The Meaning of the JR Suffix
In EN 10025-2 the letter after the strength figure states the impact test condition, not the delivery condition. For S355JR the requirement is a minimum absorbed energy of 27 J in a longitudinal Charpy V-notch test carried out at plus 20 degrees C. The other designations in the same standard move the temperature and, for one grade, the energy:
| Designation | Test temperature | Minimum absorbed energy |
|---|---|---|
| S355JR | plus 20 degrees C | 27 J |
| S355J0 | 0 degrees C | 27 J |
| S355J2 | minus 20 degrees C | 27 J |
| S355K2 | minus 20 degrees C | 40 J |
These values apply to longitudinal specimens of full size. The impact-tested variants also carry tighter limits on phosphorus and sulphur than JR, which is one reason a J2 channel is specified for a structure that will see winter service, even when the design stress is the same.
Charpy Testing to EN ISO 148-1
The test method is EN ISO 148-1, which replaced the older EN 10045-1. A notch is machined into a 10 mm by 10 mm specimen, the specimen is cooled to the specified temperature and struck by a pendulum in a single blow, and the absorbed energy is read in joules. For channel steel the specimen is taken longitudinally from the flange or web, and because the specimen length exceeds a channel web thickness, a full-size test piece is normally prepared from the thicker part of the section or from a rolled-on test coupon.
Where the product is thinner than 10 mm, sub-size specimens of 10 mm by 7.5 mm or 10 mm by 5 mm are permitted. Their absorbed energies are lower than full-size values for the same steel, so an order that accepts sub-size testing should state the acceptance energy for that specimen size rather than assuming the 27 J figure transfers unchanged.
Chemistry and Mechanical Properties Behind the Toughness
| Element | S355JR limit | Note |
|---|---|---|
| Carbon | 0.24 per cent max | For nominal thickness up to 16 mm |
| Silicon | 0.55 per cent max | - |
| Manganese | 1.60 per cent max | - |
| Phosphorus | 0.035 per cent max | - |
| Sulphur | 0.035 per cent max | - |
| Nitrogen | 0.012 per cent max | - |
| Carbon equivalent | 0.45 max | Supports weldability |
Mechanically, S355JR in the thickness range up to 16 mm has a minimum yield strength of 355 MPa and a tensile strength of 470 to 630 MPa, with a minimum elongation of 22 per cent for thicknesses up to 40 mm. Low carbon and controlled manganese give the ferrite-pearlite structure that keeps the transition temperature well below zero, which is what makes the plus 20 degrees C test a meaningful but not restrictive requirement.
UPE and UPN Profiles: Where the Requirement Applies
UPN is the taper-flange channel series and UPE the parallel-flange series; section dimensions and masses are tabulated in EN 10365 and dimensional tolerances are covered by EN 10279. The impact property certified for the steel applies to the material of the channel, tested on a specimen from the same heat or rolling lot. It does not certify the local toughness of a cold-formed lip, a bent zone or a heavily restrained welded detail. Where a channel is cold bent or where the web is punched or notched at a critical location, the fabrication drawing should state whether the affected zone has to be re-tested or the design stress reduced.
Service Temperature and Grade Selection
A JR channel is qualified at plus 20 degrees C and is intended for moderate climates and non-critical dynamic duty. For structures exposed below zero, or for repeated impact and fatigue loading, the designation should be raised: J0 for service down to about 0 degrees C, J2 for service down to minus 20 degrees C, and K2 where higher energy absorption is demanded. EN 1993-1-10 provides the formal route, matching toughness class to the lowest service temperature, the element thickness and the stress level. Selecting a lower test temperature is almost always cheaper than repairing a brittle fracture.
Documentation and Verification
An inspection certificate to EN 10204 type 3.1 should report the heat number, product analysis, tensile results and the impact results with the test temperature and specimen size stated individually. If a purchaser intends to verify the property by independent testing, the order should reserve the right to take a sample from the delivered channel and to name the acceptance energy for the specimen size that can actually be prepared from that section.
Frequently Asked Questions
Q: At what temperature is an S355JR channel impact tested?
A: At plus 20 degrees C, with a minimum absorbed energy of 27 J on longitudinal full-size Charpy V-notch specimens. That is the property defined by the JR designation in EN 10025-2.
Q: Is S355JR suitable for minus 20 degrees C service?
A: No. The JR designation certifies toughness only at plus 20 degrees C. For service down to minus 20 degrees C the correct grade is S355J2, which is tested at that temperature, or S355K2 where 40 J is required instead of 27 J.
Q: Which test method applies?
A: EN ISO 148-1, which superseded EN 10045-1. Specimens are 10 mm by 10 mm unless the product is too thin, in which case sub-size specimens are used and the acceptance energy has to be stated for that size.
Q: Where is the specimen taken from a channel section?
A: Longitudinally from the flange or web, or from a rolled-on test coupon. Because the Charpy specimen is longer than a channel web is thick, a full-size specimen usually has to come from the thicker region of the section or from a coupon.
Q: Does the impact test apply to every channel produced?
A: No. It is a property of the declared steel grade and is verified at the frequency set by EN 10025-1 and the order, normally tied to heat or rolling lot. Certificates report the result for the lot rather than for each individual piece.
Q: Can a J2 channel be substituted for JR without changing anything else?
A: Mechanically the grade is the same strength class, but the phosphorus and sulphur limits are tighter and the delivery condition may differ. Substitution is acceptable when the drawing cites JR as a minimum and the engineer accepts the certificate, but it should be recorded as a deviation.