The effect of microalloying elements on prior austenite grain growth of low-carbon slab material

Abstract

The effect of microalloying elements on the prior austenite grain growth of slab materials during slab reheating has been investigated. The investigated materials were laboratory castings with two levels of carbon (0.05 and 0.09 wt.%) and different combinations of microalloying elements, such as V, Nb, Mo and Ti. Experimental results were compared to equilibrium Thermo-Calc® simulations predicting the solubility of different precipitates during slab reheating. Based on slab reheating experiments at temperatures between 1100 – 1250 °C, Ti is the only alloying element to hinder prior austenite grain growth effectively above 1200 °C. For the steel containing high carbon with Nb, V and Ti microalloying, the average prior austenite grain size was less than 50 μm after the slab reheating to 1250 °C, which can be considered very small. According to Thermo-Calc® calculations, stable Ti(CN) precipitates are formed from the liquid and are in solution until 1500 °C. Until 50-60 % of soluble NbC -precipitates, austenite grain size remained relatively small in Nb-alloyed compositions without Ti, but after that grain size increased drastically. For only V-alloyed steels, already at the soaking temperature of 1100 °C hardly any VC precipitates exists based on Thermo-Calc® simulations, and after that grain coarsening can be assumed to be controlled only by the coarsening rate of austenite grains.