Faculty Publications
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Item Multi-response optimization of the turn-assisted deep cold rolling process parameters for enhanced surface characteristics and residual stress of AISI 4140 steel shafts(Elsevier Editora Ltda, 2020) Prabhu, P.R.; Kulkarni, S.M.; Sharma, S.Surface and near-surface areas play an important role as far as safety and dependability ofengineering components particularly when it is subjected to fatigue loading. By applyingdiverse mechanical surface enhancement (MSE) strategies, close to surface layers can becustom-made bringing about enhanced fatigue strength. MSE methods are used to gener-ate surface hardened components without the time and energy-consuming heat treatment.Deep cold rolling (DCR) is one such method that can be employed where the mechanicalenergy induced enables surface-hardening of steels and thereby the combination of hard-ening and finishing in one single step. The objective of this work is to enhance residualstress and near-surface properties of AISI 4140 steel which is the most commonly usedmaterial in the automobile and aerospace industry. The samples were first turned and thendeep cold rolled with various process parameters. Microstructure, surface hardness, sur-face finish, fatigue life, and residual compressive stress after the treatment were examined.Response surface methodology (RSM) and desirability function approach (DFA) was used torelate the empirical relationship between the various process variables and responses andalso to determine the optimum parameter settings for better responses. Further, numericalsimulation of turn-assisted deep cold rolling (TADCR) process was done by utilizing ANSYS-LS-DYNA software to understand the state of residual stress under various treating settings.Confirmation experiments conducted with the optimum parameter setting to validate theimprovements in response and it is found that the deviation between optimum predictedand confirmatory experimental values is about 5%. © 2020 The Authors.Item Surface Properties and Corrosion Behavior of Turn-Assisted Deep-Cold-Rolled AISI 4140 Steel(Springer, 2020) Prabhu, P.R.; Prabhu, D.; Sharma, S.; Kulkarni, S.M.In this research, the effect of various turn-assisted deep-cold-rolling process parameters on the residual stress, microstructure, surface hardness, surface finish, and corrosion behavior of AISI 4140 steel has been investigated. The examination of the surface morphology of the turned and processed samples was performed by using a scanning electron microscope, energy-dispersive spectroscopy, and atomic force microscopy. Response surface methodology and desirability function approach were used for reducing the number of experiments and finding local optimized conditions for parameters under the study. The results from the residual stress measurements indicate that the rolling force has the highest effect by generating a deeper layer of residual compressive stress. The outcomes of surface hardness and surface finish emphasize that rolling force and number of tool passes are the most significant parameters affecting the responses. Surface studies confirmed the corrosion and its intensity onto the metal surface, and according to atomic force microscopy studies, the surface had become remarkably rough after exposure to the corrosive medium. Improvements in surface microhardness from 225 to 305.8 HV, the surface finish from 4.84 down to 0.261 ?m, and corrosion rate from 6.672 down to 3.516 mpy are observed for a specific set of parameters by turn-assisted deep-cold-rolling process. The multiresponse optimization for surface finish and corrosion rate together shows that a ball diameter of 10 mm, a rolling force of 325.75 N, initial roughness of 4.84 µm, and number of tool passes of 3 give better values for the two responses under consideration with composite desirability of 0.9939. Based on the experimental work at the optimum parameter setting, the absolute average error between the experimental and predicted values for the corrosion rate is calculated as 3.2%. © 2020, The Author(s).Item Thermomechanical Simulation of Ferritic Rolling of Titanium-Niobium Interstitial-Free Steel(ASTM International, 2021) Satish Kumar, D.; Sambandam, S.; Kuruveri, U.B.Austenitic or two-phase rolling of ultra-low carbon steels face temperature control issues and generate shape defects. Ferritic rolling has been developed as a solution, and ferritic hot-rolled sheets are used as final products, replacing hot-rolled followed by cold-rolled sheets. However, it is not in regular industrial production because of mill limitations. Hence, ferritic hot rolling must be optimized for developing a ferritic cold-rolled and close-annealed sheet through subsequent processing. In this work, industrial ferritic rolling process was simulated for a titanium-niobium interstitial-free steel using a thermomechanical simulator. Multi-hit plane strain compression tests were carried out at three different regimes below the lower transformation temperature (Ar1). Steels were processed under high strain and strain rates as experienced during industrial hot rolling operation, and the results were compared with the conventional austenitic rolling. The flow stress of the material in the ferritic regime decreased with decreasing deformation temperatures but increased at temperatures below 700°C. Nonuniformity in grains and texture also increased with decreasing temperatures. High-temperature rolling in ferritic condition close to Ar1 temperature does not differ significantly from the austenitic condition, whereas the low-temperature ferritic rolled material had through-thickness microstructural nonuniformity and unwanted goss and brass fibers. The intensity of gamma-fiber {111}Item Formability behaviour of ferritic and austenitic rolled Nb–Ti stabilized IF grade steel(Springer, 2023) Satish Kumar, D.; Sambandam, S.; Udaya Bhat, K.Recently, soft hot strip and hard hot strip produced through ferritic rolling are projected as a direct replacement to austenitic cold-rolled sheets for many forming applications. However, industrial hot-rolling mills, with final rolling thickness limitations cannot produce these thinner products and have to be subsequently cold-rolled to the desired application thickness and further annealed. Under ferritic rolling conditions, the hot-rolling temperature of these coils governs the final properties. The temperature difference in hot-rolled sheets generates the difference in the microstructure and texture of these coils after cold-rolling and annealing and variation in their formability behaviour. In the present work, an Nb–Ti stabilized IF grade steel was hot-rolled at two different temperatures in the ferritic regime and subsequently cold-rolled and annealed for structure-property comparison. As formability is an application-specific requirement, the annealed sheets were tested for different formability characteristics. Industrially rolled samples were tested for fracture criterion, stretch-flangeability, deep drawability and stretch formability through the formability limit diagram, hole expansion ratio, earing test and Erichsen cupping test respectively. These parameters were compared with those of the austenitic regime rolled sheets. High temperature ferritic rolled sheets show improved formability in all tests due to better r ˙ , higher n-value, low Δr and stronger gamma fibre maxima at 111<121>. Low temperature ferritic rolled sheets show the lowest Δr and improved n-value, but has reduced r ˙ and higher alpha fibre texture. High temperature ferritic rolled sheets show higher formability limits in uniaxial tension and low temperature ferritic rolled sheets in biaxial tension of the FLD curve. Various tests established that high temperature ferritic rolled sheets are best suited for deep drawing and stretching applications whereas low temperature ferritic rolled sheets should be preferred for stretch forming applications. © 2022, Indian Academy of Sciences.Item Effect of equiaxed grains and secondary phase particles on mechanical properties and corrosion behaviour of CMT- based wire arc additive manufactured AZ31 Mg alloy(Elsevier Ltd, 2023) Manjhi, S.K.; Sekar, P.; Bontha, S.; Balan, A.S.S.Wire arc additive manufacturing (WAAM) has drawn tremendous attention for manufacturing large and complex components of lightweight material at a moderate cost due to its high deposition rate and energy efficiency. Generally, WAAM-Mg alloy comprises columnar and columnar dendrite grains due to high cooling rates and thermal gradients responsible for anisotropic mechanical properties. To overcome this challenge, in this work, CMT-WAAM, which generally uses comparatively low heat input (33% lower than conventional WAAM), was used to deposit AZ31 Mg thin wall. The metallurgical characterization of the deposited thin wall of the top (T), middle (M) and bottom (B) sections reveals equiaxed grains of average sizes ∼ 58, ∼ 63 and ∼ 38 µm, respectively. In addition, TEM results exhibit the formation of secondary phase particles, i.e., β-Mg17Al12 and ɳ-Al8Mn5. Further, the ultimate tensile strength (UTS) and % elongation (% EL) in the travel direction (UTS = 224 MPa, % EL= 23.47%) are superior to that obtained in the build direction (UTS = 217 MPa, % EL = 20.82%). The corrosion resistance of WAAMed AZ31 Mg alloy is higher than wrought (cold rolled) AZ31 Mg alloy in Hank's balanced salt solution (HBSS). The results of this study reveal the potential of CMT-WAAM to deposit different grades of Mg with desired microstructure, mechanical properties and corrosion resistance. © 2023 CIRPItem Role of δ-phase on recrystallisation behaviour of Inconel 718(SAGE Publications Inc., 2024) Padasale, B.; Potphode, L.; Dsilva, P.C.; Hegde, S.R.The present work investigates the annealing behaviour of prior-coldworked Inconel 718 (IN718) sheets over wide reduction and temperature ranges by performing cold-rolling and isothermal annealing, followed by mechanical testing and structural characterisation. The study reveals that, with increasing annealing temperature, the prior-coldworked alloy shows non-monotonic M-Type variation with double peak-hardening at 0.3Tm and 0.6Tm. The study discovers that the first peak is due to the ‘static–strain–aging phenomenon’ that precedes recovery-softening. The second peak-hardening is due to precipitation-hardening, following which, the alloy softens due to recrystallisation. Supported by SEM, electron back-scattered diffraction and X-Ray diffraction results, the investigation suggests that the precipitation of fine rod-shaped δ-phase creates numerous nucleation sites at the shear bands that cause recrystallisation-burst at 0.75Tm. However, above 0.75Tm absence of the δ-phase activates grain-boundary migration resulting in rapid grain-coarsening. © The Author(s) 2024.Item Annealing Behavior of Cold-Rolled Inconel 601(Springer, 2024) Dsilva, P.C.; Padasale, B.; Vasavada, J.; Mishra, S.; Hegde, S.R.Present study investigates isothermal annealing behavior of prior cold-worked Inconel 601 (aka, IN 601) sheets. The study comprehensively covers the annealing response of the material over wide cold-reduction and temperature ranges. Using structural characterization and mechanical testing, the study tracks strain-hardening, strain-aging, recovery, and recrystallization stages of IN 601 sheets as a function of degree of cold-reduction and annealing temperature. Using X-Ray diffraction analysis, hardness measurements, and tensile tests, the study reveals that prior cold-worked IN 601, irrespective of the degree of cold-reduction, consistently exhibits strain-aging during low-temperature (~ 0.4Tm) annealing. The investigation establishes that the ‘recovery stage’ is preceded by ‘strain-aging-stage’ during which the alloy exhibits superior strength and hardness than the strain-hardened and recovered states. Based on the thermomechanical experimental results, the current work proposes a recrystallization map that integrates the ‘strain-hardening’ and ‘strain-aging’ stages with the recovery and recrystallization stages. Additionally, microstructural analysis and SEM-EBSD analysis presented in this work indicate that, by suitably controlling strain-hardening and the recrystallization annealing, a refined microstructure comprising high aspect-ratio grains having high-angle grain-boundaries can be obtained that may improve both fatigue and creep properties of IN 601 sheets. © ASM International 2023.