Effect of h-BN on the turning performance of high-strength vermicular graphite cast iron

Abstract

Hexagonal boron nitride (h-BN) is an excellent solid lubricant that can be used to improve the processability of difficult-to-cut materials. We tried to solve the processing difficulty of vermicular graphite cast iron (VGI) by adding 0.0144 wt% of h-BN micro-powders into VGI (tensile strength Rm ≥ 450 MPa). Then, we use coated cemented carbide tools (CCC tools, coatings TiC + Al2O3) to carry out the turning test on VGI. By analyzing the maximum wear maxVB of the flank face, the wear morphology characteristics of rake face, and the residue on rake face, the wear mechanisms of the tool are studied. Finally, the role of h-BN in the processing process is assumed and the Gray-Markov model of maxVB is modeled. It can be found that: when v = 100~200 m/min, the tool life of cutting VGI with h-BN (sample A) was twice that of cutting VGI without h-BN (sample B). In particular, when v = 200 m/min, the tool life of cutting sample A is as high as 8 min. It is shown that h-BN can make CCC tools have the same advantages as PCBN tools in cutting VGI. In cutting sample A, the wear mechanisms of rake face are abrasive wear, adhesive wear, and oxidation wear, and adhesive wear is the main cause of tool failure. Given the cutting speed, when t ≥ 2 min, the adhesive wear of the rake face in cutting sample A is slighter than that in cutting sample B. h-BN can effectively reduce the adhesive wear. The error of maxVB predicted by Gray-Markov model is Δ ≤ 1.25%, which can be used to analyze and predict the tool wear of VGI with h-BN.