Can welding be performed on high strength anchor bolts and fasteners?
The short answer is that in most cases, welding high strength bolts is not allowed. In the fastener industry, the term “high strength” typically refers to any medium carbon or alloy steel which undergoes a heat-treating process to develop the strength properties necessary to meet the requirements of a given specification. These ASTM specifications include A449, A325, A193 Grade B7, A320 Grade L7, F1554 Grade 105, A354 Grades BC and BD, and A490 among others. When heat is reapplied to a bolt that has been heat-treated, it is likely that the physical properties (strength) of the bolt may be altered. When heat is applied in an uncontrolled environment, it is impossible to determine what effect this application of heat has had on the fastener. Therefore, welding to high strength bolts is not recommended.
Three references occur to back up this statement.
Section 4.5.1 of the AISC Design Guide 21 addresses most ASTM anchor rod specifications individually and prohibits the welding of all quenched and tempered grades.
On page 2-25 of the Fourteenth Edition of the AISC Manual (American Institute of Steel Construction), the following statement occurs:
“As a heat-treated material, Grade 105 rods cannot be welded.”
The final reference prohibiting the heating of high strength bolts (which would occur during welding) can be found in the ASTM F1554 specification. Section 6.5.3 of the ASTM F1554 specification states:
“The maximum hot bending temperature for heat treated anchor bolts shall be less than…..1000F for grade 105.”
Although this statement refers to hot bending, it implies that any process (including welding) that applies heat approaching or exceeding the tempering temperature to a high strength bolt may potentially alter the mechanical properties of the fastener and should, therefore, be avoided.
The issue of altering the high strength bolt’s mechanical properties when welding can potentially be avoided by performing the welding operation prior to the fastener undergoing the heat-treating process. In other words, a plate, a nut, or another component could potentially be welded to a bolt prior to the fastener being heat treated. The problem is, the base medium carbon or alloy steel used to make high strength bolts is technically not weldable due to high levels of carbon and manganese. This could perhaps be overcome with special welding procedures, but the bottom line is that it would be best to avoid welding high strength bolts altogether.
For anchor bolt applications, instead of welding a nut and/or plate to the bottom of a high-strength anchor rod, consider using an anchor bolt with a forged hex head, peening the thread to prevent the nut from backing off, jamming two nuts together to lock them in place, or sandwiching a square plate between two nuts on the embedded end of the anchor rod.
If welding to material grades mentioned in this FAQ is specified on your project, consult with the Engineer of Record for special welding procedures or guidelines.