CAUSE OF DEFECTS IN ENAMEL FIRED ON CAST IRON AT TEMPERATURES ABOVE 725°C., I*

A previous investigation on enameling cast iron is continued. Various wet-process enamels were fired at temperatures above 725 °C. (1335°F.). Blistering and pinholing, even at high temperatures, were found to be caused principally by hydrogen contained in the iron and not by carbon oxides. If carbon oxides form, they do not occur in sufficient quantities to deface the enamels. Dehydrogenized cast iron may be fired as high as 790°C. (1455°F.) with a direct application of sheet-steel white cover coat and at 840°C. (1545°F.) with sheet-steel ground coat without incurring defacement. The moisture content of certain constituents in wet-process enamels at higher temperatures causes an important gas effusion by reacting with the metal. The characteristics of the behavior of hydrogen in cast iron during enameling are compared with those of hydrogen in steel.