Color deepening or local discoloration: The area directly heated by the fire may see the rust layer turn darker (from reddish-brown to dark brown or black) due to the oxidation of surface iron oxides at high temperatures, but this is only a superficial color change and does not affect the protective function of the rust layer.
Loosening of surface powder: Prolonged high-temperature baking may cause a small amount of loose iron oxide powder to form on the rust layer's surface (especially in areas with uneven initial rust formation), but this powder can be easily brushed off without damaging the dense underlying patina.
Thermal expansion and contraction of the rust layer: Rapid temperature changes (e.g., pouring cold water on the fire pit immediately after extinguishing the fire) may cause tiny cracks in the surface rust layer due to thermal stress, but these cracks are generally shallow and will be repaired by natural re-oxidation of the steel surface over time.
Avoid extreme temperature shocks: Do not rinse the fire pit with cold water while it is still hot, as sudden temperature drops can cause micro-cracks in the rust layer or steel base.
Regularly remove surface ash: Accumulated ash and debris may trap moisture on the surface, so cleaning it occasionally helps maintain the uniformity of the rust layer and prevents localized corrosion in non-heated areas.
Do not use strong corrosive fuels: Avoid burning fuels with high sulfur or chemical additives (e.g., some industrial waste or treated wood), as their combustion byproducts may corrode the rust layer over time.
