Frication behaviors, wear and failure mechanisms of CBN tool and machined surface morphology in high-speed turning of high strength refractory alloy cast steel

Abstract

High strength refractory alloy cast steel GX23CrMoV12-1 is widely used in the combustion chambers of heavy duty gas turbine due to the high strength, hardness and heat resistant. However, the poor machinability and severe tool wear seriously hinder the further application of GX23CrMoV12-1. To reduce the tool wear, the cubic boron nitride (CBN) tool was used for turning GX23CrMoV12-1 considering the extreme hardness and chemical inertness of CBN. The wear curve and evolution, frication behaviors, wear and failure mechanisms and their transformation of CBN tool, and machined surface morphology of workpiece at various cutting speed were investigated in turning of GX23CrMoV12-1. The results show that: The wear life of CBN tool increases and then decreases with the increment of cutting speed, and the optimal cutting speed is 200 m/min. The CBN tool is mainly characterized by brittle fracture and adhesive wear. At medium-low cutting speed (100–150 m/min), the tool substrate is easily peeled off due to the frication and scratch of chips, resulting in large pieces peeling off, finally, forming catastrophic fracture. At high cutting speed (200–300 m/min), the frequency of the tool substrate peeling off decreases and no catastrophic fracture forms, but abrasive wear increases. The frication coefficient of CBN tool is about 0.2 in dry turning of GX23CrMoV12-1. Additionally, roughness Sa of workpiece decreases and then increases with the increment of tool wear. These findings provide significant guidance for parameters selection and tool wear suppression in machining of heavy-duty gas turbine.