Specific Features of the Structure, Properties, and Technological Plasticity of Metal Products Made of 03Kh22N5AM3 Corro
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OSION-RESISTANT AND STRUCTURAL STEELS UDC 669.14.018.8
SPECIFIC FEATURES OF THE STRUCTURE, PROPERTIES, AND TECHNOLOGICAL PLASTICITY OF METAL PRODUCTS MADE OF 03Kh22N5AM3 CORROSION-RESISTANT DUPLEX STEEL I. N. Kunitskaya,1 Ya. I. Spektor,1 A. S. Sal’nikov,2 and L. K. Orzhitskaya1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 3 – 14, June, 2020.
We consider specific features of formation of the structure and properties of 03Kh22N5AM3 corrosion-resistant duplex steel in the process of deformation and thermal treatment of rolled milled bars. We analyze the influence of the chemical composition and the conditions of smelting, casting, hot deformation, and heat treatment on the formation of intermetallic phases, which reduce the ductility of the metal. We also give recommendations aimed at increasing the impact toughness of 03Kh22N5AM3 steel at –40 and –46°C.
Key words: ferritic-austenitic steels, phase transformations, nonmetallic inclusions, intermetallic phases, hot deformation, quenching, defects, impact toughness.
in the quiet state begins from the formation of d-ferrite [10, 16]. At 1250°C, d-ferrite transforms into austenite containing larger amounts of Ni, Mn, C, and N, whereas ferrite contains more Cr, Mo, Si, and W. For lower amounts of Cr, Mo, Si, and W, the transformation of ferrite into austenite is facilitated. If the aluminum content is higher than 0.02 – 0.03%, then we observe the formation of aluminum nitride (AlN) whose coarsest particles form in the melt, whereas the main part of fine particles is formed in the process of cooling of the solidified metal within the range 700 – 900°C. Dark hexagonal AlN plates on the boundaries of austenite grains promote a decrease in the ductility and corrosion resistance of steel. The aluminum-nitride particles in the form of elongated prisms and thin light-gray needles are arbitrarily distribution inside the grains and do not lead to the embrittlement of steel. As the temperature of ingot decreases to 900 – 700°C, then we mainly observe the precipitation of Cr2N chromium nitride inside the grains of the ferrite phase [2, 16, 19]. This is explained by a decrease in the solubility of nitrogen in ferrite and the lack of time for its redistribution into the austenite phase caused by the high cooling rate. Chromium nitride located inside the grains decreases the level of plasticity to a less extent than chromium nitride precipitated along the phase boundaries [3, 12, 17, 19, 21].
INTRODUCTION High levels of strength and impact toughness at temperatures from –50 to 300°C in combination with high corrosion resistance and, especially, with high corrosion crack-growth resistance, explain the extensive application of duplex steels in manufacturing of the components and welded structures operating in aggressive media of chemical, oil-and-gas transportation, desalination, and other industries [1 – 11]. After hot rolling, the structure of 03Kh22N5AM3 steel consists of alternating ferrite and austenite grains elongated along the rod in a proporti
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