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Overview
ASTM A572 is one of the most widely used specifications for high-strength, low-alloy (HSLA) structural steel plates, shapes, sheet piling, and bars. Its primary characteristic is the achievement of higher strength-to-weight ratios compared to mild carbon steels like ASTM A36. This is accomplished through the addition of small amounts of alloying elements, primarily Columbium (Niobium) and/or Vanadium, which provide strengthening through grain refinement and precipitation hardening.
The key advantages of A572 steel include:
- Higher Strength: Allows for lighter, more economical structures by reducing the required steel weight.
- Good Weldability: Generally exhibits excellent welding properties with common techniques.
- Improved Atmospheric Corrosion Resistance: Offers approximately twice the corrosion resistance of plain carbon steel, though not to the level of ASTM A588 "weathering steel."
- Good Formability: Can be fabricated using standard methods.
Grades
ASTM A572 specifies several grades differentiated by their minimum yield strength (in ksi - kips per square inch). The most common grades are:
- Grade 42: Minimum Yield Strength = 42 ksi (290 MPa)
- Grade 50: Minimum Yield Strength = 50 ksi (345 MPa) - This is the most common grade.
- Grade 55: Minimum Yield Strength = 55 ksi (380 MPa)
- Grade 60: Minimum Yield Strength = 60 ksi (415 MPa)
- Grade 65: Minimum Yield Strength = 65 ksi (450 MPa)
Forms
A572 steel is produced in a variety of different steel forms,[1] which include:
- Plates
- Bars
- Structural Shapes
- Channels
- I-Beams
- Angles
- Wide Flange Beams
- Sheet Piling
[1] ASTM International. (2021). Standard Specification for High-Strength Low-Alloy Columbium-Vanadium Structural Steel. (Designation: A572/A572M – 21).
Chemical Composition (Grade 50)
The chemical composition is carefully controlled to achieve the desired mechanical properties. Requirements vary slightly by grade and product form (plate, shape, etc.). The following is a typical composition range for the most common, Grade 50:
| Element | Composition (%, max, unless range is given) | Purpose |
|---|---|---|
| Carbon (C) | 0.23% max | Increases strength but reduces ductility and weldability. Kept low. |
| Manganese (Mn) | 1.35% max | Contributes significantly to strength and hardenability. |
| Phosphorus (P) | 0.04% max | Impurity, harms toughness and weldability. |
| Sulfur (S) | 0.05% max | Impurity, causes brittleness (hot shortness). |
| Silicon (Si) | 0.40% max | Deoxidizer, contributes to strength. |
| Columbium (Cb/Nb) | 0.005 - 0.05% | Key alloy. Forms carbides/ni-trides that refine grain size and precipitate to strengthen steel. |
| Vanadium (V) | 0.01 - 0.15% | Key alloy. Similar strengthening effect to Columbium via precipitation. |
| Nitrogen (N) | 0.015% max | Impurity, can be used for strengthening with V or Cb. |
Note: Grades 60 and 65 may have slightly lower maximums for Carbon and Phosphorus and may include restrictions on Carbon Equivalent (CE) for improved weldability.
Mechanical Properties
The mechanical properties are the defining feature of each grade. The following table summarizes the requirements:
| A572 Grade | Yield Point (KSI) [MPa] | Tensile Strength (KSI) [MPa] | Min. 8" Elongation % |
|---|---|---|---|
| Grade 42 | 42 [290] | 60 [414] | 20 |
| Grade 50 | 50 [345] | 65 [448] | 18 |
| Grade 55 | 55 [379] | 70 [483] | 17 |
| Grade 60 | 60 [414] | 75 [517] | 16 |
| Grade 65 | 65 [448] | 80 [552] | 15 |
Elongation requirements vary with plate thickness; thicker material has slightly reduced elongation requirements.
Applications
Due to its excellent balance of strength, cost, and fabricability, ASTM A572 Grade 50 is the workhorse of the structural steel industry in the United States.
- Building Construction: Structural frames, beams, columns, and trusses.
- Bridge Construction: Girders, cross-frames, and other load-bearing components.
- Heavy Equipment: Cranes, booms, truck frames, and trailer beds.
- Transmission Towers & Poles
- Barges and Other Industrial Structures
Comparison with Other Common Structural Steels
- vs. ASTM A36 (Carbon Structural Steel): A572 has a higher minimum yield strength (50 ksi vs. 36 ksi for A36), allowing for lighter designs. A36 is generally easier to form and slightly less expensive but heavier for the same load.
- vs. ASTM A588 (High-Strength Low-Alloy Weathering Steel): Both have similar strength (50 ksi or higher). The key difference is that A588 is designed to form a protective, self-healing rust patina when exposed to the atmosphere, eliminating the need for painting in many applications. A572 does not have this weathering characteristic.
In summary, ASTM A572 is a family of high-strength, low-alloy steels strengthened primarily with Columbium and Vanadium. Its various grades, especially the ubiquitous Grade 50, offer an optimal combination of high strength, good weldability, and cost-effectiveness, making it a premier choice for a vast array of structural and industrial applications.
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