Qualities of strand cast resulfurized free-machining steels

Inclusion characterisation for clean steelmaking and quality control

“…Ohtani et al reported the relationships between the character of the MnS inclusions and the machining properties 22. In their work, both tool life and drill life improved with decreasing MnS aspect ratio; in other words, globular MnS inclusions were beneficial for machinability.…”

“…In contrast to these results, for the surface roughness in the plunge cut test, elongated MnS inclusions were found preferable. Thus, the size and shape of MnS inclusions play a major role in determining the machinability of low carbon, resulphurised LCMK steels 22…”

“…Controlling dissolved oxygen in the range of 80-130 ppm for continuously cast LCMK steel product helped in minimising the undesirable Al-Si containing oxide inclusions and obtaining larger MnS inclusions for better machinability. [19][20][21][22] The reduction in dissolved oxygen was achieved by modification of the ladle slags in stages at the LMF.…”

“…Thus, the size and shape of MnS inclusions play a major role in determining the machinability of low carbon, resulphurised LCMK steels. 22 In general, it was found that larger MnS inclusions are more desirable than smaller inclusions. If 60-150 ppm oxygen is retained in molten steel, on solidification, the dissolved oxygen ([O]) combines with the MnS to form manganese oxysulphide inclusions, which are more resistant to deformation or elongation during rolling than those MnS inclusions formed in steel containing very little [O].…”