Could you try putting them in a big garbage bag stand up in tub or laundry sink and add a cup of ammonia? Seal bag and let sit over night.
When you are going to open bag....MAKE SURE YOUR FACE IS NOT OVER THE BAG>>>the direct fumes could make you pass out. Pour ammonia down drain and rinse racks.
This is the way that I do my oven racks and the grid from top of stove.