It's highly likely that it will affect the strength and hardness of the pipe negatively. And that is the reason this should not be used in structural things like roll cages.
Anti-corrosion, maybe. Hardness, no. You are NOT supposed to use hardenable materials for chassis or exhaust parts. A hard part is capable of a sudden brittle fracture event. As long as the material doesn't develop "Sugaring", you will be fine. As far as I know, this is the only way to build headers with gradual bends. In my experience, statistically, it's better to build an exhaust out of mandrel bends if possible. Reason being, it's easier to compute the harmonic properties of the header, plus it forces you to have a design focus on symmetry, which improves longevity overall.
