Yes, during the rusting process, Corten steel can leach rust water or particles. This is normal and is part of the development of the protective rust layer. Once the process is complete, leaching stops and the steel becomes more resistant to wear and corrosion.
Want to prevent stains? Then temporarily place a tarpaulin under the product or allow the rusting process to take place on grass or soil. This way, you protect your patio or paving and enjoy the robust appearance of Corten steel without worry.