Research Publications
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Item Effect of cooling medium on microstructure evolution and tensile properties of creep-strength-enhanced ferritic steel(2018) Pandey C.; Saini N.; Thakre J.G.; Mahapatra M.M.; Kumar P.In creep-strength-enhanced ferritic steels, hydrogen-induced cold cracking of weldments is a serious issue. In the present research work, the effect of cooling medium on tensile properties and microstructure evolution of P91 steel weldments has been studied. For water-cooling condition, the diffusible hydrogen metal in deposited metal was measured by the mercury method. The microstructure of weldments in different cooling condition was characterized by using the field-emission scanning electron microscope (FE-SEM) and optical microscope. The fractured tensile test samples were characterized using the FE-SEM. The maximum tensile strength was measured to be 624 MPa for air-cooling medium (very low level of diffusible hydrogen). � 2018 Sociedade Portuguesa de Materiais (SPM)Item Comparative study of autogenous tungsten inert gas welding and tungsten arc welding with filler wire for dissimilar P91 and P92 steel weld joint(2018) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.Creep strength enhanced ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel is also designated as ASTM A335 used for out-of-core and in-core (piping, cladding, ducts, wrappers, and pressure vessel) of Gen IV reactors. In present investigation, the dissimilar weld joint of P91 and P92 steel were made using the autogenous tungsten inert gas (TIG) welding with single pass, double side pass and multi-pass gas tungsten arc (GTA) welding with filler wire. Microstructure evolution in sub-zones and mechanical properties of dissimilar welded joints were studied in as-welded and post weld heat treatment (PWHT) condition. Formation of ?-ferrite patches in weld fusion zone and heat affected zones (HAZs) and their influence on the mechanical behaviour of the welded joints were also studied. Presence of higher content of ferrite stabilizer in P92 steel have resulted the formation of ?-ferrite patches in weld fusion zone as well as HAZs. The ?-ferrite was observed in autogenous TIG welds joints. The ?-ferrite patches were formed in as-welded condition and remained in the microstructure after the PWHT. The ?-ferrite patches leads to reduction in Charpy toughness of autogenous TIG welds joint and also lower down the average hardness of weld fusion zone. Peak hardness and poor impact toughness were observed for autogenous TIG welds joint as compared to GTA welds. For microstructure characterization, field-emission scanning electron microscope (FESEM) with energy dispersive spectroscopy (EDS) and optical microscope were utilized. � 2017 Elsevier B.V.Item Autogenous tungsten inert gas and gas tungsten Arc with filler welding of dissimilar P91 and P92 steels(2018) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.Creep strength ferritic/martensitic modified 9Cr-1Mo-V-Nb (P91) steel also designated as ASTM A335 and P92 steel are used for piping, cladding, ducts, wrappers, and the pressure vessel in Gen IV nuclear reactors. In the present investigation, a comparative study of the effect of autogenous tungsten inert gas welding (A-TIG) with double pass and multipass gas tungsten arc (GTA) welding with filler on microstructure evolution in the weld fusion zone and the mechanical properties of P91 and P92 steel welded joints was carried out. The microstructure evolution was studied in as-welded and postweld heat treatment (PWHT) condition. The study also focused on the evolution of d-ferrite patches and their influence on the tensile properties of welded joints. PWHT was carried out at 760 C with durations from 2 to 6 h. To study the effect of d-ferrite evolution on mechanical properties, Charpy toughness, microhardness, and tensile tests were performed. The acceptable microstructure and mechanical properties were obtained after the 6 h of PWHT for A-TIG arc welding process while for GTA weld with filler wire, it was obtained after the 2 h of PWHT at 760 C. � 2018 by ASME.Item Some studies on P91 steel and their weldments(2018) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.In present research article, microstructure evolution in P91 steel and their weldments are reviewed in as-virgin and heat treatment and creep exposure condition. The thermal stability of P91 steel is derived from solid solution strengthening, sub-grain hardening and precipitation hardening. The initial microstructure plays an important role in deciding the mechanical properties of P91 steel and their weldment in long-term ageing and creep exposure condition. Effects of various alloying elements present in P91 steel and their related phase have also been discussed in details. The role of grain coarsening, Cr/Fe ratio, lath widening and dislocation density on creep rupture life of base metal and weldments are discussed. The combined effects of lath martensitic microstructure, residual stress and diffusible hydrogen content on performance of P91 steel material are also discussed. � 2018 Elsevier B.V.Item Effect of normalization and tempering on microstructure and mechanical properties of V-groove and narrow-groove P91 pipe weldments(2017) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.In Very High Temperature Reactor (VHTR), The Nb-V modified 9Cr-1Mo (P91) creep strength enhanced ferritic (CSEF) steel is currently considered as a candidate material for reactor internals and reactor pressure vessels (RPVs). After the welding of P91 steel, the inhomogeneous microstructure of weldment is a serious issue because it promotes the well-known Type IV cracking in P91 weldments. The present research work is focused on how the microstructure evolve in various zone of P91 pipe weldment during the sub-critical post weld heat treatment (PWHT) and normalized and tempered (N&T) heat treatment. The effect of PWHT and N&T heat treatment are also considered on tensile properties and hardness variation of P91 weldments. To characterize the sample scanning electron microscope (SEM), X-ray diffraction (XRD) and optical micrograph was used. It was observed that the N&T heat treatment provides the homogeneous microstructure compared to PWHT. The superior mechanical properties was also measured in N&T condition compared to PWHT. Study of fracture surface morphology of tensile tested specimen in different heat treatment condition is also presented. � 2017 Elsevier B.V.Item Characterization of Cast and Forged (C&F) Gr. 91 Steel in Different Heat Treatment Condition(2017) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.The present research work deals with the results of influence of different heat treatment conditions on the microstructure stability and mechanical properties of high-chromium X10CrMoVNNB9-1(P91) cast and forged (C&F) P91 steel. The C&F P91 steel was subjected to various tempering condition in the temperature range of 350�760 �C and tempering time of 2 h, after the normalizing at 1040 �C for 40 min. The steel was also subjected to furnace cooled and water quenched heat treatment. Tempering at 650 and 760 �C produced the fully tempered lath martensitic structure with M23C6, M7C3, M3C and MX precipitates along the prior austenite grain boundaries, lath boundaries and matrix region. Tempering at 350 and 1000 �C produced the partially tempered columnar laths and untempered columnar laths martensite, respectively. The tempering time was also varied from 2 to 8 h for fixed tempering temperature of 760 �C. The optimum microstructure evolution was obtained for 6 h of tempering at 760 �C that led to improved mechanical properties. � 2017 The Indian Institute of Metals - IIMItem Microstructure and transverse shrinkage stress analysis in GTA welds of P91 steel pipe(2017) Pandey C.; Narang H.K.; Saini N.; Mahapatra M.M.; Kumar P.In a steam power plant, several components such as boiler tube, condenser and steam lines are made of high creep resistant steel. The P91 steel pipes are generally used in steam power plant because of high creep strength at service temperature of approximately 600oC. In the present research work, the study about shrinkage stresses and their distribution in the four quadrants of P91 pipe weld of 11 mm thickness is reported. The conventional-V and narrow-groove welds were prepared by using the gas tungsten arc welding (GTAW) process. Welding current, arc voltage, groove design, and straining length were the main parameters that affect the transverse shrinkage stresses. In the present research work, the effect of groove design on transverse shrinkage stresses has been evaluated. It also describes the effect of the number of passes on shrinkage. It is concluded that, for a given heat input, the narrow groove pipe weld joint exhibits comparatively less transverse shrinkage stress. Scanning electron microscope (SEM) with field emission gun and optical microscope has been used to characterize the weld fusion zone and HAZs of P91 pipe weldments. � 2017, Korean Society of Steel Construction and Springer-Verlag GmbH Germany.Item Microstructure and mechanical property relationship for different heat treatment and hydrogen level in multi-pass welded P91 steel joint(2017) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.; Srivastava A.The effect of heat treatment condition and diffusible hydrogen level on microstructure and mechanical properties of multi-pass shielded metal arc welded (SMAW) P91 steel butt joints of 18�mm thickness has been studied. Field-emission scanning electron microscope (FESEM), Mercury diffusible hydrogen measurement, Charpy test, room-temperature tensile testing, hardness measurement and energy dispersive X-ray spectroscopy (EDS) were performed to characterize the multi-pass SMAW joints in as-welded, post-weld heat treatment (PWHT) and normalizing/tempering (N&T) state. The P91 steel butt joints with low level of diffusible hydrogen exhibited higher tensile strength and toughness. Both PWHT and N&T treatment provided similar mechanical properties but a significant microstructure variation was noticed for different zones of P91 welds. N&T treatment produced the homogenize microstructure along the P91 weldments both in terms of microstructure and micro-hardness. � 2017 The Society of Manufacturing EngineersItem Nano-size Particle Evolution During Heat Treatment of P91 Steel and Their Effect on Micro Hardness(2017) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.; Thakre J.G.In the present research work, creep strength enhanced ferritic/martensitic P91 steel was subjected to varying normalizing (950�1150 �C) and tempering temperature (730�800 �C). The varying normalizing and tempering temperature effect on microstructure evolution (precipitate size and their distribution and grain size) and microhardness were performed. The heat treatment consequences on microstructure evolution revealed an increase in grain size, and decrease in fraction area of precipitates, with increase in normalizing temperature. The grain size was found to be decreased with increase in tempering temperature while fraction area of precipitates and precipitate diameter increased. For microstructure characterization, optical microscope and field emission scanning electron microscope were utilized. The microhardness was found to be increased with increase in normalizing temperature while it decreased with increase in tempering temperature. � 2017 The Indian Institute of Metals - IIM