MANUFACTURE OF SUPER FREE CUTTING STEEL BAR WIRE ROD AND SUPER FREE CUTTING STEEL BAR WIRE ROD THEREBY

摘要

PROBLEM TO BE SOLVED: To obtain a bar wire rod excellent in machinability, by hot-rolling and cooling a cast or steel slab specifying a component composition and a graphitization index under specified conditions. ;SOLUTION: A cast or steel slab which has a composition consisting of by weight, 1.00-1.50% C, 1.00-2.80% Si, 0.01-2.00% Mn, ≤0.050% P, ≤0.10% S, ≤0.0050% O, ≤0.20% N and the balance Fe with inevitable impurities and in which a graphitization index CE determined by equation is ≥1.30, is prepared. The slab is heated to 850 to 1,150°C and hot rolled and rolled into a bar wire rod while making a final finishing temperature 700 to 950°C by applying intermediate water cooling among a rolling mill group at this hot rolling. Then, cooling is performed between the final finishing temperature of the resultant wire rod and 600°C at ≤60°C/min average cooling rate. By this method, graphite of ≥1.0 μm average grain size is precipitated by ≥100 pieces/mm2 in the wire rod, and the metallic structure is provided with a composition consisting of ≥30% ferrite and the balance pearlite and further, Vickers hardness is regulated to ≤200.;COPYRIGHT: (C)2000,JPO