Multi-physics modelling of semi-solid deformation and hot tearing in advanced high strength steels

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Advanced high strength steels (AHSS) represent a key component in reducing vehicle weight and hence reducing fuel consumption related greenhouse gas emissions. In comparison to traditional high strength steels, AHSS achieve significant strength while retaining formability. The increased formability enables greater component complexity, which leads to fewer individual parts and more manufacturing flexibility. However, due to their high alloy contents - manganese up to 5%, silicon up to 2% and aluminum up to 2% - AHSS slabs routinely exhibit transverse surface cracks and centreline cracks caused by hot tearing of the solidifying shell. These cracks result in operational delays and poor product quality for steel producers. In this collaborative study with ArcelorMittal Dofasco, a major producer and supplier of steels to the automotive industry in Ontario, we intend to examine the formation and propagation of hot tears in AHSS. The proposed research is divided into two areas of study. The first is the development of a new multi-physics model that concurrently simulates the solidification, percolation, feeding, and deformation of a network of columnar and columnar/equiaxed grains during continuous casting, for modelling of hot tearing. The second is the direct measurement of the constitutive behaviour of semi-solid AHSS to determine the degree to which this alloy family is susceptible to hot tearing. The joint goal of the proposed research program is to identify the optimal processing routes for reducing hot tearing formation in AHSS alloys.