Influence of Cooling Rates and Titanium Content on Hot Ductility in Niobium‐Fixed Microalloyed Steels

This study aims to understand the fracture mechanisms within the hot ductility trough by investigating four microalloyed steels with varying Ti content and balanced Nb. Variations in the cooling rate and Ti content significantly influence intergranular cracking by affecting proeutectoid ferrite formation and TiNb(CN) precipitation. Thermomechanical tests are conducted at three critical temperatures (700, 800, and 900 °C), under cooling rates of 10 and 1 K·s −1 , and a strain rate of 0.001 s −1 . The effect of cooling rate on hot ductility is examined by analyzing ferrite thickness, and TiNb(CN) precipitates through microstructural investigation and MatCalc simulation. At 700 °C, a thin ferrite layer at grain boundaries causes intergranular cracking. A slower cooling rate increases ferrite thickness, thereby, reducing crack susceptibility. At 800 and 900 °C, precipitation behavior and dynamic recrystallization dominate the hot ductility. Coarser precipitates formed under slow cooling result in lower microvoid density at TiNb(CN)‐grain boundary interfaces, thereby limiting crack propagation. Among the Ti‐containing steels, steel S1 exhibits the highest ductility recovery, while steel S2 demonstrates the most favorable overall hot ductility performance. The high Ti content in S3 promotes excessive TiNb(CN) formation, which increases microvoids and suppresses the recovery of hot ductility.