Theory of smelting (Reduction Process):- Thermodynamics and Ellingham explains the reduction of FeO to Fe. One of the main reduction steps is:

The reduction process can be divided into two steps

Δ_rG⁰ = ΔG⁰_(FeO,Fe)+ ΔG⁰_(C,CO)

For the reaction to occur Δ_rG⁰ should be – ve. From Diagram at low temperature the line lie above iron hence can’t reduce it but at high temperature it lie below hence can reduce it i.e. FeO to Fe.

But  

line lie below Fe line at low temperature also hence can reduced FeO to Fe even at low temperature.