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This paper is focused on the study of the effect of high heating rates on austenite
formation of 18NiCrMo5 steel. The prior martensitic microstructure was characterized with
scanning electron microscopy and Vicker micro-hardness. Then dilatometric tests were
performed at 12 different heating rates (in the range of 100 - 3000œC/s), to evaluate the
critical points and the key factor governing the austenite formation with high heating rates.
After these tests, the microstructures obtained were analyzed by optical microscopy, scanning
and transmission electron microscopy. The Ac1 and Ac3 temperatures initially increased with
heating rate, reaching a maximum and then decrased. The formation of austenite from
martensite, with low heating rates, was diffusive, whereas with high heating rates, it took
place through a displacive mechanism. Moreover, a higher dislocation density characterized
the austenite obtained with high heating rates.
Keywords: low alloyed steel, 18NiCrMo5, austenitization, heating rate, austenite, martensite |
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