The short answer is, “No, you cannot match the A325 strength with stainless steel.” Some grades of strain hardened or quenched and tempered stainless steel fasteners will exceed the A325 strength requirements, but most standard stainless fasteners are not nearly as strong as A325 bolts. These bolts are very different chemically. Whereas stainless steels consist of chrome and nickel, A325 bolts have a chemical composition of medium carbon or medium carbon alloy steel that is quenched and tempered. Stainless steel is naturally corrosion-resistant. However, for an A325 bolt to be corrosion-resistant , one would need to move to a hot-dip galvanized finish or the type 3 (weathering steel) version of the A325 specification.
The other major difference is in the thread length. A325 bolts have a reduced thread length to keep the threads out of the shear plane. Stainless steel bolts will have standard thread lengths. Another difference could be the head type. A325 calls for a heavy hex head (unless otherwise specified), whereas F593 stainless steel bolts have a standard hex head. A193 stainless steel bolts will have a heavy hex head. A325 bolts also require a full body diameter due to their structural application, while stainless steel bolts can be manufactured with a reduced body diameter and rolled threads.
| Grade | Diameter | Tensile min psi | Yield min psi | Elongation min % | Red of Area min % |
|---|---|---|---|---|---|
| A325 | 1/2" thru 1-1/2" | 120,000 | 92,000 | 14 | 35 |
| A193 class 1 | 1/2" thru 1-1/2" | 75,000 | 30,000 | 30 | 50 |
| A193 B8 class 2 | 1/2" thru 3/4" | 125,000 | 100,000 | 12 | 35 |
| 7/8" thru 1" | 115,000 | 80,000 | 15 | 35 | |
| 1-1/8" thru 1-1/4 | 105,000 | 65,000 | 20 | 35 | |
| 1-3/8" thru 1-1/2" | 100,000 | 50,000 | 28 | 45 | |
| A193 B8M class 2 | 1/2" thru 3/4" | 110,000 | 95,000 | 15 | 45 |
| 7/8" thru 1" | 100,000 | 80,000 | 20 | 45 | |
| 1-1/8" thru 1-1/4 | 95,000 | 65,000 | 25 | 45 | |
| 1-3/8" thru 1-1/2" | 90,000 | 50,000 | 30 | 45 | |
| F593 CW 304/316 | 1/2" thru 5/8" | 100,000-150,000 | 65,000 | 20 | no minimum |
| 3/4" thru 1-1/2" | 85,000-137,0000 | 45,000 | 25 | no minimum |
Any coating will be available when we are purchasing normal A325 bolts? Will it be affected by corrosion like other uncoated steel sections?
Anoop- A325 bolts are normally available in plain finish and hot dip galvanized. Plain steel will corrode in the same way that other, uncoated steel will corrode. Galvanized bolts will corrode slower due to the effects of the zinc coating. Other standard and proprietary coatings are available, and they all have their own pros and cons, which are too numerous to address here and are best handled by someone more knowledgeable about those various coatings.
I need to replace structural steel bolts (A325) used in a structural steel frame for an outdoor structure. Galvanized or painted A325 bolts are too easily scratched during assembly, and are difficult to paint once in place.
What can you recommend in stainless to replace the 3/4″ dia, 11″ long structural steel bolts?
Thank You,
John.
@John- The stainless choices we can offer are outlined in this FAQ. Apart from those, you’d have to get into exotic and less common hybrid alloys in order to mimic the strengths of A325 bolts – however those materials can be prohibitively expensive and hard to work with.