This study deals with the nondestructive discremination between the corona bond and the nugget in the spot welds using a newly developed ultrasonic measurement with the line focussed probe. Four types of spot welded specimens were prepareed. The transmission charactaristics of ultrasound in the nugget was investigated by the measurement of one sheet specimen, which were made by grinding after removing upper plate of spot welds. The nugget size was measured by the scanning measurement over the spot welded specimens with and without the indentation. The measurement result of one sheet specimen showed that the reflected wave from the back wall in the nugget exhibited higher or lower amplitude than that in the base metal, which depended on the water path in the measurement. The scannning results of spot welds also showed that the nugget was possible to discriminate from the corona bond as long as the indentation in the surface was shallow.
