Numerous holes and voids 

Areas where the braze alloy did not stick to the steel

Areas where the braze alloy did not sick to the carbide

This is the corner of the carbide at 50x.  There is a brown film over the back of the braze alloy.  You can see a round area of braze alloy in the lower right.  There are numerous bubbles which was trapped gas from the flux or from zinc that came out during brazing or from another material, possible a cleaning agent. 

There are large areas of bare steel.   These are most obvious in the duck shaped patches at the bottom of the first picture.  There are also several other areas.