Mild steel is

A low carbon steel $(0\mathrm{.}05$ to $0\mathrm{.}3\%$ carbon$)$

Highly resistant to corrosion $($as much as stainless steel$)$

A high carbon steel $(0\mathrm{.}5$ to $1\mathrm{.}5\%$ carbon$)$

Very poor in strength & ductility