Microstructure, Residual Strain and Stress Corrosion Cracking Behavior in 316L Heat-Affected Zone

Abstract

Austenitic stainless steels are usually chosen to make many components of nuclear power plants (NPPs). However, their microstructure in the heat-affected zone (HAZ) will change during the welding process. Some failures of the weld joints, mainly stress corrosion cracking (SCC), have been found to be located in the HAZ. In this research, the microstructure, micro-hardness, residual strain and SCC behavior at different locations of the 316L HAZ cut from a safeend dissimilar metal weld joint were studied. However, traditional optical microscope observation could not find any microstructural difference between the HAZ and the base metal, higher residual strain and micro-hardness, and higher fraction of random high-angle grain boundaries were found in the HAZ than in the base metal when studied by using electron back-scattering diffraction scanning and micro-hardness test. What's more, the residual strain, the microhardness and the fraction of random grain boundaries decreased, while the fraction of coincidence site lattice grain boundaries increased with increasing the distance from the fusion boundary in 316L HAZ. Creviced bent beam test was applied to evaluate the SCC susceptibility at different locations of 316L HAZ and base metal. It was found that the HAZ had higher SCC susceptibility than the base metal and SCC resistance increased when increasing the distance from the fusion boundary in 316L HAZ.

Effects of Temperature on Fretting Corrosion Between Alloy 690TT and 405 Stainless Steel in Pure Water

“…As a result, during the fretting wear process, abrasion is not the only damage, microstructure changes, including nano-grain layer, deformation slips with high residual strain concentration and even micro-cracks will also have a detrimental effect to the service performance of the heat exchanger tubes in NPPs. For instance, high residual strain concentration and deformation slips will promote the SCC or fatigue initiation and propagation in nickel-based alloys and stainless steels in HTHP water [36,37].…”

Comparison of the Stress Corrosion Cracking Behaviour of AISI 304 Pipes Welded by TIG and LBW

“…Due to the excellent weldability, high-temperature performance and corrosion resistance, AISI 304 austenitic stainless steel has been widely used in various fabrication industries as a structural material, especially in the nuclear power industry [1]. Stainless steel pipes made of AISI 304 are commonly welded by using tungsten inert gas (TIG) welding and laser beam welding (LBW).…”

Numerical Investigation on Residual Stresses of the Safe-End/Nozzle Dissimilar Metal Welded Joint in CAP1400 Nuclear Power Plants

“…As an important part of a loop pressure boundary, the joint is subjected to high temperature, high pressure and complex alternating stress in the operation of nuclear power plant equipment. Extensive research and experience in nuclear power plants indicate that the dissimilar metal welds of safe-end and nozzle are a weak component of the system, which is prone to stress corrosion cracking (SCC), and the service life is much shorter than the design life [1][2][3]. Residual stress is one of the important factors that leads to the SCC problem [4][5][6][7].…”