Study on Behavior of Carbonitride in Nb Micro-Alloyed Steel in CC-HR Region

Abstract

As for the techno -interface of CC-HR region, the precipitation and dissolution of carbonitride in Nb micro-alloyed steel E36 were studied during continuous casting, roller conveying, stack cooling, heat-preserved and heating units in typical slab process flow by hot simulation experiment based on study of heat transfer. The results are as follows: Ti(C,N), and (Ti,Nb)(C,N) precipitate in turn in continuous casting and conveying. A few (Ti,Nb)(C,N) particles are not solid solute completely after heating. The precipitation of carbonitride is effected significantly by different cooling rate in conveying. When slab conveied at the rate of 6.00 °C/min and then cooled down to 600°C, the distribution density of carbonitride particles is higher, and the average equivalent diameter of carbonitride particles is smaller, some carbonitride particles distribute along the austenitic grain boundaries and the generation elements of carbonitride particles are under over-saturation state. When slab conveyed at the rate of 0.30 °C/min or 0.15 °C/min and then cooled down to 400°C, the distribution density of carbonitride particles is lower, and the average equivalent diameter of carbonitride particles is bigger, the carbonitride particles precipitate fully. The behavior of carbonitride in slab are effected by different thermal history in heating. The status of carbonitride is effected insignificantly by different thermal history after heating.