Study of inclusion cleanliness and alloys purity of FeMn using automated mineralogy

The ferromanganese FeMn alloy is a high added-value product for Eramet, with strong specifications for final users. More and more foundries using FeMn want to get information concerning the inclusion cleanliness and trace elements of these alloys. Indeed, some non-metallic inclusions such as manganese sulfide could be deleterious for future steel causing embrittlement and crack initiation site under mechanical solicitations. Moreover, the mass content of trace elements such as gaseous elements will have a big impact on the microstructure and mechanical behavior of steels after elaboration. Specific sampling has been performed on one of the FeMn Eramet plants to draw up an «identity card» of the product depending on several granulometric fractions. Eramet Ideas (France) performed microstructural investigations on FeMn samples using an automated mineralogy system. Oxygen in the rock is not homogenous and ad hoc measurements makes the oxygen assessment inconsitant. The measurement of oxygen on powder is more representative of the totality of the material including the impurities like sand, slag entrapment... However the oxidation of the material during the milling is a concern  and different milling conditions conduct to variation in the oxygen analyses. According to the milled powder analyses, other chemical variations were observed from one granulometric fraction to another. The inclusion cleanliness was carried out using an automated mineralogy system (Qemscan system) to determined the nature of non-metallic inclusions and their dispersion trough the ferromanganese alloy. Using theoritical phase density, a reconciliation between Qemscan measurements and chemical analyses has been performed. It is observed that oxygen content is in a better agreement with chemical analyses on milled powder. The main non-metallic inclusions corresponds to manganese oxyde and sulfide. Some complementary electron microprobe measurements have been carried out to determine the nature of manganese oxide. Then, polution such as slag particles, oxide layer and cooling belts sands were indexed in the milled samples whereas no traces were observed on the selected rock samples.