Nitric acid oxidizes the steel to +three ions, but only in moment quantities, normally undetectable while in the pure acid due to chemical equilibrium with the reaction. Having said that, the ions are removed from the equilibrium by hydrochloric acid, forming AuCl−4 ions, or chloroauric acid, therefore enabling additional oxidation: https://gold86420.wiki-cms.com/6855187/top_guidelines_of_gold