ASTM A490 – Structural Bolts Specification
The ASTM A490 specification governs the requirements for quenched and tempered, alloy steel, heavy hex structural bolts. These fasteners are engineered for high-load structural connections and provide a high tensile strength range of 150 to 173 ksi. Whether you are an engineer specifying these for a project or a technician ensuring compliance, the following overview outlines the practical application and technical scope of this standard.
Core Technical Scope
ASTM A490 is specifically tailored for heavy hex structural bolts used in steel-to-steel connections. It covers two primary types based on their chemical composition:
- Type 1: Produced from medium carbon alloy steel.
- Type 3: Produced from weathering steel, offering enhanced atmospheric corrosion resistance.
- Note: Type 2 was withdrawn from the specification in 2002.
The standard applies to bolt diameters ranging from 1/2 to 1-1/2 inches, inclusive.
To maintain structural integrity and prevent brittle failure, ASTM A490 mandates strict manufacturing controls:
- Heat Treatment: Bolts must be quenched in oil and tempered at a minimum of 800°F (427°C).
- Prohibited Coatings: These bolts cannot be hot-dip galvanized, mechanical galvanized, or electroplated with zinc. These metallic coatings are prohibited because they significantly increase the risk of hydrogen embrittlement and stress corrosion cracking in high-strength alloy steels.
- Banned Elements: Heats of steel containing intentionally added lead, bismuth, selenium, or tellurium are strictly prohibited.
Quality Assurance and Testing
Compliance is verified through several mandatory tests:
- Mechanical Testing: Includes hardness testing (Table 3), proof load testing, and axial or wedge tensile testing (Table 4).
- Magnetic Particle Inspection: 100% of the sample lot must be inspected for longitudinal discontinuities and transverse cracks.
- Carburization/Decarburization: Evaluated via microhardness to ensure the heat treatment process did not adversely affect the surface chemistry.
Mechanical Properties
| Hardness Requirements for Bolts (1/2 to 1-1/2 in. Nominal Size) | |||
|---|---|---|---|
| Size and Length | Brinell | Rockwell C | |
| 1/2 to 1 in., incl. | Less than 2D | 311 – 352 | 33 – 39 |
| 2D and longer | Max 352 | Max 39 | |
| Over 1 to 1-1/2 in., incl. | Less than 3D | 311 – 352 | 33 – 39 |
| 3D and longer | Max 352 | Max 39 | |
| Note: Heavy hex structural bolts 1 in. and smaller that are shorter than 2D are subject only to minimum and maximum hardness. Bolts larger than 1 in. through 1-1/2 in. that are shorter than 3D are likewise subject only to minimum and maximum hardness requirements. | |||
| Tensile Load Requirements for Full-Size Bolts | |||
|---|---|---|---|
| Bolt Size, Threads per Inch, and Series Designation | Tensile Load, lbf (min / max) | Proof Load, lbf (Length Measurement Method) | |
| 1/2-13 UNC | 24 600 / 21 300 | 17 050 | |
| 5/8-11 UNC | 33 900 / 39 100 | 27 100 | |
| 3/4-10 UNC | 57 800 / 50 100 | 40 100 | |
| 7/8-9 UNC | 69 300 / 79 950 | 55 450 | |
| 1-8 UNC | 104 850 / 90 900 | 72 700 | |
| 1-1/8-7 UNC | 114 450 / 132 000 | 91 550 | |
| 1-1/8-8 UN | 136 700 / 118 500 | 94 800 | |
| 1-1/4-7 UNC | 145 350 / 167 650 | 116 300 | |
| 1-1/4-8 UN | 150 000 / 173 000 | 120 000 | |
| 1-3/8-6 UNC | 173 250 / 199 850 | 138 600 | |
| 1-3/8-8 UN | 185 000 / 213 350 | 148 000 | |
| 1-1/2-6 UNC | 210 750 / 243 100 | 168 600 | |
| 1-1/2-8 UN | 223 800 / 258 150 | 179 000 | |
| Note: Loads for full-size bolts are based on specific stress areas calculated from the nominal bolt size and threads per inch. The stress area formula used is As = 0.7854 [D - (0.9743/n)]2. For bolts 1/2 to 1-1/2 in., the tensile strength range is 150,000 to 173,000 psi. | |||
| Tensile Strength Requirements for Specimens Machined from Bolts | ||||
|---|---|---|---|---|
| Bolt Size, in. | Tensile Strength, psi | Yield Strength (0.2% offset), min, psi | Elongation in 2 in. or 50 mm, min, % | Reduction of Area, min, % |
| 1/2 to 1-1/2 in., incl. | 150,000 – 173,000 | 130,000 | 14 | 40 |
| Note: These requirements apply when the bolt length makes full-size testing impractical. When bolts are tested by both full-size and machined specimen methods, the full-size test results take precedence. | ||||
Material Properties
| Chemical Requirements for Type 1 Bolts | |||
|---|---|---|---|
| Element | Heat Analysis, % | Product Analysis, % | |
| Carbon | For sizes through 1 in. | 0.30–0.48 | 0.28–0.50 |
| For size 1-1/2 in. | 0.35–0.53 | 0.33–0.55 | |
| Phosphorus, max | 0.040 | 0.045 | |
| Sulfur, max | 0.040 | 0.045 | |
| Alloying Elements | See Note | ||
| Note : Type 1 bolts must be alloy steel as defined by the AISI. This requires the steel to either exceed specific limits for manganese (1.65%), silicon (0.60%), or copper (0.60%), or contain a specified minimum of other recognized alloying elements—such as chromium, molybdenum, or nickel—to achieve the necessary properties. | |||
| Chemical Requirements for Type 3 Bolts | |||
|---|---|---|---|
| Element | Heat Analysis, % | Product Analysis, % | |
| Carbon | Sizes 0.75 in. and smaller | 0.20–0.53 | 0.19–0.55 |
| Sizes larger than 0.75 in. | 0.30–0.53 | 0.28–0.55 | |
| Manganese, min | 0.40 | 0.37 | |
| Phosphorus, max | 0.035 | 0.040 | |
| Sulfur, max | 0.040 | 0.045 | |
| Copper | 0.20–0.60 | 0.17–0.63 | |
| Chromium, min | 0.45 | 0.42 | |
| Nickel, min | 0.20 | 0.17 | |
| Molybdenum, min | 0.15 | 0.14 | |
| Note: Type 3 bolts must be weathering steel. As per the AISI definition, alloy steel must exceed limits such as 1.65% manganese, 0.60% silicon, or 0.60% copper, or include a specific range of other alloying elements like chromium, nickel, or molybdenum to reach the desired properties. | |||