We blast and powder coat coil springs, leaf springs and torsion bars all the time here. We've done them for cars, 4 wheelers, motorcycles, trailers, mudders, etc. (JIT Powder Coating, Farmington, MN) In 10 years of catering to the hobbiest I've yet to have any come back for paint failure.

We use a crushed glass/plastic media combo for blasting which works very well for maintaining a good surface appearance. The cure cycle on most typical blacks like we put on springs is 18-20 minutes at 340-360 degrees F. This is the desired surface temp of the painted part, not the cure oven temp set point. This isn't enough temp or dwell time to affect the spring.

If you've ever visited a spring shop and seen how they're made I don't think you'd be concerned about cure oven temps.

As previously mentioned there is no similarity at all between chrome plating and powder coating.