4432

4182

كارشناسي ارشد

شناسايي وانتخاب مواد

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1387

ده،91،[II]ص:مصور،جدول،نمودار

ص.ع به: فارسي وانگليسي

عباس نجفي

احمد كرمانپور

23/1/1388

محمدرضا طرقي نژاد، خسروفرمنش

مهندسي مواد

ID4182

به فارسي وانگليسي: قابل رويت درنسخه ديجيتال

AbstractMetastable stainless steels are promising engineering materials demonstrating good corrosionresistance and good formability but they have also relative low yield strength Among thedifferent strengthening mechanisms grain refinement is the only method to improve bothstrength and toughness simultaneously Producing nano submicron grain size metastableaustenitic stainless steel by an advanced thermomechanical process is the aim of thisthesis Metastable austenitic stainless steels undergo a strain induced martensitictransformation where the metastable austenite phase is transformed to thethermodynamically more stable martensite phase due to the plastic deformation The straininduced martensitic transformation enhances the work hardening of metastable austeniticstainless steels This thesis concentrated on the effects of the strain induced martensitictransformation on the mechanical properties of AISI 304L Metastable austenitic stainlesssteel focusing on increasing yield strength by grain refinement The experiments were carriedout on steel AISI 304L Mechanical testing was performed by means of uniaxial tensiletests The martensite volume fractions were measured with a Ferritescope X raydiffraction was used for the phase identification of the test materials Microstructureinvestigations were carried out by means of the scanning electron microscopy and opticalmetallography Industrial hot rolled and annealed samples whose thickness were 10 mm were cold rolled using different thickness reductions from 10 to 90 Cold reductions at0 C of 10 90 were carried out with inter pass cooling In order to obtain homogeneousaustenitic microstructures 90 deformed samples were annealed at different temperatures 700 C 900 C and times 30 s 1800 s The grain size before cold reduction wasapproximately 36 m Nano crystalline grains of about 300 nm were obtained in theAISI304L metastable austenitic steel by a thermomechanical process consisting of coldrolling at 0 C and 90 reduction and annealing at 700 C and 300 min The nano structuredaustenitic steel exhibits not only high strength 1010 MPa but also good elongation above50

عباس نجفي

احمد كرمانپور

محمدرضا طرقي نژاد، خسروفرمنش