Effect of Ultra‐high Mg on Carbide Spheroidization and Properties of Alloy Tool Steel

In this study, Mg in L6 steel was increased by pressure smelting raised to high level (0.046‐0.2%), which was difficult to reach under conventional conditions. It is found that Mg can form MgC₂ carbide and become the heterogeneous nucleation core of granular pearlite in steel. The precipitation amount and temperature of MgC₂ will 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 will appear, resulting in uneven structure. The effect of pearlite spheroidization induced by MgC₂ carbide is still effective in full annealed state, and can significantly reduce the strength and hardness of full annealed steel. When the mass fraction of Mg is 0.046%, the best performance of 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.

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