Finding
The third viewpoint is that the white layer is a result of combined action between cutting heat and plastic deformation(Bosheh and Mativenga, 2006; Han et al., 2008; Rancic et al., 2017).
Paper
White layer formation mechanism in dry turning hardened steel
Abstract
Dry-hard high speed turning has advantages in high efficiency, environmental protection and so on compared with traditional machining, so it is more and more used in machining hardened steel( Guo and Waikar, 2010; Zhang et al., 2017). However, the researches have shown that the microstructure of machined surfaces produced by dry-hard turning is different from that of substrate and the white layers can be observed under optical microscope ( Guo and Waikar, 2010; Huang et al., 2015). White layer is at top surface of machined surface, so the microstructure and formation law of white layer have great effect on performance and service life of workpiece. The studies have been conducted on white layer formation mechanism, one viewpoint is that white layer is a product of phase transformation(Kundrák et al., 2012; Pálmai and Kundrák, 2016; Umbrello, 2013). Chou and Evans (1999)used the Al2O3-TiC ceramic tool to cut hardened AISI52100 steel, the result shows the volume fraction of austenite in the white layer is more than that in the substrate, so they consider that large amount of cutting heat generated in cutting process causes surface temperature up to austenite phase transformation temperature, then the machined surface is rapidly cooled after contacting with air and undergoes martensite transformation. Another viewpoint is that the plastic deformation is a main factor in formation process of white layer(Hosseini et al., 2015; Ranganath et al., 2009; Zhang et al., 1997). Rice et al.(1991) observed the white layer through transmission electron microscopy(TEM),the result shows that the dislocations with high density exist in the machined surface. Severe plastic deformation forms a mass of dislocation, resulting in the refinement of grain size. The third viewpoint is that the white layer is a result of combined action between cutting heat and plastic deformation(Bosheh and Mativenga, 2006; Han et al., 2008; Rancic et al., 2017). Ramesh et al.(2005) investigated the white layers at different cutting speed, they demonstrate that the white layers are produced by grain refinement caused by plastic deformation at low cutting speed, while it is produced by phase transformation induced by cutting heat when cutting speed is high. Hard turning is a process of thermal-mechanical coupling, the formation of white layer is accompanied by both cutting heat and plastic deformation, so the formation
Authors
C. Duan, Zhang Fangyuan, Wei Sun
Journal
Journal of Advanced Mechanical Design Systems and Manufacturing