Two Structural Grades, Two Standards
ASTM A36 and S275JR are the two structural steel grades that appear most often on drawings for buildings, bridges, general fabrication and steel structures intended for export. They are frequently treated as equivalents in the workshop, and that is where mistakes start: the grades come from different standards and differ in minimum yield strength, in chemical limits and in impact requirements.
ASTM A36 is published by ASTM International and covers carbon structural steel in the form of plates, shapes and bars, with a minimum yield point of 250 MPa. S275JR is published in EN 10025-2, which covers non-alloy structural steels in hot-rolled condition. The suffix JR identifies the impact quality of the material, and the number 275 identifies the minimum yield strength for the reference thickness range.
Mechanical Properties and Chemistry Compared
| Grade | Standard | Min yield | Tensile | Impact requirement |
|---|---|---|---|---|
| A36 | ASTM A36/A36M | 250 MPa | 400-550 MPa | Not required by the specification |
| S235JR | EN 10025-2 | 235 MPa | 360-510 MPa | 27 J at +20 degrees C |
| S275JR | EN 10025-2 | 275 MPa | 410-560 MPa | 27 J at +20 degrees C |
| St37-2 | DIN 17100, withdrawn | 235 MPa | 340-470 MPa | 27 J at +20 degrees C |
The tensile and yield values above apply to the reference thickness range, up to 16 mm for the EN 10025-2 grades; both values fall as section thickness increases, and the standard tabulates them thickness by thickness. On the chemical side, A36 controls carbon to a maximum of 0.26% and specifies manganese ranges that widen with section thickness, with phosphorus limited to 0.04% and sulphur to 0.05%. The EN 10025-2 grades apply tighter limits on phosphorus and sulphur, at 0.035% each, and add a carbon equivalent requirement for the grades and thicknesses where weldability control is needed.
Where the Old St37 Grade Fits
St37 is a designation from the withdrawn German standard DIN 17100. It defined a structural steel with a minimum yield strength of 235 MPa and was widely used in machinery, construction and general fabrication. When EN 10025 replaced DIN 17100, St37-2 and St37-3 were superseded by S235JR and S235J2 respectively, so a drawing that still calls for St37 today is normally satisfied by S235JR. Because St37 and ASTM A36 share a similar yield strength range, the two are often equated in practice, but their chemistry limits are not identical and the substitution should be confirmed against the design requirement rather than assumed.
Are A36 and S275JR Equivalent?
They are close, but not equal. S275JR carries a 10% higher minimum yield strength, an explicit Charpy V-notch requirement of 27 J at +20 degrees C, and lower limits on phosphorus and sulphur. A36 carries no impact requirement in the base specification and allows slightly higher residuals. That means:
Where a design is governed by yield strength, A36 cannot be substituted for S275JR without a design check.
Where a project specification requires notch toughness, A36 alone does not demonstrate it, and impact testing must be ordered as a supplementary requirement.
Where weldability is critical, the tighter chemistry of the EN grade is an advantage, particularly in thick sections.
A36 is nevertheless fully acceptable for a large range of general structural work, and it is the more widely available of the two in North American practice.
Choosing the Right Grade for a Project
Start from the design code, not from the grade name. Design codes reference particular standards and particular strength values.
Confirm the thickness range of the heaviest section, because the yield value stated for a grade only applies to the reference thickness.
Establish whether impact toughness is a design requirement, a client specification or a regulatory requirement before ordering.
Check the carbon equivalent or the welding procedure requirement before welding thick sections of either grade.
When a substitution is proposed, record it as a formal deviation with the supporting test certificates, rather than as a workshop decision.
FAQ
Q: Is ASTM A36 the same as S275JR?
No. A36 has a minimum yield strength of 250 MPa and no impact requirement in the base specification, while S275JR has a minimum yield of 275 MPa for the reference thickness plus a 27 J Charpy requirement at +20 degrees C.
Q: What is the modern equivalent of St37?
St37-2 of the withdrawn DIN 17100 standard is superseded by S235JR in EN 10025-2, and St37-3 corresponds to S235J2.
Q: What does the JR suffix mean?
It identifies the impact quality of the steel. In EN 10025-2 the JR suffix means a minimum Charpy V-notch absorbed energy of 27 J at +20 degrees C, J0 means 0 degrees C and J2 means minus 20 degrees C.
Q: Can A36 be used to replace S275JR?
Only after a design check. Replacing a higher strength grade with a lower one reduces the load carrying capacity of the member unless the section is increased.
Q: Which grade is more suitable for welded structures?
Both are readily welded, but the EN 10025-2 grades have tighter phosphorus, sulphur and carbon equivalent limits, which helps in thick welded sections where cracking risk rises.
Q: Do the stated yield values apply to all thicknesses?
No. Yield and tensile values apply to a reference thickness range and decrease as the section becomes thicker, so the applicable values must be read from the thickness table of the governing standard.
