During fabrication of the EGCR steam generator cracking occurred in tube sheet of 1 1/4 Cr-1/2 Mo steel. Cracks were found at the torch-cut surface of the tube sheet following oxyacetylene torch cutting and a subsequent 1300 deg F stress relief. Metallographic examination of specimens containing the cracks showed that the tube sheet had fractured brittlely. The microstructure consisted of fernite and pearlite which had spheroidized to some extent by the stress relief treatment. Microhardness of the specimens ranged from 132.9 to 218 Vickers hardness (116 to 175 Brinell hardness). It would appear that the brittle fractures resulted primarily from the restraint imposed by the heavy section taickness (12 in.) of the tube sheet. (auth)