Hardening treatment for the sliding supports of drill bits

Abstract

TECHNOLOGY HARDENING TREATMENT FOR THE SLIDING SUPPORTS OF DRILL BITS O. V. Sizova, A. V. Kolubaev, V. I. Koveshnikov, G. V. Trusova, and S. Yu. Tarasov UDC 622.4.051 An increase in the driving rate and a reduction in expenditures for the drilling of wells in modern oil fields depend on the longevity and operating efficiency of the drill bits. The support is an important bit component, which determines the reliability of the structure on the whole. The most common problem in constructing the sliding supports consists in creating sur- faces of high hardness, which are uniform throughout the structure and which are formed from carburized and hardened steels [i] and composition anti-friction materials (for exam- ple, stellite) having a low coefficient of friction and high wear resistance [2]. Broad use of this type of hard-alloy materials as wear-resistant facings suppresses cracking of the facing layer, which significantly lowers the strength and fatigue properties of the sliding surface and is frequently the cause of so-called seizure due to separation of par- ticles in the failed layer. The firm Hughes Tool (United States) has adopted one of the recent technical solutions directed toward support surfaces with a high hardness. According to [3], the sliding sur- face of the bit journal is borided, as a result of which the strength and wear resistance of the support is increased by many times. This form of case hardening (CH) is not em- ployed in the domestic bit industry due to inadequate technical development of the method. We are proposing an original method for the complex boriding of the surface of a bit journal to replace the facing. The developed technology is a variety of CH and makes it possible to produce a wear-resistant layer of from 0.04 to 0.15 mm deep by the method of diffusion saturation with boron and other alloying elements. The studies were conducted on precarburized steel 15N3MA. Commercial boron carbide (GOST 5744-85) with a filler formed from aluminum oxides and other metals and commercial carbon was used as the boriding agent. The boriding was carried out over a period of 5 h0 After boriding, the specimens were subjected to hardening heat treatment. The phase com- position and thickness of the borided layer were determined by the metallographic method of "color etching" [4], from the results of microhardness measurements, and with the use of x-ray spectral analysis. The microstructure of the boride layers produced at different temperatures of the pro- cess is shown in Fig. i. The dark color belongs to the Fe2B phase, and the lighter color on the surface to the FeB phase. Attention is turned to the increase in the content of the FeB phase with increasing CH temperature. The maximum thickness of the FeB phase, as mea- sured over the ends of the boride needles, reached 60 ~m at a temperature of 940~ and the overall thickness of the dual-phase layer amounted to 160 ~m (see Fig. la). Only indi- vidual particles of the FeB phase are exposed at a treatment temperature of 920~ (see Fig. Ib), and iron monoboride is absent at 900~ (see Fig. le). The microhardness of the bo- rides under a loading of 1N amounted to H u = 19500-21500 MPa for the FeB, and H~ = 14000- 17000 MPa for the Fe2B. A characteristic feature of the boride layer produced at temperatures of 900 and 920~ is the "serration" of its structure, in the bed of whose roots a phase that cannot be tin- ted during color etching is present. This phase is manifested in the carburized layer as a result of the boron repelling the carbon back into the depths of the metal, and is, most likely, ultradisperse martensite. Its microhardness, as measured under a load of 1 N, is H u = 10000-11000 MPa. By varying the CH temperature, therefore, it is possible to obtain qualitatively dif- ferent structures of the boride coatings. The phase composition of the boride layer assumes Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 4, pp. 25-27, April, 19937 188 0009-2355/93/0304-0188512.50 9 1993 Plenum Publishing Corporation