THE ASSESSMENT OF THE EFFICIENCY OF CARBONITRIDING PROCESS APPLICATION FOR HARDENING OF THE THREADED JOINTS OF DRILL PIPES MADE OF FOREIGN BLANK PARTS

Currently, one of the effective methods of surface hardening of steels and alloys is chemical heat treatment (ChHT) - carbonitriding - simultaneous saturation of steel surface with nitrogen and carbon in molten salts at the temperature of 540-580 °С. This method of surface hardening allows achieving high performance of a hardened layer; however, the influence of carbonitriding on the properties of the base metal, which is inevitably exposed to heating during the saturation process, remains unexplored. It is particularly topical for steels, in which temperature interval of technological process implementation of 540-560 °С coincides with the interval of temper embrittlement manifestation. In this work, the authors tested the carbonitriding technology to strengthen the threaded joints of drill pipes for the complexes with removable core receivers, studied the kinetics of the carbonitrided layer formation on the Drillmax 950, 4130 and 1541 grades of steels. The paper considers the influence of the carbonitriding process on the mechanical properties of steels under the study. The authors carried out the analysis of the structure of fractures of Drillmax 950, 4130, and 1541 steel before and after carbonitriding and identified that the influence of carbonitriding in the Drillmax 950 steel is more visible in the form of development of the temper embrittlement processes. The authors estimated the dependence of the performance characteristics of a finished threaded connection on the duration of the carbonitriding process. The study shows that the threaded connections of 1541 steel have a high level of fatigue resistance. The authors recommended 1541 steel to produce the locking joints of drill pipes with the thread surface hardening by carbonitriding.

drill pipe, threaded joints, carbonitriding, impact strength, temper embrittlement, cyclic durability, tightening limit moment