Machinability and surface integrity issues in finish turning of hardened steel with coated carbide, deep cryogenically treated uncoated/coated carbide inserts

Abstract

In this study, coated carbide, deep cryogenically treated uncoated/coated carbide inserts were used for finish turning of hardened AISI H11 steel (50 HRC) under dry conditions. Both uncoated and coated carbide inserts were deep cryogenically treated at –196°C. The turning performance of both treated and untreated carbide inserts was evaluated in terms of maximum flank wear of inserts, surface roughness, white layer formation, micro–hardness variation and residual stress generated on the machined surface. The machining experiments showed that the performance of carbide inserts was better up to cutting speed of 137 m/min, while the performance deteriorated at higher cutting speeds. The white layer thickness varies from 1.2 µm to 2.2 µm for all the cutting conditions tested. The coated inserts with wiper geometry produced a surface finish less than 1.6 µm for all the cutting conditions tested, while in some of the cases with uncoated carbide inserts the Ra value was higher than 1.6 µm. The performance of deep cryogenically treated inserts was better as compared to the untreated carbide inserts in terms of both tool wear and surface integrity of machined surface.