Quick Answer
Quick Answer
Common structural carbon steel grades include ASTM A36 (YS ≥ 250 MPa) and EN S275/S355 (YS ≥ 275/355 MPa). These grades are primarily specified by yield strength and carbon equivalent (for weldability), with composition limits designed to ensure adequate toughness, ductility, and fabricability at low cost.
Overview
Carbon steels are iron–carbon alloys with carbon content generally below 2.0 %, though structural grades typically contain 0.15–0.30 % C. They are the most produced steels globally and form the backbone of civil structures, pressure vessels, storage tanks, and general fabrication.
Unlike stainless steels — which are identified primarily by alloy composition — carbon steel grades are often defined by minimum mechanical properties, particularly yield strength, with composition limits acting as secondary constraints to ensure weldability and toughness.
The two most important parameters on a carbon steel MTC are:
- Yield strength — must meet the minimum specified (e.g., ≥ 250 MPa for A36)
- Carbon equivalent (CE) — governs preheat requirements for welding
ASTM A36 — Composition & Properties
ASTM A36 is the most commonly used structural steel specification in North America, covering plates, shapes, and bars.
Chemical Composition (A36 Plate, thickness ≤ 20 mm)
| Element | Maximum (wt%) |
|---|---|
| Carbon (C) | 0.25 |
| Manganese (Mn) | — (no limit for plates) |
| Phosphorus (P) | 0.04 |
| Sulfur (S) | 0.05 |
| Silicon (Si) | 0.40 |
For structural shapes, maximum carbon is 0.26 %; for bars, 0.27–0.29 % depending on diameter. Carbon limits vary with product form and thickness — always verify the applicable sub-clause.
Mechanical Properties (A36)
| Property | Requirement |
|---|---|
| Yield Strength (YS) | 250 MPa (36 ksi) min |
| Tensile Strength (UTS) | 400 – 550 MPa (58–80 ksi) |
| Elongation (200 mm gauge) | 20 % min |
| Elongation (50 mm gauge) | 23 % min |
EN S275 — Composition & Properties
EN 10025-2 grade S275 is the European structural steel broadly comparable to ASTM A36 in service use, though its requirements are expressed differently.
Chemical Composition — S275JR (Heat Analysis)
| Element | Maximum (wt%) |
|---|---|
| Carbon (C) | 0.21 |
| Manganese (Mn) | 1.50 |
| Phosphorus (P) | 0.040 |
| Sulfur (S) | 0.040 |
| Silicon (Si) | — |
| Nitrogen (N) | 0.012 |
| Carbon Equivalent (CE) | 0.40 |
Mechanical Properties (S275JR, t ≤ 16 mm)
| Property | Requirement |
|---|---|
| Yield Strength (ReH) | 275 MPa min |
| Tensile Strength (Rm) | 410 – 560 MPa |
| Elongation (A80) | 23 % min |
| Charpy impact (20 °C) | 27 J min (JR sub-grade) |
EN S355 — Composition & Properties
S355 is the higher-strength structural grade widely used where weight savings or thinner sections are required.
Chemical Composition — S355JR (Heat Analysis)
| Element | Maximum (wt%) |
|---|---|
| Carbon (C) | 0.24 |
| Manganese (Mn) | 1.60 |
| Phosphorus (P) | 0.040 |
| Sulfur (S) | 0.040 |
| Silicon (Si) | 0.55 |
| Nitrogen (N) | 0.012 |
| Carbon Equivalent (CE) | 0.45 |
Mechanical Properties (S355JR, t ≤ 16 mm)
| Property | Requirement |
|---|---|
| Yield Strength (ReH) | 355 MPa min |
| Tensile Strength (Rm) | 470 – 630 MPa |
| Elongation (A80) | 22 % min |
| Charpy impact (20 °C) | 27 J min (JR sub-grade) |
Grade Comparison Table
| Property | A36 | S275JR | S355JR |
|---|---|---|---|
| Min YS | 250 MPa | 275 MPa | 355 MPa |
| UTS range | 400–550 MPa | 410–560 MPa | 470–630 MPa |
| Max C (heat) | 0.25 % | 0.21 % | 0.24 % |
| Max CE | ~0.40 | 0.40 % | 0.45 % |
| Charpy required | No (standard) | Yes (JR: 27 J @ 20 °C) | Yes (JR: 27 J @ 20 °C) |
| Standard | ASTM A36 | EN 10025-2 | EN 10025-2 |
Carbon Equivalent and Weldability
The carbon equivalent (CE) is used to estimate preheat requirements for welding. The IIW formula is most widely used:
CE = %C + %Mn/6 + (%Cr + %Mo + %V)/5 + (%Ni + %Cu)/15
| CE Value | Weldability | Preheat Guidance |
|---|---|---|
| ≤ 0.35 | Excellent | None required (t ≤ 25 mm) |
| 0.35 – 0.40 | Good | 75–100 °C for thicker sections |
| 0.40 – 0.45 | Fair | 100–150 °C |
| > 0.45 | Poor | 150–200 °C or higher |
Standards Coverage
| Grade | Applicable Standards |
|---|---|
| A36 | ASTM A36, ASME SA-36 |
| S275 | EN 10025-2, EN 10025-3, EN 10025-4 |
| S355 | EN 10025-2, EN 10025-3, EN 10025-4 |
| A516 Gr 70 | ASTM A516 (pressure vessel plate) |
| A106 Gr B | ASTM A106 (seamless pipe) |
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Try TestCert freeFrequently Asked Questions
Are ASTM A36 and EN S275 interchangeable?
They are broadly comparable in yield strength and tensile range, but they are not interchangeable without engineering review. A36 does not mandate impact testing as a standard requirement; EN S275JR requires 27 J at 20 °C. Composition limits also differ — EN S275 has stricter carbon and manganese limits in some sub-grades. Cross-qualification requires checking each requirement against the specific design code.
What is the significance of the J0, J2, JR suffixes on EN steel grades?
These suffixes denote the Charpy impact test temperature sub-grade: JR = 27 J at +20 °C, J0 = 27 J at 0 °C, J2 = 27 J at −20 °C. Selecting the correct sub-grade for the design minimum temperature is critical for structural integrity — a structure designed for −20 °C service must specify at minimum the J2 sub-grade.
What is the maximum thickness for A36 with minimum 250 MPa yield?
ASTM A36 yield strength requirements are thickness-dependent. For plates over 200 mm (8 in) thick, the minimum yield drops to 220 MPa (32 ksi). The applicable thickness range must be checked against the relevant table in the current edition of ASTM A36 when ordering or verifying certification for heavy plates.
How does TestCert validate carbon steel MTCs?
TestCert checks carbon steel MTCs by identifying the specific grade, thickness range, and product form, then applying the correct composition and property limits from the applicable standard table. For EN grades, the platform also verifies that the reported CE value does not exceed the grade maximum and checks that the Charpy sub-grade temperature matches the purchase order requirement.