Nanoindentation for investigation of microstructural compositions in SM490 steel weld zone

• Nanoindentation tests on 1089 points at SM490 steel weld zone were conducted.
• Elastic modulus and hardness spectra are obtained using statistical deconvolution.
• The volume fractions of the microstructures in the weld zones are identified.
• Pearlite and 2 types of ferrite are verified from the different mechanical properties.

Microstructural compositions in the weld zone of structural steel with 0.16 wt.% C were investigated using optical microscopy and nanoindentation. Nine grid indentation experiments of 121 points were performed on different locations of three regions, base metal (BM), heat-affected zone (HAZ), and weld metal (WM) of the weld zone. The elastic modulus and hardness for each indenting point were then extracted from the nanoindentation results. Using the statistical analysis of 121 nanoindentation test results for each location, the microstructural compositions and the corresponding volume fractions of individual weld zone were investigated. Microstructures of BM, HAZ, and WM were observed using optical microscopy. The results showed that BM, HAZ, and WM are composed of three microstructural phases, low stiffness ferrite, high stiffness ferrite, and pearlite with different mechanical properties. The influence of the number of indenting points on the application of statistical analysis was also discussed.