Microstructure evolution, phase formation, mechanical and tribological response of deep cryogenically treated hard WC-6%Co cutting bits

Abstract

Improving the productiveness of rock cutting bit is an essential requirement for sustainable mining. Different heat treatment techniques are employed in the past to improve the proficiencies of cutting bits. Out of them, cryogenic treatment (CT) is accepted as a viable method for expanding the service life of a variety of cutting tool materials. The intention of the present study is to evaluate the effect of cryogenic treatment under varying soaking duration (12, 24 and 36 h) on hardness and wear resistance of WC-6%Co rock cutting bits. It also addresses the underlying mechanisms that CT carries in the modifications of microstructure and phase transformation. The β-Co phase fraction has been significantly reduced due to cryogenic treatment. The wear resistance of both cryo-treated and untreated bits was examined by scratch test and sliding wear test. From the results, an increase in hardness (CT 24–13.09 %) was observed as compared to UT, which is associated with a transformation from face-centered cubic α-cobalt (FCC α-Co) to hexagonal close-packed ε-cobalt (HCP ε-Co) phase due to cryogenic treatment. The coefficient of friction and wear resistance for the cryo-treated bits correspondingly increases in comparison to the untreated bit. CT 24 bit exhibits the maximum hardness of 2212 HV, an elevated COF (16.64 %) and the highest wear resistance (87.15 %) compared to UT and other CT bits. From the results, cryogenic treatment of cutting bits can be recommended for rock cutting application in mining industries.

Keywords

• Tungsten carbide
• Cryogenic treatment
• Hardness
• Martensitic transformation
• Wear
• Rock cutting bit