Net emission coefficient (NEC) is the most implemented method in the numerical models developed for thermal plasma. This paper is devoted to the calculation of NECs for ［82%Ar-18%CO2］-Fe plasmas with different iron contents between 3 and 25 kK. By considering various radiative mechanisms (spectral lines, continuum and molecular bands), we developed a complet database of radiative proerty for the modelling of GMAW arcs (with 82%Ar-18%CO2 shielding gas and a steel wire). Also, it was found that the presence of iron vapour in the plasmas (even with very low content) can greatly improve the NEC and make the contribution of molecular bands and continuum, which are considerable in the NEC of 82%Ar-18%CO2, negligible.