Computer simulation of carbonitride precipitation during deformation in Nb-Ti microalloyed steels

Computer simulation of carbonitride precipitation during deformation in Nb-Ti microalloyed steels

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Computer simulation of carbonitride precipitation during deformation in Nb-Ti microalloyed steels Y. Zeng Æ W. Wang Received: 30 October 2006 / Accepted: 10 September 2007 / Published online: 31 October 2007 Ó Springer Science+Business Media, LLC 2007 Abstract A thermo/kinetics computer model has been developed to predict the precipitation behavior of complex precipitates in Nb-Ti bearing steels under hot deformation condition. The equilibrium concentration of substitutional elements in austenite and the driving force for precipitation are calculated by the thermodynamic model. The time dependence of volume fraction and mean radius of pre- cipitates is predicted by the kinetics model on the basis of classical nucleation and growth theory. In the kinetics model, the effect of hot deformation on precipitation is taken into account in terms of increase in nucleation sites and the enhanced diffusivity of substitutional solutes along dislocation, the decrease of solute concentration in austenite, and the driving force for precipitation are determined by a mean Feld approximation method. More importantly, the present model treats nucleation and growth as a concomitant process by using the Fnite differential method, which is different from the traditional one that treats nucleation and growth as a sequential stage. The model has been further validated by the experimental data in the literature. Introduction High strength, good toughness and improved weldability of HSLA steels can be achieved by the combination of mic- roalloying and controlled rolling. The improvement in mechanical properties results mainly from the reFnement of ferrite grain size together with a controlled amount of precipitation strengthening. The microalloying elements such as titanium, niobium and vanadium facilitate grain reFnement through precipitation in austenite and contribute to dispersion hardening through precipitation in ferrite. The contributions of titanium, niobium and vanadium to these two processes are signiFcantly in±uenced by the solubility of their nitrides and carbides in austenite and ferrite. One of the beneFcial effects of titanium additions in HSLA steels is an improvement in the weld heat affected zone (HAZ) toughness owing to the stable Ti -rich particles formed at high temperature. Niobium can effectively retard the recovery and recrystallization during hot rolling, thus facilitating ferrite grain reFnement, whereas vanadium produces less grain reFnement but greater dispersion hardening since it has a higher solubility in austenite and precipitates at lower temperatures [ 1 , 2 ]. Recently, attention has been paid to the combination of Ti and V or Ti and Nb ,o r Ti , Nb and V micro-additions, with the expectation that the potential of each element can be fully exploited. Since the binary carbides and nitrides of Nb , V and Ti are mutually soluble owing to their B1 type structure, this combined addition of metallic elements in steels (multi-microalloying technology) can lead to the
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/08/2009 for the course CME MAT E 630 taught by Professor Dr. during the Fall '09 term at University of Alberta.

Page1 / 9

Computer simulation of carbonitride precipitation during deformation in Nb-Ti microalloyed steels

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online