Impact of annealing treatment on the microstructural-dependent mechanical properties of a cold-rolled Fe-Co-10V alloy

Various contributors have been suggested so far to explain the variation of mechanical properties of Fe-Co-V magnetic alloys, but a comprehensive understanding is still lacking. In the present study, the variation of hardness, tensile yield strength (YS), and elongation at room temperature were determined for an 86% cold-rolled Fe-50Co-10V (wt.%) alloy after annealing at the temperature range of 300-1050 degrees C for holding times from 10 to 240 min. The potential contributing factors were analyzed and discussed. Detailed microstructural evolution and magnetic properties have been reported earlier for this alloy. The results showed an increase in hardness and YS but a reduction in elongation after annealing at temperatures between 450 and 550 degrees C for all holding times. The activation energy of the contributing process in increasing the hardness after annealing between 300 and 550 degrees C was 132-144 kJ/mol, being a typical value for the ordering transition in ferrite in Fe-Co and Fe-Co-2V alloys. The YS increased up to an annealing temperature of 450 degrees C, followed by a decreasing trend at higher annealing temperatures even in the ordered state, obviously due to i) the recovery and recrystallization of ferrite, ii) decreasing the number of (Co,Fe)(3)V precipitates and iii) increasing fraction of retained austenite. The elongation decreased to nil after annealing at 450-550 degrees C, but it was improved even in the ordered state at 600 degrees C and above due to the same factors which decreased the YS. The intergranular failure mode after annealing below 600 degrees C converted to ductile mode at 650 degrees C. Considering the combination of mechanical and magnetic properties, the annealing treatment at 650 degrees C for 10 min can be recommended for this alloy, providing high YS, a few percent elongation, and high magnetic hardness.