Effects of Si on the Ductile‐to‐Brittle Transition Behavior of As‐Cast Advanced High‐Strength Steels

Abstract

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.