Numerical Analysis on Columnar-to-equiaxed Transition of δ-Ferrite Dendrite in Carbon Steel Induced by Titanium Carbonitride Particles

Abstract

Dendrite growth simulations have been performed to analyze Columnar-to-Equiaxed Transition (CET) of dferrite dendrite structure triggered by fine particles of a primary Ti(C, N) crystal. The CET position estimated by Hunt's criterion and the present simulation indicated that the existence of a large number of the Ti(C, N) particles gives rise to the CET of the dendrite structure even in the vicinity of the mold wall under the present casting condition. Furthermore, the capability of the Ti(C, N) leading to the CET was discussed in the light of the different number of Ti(C, N) particles and the different thickness of cast ingot. It was shown that a sufficient number of Ti(C, N) leads to the formation of fully equiaxed dendrite structure irrespective of the ingot thickness.KEY WORDS: columnar-to-equiaxed transition; hyperperitectic steel; titanium carbonitride; casting; solidification; simulation; dendrite structure.Ti(C, N) giving rise to the CET of d dendrite solidification. When the values of N 0 and DT N are given, one can predict the occurrence of the CET based on the relation between G and DT t (or the growth velocity of columnar dendrite described as a function of DT t , V(DT t )) within the Hunt's model. It should be pointed out that G and DT t (and V) are essentially time-dependent quantities during the casting process and the analysis of the CET requires such a time dependency to be addressed in detail.The main objective of this study is twofold; one is to substantiate the occurrence of the CET of d dendrite morphology induced by the primary Ti(C, N) in the light of the time-dependent behavior of G-V relation during the casting process and the other is to analyze the capability of Ti(C, N) giving rise to the CET under various casting conditions. To this end, we carry out a columnar dendrite growth simulation describing the time-dependent behavior of G-V relation. The input parameters for the simulation are obtained from the results of casting experiment. The relation between our calculated results and the Hunt's criterion suggests that the Ti(C, N) particles induce the CET of d dendrite morphology in the vicinity of the side surface of the ingot, which is fairly consistent with the metallographic observations. Finally, the capability of the Ti(C, N) giving rise to the CET is discussed in terms of several solidification conditions with the different number of Ti(C, N) particles and the different cooling conditions. In the conventional continuous casting process of the steel, the slab thickness is one of parameters to change the cooling rate of the cast. Therefore, we will discuss the occurrence of the CET in the different cast thickness. One will see that a sufficient number of the Ti(C, N) particles lead to the formation of the equiaxed dendrite over almost the entire cast ingot irrespective of the cast thickness. ExperimentalThe casting experiments were carried out for samples of S45C steel with and without titanium addition. The S45C steel employed in this study consists of 0.436 wt% C, 0.204 wt% Si, 0...

Morphology of Solidification Structure and MnS Inclusion in High Carbon Steel Continuously Cast Bloom

“…However, a slight decrease of PDAS appears at the bloom centre, which is also mentioned in other research works. [36][37][38] Some reasonable explanation for this phenomenon may be that an extensive undercooling in the bulk liquid ahead of the columnar crystal promotes equiaxed crystal nucleates significantly and leads to the solidification acceleration at the late period of solidification process. Figure 7 shows both the 2D and 3D morphology of MnS inclusions in different region of rail steel U75V continuously cast bloom.…”

The Interrelation between Casting Size, Steel Grade, and Temperature Evolution Along the Mold Length and at the Strand Surface during Continuous Casting of Steel

“…The thermal responses of thermocouples have been used to analyze the thermomechanical behavior of molds during casting and to relate the thermal behavior to defect formation [22]. The heat flux between metal and mold has been characterized in continuous casting molds by the inverse heat conduction technique using measured temperatures in the mold and at the strand surface [8,[23][24][25].…”