Effect of aging treatment on microstructure,hardness and fatigue properties of microalloyed steel MFT8 for fastener with 22.5% in draft was investigated by employing optical microscope,transmission electron microscope,Rockwell hardness and fatigue testing method.The results show that comparison with the original sample,the sample aged at 300 ℃ for 2 h have highest values of hardness and fatigue limit,which is increased by 21.5% and 5% respectively.It is attributed to the formation of stable microstructure r...