Wear analysis of ultra-fine grain coated carbide tools in hard turning of AISI 420C stainless steel

Hardened AISI 420C stainless steel is a material used in surgical and dental tools due to its mechanical properties, allied with corrosion resistance. However, despite its advantages, this material presents poor machinability. Also, practitioners have often found difficulties using this material due to the lack of information concerning its behavior in machining processes, especially after heat treatment. The present paper investigates tool wear and wear mechanisms involved in hard turning of AISI 420C stainless steel with TiAlN coated ultra-fine grain carbide tool under different cutting conditions. Tool life tests were carried out using different feed rate and cutting speed levels. Machining tests were periodically interrupted in order to evaluate flank wear. The surface finish of the machined parts were evaluated throughout tool life, and the tools were analyzed through both optical and scanning electronic microscopy (SEM/EDS). Test results indicate influence of both cutting speed and feed rate over tool life. After reaching the tool life criterion of 0.2 mm flank wear, SEM microscopy evidenced abrasive wear for all tested conditions. Delamination of tool coating and crater wear were observed in some specific tested conditions. EDS analysis revealed significant amounts of iron and chrome adhered on all tools and oxygen at the highest cutting speed, indicating oxidation wear mechanism. The observation of built up edge in some tested conditions along with extensive adhesion suggests the occurrence of attrition wear mechanism over tool life.