Evaluation of Embrittlement in Isochronal Aged Fe-Cr Alloys by Magnetic Hysteresis Loop Technique

Abstract

Fe-Cr alloys with different Cr contents were prepared by an arc melting technique. The alloys were isochronally aged in the range from <TEX>$400^{\circ}C$</TEX> to <TEX>$900^{\circ}C$</TEX> with <TEX>$50^{\circ}C$</TEX> steps with a holding time of 100 hours. The ageing produced embrittlement in the alloys due to either the formation of a Cr-rich <TEX>${\alpha}'$</TEX> phase or a <TEX>$\sigma$</TEX> phase at high temperatures. Magnetic Hysteresis Loop (MHL) and Micro-Vickers hardness were measured at each step to correlate the magnetic and mechanical properties. Coercivity and hardness of the alloys were increased and remanence decreased up to 500-<TEX>$550^{\circ}C$</TEX> due to formation of a Cr-rich <TEX>${\alpha}'$</TEX> phase. Beyond 500-<TEX>$550^{\circ}C$</TEX> range, the coercivity and hardness decreased and remanence increased due to the coarsening or dissolution of the Cr-rich <TEX>${\alpha}'$</TEX> phase. In the Fe-48% Cr alloy, formation of the <TEX>$\sigma$</TEX> phase at <TEX>$700^{\circ}C$</TEX> reduced the maximum induction of the alloy significantly.