Effect of Total Oxygen Content on the Machinability of Low Carbon Resulfurized Free Cutting Steel

Abstract

The effect of total oxygen content on the machinability of low carbon resulfurized free cutting steel was studied by means of machinability tests, metallographic, and scanning electron microscopy observation. The results showed that the total oxygen content had a notable effect on the machinability of SAE 1215 steel. The best machinability of the steel in terms of tool life and surface roughness could be obtained by controlling the total oxygen content at 0.0105 and 0.0125 wt%. When total oxygen content in the steel was less than 0.0105 wt%, the machinability of the steel was increased with the increase of total oxygen content because of the significant reduction of the aspect ratio of MnS inclusions. However, when total oxygen content in the steel was more than 0.0125 wt%, the machinability of the steel was deteriorated dramatically with the increase of total oxygen content, which was attributed to that the amount and the size of oxide inclusions (MnO–Al2O3, MnO–SiO2, and 2MnO–SiO2) with high hardness and high melting point both had a significant increase, and some MnS inclusions were also wrapped by the MnO–SiO2 and 2MnO–SiO2 hard oxides. Furthermore, the tool wear would reach the maximum when total oxygen in the steel rose to 0.0150 wt%.

Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

“…In non-quenched and tempered steel, MnS may cause the deterioration of transverse impact properties because the MnS inclusions become relatively large and elongated in the hot rolling or forging direction. According to the differences in morphology and distribution among various types of MnS, Type I and Type III MnS are more beneficial compared with Type II MnS due to their appropriate sizes and uniform distributions [15][16][17][18]. As a consequence, studies on classifying and controlling MnS in non-quenched and tempered steel are necessary.…”

Effect of Rare Earth Yttrium on the Hot Ductility of Eco-friendly Bi-S Based Free Cutting Steel

“…So the need for the replacement of Pb-S based steels has been strongly suggested, and an eco-friendly Bi-S based free cutting steel has been developed, in which lead is replaced by bismuth [1][2]. The Bi-S based steels have a similar excellent machinability compared to the Pb-S based steels since bismuth and lead have similar physical properties [3][4][5][6].…”

“…These steel easily crack during hot rolling and have a poor ductility [9][10][11][12]. In addition, recent investigations on these steels were mainly focused on their machinability rather than their hot ductility [3][4][5][6]10]. However, some research has been suggested that rare earth element could segregate to the grain boundaries preferentially and suppress the segregation of impurity effectively when the rare earth and impurity elements existed simultaneously in the steel, then increasing the grain boundary cohesion strongly and in turn improving the steel hot ductility [13][14][15][16].…”

Formation and Evolution of Inclusions in Si-killed Resulfurized Free-cutting Steel

“…2) In order to improve the machinability and mechanical property of resulfurized free-cutting steel, it is necessary to control the composition, distribution and morphology of sulfide inclusions. The precipitation of sulfide inclusions is controlled by the steel composition 3,4) and deoxidization products 5,6) in the process of refining and solidification. Therefore, it is significant to clarify the formation and evolution mechanism of inclusions in resulfurized free-cutting steel.…”