FREE-CUTTING STEEL HAVING EXCELLENT MACHINABILITY AND METHOD FOR MANUFACTURING THE SAME

摘要

PURPOSE: A free cutting steel with excellent cutting ability and a manufacturing method thereof are provided to secure excellent cutting ability and to prevent coarse MnS from being extracted. CONSTITUTION: A free cutting steel with excellent cutting ability is composed of, in wt%: C: 0.4-0.5; Si: 0.3 or less; Mn: 1.3-1.7; P: 0.04 or less; S: 0.24-0.33; Bi: 0.02-0.08; N: 0.012 or less; Al: 0.05 or less; O: 0.002-0.006; the remainder Fe and inevitable impurities. The number of inclusions whose sizes are 5μm^2 or more in the extrusion direction of a wire is 600-1300 per mm^2. The mass ratio of Mn to S (Mn/S) is 4.0 or greater. The free cutting steel additionally includes at least one kind which is selected from a group composed of, in wt%: Te: 0.01-0.1; Cr: 0.1-0.5%; and Ti: 0.01-0.2.