Effect of heat treatment process on microstructure and properties of KD sucker rod steel

Mechanical properties and microstructure of KD grade experimental steel used for sucker rod, after three different heat treatment processes, were studied by means of mechanical properties test, OM, SEM and TEM. The results show that the comprehensive mechanical properties of the material are the best when tempering temperature starts from room temperature. The impact property of the material obtained is worst when tempering temperature starts from 500℃,which is due to the uneven distribution of M+A islands in granular bainite with different shapes, and the majority is large blocks with sharp corners, which results in stress concentration. The second phase precipitates make the material have higher strength.