To improve the high yield ratio and narrow tempering range of high strength hull steel,the effect of intercritical quenching temperature on the microstructure and properties of Ni-Cr-Mo-V steel was investigated.The impact tensile properties and microstructure of the experimental steel were examined by changing the secondary quenching temperature,and characterized by MO,TEM,X-ray diffraction and other methods.The results show that in quenching temperature range,the properties of the material show two phenomena:when the quenching temperature between 640 to 700 ℃,the strength of steel increases with the increase of intercritical temperature,and the toughness decreases.In this quenching temperature range,the mechanical properties of the material are determined by the composition of F&M microstructure and the formation of reversed austenite.With the increase of the intercritical quenching temperature,the proportion of F in the dual phase structure decreases from 40％to 10％and the content of reversed austenite reduces from 11％to 1％.When the quenching temperature varies from 700 to 780 ℃,the change of strength and toughness of test material is not obvious.The main reason is that the intercritical quenching temperature exceeds the A3 temperature,the steel transforms into a single martensite structure after cooling,and the change of austenite grain size is not significant,specifically between 7.3～8.5 µm.The results show that the best match of strength and toughness can be achieved by intercritical quenching at 680 ℃.
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