According to the Pourbaixs' Atlas of Electrochemical Equilibria in Aqueous Solutions, there are two stable iron oxides, Fe2O3 and Fe3O4, at relatively high pH. This passivates the surface. However, near electrode potential of -1 V and pH 14-16 there is corrosion, as the thermodynamically stable spesies is HFeO-.

The short answer is yes.

Sodium hydroxide will not react with iron or steel, in fact the alkaline conditions will not allow rust to grow; if you make the conditions oxidizing, the black magnetic oxide will grow in its stead; hence the use of alkaline solutions of sodium nitrate for hot bluing baths.

Hot alkali solutions such as caustic soda (sodium hydroxide) and caustic potash (potassium hydroxide) will remove rust from iron and steel, and when combined with sequestering agents to hold the dissolved iron in solution, they can be very effective, particularly at near boiling temperatures. One common combination of sequestering agents:

61.7700 Water

20.0000 Caustic Soda, 50%

18.0000 Sod Gluconate (chelating agent)

0.1000 Triton BG-106 (surfactant)

0.0300 Dowfax 3B2 (surfactant)

0.1000 SAG-10 (antifoam)

See link for Pourbaix (eHpH) or phase stability diagram and set of equations:

https://corrosion-doctors.org/Corrosion-Thermodynamics/Potential-pH-diagram-iron.htm

Hi Ka fai Yuen,

I don't know about sodium hydroxide. But usually, in the lab, we remove with HCl 1:1 solution.