Evaluation of tensile properties using uni-axial and ball indentation testing and correlation with microstructure variations across the 316LN stainless steel weld joints

Abstract

Automated ball indentation (ABI) tests were conducted across the 316LN stainless steel (SS) weld joints at 298 K, and 823 K. Zone wise tensile properties of 316LN SS weld joints such as weld metal, heat affected zone (HAZ), and base metal region are evaluated in this work. Uniaxial tensile tests were conducted to assess the effect of welding processes on the tensile properties. The weld joints were initially fabricated using arc based and laser based welding processes. The variations of tensile properties such as yield strength, ultimate tensile strength and strain hardening component values across the heterogeneous microstructure zones of the weld joints were evaluated. The correspondence between the microstructure variations and the tensile properties have been studied. The variations in grain size, secondary dendrite arm spacing (SDAS) and δ-ferrite content are found to be the primary cause of tensile strength variation across the weld joints. The gradient in tensile strength across the weld joints was higher at 298 K than at 823 K which was attributed to the microstructural changes at higher temperature causing material softening. It was noticed that the 316LN stainless steel weld joint made by hybrid laser MIG welding exhibited the highest values of strength and ductility among all the weld joints. It was attributed to the combined effect of higher δ-ferrite content and finer SDAS values. Therefore, the HLM welding process is recommended for welding of 316LN stainless steel components from the point of view of better tensile properties.