility (≥35% reduction) per EN 10164, ideal for thick plates.

What is S355N Z15?
S355N Z15 is the basic Z-quality with ≥15% reduction of area, suitable for less demanding welds in moderate-thickness plates.

Are S355N Z-grades weldable?
Yes, S355N Z-grades are weldable with CEV ≤0.43%, using GMAW/SAW with preheating (100-150°C for >20 mm); Z-quality reduces lamellar tearing risks.

What applications use S355N Z25?
S355N Z25 is used in moderate welded structures like cranes and frameworks, with ≥25% through-thickness ductility ensuring weld reliability.

Summary

S355N Z35, Z25, and Z15 grades under EN 10025-3 offer a minimum yield strength of 355 MPa and -20°C toughness (≥27 J), with varying levels of through-thickness ductility (≥35%, ≥25%, ≥15% reduction of area per EN 10164).

These Z-grades prevent lamellar tearing in heavy welds, making them essential for thick plates in bridges, cranes, building frameworks, and heavy machinery.

Gangsteel’s inventory supports thicknesses from 6–200 mm, with global delivery in 7-30 days and certifications like EN 10204 3.1/3.2 and Z-test (EN 10164).

Compared to S460N, S355N Z-grades provide a cost-effective solution with superior ductility for moderate-load applications in temperate climates.