Abstract
As-cast austenite grain size (dγ) in low carbon steels has been studied at a cooling rate from 0.1 to 40 K/s. An analytical model has been proposed to predict dγ. The model is based on the classical grain growth theory of Burke-Turnbull, by assuming a normal grain growth with a parabolic law in the temperature range of a γ single phase. The proposed equation is expressed as follows:
d2γ-d20=Kg[g(Trg)-g(Tf)]/T,
where Kg is a material constant; Trg and Tf are starting and finishing temperatures of the rapid growth, and g(T) is the dimensionless number indicating the square growth amount below T. The square growth amount of the as-cast γ grain is proportional to the inverse of the cooling rate, T-1. The square growth amount decreases to 20% by phosphorus addition, which decreases Kg and Trg. The prediction agrees well with the experimental data of the continuously cast 100 mm-thick slab and the 2 mm-thick strip.
