Wear mechanisms in austenitic stainless steel drilling : A comprehensive wear study

Abstract: This thesis is meant to serve as part of a competence platform for future product development projects at Sandvik Coromant AB, Solid Round Tools Department, Västberga, Sweden. The project objective is to gain generic knowledge of the wear mechanisms that restrict tool lifetime when drilling austenitic stainless steel. Thus, identifying if the weakest link of the tool is located within the coating, the coating adherence or in the strength of the substrate. A theoretical review of the work-piece and tool materials has been conducted as a background, along with definition of tool geometry and process parameters. Furthermore, the review includes chemical and process design effect on mechanical properties of the austenitic stainless steel, TiAlN coatings and cemented carbide substrates. Additionally, the basic principles of the wear mechanisms and wear types that are specific to drilling have been reviewed. During the experimental procedures both solid and exchangeable tip drills from cemented carbide with multilayered PVD TiAlN coatings were tested. Two series of tests were conducted, the first series aimed to identify wear type dependency on cutting speed, focusing on wear of the tool margin. The second test series was performed to map the wear progression depending on distance. Analyses including identification the main wear mechanism, quantification the amount of wear, identify wear location on the tool, crack investigation and WDS analysis of chemical wear. Adhesive coating wear was found on the tool margin at an early stage. The adhesive wear rapidly progressed into a stable intermediate stage. Leaving the substrate exposed and more susceptible to other wear types resulting in crack and oxide layer formation.