Effects of deoxidation and chemical composition on the machinability based on tool life in machining low carbon resulphurized steels and medium carbon steels with high speed steel tool are investigated.
In turning low carbon resulphurized steels, core of rimmed steel has superior tool life characteristics, while rimmed layer has poor one due to its cleanliness. Mn-S killed steels with very low Si content, which are killed due to high Mn and high S contents, have good machinability uniformly from outer layer to core.Si deoxidation is very detrimental to the machinability. High oxygen content is favorable to the formation of round sulphides in Mn-S killed steels, and their machinability are improved with increasing ΣO content up to 0.026%. Sulphide shape substantially affects chip formation behavior and cutting temperature.The poor machinability of Si deoxidized resulphurized steels is due to formation of elongated sulphides and hard oxide particles.Tool life is well correlated to the cutting temperature and amount of hard particles such as SiO2 and Al203 in steels.
In machining medium carbon steels with different S contents, deoxidation seems to have minor effects on their machinability.
Concerning with dependence of machinability on sulphide shape, the effects of cutting direction on the machinability of resulphurized steels are also discussed.
