The thermo-mechanical attributes of DMR-249 A steel weld joints manufactured by shielded metal arc welding(SMAW) and activated gas tungsten arc welding(A-GTAW) processes were studied using Finite Element Model(FEM) si...The thermo-mechanical attributes of DMR-249 A steel weld joints manufactured by shielded metal arc welding(SMAW) and activated gas tungsten arc welding(A-GTAW) processes were studied using Finite Element Model(FEM) simulation. The thermal gradients and residual stresses were analyzed with SYSWELD software using double ellipsoidal heat source distribution model. The numerically estimated temperature distribution was validated with online temperature measurements using thermocouples. The predicted residual stresses profile across the weld joints was compared with the values experimentally measured using non-destructive techniques. The measured and predicted thermal cycles and residual stress profile was observed to be comparable. The residual stress developed in double sided A-GTAW joint were marginally higher in comparison to five pass SMAW joint due to phase transformation associated with high heat input per weld pass for A-GTAW process. The present investigations suggest the applicability of numerical modeling as an effective approach for predicting the thermo-mechanical properties influenced by welding techniques for DMR-249 A steel weld joints. The tensile, impact and micro-hardness tests were carried to compare the welds.Considering benefits of high productivity and savings of labor and cost associated with A-GTAW compared to SMAW process, the minor variation in residual stress build up of A-GTAW joint can be neglected to develop A-GTAW as qualified alternative welding technique for DMR-249 A steel.? 2016 China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.展开更多
High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grad...High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.展开更多
文摘The thermo-mechanical attributes of DMR-249 A steel weld joints manufactured by shielded metal arc welding(SMAW) and activated gas tungsten arc welding(A-GTAW) processes were studied using Finite Element Model(FEM) simulation. The thermal gradients and residual stresses were analyzed with SYSWELD software using double ellipsoidal heat source distribution model. The numerically estimated temperature distribution was validated with online temperature measurements using thermocouples. The predicted residual stresses profile across the weld joints was compared with the values experimentally measured using non-destructive techniques. The measured and predicted thermal cycles and residual stress profile was observed to be comparable. The residual stress developed in double sided A-GTAW joint were marginally higher in comparison to five pass SMAW joint due to phase transformation associated with high heat input per weld pass for A-GTAW process. The present investigations suggest the applicability of numerical modeling as an effective approach for predicting the thermo-mechanical properties influenced by welding techniques for DMR-249 A steel weld joints. The tensile, impact and micro-hardness tests were carried to compare the welds.Considering benefits of high productivity and savings of labor and cost associated with A-GTAW compared to SMAW process, the minor variation in residual stress build up of A-GTAW joint can be neglected to develop A-GTAW as qualified alternative welding technique for DMR-249 A steel.? 2016 China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.
文摘High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.
