An analytical review on microalloy segregation and the resultant inhomogeneous precipitate distribution in as-cast high-strength low alloy steel

Thermomechanically processed high-strength low alloy steels containing microalloying elements such as Nb, Ti and V are extensively used in the pipeline, shipping, construction and automobile industries. However, microalloying elements like Nb and Ti can be prone to interdendritic segregation, that is, microsegregation. Microsegregation can lead to inhomogeneous precipitate distributions and the formation of coarse particles, grain size variation and microstructural banding in the final product. Microalloy segregation can result in the formation of large eutectic phase particles, which can cause hot-cracking of cast slab as well as affecting the final product properties like toughness and formability. Although microsegregation of elements like Mn, Si, Ni, Cr etc. have been widely investigated in steels, studies on microalloy segregation are more limited. Particularly, it is important to understand the influence of industrial casting practices (such as thick-slab continuous casting, thin-slab casting, and strip casting) on microalloy segregation and precipitation to determine the level of microalloy additions needed to provide the beneficial grain size control and precipitate strengthening but avoid the formation of coarse particles. Therefore, a comprehensive review is presented here on the characterization and prediction of interdendritic segregation of microalloying elements and the consequent precipitate distribution for different casting practices. The microsegregation of Nb and Ti at very high cooling rates, that is, welding and additive manufacturing, is also covered briefly to provide an insight for solidification under these conditions.