S690Q High Strength Structural Steel Plate

1. What is S690Q High Strength Structural Steel Plate?

S690Q high-strength structural steel plate is a fine-grained, high-strength structural steel plate that complies with the European standard EN 10025-6; its material number is 1.8931.

S690Q high-strength structural steel plate is quenched and tempered (Q+T) and features a high yield strength (≥ 690 MPa), good impact toughness (impact energy absorption ≥ 30 J at -20°C), good weldability, and comprehensive mechanical properties suitable for engineering and manufacturing applications.

S690Q high-strength structural steel plates are primarily used in engineering equipment and steel structures that demand high structural strength, load-bearing capacity, and lightweight design, such as heavy-duty construction machinery, lifting equipment, excavators, mining machinery, mining engineering vehicles, high-load steel structures, and heavy-duty load-bearing components.

We supply S690Q high-strength structural steel plates in a full range of specifications, accompanied by Material Test Certificates (MTCs), and support third-party inspections. We also offer services such as custom sizing, precision cutting, acid pickling, shot blasting, and anti-corrosion coatings.

2. Meaning of the Grade Designation “EN10025-6 S690Q”

1. The chemical composition achieves a balance of high strength and toughness through alloying elements (such as Cr, Mo, Ni) and microalloying elements (Nb, V, Ti), while controlling the content of harmful elements (P, S).

2. Cr and Mo enhance hardenability and strength; Ni improves low-temperature toughness; Nb, V, and Ti refine the grain structure, increasing strength and toughness; low P and S reduce inclusions and decrease brittleness.

Mechanical properties are the core advantages of S690Q, particularly the combination of high yield strength and good toughness:

Impact toughness: For "Q" grade material, the impact test temperature is -20°C. If it is "S690QL," the impact temperature drops to -40°C ("L" stands for low-temperature toughness).

Thickness influence: When the plate thickness exceeds 16mm, a reasonable reduction in yield strength is allowed (e.g., ReH ≥ 650MPa for thicknesses of 50-100mm). Specific values should be referenced according to the standard or the steel mill’s quality assurance certificate.

EN 10025-6 S690Q is widely used in fields requiring heavy load-bearing, impact resistance, or lightweight design due to its combination of advantages, including "high strength, high toughness,  machinability, and weldability":

Construction Machinery: Key load-bearing structures such as booms, arms, and frames of excavators, cranes, and loaders.

Mining Machinery: Beds of mining dump trucks, crusher frames, and middle troughs of scraper conveyors.

Construction and Bridges: Load-bearing components of long-span steel bridges, steel skeletons of high-rise buildings, and tower crane bodies.

Energy Equipment: Flanges and connecting plates of wind turbine towers, as well as load-bearing components of oil and gas extraction platforms.

Special Vehicles: Frames of heavy-duty trucks and armored plates of bulletproof vehicles (some high-toughness specifications).

Delivery Conditions

Must be in the quenched and tempered (QT) condition: The steel is first subjected to high-temperature quenching (rapid cooling) to obtain a martensitic structure, followed by medium-to-high temperature tempering to transform the structure into tempered sorbite. This process ultimately achieves a balance of "high strength + high toughness" (avoiding the brittleness of the quenched state).

Surface Condition: Typically "as-rolled" or "finished surface." Subsequent treatments such as shot blasting or painting can be applied as needed.

Weldability

S690Q is weldable, but it requires strictly controlled welding procedures due to its high carbon equivalent (CEV). 

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

Clearly Define Technical Requirements: During procurement, specify thickness, width, length, impact temperature (Q/-20°C or QL/-40°C), surface condition, and additional inspection requirements (such as non-destructive testing and Z-direction properties).

Welding Process Control: Preheating is required before welding (recommended preheating temperature: 80-150°C, depending on plate thickness) to avoid cold cracks. Stress relief heat treatment (e.g., 600-650°C tempering) can be performed after welding.

Tool Selection for Machining: Due to high strength, use carbide tools (e.g., WC-Co alloy), reduce cutting speed, and increase feed rate to minimize tool wear.

Verification of Quality Certificate: Ensure the steel mill provides a quality certificate compliant with EN 10204 Type 3.1, confirming compliance with chemical composition, mechanical properties, heat treatment status, and other indicators.

Summary

EN 10025-6 S690Q is a premium, ultra-high-strength structural steel offering an exceptional strength-to-weight ratio. Its use allows for lighter and more efficient designs but demands a high level of expertise and controlled procedures during fabrication, especially welding.