Is S275JR Structural Tube Hot Rolled?
The short answer is that the steel itself is delivered hot rolled, while the tube is usually cold-formed from hot-rolled strip. S275JR is a non-alloy structural steel defined in EN 10025-2, and the standard delivery condition of the product form is hot rolled: the strip, plate or section is cooled directly after rolling at high temperature and is used in that condition for the great majority of structural applications. No heat treatment is required to reach the specified properties, which keeps the cost low and the production route simple.
When S275JR is made into square or rectangular hollow section tube, two routes exist. The most common is cold forming: hot-rolled strip is slit to width, roll-formed into the hollow profile at ambient temperature, and the seam is closed by high-frequency electric-resistance welding. The second route is hot finishing to EN 10210-1, where the section is formed and finished at elevated temperature. So a structural tube ordered as S275JR is typically a cold-formed, high-frequency-welded product whose feedstock is hot-rolled steel.
Manufacturing Routes
Cold-Formed Welded Tube (EN 10219-1)
The strip is uncoiled, leveled and slit to the exact width for the required section. It is then progressively roll-formed into a square or rectangular profile, and the open seam is closed by high-frequency welding, which fuses the edges without filler metal. The weld bead is trimmed inside and outside, the tube is sized in a calibration stand, straightened, and cut to length. This route gives accurate dimensions, a smooth surface and high productivity, and it is the default for S275JR hollow sections in building and machinery work.
Hot-Finished Tube (EN 10210-1)
The section is formed at elevated temperature, either from hot-rolled strip or from a continuously welded hollow preform, and is finished by hot sizing. Hot-finished sections have a different corner profile and slightly different section properties from cold-formed sections, and they are specified when the design or the local practice requires hot-finished product.
Quality Control During Production
Raw material inspection: incoming strip is checked against the material certificate to confirm the chemistry and mechanical values correspond to S275JR. Forming control: roll settings are adjusted so that the cross-section shape, side dimensions and corner radii stay within the tolerance class of EN 10219-1. Welding control: welding current and line speed are monitored so that the seam has full penetration and no open or cold welds. Finishing checks: the tube is straightened, the weld flash is trimmed, and the surface is inspected for cracks, folds, laminations or handling damage. Final testing: each production lot is sampled for tensile and flattening tests, and dimensions and straightness are verified on a sampling basis, so that every batch released conforms to the ordered standard.
Mechanical Properties of the Finished Tube
| Property | Value (base material, t <= 16 mm) |
|---|---|
| Minimum yield strength | 275 MPa |
| Tensile strength | 430 - 580 MPa (structural sections) / 410 - 560 MPa (plate) |
| Minimum elongation | 14 - 22 % depending on product form |
| Impact energy at 20 deg C, min | 27 J |
Yield strength steps down with thickness: at least 265 MPa for 16 - 40 mm and 255 MPa for 40 - 63 mm, so the design must use the value for the actual wall thickness. The carbon equivalent of S275JR is low (about 0.40 max for common thicknesses), which keeps crack sensitivity low during welding and allows bolted, riveted and welded connections without special precautions in most sections.
Machining and Fabrication
S275JR tube supports laser cutting, sawing, drilling, bending and rolling. Heat treatment such as normalizing or tempering can be applied if a special microstructure is required. Surface quality is controlled so that cracks, folds and other defects are rejected at the mill; where a higher surface class is needed for exposed architecture, specify it explicitly because standard supply tolerates minor surface imperfections.
How to Specify the Delivery Condition
For the great majority of structural applications, order S275JR hollow sections to EN 10219-1 in the cold-formed welded condition with hot-rolled feedstock, and request the EN 10204 3.1 mill certificate for traceability. If the project specification calls for hot-finished sections, order to EN 10210-1 and confirm the corner profile and section properties with the designer, because the two families have different section moduli and are not freely interchangeable without a design check. For welded structures, confirm the required impact-test temperature: JR is 20 deg C, J0 is 0 deg C and J2 is -20 deg C.
Frequently Asked Questions
Is S275JR always hot rolled?
The base steel is delivered hot rolled in nearly all cases, which is the economical standard condition. The tube made from it is usually cold-formed and high-frequency welded, while hot-finished hollow sections per EN 10210-1 are the alternative route. None of these routes requires a separate heat treatment to meet the grade.
What is the difference between cold-formed and hot-finished S275JR tube?
Cold-formed welded tube (EN 10219-1) is roll-formed from strip at ambient temperature and seam-welded; it has sharp corners, tight tolerances and a smooth surface. Hot-finished tube (EN 10210-1) is formed at elevated temperature and has a different corner radius and slightly different section properties. The choice is normally dictated by the design specification.
Does the weld seam weaken the square tube?
No, when the tube is produced and tested to the standard. The high-frequency weld is formed from the base strip itself, and the tube passes flattening and tensile tests that prove the seam. The weld zone is, however, the area to inspect first in service.
Can S275JR tube be used without painting?
Outdoors, no. S275JR is a carbon steel and will rust when exposed to weather. It must be painted, galvanized or otherwise protected. Indoors in a dry environment it can be left as-rolled if appearance permits.
What does the 3.1 mill certificate contain?
The EN 10204 3.1 certificate is issued by the manufacturer and confirms that the delivered product conforms to the order, with the heat number, chemical analysis, mechanical test results, dimensions and quantities. It is the standard inspection document for structural steel with traceability requirements.
Is preheat required when welding S275JR tube?
For typical wall thicknesses up to about 20 mm, no preheat is needed because the carbon equivalent is low. For thicker walls, highly restrained joints or low ambient temperatures, a modest preheat of 50 - 100 deg C is good practice and should be covered by the welding procedure qualification.