Lee cartridge molds are aluminum blocks, in permanently attached steel handles with sturdy grips. Aluminum blocks won't rust, lead won't adhere, and they heat quickly. But they are softer than blued steel and require gentle handling. If you treat these high precision molds with care and respect, they will last a lifetime. The cavity cannot rust.
Gently break in your new mold. New molds require a break in period, and are most likely to be damaged during first use. Wash the mold cavity, dry, and lubricate the cavity and the underside of the sprue plate with candle smoke. As you cast, increase your casting speed to increase temperature and bullet quality. Apply more smoke, as needed. Be gentle!