Microstructural changes in HAZ of weld joints of S960 MC steel

An important role in preventing failures of S960 MC weld joints is analysing and understanding the microstructural changes in the heat-affected zone (HAZ). The HAZ comprises four key subzones with different mechanical properties and microstructures. Referenced to previous discussions, the most critical appears to be the inter-critical (ICHAZ) and sub-critical (SCHAZ) HAZ, likewise the coarse-grained HAZ (CGHAZ). This study investigated microstructural changes in each subzone using the electron backscatter diffraction (EBSD) and microhardness measurements. The microstructures within the HAZ were preponderantly martensitic with some self-tempered martensite and a small amount of upper and lower bainite. The grain size reduced gradually, moving from the CGHAZ to ICHAZ. Enhancing the insufficient knowledge of HAZ behaviour will ensure welds quality and expand the use of these steels.