Strength Deterioration of Samples of Iron Ore-5-10%CaO Systems during the Reduction at 550°C in 30%CO-N2 Gas

Samples with homogeneous microstructure of iron ore -5, 8.5 and 10% CaO systems were sintered in the temperature range, 1200-1350°C in air. Their strength deterioration caused by the reduction at 550°C for 60min in 30%CO-N2 gas stream was studied by means of a device for evaluating the mechanical strength from their, fragility, comparing with that of six kinds of self-fluxing sinters. The results obtained are as follows:(1) Samples contain only granular hematite crystals and yet some of them show a severe strength deterioration caused by a conspicuous development of cracks during the reduction.(2) The extent of crack development changes depending mostly on the porosity and the microstructure of samples.(3) Pores work as obstacles to the propagation of cracks. So, the extent of crack development decreases with the increase of porosity, leading to less strength deterioration.(4) Minerals surrounding hematite particles have a great influence on the strength deterioration. Either coarsening of calcium ferrite grains or decreasing of glassy silicate in amount lessens their mechanical strength, leading to the great strength deterioration.