thanks for the replies
I infer that the the heat treatment makes the steel brittle, like tempering. I'm just wondering why, from a metalurgical point of view, 753 is so fragile.
Internetting tells me that elongation of 7075 alloy is 11%, 4130 steel is 25% and 531 is 10%
Is this even the correct measurement when discussing how much deformation you can safely apply to a tube?