What S355J2 Is and Which Standard Covers It
S355J2 is a non-alloy structural steel plate covered by EN 10025-2, the European standard for hot rolled products of structural steels in the technical delivery conditions for non-alloy steels. Each character carries information: S for structural steel, 355 for the minimum yield strength in MPa at the thinnest end of the range, J for a minimum impact energy of 27 J, and 2 for the impact test temperature of -20 °C. The equivalent Chinese designation is Q355D under GB/T 1591, which uses a D suffix for the -20 °C impact class. Normalized delivery, widely ordered for heavy plate and for welded fabrication with post-weld heat treatment, is designated S355J2+N.
Chemical Composition and Mechanical Properties
Carbon and manganese are the strength carriers, and the J2 quality class adds restrictions on phosphorus and sulphur so that toughness is repeatable.
| Element | Requirement |
|---|---|
| C | 0.20 % max up to 16 mm; 0.22 % max over 16 to 40 mm |
| Mn | 1.60 % max |
| Si | 0.55 % max |
| P | 0.030 % max |
| S | 0.030 % max |
| Yield strength (min, up to 16 mm) | 355 MPa |
| Yield strength (min, over 40 to 63 mm) | 335 MPa |
| Tensile strength (up to 100 mm) | 470-630 MPa |
| Impact energy at -20 °C | 27 J min |
Minimum yield strength steps down as thickness rises: 355 MPa up to 16 mm, 345 MPa over 16 to 40 mm, 335 MPa over 40 to 63 mm, 325 MPa over 63 to 80 mm and 295 MPa above 100 mm. Tensile strength stays in the 470-630 MPa band up to 100 mm and falls slightly in heavier sections. Carbon equivalent is capped by the standard, at approximately 0.45 % for medium thickness and slightly higher for heavy plate, which keeps the steel weldable without exotic procedures.
Delivery Conditions and Forming Route
EN 10025-2 permits delivery in the as-rolled, normalized or normalized rolled condition, and the suffix in the designation records the condition actually applied, for example S355J2+N for normalized. The steel is ordered in thicknesses from 3 mm to 200 mm, with normalized plate preferred when the fabrication will later receive post-weld heat treatment, since normalization stabilises the structure against further thermal cycles. Where a welded connection is at risk of lamellar tearing, plate is ordered with a through-thickness quality designation under EN 10164, such as Z15, Z25 or Z35, verified by a through-thickness tensile test.
Applications
S355J2 is one of the most widely used structural plate grades in the world. Applications include bridge girders and cross bracing, high-rise and industrial building frames, crane runway beams and crane booms, offshore platform structure, heavy machinery base frames, storage tank shells for non-pressure duties, transmission tower components, shipbuilding secondary structure, and transport equipment. It is also used in pressure equipment where the design temperature range and the applicable code allow a structural grade, and in general welded fabrication where 355 MPa yield strength gives a useful weight saving over a 235 MPa grade.
Welding and Fabrication Notes
S355J2 welds readily with all common arc processes. Filler metals of the matching strength class are used together with low-hydrogen consumables, and preheat is determined from the carbon equivalent and the combined thickness at the joint, typically starting from about 100 °C for thickness above 30 mm and rising for very heavy or highly restrained joints. Heat input and interpass temperature are controlled to limit heat-affected zone hardening. Post-weld heat treatment, where required, is normally carried out in the 580-620 °C range, and the holding time is based on thickness. Flame cutting, plasma cutting, drilling, punching and cold forming are all standard, though the cold forming of narrow radii on heavy plate calls for re-checking of the material ductility. Designers should also control the weld detail class for fatigue, since structural plate is frequently the fatigue-governed element in crane and bridge structures.
Quality Control and Ordering Points
The order should state the full designation including delivery condition, the thickness and tolerance class, any Z-direction requirement, the ultrasonic examination acceptance class where relevant, and the impact test requirement at -20 °C. Plates are supplied with an EN 10204 type 3.1 certificate listing heat analysis, tensile and impact results, and are marked with the heat number, grade and plate identification. Type 3.2 certification with third-party witnessing and dimensional inspection reports are available for projects with notified body involvement.
Frequently Asked Questions
Q: What is the difference between S355J2 and S355JR?
A: Both have the same strength class. S355JR requires only a 20 °C impact test, while S355J2 requires 27 J at -20 °C, which makes J2 the correct choice for structures in cold climates or subject to dynamic loading.
Q: What does the +N suffix mean?
A: It records the delivery condition: N means normalized. The impact and tensile properties on the certificate refer to the plate in that condition.
Q: Which steel is equivalent to S355J2?
A: In the Chinese system the closest equivalent is Q355D under GB/T 1591, which shares the 355 MPa yield class and the -20 °C impact temperature.
Q: Can S355J2 be used below -20 °C?
A: Not on the basis of the standard impact guarantee. For lower design temperatures a grade tested at the lower temperature, such as S355K2 at -20 °C with a higher energy requirement or a thermomechanically rolled low-temperature grade, should be specified.
Q: Is post-weld heat treatment allowed?
A: Yes, and normalized plate is often chosen precisely so that the properties remain stable. Treatment is typically in the 580-620 °C range with time based on thickness.
Q: What thickness can be supplied?
A: Normalized structural plate is commonly supplied from 3 mm to 200 mm, with the minimum yield strength stepping down in defined thickness bands.
