This work linked properties and performance in as-cast condition for 3rd generation advanced high strength steel (AHSS) by examining the effects of chemical composition and microstructure on mechanical properties. Elevated levels of carbon, manganese, and silicon in new AHSS grades lead to a complex evolution of microstructure during solidification that can lead to castability problems. Three lab cast ingots with 0.2 wt% C, 3 wt% Mn, and 0.5, 1.5, and 3 wt% Si were characterized by their microstructure and mechanical properties. Light optical microscopy (LOM) and Scanning Electron Microscopy (SEM) confirmed that the microstructure of steels was mostly granular bainite, with some proeutectoid ferrite allotriomorphs at 3 wt% Si. Tensile testing showed Si increased strength and that ductility of all samples was low. Higher silicon levels were found to promote formation of proeutectoid ferrite allotriomorphs and changed the cracking propagation behavior. Some comparisons between the observed microstructures and those expected in continuously cast slabs were also discussed.

High Si concentrations in third‐generation advanced high‐strength steels (AHSS) are known to cause cracking in continuous cast slabs during cooling at temperatures below 300 °C. To investigate the mechanism connecting Si to this embrittlement, impact toughness tests are conducted on as‐cast Fe–0.2C–3.0Mn steels with 0.5, 1.5, and 3.0 wt% Si at temperatures between 100 and 400 °C. The propagation path of the cracks through the microstructure of the specimens is examined. The ductile‐to‐brittle transition (DBT) behaviors of the three steels are compared. Higher Si concentrations raise the DBT temperature of the steels. The influence of Si on both solid‐solution strengthening and autotempering during cooling likely contributes to this by increasing the hardness of these as‐cast microstructures. In addition, the precipitation of pro‐eutectoid ferrite (αPE), which is promoted by higher Si concentrations, significantly lowers the upper shelf energy of the DBT curve. The αPE phase also alters the propagation path of brittle fracture in the specimens, potentially contributing to the increase in DBT temperature. The increase in DBT temperature and decrease in upper shelf energy may contribute to the as‐cast AHSS slab embrittlement at low temperatures observed in the industry.

Resumo A cada sequencial iniciado, as primeiras toneladas de aços que caem no distribuidor podem ser contaminadas pelos refratários, bem como pelo oxigênio do ar. Na Aciaria da Vallourec Soluções Tubulares do Brasil (VSB), em Jeceaba, desde o start up tem-se como prática o sucateamento de aproximadamente 17 toneladas de aço no início de lingotamento, com o objetivo de minimizar problemas de qualidade no tubo devido fornecimento de barras com baixa qualidade. Neste contexto, estudos foram realizados para avaliar a qualidade destas primeiras barras de primeira corrida do sequencial, com foco em barras de diâmetro de 310mm. A avaliação compreendeu a análise do teor de oxigênio total ao longo da primeira barra e qualidade de tubos laminados provenientes das mesmas. Os resultados indicaram que parte da primeira barra apresenta boa qualidade para ser aplicada na laminação de tubos, reduzindo o sucateamento de barras de início de lingotamento em 7 t.

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