PRECIPITATION KINETICS OF MICROALLOYING ADDITIONS DURING HOT-ROLLING OF HSLA STEELS

The control of the precipitation of microalloying elements (Nb-Ti-V) during hot-rolling processes is of prime importance for the development of HSLA steels, ensuring reproducibility and homogeneity of the mechanical properties. In the present work, the effects of processing parameters and steel chemistry on the precipitation kinetic during hot-rolling, are quantified using SED method (selective electrolytic dissolution). Anisothermal and isothermal precipitation kinetic in austenite during rolling and in ferrite are compared and discussed. In ferrite, during or after transformation, an important distinction is made between coherent and incoherent precipitated forms. The coherent precipitation kinetic, which appears to be very fast in ferrite at high temperature, is studied by hardness measurements. It is shown that cooling rates higher than 20-degrees-C s-1 are needed to avoid coherent precipitation on the runout table of a finishing mill.