Effect Of La On The Precipitation Of Inclusions In As-bearing High Carbon Steel

With the increase using of low-grade iron ore and recycling of scrap,the continuous integration of residual elemental Arsenic in steel remains one of the important issues in metallurgical industry.Arsenic would cause segregation and grain boundary segregation during solidification of molten steel,which could dramatically affect the hot-workability and mechanical properties of steel.Since the oxidation potential of Arsenic is lower than that of iron,it is difficult to remove by oxidation under the current mainstream steelmaking process,yet it is feasible to add inhibitors to improve occurrence form of Arsenic.Due to overcapacity,the high-quality steel is the core competitiveness of domestic and foreign steel companies,while the control of residual elements in steel is one of indispensable means to produce the superior steel.The rare earth element can not only purify the molten steel by removing O and S,but also react with the residual elements As,Sn,P,etc.,and thereby improving the occurrence of those elements in steel.In order to clarify the mechanism of rare earth improving the residual elemental arsenic in steel,this paper takes arsenic-containing high carbon steel produced by a domestic steel mill as object,and combines with thermodynamic calculation and laboratory experiments,the formation of La-O-S-As inclusions in arsenic-containing steel is studied,and the mechanism of the influence of rare earth La on residual element As is clarified.The experimental results show that the initial contents of La,O,S and As can significantly affect the formation of inclusions in steel.When La is not added,the inclusions in the steel are mainly MnS and Al₂O₃;when the amount of La added increases from 0.05%to 0.20%,the inclusions in steel is LaAlO₃?La₂O₃?La₂O₂S?LaS?La-S-As?La-O-S-As?LaAsO₄?La-As.When La amount is 0.15%,and the initial O content is increased from 0.004%to 0.008%,La-S-As and LaAsO₄ disappears,the inclusions in the steel are La-O-S-As and La₂O₂S;when the initial S content increases from 0.014%to 0.030%,0.15%of La is not enough to completely consume O and S,and no arsenic-containing inclusions are formed.At this time,the inclusions in the steel are La-S and La₂O₂S;when the initial As content increases in the range of0.01%⁰.10%,the inclusions are all La-S-As because the initial S/O ratio in the steel is not changed.Apart from LaAsO₄ inclusions,La-As inclusions were formed after the initial As content was greater than 0.055%.Furthermore,the distribution of La-O-S-As inclusions in steel ingots shows an obvious regularity.Since La₂O₃ and La₂O₂S are mainly formed in the liquid phase,they float up to the surface of the ingot to form a"slag layer".Meanwhile,due to the adsorption,a certain amount of La₂O₃,La₂O₂S and La-S are also concentrated on the side and bottom of the crucible.As the main form of arsenic-containing inclusions,La-S-As mainly exists in the upper part of the ingot near the"slag layer",which is distributed in a sheet shape,and is less distributed in the middle and bottom of the ingot.LaAsO₄ and La-As inclusions are sporadically distributed evenly in steel ingots.