http://localhost:8081/jspui/handle/123456789/15 2025-07-01T00:28:30Z http://localhost:8081/jspui/handle/123456789/17421 Title: THERMO-MECHANICAL BEHAVIOUR OF 23-8-N AUSTENITIC STAINLESS STEEL Authors: Sahu, Nilamadhaba Abstract: The hot workability, flow behaviour and initiation of dynamic recrystallization during hot deformation of 23-8-N steel are investigated in the temperature range of 950-1 100 °C and the strain rate range of 0.01-10s' using Gleeble 3800 thermomechanical simulator. Based on the experimental results a constitutive equation is predicted for the peak flow stress embracing the Zener-Hollomon parameter. The deformation activation energy and stress exponent are calculated to be 671.66 KJ/mole and 3.762 respectively by regression analysis. The critical stress for initiation of dynamic recrystallization is determined by the identification of an inflection point in the strain hardening rate versus stress plot. The average normalized critical stress is found to be 0.806. This is correlated with the microstructures and micro hardness values. The power dissipation efficiency and instability maps for the 23-8-N steel are developed adopting modified Dynamic material model (DMM). The power dissipation efficiency calculated using DMM is compared with that of modified DMM. Based on the shape of flow stress- strain curve and Comparison of J/P value with strain rate sensitivity, the validity of power law during the deformation process for the above material is analysed. The processing maps in connection with microstructures and experimental flow curves are used to interpret the possible safe processing conditions of the above material during hot metal working. This thesis comprises seven chapters. Chapter-I introduces briefly austenitic steel and nitrogen containing steels and dynamic recrystallization. Chapter-2 discusses about literature survey and the work related to the present research. Chapter-3 is about the formulation of problem. Chapter-4 describes the experimental work and equipments used to conduct this research work. Results and discussion comprise Chapter-S. This chapter critically discusses the results obtained during the research work. Chapter-6 highlights the significant conclusions obtained from the research work. Chapter-7 predicts the future work that can be carried out with this research work. References are given at the end of this thesis. 2013-06-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/17419 Title: THERMOMECHANICAL PROCESSING OF HSLA STEEL AND ITS WEAR BEHAVIOR Authors: Agrawal, Neeraj Abstract: SAILMA grade HSLA steel is thermally and thermo-mechanically processed in order to obtain different microstructures and mechanical properties. Multidirectional forging (MDF) and inter critical annealing techniques at different heating rate are used. MDF was conducted using a laboratory open die forging machine and Gleeble 3800 thermo mechanical simulator is used for the intercritical annealing operation to obtain UFG DP steels. Ultrafine grained (UFG) (i.e. grain size of the order I tm) steels have been investigated in order to obtain fine ferrite-martensite after intercritical annealing. The effects of initial starting microstructures and processing parameters like heating rate on the mechanical properties have been quantified. Experimental work was conducted on low carbon low alloy high strength steel (HSLA). Higher heating rates are necessary for achieving fine microstructures as well as better mechanical properties. The tensile strength of UFG dual phase steels was much higher than that of the coarse-grained counterpart, and the uniform and total elongations were significantly enhanced. Individual slurry erosion and cavitation damage of the processed HSLA steels is also assessed used for containing, transporting and processing of coal, ore and mineral slurries. The most erosion resistant steel has a dual phase ferrite-martensite microstructure and its erosion resistance is 1.5 times superior to that of the least resistant as-received HSLA steel. This is attributed to high hardness, toughness and greater strain hardening capacity of dual phase 14SLA steel as compared to that of the as-received and multi directionally forged HSLA steels. Mechanisms of erosion operating in differently processed steels for either forms of damage are discussed. 2013-06-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/17416 Title: NICKEL-SILICON CARBIDE COMPOSITE COATINGS SYNTHESIZED THROUGH ELECTRODEPOSITION ROUTE Authors: Priyadarshi, Piyush Abstract: Nickel silicon carbide composite coatings over copper substrate were synthesized using pulsed and direct current electrodeposition technique. The coatings were characterized using x-ray diffraction for crystal structure and grain size. Scanning electron microscopy investigations were conducted for determining surface morphology, reinforced particles and amount of SiC particles reinlbrced. The wear rate of coatings was studied using ball on disc technique. Vickers microhardness at coating surface was also measured and its value varies from 185± 5 to 440:. 5 VIfN. Eleetrodeposition were done by pulse current method at different frequency (10. 50, 1001 lz) and direct current, kept other parameters constant like temperature, p11. current density, duty cycle (for pc method) etc. Corrosion rate of composite coatings calculated from Tafel extrapolation and its value varies from 0.7779 to3.5990 iAJcm2 Measure the advanced mechanical properties at different Frequency and compare among them. 2013-06-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/17415 Title: MODELING AND SIMULATION OF OXIDATION OF COATINGS ON SUPERALLOYS Authors: Gupta, Mayank Abstract: In the present work a study has been undertaken to understand the kinetics of cyclic oxidation process in superalloys, review the models available and check if these models can be applied to model the oxidation process of the coatings on superalloys. AICrN based PVD coated samples of Superni 76 substrate were used. Cyclic oxidation tests in air environment and molten salt (Na2SO4.60%V205) salt environment were carried out at 900°C for 100 cycles. The parabolic scaling constant K, Cm, (L\W/A)max and C. were calculated on the weight change data. Various models were considered, used for efficiently modeling the cyclic oxidation process. Cyclic oxidation spalling program (C.O.S.P) was chosen for the air oxidation process. Cm, (AW/A)max and C0 were used as inputs for the model and K and Wm values was calculated using the model. The K value calculated by the inverse square method and Wm value calculated from the weight change curve were used for validating the model. Interfacial Spallation model was chosen for the modelling of cyclic oxidation process in the molten salt environment. K and FA were used as the inputs for the model and a curve between specific weight change and number of cycles was plotted using the model. The curve generated experimentally was matched with the theoretical curve and hence the model was validated. 2013-06-01T00:00:00Z