%0 Journal Article
%T Precipitation of Phase Using General Diffusion Equation with Comparison to Vitek Diffusion Model in Dissimilar Stainless Steels
%A Chih-Chun Hsieh
%A Weite Wu
%J Journal of Metallurgy
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/154617
%X This study performs a precipitation examination of the phase using the general diffusion equation with comparison to the Vitek model in dissimilar stainless steels during multipass welding. Experimental results demonstrate that the diffusivities ( , , and ) of Cr, Ni, and Si are higher in -ferrite than ( , , and ) in the phase, and that they facilitate the precipitation of the ¦Ò phase in the third pass fusion zone. The Vitek diffusion equation can be modified as follows: . 1. Introduction ASSs (austenitic stainless steels) are used widely in high-temperature conditions such as energy conversion systems. For instance, to ensure economy in central power systems, sections of boilers subjected to lower temperatures are constructed from FSS (ferritic stainless steel) for economic reasons [1]. However, ASS and FSS composites have acid, alkali, and high-temperature resistances, and so have many applications in a wide variety of industries, such as chemical, oil refining, artificial fiber, food, and medicine [2]. When stainless steels are heated to temperatures between 700¡ãC and 1000¡ãC for prolonged periods of time, several harmful second phases, such as , , and , can precipitate [3¨C6]. While the phase was first observed in the Fe-Cr system, it has also been observed in Fe-Mo, Fe-V, and Cr-Mo-Ni alloy systems [7]. The crystallographic lattice of the phase is a tetragonal structure with 30 atoms per unit cell. The phase is the most important of these intermetallic phases due to its impact on the mechanical properties, corrosion resistance or weldability of stainless steels, as well as other properties [8¨C11]. Previous studies on the properties of stainless steels containing the phase have focused on microstructural observation and the mechanical property in the fusion zone (FZ) of similar stainless steels [12¨C18]. Very few researchers have discussed the precipitation of the phase through the diffusion theory in the fusion zones (FZ) of dissimilar stainless steels. The precipitation behavior of the phase in fusion zones during the welding process is unclear for ferritic and austenitic stainless steels. Hsieh and Wu [19] first reported the precipitation of the phase using the Vitek diffusion model in the multipass fusion zone of dissimilar stainless steels. Autogenous GTAW (gas tungsten arc welding) was used to manufacture dissimilar stainless steels for this present study. The precipitation behavior of the phase in the multipass fusion zone of dissimilar stainless steels taking place during the multipass GTAW process has been discussed via a calculation of the
%U http://www.hindawi.com/journals/jm/2012/154617/