Effect of Vanadium Microalloying on the HAZ Microstructure and Properties of Low Carbon Steels

摘要

@@ Four Steels, C-Mn-0.05V, C-Mn-0.11V, C-Mn-0.03Nb and C-Mn were subjected to heat treatment to simulate the microstructureof a coarse grained heat affected zone (CGHAZ) and an intercritically reheated coarse grained heat affected zone (ICCGHAZ).This involved reheating to 1350℃, rapid cooling (t8/5=24s) to room temperature and then reheating to either 750℃ or 800℃.The toughness of the HAZs was assessed using both Charpy and CTOD tests. Microstructural features were characterised byoptical, scanning` and transmission electron microscopy. Fractographic examinations of the Charpy and CTOD specimens werecarried out to understand the micromechanism of fracture under different microstructural and test conditions. The CGHAZtoughness was similar for the steels except that Steel C-Mn-0.05V had a slightly lower ITT compared to the others. Thetoughness deteriorated in the ICCGHAZ for all the steels, again Steel C-Mn-0.05V had a superior toughness compared to theother three steels in both ICCGHAZ conditions. Raising the level of vanadium to 0.11% caused a decrease in ICCGHAZtoughness. Steel C-Mn-Nb exhibited a greater degradation of impact toughness after the intercritical cycles. The presence of M-Aconstituents was the dominant factor in determining the toughness of the ICCGHAZs. The size and area fraction of the M-Aconstituents were the smallest in Steel C-Mn-0.05V. Increasing vanadium level to 0.11% resulted in a greater area fraction of theM-A constituents, larger average and maximum sizes of M-A particles, and significantly more fields containing the M-A. Theaddition of 0.031% Nb produced the largest M-A particles and the greatest area fraction for the steels tested.