Junior Nomani

Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

Stagnation zone during the turning of Duplex SAF 2205 stainless steels alloy

ABSTRACT Duplex stainless alloys are extremely sensitive to cutting speed for strain hardening during machining. Tool wear for these materials is dominated by the adhesion wear because of formation of built-up edge (BUE) that upsurges the flank wear considerably. In addition, flute damage is a significant problem during drilling of those alloys. To address this issue, this paper investigates the mechanism of BUE creation in stagnation region of duplex SAF 2205 alloys during material removal by turning process. The investigation of chip root through SEM and electron backscatter diffraction (EBSD) revealed build-up of ferritic bands at the stagnation zone. Higher capacity of austenite phase to deform plastically is accountable for the ferrite build-up. This was detected as a possible activating mechanism of built-up edge. The flow pattern of austenite phase designates faster deforming compare to that of ferrite phases.

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

The AL6XN Super Austenitic Stainless Steel alloy is a commonly used steel in corrosive environments and tough applications. This paper aims to investigate the execution of a machining process on the AL6XN alloy. A wet machining process has been executed to machine the alloy under a combination of various cutting conditions using an up milling approach. Two cutting speeds, two cutting depths and two feeds were used. The outputs obtained and listed in this paper are the microstructure analysis, surface microhardness and the chip morphology. The microstructure of the AL6XN alloy was revealed using Electron Microscope and Electron Backscatter Diffraction (EBSD). Work hardening layer was located in the subsurface of the machined alloy. EBSD data assured that no phase transformation was occurred within the deformed microstructure due to machining. The chip cross-section was revealed to identify the presence of the shear bands and to calculate the alloy serration degree. KEywoRdS Chip Morphology, Machinability, Microstructure Analysis, Super Austenitic Stainless Steel, Surface Microhardness

Chip formation characteristics of selective laser melted Ti–6Al–4V

Abstract In this research work, chip formation characteristics of selective laser-melted (SLM) Ti–6Al–4V in both ‘as built’ and ‘heat treated’ conditions are studied and compared with conventional wrought Ti–6Al–4V. Machined chips and partially deformed chips were collected from turning trials and quick stop experiments to study the nature of chip formation characteristics. Chip formation studies reveal that, ‘segmented’ or ‘saw tooth’ chips were produced during machining of SLM Ti–6Al–4V materials. The tendency to form segmented chips was higher in SLM Ti–6Al–4V materials as compared to conventionally produced wrought Ti–6Al–4V. In addition, cracks were found to be a common feature in primary and secondary deformation zones of SLM Ti–6Al–4V chip samples, illustrating that periodic crack initiation is the root cause of ‘saw tooth’ formation during machining. Furthermore, the tendency to form build up edge during machining was less in SLM Ti–6Al–4V materials compared to wrought Ti–6Al–4V, influencing the machined surface finish.

Current Trends in Machinability Research

The manufacturing index of a country relies on the quality of manufacturing research outputs. Theemergence of new materials such as composites and multi component alloy has replaced traditionalmaterials in certain design application. Materials with properties like high strength to weight ratio,fatigue strength, wear resistance, thermal stability and damping capacity are a popular choice for adesign engineer. Contrary, the manufacturing engineer is novice to the science of machining thesematerials. This paper is an attempt to focus on the current trends in machinability research and anaddition to the existing information on machining. The paper consist of information on machiningAustempered Ductile Iron (ADI), Duplex Stainless Steel and Nano-Structured Bainitic Steel. Thevarious techniques used to judge the machinability of these materials is described in this paper.Studying the chip formation process in duplex steel using a quick stop device, metallographic analysisusing heat tinting of ADI and cutting force analysis of Nano-structured bainitic steel is discussed.