DEVITRIFICATION HARDENING OF CUPOLA SLAG GLASS WITH CAO AND SIO2 ADDITIONS

Slag from the cupola melting of pig and scrap iron was melted, air quenched into a glass and then devitrified forming an abrasion resistant fibrous microstructure. This crystallization behavior was further investigated by altering the composition of the major constituents of the slag, namely, CaO and SiO2. The resulting structural and microstructural changes were measured with XRD, SEM, optical microscopy and DTA techniques. The first crystalline phase formed at approximately 900-degrees-C was Mg-wollastonite, with a microstructure of finely intertwined fibrous growth. Diopside was detected at approximately 950-degrees-C, with a comparatively coarse fibrous microstructure. CaO addition enhanced the formation of Mg-wollastonite while SiO2 addition resulted in enhanced diopside formation. After heat-treating the samples to 1000-degrees-C and holding for 60 min, the CaO-rich samples, having formed predominantly dense fibrous Mg-wollastonite, showed a hardness of 903 +/- 40 on the Vickers scale, an increase of a factor of 2 over amorphous samples. The maximum hardness in silica-rich samples after a suitable heat treatment was 771 +/- 69 kg/mm2.