Welding fasteners, such as bolts and nuts, significantly alters their mechanical properties, particularly when heat treatment is compromised. When a bolt or nut is welded, it can lose its heat-treated state, becoming essentially annealed, which drastically reduces its strength. For instance, a grade 8 bolt may experience a decrease in yield stress, making it prone to sudden failure rather than gradual deformation. It is crucial to avoid welding on structural fasteners unless using specifically designed weld-on fasteners, as this can lead to thread stripping and other failures.
PREREQUISITESEngineers, welders, and quality assurance professionals involved in structural design and fastener selection will benefit from this discussion, particularly those focused on maintaining the integrity of welded joints in high-strength applications.
You are posing a problem that is not possible to resolve with charts and tables. How much heat was applied during welding? What type of welder was used, and what is the operating temperature of the arc? How much of the bolt's surface was in contact with underlying metal, and what is the thermal conductivity of that metal? You can pile on complication on complication very easily with a bit of thought.CruiserFJ62 said:Does anyone know of a table shows annealed vs tempered&quenched steel properties? What is the decrease in yeild stress on a grade 8 bolt that is annealed due to the heat from welding?
turbo-1 said:You are posing a problem that is not possible to resolve with charts and tables. How much heat was applied during welding? What type of welder was used, and what is the operating temperature of the arc? How much of the bolt's surface was in contact with underlying metal, and what is the thermal conductivity of that metal? You can pile on complication on complication very easily with a bit of thought.
If the bolt is in its annealed state, it will have no more strength than a common fastener, and possibly less, since you might have created discontinuities in its internal structure that would make it prone to sudden complete failure, instead of just stretching/distortion that you might have gotten with a common fastener.CruiserFJ62 said:I'm not really trying to get an exact answer but an understanding of what the worst case would be if the material was in its annealed state?
turbo-1 said:If the bolt is in its annealed state, it will have no more strength than a common fastener, and possibly less, since you might have created discontinuities in its internal structure that would make it prone to sudden complete failure, instead of just stretching/distortion that you might have gotten with a common fastener.