We report recent results on the crystallization kinetics of four iron-based amorphous metallic alloys using the instrumentation of the SAXS beamline of the LNLS - National Synchrotron Light Laboratory, Brazil. The evolution of the crystallization products was analyzed in-situ during Joule heating for each investigated alloy. For Fe78B13Si9 and Fe81B13.5Si3.5C2 alloys the crystallization processes start with the formation of large alpha-Fe and Fe3B crystalline particles. In the case of Fe74B17Si2Ni4Mo3 and Fe86B6Zr7Cu1 alloys we observed the initial formation of alpha-Fe nanocrystalline grains, followed by Fe3B or small amounts of ZrO2 and B2Zr. From isochronal differential scanning calorimetry we determined the crystallization activation energy and the Avrami exponent for the main exothermal reaction of each alloy. It was observed that after Joule heating all studied alloys presented a higher ductility when compared to conventional furnace annealed samples.