Manufacture of A193 Grade B7 Q&T Bolting 2

[Guest102023]

I am currently examining a fractured stud and trying to characterize the metallurgy. I have seen rolled threads in the past with (a) higher hardness than the core, and now with (b) essentially the same hardness (~34 HRC). Thread rolling is evident only from the deformation of the stringers and crest defects, not from the structure.

My question is this: is there a 'standard' (i.e., most commonly used) sequence to manufacture of Q&T bolts? Could the threads in (b) have been rolled before austenitizing, or after austenitizing and before tempering?

 

[TVP]

The answer to your question is yes, the threads could have been rolled prior to austenitizing, hence obliterating any evidence of cold rolling (strain hardening, flow lines, etc.). In fact, this is the more common method for the vast majority of threaded fasteners.