Production manner and high S free-cutting steel null of the high S free-cutting steel which is superior in

摘要

PROBLEM TO BE SOLVED: To establish a technology for balancing prevention for the generation of a surface flaw and improvement for the roughness of a finished surface, in a high-S free cutting steel having improved machinability (particularly swarf disposability).;SOLUTION: The high-S free cutting steel comprises 0.01-0.25% C (by mass%, hereafter the same), 0.01% or less Si (excluding 0%), 1.3-3.5% Mn, 0.2% or less P (excluding 0%), 0.38-0.8% S, 0.01% or less Al (excluding 0%), 0.007% or more N, 0.008% or more O, while controlling a Mn/S ratio (mass ratio) to 3.5 or higher, and the balance Fe with unavoidable impurities. The manufacturing method also comprises controlling the concentration of free oxygen in molten steel just before being cast to 0.004% or more and an average area of MnS in the steel to 10 μm² or larger.;COPYRIGHT: (C)2005,JPO&NCIPI