Wear characteristics and micro-cutting damage model of cemented carbide by deep cryogenic treatment

Abstract

Wear failure of oil drill bits leads to cost increase, and how to improve the abrasion resistance of cemented carbide (WC–Co) drill bits is an urgent problem, and deep cryogenic treatment (DCT) is a feasible method. The effect of DCT time (i.e., 0, 3, 6, 9, 12, 24, and 48 h) on the Vickers hardness, flexural strength, and wear rate of WC-Co with different Co contents (i.e., 5 wt%, 8 wt%, 10 wt%, and 12 wt%) was investigated. The results showed that the best DCT time for hardness, flexure strength, and abrasion resistance of WC-Co was 12 h. Compared with untreated (e.g., 0 h), the wear rates of WC-Co with different Co contents were reduced by 36%, 34%, 30%, and 19%, respectively at DCT-12. Compared with WC-12Co, the wear rate of WC-5Co with different DCT times was reduced by 75%, 77%, 78%, 78%, 80%, 79%, and 78%, respectively. The precipitation of η phase (Co6W6C), martensite phase transformation (α-Co to ε-Co), and the increase of residual compressive stress (RCS) of WC after DCT improved the hardness, flexural strength and reduced the wear rate of WC-Co. Based on the principle of frictional wear, a micro-cutting wear model considering Co content and DCT time is proposed, which can predict the evolution of the wear rate of WC-Co. The results of the study guide improving the wear resistance of drill materials.

Keywords

• Cemented carbide
• Deep cryogenic treatment
• Wear rate
• η phase
• Martensite phase transformation
• Residual compressive stress