Analyses Of Relation Between Compositions And Perietctic Reaction For Regular Carbon Steels During The Solidification Process

The characteristics of steel solidification in the continuous casting, especially theperitectic reaction, have a great effect on the surface qualities of continuously cast slabs.In order to avoid the surface longitudinal crack, the basicity, the break temperature andcrystalline properties of the mold fluxes are usually increased to control the heat transferin the meniscus. However, the degree of the crack susceptibility is various for thedifferent steel grades in the actual casting process. If the basicity is increased blindly forthe steel grades of which the crack susceptibility is not high, the casting speed is thusrestricted, and some problems maybe also present such as sticking breakouts, bulgedeformation and fluid level fluctuation in the mold. Therefore, it is essential to analysethe crack susceptibility deeply to provide a reference for setting the process parametersand selecting mold fluxes in continuous casting.In this study, the FactSage thermodynamic software were used to analyse the effectof the composition on the peritectic reaction. The peritectic reaction during thesolidification process was observed directly by Confocal Laster Scanning Microscopy.On the basis of it, the solidification shrinkage characteristic index (R_V) was proposed topredict and interpret the crack susceptibility according to the solidification characteristicof steel, and the calculations were validated by the experimental observations in thecommercial steel plant. The following results have been drawn.①The elements of Mn, Si and S cause the peritectic point to move to the leftwhile P and Al in molten steels move it to the right. Generally, Mn and S have a greateffect on the carbon content of the pertectic point, whereas Si, Al and P have a lesssignificant effect.②The relationship between the elements of Si, Mn, P, S, Al and the carboncontent of peritectic starting point (C_S), peritectic point (C_P) and peritectic end point(C_L)was fitted in the range of the compositions of regular carbon steels by multivariatenonlinear regression.③The process of the peritectic reaction was observed directly by Confocal LasterScanning Microscopy, the shrinkage caused by the peritectic reaction can be seen as theliquid phase was disappearing. The phases transformation observed in the experimentshow good agreement with the calculations. In addition, the generation mechanism of the longitudinal crack was discussed according to the time of peritectic reaction and theinterfacial shapes.④The calculated R_Vwas in good agreement with the experimental observationsin the commercial steel plant based on the zone of the peritectic reaction undernon-equilibrium condition, which could be used to predict the crack susceptibility ofregular carbon steels. The degree of the crack susceptibility was divided into four partsaccording to the value of R_V, that is, R_Vhigher than2.1,1.9~2.1,1.7~1.9and less than1.7corresponding to the strongest, stronger, less stronger and weak of the cracksusceptibility, respectively.⑤The relationship between the peritectic reaction and the longitudinal crack wasfurther discussed based on the zero strength temperature, the zero ductility temperatureand the residual liquid phase. Furthermore, the crack susceptibility was analysedaccording to the evolution of mass fraction of phases during solidification process, andthe results were consistent with the experimental observations of steel slabs.