What are the machining guidelines for S690Q?
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)
Machining S690Q steel requires specific practices due to its high strength and hardness (typically 240-300 HBW). Following proper guidelines is essential to achieve good results, maintain tool life, and avoid work hardening or damage to the component.
1. Tooling Selection
Material: Use high-performance tool materials such as Carbide (C2/C3 grades) or Cermet. For heavy roughing, coated carbides or even Ceramic inserts (for continuous cuts) can be considered.
Geometry: Tools should have a positive rake angle, sharp cutting edges, and robust geometries to reduce cutting forces and heat generation.
Rigidity: The entire setup (machine, workpiece, tool holder) must be extremely rigid to minimize vibration and chatter.
2. Cutting Parameters (General Guidelines)
Cutting Speed (Vc): Moderate to low. Typically in the range of 80 - 150 m/min for carbide tools. Start at the lower end and adjust based on tool performance.
Feed Rate (fn): Use adequate feed rates to prevent excessive rubbing and work hardening. Too light a feed can glaze the surface and accelerate tool wear.
Depth of Cut (ap): Use a sufficient depth of cut to ensure the cut is made beneath any work-hardened layer from previous passes.
3. Process-Specific Tips
Turning: Ensure secure clamping. Use coolant effectively. Chip breakers are important as the material can produce tough, continuous chips.
Milling: Prefer climb milling (down-milling) over conventional milling to improve tool life and surface finish. Use tools with a reduced number of flutes for better chip evacuation.
Drilling & Tapping:
Drilling: Use high-quality carbide drills with precise geometry. Peck drilling is recommended for deeper holes to clear chips and cool the tool.
Tapping: It is a challenging operation. Use premium taps designed for high-tensile steels, ensure perfect alignment, and consider thread milling as a superior alternative for better control and tool life.
4. Coolant and Lubrication
Essential: Use a high-quality, water-soluble coolant at the correct concentration.
Function: It is critical for heat dissipation, chip evacuation, and reducing built-up edge. Flood cooling is generally preferred.
5. Workpiece Preparation & Clamping
Remove any scale or decarburized surface layer from the plate (often present on as-delivered material) before machining, as it is abrasive and can cause premature tool wear.
Secure clamping is vital to withstand high cutting forces without vibration.
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.
