S690Q steel is a high-strength, fine-grain structural steel (HSLA) that's quenched and tempered (Q) for exceptional strength (minimum 690 MPa yield) and toughness, used in heavy-duty applications like bridges, cranes, and machinery where weight savings and high load capacity are critical, conforming to EN 10025-6 standards. Its designation breaks down as 'S' (Structural), '690' (min yield strength in MPa), and 'Q' (Quenched & Tempered).
Key Characteristics
High Strength: Minimum yield strength of 690 MPa, with typical tensile strength between 770-940 MPa, providing excellent load-bearing capacity.
Toughness: Good impact toughness, often guaranteed at temperatures down to -20°C.
Fine Grain: Achieved through heat treatment, contributing to its strength and toughness.
Weldability: Considered to have good weldability for its strength class, though proper procedures like preheating are usually needed, especially for thicker plates.
Low Alloy: A controlled chemical composition that supports its high performance.
Applications
Heavy construction equipment (excavators, loaders)
Bridges and offshore structures (drilling rigs, windmill supports)
Cranes and lifting equipment
Pressure vessels
High-load structural elements in various machinery
Designation Breakdown
S: Structural Steel
690: Minimum Yield Strength (690 MPa)
Q: Quenched and Tempered (heat treatment condition)
How to weld S690Q steel?
Welding S690Q steel requires strict procedures to maintain its high strength and toughness by preventing defects like cracking and preserving the properties of the Heat-Affected Zone (HAZ). Here is a concise, step-by-step guideline:
Core Principles:
Prevent Hydrogen-Induced Cracking (Cold Cracking): This is the greatest risk.
Control Heat Input: To avoid excessive softening or embrittlement of the HAZ.
Match or Undermatch Strength: Use suitable filler metals.
Step-by-Step Welding Procedure:
1. Preparation & Joint Design
Cleanliness: Remove all rust, oil, paint, and moisture from the joint area (min. 20-30mm edge).
Joint Design: Use generous bevel angles to ensure good access and penetration, avoiding overly restrictive joints.
Preheating: Mandatory.
Temperature: Typically 100°C - 150°C (212°F - 302°F). The exact temperature depends on plate thickness (higher for thicker sections) and the specific grade (e.g., S690QL may have stricter requirements).
Purpose: Slows the cooling rate, allowing hydrogen to diffuse out and reducing hardening in the HAZ.
Interpass Temperature: Maintain this preheat temperature as the maximum interpass temperature (usually not exceeding 200-250°C / 392-482°F).
2. Filler Metal Selection
Type: Use low-hydrogen (basic-coated) electrodes for SMAW (stick) or low-hydrogen flux-cored wires (FCAW) and solid wires (GMAW/MIG, SAW) classified for high-strength steels.
Strength: Common practice is to use filler metals with matching strength (69 MPa yield) or, more frequently, slight undermatching (e.g., 620 MPa yield). This can improve weld metal toughness and reduce cracking risk. Common designations: EN ISO 16834-A: G 69 4 M21 Mn3Ni1CrMo or AWS A5.28: ER110S-G.
Storage: Keep electrodes/flux in their original, sealed containers. Use a holding oven at 80-120°C (176-250°F) after opening.
3. Welding Process & Parameters
Suitable Processes: SMAW (111), GMAW/MIG (135), FCAW (136), SAW (12), GTAW/TIG (141).
Heat Input: Control strictly.
Typical Range: 0.5 - 1.5 kJ/mm. Stay within the procedure specification (WPS).
Avoid excessive heat input (slow speed, high current), which can create a wide, softened HAZ and lower toughness.
Use the lower end of the approved range for optimal HAZ properties.
Technique: Use stringer beads or a slight weave. Avoid long arcs. Ensure proper fusion at the toes.
4. Post-Weld Treatment
Slow Cooling: Allow the weldment to cool slowly, often by insulating with a fire blanket, especially in cold environments.
Post-Weld Heat Treatment (PWHT): Not always required but may be specified for very thick sections or critical applications to relieve residual stresses and temper the HAZ. Follow the specific engineering requirement.
5. Essential Best Practices
Qualified WPS: Always work from a Welding Procedure Specification (WPS) that has been qualified by testing (e.g., according to EN ISO 15614-1 or AWS D1.1).
Qualified Welders: Welders must be qualified for the specific procedure.
Preheat Monitoring: Use temperature-indicating sticks or thermocouples to verify preheat and interpass temperatures.
Summary of Key "Do's and Don'ts":
DO: Meticulously clean, preheat, use low-hydrogen filler, control heat input.
DON'T: Weld on dirty material, skip preheat, use cellulose (E6010) or general-purpose rods, or apply excessive heat.
For any critical application, the final welding procedure must be developed and qualified by a certified welding engineer based on the specific design code, joint details, and service conditions.
Technical data
EN10025-6 S690Q quenched and tempered steel plate Chemical composition
| Grade | C % | Si % | Mn % | P % | S % | N % | B % | Cr % |
| S690Q | 0.200 | 0.800 | 1.700 | 0.025 | 0.015 | 0.015 | 0.005 | 1.500 |
| Cu % | Mo % | Nb % | Ni % | Ti % | V % | Zr % | ||
| 0.500 | 0.700 | 0.060 | 2.000 | 0.050 | 0.120 | 0.150 |
EN10025-6 S690Q quenched and tempered steel plate mechanical properties
| Grade | Thickness | Min Yield | Tensile | Elongation | Min Impact Energy | |
| S690Q | 8mm-50mm | Min 690Mpa | 770-940Mpa | 14% | -20 | Min 30J |
| 51mm-100mm | Min 650Mpa | 760-930Mpa | 14% | -20 | Min 30J | |
| 101mm-150mm | Min 630Mpa | 710-900Mpa | 14% | -20 | Min 30J |
What is S690Q steel?
S690Q is a high-strength quenched and tempered structural steel grade with a minimum yield strength of 690 MPa, often used in demanding construction and lifting applications.
What are the properties of S690Q steel?
S690Q offers high strength, good toughness at low temperatures, and excellent weldability due to its quenched and tempered microstructure.
What is the difference between S690QL and S690Q?
S690QL is a sub-grade with specified low-temperature impact toughness, while S690Q is the base grade; both share the same minimum yield strength.
Where is S690Q steel used?
It is commonly used in heavy machinery, mobile cranes, mining equipment, and advanced structural components where high strength-to-weight ratio is critical.
How to weld S690Q steel?
Welding S690Q typically requires low-hydrogen electrodes, preheating, and controlled heat input to maintain its mechanical properties and prevent cracking.
What is the chemical composition of S690Q?
S690Q contains elements like carbon, manganese, silicon, and micro-alloys such as niobium, vanadium, and titanium, with precise limits to ensure its properties.
Is S690Q steel corrosion resistant?
No, S690Q is not inherently corrosion-resistant; it requires protective coatings or paints for use in corrosive environments.
What are the machining guidelines for S690Q?
Machining S690Q requires robust tools, adequate cooling, and slower speeds due to its high strength and hardness.
What is the price of S690Q steel plate?
The price of S690Q varies based on thickness, quantity, and market factors, but it is generally more expensive than standard structural steels due to its advanced processing.
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.
