Grade Designation and Standard Basis
S355JR is a weldable structural steel plate defined in EN 10025-2, the part of the European hot rolled products standard that covers technical delivery conditions for non alloy structural steels. The designation is a set of instructions for the user. S identifies structural steel, 355 is the minimum specified yield strength in MPa for the lower thickness range, and JR records the impact quality: J means that a minimum Charpy V notch energy of 27 J is guaranteed, and R means that the test is carried out at plus 20 C, that is, at room temperature.
The grade sits in the middle of the structural family. It is stronger than S235 and S275, and it costs less than the specialised plate grades used for offshore or low temperature duty, which is why it appears in an enormous number of projects as the default structural plate where the design temperature does not fall below room temperature.
Chemical Composition and Mechanical Properties
The steel is a carbon manganese grade with a deliberately modest alloy content so that it remains easy to weld and to form. EN 10025-2 limits carbon to about 0.24 percent for the common plate thickness range, silicon to 0.55 percent, manganese to 1.60 percent, and phosphorus and sulphur to 0.035 percent each, unless a more severe analysis restriction is agreed. Maximum carbon equivalent values are also specified, which is what keeps the steel weldable in field conditions with ordinary consumables and sensible procedures.
| Property | S355JR requirement |
|---|---|
| Minimum yield strength | 355 MPa up to 16 mm, stepped down for thicker plate |
| Tensile strength | 470 to 630 MPa |
| Charpy V notch, longitudinal | 27 J at +20 C |
| Typical carbon | 0.24 percent maximum |
| Typical manganese | 1.60 percent maximum |
| Carbon equivalent | Limited by thickness class in EN 10025-2 |
The yield strength is quoted for a thickness band, not for all thicknesses. Through the standard the minimum yield drops as the plate gets thicker, and the tensile range is also tabulated by thickness, so the design values have to be read from the table entry that matches the ordered thickness. Microalloying with niobium, vanadium or titanium, and grain refining with aluminium, are permitted within the analysis limits and help the mill meet the strength and toughness combination without excessive carbon.
Applications
The plate is consumed across general engineering and construction. Typical uses are building frames and connections, bridge structural members and stiffeners, ship and offshore structural components not covered by classification society grades, vehicle and crane structures, industrial plant platforms and supports, transmission towers, storage structures and the structural parts of pressure equipment that are not on the pressure boundary. Where the design temperature falls below room temperature, the designer moves to the J0 or K2 qualities with their lower impact test temperatures or to a different grade family altogether.
Fabrication and Quality Control
Cutting is carried out by shearing, plasma or flame cutting, with edges dressed to the joint preparation on the drawings.
Welding follows a qualified procedure matched to the plate thickness and the carbon equivalent; typical practice uses low hydrogen electrodes for thicker plate and controls heat input to preserve the heat affected zone toughness.
Cold forming is straightforward, and hot forming is followed by normalizing where the design code requires the original properties to be restored.
Tensile and impact tests on specimens from the delivered plate confirm the grade, and the impact test at plus 20 C reproduces the JR condition of the standard.
Thickness, width, length, flatness and edge condition are verified against the standard, and the plate is marked with the grade, the heat number and the cast identity.
Inspection documents record the chemical analysis, the property tests and any supplementary requirements such as ultrasonic examination that the order specifies.
Marking the grade on the plate is not decorative. Because S355JR and other qualities of the same family look identical, correct stencil marking and heat number identification are what allow the fabricator to prove that the right material has been used in the right place.
Frequently Asked Questions
Q: What does the R in S355JR mean?
A: It means the Charpy V notch impact test is carried out at plus 20 C. The J indicates the minimum absorbed energy of 27 J. A grade such as S355J0 would instead be tested at 0 C.
Q: What is the tensile strength of S355JR?
A: EN 10025-2 gives a tensile strength range of 470 to 630 MPa for the common thickness range, in addition to the minimum yield strength of 355 MPa for plate up to 16 mm.
Q: Is S355JR suitable for pressure vessels?
A: It is a structural grade. It can be used for structural parts and attachments, while pressure retaining components are normally built from plate grades specified for pressure equipment with the impact and testing provisions of the applicable vessel code.
Q: How does the grade perform when welded in cold weather?
A: The restricted carbon and carbon equivalent keep the steel weldable, but low ambient temperature increases the risk of cracking, so preheat and heat input are adjusted to the conditions and the welding procedure is followed strictly.
Q: Which thicknesses are available?
A: Plates are commonly supplied from about 3 mm up to 100 mm and beyond, depending on the mill, with the minimum yield strength taken from the thickness band table of the standard.
