Effect of Microstructure on Chip Formation during Machining of Super Austenitic Stainless Steel

Introduction

Austenite stainless steel (ASS) is distinguished from typical stainless steel by its chromium content, and has high ductility, extraordinary strength and toughness, and corrosion resistance (Abou-El-Hossein & Yahya, 2005; Fonda et al., 2007). The AL6XN alloy is a variety of ASS but it has been developed into a Super Austenitic Stainless Steel (SASS). The AL6XN SASS alloy is suitable for use in nuclear power and marine, food and chemical industry applications owing to its elevated resistance to corrosion (Koutsoukis et al., 2013). However, high percentages of alloying elements in the microstructure of the material affect its properties when applied to various manufacturing processes.

Machinability is the intrinsic ability of a material to deliver satisfactory performance when it is subjected to metal removal processes to form or shape a specific part that has a high surface finish obtained at a low cost (Lalbondre et al., 2013). The machinability of any work material depends on the properties of the material, the cutting tool geometry, the level of process parameters and the machining environment (i.e. dry or wet machining) (Kalpakjian & Schmid, 2014). A poor machinability feature of ASS is related to the work hardening layer produced that, along with its low thermal conductivity properties, produces segmented and serrated chips during the machining process. Vibrations owing to high cutting forces associated with cutting tool failure are a possible consequence when segmented chips are created. Surface microstructure and microhardness variations are utilised as quality indicators of the machined surfaces (Jang et al., 1996). Surface integrity, especially surface microhardness, is an essential factor when excessive mechanical and thermal loads are requested for special applications such as pumps and transformers (Grzesik et al., 2005).