EN 10025-6 S690QL High Strength Structural Steel Plate

EN10025-6 S690QL is a high-strength quenched and tempered structural steel under the European Standard (EN), widely used in heavy-duty structural applications that require stringent material strength, toughness, and load-bearing capacity.

1. Standard: EN 10025-6

The full title is "Hot-rolled structural steels - Part 6: Technical delivery conditions for flat products of high yield strength structural steels in the quenched and tempered condition," which is a unified European standard for high-strength structural steel.

2. Grade: S690QL

S: Structural steel.

690: The specified minimum yield strength is 690MPa.

Q: The delivery condition is Quenched and Tempered.

L: Low temperature impact toughness (Tested at -60°C or -40°C, depending on the sub-grade and thickness).



Key Characteristics and Properties

Extremely High Strength: The primary feature is its very high yield strength (690 MPa min) and tensile strength (770-940 MPa). This allows for the design of lighter and stronger structures, which is crucial in applications where weight savings are critical (e.g., mobile machinery, transportation).

Excellent low-temperature toughness: Impact energy at -40℃ is ≥40J, suitable for low-temperature environments such as cold regions and high altitudes.

Weldability: S690QL has good weldability, but it requires strictly controlled welding procedures. Its high carbon equivalent (CEV) means pre-heating, specific consumables, and controlled heat input are mandatory to avoid cracking and to preserve the mechanical properties in the Heat-Affected Zone (HAZ).

* Heat Analysis, wt. %, maximum unless indicated

Carbon Equivalent

Charpy V-notch Impact Test For S690QL

S690QL is primarily used for structural components under heavy loads and harsh environments due to its combination of "high strength + toughness." Typical application areas include:

Construction machinery: booms, arms, and frames of excavators, cranes, and loaders.

Mining equipment: hydraulic supports for mines, scraper conveyors, and crusher frames.

Special vehicles: heavy-duty truck frames and armored plates for bulletproof vehicles.

Large structures: bridge load-bearing components, offshore platform support structures, and wind turbine tower flanges.

Pressure vessels: heads or cylinders of high-pressure storage tanks and large pressure vessels (must additionally comply with pressure vessel standards).

Delivery Conditions

S690QL steel plates are delivered in the quenched and tempered(Q&T) condition.

Processability

Weldability: It falls under the "weldable steel grade," but note the following: Preheating is required before welding (preheating temperature adjusted based on thickness, typically ≥100°C), and stress relief heat treatment is recommended after welding to avoid welding cracks. The use of low-hydrogen welding materials (such as E11018-G) is advised.

Machinability: The high strength results in significant cutting resistance. It is necessary to use carbide tools and reduce cutting speeds.

Formability: Cold forming processes such as bending and stamping can be performed at room temperature, but the forming force must be increased accordingly. High-temperature forming should be avoided (temperatures exceeding 250°C may affect the tempered microstructure).

Temperature Grade and Quality Grade Differences

The impact performance of the S690 series steel grades is distinguished by suffix letters:

S690Q: Impact energy ≥30J at -20°C (longitudinal), ≥27J (transverse)

S690QL: Impact energy ≥30J at -40°C (longitudinal), ≥27J (transverse)

S690QL1: Impact energy ≥30J at -60°C (longitudinal), ≥27J (transverse)

Precautions for Procurement and Use

Requirements for the Mill Test Certificate: When purchasing, it is essential to explicitly require the steel mill to provide a Mill Test Certificate compliant with EN 10025-6, which includes mechanical properties, chemical composition, nondestructive testing grades (such as EN 10160 Class B inspection), and other relevant details.

Thickness Impact: Properties may degrade when the thickness exceeds 63mm. It is necessary to confirm specific performance indicators for large thicknesses (e.g., >100mm) with the steel mill in advance.

Welding Process: A suitable Welding Procedure Specification (WPS) must be developed, with strict control over preheating and post-weld heat treatment parameters.

Summary

S690QL is a premium, ultra-high-strength steel chosen for the most demanding structural applications. Its use requires expertise, particularly in welding and fabrication, to fully leverage its exceptional properties.