having read the post no. 4, i was about to also suggest ground up walnut shells, the cutter i served on had two Solar 1000 HP gas turbine engines (as well as two 1500 HP diesels), and we would occasionally have to clean the crud off the blades, we'd slowly dump a sack of ground walnut shells in the air intake. worked a treat. nice smoke and sparks out the stern exhausts too!
other forms of shells were tried, but walnut worked the best and was the least destructive.
glass bead blasting, a less intensive form of shot blasting, can also increase the surface hardness of the metal slightly due to the compression of the metal in the teeny dimples created by the impact, where sharp abrasives are more likely to cut away material.
you can also get plastic beads for even more benign bead blasting crud removal.
linky on available mtls.