Hot Ductility Evolution Mechanism of Titanium-Bearing Microalloyed Steels

Titanium-bearing (Ti-bearing) microalloyed steels have high strength and toughness by grain refinement effect of carbonitride precipitates. However, they can induce surface cracks of continuous casting slab when the Ti alloyed content is high. A microalloyed steel with Ti content (0.10-0.15 wt%) is carried out by thermalmechanical simulator over 600-1350 & DEG;C to analyze hot ductility evolution mechanism. Fracture surface morphology, phase transition, and behavior of precipitates of the tensile samples are investigated by experimental detection and thermodynamic calculation. The ductility-temperature curves show that the third brittle temperature range is 600-890 & DEG;C, which is mainly attributed to the thin proeutectoid ferrite film and precipitated titanium carbonitride particles, widening the embrittlement temperature ranges through of steel. In addition, the tensile samples at 890-1350 & DEG;C have good hot ductility, indicating the dynamic recrystallization of deformed austenite can trigger grain boundaries migration away from cracks and avoid the side effect of the Ti (C,N) particles on hot ductility. The first brittle temperature range of 1350 & DEG;C-melting point is mainly ascribed to the partial melting of the grain boundaries with element segregation of sulfur and phosphorus, and microporosity loose among dendrites.