Microstructural model for hot strip rolling of high-strength low-alloy steels

The microstructural evolution during hot-strip rolling has been investigate d in four commercial high-strength low-alloy (HSLA) steels and compared to that of a plain, low-carbon steel. The recrystallization rates decrease as the Nb microalloying content increases, leading to an increased potential t o accumulate retained strain during the final rolling passes. The final mic rostructure and properties of the hot band primarily depend on the austenit e decomposition and precipitation during run-out table cooling and coiling. A combined transformation-ferrite-grain-size model, which was developed fo r plain, low-carbon steels, can be applied to HSLA steels with some minor m odifications. The effect of rolling under no-recrystallization conditions ( controlled rolling) on the transformation kinetics and ferrite grain refine ment has been evaluated for the Nb-containing steels; Precipitation of carb ides, nitrides, and/or carbonitrides takes place primarily during coiling, and particle coarsening controls the associated strengthening effect. The m icrostructural model has been verified by comparison to structures produced in industrial coil samples.