What the Number 1.0570 Identifies
The five-figure numbers used in European steel designation come from the German system that was carried into the European standards, and 1.0570 identifies a specific unalloyed structural steel rather than a separate material grade. In its most familiar form the number is attached to S355J2G3, the designation used in the edition of EN 10025 that preceded the current part 2, and the same steel is known from the older German standard DIN 17100 as St52-3 or St52-3N depending on the delivery condition. When the current edition of EN 10025-2 was published the delivery condition was moved out of the grade name, so normalized material is now written S355J2+N and carries the steel number 1.0577 rather than 1.0570. The practical point for buyers is that an enquiry quoting 1.0570 is asking for the S355J2 composition in a fully killed, usually normalized condition, and the equivalent modern designation should be confirmed on the order.
Chemical Composition
| Element | C | Si | Mn | P | S |
|---|---|---|---|---|---|
| Content, % by mass | 0.22 max | 0.55 max | 1.60 max | 0.035 max | 0.035 max |
The composition is a plain carbon-manganese balance with no deliberate alloying additions, which is what keeps the grade inexpensive and readily weldable. The current edition of EN 10025-2 caps carbon at 0.20 % for thickness up to 30 mm and tightens the phosphorus and sulphur limits further for the J2 and K2 impact classes, so the delivered analysis of modern material is usually cleaner than the window shown above. Manganese is kept high enough to reach the required strength while the low carbon content controls the carbon equivalent and therefore the welding behaviour.
Mechanical Properties
| Thickness | Minimum yield strength | Tensile strength |
|---|---|---|
| Up to 16 mm | 355 MPa | 470 to 630 MPa |
| 16 to 40 mm | 345 MPa | 470 to 630 MPa |
| 40 to 63 mm | 335 MPa | 470 to 630 MPa |
| 63 to 80 mm | 325 MPa | 470 to 630 MPa |
| 80 to 100 mm | 315 MPa | 470 to 630 MPa |
| 100 to 150 mm | 295 MPa | 450 to 650 MPa |
| 150 to 200 mm | 285 MPa | 450 to 650 MPa |
| 200 to 250 mm | 275 MPa | 450 to 650 MPa |
| Over 250 mm | 265 MPa | 450 to 650 MPa |
Minimum elongation is 20 % in plate up to 40 mm thick and eases to 18 % in heavier sections. Density is 7850 kg per cubic metre, so a plate of 20 mm thickness weighs 157 kg per square metre. The Charpy V-notch requirement at minus 20 degrees Celsius is 27 J in the longitudinal direction for the J2 quality, and 40 J for the K2 quality, which is the property that allows the grade to be used in cold climates and in dynamically loaded structures.
Impact Classes and the Meaning of the Sub-Symbols
| Symbol | Meaning |
|---|---|
| JR | Impact tested at room temperature, 20 degrees Celsius |
| J0 | Longitudinal Charpy V-notch energy of 27 J at 0 degrees Celsius |
| J2 | Longitudinal Charpy V-notch energy of 27 J at minus 20 degrees Celsius |
| K2 | Longitudinal Charpy V-notch energy of 40 J at minus 20 degrees Celsius |
| AR | Supplied as rolled |
| N | Supplied normalized or normalized rolled |
| G3, G4 | Deoxidation measure applied to the steel |
Reading the designation from left to right therefore gives the strength class, the impact class and the delivery condition, which is everything a fabricator needs in order to match the material to the design code. A normalized delivery condition refines the grain structure, improves toughness and reduces internal stress, which is why it is chosen where heavy sections or low service temperatures are involved, at the cost of a slightly higher price than as-rolled material.
Equivalent Grades in Other Systems
| System | Designation |
|---|---|
| EN 10025-2 | S355J2+N, steel number 1.0577 |
| DIN 17100, former | St52-3 or St52-3N |
| GB/T 1591 | Q355D, formerly written Q345D |
| ASTM | A572 Grade 50, A992/A992M for shapes |
| JIS G3106 | SM490YB |
| Former French and Italian practice | E36-3 and Fe 510 equivalents |
The equivalent grades are close in yield strength but differ in impact class, chemical limits and thickness capability, so a substitution has to be checked against the design requirement. Offshore and shipbuilding work sometimes quotes the higher-strength hull grades DH36 and EH36 as substitutes, and their higher impact energy is more than adequate, but they are produced to a different approval regime and are therefore treated as an alternative rather than an equivalent.
Common Misconceptions and Quality Control
Two errors recur in cross-reference tables. The first is the claim that 1.0570 corresponds to AISI 1024; that grade is a case-hardening bar steel with a different chemistry, no impact requirement and a different product range, so the mapping is meaningless for a structural plate enquiry. The second is the belief that S355J2 and S355J2+N are different steels; they are the same grade supplied in different delivery conditions, and the +N simply states that the plate has been normalized. For quality control the certificate should be checked for the heat number, chemical analysis, tensile results and the Charpy values at the specified test temperature, with ultrasonic examination to EN 10160 where the application requires it. Plates are marked with the grade and delivery condition so that the delivered item can be traced to the mill test certificate at EN 10204 3.1, and third-party inspection at 3.2 is available for project work. Normalizing for this grade is carried out between about 890 and 950 degrees Celsius with a hold long enough to complete the ferrite to austenite transformation, followed by cooling in still air.
Frequently Asked Questions
Q: What is 1.0570 steel?
A: It is the German steel number for the S355J2 grade of unalloyed structural steel, historically written S355J2G3 in the earlier edition of EN 10025 and known as St52-3 in DIN 17100. Under EN 10025-2 the normalized condition is written S355J2+N with the number 1.0577.
Q: What is the yield strength of 1.0570 steel?
A: A minimum of 355 MPa for thickness up to 16 mm, falling progressively to 265 MPa in sections over 250 mm, with a tensile range of 470 MPa to 630 MPa in the normal plate range.
Q: What does J2 mean in the designation?
A: It states that the steel is impact tested in the longitudinal direction with a minimum Charpy V-notch energy of 27 J at minus 20 degrees Celsius, which is what qualifies the grade for cold-climate service.
Q: Is S355J2 the same as S355J2+N?
A: Yes, the material is identical and the +N only records the normalized delivery condition. Normalizing refines the grain structure and improves toughness, and is specified for heavy plate and low-temperature duty.
Q: Does 1.0570 correspond to AISI 1024?
A: No. AISI 1024 is a case-hardening bar grade with a different composition and no structural impact requirement. It appears in some cross-reference tables but is not an equivalent of this plate steel.
Q: What must be checked on the mill certificate?
A: The heat number, the chemical analysis against the specified limits, the tensile results, and the Charpy impact energy at the required test temperature, together with the ultrasonic examination report where the project specifies one.
