Influence of Microalloying Elements and Deformation Parameters on the Recrystallization and Precipitation Behavior of Two Low‐Alloyed Steels

The alloy design of modern high‐strength low‐alloy (HSLA) steels aims for a well‐balanced combination of high toughness and strength. Using niobium and titanium as microalloying elements together with thermomechanical processing is a common way to obtain a fine‐grained microstructure and therefore enhance the strength and toughness of HSLA steels. Herein, a low‐alloyed steel and a microalloyed HSLA steel are investigated in the as‐rolled condition and by double‐hit experiments using various deformation parameters. Atom probe tomography, scanning transmission electron microscopy inside a scanning electron microscope, transmission kikuchi diffraction, and energy‐dispersive X‐ray spectroscopy are used to investigate the precipitates in the as‐rolled condition and after deformation. It is shown that Nb‐enriched TiN precipitates with an average size of around 15 nm are responsible for grain refinement in the as‐rolled condition. The annealing temperature prior to the rolling process is set below the solution temperature of Nb(C,N). Enhancing the annealing temperature in the double‐hit deformation tests above the solution temperature of Nb(C,N) leads to the precipitation of fine NbC precipitates with a size of around 5 nm. These precipitates are responsible for inhibited static recrystallization behavior. Herein, the recrystallization behavior of a low‐alloyed steel and a Nb−Ti microalloyed steel with a C content of 0.23 wt% is dealt with. The results show that the annealing temperature prior to the rolling process is decisive for the recrystallization behavior of the microalloyed steel. Responsible for this is the formation of strain‐induced NbC particles and the solute‐drag effect.