Analysis of Causes for Cracking of 37CrMnMo Drill Pipe Joint

With the magnetic particle test cracks are found in some of the 37Cr MnMo drill pipe joints of a certain lot as quenched and tempered.In order to identify the causes for the cracking,the joints and crack-bearing parts of the joints are analyzed in terms of chemical composition, metallographic structure, mechanical properties and crack morphology,etc.As a result,the following reasons for the cracks are identified.Before forged,temperature of the joints as heated in the MF induction furnace is so high that they are overheated,and even over burnt,resulting in the alloy element segregation along the grain boundary,and grain boundary weakening which are not fully eliminated in the subsequent heat treatment process so as to get cracks produced during the quench-temper process as follows.Accordingly,necessary measures are proposed,including strengthening in-process inspection of the chemical composition of the drill pipe joint as forged,strictly monitoring the heating temperature and soaking time of the steel blank, and properly determining the process parameters so as to prevent over-burning of the joint,and improve the quality thereof.