Effect of magnesium addition in low-carbon steel part 1: behaviour of austenite grain growth

To reveal the effect of Mg addition on the austenite grain growth in low-carbon steel, the steels containing different Mg contents were refined with a vacuum induction furnace. First, the steels were subjected to the temperature range of 1000-1300 degrees C for a holding time of 30 min. Moreover, using a confocal scanning laser microscope, the growth of austenite grains was investigated under isothermal holding conditions (1400 degrees C), and the gamma-alpha phase transformation was also identified after the samples were subjected to a cooling rate of 5 degrees C s(-1). It reveals that the grain growth is inhibited by Mg addition after increasing the temperature to 1300 degrees C. The kinetic equations of austenite grain growth were further established by regression analysis based on the experimental results. Furthermore, a significant increase in the proportion of intra-granular ferrite takes place in 0.0026%Mg-added steel at the initial stage of gamma -> alpha with a cooling rate of 5 degrees C s(-1). This is mainly attributed to the plenty of Mg-containing inclusions, which are demonstrated to be effective nuclei for acicular ferrite, being in the Mg-added steel.