Austenitic Grain Growth Behavior during Austenization in an Aluminum-Alloyed 5% Cr-Mo-V Steel

Abstract

The influence of Al on the grain size, morphology, and grain size distribution of austenite is investigated in a wide range of austenitizing temperatures and holding times. In general, the addition of 1.1 wt% Al significantly increases the austenitic grain size at all the corresponding austenitizing conditions. The austenitic grain growth mode of the none Al-added steel is abnormal grain growth at the austenitizing temperature in the range of 1100–1200 °C, while that of the high Al-added steel has already become normal grain growth in the same temperature range. The results indicate that the Al addition can significantly accelerate the growth of austenite grains, mainly because the high content of Al affected the Zener drag and solute drag on the grain growth by reducing the activity and diffusivity of Mo and V atoms in austenite. In addition, the kinetic equations of austenite grain growth in both steels are proposed. The calculated grain growth exponents are n = 0.33 and n = 0.35, and the activation energies of grain growth are Q = 1.51 × 105 J mol−1 and Q = 1.85 × 105 J mol−1 for 0Al and 1.1Al, respectively.