I would look at H35 (35%hydrogen/balance argon) for the plasma gas, 100% nitrogen for the shielding gas. This is very common for thick (3/4" and up) stainless and aluminum cutting. You would have to verify that your machine is capable of using this mix, and generally, some slightly different consumables are needed in the torch. If your material is thinner, you can sometimes use lesser percentages of H2 in the plasma gas. Jim Colt from Hypertherm is a real good source for plaz cutting info. He is on this forum as "jimcolt" and would be a great resource. I do not know what the impact of H2 is on the base metal, but that should be carefully investigated.