The magnetic transformation temperature of residual iron-chromium ferrite during the sigma transformation in ironchromium alloys containing 35 to 60% chromium were investigated by thermomagnetic analysis. It has been found that, with increasing annealing time the sigma phase content increases but the magnetic transformation temperature does not change. Thus the composition of the residual iron-chromium ferrite during the sigma transformation may be always considesed to be the same. Based on

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... consideration, the content of the residual ferrite is determined quantitatively by measuring the saturation magnetization which depends on both the content and composition of the iron-chromium ferrite. For the above reasons, the content of the sigma phase at each annealing time was determined for several iron-chromium alloys.