EN 10028-6 P690Q is a top-tier ultra-high-strength quenched and tempered steel plate under the European standard. Its core advantages lie in achieving a high yield strength of 690 MPa grade while maintaining excellent low-temperature toughness and weldability. It is specifically designed for pressure vessels and heavy structures with stringent requirements for safety and lightweighting.

It is characterized by ultra-high strength, good weldability, and excellent low-temperature toughness. This steel is primarily used in the manufacturing of welded structural components subjected to high stress, especially in applications such as pressure vessels, heavy machinery, bridges, and offshore platforms where high material strength and toughness are critical.

Key Features and Advantages

1. High Strength: High yield strength (≥690 MPa) and tensile strength (770-940 MPa), suitable for high-pressure environments.

2. Good Weldability: Fine-grained structure and strict composition control ensure excellent welding performance.

3. Good Plasticity and Toughness: Ensures structural safety and deformation resistance, maintaining high toughness even at low temperatures (-20℃) with strong resistance to brittle fracture.

4. Heat Resistance: Suitable for high-temperature working conditions (though not as good as P690QH).

5. Fatigue Resistance: Suitable for applications subjected to cyclic loads.

Due to its excellent strength-to-weight ratio and reliability, P690Q steel plate is widely used in:

1. Pressure vessels: High-pressure reactors and separators in petrochemical and refining equipment

2. Boiler equipment: Pressure-bearing components of power plant boilers and industrial boilers

3. Storage containers: LNG storage tanks and large oil storage tanks

4. Construction machinery: Large excavator arms, crane booms, and structural components of mining machinery

5. Bridge engineering: Key load-bearing components of long-span bridges (such as steel box girders and pylons)

6. Shipbuilding and marine engineering: High-strength structures like ship decks and bulkheads

7. Energy equipment: High-strength structural components for hydropower and wind power (such as wind turbine tower flange connections).

Processing and Welding Considerations

When using ultra-high-strength steels such as P690Q, processing techniques are critical. Improper operations can lead to severe degradation of material properties.

1. Cutting: Plasma cutting or laser cutting is preferred. If flame cutting is used, strict preheating is required, and the heat-affected zone must be evaluated.

2. Cold Forming: Moderate bending or shaping is possible, but the bending radius generally needs to be larger than that for ordinary steel, and springback must be taken into account.

3. Welding (Top Priority):

a)Consumables Matching: Special welding consumables with equal or higher strength matching (e.g., according to EN ISO 16834-A standards) must be used.

b)Preheating: Preheating is mandatory, typically within the range of 100–200°C, depending on plate thickness, restraint conditions, and ambient temperature. The Welding Procedure Specification (WPS) provided by the steel manufacturer must be followed.

c)Heat Input Control: Strict control of welding heat input is necessary to prevent softening and toughness reduction in the heat-affected zone.

d)Post-Weld Heat Treatment: Stress relieving annealing is generally not recommended unless specified by design requirements, as improper tempering temperatures may adversely affect the base metal properties.

4. Drilling and Machining: High-quality carbide tools are required, along with appropriate cutting parameters and coolant.

The Differences Between Grades Within The Same Series

* The P690QH is a high-temperature variant of the P690Q, with its chemical composition and heat treatment process placing greater emphasis on strength retention and creep resistance at elevated temperatures.

* If the project involves low-temperature environments, P690QL1 (-40°C) or P690QL2 (-60°C) should be selected.

* All grades (Q / QH / QL1 / QL2) have a lower limit of yield strength of 690 MPa, but differ in toughness and temperature adaptability.

International Equivalent Steel Grades