317 eva‎luation of microstructural and mechanical properties of Dissemillar welding bitween Incoloy 825 and low strength alloy steel API 5L X70 using two filler metals ER NiCrMo 3 and austenitic stainless steel 309L Afzal ravand Email address a ravand@ma iut ac ir Date September 16 2020 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language PersianSupervisor Morteza Shamanian Professor shamanian@cc iut ac irAbbas bahrahi Assist Professor a n bahrami@cc iut ac irAbstractInfluence of chemical composition on the microstructural evolution and mechanicalproperties in dissimilar weld between Incoloy 825 superalloy and high strength low alloyAPI X70 steel was investigated in this research Samples of base metals were welded withNiCrMo 3 and 309L austenitic stainless steel fillers using gas tungsten arc welding process The microstructure of different regions including base metals fusion zone and heat affectedareas was characterized by optical microscopy OM scanning electron microscopy SEM linear scan technique of energy dispersive spectroscopy EDS and X ray diffraction XRD analysis The mechanical properties of the specimens were assessed by tensile impact andmicro hardness tests Microstructural studies showed that the structure of NiCrMo 3 weldmetal was mostly austenitic and segregation of Mo and Nb to the inter dendrite spaces andsolidication grain boundaries led to the deposition secondary phases It was alsodemonstrated that 309L weld with its austenite ferrite FA solidification mode has adendritic microstructure with skeletal ferrite segregated with a skeletal or worm morphologyat the boundaries between dendrites or cells The results of tensile test showed that NiCrMo 3 weld had the highest tensile strength and the rupture occurred in ferritic base material Fractography examinations of tensile test specimens revealed that the fractures were mostlysoft type Results of impact test indicated that NiCrMo 3 weld had the highest toughness Examination of fracture surfaces revealed that the fractures were mostly soft type in impacttest This was due to the austenitic structure of NiCrMo 3 weld alloy This is also true forthe soft type failure of the tensile test samples According to the micro hardness test results the NiCrMo 3 weld the highest hardness due to the formation of hard Nb and Mo richphases as well as Lava Also the lowest hardness obtained was related to the heat affectedzone of API X70 It can be attributed to the dissolution of precipitations and grain growth inthis area because of the heat cycles applied during welding key wordsIncoloy high strength low alloy steel dissimilar welding transition zone heat input dendrites

مرتضي شمعانيان، عباس بهرامي

علي شفيعي، احمد رضاييان