P355N is a standardized European steel grade primarily used for pressure vessels, boilers, and industrial piping. It is defined under the EN 10028-3 (flat products) and EN 10216-3 (seamless tubes) standards.
Technical Specifications
Material Number: 1.0562.
Classification: Normalized, weldable, fine-grain structural steel.
Yield Strength: Minimum 355 MPa for thicknesses up to 16mm. For thicker sections, the yield strength gradually decreases (e.g., ~295 MPa for 100–150mm).
Tensile Strength: Typically ranges from 490 to 630 MPa.
Delivery Condition: Normalized (+N), meaning it is heat-treated to refine its grain structure, which improves toughness and weldability.
Variants & Subgrades
P355 is part of a family of steels, each optimized for different environmental conditions:
P355N: Standard room-temperature quality grade.
P355NH: High-temperature grade, characterized by elevated strength at temperatures up to 500°C.
P355NL1: Low-temperature grade, impact tested at -40°C.
P355NL2: Special low-temperature grade, impact tested at -50°C.
Key Features
Excellent Weldability: Its fine-grain structure and controlled carbon content allow for reliable welding in heavy structural projects.
High Impact Toughness: The normalization process ensures resistance to brittle cracking, even at lower temperatures (P355N is typically tested down to -20°C).
Corrosion Resistance: It has moderate resistance to general corrosion, though it is often further treated or coated for harsh environments.
P335N Chemical Properties:
| Grade | C % | Mn % | S % | N % | Cu % | Nb % | Ti % | Si % | P % | AL % | Cr % | Mo % | Ni % | Vi % |
| P 355 N | 0.10-0.22 | 0.10-1.70 | 0.015 | 0.012 | 0.30 | 0.020 | 0.03 | 0.60 | 0.025 | 0.020 | 0.30 | 0.08 | 0.30 | 0.02 |
P335N Mechanical Properties:
| Grade | Type | Thickness mm | Yield strength Mpa(min) | Tensile Strength MPa | Elongation % (min) | Impact Energy (KVJ) (min) | ||
| -20° | 0° | +20 | ||||||
| P 355 N | Normalized | t≤16 | 355 | 510-650 | 20 | 27 | 34 | 40 |
| 16＜t≤40 | 345 | 510-650 | 20 | 27 | 34 | 40 | ||
| 40＜t≤60 | 335 | 460-580 | 20 | 27 | 34 | 40 | ||
| 60＜t≤100 | 315 | 490-630 | 20 | 27 | 34 | 40 | ||
| 100＜t≤150 | 295 | 480-630 | 20 | 27 | 34 | 40 | ||
| 150＜t≤250 | 280 | 470-630 | 20 | 27 | 34 | 40 | ||
P355N Steel Processing
Welding Processing: Adopts conventional welding processes such as manual arc welding, gas metal arc welding (GMAW) and submerged arc welding. Preheating is generally not required under normal temperature conditions, but preheating to 50-100°C is recommended for thick workpieces or low-temperature environments to prevent cold cracks. Post-weld heat treatment (PWHT) can be performed as needed to eliminate residual stress and ensure the mechanical properties of the weld joint.
Forming Processing: Suitable for both cold forming and hot forming. Cold forming includes bending, stamping and rolling, which requires controlling the forming speed and deformation to avoid material cracking. Hot forming is applicable to complex structural parts, with the optimal forming temperature range of 900-1100°C, followed by air cooling or controlled cooling to maintain the material's fine-grained structure and toughness.
Heat Treatment Processing: The standard supply state is normalized heat treatment-heating the steel to 890-950°C, holding it for a sufficient time to ensure uniform heating, then air cooling. This process refines the grain structure, improves tensile strength and yield strength, and enhances low-temperature impact resistance (-20°C) to meet pressure-bearing equipment requirements.
Machining Processing: Compatible with conventional machining methods such as turning, milling, drilling and planing. The material has moderate hardness and good cutting performance; select high-speed steel or cemented carbide tools, and match appropriate cutting parameters (cutting speed, feed rate) to reduce tool wear and ensure processing accuracy and surface finish.
Surface Treatment Processing: After processing, surface treatment is required to prevent corrosion. Common methods include derusting (shot blasting, pickling), phosphating and painting. For outdoor or humid working environments, anti-corrosion coatings with high adhesion and weather resistance are recommended to extend the service life of the processed parts.
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What is P355N steel primarily known for in industrial applications?
P355N is a low-alloy structural steel renowned for its excellent toughness at normal temperatures and high strength. It offers good weldability and formability, making it ideal for load-bearing structural components in construction, machinery, and pressure vessel manufacturing where reliability is critical.
How does P355N differ from P355NH steel in application?
P355N is for normal temperature use, while P355NH is a heat-resistant grade for elevated temperatures up to 450°C. P355N suits general structural and pressure vessel work at ambient temps, and P355NH is for boiler and heat exchanger components with high thermal loads.
What quality standards govern P355N steel production?
P355N is specified under European standard EN 10025-3, which regulates low-alloy structural steels for normalized/normalized rolled delivery conditions. This standard defines its chemical composition, mechanical properties, testing methods, and dimensional tolerances strictly.
What is the typical tensile strength range of P355N steel?
P355N steel has a tensile strength range of 470 to 630 MPa, complementing its high yield strength. This range ensures it has sufficient ductility and fracture resistance while bearing maximum loads, making it stable for structural and load-bearing applications.
How does P355N compare to S355JR steel in mechanical properties?
P355N has the same minimum yield strength as S355JR (355 MPa) but superior toughness, especially at low temperatures. S355JR is a general-purpose grade with lower impact resistance, while P355N is normalized for consistent toughness and is suitable for more demanding applications.
What is the carbon content limit for P355N steel?
P355N has a maximum carbon content of 0.20%, a critical limit for ensuring weldability and toughness. Low carbon content prevents the formation of hard, brittle martensite during welding and cooling, maintaining the steel's structural integrity in welded joints.
What are the key chemical composition features of P355N steel?
P355N has a controlled chemical makeup with low carbon content to enhance weldability, balanced manganese for strength, and trace amounts of silicon for deoxidation. It contains minimal impurities like sulfur and phosphorus, ensuring structural integrity and consistent mechanical performance across batches.
What industrial sectors are the biggest users of P355N steel?
The top sectors for P355N include construction (for bridges, high-rise structures), heavy machinery (frames, components), pressure vessel manufacturing, and automotive (commercial vehicle chassis). It's also used in pipework and storage tank fabrication for industrial plants.
How does P355N resist corrosion in natural environments?
P355N has moderate natural corrosion resistance due to its low alloy content. In mild environments, it forms a thin oxide layer, but in humid, coastal, or industrial corrosive settings, additional surface protection (painting, galvanizing) is required to prevent rusting.
What is the minimum yield strength of P355N steel?
P355N steel has a minimum yield strength of 355 MPa, which is the core reason for its naming. This high yield strength ensures it can withstand significant static and dynamic loads without permanent deformation, suiting heavy-duty structural and industrial uses.