Effect of different mo contents on tensile and corrosion behaviors of CD4MCU cast duplex stainless steels
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I. INTRODUCTION
THE use of duplex stainless steel is gradually increasing in areas where the combination of good mechanical and corrosion properties is required.[1,2,3] Since the development of first-generation duplex stainless steels in the 1930s, continuing research efforts have been exerted to improve the mechanical and corrosion properties, particularly by the various alloying additions of N, Cr, W, Mo, etc.[4–11] At present, however, most of the research on duplex stainless steel has been performed on the wrought products, and only a limited number of studies have been reported on the cast products of duplex stainless steels, despite their significance in the industry. Previously, the authors examined the tensile and corrosion behaviors of CD4MCU cast duplex stainless steels with different N and Cr contents and reported that the mechanical and corrosion properties were strongly influenced by the change in the shape and volume fraction of austenitic phase with different amounts of N or Cr.[4,5,7] Mo is a strong ferrite-stabilizing element and is known to improve the resistance to corrosion by the formation of a stable passive film on the surface of the stainless steel.[12–15] Despite the beneficial effect of Mo in stainless steel, the effect of Mo on the mechanical and corrosion behaviors of cast duplex stainless steels has not been well established. The objective of the present study was, therefore, to examine the effect of Mo on the tensile and corrosion behavior of CD4MCU cast duplex stainless steels. The in-situ slowstrain-rate (SSR) tests were conducted in air and in a 3.5 pct YOUNGHWAN JANG, Graduate Student, and SANGSHIK KIM, Associate Professor, are with the Division of Materials Science and Engineering, Engineering Research Center, Gyeongsang National University, Chinju, 660-701, Korea. Contact e-mail: [email protected] JEHYUN LEE, Associate Professor, is with the Department of Metallurgical Engineering, Changwon National University, Changwon, 641-773, Korea. Manuscript submitted July 13, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
NaCl 5 pct H2SO4 aqueous solution to quantify the resistance to stress-corrosion cracking (SCC) with different Mo contents. The changes in the volume fraction and shape of the austenitic phase with different Mo contents were correlated with the tensile and corrosion behavior of the present alloys based on the optical and scanning electron microscope (SEM) micrographic and fractographic observations. II. EXPERIMENTAL PROCEDURES In the present study, CD4MCU cast duplex stainless steels with different Mo contents of 0, 2, and 4 pct, respectively, were used. Table I represents the actual chemical compositions of the alloys used in the present study. The alloys were designated as CD4MCUMo0, CD4MCUMo2, and CD4MCUMo4, respectively, depending on the Mo content. The alloys were melted at 1620 °C using an induction furnace and, subsequently, were sand cast into a Y-block mold. Each alloy was solution heat treated at 1050 °C for 2 hours. The microstructure of each alloy specimen
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