To provide a composite which can be used for lightweight applications, achieves an increased strength and an increased fatigue resistance without requiring a large amount of energy in an iron-making step, by reducing the use of iron, an iron alloy, pig iron and a pig-iron substrate, and a manufacturing method thereof.

The composite comprises iron, an iron alloy, pig iron, a pig-iron alloy, etc. as a substrate, and a three-dimensional lattice compounded with trace amounts of silicon carbide lattice, alumina lattice, zircon lattice and other inorganic stable substances. The substrate is melted, and casting is carried out by continuously feeding the molten metal to an ingot case in which the three-dimensional lattice is placed. In case of continuous casting, the three-dimensional lattice is continuously fed while casting is performed. The three-dimensional lattice is set so that an excess metal decoration part is previously formed on the ingot case and subjected to pre-heating in vacuum or in an argon-nitrogen atmosphere. Immediately before casting, the three-dimensional lattice is subjected to a contact catalytic reaction with various inoculation materials. A variant similarly obtained through continuous casting is subjected to mechanical pressurization or free pressurization (dressing treatment) of the decoration part and used as a structure.