Microstructural transformation analysis of cryogenic treated conical rock cutting bits for mining applications

Enhancing the performance of rock cutting bit is an important aspect in reducing mining cost. To enhance their cutting characteristics, rock cutting bits are exposed to different heat treatment techniques. In this research work, an attempt has been made to strengthen the wear resistance of rock cutting bits through sub-zero heat treatment process called cryogenic treatment. The influence of cryogenic treatment (−196 °C) with different soaking duration (6, 12, 18, 24, 30, 36 h) on the microstructure of tungsten carbide (WC-Co) rock cutting bits is investigated through FESEM with the treatment mechanism being elucidated. Hardness of treated and untreated bits was measured using Vickers micro-hardness tester and the variation of crystal phases was examined through X-ray diffraction studies. Rate of bit wear was observed by performing wear studies through pin on disc tribo-meter with different load (5, 10, 15 N) and sliding speed (1, 1.5, 2 m/s). The results showcased the increase in bit hardness, microstructure transformation of martensitic phase (fcc α-Co to hcp ε-Co), hard η carbide formation (Co ₃W ₃C, Co ₆W ₆C) and enhanced wear rate for treated bit as compared to untreated bit. From the results, it was revealed that CT 24 treated bit possessed highest hardness (1078 HV) and nominal wear rate (87.50%) than UT and other CT bits under 15 N load at 2 m/s.