Below are the chemical and mechanical requirements per the ASTM A325 specification. In addition, you will find the estimated mechanical property requirements for each diameter of bolt required. One thing to note is that with the implementation of ASTM F3125 Grade A325, the mechanical properties differ slightly as indicated below.
A325 Type 1 Chemical Properties
| Heat Analysis | 120ksi, % | 150ksi, % |
|---|---|---|
| Carbon | 0.30 – 0.52 | 0.30 – 0.48* |
| Manganese | 0.60 min | 0.60 min |
| Phosphorus | 0.035 max | 0.035 max |
| Sulfur | 0.040 max | 0.040 max |
| Silicon | 0.15 – 0.30 | - |
| Boron | 0.003 max | 0.003 max |
| Copper | - | - |
| Nickel | - | - |
| Chromium | - | - |
| Molybdenum | - | - |
| *Carbon 0.35-0.53% for 1-1/2” A490/150ksi bolts | ||
A325 Type 3 Chemical Properties
| Heat Analysis | 120ksi, % Comp A | 120ksi, % Comp B | 120ksi, % Index | 150ksi, % Index |
|---|---|---|---|---|
| Carbon | 0.33 – 0.40 | 0.38 – 0.48 | 0.30 – 0.52 | 0.30 – 0.53 |
| Manganese | 0.90 – 1.20 | 0.70 – 0.90 | 0.60 min | 0.60 min |
| Phosphorus | 0.035 max | 0.035 max | 0.035 max | 0.035 max |
| Sulfur | 0.040 max | 0.040 max | 0.040 max | 0.040 max |
| Silicon | 0.15 – 0.30 | 0.30 – 0.50 | ||
| Copper | 0.25 – 0.45 | 0.20 – 0.40 | 0.20 – 0.60 | 0.20 – 0.60 |
| Nickel | 0.25 – 0.45 | 0.50 – 0.80 | 0.20 min* | 0.20 min* |
| Chromium | 0.45 – 0.65 | 0.50 – 0.80 | 0.20 min | 0.20 min |
| Molybdenum | 0.06 max | 0.10 min* | 0.10 min* | |
| *Either Nickel or Molybdenum must be present in the amount specified *Corrosion Index based on ASTM Guide G101 | ||||
A325 Mechanical Properties
| Size | Tensile, ksi | Yield, ksi | Elong. %, min | RA %, min |
|---|---|---|---|---|
| 1⁄2 - 1 | 120 min | 92 min | 14 | 35 |
| 11⁄8 - 11⁄2 | 105 min | 81 min | 14 | 35 |
Mechanical Requirements per Diameter
The minimum strength requirement of a specified grade of bolt is given in pounds per square inch (psi) or thousands of pounds per square inch (ksi). This works when analyzing what grade of material should be used for a given application, but this doesn’t tell us the actual or ultimate strength of that material for a specific diameter. Below are the approximate minimum mechanical properties specific to a given diameter of A325 fastener.
| Diameter | Ultimate Yield, lbs. | Ultimate Tensile, lbs. |
|---|---|---|
| 1⁄2" | 13,054 | 17,028 |
| 5⁄8" | 20,792 | 27,120 |
| 3⁄4" | 30,728 | 40,080 |
| 7⁄8" | 42,504 | 55,440 |
| 1" | 55,752 | 72,720 |
| 11⁄8" | 61,803 | 80,115 |
| 11⁄4" | 78,489 | 101,745 |
| 13⁄8" | 93,555 | 121,275 |
| 11⁄2" | 104,814 | 147,525 |
Mechanical Property Requirement Comparison Between A325 & F3125 Grade A325
Below is a chart comparing the mechanical property requirements for A325 versus F3125 Grade A325. As you can see, the requirements are identical through 1” diameter, but beyond that, F3125 Grade A325 has a higher minimum strength requirement. Note: Under the new F3125 specification, strenths are the same for all diameters. The values below represent the strength requirements when A325 was a stand-alone specificaiton.
A325 Mechanical Properties
| Size | Tensile, ksi | Yield, ksi | Elong. %, min | RA %, min |
|---|---|---|---|---|
| 1⁄2 - 1 | 120 min | 92 min | 14 | 35 |
| 11⁄8 - 11⁄2 | 105 min | 81 min | 14 | 35 |
F3125 Grade A325 Mechanical Properties
| Size | Yield, ksi | Tensile, ksi | Elong. %, min | RA %, min |
|---|---|---|---|---|
| 1⁄2" - 11⁄2" | 92 min | 120 min | 14 | 35 |
Ultimate Mechanical Property Comparison
| Diameter | A325 Ultimate Yield, lbs. | F3125 A325 Ultimate Yield, lbs. | A325 Ultimate Tensile, lbs. | F3125 A325 Ultimate Tensile, lbs. |
|---|---|---|---|---|
| 1⁄2" | 13,054 | 13,054 | 17,028 | 17,028 |
| 5⁄8" | 20,792 | 20,792 | 27,120 | 27,120 |
| 3⁄4" | 30,728 | 30,728 | 40,080 | 40,080 |
| 7⁄8" | 42,504 | 42,504 | 55,440 | 55,440 |
| 1" | 55,752 | 55,752 | 72,720 | 72,720 |
| 11⁄8" | 61,803 | 70,196 | 80,115 | 91,560 |
| 11⁄4" | 78,489 | 89,148 | 101,745 | 116,280 |
| 13⁄8" | 93,555 | 106,260 | 121,275 | 138,600 |
| 11⁄2" | 104,814 | 129,260 | 147,525 | 168,600 |