P355M is a premium low-alloy high-strength steel grade that is explicitly specified in the European standard EN 10025-4, which governs the technical delivery conditions for structural steels with required impact energy values. It is primarily utilized in the manufacturing of pressure vessels, thanks to its exceptional weldability that allows for reliable joint formation without excessive preheating, as well as outstanding impact toughness-particularly critical when operating in low-temperature environments where brittle fracture risks are heightened. This steel grade balances high strength and good ductility, making it a preferred choice for equipment subjected to moderate pressure and cold working conditions across multiple industrial sectors.
P355M Vessel Plate Chemical Composition:
| C | Si | Mn | Ni | P | S | Mo | V | N | Nb | Ti | Al |
| max 0.14 | max 0.5 | max 1.6 | max 0.5 | max 0.025 | max 0.01 | max 0.2 | max 0.1 | max 0.015 | max 0.05 | max 0.05 | max 0.02 |
P355M Boiler Plate Mechanical Properties:
| Rm - Tensile strength (MPa) | 450-610 |
| Nominal thickness (mm): | to 40 | 40 - 63 |
| ReH - Minimum yield strength (MPa) | 355 | 345 |
| KV - Impact energy (J) transverse, | -20° 27 |
0° 40 |
+20° 60 |
| A - Min. elongation at fracture (%) | 22 |
Applications
Pressure vessel and storage equipment: Widely used in manufacturing pressure vessels, storage tanks, and reactors for oil, gas, chemical, and petrochemical industries, which need to bear medium and high pressure and corrosive media.
Power industry equipment: Applied in boilers, heat exchangers, and steam pipelines of thermal power plants and nuclear power auxiliary systems, adapting to high-temperature and high-pressure operating environments.
Pipeline engineering: Suitable for large-diameter water supply and drainage pipelines, oil and gas transmission pipelines, and industrial process pipelines, especially for long-distance transportation and outdoor laying scenarios.
Heavy machinery and structural parts: Used to fabricate load-bearing components of construction machinery, mining machinery, and port machinery, as well as large steel structures such as bridges and factory buildings that require high strength and toughness.
Offshore and marine engineering: Applied in offshore platforms, ship hull structures, and marine pipelines, resisting harsh marine environments such as salt spray corrosion and low temperatures.
Application Conditions
Temperature range: Suitable for working temperatures from -20℃ to 400℃. Its good low-temperature toughness ensures no brittle fracture at low temperatures, and it maintains stable mechanical properties at high temperatures without obvious softening.
Pressure bearing capacity: Applicable to medium and high pressure environments with working pressure up to 10MPa, relying on its minimum yield strength of 355MPa to meet the load-bearing requirements of structural parts.
Corrosion environment: Adaptable to mild to moderate corrosive environments such as atmospheric corrosion, fresh water corrosion, and weak chemical media corrosion. For strong corrosive environments, additional anti-corrosion treatments (e.g., coating, galvanizing) are required.
Fabrication conditions: Compatible with common welding processes (SMAW, GMAW, SAW, etc.) with low preheating temperature (usually 50-100℃) and no post-weld heat treatment required in most cases, suitable for on-site and factory fabrication.
Environmental adaptability: Resistant to humidity, wind, and snow in outdoor and open-air environments, and can be used in cold regions, coastal areas, and industrial zones with stable performance without being easily affected by environmental factors.
main processes
Thermomechanical rolling (TMR): This is the primary process used to produce P355M. The steel is heated to a controlled temperature range, typically between 1050–1150°C, and then subjected to precise rolling passes. The deformation is carefully controlled to refine the grain structure, and accelerated cooling may be applied to further enhance toughness and strength. This process ensures a uniform fine-grained microstructure without the need for subsequent normalization.
Controlled heating and cooling cycles: During production, the steel undergoes strict temperature control during both heating and cooling stages. This helps to achieve the desired balance of strength and toughness, particularly important for low-temperature applications.
Welding processes: P355M is designed to be readily weldable using standard methods such as SMAW, GMAW, FCAW, and SAW. Preheating is generally minimal, often in the range of 50–100°C, and post-weld heat treatment is usually not required, simplifying fabrication.
Forming and shaping processes: The steel can be formed using both cold and hot methods. Hot forming is often carried out between 800–900°C to improve ductility and reduce forming forces, while cold forming is suitable for thinner sections where precision is required.
Machining and finishing: P355M can be efficiently machined using conventional turning, milling, drilling, and grinding operations. Proper cutting parameters are recommended to maintain tool life and ensure dimensional accuracy. Surface treatments such as shot blasting, priming, or coating may also be applied to enhance corrosion resistance.
For more details about GNEE's steel products, contact us at beam@gneesteelgroup.com. We look forward to working with you.
Can P355M be used in offshore oil and gas platforms?
Yes, P355M is suitable for offshore oil and gas platforms. Its high strength, good weldability, and low-temperature toughness can withstand harsh marine environments and pressure loads, ensuring structural stability and safety.
What is the melting point range of P355M steel?
The melting point range of P355M steel is approximately 1450℃ to 1500℃, similar to other low-alloy steels. This range is important for welding, casting, and other thermal processing operations.
What is the difference between P355M and P355ML?
P355ML is a thermomechanically rolled version of P355M. P355ML has finer grain structure, better toughness, and higher strength than P355M, suitable for more demanding low-temperature and high-pressure applications.
Does P355M need to be normalized?
P355M may need normalization (heating to 890-950℃, holding, then air cooling) in some cases, especially for thick plates. Normalization refines grain structure, improves uniformity of mechanical properties, and reduces internal stress.
What is the application of P355M in boiler manufacturing?
In boiler manufacturing, P355M is used to make pressure-containing components like boiler drums, headers, and pipes. Its high strength and low-temperature toughness can withstand high pressure and temperature fluctuations during boiler operation.
What is the maximum operating temperature for P355M?
The maximum recommended operating temperature for P355M is around 400℃. Beyond this temperature, its strength and toughness will gradually decrease, which may affect the safety and service life of the components.
Can P355M be used for structural steel beams?
Yes, P355M can be used for structural steel beams, especially in projects requiring high strength and low-temperature resistance (such as cold regions). Its good weldability and ductility facilitate beam fabrication and installation.
What is the phosphorus content limit in P355M?
The maximum phosphorus content in P355M steel is 0.025%. Phosphorus can improve strength but reduce toughness, so strict control of phosphorus content ensures the steel's low-temperature impact performance.
What is the sulfur content limit in P355M?
The maximum sulfur content in P355M steel is 0.015%. Sulfur forms brittle inclusions, which seriously affect weldability and toughness, so low sulfur content is essential for ensuring the steel's quality.
How to store P355M steel plates to prevent corrosion?
P355M steel plates should be stored in a dry, well-ventilated warehouse, away from moisture and corrosive media. They should be placed on wooden pallets to avoid contact with the ground, and covered with waterproof cloth if stored outdoors.