"Faaaaaarrk!", said the crows, as Graham Kennedy was known to say .. HTH would you pick up minute fractures in the threaded section of tie rods - apart from magnafluxing??
Sounds like there's a possibility someone might have specified an incorrect steel specification for the replacement tie rods?
The only way threaded sections fracture in this manner, is if;
1. The steel used does not have adequate tensile strength ..
2. The steel used is too brittle and does not have adequate elongation abilities under load stress ..
3. The steel used is affected too readily by minute amounts of corrosive attack, thus creating a reduction in cross-section thickness (and surprisingly to many, high tensile steels corrode much more readily than low-grade steels).
H37869A - Fuselage Joint "H" Tie Rod
There's also a major difference between hot-rolled threads and threads cut on a lathe. Hot-rolled threads are inherently stronger, because the grain in the steel follows the thread form - whereas a lathe cuts the grain, and thereby weakens the grain structure.