PURPOSE: To form a uniform and superfine austenite structure and to produce a hot rolled bar steel excellent in strength, toughness, and corrosion resistance by inversely transforming ferrite phase into austenite phase while applying plastic working to a round billet, in which at least a part of structure is composed of ferrite, by means of an incline rolling mill.

CONSTITUTION: A solid or hollow round billet 4 composed of ordinary carbon steel or alloy steel is subjected to plastic working by means of elongator rolling at ≥1.5 stretching ratio by using an incline rolling mill having three cone-shaped rolls 1-3 while raising temp. from a temp. lower than the Ac1 point to a temp. not lower than the Ac3 point by utilizing temp. increase by plastic working. Successively, the above steel material is held at a temp. in the region between the Ac1 point and the Ac3 point to undergo the inverse transformation of the structure from ferrite to austenite, followed by cooling. By this method, the structure can be formed into a uniform and superfine austenite structure and the bar steel material having various superior physical properties can be stably produced.