To examine the reduction behavior of commercial sinter in the initial stage, the following analyses were done : Quantitative analysis of sinter before reduction was done by EPMA and the contents of hematite, calcium ferrite (CF), magnetite and slag were determined. Comparison between EPMA surface analyses of sinter before reduction and reduced to magnetite stage at 1 133 K suggests that CF breaks up into magnetite and slag during reduction. Quantitative analysis of sinter minerals during reduction to magnetite stage was done by the X-ray internal standard method using the above-stated contents. Variations in the amount of hematite, CF and magnetite with fractional reduction are revealed ; CF is reduced to magnetite at 1 033 and 1 133 K but is not at 933 nor 983 K. Microstructures of samples reduced up to magnetite stage show that CF is reduced at 1 033 K but not at 983 K. Final fractional reduction in the hematite to magnetite stage under rising temperature conditions up to 1 173 K, Ff', was measured after measuring the one at a predetermined temperature, Ff; below about 1 003 K, CF is hardly reduced and Ff_??_0.7 when oxygen reducible in this stage is assumed to come from hematite and CF. The ratio Ff/Ff' is given as a function of reduction temperature.
