ASTM A572/A572M Grade 50
High-strength low-alloy (HSLA) structural steel · ASTM A572/A572M-25 — High-Strength Low-Alloy Columbium-Vanadium Structural Steel · ASTM A6/A6M-26a — General requirements for rolled structural steel bars, plates, shapes, and sheet piling
ASTM A572 Grade 50 is a widely used 50 ksi minimum-yield HSLA structural steel for plates, bars, shapes and sheet piling. Its strength is developed through controlled composition and niobium, vanadium or titanium-nitrogen microalloying rather than through a uniquely prescribed heat treatment. The designation establishes minimum tensile properties and composition limits, but does not by itself guarantee Charpy toughness, atmospheric-corrosion resistance, a maximum carbon equivalent, a maximum yield strength or a maximum yield-to-tensile ratio. Product form, dimensions, toughness requirements, welding code and any supplementary testing therefore remain essential parts of a complete specification.
- 50 ksi [345 MPa]Minimum yield point · The value from which the Grade 50 designation is derived.
- 65 ksi [450 MPa]Minimum tensile strength · ASTM A572/A572M does not impose a general maximum tensile strength for this grade.
- Up to 4 in. [100 mm]Plate and bar thickness · Round bars may be furnished through 11 in. [275 mm] diameter; commercial availability can be narrower than the specification scope.
- Type 1, 2, 3 or 5Microalloy route · The producer selects the permitted niobium, vanadium or titanium-nitrogen route unless the purchaser specifies otherwise.
- Not included in the base gradeNotch toughness · Required CVN energy, temperature, orientation and test frequency must be added when toughness is important.
- Not a weathering-steel designationImportant limitation · A572 Grade 50 must not be treated as interchangeable with ASTM A588 Grade 50.
Overview
- Designation system
- ASTM product-specification grade
- Product forms
- Structural plates, Structural bars, Hot-rolled structural shapes, Sheet piling, Zees, Rolled tees, Finished structural products processed from coil
- Condition
- Killed steel, Hot-rolled structural product, Delivery and testing in accordance with ASTM A572/A572M and ASTM A6/A6M, No single normalized or quenched-and-tempered delivery condition is inherent in the grade
- Density
- 7850 kg/m³ (Representative engineering value for structural steel; density is not a grade acceptance requirement in ASTM A572/A572M.)
What the designation controls
ASTM A572/A572M covers five strength grades of HSLA structural steel. Grade 50 is intended for riveted, bolted or welded structures. The specification applies to rolled structural products rather than to every steel product having approximately 50 ksi yield strength; tubing, pipe, sheet, strip, forgings, castings and fasteners require their own product specifications.
ASTM A572/A572M supplies the grade-specific composition, microalloy and tensile requirements. ASTM A6/A6M supplies the common rules for ordering information, manufacturing, test specimens, retesting, dimensional tolerances, permissible variations, marking, certification and supplementary requirements. Where the documents conflict, the product specification governs.
ASTM inch-pound and SI requirements are independently standardized, not exact converted values. An order should identify either ASTM A572 or ASTM A572M and should not mix the two systems when assessing conformity.
Specified tensile properties
| Property | Inch-pound requirement | SI requirement | Applicability |
|---|---|---|---|
| Yield point, minimum | 50 ksi | 345 MPa | Specified minimum; no general maximum yield limit in A572 Grade 50 |
| Tensile strength, minimum | 65 ksi | 450 MPa | Specified minimum; no general maximum tensile limit |
| Elongation in 8 in. [200 mm], minimum | 18% | 18% | Subject to specimen and product-form rules in ASTM A6/A6M |
| Elongation in 2 in. [50 mm], minimum | 21% | 21% | Subject to specimen and product-form rules in ASTM A6/A6M |
| Plate wider than 24 in. [600 mm] | Two percentage-point reduction permitted | Two percentage-point reduction permitted | Applies to the specified Grade 50 elongation requirement |
| Wide-flange shape over 426 lb/ft [634 kg/m] | 19% in 2 in. | 19% in 50 mm | Special minimum for these very heavy shapes |
| Floor plate | Elongation need not be determined | Elongation need not be determined | The strength requirements still apply when ordered to A572 Grade 50 |
Test orientation, specimen selection and permitted elongation adjustments must be taken from the applicable editions of ASTM A572/A572M and ASTM A6/A6M.
The grade provides a minimum-strength floor, not a narrow mechanical-property band. Actual mill yield strength can exceed 50 ksi, and A572 Grade 50 does not contain the maximum yield strength or maximum yield-to-tensile ratio controls found in ASTM A992. This distinction can matter in seismic systems, inelastic analysis, plastic mechanisms, connection design and other applications sensitive to actual rather than minimum strength.
Composition and microalloying
| Element or control | Requirement | Technical qualification |
|---|---|---|
| Carbon | 0.23% maximum | Applies through the Grade 50 product-size limits |
| Manganese | 1.35% maximum | For each 0.01 percentage-point reduction below the carbon maximum, Mn may increase by 0.06 percentage point, to 1.60% maximum |
| Manganese minimum | 0.80% for plate over 3/8 in. [10 mm]; 0.50% for thinner plate and other products | Heat-analysis values; corresponding product-analysis minima are lower |
| Manganese-to-carbon ratio | At least 2:1 | Mandatory composition relationship |
| Phosphorus | 0.030% maximum generally | Up to 0.040% is permitted for structural shapes, sheet piling, bars and plates no wider than 15 in. [380 mm] |
| Sulfur | 0.030% maximum generally | Up to 0.050% is permitted for structural shapes, sheet piling, bars and plates no wider than 15 in. [380 mm] |
| Silicon | 0.40% maximum, or 0.15–0.40% for specified heavy sections | The applicable limit depends on product form and section thickness |
| Copper, when specified | 0.20% minimum by heat analysis | Copper is optional and does not convert the grade into ASTM A588 weathering steel |
These are heat-analysis requirements. Product-analysis tolerances and limits are governed by ASTM A572/A572M and ASTM A6/A6M.
| Type | Required microalloy system, heat analysis | Practical meaning |
|---|---|---|
| Type 1 | Niobium: 0.005–0.05% | Niobium-microalloyed route |
| Type 2 | Vanadium: 0.01–0.15% | Vanadium-microalloyed route |
| Type 3 | Niobium: 0.005–0.05%; vanadium: 0.01–0.15%; Nb + V: 0.02–0.15% | Combined niobium-vanadium route |
| Type 5 | Titanium: 0.006–0.04%; nitrogen: 0.003–0.015%; vanadium: 0.06% maximum | Titanium-nitrogen controlled route with limited vanadium |
The producer may select Type 1, 2, 3 or 5 unless the purchase order invokes the applicable requirement to control the type. The relevant microalloy contents are reported on the material test report.
A572 Grade 50 is not a single fixed alloy composition. Different mills and product forms can use different permitted microalloy systems and rolling practices while meeting the same grade. Consequently, weldability calculations, thermal-cutting behavior and fabrication controls should be based on the actual heat chemistry shown on the material test report, not on a generic nominal composition.
Product range and condition-dependent requirements
| Product | ASTM A572/A572M Grade 50 limit | Qualification |
|---|---|---|
| Plate and rectangular or square bar | 4 in. [100 mm] maximum thickness or size | Dimensions and tolerances are governed by ASTM A6/A6M |
| Round bar | Up to and including 11 in. [275 mm] diameter | Specific exception to the general 4 in. size limit |
| Structural shapes | All flange or leg thicknesses covered by the specification | This does not guarantee that every section is commercially produced in A572 Grade 50 |
| Sheet piling | All sizes covered by the specification | Availability and section series should be confirmed |
| Zees and rolled tees | All sizes covered by the specification | Product availability may be mill- and region-dependent |
Specification scope and market availability are different matters. Availability should be confirmed before design or procurement is finalized.
Coil itself is not qualified as A572 Grade 50 until it has been processed into a finished structural product. The processor is responsible for decoiling, leveling or straightening, cutting, testing, inspection, marking and certification. Finished structural products from coil that are furnished without heat treatment, or with stress relief only, are subject to the additional testing and reporting provisions of ASTM A6/A6M.
Welding, cutting and forming
Grade 50 is intended for welded construction, but the material designation is not a welding procedure. Building and general structural fabrication commonly falls under AWS D1.1/D1.1M; bridge work may invoke AASHTO/AWS D1.5M/D1.5. The applicable code, joint detail, thickness, restraint, service temperature, heat input, hydrogen control and actual heat chemistry determine preheat, interpass temperature, filler-metal classification and procedure qualification.
ASTM A572 Grade 50 does not impose a general maximum carbon-equivalent value. Do not assume the carbon-equivalent control associated with ASTM A992. Use the mill heat analysis and the governing welding code when evaluating weldability.
Thermal cutting and cold forming are routinely practicable, but procedure selection must account for thickness, edge quality, bend direction, bend radius and the possibility that cold work reduces local ductility. ASTM A6/A6M provides informative guidance on cold bending. Tight bends, heavy plate, low-temperature service and highly restrained welded details warrant specific engineering review rather than reliance on the grade name alone.
The base specification does not guarantee through-thickness ductility or freedom from internal discontinuities beyond its normal quality provisions. Heavy welded attachments that impose significant through-thickness strain may require improved detailing, ultrasonic examination or other purchaser-specified quality controls.
Toughness, corrosion and service limitations
Charpy V-notch impact properties are not part of the basic Grade 50 requirements. Where brittle-fracture resistance is important—such as low-temperature service, welded bridges, fracture-critical details, heavy tension members or dynamically loaded structures—the purchase documents must define the required impact energy, test temperature, specimen orientation, test location and test frequency under the governing material and design specifications.
A572 Grade 50 has the normal corrosion behavior of unprotected structural steel. It does not carry the composition or atmospheric-corrosion index requirements of ASTM A588. Exposure protection must therefore be provided through an appropriate coating, galvanizing system, corrosion allowance or other project-specific strategy.
The grade is not a pressure-vessel, elevated-temperature or fire-resistant material specification. Use at unusual temperatures or in specialized service requires the applicable design code and service-specific material data.
Specifying and purchasing
| Order item | Why it matters |
|---|---|
| ASTM A572 or ASTM A572M, Grade 50, and required edition | Fixes the applicable unit system and contractual requirements |
| Product form, shape designation, dimensions, quantity and tolerances | A572 covers several product forms whose testing and dimensional rules differ |
| Required microalloy type, if any | Otherwise Type 1, 2, 3 or 5 is selected by the producer |
| Copper-bearing requirement, if wanted | Copper is optional and must be stated; it does not create a weathering grade |
| Charpy V-notch requirements | Notch toughness is absent unless specifically ordered |
| Ultrasonic examination or other internal-quality requirements | Not part of the basic grade and potentially important for heavy or highly restrained details |
| Welding or fabrication code and any project-specific restrictions | Controls procedure qualification, preheat, consumables, workmanship and inspection |
| Material test reports and traceability | Needed to verify heat chemistry, microalloy route, tensile results, heat number and multi-certification claims |
| Whether the product is processed from coil | Triggers additional ASTM A6/A6M testing and reporting provisions |
| Any design-code-specific toughness, seismic or fracture-critical provisions | The base material designation alone may not satisfy these applications |
On receipt, verify that markings and certification identify the correct specification, grade, heat number, product and dimensions. Review the MTR for tensile compliance and the reported heat analysis, including the microalloying elements. A multi-certified product is acceptable only when its certification demonstrates full compliance with every specification claimed; visual similarity or a distributor cross-reference is not evidence of equivalence.
Selection within structural-steel practice
A572 Grade 50 remains particularly important for plates, bars, angles, channels, miscellaneous shapes and fabricated structural components requiring a 50 ksi minimum yield level. For modern wide-flange building framing, ASTM A992 is generally the preferred specification because it adds tighter controls relevant to structural behavior and welding, including a maximum yield strength, yield-to-tensile ratio and carbon equivalent.
For bridges, ASTM A709 Grade 50 is normally the more appropriate ordering designation because ASTM A709 is organized around bridge products and can impose additional bridge-specific impact and supplementary requirements. Matching the nominal 50 ksi yield level does not remove the need to comply with the project material specification.
Sources
- ASTM A572/A572M-25 — Standard Specification for High-Strength Low-Alloy Columbium-Vanadium Structural SteelASTM International
- ASTM A6/A6M-26a — Standard Specification for General Requirements for Rolled Structural Steel Bars, Plates, Shapes, and Sheet PilingASTM International
- Mill Production and Tolerances — Engineering FAQsAmerican Institute of Steel Construction
- Code of Standard Practice for Steel Buildings and Bridges, ANSI/AISC 303-22American Institute of Steel Construction
- AWS D1.1/D1.1M:2025-AMD1 — Structural Welding Code—SteelAmerican Welding Society
- AASHTO/AWS D1.5M/D1.5:2025 — Bridge Welding CodeAmerican Welding Society and AASHTO
- ASTM A709/A709M-26 — Standard Specification for Structural Steel for BridgesASTM International
Ask MetalMate about ASTM A572/A572M Grade 50
Discussing: ASTM A572/A572M Grade 50
AI assistant · Responses are generated and can contain errors; verify specifications before acting.