Microstructure-Based Strength Distribution Across the Welds of Nickel-Based Superalloy Inconel 751 and Austenite Steel 2
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INTRODUCTION
AS a nickel-based superalloy, Inconel 751 has high heat and corrosion resistance, making it an attractive material for application in aircraft, marine vehicles, nuclear reactors, submarines, and steam power plants. However, nickel-based alloys usually suffer from low wear resistance. Thus, under wear conditions, nickelbased alloys are typically welded with high-wear-resistance material, such as steels.[1–6] For instance, if the superalloy Inconel 751 is used as a valve material, then steel is often welded with it to achieve high strength and high wear resistance at elevated temperatures. Inconel 751 has a face-centered cubic (fcc) structure strengthened by secondary phases, such as carbides or intermetallic phases of Al, Ti, Nb, and c¢. Usually, martensite stainless steel has high hardness and high wear resistance. Cases of welding nickel-based superalloys with martensite stainless steel have been reported.[7–9] However, the martensite phase in steels may decompose at temperatures higher than 973 K (700 C),[10] thereby considerably diminishing wear resistance. Thus, this YUANZHI ZHU, Professor, is with the Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, P.R. China, and with the College of Mechanical Electronical and Engineering, North China University of Technology, Beijing 100144, P.R. China. Contact e-mail: [email protected] YINGYING GUO, Postgraduate, is with the Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology. LIBIN YANG, Ph.D., is with the School of Mechanical Engineering, Beijing Institute of Technology, Zhuhai 519085, P.R. China. Manuscript submitted July 28, 2012. Article published online January 25, 2013. 396—VOLUME 44B, APRIL 2013
type of compound valve cannot be used at temperatures higher than 973 K (700 C). Furthermore, the fcc structure of nickel-based alloys differs from the bodycentered cubic (bcc) structure of the martensite in steels. Welding materials with completely different structures may cause high residual stress in the welds. The difference in the heat-expansion coefficients of fcc nickel-based alloy and bcc martensite steel should also be considered in the fabrication and service processes of the compound valve parts. Welding martensite steel to a nickel-based alloy to enhance wear resistance is not an ideal solution to achieving both high wearing resistance and high strength at high temperatures. An austenitestructured steel strengthened by solid solution and secondary precipitates may be a better option for being welded with nickel-based alloys. This combination may result in both high wear resistance of the compound parts and low residual stress in the welds. For instance, 21-4N is an austenite steel with high wear resistance at temperatures even as high as 873 K to 1073 K (600 C to 800 C) in the presence of carbides and nitrides in the steel matrix. These temperatures coincide with the operatin
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