Two Grades That Dominate Structural Steelwork
S235JR and S355JR are the two most widely used non-alloy structural steel grades in EN 10025-2, the European standard for hot rolled structural steel products. Both are weldable, both are delivered in the same product forms, and both carry a JR suffix that requires a Charpy V-notch impact test at plus 20 degrees C with a minimum absorbed energy of 27 J. The difference is written into the name: the number is the minimum yield strength in MPa for plate up to 16 mm thick, so S355JR is roughly 50% stronger than S235JR.
Yield and Tensile Strength
| Property | S235JR | S355JR |
|---|---|---|
| Minimum yield strength ReH, t up to 16 mm | 235 MPa | 355 MPa |
| Minimum yield strength ReH, t 16-40 mm | 225 MPa | 345 MPa |
| Minimum yield strength ReH, t 40-63 mm | 215 MPa | 335 MPa |
| Minimum yield strength ReH, t 63-80 mm | 215 MPa | 325 MPa |
| Tensile strength Rm, t 3-100 mm | 360-510 MPa | 470-630 MPa |
| Charpy V-notch impact energy at plus 20 degrees C, min | 27 J | 27 J |
Yield strength decreases with thickness in both grades, because thicker plate cools more slowly after rolling and develops a coarser microstructure. The relative gap between the grades stays close to 100 to 140 MPa across the whole thickness range, and S355JR is consistently about 110 MPa higher in tensile strength at both ends of its range. Because both grades are verified at the same impact energy and temperature, the additional strength of S355JR is not obtained at the expense of toughness at room temperature.
Chemical Composition and Weldability
| Element (max, % by mass) | S235JR | S355JR |
|---|---|---|
| Carbon, C, t up to 40 mm | 0.17 | 0.24 |
| Silicon, Si | 0.55 | 0.55 |
| Manganese, Mn | 1.40 | 1.60 |
| Phosphorus, P | 0.045 | 0.045 |
| Sulphur, S | 0.045 | 0.045 |
| Nitrogen, N | 0.012 | 0.012 |
S355JR achieves its higher strength with more carbon and manganese, which lifts its carbon equivalent and makes welding slightly more demanding. The carbon equivalent is normally controlled to around 0.45% for plate up to 30 mm and about 0.47% above that for S355JR, against roughly 0.35% and 0.38% for S235JR. In shop terms this means S235JR can be welded in thin sections with little or no preheat, while S355JR needs a controlled preheat and interpass temperature as thickness and restraint increase, and low-hydrogen consumables on heavily restrained joints.
Practical Design Consequences
Thinner sections: because the design yield strength is higher, S355JR allows a thinner plate or a lighter rolled section for the same load, which reduces steel tonnage, coating area and handling effort.
Stiffness is unchanged: the modulus of elasticity is essentially the same for both grades, so deflection, vibration and buckling-limited members gain nothing from S355JR.
Fatigue and stability: fatigue performance depends on detail geometry and stress range rather than on the grade, and slender compression members are governed by slenderness.
Cost: S355JR costs more per tonne, so the mass saving has to offset the higher unit price, the additional preheat and the more careful welding control.
Availability: both grades are readily stocked in plate and sections, but S235JR remains the more common commodity and is easier to source at short notice for small orders.
Typical Applications
S235JR is the everyday choice for low-rise building frames, general fabrication, storage and racking, walkways, machine guards and light welded structures where strength is not the governing limit. S355JR is specified for heavy-duty work: long-span bridges, high-rise and large commercial frames, crane girders and jibs, heavy machinery bases, transport and port equipment, and any structure that must combine high load-bearing capacity with a controlled plate weight. In mixed structures the two grades are frequently used side by side, with S355JR concentrated in the most highly stressed members and S235JR used elsewhere.
Approximate Equivalent Grades
| Country | Standard | S235JR equivalent | S355JR equivalent |
|---|---|---|---|
| United States | ASTM | A36, A283 Grade C | A572 Grade 50 |
| China | GB | Q235B | Q355B |
| Japan | JIS | SS400 | SM490B |
| India | IS | IS 2062 E250 | IS 2062 E350 |
| Germany | DIN | St37-2 | St52-3 |
These correspondences are approximate only. Yield strength, toughness class, chemistry and impact temperature differ between specifications, so an equivalence table is a starting point for discussion rather than a basis for substitution on a certified structure.
Frequently Asked Questions
Q: What is the main difference between S235JR and S355JR?
Strength. S355JR offers a minimum yield strength of 355 MPa against 235 MPa for S235JR in plate up to 16 mm thick, and a higher tensile strength range, while both grades require 27 J of Charpy impact energy at plus 20 degrees C.
Q: Is S355JR harder to weld than S235JR?
It is slightly more demanding because of its higher carbon and manganese content. S355JR generally needs controlled preheat and interpass temperature as thickness increases, while S235JR can often be welded without preheat in thin sections.
Q: Can S355JR be substituted for S235JR?
Usually yes, provided the welding procedure and the connection design suit the higher strength grade. Substitution in the other direction requires a full re-check of the strength limit states.
Q: Which grade is more economical?
It depends on the limit state. For load-controlled members S355JR often wins because thinner plate means less steel and less welding; for deflection or stability-controlled members S235JR is usually the cheaper solution.
Q: Do both grades keep their yield strength in thick plate?
No. Both lose yield strength as thickness increases; for example S355JR falls from 355 MPa to 325 MPa and S235JR from 235 MPa to 215 MPa as the section moves from thin plate into the heavier thickness bands.
Q: Does the JR suffix mean the steel is suitable for cold climates?
Not necessarily. JR verifies impact energy at plus 20 degrees C only. For low-temperature service the J0 or J2 impact classes should be specified instead.
