Effects of Oxygen Content of Molten Steel on the Machinability of Low-carbon S-Pb Free-machining Steel Cast by Continuous Casting

A study was made to clarify the effects of oxygen content of molten steel on the machinability of low-carbon S-Pb free-machining steel cast by continuous casting. The machinability of this steel was deteriorated by increase of the oxygen content of molten steel and oxygen potential of slag: (%T.Fe)+(%MnO) after LF treatment. It was estimated that the cause of the deterioration of machinability was the increase of amount of MnO rich, MnO·SiO2system large oxides, which promoted the abrasive wear of tool because of their hardness and the size of oxides also promoted the wear. And it was supposed that the large oxides were formed by the contamination of Si and SiO2from added alloy and firebrick, and reoxidation by the involved high oxygen potential slag on Pb-injection, and the oxides trapped by solidified shell on the continuous casting, give the effects on the machinability. From the results of previous and this study, it seemed that the proper control of the oxygen content of molten steel considering the effect of oxygen content on the machinability through the size, shape and formability of MnS and the amount of MnO·SiO2system large oxides, was very important to improve the machinability on the production of this steel by continuous casting process.