S235JR and S355JR are the two most widely stocked hot rolled structural steel plate grades in EN 10025-2. They come from the same non-alloy steel family, are welded with the same consumables and are inspected under the same test regime. The decisive difference is strength: S235JR guarantees a minimum yield strength of 235 MPa, while S355JR guarantees 355 MPa at the same nominal thickness. That 120 MPa gap decides which grade is economical for a given structure.
One Standard, Two Strength Levels
Both grades are specified in EN 10025-2, the technical delivery condition for hot rolled non-alloy structural steels. The suffix JR shows that the Charpy V-notch impact test is performed at +20 °C with a minimum average energy of 27 J on longitudinal specimens, so both are room-temperature grades. Where service temperature falls below zero, J0, J2, K2 or a normalized EN 10025-3 grade is the correct specification instead.
Because the two grades share one composition table and one property table, plates of the different grades weld to each other directly, and mixed-grade fabrication is standard practice in frames where only the highly stressed members need the stronger plate.
Chemical Composition
| Element, heat analysis, max % | S235JR | S355JR |
|---|---|---|
| Carbon (C) | 0.17 | 0.24 |
| Silicon (Si) | 0.55 | 0.55 |
| Manganese (Mn) | 1.40 | 1.60 |
| Phosphorus (P) | 0.035 | 0.035 |
| Sulphur (S) | 0.035 | 0.035 |
| Nitrogen (N) | 0.012 | 0.012 |
| Copper (Cu) | 0.55 | 0.55 |
S355JR reaches its higher strength through additional carbon and manganese. The same alloying also raises the carbon equivalent, which is why welding procedures for the stronger grade pay closer attention to heat input and, in thick sections, to preheating.
Mechanical Properties by Nominal Thickness
| Nominal thickness (mm) | ReH min, S235JR (MPa) | ReH min, S355JR (MPa) | Rm, S235JR (MPa) | Rm, S355JR (MPa) |
|---|---|---|---|---|
| ≤ 16 | 235 | 355 | 360-510 | 470-630 |
| > 16 - 40 | 225 | 345 | 360-510 | 470-630 |
| > 40 - 63 | 215 | 335 | 360-510 | 470-630 |
| > 63 - 80 | 215 | 325 | 360-510 | 470-630 |
| > 80 - 100 | 215 | 315 | 360-510 | 470-630 |
| > 100 - 150 | 195 | 295 | 350-500 | 450-600 |
| > 150 - 200 | 185 | 285 | 340-490 | 450-600 |
| > 200 - 250 | 175 | 275 | 340-490 | 450-600 |
Yield strength is specified as a minimum and tensile strength as a range, both measured on longitudinal specimens. Minimum elongation (A, gauge length Lo = 5.65 times the square root of So) for S235JR falls from 26% at 3-40 mm to 21% at 150-250 mm. S355JR carries lower minimum elongation values across the same bands, a normal trade-off for a higher strength grade, and cold forming limits have to reflect it. For plate thinner than 3 mm, S355JR is supplied with a tensile range of 510-680 MPa.
Impact Toughness and Test Requirements
Both grades are delivered with a guaranteed Charpy V-notch energy of 27 J at +20 °C on longitudinal specimens. Impact tests are taken per heat and, for heavy plate, per rolling batch as agreed at order stage. The requirement is identical for the two grades, so impact toughness never decides the choice between S235JR and S355JR; the strength level does.
Welding, Forming and Machining
S235JR is the easier of the two to fabricate. Its lower carbon equivalent allows welding without preheat in ordinary thicknesses, and its higher elongation makes cold bending, flanging and roll forming straightforward. S355JR welds readily as well, but welding procedure qualification must account for the higher carbon equivalent, and cold forming limits are tighter, so sharp bend radii may need larger tooling radii or a warm forming step. Both grades cut cleanly by flame, plasma and laser, machine without difficulty in the as-rolled or normalized condition, and accept standard surface preparation and coating systems.
How to Choose Between S235JR and S355JR
S235JR: general fabrication, platforms and walkways, low-rise frames, brackets, support structures and tanks where stiffness rather than stress governs the design.
S355JR: bridge girders, crane runway beams, heavy machinery frames and base plates, transport equipment, and any structure where a weight reduction offsets the higher plate price.
Commercial view: S235JR is normally the lower priced grade per tonne. S355JR costs more but allows thinner sections for the same load, and on many projects the weight saving is worth more than the price difference.
Frequently Asked Questions
Q: Is S355JR stronger than S235JR?
Yes. S355JR guarantees a minimum yield strength of 355 MPa and S235JR 235 MPa at the same nominal thickness, and the tensile ranges differ in the same direction.
Q: Can S235JR and S355JR be welded to each other?
Yes. Both grades are covered by EN 10025-2, so they share the same welding framework; consumables are normally matched to the stronger of the two plates.
Q: What does the JR suffix mean?
JR identifies the impact test condition: Charpy V-notch specimens tested at +20 °C with a minimum average energy of 27 J in the longitudinal direction.
Q: Are S235JR and S355JR the same as St 37-2 and St 52-3?
The DIN 17100 designations St 37-2 and St 52-3 describe comparable strength levels, but the current properties are those defined for the EN 10025-2 grades, which are the grades to order today.
Q: Can S355JR be used at sub-zero service temperature?
Not as the primary choice. JR is a room-temperature grade; J0, J2 or K2 sub-grades, or normalized EN 10025-3 grades, provide the low-temperature toughness required below 0 °C.
Q: Which grade is easier to bend or form?
S235JR. Its lower yield strength and higher minimum elongation give a wider forming window than S355JR for the same thickness.
