Adding new dishwasher

I have recently moved our dryer from the kitchen to a location closer the washer. I want to add a dishwasher where the dryer was. The dryer used 12/3 (I think) wire connected to a 30A breaker, but I only need a 20A breaker for the dishwasher. Can I use the 12/3 for the dishwasher and just cap off the red wire and then connect it to the new 20A breaker?