In order to study the effects of long-term tempering on properties and microstructure,the performance and microstructure changes of 700 MPa high-strength steel in hot rolling and tempering conditions were analyzed using muffle furnace,SEM,EDS,tensile testing machine,and impact testing machine.The results show that there is a significant change in performance after tempering,which is closely related to the hot rolling process.When tempering temperature is 600℃ and tempering time is 60 min,the ferrite grows significantly,and the M/A constituent decomposes significantly,reducing strength and improving toughness;When the tempering temperature is 570℃ and and tempering time is 65 min,the growth of ferrite is not significant,and the decomposition of M/A constituent is incomplete,which is beneficial for high strength;Granular bainite and fine M/A constituent are the basis for high strength and toughness in 700 MPa high-strength steel.In the presence of large-sized TiN,the transverse impact energy after tempering at-20℃ can reach about 100 J.
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