Preparation of a Low Carbon Steel with Ultrafine Grained Microstructure through Rare Earth Micro-Alloying

The effects of the rare earth (RE) element on the microstructure of a hot-rolled low carbon steel (B450NbRE) were investigated under different heat treatment conditions. It was found that the B450NbRE steel with ultrafine grained structure could be successfully prepared with a certain content of RE additive under an appropriate heat treatment temperature between A(1)(717 degrees C) and A(3) (880 degrees C). The corresponding critical temperature increases with decreasing the RE content. For instance, the critical temperature is 800 degrees C for the RE content of 0.0140 wt.%, but it increases to 850 degrees C as the RE content decreases to 0.0075 wt.%