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Key words: peritectic steel, mold flux, property of mold flux
Abstract: As peritectic steel is crack sensitive steel, peritectic-steel mold flux needs a higher performance requirement, In this paper, it is analyzed in detail that various properties of peritectic steel mold flux have effects on the quality of peritectic steel billet. And cited several peritectic fluxes design.
1. INTRODUCTION
In continuous casting process, mold flux is considered one of the key technology because it plays a vital role on ensuring running smoothly along the line and improving the quality of the slab. To the crack sensitive steel, in the solidification process the peritectic reaction occurs, that is in 1495 Dfor the Fe-C alloy with w ([C]) = 0.09% ~ 0.53% peritectic reaction occurs during solidification: 8Fe (ferrite) + L (liquid) -> yFe (austenite)1'1. In this reaction, three phases containing ôFe (w (C) = 0.09%), yFe (w (C) = 0.17%) and L (w (C) = 0.53%) coexist. Usually the steel, carbon mass fraction of which range 0.09% to 0.53%, is called peritectic-steel. For this steel at 50mm below mold meniscus region shell is bom and its shrinkage is large, grain coarsening, the growth solidified shell uneven121. When heat flux is too large, the index of slab surface cracking increases rapidly, so it is easy to crack, which is the main reason for peritectic-steel cracking. Therefore, in production it is the primary and effective means to solve the surface quality problem of crack sensitive steel that the strength of the heat flux is controlled and weakened as the cooling intensity of mold reduced.
2. THE SOLIDIFICATION CHARACTERISTICS AND DEFECTS OF PERITECTIC STEEL
Solidification of peritectic steel is just in the peritectic region (5 + L -> y). The contraction of steel is largest at 20-50°Cbelow the solidus temperature line, and at the meniscus of mold with the temperature dropping for just solidified shell the change from ô-Fe to y-Fe occurred. Along with volume shrinkage enlarging( the ratio of volume contraction is 0.38%), solidified shell is separated from the copper and air gap forms, resulting in the minimum heat flux and the thinnest solidified shell, which cause the formation of depressions in the surface. The cooling and solidification rate of sunken parts is slower than others,...