Research Publications
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Item Role of evolving microstructure on the mechanical behaviour of P92 steel welded joint in as-welded and post weld heat treated state(2019) Pandey C.; Mohan Mahapatra M.; Kumar P.; Thakre J.G.; Saini N.An autogenous gas tungsten arc welded P92 weld joint was subjected to two different post weld heat treatment (PWHT). One PWHT involved tempering of the as-welded sample at 760 �C for 2 h (referred to as PWDT) followed by natural air cooling. The other PWHT involved normalizing (re-austenitizing) the as-welded sample at 1040 �C for 40 min followed by PWDT (referred as PWNT). The cross-section of the as-welded sample exhibited a higher degree of microstructural heterogeneity. Both the PWDT and PWNT heat treatment procedures reduced the heterogeneity gradient along the weld cross section. The heat affected zone (HAZ) of the as-welded and PWDT samples showed Charpy toughness values of 3 � 4 J and 64 � 6 J, respectively, which were lower than that of the base metal (72 � 5 J). The PWNT treated sample exhibited a HAZ Charpy toughness value of 83 � 4 J which was higher than that of the base metal. The brittle mode of the fracture with river patterns was observed for the as-welded and PWDT treated sample while a ductile mode of fracture with fine and shallow dimples was observed for the PWNT condition. The PWNT treatment resulted in dissolution of the ferrite patches and formation of a uniform microstructure along the weld cross section. The PWNT treated samples exhibited the lowest yield strength to tensile strength ratio supporting the enhanced ductility as a result of this re-austenizing heat treatment. The as-welded and PWDT treated weld joints showed the presence of detrimental ? ferrite phase in the weld fusion zone and the coarse grained heat affected zone. The PWNT completely removed the ? ferrite patches from the microstructure whereas the PWDT treatment merely reduced the range of the hardness of the ? ferrite from 179 to 301 HV (as welded) to 204�228 HV. � 2018 Elsevier B.V.Item Study on effect of double austenitization treatment on fracture morphology tensile tested nuclear grade P92 steel(2019) Pandey C.; Mahapatra M.M.; Kumar P.; Kumar P.; Saini N.; Thakare J.G.; Kumar S.Effect of �conventional normalizing and tempering� (CNT) and �double austenitization based normalizing and tempering� (DNT) process on microstructure characteristic and mechanical behavior was studied forP92 steel. In CNT heat treatment, P92 steel is normalized at 1040 �C/air cool and tempered with 760 �C/2 h/air cool. In DNT heat treatment, initially normalizing was performed at 1040 �C for 1 h followed by water quenching. After that sample was normalized in the temperature range of 950�1150 �C for 1 h and tempered at 760 �C/2 h/air cool (950 �C-DNT1, 1050 �C-DNT2, 1150 �C-DNT3).Grain size for CNT and DNT1 treatment were measured 17 � 7 ?m and 12 � 5 ?m. A DNT treatment resulted in homogeneous microstructure formation that led to improved mechanical properties as compared to CNT treatment. The DN based heat treatment produced complete martensitic microstructure formation by complete dissolution of carbide precipitates. The optimized room temperature condition was obtained for the DNT 1 heat treatment. � 2018 Elsevier LtdItem Effect of strain rate and notch geometry on tensile properties and fracture mechanism of creep strength enhanced ferritic P91 steel(2018) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.Creep strength enhanced ferritic (CSEF) P91 steel were subjected to room temperature tensile test for quasi-static (less than 10?1/s) strain rate by using the Instron Vertical Tensile Testing Machine. Effect of different type of notch geometry, notch depth and angle on mechanical properties were also considered for different strain rate. In quasi-static rates, the P91 steel showed a positive strain rate sensitivity. On the basis of tensile data, fracture toughness of P91 steel was also calculated numerically. For 1 mm notch depth (constant strain rate), notch strength and fracture toughness were found to be increased with increase in notch angle from 45� to 60� while the maximum value attained in U-type notch. Notch angle and notch depth has found a minute effect on P91 steel strength and fracture toughness. The fracture surface morphology was studied by field emission scanning electron microscopy (FESEM). � 2017 Elsevier B.V.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 Characterization of P92 Steel weldments in as-welded and PWHT conditions: Room-temperature tensile tests and microhardness measurements led to improving the ductility of the weld joints(2018) Saini N.; Pandey C.; Mahapatra M.M.; Mulik R.S.P92 steels have been developed as a candidate material for power plant components that operate in a temperature range of 620o-650�C. A heterogeneous microstructure formation across the P92 weldments makes the wettability of P92 steel a serious issue. The other problem that arises in P92 steel weldments is the formation of ?-ferrite due to the presence of a higher weight percentage of ferrite stabilizers such as V and Nb. as well as W and Mo. In the present work, the shielded metal arc welding (SMAW) process was utilized to prepare the P92 steel weld joints. After welding, postweld heat treatment (PWHT) was performed at 760�C for 2 h. To characterize the weld joints, room-temperature tensile tests and microhardness measurements were performed in the as-welded and PWHT conditions. The subsequent PWHT resulted in a decrease in the hardness gradient across the weldments. The PWHT resulted in enhancing the : ductility of the weld joints. � 2018 American Welding Society. All rights reserved.Item Grain refinement of P91 steel using double austenitization treatment(2018) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.; Thakre J.G.; Kumar P.The effect of conventional normalizing and tempering (CNT) and double austenitization-based normalizing and tempering (DNT) heat treatments on the microstructure evolution and mechanical properties of creep strength-enhanced ferritic P91 steel were studied. CNT treatment was performed at 1,050�C and air cooled for 1 h and also at 760�C and air cooled for 2 h. In double austenitization- based normalizing heat treatment, steel was austenitized at 1,050�C and air cooled for 1 h and then normalized in a temperature range of 950�C -1,150�C for 1 h followed by water quenching. After the double normalizing, tempering is performed at 760�C for 2 h. A DNT treatment resulted in homogeneous microstructure formation that led to improved mechanical properties as compared to CNT treatment. The incomplete dissolution of precipitates in single-stage tempering resulted in incomplete martensitic structure formation. � 2018 by ASTM International.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 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 Effect of creep phenomena on room-temperature tensile properties of cast & forged P91 steel(2017) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.In present research work, the as-received cast & forged (C&F) P91 steel was subjected to the creep test at temperature of 620 �C and 650 �C for applied stress of 120 MPa. The room temperature tensile test was conducted after normalizing and tempering (N&T) treatment of the ruptured creep specimen. The standard tensile-test specimen was prepared from the gauge section of creep ruptured specimen. The N&T treatment was performed to restore the microstructure and mechanical properties of virgin P91 steel (N&T P91 steel). The microstructure of creep fractured specimen in ruptured state and N&T condition were characterized by using field-emission scanning electron microscope (FE-SEM) with energy dispersive X-ray spectroscopy (EDS). The fracture surface morphology of crept specimen and the tensile tested specimen was also studied. The effect of prior creep deformation on the mechanical strength was more significant in the sample with longer creep rupture life. � 2017