Processing of a new high strength high toughness steel with duplex microstructure (Ferrite + Austenite)

Effects of isothermal transformation conditions on the microstructure and hardness values of a high-carbon Al–Si alloyed steel

“…13 that the hardness increases as the transformation temperature is reduced. Two opposing trends have been reported [2][3][4]57] in the variation of hardness with austempering temperature. Putatunda [2] reported that hardness was increased with increasing transformation temperature over the range of 316-371°C, although no argument was presented.…”

“…Putatunda [2] reported that hardness was increased with increasing transformation temperature over the range of 316-371°C, although no argument was presented. On the other hand, Putatunda et al [3], Martis et al [4] and Yoozbashi and Yazdani [57] reported that the hardness decreased as the transformation temperature increased within the ranges of 260-400°C, 371-399°C and 200-300°C, respectively. This Fig.…”

“…Carbide-free bainitic microstructures lead to high strength combined with respectable levels of ductility [4,18,[40][41][42]. Fig.…”

“…Nucleation driving force as a function of temperature for the investigated steel, calculated using MAP program MUCG83, and change in retained austenite volume fraction with austempering temperature, estimated by MIP image analyzer system. was attributed to the coarsening of both bainitic ferrite and retained austenite [4,57] and presence of the larger volume fraction of austenite [3,4] at higher austempering temperatures. As discussed in Sections 3.1.1 and 3.1.2, in the present case, no substantial refinement of bainitic ferrite was detected with decreasing transformation temperature.…”

“…Notable mechanical properties of austempered steels make them ideal replacement materials for quenched and tempered (QT) steels and austempered ductile cast irons (ADI) in an increasingly large number of applications, especially in railway and automotive industries [1][2][3][4][5][6][7]. The microstructural features of austempered steels, especially plate size of bainitic ferrite and volume fraction of retained austenite, are most seriously affected by the austempering variables, i.e., austempering temperature and time [8][9][10].…”