Carbon Steel Weld Nut

Structural Nuts
In general, steel items which have been heat treated for strength should generally not be welded since welding inevitably heats the items past the tempering point, resulting in a loss of strength in the heated area and other more unpredictable effects like cracking. Structural nuts are typically heat treated, so welding to them could cause issues and loss of strength. In cases where a weld is called for, it will be up to the engineer of record on the job; whether a particular weld would have noticeably detrimental effects is largely a matter of engineering judgment. Some engineers are comfortable with a small tack weld in certain applications, while others are not. In the case of A563 Grade C and C3, where it is uncertain if the nuts were heat treated, attention should be paid to the chemistry of the nuts. In many cases the carbon and manganese contents may be too high to allow welding, regardless of heat treatment.

Non-Structural Nuts
The non-structural grades are where weldability gets a bit gray. These are often referred to as low carbon nuts, and little attention is paid to their specific chemistry. In a random sampling of numerous sizes of nuts in our inventory, representing five different manufacturers, it appears that smaller nuts, those 1″ and below, are cold formed and made from 1008 or 1010 steel, which has low carbon, low manganese, and would chemically be considered weldable. Above 1″ diameter however, the nuts are hot formed and are made from medium carbon steel similar to AISI 1045. These nuts have a carbon content of approximately 0.45%, much too high to fall under the umbrella of what is normally considered weldable.