What Are S355JR and S355J2?
S355JR and S355J2 are hot-rolled structural steels defined by EN 10025-2, the European standard for non-alloy structural steels. The S denotes structural steel, 355 is the minimum yield strength in MPa for thickness up to 16 mm, and the suffix letters identify the required impact toughness. JR means the steel is impact tested at 20 degrees Celsius, while J2 means the steel is impact tested at minus 20 degrees Celsius. Both grades deliver the same 27 joules minimum absorbed energy, but at different test temperatures.
This single difference in impact test temperature is the deciding factor in most material selections between the two grades.
The Critical Difference: Impact Toughness
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| Grade | Minimum Yield Strength | Charpy V-notch Impact Test | Typical Use |
|---|---|---|---|
| S355JR | 355 MPa | 27 J at 20 degrees Celsius | General building and machinery at normal temperature |
| S355J2 | 355 MPa | 27 J at minus 20 degrees Celsius | Cold regions, bridges, dynamically loaded structures |
In the EN 10025-2 designation system, J0 means 27 J at 0 degrees Celsius, J2 means 27 J at minus 20 degrees Celsius, and K2 means 40 J at minus 20 degrees Celsius. The higher the number after J, the lower the test temperature and the better the low-temperature toughness.
Chemical Composition
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| Element (max, mass %) | S355JR | S355J2 |
|---|---|---|
| Carbon (C) | 0.24 | 0.20 |
| Manganese (Mn) | 1.60 | 1.60 |
| Phosphorus (P) | 0.035 | 0.025 |
| Sulfur (S) | 0.035 | 0.025 |
The lower carbon, phosphorus and sulfur limits of S355J2 improve weldability and toughness. These limits apply to the maximum thickness ranges; for thicker plates the values may be relaxed slightly according to the standard tables.
Mechanical Properties
Both grades have a minimum yield strength of 355 MPa for thickness up to 16 mm, a tensile strength range of 470 to 630 MPa, and a minimum elongation of 22%. The strength values are identical; the difference lies in the guaranteed impact energy at low temperature and in the delivery condition. S355J2 is frequently supplied in the normalized or normalized rolled condition, which produces a finer, more uniform microstructure and more stable mechanical properties across the plate thickness.
Delivery Conditions
S355JR is normally supplied in the as-rolled condition. S355J2 can also be supplied as-rolled, but is often ordered in the normalized or normalized rolled condition for demanding applications such as offshore and bridge structures. Normalizing refines the grain structure and improves through-thickness properties. For special requirements, S355J2 can be supplied quenched and tempered to further enhance strength and toughness.
Application Areas
S355JR is the economical choice for general building structures, machine frames, agricultural equipment and other applications where service temperature stays above freezing. S355J2 is preferred for bridge girders, cranes, offshore structures, silos and tanks, and any component that must resist impact at sub-zero temperatures or under dynamic loading.
How to Select the Right Grade
Consider the minimum design temperature of the structure. If the lowest ambient temperature approaches minus 20 degrees Celsius or below, choose S355J2. Consider the loading: structures subject to frequent dynamic loads, vibration or impact benefit from the certified low-temperature toughness of J2. Consider welding: both grades weld well, but the lower carbon equivalent of S355J2 eases welding in thick sections. Finally, compare cost: S355JR is slightly cheaper, while S355J2 adds a small premium for the tighter chemistry and impact testing.
Common Misconceptions
One misconception is that S355J2 contains special alloying elements that make it corrosion resistant; in fact neither grade is a weathering steel, and corrosion protection comes from coatings. Another error is assuming S355J2 has higher strength; the yield and tensile values are the same as S355JR. A third misconception is that S355JR cannot be used outdoors; it can, provided the design temperature and coating are appropriate. The real distinction is impact toughness at low temperature, not strength or corrosion resistance.
FAQ
What does the JR in S355JR mean?
JR indicates that the steel must absorb at least 27 J in the Charpy V-notch impact test at 20 degrees Celsius, per EN 10025-2.
What does the J2 in S355J2 mean?
J2 indicates that the steel must absorb at least 27 J in the Charpy impact test at minus 20 degrees Celsius, giving certified low-temperature toughness.
Are S355JR and S355J2 the same strength?
Yes. Both have a minimum yield strength of 355 MPa and a tensile strength of 470 to 630 MPa. Only the impact test temperature and chemistry differ.
Is S355J2 more expensive than S355JR?
Slightly. The tighter chemistry limits and the impact testing at minus 20 degrees Celsius add a small cost premium to S355J2.
Can S355JR be used at minus 20 degrees Celsius?
It is not recommended for design temperatures at or below minus 20 degrees Celsius because its impact properties are only guaranteed at 20 degrees Celsius. Specify S355J2 for such service.
Do these grades apply to pipe and tube products?
Yes. EN 10025-2 plates and sections are widely converted into welded pipe, and structural hollow sections are supplied to EN 10210 or EN 10219 using the same S355 chemistry and toughness classes.