S690QL1 steel is a high-strength, quenched and tempered structural steel plate, defined by the EN 10025-6 standard. It is primarily used for demanding applications that require exceptional strength and toughness, particularly in cold environments.
Key Properties
The 'S' in S690QL1 stands for structural steel, '690' indicates the minimum yield strength in MPa, 'Q' means it is supplied in the quenched and tempered condition, and 'L1' specifies that it has enhanced impact toughness tested at -60°C.
| Property | Value (for nominal thickness ≤ 50mm) | Source |
|---|---|---|
| Minimum Yield Strength | 690 MPa | |
| Tensile Strength | 770 - 940 MPa | |
| Elongation | Minimum 14% | |
| Impact Toughness | Minimum 30 J at -60°C (Transverse) |
Common Applications
S690QL1 steel is known for its high strength-to-weight ratio, which allows for lighter designs without compromising safety or performance. Its superior mechanical properties make it suitable for:
Heavy engineering and construction machinery
Cranes and lifting equipment
Bridges and offshore platforms
Mining equipment
Pressure vessels and structural components
Welding S690QL1 correctly requires a strict, procedure-driven approach to preserve its exceptional low-temperature toughness (guaranteed at -60°C) and high strength while preventing defects like hydrogen-induced cracking (cold cracking) or excessive softening of the heat-affected zone (HAZ).
Here is a concise, step-by-step guide based on industry best practices and standards (EN 1011-2, EN ISO 15614-1):
1. Essential Pre-Weld Requirements
Procedure Qualification: A Welding Procedure Specification (WPS) must be qualified by testing (e.g., according to EN ISO 15614-1) before production welding. This is mandatory.
Material Certification: Verify base metal and filler metals meet required standards (EN 10025-6 for S690QL1).
Joint Design & Preparation: Use well-machined bevels (avoid notches). Remove all contaminants (rust, oil, paint, moisture) at least 30 mm from the joint edges.
2. Filler Metal Selection
Type: Use only low-hydrogen electrodes/wires. Common choices:
SMAW (MMA): Basic-coated electrodes (e.g., classification per EN ISO 18276-A: E 69 6 2Ni B 6 2 H5).
GMAW/FCAW: Flux-cored or metal-cored wires (e.g., T 69 6 2Ni M H5).
Strength Matching: Typically, undermatching filler metals (e.g., with ~620 MPa yield strength) are preferred to improve weld metal toughness and reduce cracking sensitivity, unless the design specifically requires matching strength.
Storage & Handling: Store electrodes/flux in a drying oven at 100–150°C after opening. Use immediately after removal to avoid hydrogen absorption.
3. Critical Welding Parameters
Preheat & Interpass Temperature: Strictly controlled.
Typical Preheat: 125–175°C, depending on thickness and restraint (higher for thicker sections).
Interpass Range: Maintain preheat as a minimum, but do not exceed 200–225°C to avoid excessive HAZ softening.
Heat Input: Must be within a narrow, qualified range (e.g., 0.6–1.2 kJ/mm).
Too low → risk of hard, brittle HAZ.
Too high → excessive grain growth and loss of toughness in HAZ.
Welding Technique: Use stringer beads or a slight weave. Avoid long arcs and ensure proper sidewall fusion. Use a low current for root passes.
4. Post-Weld Treatments
Post-Weld Heat Treatment (PWHT): Often required for thick sections (>30 mm) or highly restrained joints. Common practice is stress relieving at 550–600°C to reduce residual stresses and temper the HAZ.
Slow Cooling: After welding, insulate the weldment to allow gradual cooling to ambient temperature, especially in cold environments.
5. Inspection & Testing
Non-Destructive Testing (NDT): Mandatory for critical welds (Ultrasonic Testing - UT, Magnetic Particle Testing - MT).
Hardness Testing: To verify HAZ hardness remains within acceptable limits (typically ≤ 380 HV10).
Charpy Impact Testing of Weld & HAZ: Often required at -60°C to qualify the procedure.
Summary:
Welding S690QL1 is a highly controlled process best executed by qualified welders under engineering supervision. The goal is to minimize hydrogen, control thermal cycles, and preserve base metal toughness. For any structural application, collaboration with a welding engineer and strict adherence to the qualified procedure are non-negotiable for safety and performance.
Chemical composition % of steel S690QL1 (1.8988): EN 10025-6-2004
| C | Si | Mn | Ni | P | S | Cr | Mo | V | N | Nb | Ti | Cu | Zr | B | CEV |
| max 0.2 | max 0.8 | max 1.7 | max 2 | max 0.02 | max 0.01 | max 1.5 | max 0.7 | max 0.12 | max 0.015 | max 0.06 | max 0.05 | max 0.5 | max 0.15 | max 0.005 | max 0.83 |
Mechanical properties of steel S690QL1 (1.8988)
| Nominal thickness (mm): | 3 - 50 | 50 - 100 | 100 - 150 |
| Rm - Tensile strength (MPa) | 770-940 | 760-930 | 710-900 |
| Nominal thickness (mm): | 3 - 50 | 50 - 100 | 100 - 150 |
| ReH - Minimum yield strength (MPa) | 690 | 650 | 630 |
| KV - Impact energy (J) longitud., | 0° 60 |
-20° 50 |
-40° 40 |
-60° 30 |
| A - Min. elongation Lo = 5,65 √ So (%) | 14 |
What is S690QL1 steel?
S690QL1 is a high-strength quenched and tempered structural steel grade with a minimum yield strength of 690 MPa, optimized for enhanced toughness at low temperatures (down to -60°C).
What does "QL1" mean in S690QL1?
The "QL1" indicates a sub-grade with specific impact toughness requirements at -60°C, ensuring higher resistance to brittle fracture in extreme cold environments.
What are the main applications of S690QL1?
It is used in critical components for Arctic engineering, offshore platforms, wind turbine towers in cold climates, and heavy-duty mining equipment operating below -40°C.
How does S690QL1 differ from S690QL?
S690QL1 guarantees impact toughness at a lower temperature (-60°C) compared to S690QL (typically -40°C), making it suitable for more severe cold conditions.
What is the chemical composition of S690QL1?
It contains low-carbon alloying elements like manganese, silicon, nickel, chromium, molybdenum, and vanadium, with strict control of impurities to ensure weldability and toughness.
How to weld S690QL1 steel correctly?
Welding requires low-hydrogen electrodes, preheating (100-150°C), controlled heat input, and post-weld stress relief to maintain toughness and prevent hydrogen-induced cracking.
Is S690QL1 corrosion resistant?
No, S690QL1 is not inherently corrosion-resistant. It requires protective coatings (e.g., galvanizing or painting) for use in corrosive environments.
What standards apply to S690QL1?
It is defined under European standard EN 10025-6, with additional specifications for low-temperature impact testing and quality levels.
Can S690QL1 be machined easily?
Machining S690QL1 is challenging due to its high strength; it requires rigid tools, adequate cooling, and optimized cutting parameters to avoid excessive tool wear.
Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.
