Dilution from base metal or buffer layer will decrease the carbon content of the weld nugget. In such case you will not see a heat check crack running through a softer phase. I think the faceted carbides are M7C3 type (mostly Cr7C3)? The different orientations of carbides indicate a strong weld pool convection due to high welding current, and surface tension gradient across the weld center and fusion line. The dense carbide band could be a boundary between two convection pools. Microhardness and EDS analyses of the carbides may throw more light....

Thank you Dr. Krishnan for your valuable insight