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- 저자 : Kausik Chattopadhyay (검색결과 1 건)
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Sandeep Kumar Gupta,R. Manna,Kausik Chattopadhyay 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.9
In the present study, carbide-free nanostructured bainite is produced by austempering high carbon and silicon steels at 250 °C. Fine pearlitic structure is also made by patenting the steels of selected compositions at 550 °C. The formation of carbidefreenanostructured bainite and retained austenite in the austempered steels and ferrite and cementite in patented steels wereconfirmed through X-ray diffraction and TEM studies. The optical, scanning and transmission electron microscopies revealthe presence of nanoscale bainite, filmy and blocky austenite in austempered steels and the presence of lamellar pearlite inpatented steels. Increasing austempering time enhances the amount of bainite but decreases the blocky retained austenite. Thecorrosion behaviour of the newly developed bainitic steels is compared with that of pearlitic steel of the same compositions. Electrochemical and immersion corrosion tests are conducted in an aqueous 3.5% NaCl solution. The corroded surfaces areanalyzed with the scanning electron microscope (SEM) and X-ray photoelectron spectrometer (XPS). Corrosion resistanceincreases with increasing carbon percentage due to the formation of magnetite (Fe3O4), provided the content of other alloyingelements remains the same. The presence of Ni decreases corrosion rate significantly, i.e., enhances corrosion resistance,charge transfer resistance (Rct) and polarization resistance (Rp). Reducing retained austenite in nanostructured steel decreasesthe corrosion rate due to the lesser area of Galvanic couples and the formation of uniform, compact, and non-porous passivelayer. The bainitic steel samples demonstrated superior corrosion resistance to that of the pearlitic steel due to lesser cellformation. The corrosion mechanisms of high-carbon bainitic and pearlitic steel are discussed.
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