Generally due to the method of construction of staircases in residential buildings, staircases get damaged due to corrosion very quickly.
The main reason for this is the landing / midlanding jalli work. The jalli is prone to seepage of water from rain beating side.

Many times there is no weathershed from this side. As a result, rainwater seeps through the stairway. This also gets accumulated on steps and landing (which generally do not have proper slope). It then seeps through the staircase and causes corrosion of reinforcement.

Treatment methodology is similar to the procedure for repairs to concrete damaged by corrosion. If the reinforcement is damaged a great extent, then provide wiremesh from underside of staircase while repairing.

The best long remedy is to provide weathershed (made from ferrocement) or from GI sheets / FRP sheets etc so that rain water entry into landing / midlanding is prevented.

Corrosion on the midlanding and steps due to rain water beating