Microstructural Correlation of Hardness Profile in Martensitic Stainless Steel Weldment

The correlation between microstructures and hardness profiles in low carbon martensitic stainless steel girth weldment were investigated. Optical microscopy and a scanning electron microscope equipped with electron back scatter diffraction system were used for assessment of microstructural phases, grain sizes, and grain misorientation across the weldment. The hardness value fluctuated between the peak and lowest values in the heat-affected zone of the weldment. The hardness profile observed is consistent with microstructural evolution across the weldment. The low hardness value observed in the weld metal was attributed to the large proportion of ferrite introduced by the superduplex filler metal used for the fabrication and grain coarsening caused by prolonged cooling of the weld metal. The electron backscatter diffraction data showed that higher grain sizes occurred in the weld metal and this is consistent with the highest degree of misorientation and recrystallisation observed in the weld metal than parent and HAZ region of weldment.