Study on Micro-Structure and Tensile Mechanical Properties of Dissimilar Metal Weld Joint Connecting Steam Generator Nozzle and Safe-End

Shuang Qi,Jinhua Shi,Xiaokun Liu,Lixun Cai,Fangmao Ning,Weiwei Yu,Lei Qi,Wenxin Xiang,Yonggang Wang

doi:10.3390/cryst11121470

Abstract

The safe-end of a steam generator (SG) nozzle dissimilar metal weld (DMW) for pressurized water reactors (PWRs) is the weakest point of failure which is crucial for the safe operation of a nuclear power station. Related to materials micro-structures, a uniaxial stress–strain relationship is the basic input parameter for nuclear power plant design, safety evaluation, and life management. In this paper, the micro-structure and tensile mechanical properties of a DMW of a European pressurized water reactor (EPR) were studied. Vickers hardness tester, optical microscope, and electron back scatter diffraction were used to analyze the micro-structure of the DMW joint. In addition, the residual strain of the DMW joint base material, heat-affected zone, weld metal, and fusion boundary region were studied. Based on digital image correlation (DIC) technology, tensile mechanical properties of the DMW joint were obtained. The results show that an accurate tensile stress–strain relationship of dissimilar metal welded joints can be obtained by using the DIC technique, the weld is the relatively weak link, and the residual strain is concentrated in the heat-affected zone. This study provides valuable engineering information regarding nuclear power plant design, in-service performance testing, and structural analysis and evaluation of welds containing defects.

Highlights

Welding joints are widely used in various key structures, such as steam generators (SG) and reactor pressure vessels (RPV) in reactor engineering
According to the differences in welding alloy materials and base materials (BMs), welding joints can be divided into a same-metal welding joint or a dissimilar metal weld joint (DMW joint) [1,2]
Due to a huge difference in grain size between 20MND 5 and weld material (WM) INCONEL 52, the Electron backscatter diffraction (EBSD) analysis was performed with a step size of 5 μm at a voltage of 20 keV to show the micro-structure of WM INCONEL 52 and Z2 CND 18.12 N2 controlled, while a step size of 2 μm was used

Summary

Introduction

Welding joints are widely used in various key structures, such as steam generators (SG) and reactor pressure vessels (RPV) in reactor engineering. Crystals 2021, 11, x FOR PEER REVIEvWanced Proto iXRD portable X-ray stress meter, shown, was used to tes4t aonf d13 obtain the welding residual stress of a narrow-gap automatic welding seam. The advanced Proto iXRD portable X-ray stress meter, shown, was FuFiisggeuudrreet4o4..tLeLosotccaaattinioodnnssofbfootrraoionbbssteehrrevviinwnggemlmdiiicncrrgoo--srstetrrsuuicdcttuuurareelsss(t(frfrreoosmms oAAf tatooFnF)a)ararnondwdm-mgeeaaaspsuurairuningtgommmiacicrtiorco-h-whaaredrlddnneinessgs (s(aaelloaonmngg.LLlilninee))aalolonnggtthheeDDMMWWjojoinint.t. The residual stress of a DMW joint is an important part of its mechanical properties. The advanced Proto iXRD portable X-ray stress meter, shown, was used to test and obtain the welding residual stress of a narrow-gap automatic welding seam. Due to a huge difference in grain size between 20MND 5 and WM INCONEL 52, the EBSD analysis was performed with a step size of 5 μm at a voltage of 20 keV to show the micro-structure of WM INCONEL 52 and Z2 CND 18.12 N2 controlled, while a step size of 2 μm was used.

Results and Discussion

Vickers Hardness Test

Uniaxial Tensile Test Based on DIC