ASTM F3125 GRADE A490 HIGH-STRENGTH STRUCTURAL BOLTING — TECHNICAL DATASHEET
Historically governed under a standalone specification, ASTM A490 and A490M have been consolidated under the unified standard ASTM F3125 / F3125M. Designated as ASTM F3125 Grade A490 (Imperial) and Grade A490M (Metric), this standard covers quenched and tempered alloy steel heavy hex structural bolts with a minimum tensile strength of 150 ksi (1040 MPa).
Grade A490 is specifically engineered for heavy civil infrastructure, bridges, and high-rise buildings requiring the highest structural tensile strength. The consolidation standardized a uniform tensile strength requirement across all specified diameters ranging from 1/2 in. to 1-1/2 in. (M12 to M36 in metric), ensuring consistent load-bearing capacities without the historical strength step-downs of larger cross-sections.
■ Material Classifications and Connection Types
Grade A490 bolts are categorized by material chemistry and are approved for specific structural connection interfaces:
- Type 1: High-strength alloy steel or alloy steel with boron additions. Standard for general-purpose, high-load steel-to-steel connections.
- Type 2: Low-carbon martensitic steel (Officially withdrawn in 2002).
- Type 3: Weathering steel, possessing inherent atmospheric corrosion resistance (Corrosion Index $I \ge 6.0$). Forms a protective oxide patina, minimizing the need for protective paint.
- SC (Slip-Critical): Shear load is transferred entirely by friction between faying surfaces. Requires high, reliable installation preload.
- Type N & Type X: Bearing-type connections with threads included in the shear plane (N) or excluded from the shear plane (X).
■ Chemical Composition Limits
Rigorous control over alloying elements ensures complete hardenability (full martensitic conversion) during heat treatment.
| Element | Type 1 Heat Analysis (%) | Type 1 Product Analysis (%) | Type 3 Heat Analysis (%) | Type 3 Product Analysis (%) |
|---|---|---|---|---|
| Carbon (Sizes ≤ 1-3/8 in.) | 0.30 – 0.48 | 0.28 – 0.50 | 0.30 – 0.53 max | 0.28 – 0.55 max |
| Carbon (Size = 1-1/2 in.) | 0.35 – 0.53 | 0.33 – 0.55 | 0.30 – 0.53 max | 0.28 – 0.55 max |
| Manganese (Min) | 0.60 | 0.57 | 0.60 | 0.57 |
| Phosphorus (Max) | 0.035 | 0.040 | 0.035 | 0.040 |
| Sulfur (Max) | 0.040 | 0.045 | 0.040 | 0.045 |
| Copper | Not Specified | Not Specified | 0.20 – 0.60 | 0.17 – 0.63 |
| Chromium (Min) | Not Specified | Not Specified | 0.45 | 0.42 |
| Nickel (Min)* | Not Specified | Not Specified | 0.20 | 0.17 |
| Molybdenum (Min)* | Not Specified | Not Specified | 0.10 | 0.09 |
| Boron (Max) | 0.003 | 0.003 | Not Specified | Not Specified |
* For Type 3 weathering steel, either Nickel or Molybdenum must be present in the specified minimum quantity.
■ Proprietary Datasheet Download
ASTM F3125 Grade A490 — Complete Technical Yield & Tolerance Datasheet
Contains empirical data for stress simulations, slip-critical tension tables, and advanced coating guidelines. Corporate/engineering credentials required.
⬇ DOWNLOAD DATASHEET■ Mechanical Properties and Hardness
Grade A490 bolts require a precise oil quenching and tempering sequence (tempered at no less than 800°F / 427°C) to guarantee high yield strength and adequate ductility.
| Property / Specification | Imperial (1/2 to 1-1/2 in. Inclusive) | Metric (M12 to M36 Inclusive) |
|---|---|---|
| Tensile Strength (Range / Min) | 150 – 173 ksi | 1040 – 1210 MPa |
| Yield Strength (Min) | 130 ksi | 940 MPa |
| Elongation in 4D (Min %) | 14% | 14% |
| Reduction of Area (Min %) | 40% | 40% |
| Hardness Range (Rockwell C) | 33 to 39 HRC | 33 to 39 HRC |
| Hardness Range (Brinell) | 311 to 352 HBW | 311 to 352 HBW |
■ Structural Tensile and Proof Load Requirements
| Thread Designation (UNC) | Stress Area (in²) | Tensile Min (lbf) | Tensile Max (lbf) | Proof Load (Length Method) (lbf) |
|---|---|---|---|---|
| 1/2 - 13 | 0.142 | 21,300 | 24,600 | 17,050 |
| 5/8 - 11 | 0.226 | 33,900 | 39,100 | 27,100 |
| 3/4 - 10 | 0.334 | 50,100 | 57,800 | 40,100 |
| 7/8 - 9 | 0.462 | 69,300 | 79,950 | 55,450 |
| 1 - 8 | 0.606 | 90,900 | 104,850 | 72,700 |
| 1-1/8 - 7 | 0.763 | 114,450 | 132,000 | 91,550 |
| 1-1/4 - 7 | 0.969 | 145,350 | 167,680 | 116,300 |
| 1-3/8 - 6 | 1.155 | 173,250 | 199,850 | 138,600 |
| 1-1/2 - 6 | 1.405 | 210,750 | 243,100 | 168,600 |
■ Dimensions and Heavy Hex Geometry
Manufactured as heavy hex structural bolts (ASME B18.2.6), providing a wider across-flats profile and a larger head height to distribute high preloads over a broader bearing surface.
| Nominal Dia. | Body Dia. Max | Width Across Flats Basic | Width Across Corners Min | Head Height Basic | Basic Thread Length |
|---|---|---|---|---|---|
| 1/2" | 0.515 | 7/8" | 0.969 | 5/16" | 1.00 |
| 5/8" | 0.642 | 1-1/16" | 1.175 | 25/64" | 1.25 |
| 3/4" | 0.768 | 1-1/4" | 1.383 | 15/32" | 1.38 |
| 7/8" | 0.895 | 1-7/16" | 1.589 | 35/64" | 1.50 |
| 1" | 1.022 | 1-5/8" | 1.796 | 39/64" | 1.75 |
| 1-1/4" | 1.277 | 2" | 2.209 | 25/32" | 2.00 |
| 1-1/2" | 1.531 | 2-3/8" | 2.622 | 15/16" | 2.25 |
■ Coating Restrictions & Hydrogen Embrittlement
This prohibition addresses two failure modes:
- Hydrogen Embrittlement (HE): With strengths > 150 ksi and hardness up to 39 HRC, A490 bolts are highly susceptible to Internal Hydrogen Embrittlement (IHE) caused by acid pickling or plating operations.
- Thermal Microstructural Damage: Hot-dip galvanizing baths (840°F - 860°F) exceed the minimum tempering temperature of A490 (800°F), risking in-bath annealing and a permanent reduction of mechanical properties.
Approved Coatings: ASTM F3125 permits only non-electrolytic, zinc-aluminum dispersion coatings, such as ASTM F1136 Grade 3 (Geomet), ASTM F2833 Grade 1 (Magni 565), and ASTM F3393.
■ Inspection, Quality Assurance, and Hardware Integration
Non-Destructive Testing (100% MPI): All A490 production lots must undergo 100% Magnetic Particle Inspection (MPI) per ASTM F788 to detect subsurface/surface discontinuities, seams, and transverse cracks. Fasteners also undergo decarburization/carburization evaluation (ASTM F2328).
Companion Hardware: Substituting hardware with non-compatible grades can result in joint slip or premature failure.
| Fastener Type & Finish | Matching Nut Standard & Grade | Matching Washer Standard & Type |
|---|---|---|
| A490 Type 1 (Plain / Uncoated) | ASTM A563 Grade DH (or A194 Gr 2H) | ASTM F436 Type 1 Hardened Steel |
| A490 Type 1 (Coated F1136 / F2833) | ASTM A563 Grade DH (Coated to match) | ASTM F436 Type 1 (Coated to match) |
| A490 Type 3 (Weathering Steel) | ASTM A563 Grade DH3 Weathering | ASTM F436 Type 3 Weathering |
■ Engineering Conclusions and Installation Recommendations
- Absolute Prohibition of Reuse: Because Grade A490 steel is formulated with high strength and a narrow yield-to-tensile ratio, the fastener possesses limited plastic deformation reserve. Subjecting a previously tightened A490 bolt to a secondary installation risks sudden structural fracture.
- Installation Validation: Pre-tensioning must be strictly monitored via the Turn-of-Nut Method, Direct Tension Indicators (DTIs), Calibrated Wrench Method, or by utilizing Twist-Off (F2280) assemblies.
- Enforce Strict Thread Shear Exclusions: In high-load shear connections, design details should utilize the "X" connection configuration. Grade A490 structural bolts are designed with shorter thread lengths to keep threads out of the shear plane, ensuring the full cross-sectional area resists shear forces.
