Machining of martensitic stainless steel (JETHETE) with coated carbides

Tool life and wear models were fitted for machining a martensitic stainless steel (JETHETE) with three ceramic-coated carbides [CVD-Ti(C,N)/Al2O3 (T1) , CVD-Ti(C,N)/TiC/Al2O3 (T2) and PVD-TiN (T3)] using statistical regression analysis. The statistical analysis revealed the contribution of the cuttin g speed and feed rate to tool performance to be in excess of 80 per cent, w ith the cutting speed showing the greater degree of influence. Significant nose wear was the common failure mode observed at higher speed conditions. Plastic deformation and chipping/fracture at the cutting edge were addition al failure modes observed when machining with the T2 and T3 tool grades res pectively. The coarse grain size and high cobalt content contributed to the very poor performance of the multicoated T2 grade insert, while the improv ed microhardness of the PVD-TiN coating gave the single layer coated T3 gra de a comparable performance with the multicoated T1 grade. Attrition wear w as the principal wear mechanism at lower speed conditions. while dissolutio n/diffusion and abrasion were additional wear mechanisms when machining at higher speed conditions. A higher degree of diffusion wear occurred on the T3 grade insert owing to the relatively lower level of cubic carbides in th e tool composition.