Effect of Ultrahigh Mg on Carbide Spheroidization and Properties of Alloy Tool Steel

Herein, Mg in L6 steel is increased by pressure smelting raised to a high level (0.046–0.2%), which is difficult to reach under conventional conditions. It is found that Mg can form MgC 2 carbide and become the heterogeneous nucleation core of granular pearlite in steel. The precipitation amount and temperature of MgC 2 increase greatly with the increase of Mg mass fraction. When the mass fraction of Mg reaches 0.046%, the spheroidizing effect is the best, and the cutting performance is improved. When the mass fraction of Mg is higher than this range, pearlite agglomeration appears, resulting in uneven structure. The effect of pearlite spheroidization induced by MgC 2 carbide is still effective in the full annealed state and can significantly reduce the strength and hardness of the full annealed steel. When the mass fraction of Mg is 0.046%, the best performance of the full annealed steel is close to that of spheroidized annealed steel without Mg. The comprehensive properties of full annealed Q–T steel with 0.046% Mg are similar to those of spheroidized Q–T steel without Mg addition.