What S355JR Steel Plate Is
S355JR is a hot-rolled weldable structural steel plate defined in EN 10025-2 with a specified minimum yield strength of 355 MPa. The designation has three parts: S for structural steel, 355 for the minimum yield strength in megapascals at thicknesses up to 16 mm, and JR for the impact quality, where J means a minimum Charpy V-notch energy of 27 J and R means that the test is carried out at +20 C. The material number of this grade is 1.0045.
The grade is chosen for steel frames, bridges, crane runways, storage tanks, transition pieces and general fabrication because it offers a predictable strength-to-cost ratio, good toughness and straightforward welding. Plates are normally supplied as-rolled (+AR); a normalised (+N) delivery condition is available when the application or the fabricator's procedure requires it.
Chemical Composition of S355JR
| Element | C | Si | Mn | P | S | N | Cu |
|---|---|---|---|---|---|---|---|
| Maximum, % | 0.22 | 0.55 | 1.60 | 0.035 | 0.035 | 0.012 | 0.55 |
Values are maximum limits for ladle analysis under EN 10025-2 for the JR quality. Carbon is deliberately capped so that the heat affected zone keeps adequate toughness, and the phosphorus and sulphur limits are the looser room-temperature impact values that separate JR from the J2 quality. Raising either element above these limits would force the plate into a different impact class, so incoming certificates should always be checked against the ordered quality and not only against the grade name.
Mechanical Properties
| Thickness, mm | Minimum yield strength, MPa | Tensile strength, MPa | Minimum elongation, % |
|---|---|---|---|
| up to 16 | 355 | 470-630 | 22 |
| 16 to 40 | 345 | 470-630 | 22 |
| 40 to 63 | 335 | 470-630 | 21 |
| 63 to 80 | 325 | 470-630 | 20 |
| 80 to 100 | 315 | 470-630 | 20 |
| 100 to 150 | 295 | 450-600 | 18 |
| 150 to 200 | 285 | 450-600 | 17 |
Impact testing for the JR quality is carried out on longitudinal Charpy V-notch specimens at +20 C with a minimum average energy of 27 J. Density is 7.85 g/cm3 and the modulus of elasticity is about 210 GPa, which allows ordinary structural calculations to be applied without correction.
Equivalent Grades in Other Systems
| System | Designation |
|---|---|
| EN 10025-2 | S355JR, material number 1.0045 |
| ASTM | A572 Gr.50, A678 Gr.A (approximate) |
| JIS G3101 | SS490 (approximate) |
| BS 4360 | 50 B |
| NFA 35-501 | E 36-2 |
| UNI 7070 | Fe 510 B |
| UNE 36.080 | AE 355 B |
| GB/T 1591 | Q355B (approximate, similar strength class) |
These comparisons are strength and application based. Substitution between systems still requires a check of chemical limits, impact temperature, tolerances and any project specification that names one particular standard.
Fabrication, Welding and Supply Range
Supply range: thickness 6-150 mm, width up to 3500 mm, length up to 12000 mm; other sizes are cut from stock plate.
Delivery condition: hot rolled as-rolled, or normalised when specified; mill edge or sheared edge.
Tolerances: thickness and flatness to EN 10029; ultrasonic testing can be agreed to EN 10160 for critical pressure or bridge components.
Welding: covered electrodes, submerged arc and gas shielded processes are all suitable; consumables matched to a 355 MPa yield class are used, and hydrogen-controlled practice applies to thick sections.
Carbon equivalent: values are normally limited to about 0.45 % for plate up to 30 mm, which keeps preheat requirements modest. Thicker plate or high restraint joints should be assessed individually before welding.
Forming and cutting: flame cutting, plasma cutting, sawing, drilling, cold bending and hot forming are standard operations. Hot forming above 900 C followed by uncontrolled cooling can reduce toughness and should be agreed with the supplier.
Typical applications: building frames, bridge girders, crane runway beams, offshore transition structures, transmission towers, truck chassis parts and general engineering fabrication.
Frequently Asked Questions
Q: What is the difference between S355JR and S355J2?
Both have the same 355 MPa minimum yield strength and the same chemistry class. The difference is impact testing: JR is tested at +20 C with 27 J minimum, while J2 is tested at -20 C with 27 J minimum.
Q: Is S355JR the same as Q355B?
They are close equivalents from different standards. Q355B to GB/T 1591 is impact tested at +20 C with 34 J minimum, so the Chinese grade is slightly stricter on impact energy while the strength class is the same.
Q: Can S355JR be welded without preheat?
For plate up to about 30 mm with a controlled carbon equivalent and normal shop temperature, preheat is often not required. Thicker plate, high restraint or low ambient temperature calls for a qualified procedure that specifies preheat and interpass limits.
Q: How does thickness affect the yield strength I can use in design?
Design yield strength falls as thickness increases, from 355 MPa up to 16 mm down to 285 MPa at 150-200 mm. The correct value must be taken for the actual plate thickness, not from the grade name alone.
Q: What surface condition is the plate supplied in?
Plates are supplied with mill scale, free of visible defects and protected for transport. Shot blasting and priming can be arranged when the fabricator needs a prepared surface.
Q: Is a mill certificate provided?
Yes. Plates are supplied to EN 10204 3.1 with chemical analysis, tensile results and impact results for the ordered heat, and dimensional inspection records are available on request.
