P355Q is a low-alloy high-strength structural steel grade. It complies with European standards, featuring good toughness, weldability and mechanical properties. Widely used in construction, bridge and pressure vessel manufacturing that require reliable load-bearing capacity.
Key Characteristics and Designations
P: Indicates steel for Pressure purposes.
355: Represents the minimum yield strength of 355 MPa (for thickness ≤50mm).
Q: Stands for "Quenched and Tempered" heat treatment.
Standard: Governed by EN 10028-6: Flat products made of steels for pressure purposes - Part 6: Weldable fine grain steels, quenched and tempered.
P355Q pressure vessel steel chemical composition %
| Grade | Material No. | C max | Si max | Mn max | P max | S max | N min | Bmax | Cr max | Mo max | Cumax | Nb max | Ni max | Ti max | V max | Zr max |
| P355Q | 1.8866 | 0.16 | 0.40 | 1.50 | 0.025 | 0.010 | 0.015 | 0.005 | 0.30 | 0.25 | 0.30 | 0.05 | 0.50 | 0.03 | 0.06 | 0.05 |
P355Q 1.8866 pressure vessel steel Mechanical properties
| Plate Thickness(mm) | Usual delivery condition | Yield strength ReH MPa min | Tensile strength Rm MPa | Elongation A% min | Impact Energy KV2 J min at a temperature in °C of | ||||
| -60 | -40 | -20 | 0 | +20 | |||||
| ≤50 | +QT | 355 | 490-630 | 22 | - | - | 27 | 40 | 60 |
| 50<t≤100 | 335 | ||||||||
| 100<t≤200 | 315 | 450-590 | |||||||
P355Q Processing Flow
Steelmaking & Refining: Molten steel is produced via converter or electric arc furnace, then refined in a ladle furnace (LF) to adjust chemical composition. Vacuum degassing (VD) is conducted to remove impurities (hydrogen, oxygen) and ensure uniformity.
Casting: Refined molten steel is continuously cast into slabs/blooms. Surface defects (scratches, cracks) are removed by scarfing or grinding after cooling.
Hot Rolling: Cast slabs are reheated to a suitable temperature, then hot-rolled to the target thickness and width. Controlled rolling is applied to optimize grain structure.
Quenching & Tempering (Q&T): Plates are austenitized at 880–950°C, followed by water quenching to form a hardened martensite structure. Tempering at 580–680°C is performed to balance strength and toughness.
Inspection: Non-destructive testing (ultrasonic, visual inspection) and mechanical tests (tensile, impact) are carried out to verify performance compliance.
Finishing & Delivery: Final steps include shot blasting, edge trimming, and dimension calibration. Qualified products are packaged and delivered with certification.
applications
Pressure Vessels and Boilers:
As a quenched and tempered pressure vessel steel compliant with EN 10028-6, P355Q is widely used in manufacturing stationary and mobile pressure vessels. Typical scenarios include chemical reactors, storage tanks for petroleum, natural gas and chemical media, boiler drums, and heat exchangers. It is suitable for vessels bearing medium to high pressure and operating in harsh environments.
Petrochemical and Refining Industry:
It is applied in key equipment of petrochemical plants, such as hydrocracking reactors, fractionating towers, and pipeline systems for transporting high-temperature and high-pressure oil and gas. Its excellent toughness and corrosion resistance can adapt to the complex medium environment (e.g., hydrogen, sulfur-containing compounds) in refining processes.
Power Generation Equipment:
In thermal power plants and nuclear power auxiliary systems, P355Q is used to make boiler components, steam pipelines, and pressure-bearing containers for power transmission. It can withstand the long-term operation under high-temperature steam and pressure, ensuring the stability and safety of power generation equipment.
Marine and Offshore Engineering:
It is utilized in offshore oil and gas platforms, marine pressure vessels, and ship-borne boiler systems. It can resist the corrosion of seawater and humid air, and meet the strict strength requirements of marine equipment under complex sea conditions (e.g., wind, wave, and current loads).
Heavy Machinery and Construction:
For large-scale engineering machinery (e.g., excavators, cranes) and pressure-bearing structures in construction projects (e.g., high-pressure pipelines for urban heating), P355Q provides reliable structural support due to its balanced strength and ductility.
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Can P355Q be cold-formed?
P355Q can be cold-formed under appropriate conditions. Its good ductility allows for bending, stamping and other cold-forming processes. However, excessive cold deformation may reduce toughness, so post-forming heat treatment may be needed.
What is the hardness of P355Q?
The Brinell hardness of P355Q is usually between 137 and 170 HB. Moderate hardness balances machinability and strength, making it easy to process while ensuring the steel can bear the required loads.
What is the delivery state of P355Q?
P355Q is mainly delivered in the normalized state (N). Normalizing treatment optimizes its grain structure, ensuring uniform mechanical properties. Other delivery states (e.g., thermomechanical rolling) can be provided according to customer needs.
Can P355Q be used in heavy machinery manufacturing?
Yes, P355Q is widely used in heavy machinery manufacturing, such as excavators, cranes and bulldozers. Its high strength and toughness can withstand heavy loads and impact forces during machinery operation, ensuring reliable performance.
What is the difference between P355Q and P355M?
The key difference is impact test temperature. P355Q is tested at -20℃, while P355M at -15℃. Thus, P355Q has better low-temperature impact resistance, suitable for colder regions or low-temperature working environments.
Does P355Q require preheating before welding?
Generally, P355Q does not need preheating before welding for thin plates. For thick plates (over 20mm) or in low-temperature environments, preheating to 50-100℃ is recommended to reduce welding stress and avoid cold cracking.
What is the fatigue resistance of P355Q?
P355Q has good fatigue resistance. It can withstand repeated cyclic loads without fatigue failure, which is crucial for structures like bridges and machinery that are subjected to frequent load changes during service.
Can P355Q be used in building structures?
Yes, P355Q is suitable for building structures, especially high-rise buildings and large-span structures. Its high strength reduces the weight of structural components, saving materials and simplifying construction while ensuring structural safety.
What are the storage requirements for P355Q plates?
P355Q plates should be stored in a dry, well-ventilated warehouse to avoid moisture and corrosion. They should be placed on wooden pallets away from the ground and avoid contact with corrosive substances like acids and alkalis.
Is P355Q a low-alloy steel or carbon steel?
P355Q is a low-alloy high-strength steel. Compared with carbon steel, it adds a small amount of alloying elements (e.g., Mn, Si) to improve strength and toughness while maintaining good weldability and machinability.