Study On Microscopic Mechanism Of Chip Formation Of Stainless Steel During High Speed Machining

The high speed machining has been a mature modern advanced manufacturing technology. A lot of study on high speed cutting theory has been done, and the theory of chip formation is an important part of the theoretical research of high-speed cutting. The study on the theory of serrated chip formation has made some achievements, but a lot of problems has been not solved, further study is necessary, too. The chip formation mechanism during high speed cutting stainless steel has been not recognized clearly and comprehensively, the paper will study on it comprehensively.In this paper, chips formed in different cutting conditions be collected through high speed cutting0Cr18Ni9stainless steel,the cutting force be measured at the same time, to analyze the influence of cutting conditions on cutting forces and chip morphology.Then, the microstructure observation and testing methods included SEM、TEM、EPMA and XRD, be used to observed the microstructure of the adiabatic shear band and the microstructure of the bottom edge of the serrated chip,the microstructure of the fracture surface of serrated chips. Combined with the related theories, analyzed the chip formation mechanism. The main conclusions are as follows:1) As the cutting speed increases, the cutting force increases firstly and then decreases. As the cutting depth increases or the rake angle decreases, the cutting force increases. As the cutting speed increases or the cutting depth decreases or the rake angle decreases, the degree of chip saw-tooth improved.2) According to SEM observation of stainless steel adiabatic shear band microstructure, the adiabatic shear band deformation intensified, the deformation mechanism changed with the increase in cutting speed, the increase of cutting depth and rake angle decreases. According to TEM observation of the micro-organization of the adiabatic band, the austenite grain fragmentation happened at lower cutting speed, the dynamic recrystallization of austenite happened in higher speed cutting. According to the EPMA observation, the elemental composition does not change during the adiabatic band formation process. Therefore, the conclusion as follows:(1) in lower cutting speed, the adiabatic shear band happened shear deformation and formed the deformation band;(2) at higher cutting speed, the adiabatic shear band happened dynamic recrystallized and formed transformed band;(3) in the process of adiabatic shear band formation no phase transition occurred.3) According to SEM observation, the morphology of the fracture surface of serrated chips included two morphologies included the torn ridge and flat surface, is pure shear and slip fracture surface. As the increases of cutting speed, increases of cutting depths or decreases of the rake angle, the surface becomes more and more flat and torn ridge become more and more small.4) According to SEM observation, the microscopic bottom edge of the chip formed in high temperature, high pressure and big shear force microscopic structure, divided into three different degrees of metamorphism area:(1) the underside of bottom edge of chip is the amorphous microstructure;(2) Near the underside is the microstructure of refined grain;(3) Far from the underside is the deformed microstructure. As the cutting speed increases, or the cutting depth increases, or the rake angle decreases, the thickness of bottom edge increases, the amorphous microstructure increases in the amount, the recrystallized structure is denser, deformed microstructure deformation increased...