Sabine Zamberger

Atom probe study of vanadium interphase precipitates and randomly distributed vanadium precipitates in ferrite

Atom probe tomography and transmission electron microscopy were used to examine the precipitation reaction in the austenite and ferrite phases in vanadium micro-alloyed steel after a thermo-mechanical process. It was observed that only in the ferrite phase precipitates could be found, whereupon two different types were detected. Thus, the aim was to reveal the difference between these two types. The first type was randomly distributed precipitates from V supersaturated ferrite and the second type V interphase precipitates. Not only the arrangement of the particles was different also the chemical composition. The randomly distributed precipitates consisted of V, C and N in contrast to that the interphase precipitates showed a composition of V, C and Mn. Furthermore the randomly distributed precipitates had maximum size of 20 nm and the interphase precipitates a maximum size of 15 nm. It was assumed that the reason for these differences is caused by the site in which they were formed. The randomly distributed precipitates were formed in a matrix consisting mainly of 0.05 at% C, 0.68 at% Si, 0.03 at% N, 0.145 at% V and 1.51 at% Mn. The interphase precipitates were formed in a region with a much higher C, Mn and V content.

Carbo-Nitride Precipitation in Tempered Martensite - Computer Simulation and Experiment

In the present work, the precipitation behavior of a V-microalloyed, quenched and tempered steel with 0.3wt % C is investigated experimentally and by computer simulation. The specimens are analyzed by means of transmission electron microscopy using selected area diffraction (SAD) and energy dispersive x-ray spectroscopy (EDX). The analysis is done on electropolished foils and on extraction replica. The numerical simulation is performed with the thermokinetic software package MatCalc, where the precipitation kinetics is examined for the experimentally applied thermo-mechanical cycles. Good agreement between experiment and simulation is obtained and the experimentally observed precipitate microstructure can be well explained on the basis of these simulations.

Numerical simulation of the evolution of primary and secondary Nb(CN), Ti(CN) and AlN in Nb-microalloyed steel during continuous casting

Abstract The precipitation of carbides and nitrides in Nb-microalloyed steel is investigated experimentally and theoretically using light optical, scanning and transmission electron microscopy, and the thermokinetic software MatCalc. The simulations are based on a recently developed two-step methodology for precipitation simulation in primary solidification microstructures, where the compositional inhomogeneities from microsegregation are taken into account. The computed segregation is clearly evidenced in electron probe microanalyses of the as-cast microstructure. Based on the results of a Scheil–Gulliver simulation, precipitation kinetics simulations are performed with the chemical compositions corresponding either to the solute-rich interdendritic zone or the solute-depleted dendrite core zone. The predicted phase fractions, mean radii, number densities, and compositions of the precipitates are in good agreement with the experimental investigations.

A Model for the Influence Of Micro‐Alloying Elements on Static Recrystallization of Austenite

After and during hot rolling of steel, recrystallization can occur and impact severely on the resulting product properties. Recrystallization kinetics are, in particular, influenced by the addition of micro-alloying elements. On the one hand, micro-alloying elements in solid solution, such as Nb, Ti and V, exert a solute drag effect, which reduces the mobility of the grain boundaries. On the other hand, micro-alloying elements form precipitates, which exert a particle pinning force on the grain boundaries. In the present work, we formulate a physically-based recrystallization model with grain boundary mobilities that account simultaneously for the solute drag and Zener drag impact of Nb, Ti and V. We verify the model on numerous experiments on static recrystallization from literature, where good agreement is observed with a single set of simulation input parameters.