What is the difference between F3125 Grade A325 structural bolts and A193 Grade B7 bolts?
A325 and A193B7 bolts are among the most common, mass-produced bolts available in the marketplace. It is a common misconception that these bolts are interchangeable since they have a lot of similarities in their configurations, and both are considered high-strength bolts. In fact, these bolts have two very different applications and have differences in their chemical and mechanical properties.
A325 bolts are specifically designed for use in structural connections. The bolts have a heavy hex head, a full body diameter and are normally short in the overall length since they are used to connect steel to steel. A325s also have fixed thread lengths that are shorter than typical standard thread lengths. Because of their application, A325 bolts must always have a forged head in order to meet the specification. These bolts can be manufactured in diameters 1/2″ through 1-1/2” in diameter.
A193 bolts are designed for high-pressure, high-temperature applications. They are commonly found on pressure vessels and pipe valves. These bolts are typically heavy hex bolts or fully threaded studs, though there is not a configuration limitation like there is with A325 bolts. A variety of bent bolts, rods with threads on one end or both ends, and headed bolts other than heavy hex are commonly manufactured under the A193B7 specification. The diameter range available in this specification is 1/4″ through 7” in diameter.
Chemical and Mechanical Properties
The tables below show the differences between these two grades in their chemical and mechanical properties. Most notably, A193B7 has higher mechanical properties and the chemical properties are different since they are often made from different types of steel.
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|
|*Carbon 0.35-0.53% for 1-1/2” A490/150ksi bolts|
A193 Chemical Properties
|Element||B7 (AISI 4140)||B8 (AISI 304)||B8M (AISI 316)|
|Carbon||0.38 - 0.48%||0.08% max||0.08% max|
|Manganese||0.75 - 1.00%||2.00% max||2.00% max|
|Silicon||0.15 - 0.35%||1.00% max||1.00% max|
|Chromium||0.80 - 1.10%||18.0 - 20.0%||16.0 - 18.0%|
|Nickel||8.0 - 11.0%||10.0 - 14.0%|
|Molybdenum||0.15 - 0.25%||2.00 - 3.00%|