S690Q is a high-yield-strength structural steel produced to the EN 10025-6 standard, known for its excellent combination of strength, toughness, and weldability. The material is delivered in the quenched and tempered condition, which provides a minimum yield strength of 690 MPa and makes it suitable for heavy machinery, lifting equipment, bridges, and other structures where weight savings and high load capacity are critical. This article reviews the composition, mechanical properties, and applications of the grade.
Chemical Composition
The heat analysis of S690Q is limited to carbon 0.20%, silicon 0.80%, manganese 1.70%, phosphorus 0.020 to 0.025%, sulfur 0.010 to 0.015%, nitrogen 0.015%, boron 0.005%, and chromium 1.50% maximum. Copper, molybdenum, niobium, nickel, titanium, vanadium, and zirconium are controlled at 0.50%, 0.70%, 0.06%, 2.0%, 0.05%, 0.12%, and 0.15% maximum respectively. The micro-alloying system supports the response to quenching and tempering across the plate thickness and provides the toughness and hardenability required for the high strength level.
Mechanical Properties
For plates with a thickness greater than 3 mm and up to 50 mm, the minimum yield strength of S690Q is 690 MPa, the tensile strength is 770 to 940 MPa, the minimum elongation is 14%, and the minimum impact energy is 30 J at -20 C. For plates from 50 to 100 mm, the minimum yield strength is 650 MPa with a tensile strength of 760 to 930 MPa; for plates from 100 to 150 mm, the minimum yield strength is 630 MPa with a tensile strength of 710 to 900 MPa. The same elongation and impact requirements apply across the thickness range. The material is about three times stronger than common structural carbon steel, which enables thinner components and lighter structures.
Heavy Machinery Applications
In heavy machinery, S690Q is applied to high-load components such as bulldozer blades, quarry trucks, waste compactors, and excavator buckets. Its excellent toughness and abrasion resistance effectively withstand intense impact from hard materials and long-term friction during operation, avoiding premature deformation or damage and significantly extending the service life of machinery parts. In lifting equipment, the grade is used for overhead cranes, gantry cranes, mobile crane booms, and hoists, where the high strength-to-weight ratio allows more lightweight and compact structures without reducing load-bearing capacity, improving flexibility and mobility while ensuring operational safety.
Construction, Offshore and Transportation Applications
In construction, S690Q is suitable for bridges, high-rise buildings, and other large engineering frameworks where weight reduction is key. It balances high strength and low weight, reducing the overall load of the structure, simplifying construction procedures, and enhancing stability and durability under complex stress conditions. In offshore and marine applications, the grade is ideal for offshore platforms, shipbuilding, and oilfield fabrication, where its outstanding low-temperature toughness resists brittle fracture in harsh, cold marine environments with strong winds, waves, and salt corrosion. In transportation, the steel is applied to frames and chassis for heavy transporters and dump trucks, providing reliable structural support for long-term heavy-load transport and withstanding continuous pressure and vibration during driving.
Selection Between S690Q and S690QL
S690Q requires a minimum impact toughness of 30 J tested at -20 C and is typically used for cranes in temperate climates and quarry equipment. S690QL is certified for -40 C and below with a minimum impact toughness of 40 J, and is used for critical applications such as arctic pipelines, offshore platforms, and mining vehicles in cold regions. For most heavy machinery and general construction, S690Q provides the required balance of strength and cost, while projects with low design temperatures should specify S690QL. The grade is approximately comparable to ASTM A514 in strength level, and substitutes should be verified against the project specification.
Frequently Asked Questions
What is the difference between S690Q and S690QL?
S690Q has a minimum impact toughness of 30 J tested at -20 C, while S690QL is certified for -40 C and below with at least 40 J impact toughness. S690QL is used for critical cold-weather applications.
What is the yield strength of S690 steel?
S690Q has a minimum yield strength of 690 MPa for plates from 3 to 50 mm, with the value decreasing to 650 MPa for 50 to 100 mm and 630 MPa for 100 to 150 mm, in accordance with EN 10025-6.
What is S690Q comparable to?
S690Q is comparable to ASTM A514 in strength level and is often seen as a precursor or similar-strength version of S690QL, with the main difference being the low-temperature toughness.
What grade of steel is S690?
S690 is a high-yield structural steel grade produced in compliance with EN 10025-6, heat treated by the quench and temper process, with good bending and welding properties.
What type of steel is S690Q and what is its core performance?
S690Q is an EN 10025-6 quenched and tempered high-strength steel with a minimum yield strength of 690 MPa and a tensile strength of 770 to 940 MPa, enabling thinner components than common structural steels.
Can S690Q be welded?
Yes, S690Q has good weldability for its strength class. Welding requires low-hydrogen consumables, preheating, and controlled heat input to maintain the mechanical properties and prevent cracking.