Abstract
A novel microalloy Q&P steel with Nb and Mo is designed. The dilatometric curves of low-carton microalloyed Q&P steel with and without Nb and Mo are detected at different cooling rates on DIL-805 thermal dilatometer．The CCT curves are determined using thermal dilation measurement, microstructure observation and hardness measurement. In the Q&P process, the niobium carbide precipitate plays a precipitation strengthening effect, so the tensile strength of Q&P steel is enhanced. The results show that: The element Nb decreases the phase-transformation temperatures of ferrite and pearlite, which leads the proeutectoid ferrite and pearlite phase transformation finish lines to move to lower-right. For the low-carton Q&P steel microalloyed with Nb and Mo, when cooling rate is higher than 5°C•s－1, the microstructures is only martensite. Its excellent hardenability is propitious to improve the strength of the Q&P steel. While, for the traditional C-Si-Mn Q&P steel, the martensite can be only obtained until the cooling rate higher than 20°C•s－1.
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