Methods of forming at least a portion of an earth-boring tool include providing particulate matter comprising a hard material in a mold cavity, melting a metal and the hard material to form a molten composition comprising a eutectic or near-eutectic composition of the metal and the hard material, casting the molten composition to form the at least a portion of an earth-boring tool within the mold cavity, and adjusting a stoichiometry of at least one hard material phase of the at least a portion of the earth-boring tool. Methods of forming a roller cone of an earth-boring rotary drill bit comprise forming a molten composition, casting the molten composition within a mold cavity, solidifying the molten composition to form the roller cone, and converting an eta-phase region within the roller cone to at least one of WC and W2C.