Abstract: The optimum heat treatment procedure for a CB80 linepipe is determined by evaluating its quenching hardness,microstructure and grain size.The analysis shows that when the quenching temperature is 1 020℃ and the tempering temperature ranges in 560~580℃,the performance of a CB80 linepipe will meet the requirements of API Spec 5L-2012 for X80QO steel grade,and it will have pretty good low-temperature impact properties.Nb,V and Ti can fully dissolve in austenites at 1 020℃ and precipitate during tempering,which will strengthen and improve the performance of a pipe.The precipitates in a quenched and tempered CB80 linepine are mainly NbC and a small amount of TiN.The microstructure of a quenched and tempered CB80 sample is mainly composed by tempered lath martensites and precipitates.After tempering,the martensite will show fewer carbides and less dislocation density.