The physicochemical and service properties of new complex Nb–Si–Al–Fe–Ti alloys containing (wt %) 0–25 Si, 20–23 Nb, 5–6 Al, and 3–4 Ti are studied and compared with the well-known two-component Fe–60% Nb alloy. The two-component Fe–Nb alloy belongs to the group of super-refractory ferroalloys with a solidification temperature of 1720°C. A decrease in the niobium concentration and an increase in the content of Si, Al, and Ti make it possible to transfer the alloys to the group of refractory ferroalloys with a melting temperature of 1550–1584°C. The lowest solidification temperature (1550°C) is characteristic of an alloy containing the maximum silicon content (25 wt %) and the minimum niobium content (20 wt %). A pycnometric study of the densities of the complex ferroalloys shows that an increase in the silicon concentration to 21–25 wt % leads to a decrease in the alloy density to optimum values (5000–7000 kg/m3). The melting of the complex niobium alloys with a lump diameter of 2–100 mm in an iron–carbon melt under static conditions has been studied by mathematical modeling. The melting of all complex alloys is found to proceed in three stages. Due to high melting temperatures, super-refractory ferroalloys, which include the two-component alloy with 60 wt % Nb, dissolve at the temperature of liquid steel; therefore, their assimilation mechanism proceeds in two stages. The alloy containing 25 wt % Si and 20 wt % Nb has the shortest melting time at all lump sizes. The ferroalloy lump size is shown to affect the melting/dissolution time most strongly. This is explained by the fact that the alloy mass increases with the lump size, which brings about an increase in the heat content and the frozen steel skin thickness. The complex alloys are shown to have the most favorable densities and solidification temperatures as compared to standard ferroniobium. The alloy containing (wt %) 25 Si, 20 Nb, 5 Al, and 3 Ti has the best complex of physicochemical and service properties. © 2023, Pleiades Publishing, Ltd.