Green cutting is ecologically desirable and have been a tendency in the industry field. Water vapor can be introduced in metal cutting as coolant and lubricant due to its pollution-free, generating easily and unneeded disposal. Therefore, water vapor is an environment-friendly coolant and lubricant in machining. This study attempts to understand the effect of water vapor as coolant and lubricant on chip formation. In the comparison experiments to dry and wet cutting, water vapor jet flow from a developed generator is applied into cutting zone directly. When YG8 (K20 in ISO) tools are used to turn titanium alloy TC4 (Ti-6Al-4V), Ni-based super alloy GH3030 and stainless steel 1Cr18Ni9Ti in orthogonal cutting, through quick-stop tests, the photos of polished chip sections microstructure were obtained. And the results suggest that the application of water vapor produces the least BUE, tool-chip contact length but the largest deformation coefficient and shear angle. The water vapor as coolant and lubricant could be a substitution of cutting fluid to carry out green cutting in the machining of difficult-to-cut materials.