This is a very good question. Also interested in this topic.

Recently, I could not clean the grates of my grill from fat and ash - I began to look for ways to solve this problem. It's good that the site https://www.fortador-usa.com/blog/bbq-grill-steam-cleaner-how-to-steam-clean-bbq-and-grill has instructions for steam cleaning barbecue grill and when they help I managed to solve this problem. Having carefully processed the grate with steam, I was able to clean it. I recommend steam cleaning if normal cleaning does not help.