Kinetic Parameters of Secondary Carbide Precipitation in High-Cr White Iron Alloyed by Mn-Ni-Mo-V Complex

摘要

This study presents kinetics of precipitation of secondary carbides in 14.55%Cr-Mn-Ni-Mo-V white cast iron during the destabilization heat treatment. The as-cast iron was heat treated at temperatures in the range of 800-1100℃ with soaking up to 6 h. Investigation was carried out by optical and electron microscopy, dilatometric analysis, Ms temperature measurement, and bulk hardness evaluation. TTT-curve of precipitation process of secondary carbides (M_7C_3, M_(23)C_6, M_3C_2) has been constructed in this study. It was determined that the precipitation occurs at the maximum rate at 950℃ where the process is started after 10 s and completed within 160 min further. The precipitation leads to significant increase of Ms temperature and bulk hardness; large soaking times at destabilization temperatures cause coarsening of secondary carbides and decrease in particles number, followed by decrease in hardness. The results obtained are discussed in terms of solubility of carbon in the austenite and diffusion activation of Cr atoms. The precipitation was found to consist of two stages with activation energies of 196.5 kJ/g-mole at the first stage and 47.1 kJ/g-mole at the second stage.