Bismuth-How to make slabs for Hwanggyese free steel

摘要

The present invention relates to a method of manufacturing a billet for a bismuth-sulfur based free cutting lug, which is used for precision machine parts or a motor shaft, and its object is to provide a bismuth-.;(S): 0.02 to 0.09% of phosphorus (P); 0.07 to 0.09% of phosphorus (P); (Bloom) of 0.24 to 0.33%, aluminum (Al) of 0.005% or less and bismuth (Bi) of 0.05 to 0.15% at 1200 to 1300C, (Bi) to sulfur (B) having excellent hot workability, characterized in that the hot rolled steel sheet is rolled at a reduction ratio of 50 to 60% at a cross-sectional reduction rate of 2 to 10% S)-type free cutting steel.