Dry Hard Cutting Materials To Be Machined Surface White Layer

Hard turning is regarded as one kind of the new prosperous processes today. It means finishing bearing steel harder than 50HRC with superhard cutting tools . It can achieve high precision and good surface quality, so it becomes a new method to finish hardened work-pieces. Furthermore, Hard turning is the best choice to finish hardened bearing steel because of its flexibility, economy and environmental protection. The surface integrality of hard turning includes surface roughness, dimension precision, the depth of rigidification, the distributing of remaining stress and the formation of white layer. All of them are important indications which determine whether hard turning can be used as a new kind of finishing methods or not. The white layer forms a different structure during the hard turning. Its hardness is higher than bulk, and it also can resist normal eroding. Its thickness is so small that its structure is difficult to be identified. White layer has special wearing characteristics: on one hand, the high hardness can bring good wear-resisting property; on the other hand, its brittleness induces flake梠ff.White layer is found at the surface of the GCrl5 work-piece hard-turned withthe PCBN tool, and the factor of its formation is studied through experiment.The thickness of white layer is measured and its microstructure of is observedwith SEM. It is found that the white layer forms only when cutting with the worntool, and its thickness is increased with the wearing of the tool.The influence of the cutting-amount of hard turning on the thickness of white layer is studied through orthogonal experiment, such as cutting velocity, feed rate, cutting depth, based on the white layer is found at the surface of the GCrl5 work-pieces hard-turned with the PCBN tool. The formation mechanism of white layer is also discussed.The wear-resisting properties of the work-pieces turned with the PCBN tool and the traditionally grinded work-pieces are contrasted, as the white layer oduced during the hard-turning process on the surface of the work-pieces induces the change of its hardness and microstructure. The experimental results show that the work-pieces hard turned have better wear property than the ones grinded when wearing at low relative sliding velocity, even under high load; but worse when at high relative sliding velocity.