The thickness gradient of microstructure and mechanical property in an as-cast thin steel slab

Abstract

The compact strip production (CSP) technology composed of thin slab casting and direct hot rolling has attracted much attention due to its apparent cost advantage. In this paper, the microstructural and textural variations in the through-thickness direction and their effects on the plastic anisotropy gradient in a thin-slab-cast low-carbon steel are investigated by optical metallography (OM), orientation imaging microscopy (OIM), transmission electron microscopy (TEM) and quantitative X-ray texture analysis. The thin steel slab shows a relatively uniform strength-ductility balance with the exception of the surface and center layers. The textures in all the through-thickness layers are composed of relatively strong {111} 〈uvw〉 and weak {001} 〈uvw〉 components which reach their maximum intensities in the middle layer near S = 0.4 and in the center layer, respectively (5 is the normalized distance from the slab center to the specific layer and S to the slab surface is 1.0). The γ-fiber oriented ferrite exhibits a roof-shape tendency of the average grain size variation in the through-thickness direction. The lower carbon content in the surface layer is responsible for the better normal anisotropy (rm value) even with the weakest {111} 〈uvw〉 component. In spite of the relatively strong {111} 〈uvw〉 component intensity in the center layer, the lowest rm value is related to the solidified shrinkage cavities and the large MnS inclusions.