The speed at which carbon steel rusts can vary depending on several factors, including the environment, exposure to moisture, presence of corrosive substances, and the quality of the steel itself. Here are some general considerations regarding the rate of rusting for carbon steel:

1. Moisture and Humidity: Moisture is a primary catalyst for rust formation on carbon steel. The higher the moisture content in the air or the more prolonged the exposure to moisture, the faster carbon steel can rust. Additionally, high humidity levels can accelerate the rusting process.
2. Exposure to Oxygen: Rusting occurs through a chemical reaction between iron, oxygen, and water. Carbon steel will start to rust when exposed to oxygen in the presence of moisture. The more oxygen available, the faster the rusting process.
3. Corrosive Substances: Exposure to corrosive substances, such as salts, acids, or pollutants, can significantly accelerate the rusting of carbon steel. These substances can promote faster oxidation and corrosion of the steel surface.
4. Surface Condition and Coatings: The condition of the steel surface can affect its susceptibility to rusting. Rough or damaged surfaces provide more opportunities for moisture and oxygen to penetrate the steel and initiate rusting. Applying protective coatings, such as paint, oil, or specialized rust inhibitors, can help slow down the rate of rusting.
5. Quality of the Steel: The quality and composition of the carbon steel can also influence its rusting rate. Higher-quality carbon steel with proper alloying elements and manufacturing processes may have improved resistance to rust and corrosion compared to lower-quality or poorly manufactured steel.

In general, when exposed to a humid or moist environment, carbon steel can start to show signs of rust within hours or days. The rusting process can continue to progress over time, leading to more significant corrosion if the steel is not adequately protected or maintained.

Regular maintenance, proper storage, and application of protective coatings are essential in slowing down the rate of rusting and preserving the condition of carbon steel.