Precipitation Behavior and Textural Evolution of Cold-Rolled High Strength Deep Drawing Dual-Phase Steels

Low-carbon Cr-Mo micro-alloyed deep drawing dual-phase steels were designed in laboratory. As the microstructure and texture evolution in hot-rolled strips and annealed sheets were investigated using SEM, TEM and XRD technologies, the attribution of solute Mo and MoC particles to DP sheets' drawing capacity was investigated. The precipitation thermodynamics were also calculated by Thermo-calc software. Results show that the precipitates in hot-rolled strips mainly are MoC, AlN and MnS, and with the increase of Mo-addition, finer and denser MoC particles precipitated in matrix and along grain boundaries of ferrite more easily. Weak textures are shown in the hot-rolled strips, and {112}<110> and {223}<110> components tend to be stable in subsequent cold rolling process. During annealing, on one hand, the development of <111> // ND texture is suppressed because finer MoC particles prevent the grain boundary migration. On the other hand, unfavorable texture {001}<110> significantly reduces with Mo increasing, which is attributed to that part of solution C in matrix has been fixed during recrystallization. In addition, the addition of Mo can enhance hardenability strongly and MoC easily re-dissolve at high temperature, which is favor to form martensite in dual-phase steel.