On the Densification and Elastic Modulus of Sintered Cr-Mo Steels
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POWDER metallurgy (PM) processes are more competitive than other fabrication methods for numerous materials and finished parts, in part due to their high flexibility for manufacturing a variety of complex-shaped steel parts with accurate and reproducible dimensions, low cost, high performance, and ability to be processed to net or at least near-net shape regarding the manufacturing processes involved.[1–3] The PM press-and-sinter process is characterized by three quantities: powder type, compacting pressure, and sintering cycle. This enables fabrication of porous and pore-free materials and parts of widely different shape, dimensions, and mass just by consolidating powders in the cold condition and with sintering or additional consolidation, i.e., in the solid state without melting, casting, or forming metals.[2–7] More than 80 pct of structural PM parts are used for automobile applications,[1] among them PM steels are becoming more widely used in highly stressed applications, such as con rods and gears, where high fatigue performance is required. These advantages are utilized in two PM steel grades from prealloyed water-atomized powders. Astaloy CrL, which contains 1.5 pct Cr and 0.2 pct Mo, and Astaloy CrM, which contains 3 pct Cr and 0.5 pct Mo, are particularly suitable for high performance applications.[8] During actual service conditions, cyclic stresses on the parts commonly remain within the proportionality limit. Therefore, the main mechanical properties required for
MAZIYAR AZADBEH, Associated Professor, is with the Department of Materials Engineering, Sahand University of Technology, P.O. Box 51335-1996 Tabriz, Iran. Contact-email: [email protected] AHAD MOHAMMADZADEH, Researcher, is with the Young Researchers and Elite Club, Ahar Branch, Islamic Azad University, Ahar, Iran. HERBERT DANNINGER, Professor, and CHRISTIAN GIERL-MAYER, Researcher, are with the Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/CT164, A 1060, Vienna, Austria. Manuscript submitted January 11, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
these parts are high fatigue endurance strength and high Young’s modulus. The design of gears and other mechanical components requires knowledge of Young’s modulus and Poisson’s ratio to calculate the stresses at the point of contact.[9] In general, the Young’s modulus allows engineers and scientists to calculate the behavior of a material under load.[9] Usually, PM products contain pores that strongly affect the physical and mechanical properties. Under service conditions and cyclic loading, porosity reduces the effective load bearing cross-sectional area[10] and acts as a stress concentration site for strain localization and damage, decreasing both strength and ductility.[11,12] Current industrial demands require joint analytical and experimental work to simulate or model the manufacturing process before actual application. There are a number of simulation and modeling methods which are useful for applying to designs before application.
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