Investigation of the quenched cast Ti–18Nb–$х$Si alloys with silicon content from 0.6 to 1.2% wt. in comparison with the binary Ti–1Si alloy is carried out. Influence of silicon and quenching temperature on the structure and hardness of the alloys is investigated. As shown, in the Ti–18Nb–$х$Si alloys ($х$ = 0.6–1.2% wt.), the martensite of different morphology and dispersion is formed during hardening in dependence on the heat temperature. The electron microscopy and microanalysis show the presence of (Ti,Nb)$_3$Si silicides in the alloys, the size and quantity of which depend on both the silicon content and the quenching temperature.