Precipitate volume fraction estimation in high strength micro alloyed steels

Precipitate volume fraction estimation in high strength micro alloyed steels

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115 C ANADIAN METALLURGICAL QUARTERLY, VOL 48, NO 2 PRECIPITATE VOLUME FRACTION ESTIMATION IN HIGH STRENGTH MICROALLOYED STEELS K. POORHAYDARI and D.G. IVEY Department of Chemical and Materials Engineering, University of Alberta Edmonton, Alberta, Canada T6G 2G6 kioumars@ualberta.ca (Received in revised form March, 2009) Abstract — Many attempts have been made in the past to estimate the volume fraction of small precipitates in steels, both theoretically and experimentally. Theoretical analysis can be very complicated, while experimental analysis can be either difficult or can yield numbers that are inaccurate. In this paper, a simple method is presented to estimate the precipitate volume fraction of nanosize microalloy carbides. The method is based on a combination of simple and well-established thermodynamic calculations for high-temperature precipitation and a simple experimental method for the determination of solutes remaining in solid solution in the steel. Upper bound and lower bound values, as well as the results obtained from an extraction replica method, are presented and discussed. Résumé — Dans le passé, il y a eu plusieurs tentatives d’estimation de la fraction volumique de petits précipités dans les aciers, tant théoriques qu’expérimentales. L’analyse théorique peut être très compliquée, alors que l’analyse expérimentale peut être difficile ou peut produire des nombres qui sont faux. Dans ce document, on présente une méthode simple d’estimation de la fraction volumique de précipité de carbures nanométriques de micro alliage. La méthode est basée sur une combinaison de calculs thermodynamiques simples et bien établis pour la précipitation à haute température et d’une méthode expérimentale simple pour la détermination de solutés qui restent en solution solide dans l’acier. On présente et discute des valeurs limites supérieures et inférieures, ainsi que des résultats obtenus à partir d’une méthode d’extraction de répliques. INTRODUCTION Quantitative analysis of precipitation, in particular the knowledge of small-precipitate volume fraction, is required in correlation studies between microstructure and mechanical properties such as yield strength. Many attempts have been made in the past to estimate the volume fraction of small precipitates in steels, both theoretically and experimentally. It is clear that simple thermodynamic calculations cannot provide a sufficiently accurate prediction of the volume fraction of precipitates, particularly those that are smaller than 50 nm in diameter. These small microalloy precipitates form in austenite through strain-induced precipitation or in ferrite through interphase precipitation upon slow cooling or through general precipitation after accelerated cooling [1-4].
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This note was uploaded on 10/08/2009 for the course CME MAT E 112 taught by Professor Dr.atoo during the Fall '09 term at University of Alberta.

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Precipitate volume fraction estimation in high strength micro alloyed steels

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