Microstructural evolution, coarsening behavior of vanadium carbide and mechanical properties in the simulated heat-affected zone of modified medium manganese steel

The microstructural evolution, coarsening behavior of vanadium carbide (VC) and the mechanical properties of the simulated heat-affected zone (HAZ) of modified medium manganese steel (MMMS) were investigated as a function of peak temperature (T-p). Cementite precipitated at the grain boundary at 650 degrees C-850 degrees C, and the formation of a carbide network was not observed even at a higher T-p. The nucleation of VC precipitates occurred at a T-p of 650 degrees C, and with increasing T-p, they grew at a rate that is greater than the theoretical value calculated according to the volume diffusion-controlled mechanism. However, coarse VC particles disappeared when the T-p reached 1250 degrees C, and VC particles less than 2.0 nm precipitated during cooling. The lattice parameter of austenite in the simulated HAZ first decreased with VC precipitation, then increased with VC dissolution and finally decreased again at 1250 degrees C due to VC regeneration. Meanwhile, the formation of the VC nanoparticles increased the microhardness and tensile strength of the simulated HAZ. (C) 2016 Elsevier Ltd. All rights reserved.