Properties of S355JR Structural Steel
S355JR is one of the most widely used structural steels globally, defined by the European standard EN 10025-2. It offers a favorable balance of strength, weldability, and cost, making it the default choice for heavily loaded structures.
Here is a comprehensive breakdown of its key properties.
1. Mechanical Properties
Values are for nominal thicknesses ≤ 16 mm. Strength decreases for thicker sections (see table below).
Minimum Yield Strength (ReH)
355 MPa The defining property for design. Also referred to as yield stress or proof strength. Tensile Strength (Rm) 470 - 630 MPa Must fall within this range. The spread ensures consistency. Yield-to-Tensile Ratio (ReH/Rm) Max 0.85 - 0.90 (implied) A high ratio indicates less plastic reserve after yielding. Requires accurate design. Minimum Elongation (A₅) ≥ 21% (for t ≤ 40mm) Indicates good ductility for forming and energy absorption. Impact Toughness (KV) ≥ 27 Joules at +20°C The "J" indicates room temperature test. The "R" specifies the minimum energy (27J).
Thickness-Dependent Yield Strength (Key Design Data):
| Product Thickness (t) | Minimum Yield Strength (ReH) |
|---|---|
| t ≤ 16 mm | 355 MPa |
| 16 mm < t ≤ 40 mm | 345 MPa |
| 40 mm < t ≤ 63 mm | 335 MPa |
| 63 mm < t ≤ 80 mm | 325 MPa |
| 80 mm < t ≤ 100 mm | 315 MPa |
2. Chemical Composition (Maximum % by Weight)
For thickness ≤ 40mm, ladle analysis. The "JR" grade has specific limits.
Carbon (C)
≤ 0.24% Primary strengthener. Kept low for weldability. Manganese (Mn) ≤ 1.60% Increases strength and hardenability, combats sulfur brittleness. Silicon (Si) ≤ 0.55% Deoxidizer, increases strength. Phosphorus (P) ≤ 0.045% Impurity - reduces toughness (embrittlement). Tightly controlled. Sulfur (S) ≤ 0.045% Impurity - harms toughness and weldability (hot cracking). Nitrogen (N) ≤ 0.009% Controlled to prevent aging embrittlement. Aluminum (Al) min ≥ 0.020% Mandatory for fine grain practice. Forms AlN to pin grain growth. Copper (Cu) optional ≤ 0.55% Sometimes added (~0.3%) for slight atmospheric corrosion resistance.
Carbon Equivalent (CEV) - Weldability Indicator:
Formula (IIW): CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
Typical Range for S355JR: 0.40 - 0.45
Interpretation: Good to moderate weldability. Pre-heat may be required for thicker sections or restrained joints to prevent hydrogen cracking.
3. Technological & Physical Properties
Weldability
Good. Requires standard procedures: low-hydrogen consumables, controlled heat input. Pre-heat recommended for t > 25-30mm. Cold Forming Good. Can be bent, rolled, and formed with standard practices. Minimum bend radii are larger than for S235. Machinability Fair (better than low-carbon steels due to higher strength, but harder to cut). Modulus of Elasticity (E) ~210,000 MPa (Same as all steels). Stiffness depends on cross-section geometry. Density (ρ) ~7.85 g/cm³ Poisson's Ratio (ν) ~0.3 Coefficient of Thermal Expansion ~12 x 10⁻⁶ /K Corrosion Resistance Equivalent to carbon steel. Not a weathering steel. Requires painting or other protection.
4. Delivery Conditions & Standards
Governing Standard
EN 10025-2: Hot rolled products of structural steels Common Delivery Conditions As-rolled (+AR) or Normalized (+N). Material Identification S355JR is not a weathering steel. For unpainted atmospheric corrosion resistance, specify S355J0W or S355J2W (EN 10025-5).
5. Comparison with Similar Grades
| Grade | Min Yield (MPa) | Key Difference vs. S355JR |
|---|---|---|
| S275JR | 275 | Lower strength, better formability, lower cost. |
| S355JR (This Grade) | 355 | Baseline for heavy structural work. |
| S355J2 | 355 | Higher toughness: ≥ 27J at -20°C. |
| S355K2 | 355 | Even higher toughness: ≥ 40J at -20°C. |
| S355NL | 355 | Normalized, fine grain: ≥ 27J at -50°C. |
| A572 Gr. 50 (USA) | 345 (50 ksi) | Common ASTM equivalent. Slightly lower yield, no mandatory impact test. |
6. Typical Applications
S355JR is the workhorse steel for major structures:
Steel building frames (beams, columns)
Bridges and heavy industrial plants
Cranes, material handling equipment
Shipbuilding and offshore structures (when higher toughness grades are not mandated)
Heavy machinery and vehicle chassis
Summary: S355JR is a versatile, cost-effective, and readily available non-alloy structural steel with high strength, good weldability, and guaranteed basic toughness at room temperature. Its properties make it suitable for the vast majority of structural engineering applications. Designers must always use the thickness-corrected yield strength from certified mill test reports.
