Analysis of billet solidification & heat transfer and AlN precipitation on Q420C angle steel

This investigation sought to determine the effect of solidification & heat transfer behavior and AlN precipitation on the quality of a Q420C billet and rolled product during the process of high straightening strain. To accomplish this, the paper employed a ProCAST simulation and a nail-shooting experiment to calculate the surface and corner temperature of the billet and the thickness of shell, and a formula for the thickness of solidified shell was proposed. The slab has a good plasticity in the temperature range of 1008-1364℃ based on the results of the Gleeble experiment. The thermodynamics and kinetics of AlN precipitation show that the billet should be straightened avoid the "window" of AlN precipitation and before steel rolling, the billet temperature should be controlled to between 1160-1200℃, and the final rolling temperature should be above 850℃. This reduces AlN precipitation in the austenite grain boundary. After the test, the Q420C steel was successfully produced. The average qualified rate of the rolled products reached 90% and the comprehensive performance index met the needed requirements.