Abstract
In general, there is a steep decrease in cryogenic (−196 °C) impact absorbed energy of high Mn austenitic steels after aging at 600–800 °C, which is also the temperature range of aging precipitation. Thus, the precipitation hardening is hardly used in hot-rolled high Mn austenitic steel for cryogenic application and its effect on cryogenic impact toughness is also not understood up to now. In the present work, A high Mn austenitic steel alloyed with Al and V was designed, and the effect of aging temperature on the evolution of microstructure and mechanical properties was investigated by means of electron backscattered diffraction, transmission electron microscopy and X-ray diffraction. The grain size is nearly not affected by aging temperature, exhibiting similar grain size of 6.7–8.1 μm, but the volume fraction and size of precipitated particles greatly depend on aging temperature. The average particle size slightly increases from 5.6 to 6.7 nm with increasing aging temperature from 550 to 650 °C, whereas the precipitated particles are greatly coarsened at 700 °C and the average particle size reaches 16.3 nm. These fine particles can provide a sufficient precipitation hardening of about 200 MPa, leading to a high yield strength of 587 MPa. Meanwhile, this strong precipitation hardening only slight lowers cryogenic impact absorbed energy from 132 to 97 J, also implying that the above-mentioned aging brittle effect should be suppressed or very weak.
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