S550QL1 Steel (EN 10025-6) High Strength Structural Steel
S550QL1 Steel (EN 10025-6) - Quenched & Tempered High Strength Structural Steel
S550QL1 is a quenched and tempered structural steel conforming to EN 10025-6, delivering a minimum yield strength of 550 MPa and excellent low-temperature toughness at -40°C. Ideal for heavy welded constructions.
Welding, thermal cutting, cold forming (after tempering), machining, high-strength bolting
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S550QL1 Steel High Strength Structural Steel Introduction
S550QL1 is a high-yield structural steel grade defined in EN 10025-6, delivered in the quenched and tempered condition. It offers a minimum yield strength of 550 MPa, combined with good weldability and outstanding notch toughness down to -40°C (designated by the symbol QL1). The steel is suitable for heavy-duty, dynamically loaded structures where weight reduction without compromising strength is critical.
Key features:
- High strength-to-weight ratio
- Excellent low-temperature impact toughness
- Good weldability when proper procedures are followed
- Available as plates, sheets, strips, and welded tubes (e.g., ERW pipe)
S550QL1 Steel High Strength Structural Steel Chemical Composition
The following chemical composition limits apply to heat analysis according to EN 10025-6. The steel is fully killed and fine grain treated. Elements not listed should not be intentionally added without the purchaser's agreement. Fine grain practice is achieved with sufficient Al, Nb, V, or Ti content.
| Element | Maximum Value (%) | Remarks |
|---|---|---|
| Carbon (C) | 0.20 | Ladle analysis |
| Silicon (Si) | 0.80 | Ladle analysis |
| Manganese (Mn) | 1.70 | Ladle analysis |
| Phosphorus (P) | 0.020 | Ladle analysis |
| Sulfur (S) | 0.010 | Ladle analysis |
| Chromium (Cr) | 1.50 | Ladle analysis |
| Molybdenum (Mo) | 0.70 | Ladle analysis |
| Nickel (Ni) | 2.00 | Ladle analysis |
| Copper (Cu) | 0.50 | Ladle analysis |
| Vanadium (V) | 0.12 | Ladle analysis |
| Titanium (Ti) | 0.05 | Ladle analysis |
| Niobium (Nb) | 0.06 | Ladle analysis |
| Nitrogen (N) | 0.015 | Ladle analysis |
| Boron (B) | 0.005 | Ladle analysis |
| Zirconium (Zr) | 0.15 | Ladle analysis |
S550QL1 Steel High Strength Structural Steel Physical Properties
The values listed below are typical for quenched and tempered structural steel and are provided for guidance only. They are not requirements of EN 10025-6. Actual values may vary depending on exact chemical composition and heat treatment condition.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | kg/dm³ | Ambient temperature |
| Modulus of Elasticity (E) | 210 | GPa | Ambient temperature |
| Shear Modulus (G) | 81 | GPa | Ambient temperature |
| Poisson's Ratio (ν) | 0.3 | - | Ambient temperature |
| Thermal Expansion Coefficient (α) | 11.7 × 10⁻⁶ | /K | 20 °C to 100 °C |
| Thermal Conductivity (λ) | 46 | W/(m·K) | 20 °C |
| Specific Heat Capacity | 460 | J/(kg·K) | 20 °C |
| Electrical Resistivity (ρ_e) | 0.25 × 10⁻⁶ | Ω·m | 20 °C |
S550QL1 Steel High Strength Structural Steel Mechanical Properties
The following mechanical properties are mandatory for S550QL1 according to EN 10025-6. Values apply to longitudinal test pieces taken from flat products. Impact tests are performed at -40 °C on Charpy-V specimens. For thicknesses above 150 mm, properties shall be agreed at the time of enquiry and order.
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 550 | MPa | Thickness ≤ 50 mm |
| Yield Strength (ReH) | ≥ 530 | MPa | 50 mm < Thickness ≤ 100 mm |
| Yield Strength (ReH) | ≥ 510 | MPa | 100 mm < Thickness ≤ 150 mm |
| Tensile Strength (Rm) | 640 – 820 | MPa | Thickness ≤ 50 mm |
| Tensile Strength (Rm) | 640 – 820 | MPa | 50 mm < Thickness ≤ 100 mm |
| Tensile Strength (Rm) | 630 – 790 | MPa | 100 mm < Thickness ≤ 150 mm |
| Elongation (A) | ≥ 16 | % | Thickness ≤ 50 mm, long. |
| Elongation (A) | ≥ 16 | % | 50 mm < Thickness ≤ 100 mm, long. |
| Elongation (A) | ≥ 16 | % | 100 mm < Thickness ≤ 150 mm, long. |
| Impact Energy (KV2) | ≥ 27 | J | At -40 °C, longitudinal |
S550QL1 Steel High Strength Structural Steel Fully Equivalent Material Standards & Substitute Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| International (ISO) | ISO 630-3 | S550QL1 | Identical technical requirements to EN 10025-6 |
S550QL1 Steel High Strength Structural Steel Application Introduction
S550QL1 is designed for heavy welded structures that demand high strength and reliable brittle fracture resistance at low temperatures. It is widely used in transport and lifting equipment, offshore and marine engineering, and highly stressed bridges and buildings. The material can be cut, cold-formed (after suitable tempering), and welded using common methods, provided appropriate pre-heating and interpass temperature controls are followed.
Product Applications: Telescopic crane booms, Welded structural hollow sections (ERW pipes), Bridge box girders, Pressure vessels for low-temperature service, Excavator arms and buckets, Heavy-duty transport trailers
Processed into products: Welded tubular joints, High-strength bolted flanges, Chassis and frame beams, Support brackets and gusset plates, Stiffeners for plate girders, Load-bearing shafts and pins (with additional hardening if required)
Application industries: Crane and heavy lift equipment, Offshore platforms and shipbuilding, Bridge construction, Mining and earthmoving machinery, Pressure vessels and penstocks, Wind tower and renewable energy structures
S550QL1 Steel High Strength Structural Steel Similar / Comparable Alternative Materials
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| EU | EN 10025-6 | S500QL1 | Lower yield strength (500 MPa) but same low-temperature toughness |
| EU | EN 10025-6 | S550Q | Same strength but impact test at 0°C instead of -40°C |
| EU | EN 10025-6 | S550QL | Same strength, impact test at -20°C (less severe cold toughness) |
| EU | EN 10025-6 | S620QL1 | Higher yield strength (620 MPa), similar toughness at -40°C |
| International | ISO 630-3 | S500QL1 | Identical to EN 10025-6 S500QL1 |
| International | ISO 630-3 | S620QL1 | Identical to EN 10025-6 S620QL1 |
Notes:
Welding guidelines: Preheating may be necessary depending on the combined thickness and hydrogen potential of the consumables. Typical preheat and interpass temperatures range from 75°C to 150°C for moderate thicknesses. Post-weld heat treatment is generally not required for structural applications but may be considered to reduce residual stresses.
Availability: S550QL1 is normally produced as normalised rolled or thermomechanical rolled and then quenched and tempered. It can be supplied with inspection certificates according to EN 10204, types 3.1 or 3.2.
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