P355N steel is a high-strength low-alloy fine-grained structural steel compliant with European EN 10025 and EN 10028 standards, specially engineered for industrial pressure-bearing and low-temperature service scenarios, with the letter "N" denoting its normalized heat treatment supply state that optimizes its core mechanical properties. This steel grade delivers a well-balanced combination of high tensile and yield strength, excellent low-temperature toughness that resists brittle fracture at -20°C, and stable structural integrity under medium pressure and temperature working conditions, while also boasting superior process performance including excellent weldability compatible with conventional welding processes, favorable cold and hot formability for various shaping operations, easy machinability for common machining methods, and reliable structural stability after heat treatment. Widely applied in the fabrication of pressure vessels, boilers, oil and gas storage and transportation equipment, chemical process machinery and low-temperature pressure-bearing components, P355N steel is a core structural material in petrochemical, power generation, energy storage and general heavy machinery industries, meeting the strict strength, toughness and processability requirements of industrial pressure-bearing equipment manufacturing.
P355N Boiler Plate Steel Chemical Composition:
| Al% | N% | Cr% | Cu% | Mo% | Nb% | Ni% | Ti% | V% | Nb+Ti+V% |
| 0.02 | 0.012 | 0.3 | 0.3 | 0.08 | 0.05 | 0.5 | 0.03 | 0.1 | 0.12 |
P355N Pressure Vessel Plate Mechanical Properties:
| Steel Grade | Tensile Strength(MPa) | Yield Strength(MPa) | % Elongation in 2 in.(50mm) min | Impacting Test Temperature(°C) |
| P355N | 450-630 | 295-355 | 21 | +20/0/-20 |
P355N Applications
Serves as a key structural material for industrial pressure vessels, widely used in fabricating boiler drums, heat exchangers and separators for thermal power, petrochemical and chemical engineering sectors, enduring medium pressure and temperature in continuous working conditions.
Applied to manufacturing oil and gas storage & transportation equipment, including above-ground and underground storage tanks, pipeline manifolds and transfer units, withstanding static and dynamic pressure loads in energy media conveyance and storage.
Utilized in producing process equipment for chemical synthesis and refining, such as hydrogenation reactors, distillation tower internals and reaction kettles, adapting to the common working environments of non-strongly corrosive media and cyclic pressure changes.
Adopted for fabricating low-temperature pressure-bearing components in industrial systems, as its excellent low-temperature toughness prevents brittle fracture in cold working or low-service-temperature scenarios like cryogenic fluid transportation.
Used in general heavy machinery manufacturing for making pressure-bearing structural parts, such as hydraulic system cylinders, pressure pipeline networks and industrial boiler accessories, meeting the weldability and strength demands of mechanical processing.
P355N Application Conditions
Temperature Range：Suitable for service temperatures from -20°C to 400°C, maintaining excellent mechanical properties and structural stability in both low-temperature cold working and medium-high temperature pressure environments without brittle fracture or thermal deformation.
Pressure Bearing Requirement：Applicable to medium and low pressure working conditions (typically ≤40 bar) for pressure-bearing equipment, matching the stress resistance of industrial pressure vessels, pipes and storage tanks under normal operating pressure loads.
Medium Compatibility：Adaptable to non-strongly corrosive working media including water, steam, oil, natural gas and general organic/inorganic chemicals, not recommended for long-term service in acid, alkali or salt-rich highly corrosive environments.
Welding & Forming Condition：Suitable for conventional welding processes (arc, gas shielded welding) and cold/hot forming operations, requiring standard preheating and post-weld heat treatment to avoid welding cracks and ensure joint performance consistency.
Working Environment：Stable in dry, normal humidity industrial environments; for outdoor or humid working conditions, additional anti-corrosion treatment (painting, coating) is needed to prevent surface oxidation and rusting.
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 the role of manganese in P355N steel's composition?
Manganese is a key alloying element in P355N, added at 1.00–1.60% to boost strength and hardenability without reducing weldability. It also refines the grain structure during normalization and offsets the strength loss caused by low carbon content.
How is P355N steel inspected for quality control during production?
P355N undergoes rigorous QC: chemical composition analysis (spectroscopy), mechanical testing (tensile, impact), microstructure examination, and non-destructive testing (ultrasonic, radiographic) for thick plates. Dimensional and surface quality checks are also mandatory.
What is the fatigue resistance of P355N steel?
P355N has good fatigue resistance due to its uniform grain structure and high strength. It can withstand repeated cyclic loads in structural and machinery applications (e.g., bridge bearings, machine frames) when designed with proper stress relief and no surface defects.
What are the storage requirements for P355N steel plates/sheets?
P355N should be stored in a dry, covered area to avoid moisture and direct outdoor exposure. Plates should be stacked on wooden pallets to prevent ground contact, and thin sheets should be wrapped in anti-rust paper to protect against surface oxidation during storage.
How does P355N perform in cold forming operations?
P355N has excellent cold forming performance thanks to its high ductility and low yield ratio. It can be cold-bent to tight radii without cracking or excessive work hardening, making it suitable for fabricating complex structural parts without warm forming processes.
What is the difference between P355N and P355NL steel?
P355N is rated for -20°C impact resistance, while P355NL is a low-temperature grade rated for -50°C. P355NL has stricter impurity controls and a finer microstructure, suiting arctic or cryogenic applications, while P355N is for standard low-temperature industrial use.
What welding consumables are recommended for P355N steel?
For P355N, low-hydrogen welding consumables are preferred, such as E7018 electrodes (stick welding) and ER70S-6 solid wires (MIG/TIG). These consumables minimize hydrogen pickup in the weld zone, reducing cold cracking risk and matching the base metal's strength.
Can P355N steel be used in bridge construction?
Absolutely, P355N is widely used in bridge construction for girders, crossbeams, and bearing plates. Its high strength reduces structural weight, good weldability simplifies on-site fabrication, and toughness resists dynamic loads from traffic and environmental factors like wind.
What is the hardness range of normalized P355N steel?
Normalized P355N steel has a Brinell hardness range of 130 to 180 HBW, a moderate range that balances strength and machinability. This hardness ensures it is not too hard to machine or form, while still providing the structural strength required for its applications.
What factors can affect the mechanical properties of P355N steel?
Key factors include improper normalization (incorrect temperature/time), high impurity levels (S/P), thickness variation (over-thick plates with uneven cooling), and post-fabrication heat treatment. Poor welding practices can also degrade weld zone toughness and strength.