Evaluation of the tendency to the formation of defects of thermal origin of experimental steels for railway wheels

Phosphogypsum-based binding materials without pretreatment have poor physical and mechanical characteristics compared to binders made of natural raw materials. This is due to the high value of their specific surface area, which in turn leads to an increase in water demand. Besides, phosphogypsum contains fluorine and phosphorus compounds adversely affecting the final strength. Therefore, neutralization of these compounds and decreasing water demand of phosphogypsum-based gypsum binder is the priority. Based on the preliminary research, we offered a scientific hypothesis of dry neutralization of fluorine and phosphorus compounds in phosphogypsum by an activated silica/calcium carbonate mixture used in the production of phosphogypsum-based binders. Purpose. The research of the effect of various impurities (lime, calcium carbonate, crushed sand, etc.) on gypsum binder obtained from phosphogypsum as well as the improvement of water resistance and manufacturing processes of phosphogypsum-based gypsum binder (setting time, water-to-gypsum ratio, etc.) that mitigate its disadvantages and extend the scope of application. Conclusion. The research has shown that after adding crushed sand and calcium carbonate as neutralizers of water-soluble phosphorus and fluorine impurities can significantly reduce the amount of water-soluble phosphorus compounds and make water-soluble fluorine impurities disappear completely (Table 6), which makes it possible to use phosphogypsum to produce binders that can be used in civil construction. Moreover, this neutralization method almost doesn't involve emissions of fluoride compounds during the thermal treatment, and besides, physical and mechanical properties of the neutralized phosphogypsum-based hemihydrate CaSO4∙0,5H2O correspond to GVF−4 Grade.