P690QL2, as a top-grade high-strength low-temperature pressure vessel steel in the European standard EN 10028-6 system, features a minimum yield strength of 690 MPa and passes the low-temperature impact test at -60°C (QL2 grade), achieving an excellent balance of strength and toughness. It is primarily used in the manufacturing of advanced engineering machinery and special equipment that require reduced self-weight or the ability to withstand extreme loads, making it an indispensable key material in modern energy and marine engineering.

Key Features and Advantages

1. Ultra-High Strength

With a yield strength of ≥690MPa, it significantly reduces structural weight while maintaining high load-bearing capacity, enabling the design of lighter and thinner structures.

2. Exceptional Low-Temperature Toughness

QL2 grade retains excellent impact toughness even in ultra-low temperatures as low as -60°C, representing the top tier of steel for low-temperature pressure vessels.

3. Excellent Weldability

A fine-grained microstructure, combined with strict control of alloying elements, ensures strength and toughness in welded joints. However, preheating and strict welding procedures are typically required.

4. Quenched and Tempered Structure

Through quenching and high-temperature tempering, a tempered sorbite structure is achieved, providing an optimal balance of strength and toughness.

Due to its excellent combination of properties, P690QL2 is utilized in fields that demand extremely high safety and reliability:

1. Construction Machinery: Key load-bearing components such as crane booms, excavator girders, and mining truck bodies.

2. Mining Equipment: Hydraulic supports and conveyor structural parts.

3. Special Vehicles: Aerial ladder trucks for firefighting and boom arms for aerial work platforms.

4. Bridges and Buildings: Special structures subject to heavy loads or high seismic requirements.

5. Pressure Vessels and Pipelines: Applications involving high pressure, low temperatures, or large diameters (in line with its original design for "pressure purposes").

6. Wind Power: Tower sections and foundation structures (especially suitable for cold regions).

7. Marine Engineering and Shipbuilding: Certain structural components requiring high strength and toughness.

Processing and Welding Precautions

1. Cutting:

Plasma, flame, or laser cutting can be used. After flame cutting, for thick plates, the hardness in the cut area may increase, and grinding or annealing may be required.

2. Cold Bending:

Possible, but with significant springback and higher bending force required.

3. Welding:

a) Low-hydrogen welding processes (such as gas-shielded welding, submerged arc welding) must be used.

b) Strictly follow the Welding Procedure Specification (WPS), including preheating (generally required), controlling interpass temperature, and managing heat input.

c) Use matching high-strength, high-toughness welding materials (e.g., electrodes/wires compliant with EN 1600 standards).

d) Post-weld heat treatment (PWHT) or dehydrogenation treatment may be necessary.

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