Research Publications

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Author: search.filters.author.Saini N.Start date: 2018

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    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.
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    Thermomechanical analysis of tungsten inert gas welding process for predicting temperature distribution and angular distortion
    (2019) Narang H.K.; Pandey C.; Thakare J.G.; Saini N.; Mahapatra M.M.; Jha P.K.
    In present research work, discussions have been made to predict the bead geometries and shape profiles of weldments using statistical regression modeling and fuzzy logic techniques. However, the regression and fuzzy logic modeling techniques do not take into account the actual physical properties and phenomena that occur in welding. Moreover, techniques such as regression and fuzzy logic modeling are not suitable for predicting the transient temperature distribution and distortion of arc welded joints. To predict the transient temperature distributions, peak temperature distribution, and residual deformation in welding, deterministic modeling techniques such as thermomechanical analysis are preferred. However, while performing thermomechanical analysis of welded joints, size and reinforcement dimensions of the weld bead need to be incorporated into the model for accurate prediction of transient temperature distributions and distortions. In this work, circularly spread moving heat source has been used for transient thermal modeling of tungsten inert gas (TIG) welding process. In the subsequent sections of this article, the weld thermomechanical analyses for TIG square butt joints are discussed to predict the temperature distributions and angular distortion. The weld dimensions such as weld width, weld depression, and weld bulging have shown great influence on the angular distortion patterns. � 2019 Society of Naval Architects and Marine Engineers. All rights reserved.
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    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 Ltd
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    Prior-austenite grain refinement in P92 steel using double austenitization treatment
    (2019) Saini N.; Mulik R.S.; Mahapatra M.M.
    The experimental investigation of 'double austenitization based normalizing and tempering' (DNT) heat treatments on tensile behavior and microstructural morphology of the CSEF/M P92 steel was carried out and compared it with the 'conventional normalizing and tempering' (CNT) heat treatment. The CNT treatment was performed at the normalizing temperature of 1040 �C for 60 min, followed by air cooling and then tempered at 760 �C for 120 min, followed by the air cooling. The DNT treatment involved the initial austenitizing at the temperature 950, 1100 and 1150 �C for 60 min, followed by the water quenching for higher dislocation density and then further austenitized at 1040 �C for 60 min followed by the air cooling. After the double austenitization based normalizing, tempering was performed at 760 �C for 2 h. The double austenitized samples are named as DNT 1 (950 �C), DNT 2 (1100 �C) and DNT 3 (1150 �C). The fine grain structure was obtained for the DNT 3 treatment. The fracture surface morphology of tensile tested specimen was studied using the field emission scanning electron microscope (FESEM). The results of tensile tests were obtained superior for the DNT treatment as compared to CNT treatment. Microstructure also showed the refinement of the grain size and lath width after the DNT treatment. � 2018 IOP Publishing Ltd.
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    Influence of filler metals and PWHT regime on the microstructure and mechanical property relationships of CSEF steels dissimilar welded joints
    (2019) Saini N.; Mulik R.S.; Mahapatra M.M.
    The nuclear grade modified 9Cr�1Mo (P91) and 9Cr-0.5Mo-1.8W�V�Nb (P92) are commonly used material for power plant components operating in the temperature range of 600�650 �C. For such steels, the creep strength at the elevated operating temperature is the prime criteria. However, microstructure stability and notch toughness also play an important role, especially for the welded joints to meet the pressure test at room temperature. The room temperature mechanical properties of the welded joint are strongly influenced by the welding process, filler composition, composition of the base plate and heat treatment performed after the welding. In present work, P91 and P92 dissimilar multi-pass welded joints have been produced using the different filler rod. The microstructure of the welded joint has been studied for the different filler composition in various heat treatment condition. The room temperature Charpy impact toughness and tensile properties for the different welded joints (different filler) have been also studied and related with the microstructure of the welded joint. From the results, it has been concluded that a higher amount of ferrite stabilizer in P92 filler promotes the formation of the ? ferrite in the weld fusion zone. � 2019 Elsevier Ltd
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    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.
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    Dissimilar joining of CFEF steels using autogenous tungsten-inert gas welding and gas tungsten arc welding and their effect on ?-ferrite evolution and mechanical properties
    (2018) Pandey C.; Mahapatra M.M.; Kumar P.; Saini N.
    Ferritic/martensitic 9Cr-1Mo-V-Nb steel also designated as ASTM A335 used in construction of several components of power plants operating in temperature range of 600�650 �C. In present investigation, dissimilar weld joints of P91 and P92 steel were prepared using the autogenous tungsten inert gas welding (A-TIG) and multi-pass gas tungsten arc (GTA) welding process. A comparative was performed on evolution of ?-ferrite patches in weld fusion zone and heat affected zone (HAZ) of welded joints. The evolution of ?-ferrite patches was carried out in as-welded and post-weld heat treatment (PWHT) condition. PWHT was carried out at 760 �C for 2 h for both A-TIG and GTA welding process. For A-TIG weld joint higher yield strength, ultimate tensile strength (UTS) and peak hardness were measured due to higher heat input in single pass and higher carbon content in weld fusion zone. Higher heat input, fast cooling rate and higher weight percentage of ferrite stabilizer like vanadium (V) and niobium (Nb) in A-TIG weld joint were resulted in formation ferrite patches in weld fusion zone and heat affected zone. Higher weight percentage of V and Nb in A-TIG weld zone was resulted poor impact toughness of A-TIG weld fusion zone than GTA welds in as-welded condition. After the PWHT at 760 �C�2 h, Charpy toughness of A-TIG weld fusion zone (48 J) just meet the minimum required value as required by the EN: 1557:1997 (47 J). � 2017
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    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)
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    Effect of welding process and PWHT on ?-ferrite evolution in dissimilar P91 and P92 steel joint
    (2018) Pandey C.; Mohan Mahapatra M.; Kumar P.; Mulik R.S.; Saini N.; Gopal Thakre J.
    Ferritic/martensitic 9Cr-1Mo-V-Nb (P91) and 9Cr-0.5Mo-1.8W-V-Nb (P92) steel are used for high temperature (600-650�C) operating components in nuclear and thermal power plants. The present research work deals with the dissimilar joining of P91 and P92 steel using autogenous tungsten inert gas (TIG) welding and multi-pass gas tungsten arc welding (GTAW) with filler. The evolution of ?-ferrite patches in weld fusion zone and heat affected zones (HAZs) were characterized in as-welded and post weld heat treatment (PWHT) condition. PWHT was carried out at 760�C for 2 h and 6 h, for both autogenous-TIG and GTA weld joints. Charpy toughness and microhardness tests were performed for autogenous-TIG welding and GTA welding process under as-welded and PWHT condition. � 2018 Elsevier Ltd.