A comprehensive investigation on the effect of flood and MQL coolant on the machinability and stress corrosion cracking of super duplex stainless steel

Abstract

The poor machinability of super duplex stainless steels (SDSS) tends to generate detrimental tensile residual stresses that affect the service life of the component. Therefore, developing an efficient machining strategy to machine these components without any subsurface modifications is necessary. This work emphases on a detailed analysis of machinability and stress corrosion cracking resistance (SCC) of SDSS under different coolant environments (Dry, Flood, Minimum quantity lubrication). The cutting performance was evaluated using the machinability indicators such as tool wear, cutting force, surface finish, morphology of chips and residual stress. The chip morphology and residual stress results indicated that the thermally assisted deformation highly influences the machining of SDSS under all coolant environments. The overall machinability results revealed that MQL provided better performance than the other coolant and lubrication methods. To assess the SCC resistance, all the machined samples were subjected to SCC test under the chloride environment. The machined samples under MQL environment was observed with low surface crack density. This is due to presence of lower tensile residual stress with less surface defects. It was also observed that MQL samples exhibits lower localized corrosion (i.e) pit formation on the surface. These results clearly demonstrate that MQL is a recommended cooling and lubrication condition for the efficient machining of SDSS and to improve service life of the component.