You can claim warranty, but it sounds like it will be automatically denied as the problem is not a manufacturer's defect. I wouldn't waste my time shipping the motherboard, as it will likely just cost you money, to have them reject it based on what I suspect if you look closely will be, physically based evidence.
I would ask why you are switching from 230V to 115V. Did you move from one country to another?
If you remove the heat sink, you will likely be able to see scorched or blown components. Those will render you motherboard out of action until replaced, provided that's the only damage done. Sourcing and replacing those components is beyond most do-it-yourselfers, so your best bet is to stop using that power supply, and then replace the motherboard. Hopefully nothing attached to the motherboard suffered any ill-effects, such as the RAM, processor, or add-in boards.