Evolution of microstructure of 304 stainless steel joined by brazing process
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Evolution of microstructure of 304 stainless steel joined by brazing process F. García-Vázquez, I. Guzmán-Flores, A. Garza and J. Acevedo Corporación Mexicana de Investigación en Materiales (COMIMSA), Calle ciencia y tecnología No. 790, Col. Saltillo 400, C.P. 25290, Coahuila, México email: [email protected]
ABSTRACT Brazing is a unique method to permanently join a wide range of materials without oxidation. It has wide commercial application in fabricating components. This paper discusses results regarding the brazing process of 304 stainless steel. The experimental brazing is carried out using a nickel-based (Ni-11Cr-3.5Si-2.25B-3.5Fe) filler alloy. In this process, boron and silicon are incorporated to reduce the melting point, however they form hard and brittle intermetallic compounds with nickel (eutectic phases) which are detrimental to the mechanical properties of brazed joints. This investigation deals with the effects of holding time and brazing temperature on the microstructure of joint and base metal, intermetallic phases formation within the brazed joint as well as measurement of the tensile strength . The results show that a maximum tensile strength of 464 MPa is obtained at 1120°C and 4 h holding time. The shortest holding times will make boron diffuse insufficiently and generate a great deal of brittle boride components.
INTRODUCTION High temperature brazing with nickel-based filler metal, produces high performance joints with excellent load resistance as well as high corrosion resistance [1-3]. The method has been widely used in high technology industries as a cost effective means and offers a series of advantages. For instance, brazing can be used to join complicated assemblies between thick and thin sections, odd shapes, or differing wrought and cast alloys. A single step treatment is normally necessary to produce integral components with this technique in a vacuum brazing furnace. For conventional brazing, the joint gaps to be brazed are generally required to retain about 0-1.5 mm to provide capillary attraction [2]. Furthermore, one essential property of this process is a strong metallurgical reaction between the brazing alloy and the base metal that results in joints of high strength and toughness. It process is employed in the joining and repair of aeroengine hot section components manufactured from nickel-based superalloys [4]. It is also applied to components that are too badly damaged for weld repair alone and in situations where welding causes appreciable mechanical distortion. Using filler alloy containing boron and silicon are known to form hard and brittle intermetallic phases at the final microstructure of the brazed joint [5]. Formation of eutectic constituents and other second phase particles in a continuously distributed fashion either along the central region of the joint or at the base metal–braze interface are often found to be deleterious to the properties of brazed joints [6]. On the other hand AISI 304 stainless steel has excellent corrosion resistance, and operates wit
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