Development of (Nb 0.75 ,Ti 0.25 )C-Reinforced Cast Duplex Stainless Steel Composites
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IN the design of pump components, proper alloy selection is crucial for maximizing service life. In this specific context, the dominant material failure mode is erosion-corrosion[1] and therefore, the selected alloy must be able to resist the synergistic attack of erosion and corrosion simultaneously. In applications where erosive wear dominates the effects of corrosion, white cast irons such as Ni-hards and high Cr white cast irons are favored, with the latter preferred in more severe erosive conditions.[1] These alloys achieve their excellent erosion resistance by containing a significant volume fraction of extremely hard M3C and/or M7C3 carbides (where M denotes the metallic elements that form the carbides, which in this case is mainly Fe and Cr). While Cr is known to confer corrosion resistance to ferrous
WEN HAO KAN and JULIE CAIRNEY are with the School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006, Australia and also with the Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, NSW 2006, Australia. Contact e-mail: [email protected]. ZIYAN MAN, SIYU HUANG, and LI CHANG are with the School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney. KEVIN DOLMAN, TIMOTHY LUCEY, and XINHU TANG are with Weir Minerals Australia, Artarmon, NSW 2064, Australia. GWE´NAE¨LLE PROUST is with the School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia. Manuscript submitted July 10, 2019. Article published online February 18, 2020 2366—VOLUME 51A, MAY 2020
alloys, this only occurs if it is in solid solution. Therefore, despite the high Cr contents in high Cr white cast iron alloys, these alloys typically only have moderate corrosion resistance as a significant amount of Cr is usually tied up as M7C3 carbides and is not in solid solution within the ferrous matrix.[2] CD4MCu, a cast Fe-Cr-Ni-Cu-Mo duplex stainless steel (with duplex denoting near equal proportions of ferrite and austenite), is a stainless steel grade used for pump components.[3] It should be noted that the term ‘‘CD4MCu’’ is based on the recommended designation system for cast stainless steels as specified by ASTM A781/A781M which denotes the various stainless steel grades by composition and this designation system is different from the AISI or UNS numbering system commonly used to refer to wrought stainless steels.[4] Due to its Cr and Mo contents (approximately 26 wt pct and 2 wt pct, respectively), this stainless steel has excellent pitting corrosion resistance when cast according to specifications.[5] However, as pump parts are typically very large, it is extremely challenging to cast them from this stainless steel while maintaining adequate microstructural quality (i.e., obtaining the desired fraction of phases without the formation of unwanted phases) and precise dimensional control.[3] Even if a pump component is fabricated within specification, CD4MCu is mainly only suitable for environments where corrosion dominat
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