Abstract: The present study was attempted to explore the effects of V and austenitizing temperature on continuous cooling transformation (CCT) beha-vior of bainitic forging steel. Mn-Cr type bainitic forging steels microalloyed with V (0.13wt%) and without V (0wt%) were austenitized at three different temperatures (900℃, 1 050℃ and 1 150℃) and then continuously cooled by using thermal dilatometer to study their CCT beha-vior. Microstructural observations and Vickers hardness measurements of the cooled samples were carried out as complements for the accurate plot of the CCT diagrams. The results show that both V and austenitizing temperature have significant influence on the CCT diagrams. It was difficult to obtain full bainitic (≥90vol% bainite) microstructure when austenitizing temperature was 900℃, while it could be obtained at relatively lower cooling rate when the austenitizing temperature was raised to 1 050℃ and 1 150℃. When austenitizing temperature was 900℃, V showed notable effect on the CCT diagram and the cooling rate range obtaining bainite was broadened and the bainite fraction was enhanced. When the austenitizing temperature was increased to 1 050℃ and 1 150℃, the lowest cooling rate obtaining full bainitic microstructure was lo-wered from 0.86℃/s to 0.43℃/s for austenitizing temperature of 1050℃ and from 0.26℃/s to 0.16℃/s for austenitizing temperature of 1 050℃, and the bainitic transformation range was broadened to as low as 0.08℃/s by the addition of V. It is also found that the hardness was increased by the addition of V and this increase degree depends on austenitizing temperature and cooling rate. A peak value of hardness increase as high as 66HV5 at cooling rate of 0.88℃/s could be obtained for austenitizing temperature of 900℃, while the peak value of hardness increase was significantly decreased to 38HV5 at cooling rate of 0.17℃/s for austenitizing temperature of 1 050℃ and to 30HV5 at cooling rate of 0.08℃/s for austenitizing temperature of 1 150℃.
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2020, Vol. 34 
