Abstract: The dephosphorization rule of low temperature and low silicon molten iron was better studied in Masteel 70 t converter site, the limited dephosphorization reaction and low dephosphorization rate due to the slow slag formation in the early stage and the drying back in the medium stage. The FeO mass fraction in  slag was increased from 10.46 % to 24.70 % at the third minute by improving the feeding method and lance position control, the dephosphorization reaction was strengthened to achieve the purpose of slagging and dephosphorization.The dephosphorization rate at first turning down  increased from 72.1 % to 86.6 %，and tapping rate at first turning down  increased from 68.4 % to 74.3 % by the optimization, and the technical indicators such as steel consumption and oxygen lance age had been improved which provided support for fast-paced production and energy saving in the field.

Key words: low temperature, low silicon molten iron, dephosphorization, phase, viscosity