Effect of Aging on Structure and Properties of a Transformation-Induced Plasticity-Aided High-Manganese Steel

This paper reports the results of investigation on 0.1C-17Mn-5.5Ni-1.8Al-2.7W-4.6Mo-2.3Cu-0.002B steel designed to assume excellent combination of strength and toughness. The air induction melted steel was subjected to hot forging at 1200 °C followed by hot rolling in six passes from 1100 °C. The rolled samples were reheat-quenched from 1050 °C in iced water. The quenched samples were isochronally aged at temperatures within 500-650 °C at interval of 50 °C. The mechanical properties were determined by hardness measurement and tensile testing. Structural characterization was accomplished by x-ray diffraction, optical and electron microscopy. Differential scanning calorimetric study was conducted to understand the precipitation kinetics. A typical age-hardening behavior was noted in the aged samples due to the precipitation of M2C and Ni3Al. Strain hardening of martensite, precipitation hardening due to the presence of nanosized precipitates and Orowan hardening were found to be instrumental in attaining a maximum hardness of 723 HV. The microstructure of aged samples consists of retained austenite, e-martensite, α′-martensite and uniformly distributed nanosized precipitates of Ni3Al and M2C, lying broadly within two different size regimes. The sample peak aged at 550 °C attained a strength of 1.4 GPa at a total elongation value of 25%. The combination of high strength and high ductility has resulted from precipitation strengthening, TRIP phenomenon and high degree of structural fineness.