Patent ID: 6896746

Claim:
A hot-rolled steel wire rods and bars usable for machine structural use without annealing, comprising in terms of mass %, C: 0.1 to 0.5%, Si: 0.01 to 0.5%, Mn: 0.3 to 1.5% and the balance of Fe and unavoidable impurities, wherein the microstructure of steel is composed of ferrite and pearlite, the ferrite grain size is No. 11 or more as defined in JIS G 0552, a granular carbide having an equivalent-circle diameter of 2 μm or less and an aspect ratio of 3 or less is contained in an area ratio of 5 to 40%, and the steel has a tensile strength and a reduction of area specified by the following formulae (1) and (2), respectively: TS≦ 573 ×Ceq+ 257 (1) RA≧− 23 ×Ceq+ 75 (2) wherein Ceq=C+Si/7+Mn/5+Cr/9+Mo/2 (mass %) TS: tensile strength (MPa) RA: reduction of area (%).