Rusting brake disc

Do you know why the brake disc rusts? What to do with rust?
Car brake discs are generally made of cast iron, so they will gradually rust after a period of time when the vehicle is off the road or in stock. This is normal, not a problem with the quality of the brake discs. If the range of rust on the brake disc is small, you can avoid special treatment, because the small amount of rust on the brake disc will be removed by the braking when the vehicle is moving. If rust is serious, the vehicle will vibrate or vibrate when braking, such as brake pad vibration, steering wheel vibration or vibration, and body vibration. Severe rust is difficult to remove by the brake, and even if it is removed it may cause brake vibration due to uneven thickness of the brake disc. Therefore, the brake disc needs to be maintained every two months to avoid excessive rust development of the brake disc.
How to recover the brake disc through the brake first look for a safe level section, must ensure safety! Then drive the vehicle normally on the road and use the brakes normally.
1. Braking at a reduced speed of 0.3G, from 60 MPH to 0 MPH (96km/h to 0km/h), and repeating five times (during braking, the vehicle travels about 120 meters in about 10 seconds).
2. Braking at a reduced speed of 0.3G, from 40 MPH to 0 MPH (64km/h to 0km/h), and repeating 10 times (during braking, the vehicle travels about 55 meters in about 6 seconds).
3. Braking at a reduced speed of 0.3G from 30 MPH to 0 MPH (48km/h to 0km/h) and repeating 20 times (during braking, the vehicle travels about 30 meters in about 5 seconds.
4. Braking at a reduced speed of 0.3G from 60 MPH to 40 MPH (96km/h to 64km/h) and repeating 10 times (during braking, the vehicle travels about 70 meters in about 3 seconds). 5. Braking at a reduced speed of 0.3G, from 40 MPH to 20 MPH (64km/h to 32km/h), and repeating 15 times (during braking, the vehicle travels about 40 meters within 3 seconds.)