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Indrajit Dey,Rajib Saha,Swarup Kumar Ghosh 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7
The influence of isothermal holding (IH) near the pearlite start temperature (Ps≈610 °C) and above the martensite starttemperature (Ms≈245 °C) were studied in two hot-rolled (FRT≈1000 °C) high carbon steels, without (HC0) and with Nbmicroalloying (HC1). Optical microscopy (OM), field emission scanning electron microscopy (FESEM) and high-resolutiontransmission electron microscopy (HRTEM) were utilised for observing the microstructural constituents whereas, nanoindentationand microindentation were performed to estimate the average hardness and elastic modulus values of various phaseconstituents. It has been observed that hot deformation in the austenite region results in the formation of a dual phase-typemicrostructure consisting of fine pearlite lamella and ferrite grains with some amount of degenerated pearlite. IH at 570 °Cleads to a higher volume percentage of ferrite and coarsening of pearlite whereas, IH at 300 °C results in mixed phases comprisingbainite, a very low amount of martensite/retained austenite (M/RA), pearlite and some amount of ferrite. Hot rolledmicroalloyed steel when isothermally held near the Psresults in a significant enhancement of ductility than hot rolled andair-cooled condition while sacrificing tensile strength marginally, which may be attributed to a higher percentage of ferriteand refinement of pearlite due to Nb addition. The estimated yield strength values correlate well with those experimentalyield strength values, but a little discrepancy has been noticed for the ultimate tensile strength values. Possible interpretationsare suggested in this paper.