Microalloying Elements Ti Research Articles

Modeling of the Kinetics of Carbonitride Precipitation Process in High-Strength Low-Alloy Steels Using Cellular Automata Method

Proposition of a cellular automata (CA) model of carbonitride precipitation to simulate image of microstructure in HSLA steels and to predict the mechanical properties is presented in the paper. CA model proved to be very efficient in modeling various phenomena in material science. Numerical modeling played an important role in development of new processing technologies taking advantage of precipitation. By modeling, we mean a mathematical description of the relation between the main process variables and the resulting material properties, based on sound physical principles. In microalloyed steels, the microalloying elements Ti, Nb and V are added in order to control their microstructure and mechanical properties. High chemical affinity of these elements for interstitials (C, N) results in precipitation of binary compound, nitrides and carbides and products of their mutual solubility—carbonitrides. The model accounts for an increase in dislocation density due to plastic deformation and predicts kinetics of precipitation as well as shape of precipitates.

Combined Effect of Heating Rate and Microalloying Elements on Recrystallization During Annealing of Dual-Phase Steels

Adjusting ferrite recrystallization kinetics during annealing is a way to control the final microstructure and thus the mechanical properties of advanced cold-rolled high-strength steels. Two strategies are commonly used for this purpose: adjusting heating rates and/or adding microalloying elements. The present work investigates the effect of heating rate and microalloying elements Ti, Nb, and Mo on recrystallization kinetics during annealing in various cold-rolled Dual-Phase steel grades. The use of combined experimental and modeling approaches allows a deeper understanding of the separate influence of heating rate and the addition of microalloying elements. The comparative effect of Ti, Nb, and Mo as solute elements and as precipitates on ferrite recrystallization is also clarified. It is shown that solute drag has the largest delaying effect on recrystallization in the present case and that the order of solute drag effectiveness of microalloying elements is Nb > Mo > Ti.

Precipitates in microalloyed ultra-high strength weld metal studied by atom probe tomography

Gas metal arc welding with metal-cored filler wires is frequently used to weld high strength steel constructions for lightweight and transportation applications. In the current study, microalloying is considered as strengthening concept for reaching the required mechanical properties by precipitation hardening. For this purpose, the typical microalloying elements Ti, Nb, V, and Al were added to the filler metal in a comparatively high amount (up to 0.5 m.%). All-weld metal samples with a yield strength of 1000 MPa and more were produced by gas metal arc welding. Laser-pulsed atom probe tomography was used to evaluate the potential of these elements to form clusters or precipitates and strengthen the weld metal. While Al and Nb did not form clusters, a strong tendency for clustering was found for V- and Ti-alloyed samples. The cluster size evolution and changes in chemical composition depending on the microalloying contents are discussed. Furthermore, the challenges arising from local alloying element enrichments and local differences in thermal history in the all-weld metal are addressed regarding sample preparation and data evaluation.

Influence of Microalloying Elements Ti and Nb on Recrystallization during Annealing of Advanced High-Strength Steels

Microalloying elements Ti and Nb are commonly added to high-strength Dual Phase steels as they can provide efficient means for additional strengthening due to grain refinement and precipitation strengthening mechanisms. In the form of solute elements or as fine carbonitride precipitates, Ti and Nb are also expected to have a significant effect on the microstructural changes during annealing and especially on recrystallization kinetics. The present work investigates the influence of microalloying elements Ti and Nb on recrystallization in various cold-rolled Dual Phase steel grades with the same initial microstructure but different microalloying contents. Using complementary experimental and modeling approaches makes it possible to give some clarifications regarding both the nature of this effect and the comparative efficiency of Ti and Nb on delaying recrystallization. It is shown that niobium is the most efficient micro-alloying element to impede recrystallization and that the predominant effect is solute drag.