Influence Of Final Converter Slag Recycling On Slag Forming Process And Dephosphorization During Dephosphorization Period In Converter

At present,the iron and steel industry in China is under great pressure to resolve overcapacity,reduce costs,save resources and protect the environment.Domestic iron and steel enterprises began to follow the Japanese iron and steel enterprises with less slag smelting process（duplex processing and MURC）to reduce production costs,save resources and reduce the amount of slag discharge in recent years,such as Baosteel BRP dephosphorization technology etc.The key to less slag smelting process is decreasing slag and using recycling final converter slag to get a high dephosphorization rate during dephosphorization period,using recycling final converter slag is bound to have an effect on slag forming process and dephosphorization which has seldom been concerned so far.This paper studied the effect of salg forming methods on slag forming process and dephosphorization when using recycling final converter slag in lab.In order to eliminated the interference of slagging material,firstly it studied the effect of salg forming methods on slag forming process and dephosphorization when the remained slag was definitized（only add ore）,then it studied the effect of adding manner of lime on dephosphorization because of the large fluctuation of Si content in hot metal,finally the effect the amount of slag and the amount of C₂ S on the dephosphorization effect was studied,detailed work was summarized as follows:（1）The slag made in lab had similar effects with the converter slag and it’s practicable to sample during experiment.When ore was added all at once,slag’s interface oxygen potential is 3×10-13 and the dephosphorization rate was 75% in 5 min.There were more liquid slag and less solid slag in the initial slag and the slag got into the solid-liquidcoexistence zone form the liquid phase region that were almost near the C₂ S saturation line which was better for precipitating nC₂S-C3 P solid solution phase,and the dephosphorization results were good;When ore was added in batches,slag’s interface oxygen potential is 3.2×10-14 and the dephosphorization rate was 64% in 15 min.There were more C₂ S solid slag in the initial slag and the slag got into the liquid phase region form the solid-liquidcoexistence zone that was hard for phosphorus’ pervasion form liquid slag to C₂ S phase,and the dephosphorization results were not so good.（2）The Silicon content rose to 0.55% and the slag was reserved,when the ore and the lime were added all at once,the dephosphorization rate reached 72.9% in 5 min with lager amounts of 2C₂S-C3 P solid solution phase generated that were almost near the C₂ S saturated line,and the dephosphorization results were good;when ore and lime were added in batches or lime was added first and then ore was added in batches,the dephosphorization rates were 22.6% and 27.9% in 7 min that were very low and went up after 7 min,whose final dephosphorization rate were 61.3% and 56.5%,their dephosphorization results were not so good because the slag went into the solid-liquidcoexistence zone too early.There was no slag reserved,it could get high previous dephosphorization rate when the ore and the lime were added all at once,but the slag was always in the liquid phase so that there was little solid solution phase precipitated;when ore and lime were added in batches,the dephosphorization rate rose to 87.9% very slowly,the slag began to approach the C₂ S saturated line after 7 min which stayed near the C₂ S saturated line at last;when lime was added first and then ore was added in batches,the dephosphorization rate rose to 87.8% in 15 min whose previous dephosphorization speed was very low,and the slag began to approach the C₂ S saturated line after 10 min which stayed in the solid-liquidcoexistence zone at last.（3）When there was little slag reserved（17 g/500 g hot metal）,the previous dephosphorization speed was very high but it would cause rephosphorization later because basicity of slag was reduced.When 34 g slag was reserved,dephosphorization rate was 65.4% which increased quickly.The Increasing the amount of slag would move the slag forming route of dephosphorization to C₂ S saturated zone and the dephosphorization rate would be much better when it was near the C₂ S saturated line.It would be hard for previous slag to melt if we continue to increase the amount of slag which would bring bad dephosphorization results.Adding some C₂ S phase into the previous slag could increase the amount of nC₂S-C3 P solid solution phase which could move the slag forming route to C₂ S saturated zone but would cost a long time without a good dephosphorization rate.The dephosphorization rate could reach 79.6% in about 7 min when adding 6.4 g C₂ S phase for 500 g hot metal.