Study On Tmcp Schedule And Heat Treatment For Q690q Bridge Steel

The paper is mainly about the research of laboratory rolling and heat treatment processes ofa high stength low alloy bridge steel with the yield stength of690MPa.Based on the laboratoryexperiments,the impacts of the strain of accumulated defomation and finishing rollingtemperature on microstucture and property have been investigated, and from the results theappropriate rolling process was aquired: the steel begins its finishing rolling at920℃, ends at830℃, then cools down with acooling rate of12℃/s till530℃,and then air-cools to roomtemperature.After the application of above process, we obtain a Q690steel with a microstuctureof the combination of granular bainite,lath bainite and ferrite.Compared with GB/T714-2008, thetensile strength and low temperature impact property of the steel through such TMCP process arelower.In order to improve the mechanical property,some modifications have been applied on thesteel.Considering the influences of quenching temperature,quenching holding time,temperingtemperature and tempering holding time on microstucture and mechanical property,an heattreatment process was established: keep at940℃for15minutes before quenching, and temper at630℃for20minutes. After the heat treatment, the microstucture was changed to polygonalferrite and the mechanical property improved a lot, eapecially for the impact property, it was2~3times higher than before. The modification process reduced the M/A size and dislocation density,and attributed to it the experiment steel exhibited high stength while excellent low temperatureimpact toughness.