A constant heat capacity up to 2500°C makes no sense. Iron melts around 1500°C.
The very absolute minimum would be to add the heat of fusion, and use a liquid's heat capacity above the fusion temperature. The result is already quite different.
Even between 350°C and 1500°C, the heat capacity changes a lot, so a constant value isn't good enough. The best way would use an enthalpy table for iron, which is available in the Handbook of Chemistry and Physics for many elements. That would be even simpler, as the given enthalpy includes all events like melting.
Or is a "degree" misread as "zero"? Does the question rather tell 35°C and 250°C?