S355JR at a Glance
S355JR is a weldable structural steel grade defined in EN 10025-2, the European standard covering non-alloy structural steels supplied in the hot rolled condition. The designation is a specification in miniature: the "S" stands for structural steel, "355" is the minimum yield strength in MPa for plates up to 16 mm thick, the "J" fixes a minimum Charpy absorbed energy of 27 J, and the "R" sets the impact test temperature at room temperature, that is +20 °C. Plates are normally delivered as rolled, with normalised or thermomechanically rolled conditions available when agreed at the order stage.
Because EN 10025-2 describes a family rather than a single product, an engineer comparing S355JR with grades from other systems has to match three parameters instead of one: minimum yield strength, impact test temperature and permitted chemistry. Matching the yield value alone is the most common source of error in cross-reference tables.
Chemical Composition of S355JR
The ladle analysis limits below apply to S355JR and to the related S355J0 and S355J2 grades of EN 10025-2. The restrictions on carbon, sulphur and nitrogen keep the steel weldable in ordinary fabrication practice.
| Element | Limit (ladle analysis) |
|---|---|
| C | 0.24 % max |
| Si | 0.55 % max |
| Mn | 1.60 % max |
| P | 0.035 % max |
| S | 0.035 % max |
| N | 0.012 % max |
| Cu | 0.55 % max |
Carbon equivalent is also controlled as a function of thickness and delivery condition. A typical maximum value quoted for S355JR plate is 0.45 %, calculated with the CEV formula C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. Higher values indicate a greater tendency to harden in the heat affected zone, so preheating and controlled heat input become part of the welding procedure.
Mechanical Properties
Yield strength falls as plate thickness increases, so the acceptance value must always be read against the thickness ordered rather than assumed.
| Thickness (mm) | Minimum yield strength ReH (MPa) |
|---|---|
| up to 16 | 355 |
| over 16 to 40 | 345 |
| over 40 to 63 | 335 |
| over 63 to 80 | 325 |
| over 80 to 100 | 315 |
| over 100 to 150 | 295 |
| over 150 to 200 | 285 |
Tensile strength: approximately 470–630 MPa for the common 3–100 mm plate range.
Minimum elongation: 22 % for plates up to 40 mm, decreasing gradually for heavier sections.
Impact energy: 27 J minimum in a Charpy V-notch test at +20 °C.
Equivalent Grades Around the World
The table below lists the grades most often quoted as S355JR equivalents. They are near-equivalents for structural design, but they are not interchangeable in every clause of every specification.
| System | Standard | Grade |
|---|---|---|
| Europe | EN 10025-2 | S355JR |
| China | GB/T 1591 | Q355B (formerly Q345B) |
| USA | ASTM A572 | A572 Grade 50 |
| Germany | DIN 17100 | St52-3 |
| Japan | JIS G3106 | SM490B |
| ISO | ISO 630-2 | E355 |
| Sweden | SS | SS 2132-01 |
Three practical corrections are worth recording. First, Q345B was the Chinese equivalent for many years, but GB/T 1591-2018 re-designated the grade as Q355B, and new enquiries should use the current designation. Second, ASTM A572 Grade 50 is a high strength low alloy steel with a minimum yield of 345 MPa and its own chemistry limits, so it matches S355JR in strength class rather than in specification. Third, JIS G3106 SM490B combines a 325 MPa minimum yield with a 490 MPa tensile class, which is close to, but not identical with, an S355JR requirement.
S355JR, S355J0, S355J2 and S355K2 Compared
| Grade | Impact test temperature | Minimum absorbed energy |
|---|---|---|
| S355JR | +20 °C | 27 J |
| S355J0 | 0 °C | 27 J |
| S355J2 | −20 °C | 27 J |
| S355K2 | −20 °C | 40 J |
The suffix letter does not change the tensile or yield requirement; it changes only the toughness verification. When a structure is designed for service below 0 °C, S355J2 or S355K2 is normally specified instead of S355JR, because the Charpy test is then performed at −20 °C. Where the design code accepts a room temperature test, S355JR is the economically rational choice.
Fabrication and Application Notes
Welding: with a controlled carbon equivalent, S355JR is readily welded by shielded metal arc, gas metal arc and submerged arc processes; consumables matched to a 355 MPa class are used.
Forming: the grade takes cold bending and flame cutting without difficulty, but edge quality and bend radius should be confirmed for thick plate.
Through-thickness duty: welded joints carrying tensile strain in the Z direction should be ordered with through-thickness testing rather than assumed from the base grade.
Typical uses: building frames, bridges, crane booms, storage tanks, transmission towers, offshore support structures and general welded fabrication.
Frequently Asked Questions
Q: What is the Chinese equivalent of S355JR?
Q355B to GB/T 1591 is the current Chinese equivalent; the older designation Q345B still appears in legacy drawings and should be updated on new orders.
Q: What is the difference between S355JR and S355J2?
The two grades share the same strength and chemistry requirements, but S355J2 is impact tested at −20 °C while S355JR is tested at +20 °C, so S355J2 suits low temperature service.
Q: Is S355JR a low carbon steel?
Yes. It is a non-alloy structural steel with a maximum carbon content of 0.24 %, with manganese and silicon balanced to deliver strength and ductility.
Q: Is ASTM A572 Grade 50 the same as S355JR?
They are treated as strength equivalents, but A572 Grade 50 is a high strength low alloy grade with different chemistry limits and impact provisions, so substitution requires engineering review.
Q: What does the JR suffix mean?
The J indicates a minimum Charpy absorbed energy of 27 J and the R indicates that the test is performed at room temperature, that is +20 °C.
Q: Can S355JR be used for offshore or low temperature structures?
Only after impact and weldability requirements for the service temperature have been checked; most low temperature designs call for S355J2, S355K2 or a dedicated offshore grade instead.
