ASTM A490 Heavy Hex Structural Bolt
ASTM A490 is the standard for Heavy structural steel Bolts in North America ASTM A490 covers high-strength alloy steel Hex Head Structural bolts manufactured from quenched and tempered alloy steel with a minimum tensile strength of 150 ksi (1,035 MPa), designed for critical structural connections where higher strength than A325 bolts is required.
In 2016, specifications A325 and A490 were officially withdrawn by ASTM and replaced by ASTM F3125. Heavy-duty hexagonal structural bolts A325 and A490 are now grades according to the new F3125 specification.
Applications
- High-rise steel buildings
- Bridge construction (fracture-critical members)
- Heavy industrial structures
- Seismic force-resisting systems
- Wind turbine towers.
Key Features
Material: Quenched and tempered alloy steel.
Head Style: Heavy hexagon (per ASME B18.2.6)
Size: M12 to M36
Material: Alloy steel (Type 1) or weathering steel (Type 3).
Threads: Metric UNC (coarse) for diameters ≤1″, 8UN for >1″.
Head Marking: Three radial lines on bolt head.
Surface Finish: Plain or with corrosion-resistant coatings BZP, Dacromet, Geomet (except HDG).
ASTM A490
ASTM A490 bolts application and geometry is similar to ASTM A325 bolts but manufactured to a higher strength level.
ASTM A490 bolts follow the same geometry as ASTM A325 bolts but have higher strength.
Their strength classification aligns with:
ASTM A354 Grade BD (a high-strength alloy steel bolt specification).
Unlike some other bolts, A490 bolts are not coated via:Hot-dip galvanizing (risk of hydrogen embrittlement).
Electroplating (can introduce hydrogen, leading to cracking).
Mechanical deposition (e.g., zinc flake coatings without proper controls)
Reason: High-strength steel is susceptible to hydrogen embrittlement, which can cause sudden brittle failure under stress.
ISO/F568M Property Class 10.9 (metric high-strength bolts).
Allowed CoatingsASTM permits aluminum-based coatings (e.g., ASTM F1136 Grade 3, a type of Dacromet coating), which provide corrosion protection without hydrogen embrittlement risks.
Technical Specification for ASTM A490 Bolt
The ASTM A490 specification includes two grades of bolts tempered from high-strength alloy steel instead of high-tensile medium carbon steel.
There are 2 versions of this specification;
ASTM A490 covers high-strength bolts for inch sizes
ASTM A490M for metric sizes.
ASTM A490 includes 2 grades: Type 1 and Type 3 (weathered steel) . Type 2 was recalled in 2002.
BRK Industries is a reputable unit that can supply ASTM A490 Type 1 & 3 heat resistant steel bolts with zinc coating, Dacromet, Geomet.
Chemical composition of ASTM A490 Bolt
| Ingredient | Type 1 (%) | Type 3 (%) |
|---|---|---|
| Carbon | 0.20 – 0.53 (less than 3/4″) | 0.30 – 0.48 (less than 1-3/8″) |
| 0.30-0.53 ( less than 3/4″) | 0.35 – 0.53 ( use for 1-1/2″) | |
| Manganese – min | 0.40 | – |
| Phosphorus – max | 0.035 | 0.040 |
| Sulfur – max | 0.040 | 0.040 |
| Copper | 0.20 – 0.60 | – |
| Crom – min | 0.45 | – |
| Niken – min | 0.20 | – |
| Molypden – min | 0.15 | – |
ASTM A490 Bolt mechanical properties
| Nominal length | Tensile strength (min – ksi) | Yield strength (min – ksi) | Elongation (-%) | RA (min – %) |
|---|---|---|---|---|
| 1/2″ to 1-1/2″ | 150 – 173 | 130 | 14% Type 1 18% Type 3 | 40 |
ASTM A490 Comparison with ASTM A325
Comparison with A325 Bolts
Parameter | A490 | A325 |
Material | Alloy steel | Carbon steel |
Tensile Strength | 150 ksi | 120 ksi |
Cost | 30-50% higher | Lower |
Corrosion Resistance | Type 3 available | Type 2/3 available |
Fatigue Resistance | Better | Good |