Influence of Artificial Aging on Microstructure and Mechanical Properties of Dissimilar Welds between 310 Stainless Stee
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HIGH temperatures and corrosive working conditions can easily influence the microstructure and mechanical properties of the weld and base metals. Occurrence of transformation reactions in the weld and base metal of dissimilar welds at high temperature may lead to considerable detrimental changes in the mechanical properties of weldments. Thus, using suggested filler metals in dissimilar welding not only should be considered at room temperature, but also it is necessary to be studied after subjecting them to severe working conditions in order to ensure their sufficient capability of thermal stability and mechanical properties. In the case of joint between 310 austenitic stainless steel (SS) and INCONEL* *INCONEL is the trademark of INCO Alloys International, Huntington, WV.
657 superalloy in oil industries, failure of weldment under service can lead to serious dangers and vital determents. Formation of brittle and weak phases in the microstructure of weld and base metal of 310 SS-INCONEL 657 weldment may tremendously decrease impact toughness and yield-ultimate strength of the joint,[1,2] and therefore limit the choice of filler metal types. Although several types of filler metals, such as INCONEL 82, INCONEL 182, INCONEL 617, INCONEL A, INCONEL 52, INCONEL 152, and 310 SS, can be proposed for joining 310 austenitic SS to INCONEL 657, behavior and H. NAFFAKH, Graduate Student, M. SHAMANIAN, Associate Professor, and F. ASHRAFIZADEH, Professor, are with Department of Materials Engineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran. Contact e-mail: homam-naff[email protected] Manuscript submitted December 3, 2007. Article published online July 16, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A
thermal stability of these weld metals in high temperatures and for long times should be clarified in order to be able to select the most appropriate filler materials. Because the temperature can reach to 1000 C in oil-reformer towers, and the atmosphere is both carburizing and oxidizing, employing INCONEL 657 alloy for heat-flow controlling components (dampers) is suitable. In addition, because the rotating axles, which control the damper motion, are exposed to lower temperatures are made of 310 SS.[3–6] To join the dampers to the axles located in the wall tower, fusion welding is the normal process. Nevertheless, for such dissimilar joints, it appears that the type of proper filler material to be used and also physical and mechanical properties of the weld have not been sufficiently investigated, and the published work is very limited. Therefore, the main purpose of this article is to investigate the effects of aging treatment on microstructure (fusion zone (FZ), heat-affected zone (HAZ), partially melted zone (PMZ), and unmixed zone (UZ)) and mechanical properties of the joints (between 310 austenitic SS and INCONEL 657 superalloy) that have been individually welded under constant welding parameters (i.e., constant heat inputs and dilutions) in order to identify the most appropriate filler material.
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