Speaker
Description
This study investigates the effect of niobium microalloying on the recrystallization kinetics, precipitation, and mechanical properties of low carbon steels. The experimental materials consisted of three laboratory cast and laboratory rolled steel grades, where the niobium content was the only variable. Used cooling method in these steels was coiling. The experimental work included a wide series of tests using the Gleeble 3800. Relaxation tests were performed at different temperatures, strains and strain rates to study recrystallization kinetics. Coiling simulations with different holding temperatures were also carried out to study microstructure development during controlled cooling. These Gleeble coiling simulation results were compared with the laboratory rolled coiled materials. Mechanical testing was used to see differences in properties between the steel alloys. Microstructural characterization with FE-SEM and EBSD provided information on grain size, microstructural changes and recrystallization kinetics. The results show that increasing niobium content clearly delays or stops recrystallization due to the combined effects of solute drag and precipitation. The niobium content change was affecting also other results. When niobium was increasing hardness and strength was increasing and microstructure changed to more bainitic.