Effect of Structural Heterogeneity on In Situ Deformation of Dissimilar Weld Between Ferritic and Austenitic Steel
- PDF / 3,415,655 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 66 Downloads / 198 Views
ODUCTION
DISSIMILAR metals welded joint (DMW) between low-alloy steel and austenitic stainless steel is widely used as primary piping of heat transport system in pressurized water reactors (PWR) of nuclear power plants.[1] The ferritic nozzle/coolant piping material is ASTM A508 Grade 3 Class I low-alloy steel and connecting piping material is SA312 Type 304LN austenitic stainless steel. This transition joint exhibits adequate strength and satisfactory resistance against intergranular stress corrosion cracking at operating condition.[2] However, microstructure and chemical composition have been changed across fusion boundary for this type of weld. There are a number of factors responsible for these M. GHOSH, Senior Scientist, is with the Structural Characterization Group, MST Division, CSIR_National Metallurgical Laboratory, Jamshedpur 831007, India. Contact e-mail: [email protected] R. SANTOSH, Research Fellow, is with the Department of Mechanical & Manufacturing Engineering, Manipal Institute of Technology, Manipal 576104, India. S.K. DAS, Principal Scientist, G. DAS, Sr. Principal Scientist, and B. MAHATO, Tech. Officer, are with the Materials Science & Technology Division, CSIR_National Metallurgical Laboratory, Jamshedpur 831007, India, J. KORODY, Professor, is with the Department of Mechanical & Manufacturing Engineering, Manipal Institute of Technology, S. KUMAR, Scientific Officer, and P.K. SINGH, Scientific Officer ‘G’, are with the Reactor Safety Division, Bhaba Atomic Research Centre, Mumbai 400085, India. Manuscript submitted December 9, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
changes: (i) different crystal structures between bodycentered cubic (BCC) ferritic low-alloy steel and facecentered cubic (FCC) weld metal, (ii) cyclic thermal stress owing to difference in thermal expansion co-efficient (CTE), (iii) diffusional mixing of alloying elements across fusion boundary, (iv) preferential oxidation at weld metal-ferritic steel interface (v) change of base metal dilution (BMD) affecting the composition gradient in weld metal, (vi) degeneration through creep in narrow carbon-denuded zone of ferritic steel, and (vii) phase transformation near fusion boundary.[3] Initially, the common welding consumable was austenitic stainless steel and at latter stage Ni-base alloy has been used.[4–6] Ni-base alloy has CTE in-between ferritic and austenitic steel with an additional advantage of restricting carbon diffusion. Carbon has low diffusivity in FCC nickel.[7] Jang et al.[1] have attempted to join low-alloy steel with 316 SS using IN 82 buttering material and IN 182 weld metal. Microstructural investigation revealed that fusion zone contained dendritic morphology with varying arm spacing, recrystallized structure, segregation, and secondary precipitation. Tensile properties were different across the fusion boundary of low-alloy steel and buttering material. Failure occurred through ductile dimple fracture during tensile testing. In a different endeavor, Alloy 800 low carbon steel was joined with 316LN SS using four types
Data Loading...
