The weld thermal cycle in microalloyed pipeline and structural steels results in significant changes in microstructure and, consequently, mechanical properties of the weld heat-affected zone (HAZ). To have better control of the properties of the HAZ, knowledge of these changes and correlation with mechanical property variations is required. The first step in achieving this is to construct a methodology to examine different regions of the HAZ thoroughly, so that important characteristics such as grain size, microstructure, precipitate type and distribution, and mechanical properties are determined. The next step would be using this methodology to examine different regions of the HAZ under different welding conditions (the most important of which is heat input) and therefore to understand the effects of the welding process. In this paper, a methodology for studying HAZ microstructure/property relationships is demonstrated for a Grade 100 microalloyed steel welded autogenously (no filler metal). Microhardness measurements are used to assess the mechanical property variation across the HAZ. Optical microscopy (OM) and transmission electron microscopy (TEM) are used for grain structure examination and precipitate analysis. The relationship between microstructure and mechanical properties, with emphasis on precipitate reactions, is presented for different regions of the HAZ.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.