IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

A multiphase microstructure was obtained in a medium carbon microalloyed steel using two step cooling (TSC) from a lower than usual finish forging/rolling temperature (800-850°C). A low temperature anneal was then used to optimise the tensile properties. A multiphase microstructure (ferrite-bainite-martensite) resulted from forging as well as rolling. These were characterised using optical and scanning and transmission electron microscopy. X-ray diffraction, transmission electron microscopy and hardness measurements were used for phase identification. Tensile properties and work hardening curves were obtained for both the forged and the rolled multiphase variants. A Jaoul-Crussard (J-C) analysis was carried out on the tensile data to understand the basic mode of deformation behaviour. Rolling followed by the TSC process produced a uniform microstructure with a very fine grain boundary allotriomorphic ferrite, in contrast to the forged variety, which contained in addition coarse idiomorphic ferrite. The volume fraction of ferrite and its contiguity ratio in the rolled microstructure were greater than in the forged grade. The rolled microstructure exhibited a better combination of strength and toughness than that of the forged material. The rolled steel work hardened more than the forged variety owing to its fine, uniform (bainite-martensite and ferrite) microstructure. Retained austenite present in these steels underwent a strain induced transformation to martensite during tensile deformation. The J-C analysis of the work hardening rates revealed typical three stage behaviour in both varieties during tensile deformation. © 2005 Institute of Materials, Minerals and Mining.

Department of Metallurgical and Materials Engineering

World University root node

Materials Science and Technology

Microstructural evolution and tensile behaviour of medium carbon microalloyed steel processed through two thermomechanical routes

In an attempt to improve fatigue and fracture resistance, a multiphase (ferrite-bainite-martensite) microstructure was developed in a V-bearing medium carbon microalloyed steel using a two-step cooling and annealing (TSCA) treatment following finish forging. The monotonic, cyclic stress-strain and low cycle fatigue behavior of this steel are reported. These results are compared with those of ferrite-pearlite and tempered martensite microstructures obtained by air cooling (AC) and quenching and tempering (Q&T), respectively. The tensile properties of the multiphase microstructure are superior to those of the ferrite-pearlite and the Q&T microstructures. Under cyclic loading, the ferrite-pearlite microstructure showed hardening at higher total strain amplitudes (≥ 0.7%) and softening at lower total strain amplitudes (<0.7%). The quenched and tempered and the ferrite-bainite-martensite (TSCA) microstructures displayed cyclic softening at all total strain amplitudes employed. Despite the cyclic softening, the ferrite-bainite-martensite structure was cyclically stronger than the ferrite-pearlite and the Q&T microstructures. Bilinearity in the Coffin-Manson plots was observed in Q&T and the multiphase TSCA conditions. An analysis of fracture surface provided evidence for predominantly ductile crack growth (microvoid coalescence and growth) in the ferrite-pearlite microstructure and mixed mode (ductile and brittle) crack growth in Q&T and the multiphase TSCA microstructures. © 2002 Elsevier Science B.V. All rights reserved.

Materials Science and Engineering A

Low cycle fatigue behavior of a multiphase microalloyed medium carbon steel: Comparison between ferrite-pearlite and quenched and tempered microstructures

A multiphase microstructure of ferrite-bainite-martensite based microalloyed steel was developed via controlled rolling, and a two-step cooling and annealing process. The cyclic stress-strain response and low cycle fatigue (LCF) life of the quenched and tempered microstructure were obtained. Analysis of the fracture surfaces of the LCF tested microstructure revealed cleavage facets at low strain amplitudes.

Scripta Materialia

Low cycle fatigue behaviour of a multiphase medium carbon microalloyed steel processed through rolling

To improve toughness and fatigue strength, a mutiphase (ferrite (F)-bainite (B)-martensite (M)) microstructure was developed in a V-bearing medium carbon microalloyed (MA) steel through a two-step cooling process that was followed by an annealing (two-step cooling and annealing (TSCA)) treatment. In the present paper, the high cycle fatigue (HCF) response determined in terms of the endurance limit, long crack fatigue threshold (Δ K th), crack closure and fatigue crack growth rate (FCGR) in a material that has a multiphase microstructure is presented and compared with those of the same material with a ferrite-pearlite (F-P) and a tempered martensite (T-M) microstructure obtained by air-cooling (AC) and quenching and tempering (Q&amp;T), respectively. Long crack fatigue threshold (Δ K th) and crack closure were evaluated using a dynamic compliance (DYNACOMP) measurement technique. The fatigue limit of the F-B-M and the T-M microstructures (∼400 MPa) was greater than that of the F-P microstructure (∼340 MPa). At load ratios less than 0.5, the threshold for long crack growth was lower for the F-B-M microstructure compared with that of the F-P microstructure. This is attributed to the reduced roughness-induced crack closure (RICC) contribution to the threshold in the former multiphase microstructure. A quantitative analysis of the near-threshold fracture surfaces validated the above conclusion. Fatigue crack growth rate in the Paris regime was found to be independent of the microstructure but dependent on the load ratio. © 2003 Elsevier B.V. All rights reserved.

High cycle fatigue behaviour of a multiphase microalloyed medium carbon steel: A comparison between ferrite-pearlite and tempered martensite microstructures

Due to cost effective processing, micro-alloyed (MA) steels with ferrite-pearlite microstructures are increasingly used in automotive applications in place of quenched and tempered (Q&T) steels, but the toughness of MA steels is inferior to that of Q&T steels. To improve toughness, forging is followed by a two step cooling (TSC) and a subsequent annealing. In this exploratory investigation a vanadium-bearing medium carbon MA steel was subjected to the above processing but finish forged at two different temperatures. The resulting multi-phase microstructures and mechanical properties were evaluated by optical and transmission electron microscopy, hardness and tensile property measurements. A comparison of the properties corresponding to the new routes of processing with those of the same steel containing structures of ferrite-pearlite and tempered martensite (Q&T condition) is also made. © 2003 Elsevier Science B.V. All rights reserved.

Journal of Materials Processing Technology

Thermomechanical processing and characterisation of multi-phase microstructures in a V-bearing medium carbon micro-alloyed steel

This paper deals with the high-altitude simulation and testing of upper stage rocket motors with large-nozzle area ratios, using second-throat exhaust diffusers (STED). To evaluate the performance of such motors, the low-pressure environment of the flight situation has to be simulated in the ground-testing installation. The shock pattern developed outside the rocket nozzle in the diffuser system can effectively seal the vacuum test chamber and maintain the required low-vacuum condition in the test chamber. An attempt has been made, in the present study, to numerically compute the flow field in a STED coupled with a large vacuum chamber, for simulating the entire high-altitude-test configuration of a rocket motor. Simulations have been carried out for both cold- and hot-flow situations and for cases with and without a large vacuum chamber. The computational results compare favorably with available experimental results for both hot (γ = 1.2)-flow and cold (γ = 1.4)-flow situations. The operational characteristics of the STED system and the associated flow structure are discussed in detail.

Department Of Civil Engineering

Department of Mechanical Engineering

Canadian Aeronautics and Space Journal

CFD analysis for simulated altitude testing of rocket motors

Advanced high strength steels have excellent strength-to-weight ratio and are widely used for automotive and structural applications. Grinding is commonly used as a final machining process for these materials to achieve the required dimensional tolerance and surface quality. In this work, the grindability of as-received microstructure of ferrite-pearlite and in-house developed ferrite-bainite-martensite steels using polycrystalline white fused alumina and microcrystalline sol-gel alumina grinding wheels under flood and minimum quantity lubrication conditions is studied. Grindability of these steels was evaluated based on the wheel wear, grinding forces, force ratio, specific cutting energy, surface roughness (Ra), and surface morphology. The sol-gel alumina wheel was observed with higher wear flat area and forces under all the grinding conditions as compared with white fused alumina wheel. The white fused alumina wheel exhibited higher force ratio values for all the grinding conditions than the sol-gel alumina wheel. The energy required per unit volume of material removal is lower for the white fused alumina wheel in both the steels under flood and minimum quantity lubrication conditions. This is due to the retention of sharpness of abrasive grains by self-sharpening for white fused alumina wheel than the sol-gel alumina. The presence of fractured, melted, and hollow chips on the ferrite-pearlite and ferrite-bainite-martensite steels under both the grinding condition confirms the change in material removal mechanism with the presence of higher wear flat area of the sol-gel alumina wheel. Based on the obtained results, the white fused alumina wheel was found to be a suitable grinding wheel for grinding of both the steels under all grinding conditions compared to the sol-gel alumina wheel.