Machinability Of Austenitic Stainless Steel Research Articles

The Effects of Alloy Composition and Surface Integrity on the Machinability of Austenitic Stainless Steels 304 and 304L

Austenitic stainless steels, such as 304 and 304L, are extensively utilized in diverse industries due to their favorable properties, including biocompatibility, high durability, ductility, toughness at cryogenic temperatures, and excellent corrosion resistance. Additionally, these steels exhibit notable resistance to fatigue and oxidation. Despite these advantages, they are challenging to machine due to characteristics such as high work hardening, built-up edge formation, and low heat conductivity. The material 304L distinguishes itself from material 304 through its lower carbon content, making it more resistance to corrosion. 304L is experiencing a consistent rise in industrial demand. It is anticipated that this advanced material will progressively supersede 304 in various applications. The variability in alloy compositions and surface integrity of blanks can influence the tool wear and may even lead to abrupt tool breakage, necessitating supervision during machining operations. This study delves into the correlation between the alloy compositions, micro structure, surface integrity, and machinability of these special steels, focusing on turning processes. Various blanks of 304 and 304L in the form of bars, sourced from different manufacturers, were utilized in the study. These blanks exhibited slight variations in alloy composition (albeit within the standard range) and differed in the state of surface integrity characterized by variations in microstructure, grain size, microhardness, and residual stress. All blanks (across this array of materials) were subjected to turning using the same tool specifications and sets of machining parameters for comparative analysis. Various machinability indicators, including cutting forces, surface roughness, burr formation, tool wear, and chip morphology, were thoroughly examined. The findings highlight that the key factors influencing machinability include the microhardness of the surface and the residual stress state in the subsurface of the bars before the turning process. In contrast, changing the alloy composition within the standard range has hardly any effect on the machinability of these steels. The machinability of the examined specimens was adversely affected when the hardness exceeded 350 HV from the surface up to 2 mm below the surface and simultaneously the surface compressive residual stress exceeded −130 MPa.

Performance of carbide end mills coated with new generation nano-composite TiAlSiN in machining of austenitic stainless steel under near-dry (MQL) and flood cooling conditions

In the present study, a new generation nano-composite TiAlSiN coating has been deposited on 2-fluted carbide end mills using High Power Impulse Magnetron Sputtering (HiPIMS) in quadra-cathode target configuration. A highly smooth coating of about 3 μm thickness was realized and coated tools were subject to high-speed milling of austenitic stainless steel, which is otherwise known to cause severe diffusive wear on uncoated carbide tools. The effectiveness of TiAlSiN coating has been investigated on austenitic stainless steel under dry, wet (flood, 25 l/h), and near-dry (MQL, 250 ml/h) conditions. TiAlSiN coated tools experienced severe diffusive adhesion of work material on its cutting edge during dry machining. The near-dry approach with a cutting fluid consumption rate of only 250 ml/h was found to be a more effective, and greener approach. There was no sign of delamination of the coating under dry, flood, and near-dry environments. A maximum of 20 % reduction in cutting force and 45 % reduction in roughness (Ra) have been recorded in a near-dry environment compared to a flood environment. Performance of the HiPIMS deposited TiAlSiN coated tools have also been compared with that of commercial TiAlN and commercial TiAlSiN tools (deposited by DC Magnetron Sputtering) and found to be potentially more effective in milling of SS304 steel.

Machining of Austenitic Stainless Steels - the Influence of Various Factors on the Machining Result

Machining of Austenitic Stainless Steels - the Influence of Various Factors on the Machining Result

Analysis of the performance of PVD AlTiN coating with five different Al/Ti ratios during the high-speed turning of stainless steel 304 under dry and wet cooling conditions

High-speed machining of austenitic stainless steel normally causes significant tool damage and generates reduced tool life. In this paper, five AlTiN PVD coatings with different Al/Ti atomic ratios (50/50, 60/40, 67/33, 70/30 and 73/27) which deposited on cemented carbide inserts were used to conduct high-speed of 370 m/min finish turning tests. The experiments were carried out under different cooling conditions (dry and wet) on SS304 to study the tribological behavior of the AlTiN coatings with different Al/Ti ratios and the effect of the coolant under such aggressive cutting conditions. During the experiments, tool life, cutting force, wear mechanism, friction condition and surface integrity of machined workpiece were investigated. Crater wear was found to be the predominant wear mode during the cutting test, while the complex combination of oxidation, abrasion/attrition, adhesion, and chipping contributed to the tool failure. Given the machining conditions proposed in this study, the results revealed that all coated inserts possessed an improved friction behavior in the wet cutting condition. Compared to the dry machining, all five coatings had exhibited 2–3 times longer tool life. The AlTiN coated insert (Al/Ti = 60/40), in particular, exhibited a cutting length of almost 7000 m, compared to 1000 m for the AlTiN coated insert (Al/Ti = 73/27).

Experimental investigation of surface roughness and chip morphology during machining of austenitic stainless steel 303 with pvd coated (TiAlN) insert

Optimizing the influencing parameters of turning operation is a precious thing which determines the desired level of quality in Material Removal Rate (MRR) and Surface Roughness (SR). In this investigation, Taguchi based Grey Relational Analysis (GRA) has been used optimizing the effective process parameters such as depth of cut, feed rate and cutting speed on Stainless Steel 303 (SS 303) material while the specimen is turned with PVD (TiAlN) coated cutting tool. The experimental combinations have been planned based on Taguchi’s Design of Experiments technique. The optimal input parameter combination has been identified as 600 m min−1 spindle speed, 0.1 mm rev−1 feed rate and 0.2 mm depth of cut. The most influencing factor affecting the overall responses of turning process has been found out using Analysis of Variance approach as spindle speed (37.91%). Second-order mathematical models have been developed using Design Expert software for all the considered output responses, which provide the experimental values within the considered range of process parameters even without performing the actual experimentation. 3D surface plots have been generated and analyzed for interpreting the correlation between the process variables. SEM images taken on the machined surfaces and chips have been analyzed and presented in order to validate the optimization results.

Minimising carbon emissions and machining costs with improved human health in sustainable machining of austenitic stainless steel through multi-objective optimisation

Environmental and societal concerns have fuelled an ever growing need for more sustainable products and machining processes. Much research has been focused on this issue in aviation, automotive, and medical industries where austenitic stainless steels have been often used. During machining of these materials, high cutting forces and carbon emissions make the machining process significantly more challenging. Therefore, in this study sustainable orthogonal turning experiments were conducted using dry cutting, MQL, and cryogenic cooling at different cutting speeds and undeformed chip thicknesses. Experimental cutting forces were measured and used to analytically determine the carbon (CO2) emissions. In order to determine the optimal machining parameters for minimising the CO2 emissions and the overall economic cost with improved human health conditions, a multi-objective optimisation problem was established. The optimal machining parameters were determined to be a cutting speed of 100 m/min and undeformed chip thickness of 0.12 mm, while using cryogenic cooling.

Minimising carbon emissions and machining costs with improved human health in sustainable machining of austenitic stainless steel through multi-objective optimisation

Minimising carbon emissions and machining costs with improved human health in sustainable machining of austenitic stainless steel through multi-objective optimisation

Optimization of Machining Parameters for AISI 316L And 317L Austenitic Stainless Steels using Eco Cut Wire EDM Technique

Austentic stainless steel is one of the most suitable engineering material based on their superior resistance to corrosion and compatibility at high temperatures and high vacuum. However, the machinability of austenitic stainless steel is not very promising owing to lower thermal conductivity, higher degree of ductility and work hardenability. For meeting these challenges, unconventional machining procedures were evolved and can make any impenetrable design/profile on any work substance by acceptable controlling of various machining procedures. The main importance of this paper is to show the impact of machining parameters on Eco-cut Wire Electric Discharge Machining (WEDM) for disparate austenitic stainless steels (AISI 316L & 317L). Initially both the metals are machined on WEDM. Machining parameters like pulse on time(Pon), pulse off time(Poff), voltage(V) and wire tension(WT) are observed for both 316L and 317L stainless steel materials. A Box-Behnken Design (BBD) of response surface methodology (RSM) has been used for experimental work. The reaction of procedure is estimated by ANOVA analysis and response optimizer is used for optimum level checking. A series of trial runs were carried out on both the machined specimens for identifying better material removal rate(MRR), cutting speed(CS) and surface roughness(Ra).

An integrative approach to coating/carbide substrate design of CVD and PVD coated cutting tools during the machining of austenitic stainless steel

Machining of hard to cut materials such as austenitic stainless steel presents a challenge due the thermo-mechanical properties of this material, which contribute to intensive buildup edge formation and negatively affect tool life. CVD TiCN + Al2O3 and PVD AlTiN coatings deposited on cemented carbide substrates are generally recommended for machining austenitic stainless steel. These coatings were deposited by two different methods: (i) PVD AlTiN was deposited on the same substrate material at two different thicknesses (2.5 and 5 μm); (ii) CVD TiCN + Al2O3 was deposited with the same thickness (5 μm) on two different substrates. A new approach to applying various PVD and CVD (coating + substrate) integrated systems is introduced in this study for austenitic stainless steel machining. The relationship between the coating and substrate characteristics of these material systems and tool performance was assessed. The characteristics of the coating/carbide substrate design were evaluated in terms of chemical, phase composition, architecture, mechanical properties in relation to the tribological and wear performance. The obtained results demonstrate an improvement in tool wear performance and tool life brought about by the surface engineered layer/carbide material with an optimal combination of coating/substrate properties. Based on these findings, a guideline is proposed for further study of the cutting tool life and wear performance of CVD and PVD coated cemented carbide inserts.

Metallurgical changes of cryogenically treated Coated Carbide (KC-9225) and its performance during wet machining of Austenitic Stainless Steel – 310.

Various methods are employed to produce premium line of cutting tool materials with enhanced mechanical properties and improved service life. Cryogenic Treatment is one of those methods which has been considered for its benefits as a suitable add-on process. In this experimental investigation, Coated Tungsten-Carbide (KC9225) was taken as the cutting tool material and it was subjected to Deep Cryogenic-Treatment to analyse the several changes that might have taken place in its behaviour before and after the treatment. The treatment was carried out by a Dip-Stick arrangement where the temperature was gradually brought down to 100 K at the rate of ± 2 K/min. Tempering was also performed using the Dilatometer and the temperature was raised (~2 K/min) to 473 K. The changes in its mechanical properties both qualitatively as well quantitatively were investigated. Machining performance of the tool was also studied by performing wet turning on Austenitic Stainless Steel-310 where cutting force values were found to reduce by 3 to 71% in different cases thus proving its superiority as compared to the untreated tool.

Performance of supercritical carbon dioxide (scCO2) mixed with oil-on-water (OoW) cooling in high-speed milling of 316L stainless steel

During the machining of austenitic stainless steel, the main tool wear is caused by combined lubrication problems and high cutting temperatures in the cutting zone; a combination of cooling and lubrication techniques is the key to solve the problems. In this study, a new cooling–lubrication system combining supercritical carbon dioxide and oil-on-water droplets technologies (scCO2-OoW) was developed. Sprays of rapidly expanding scCO2 were utilized for the cooling and lubrication of machining processes by delivering a mixture of dry ice and OoW droplets deep into the cutting zone. 316L stainless steel was subjected to milling tests, where the efficiency of scCO2-OoW was compared with only scCO2, only OoW, and combined scCO2-minimal quantity lubrication (MQL) techniques regarding cutting force, tool life, and surface roughness. The results show that the application of scCO2-OoW was an efficient cooling–lubrication method for milling, as it reduced the cutting force and maintained a smoother cutting process than other cooling conditions. The cutting tool performed well at all cutting parameters combinations when the scCO2-OoW systems were used. The surface finish under the scCO2-OoW condition was significantly improved compared with the scCO2-MQL, only scCO2, and only OoW machining.

Surface integrity and fatigue behaviour of electric discharged machined and milled austenitic stainless steel

Machining of austenitic stainless steels can result in different surface integrities and different machining process parameters will have a great impact on the component fatigue life. Understanding how machining processes affect the cyclic behaviour and microstructure are of outmost importance in order to improve existing and new life estimation models. Milling and electrical discharge machining (EDM) have been used to manufacture rectangular four-point bend fatigue test samples; subjected to high cycle fatigue. Before fatigue testing, surface integrity characterisation of the two surface conditions was conducted using scanning electron microscopy, surface roughness, residual stress profiles, and hardness profiles. Differences in cyclic behaviour were observed between the two surface conditions by the fatigue testing. The milled samples exhibited a fatigue limit. EDM samples did not show the same behaviour due to ratcheting. Recrystallized nano sized grains were identified at the severely plastically deformed surface of the milled samples. Large amounts of bent mechanical twins were observed ~5μm below the surface. Grain shearing and subsequent grain rotation from milling bent the mechanical twins. EDM samples showed much less plastic deformation at the surface. Surface tensile residual stresses of ~500MPa and ~200MPa for the milled and EDM samples respectively were measured.

Experimental Study on Evaluating the Effect of Micro Textured Tools in Turning AISI 316 Austenitic Stainless Steel

Austenitic stainless steels show different machining characteristics as compared with the carbon steels or ferritic and martensitic steels due to their inherent properties. High ductility, low thermal conductivity, high tendency to work hardening and large built up edge formation on the cutting tools are the main reasons for the low machinability of austenitic stainless steels. The present study therefore, aims in improving the tribological characteristics at the tool-chip interface by surface texturing the cutting tools. The textures on the rake face of WC/Co carbide tools were obtained by laser machining. The effect of texture lay directions with respect to the cutting edge and chip flow was studied. The turning tests were performed using textured and conventional tools for various cutting environment. For studying the cutting performance cutting forces and tool wear were analyzed. SEM and EDS analyses were done to understand the tool surface characteristics. Results show that the textures can modify the adhesion of workpiece on the rake face as compared to the conventional tool and can help in reducing the cutting forces. Moreover, the lay direction of the groove significantly affects the tool-chip contact area and hence reduces the friction at the tool chip interface.

Grey Relational Optimization of Turning Parameters in Dry Machining of Austenitic Stainless Steel Using Zr Based Coated Tools

The present work aims at the microstructural characterization of TiAlZrN/ Al2O3 and TiAlZrN/Si3N4 coatings deposited via lateral rotating cathodes. The coatings were deposited using Lateral Rotating Cathodes (LARC) technology. The deposited coatings were studied for its cross sectional morphology using scanning electron microscopy. Energy Dispersive Spectrometry was also conducted along the cross section to determine the elemental composition. Micro Vickers hardness test was conducted to determine the hardness of the coatings. The scanning electron microscope images showed that TiAlZrN/Al2O3 coatings showed preferred columnar grain orientation with multilayered structure while TiAlZrN/Si3N4 coatings exhibit a dense grain structure. The TiAlZrN/Si3N4 coating shows a hardness of 31.58 GPa while TiAlZrN/Al2O3 coating shows a hardness of 25.40 GPa. Dry turning tests were performed on AISI 304 stainless steel. The TiAlZrN/Si3N4 coatings show reduced flank wear. Both the coatings even under severe cutting conditions impart surface roughness of less than 1.5 μm.

Influence of CVD and PVD coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts – A laboratory study

Austenitic stainless steels generally display poor tribological properties in sliding contacts partly due to their strong adhesion and transfer tendency to the counter surface. As a result machining of austenitic stainless steels is frequently associated with significant problems such as high stresses and high temperatures resulting in rapid tool wear. In the present study, the influence of coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts has been evaluated using a scratch testing equipment. Coating materials include modern CVD Ti(C,N)-Al2O3-TiN and PVD (Ti,Al)N-(Al,Cr2)O3 coatings deposited on cemented carbide and pre- and post-coating grinding and polishing treatments were used to obtain different micro topographies of the coating surface. Pre- and post-test characterization of the surfaces was performed using high resolution scanning electron microscopy, energy dispersive X-ray spectroscopy and optical surface profilometry.The results show that the intrinsic topography of the as-deposited CVD and PVD coatings promotes material transfer. For the as-deposited CVD coating the nanoscale topography of the crystals controls the transfer while for the PVD coating the µm-scale droplets and craters control the transfer. Post-polishing of the coating, especially in combination with pre-polishing of the substrate, significantly improves the tribological performance of the surface reducing the friction coefficient and the material transfer tendency. However, the presence of µm sized droplets and craters in the PVD coating limit the possibility to obtain a smooth post-polished surface and its resistance to material pick-up. In contrast, post-polishing of the CVD coating does not suffer from intrinsic coating defects which results in low friction and a very high resistance to material pick-up.

Calculating the Power Demand in Turning of AISI 316L Stainless Steel Through the Cutting Forces Data

Abstract—Austenitic stainless steel AISI 316L has been widely used for orthopedic implants due to its mechanical properties, corrosion resistance and biocompatibility. Machining of austenitic stainless steel are often regarded as 'difficult to machine' and classed a single group of steels, based on experience with the most common austenitic types. This paper presents a methodology for practical calculation of power demand based on cutting force that will be compared with experimental results especially turning process. Based on a previously proposed definition, the power demand in metal cutting is the energy required cutting. This paper provides a complete list of mathematical expressions needed for the calculation of power demand and demonstrates their utility for turning operation of austenitic stainless steel using coated and uncoated carbide.

Reliability of Al<sub>2</sub>O<sub>3</sub>/TiC Micro-Nano-Composite Ceramic Tool in the Machining of Stainless Steel

The cutting performance, failure mechanisms and reliability of Al2O3/TiC micro-nanocomposite ceramic tools with different geometry parameters in continuous machining of austenitic stainless steel were studied. The results showed that the largest metal removal amount was got at the cutting speed of 80 m/min, the feed rate of 0.15 mm/r and the cutting depth of 0.1 mm. The failure modes of the tool with small chamfering width and corner radius were mainly cutting edge fracture and tool materials peeling off, which was due to the subcritical crack growth. The life of the tool with small chamfering width and corner radius well followed the Gamma distribution.

Cutting performance and life prediction of an Al2O3/TiC micro–nano-composite ceramic tool when machining austenitic stainless steel

The cutting performance and failure modes of an Al2O3/TiC micro–nano-composite ceramic tool in the machining of austenitic stainless steel were investigated. Orthogonal test and range analysis were employed to determine the optimal cutting parameters. The largest metal removal amount was got at the speed of 80m/min, the feed rate of 0.15mm/r and the depth of cut of 0.1mm. The wear resistance of Al2O3/TiC micro–nano-composite ceramic tool were better than that of the alumina-based ceramic tool only reinforced by micro-scale TiC particles. Failure modes of the present tool were cutting edge fracture and tool material peeling off, which mainly resulted from the subcritical crack growth in the tool. The ceramic tool life was predicted based on the dynamic fatigue behavior of the tool material. Due to the inherent fatigue behavior of ceramics, the tensile stress distributing in ceramic tool would cause cracks initiation and promote the cracks extension. The life of ceramic tool for the failure mode of breakage was closely related to the fatigue behavior of the tool material. So, the ceramic tool life could be predicted by calculating the fatigue life of tool material. The stochastic tool life well scattered in the tool life prediction interval.

Prediction of Selected Aspects of Machinability of Austenitic Stainless Steels

The development of new materials and components for the development of new materials requires cutting their research in the cutting process. Currently, the increasing technical and economic requirements for the production of components (eg, increased productivity) of machining hard materials to improve the efficiency of cutting process. Finding the causes and define the conditions for efficient cutting process stainless steel is a paper.

Performance of PVD AlTiCrN coating during machining of austenitic stainless steel

In this study, the experimental results of dry, high speed turning of AISI 304 austenitic stainless steels using nanocrystalline AlTiCrN coated cemented carbide insert are presented. High power pulsed magnetron sputtering (HPPMS) and cathodic arc evaporation (CAE) techniques were used to deposit nanocrystalline AlTiCrN coating on fine grained K grade cemented carbide insert. The composition and microstructure of the deposited nanocrystalline AlTiCrN coatings were analysed using SEM. In addition, the adhesion and microhardness of the coatings were evaluated. Fine grained appearance with dense columnar structure was observed for the coating deposited by HPPMS technique. Microhardness values for nanocrystalline AlTiCrN coating deposited by HPPMS and CAE techniques were found to be 35 and 37 GPa respectively for the thickness of 4·2 μm. The effect of cutting speed and feed on the tool wear was investigated. HPPMS coated tool exhibited tool life of 24 min, whereas CAE coated tool exhibited tool life of 15 min for the same conditions.