Unfortunately, alloys with low magnetostriction like Fe-6.5 wt.% Si or Fe 15 wt.% Co 10 wt.% Si are difficult to be prepared as ribbons by conventional methods. The formation of ordered phases (B1 and D0 3 ) causes poor ductility of these alloys. The high quenching rates achieved by melt spinning are not sufficient to suppress the formation of the ordered phases. If boron is added to these alloys, amorphous ribbons may be prepared by melt spinning. These amorphous ribbons have a better workability than crystalline Fe-6.5Si or Fe 15Co 10Si ribbons. However, the composition is different from the target composition. Using annealing treatments in flowing hydrogen the boron may be extracted and the ribbon crystallizes. Thermodynamically the extraction of boron proceeds by the reaction of hydrogen with the borides formed during the crystallization of the ribbons. Thermogravimetric measurements made at three different heating rates can be used to develop a thermokinetic description of the extraction process. The extraction process is controlled by chemical reactions and diffusion. The thermokinetic description enables calculation of the degree of boron extraction for various annealing procedures. After the boron extraction the ribbon is magnetically soft, i.e. it is single phase. For Fe 15Co 10Si, the coercivity is 0.36 A/cm and the saturation polarization is 1.45 T.