A rare but deep internal oxidation of nickel-chromium alloys sometimes occurs in service. On some occasions oxidation is accompanied by deeper carburization or sulfidation, but in other cases these features seem absent. Laboratory tests showed that, with less than 9 percent chromium, exposure to air produced a thick external oxide under which there was some internal oxidation. With more chromium, however, attack in air was at a low rate. Several unsuccessful attempts to produce internal attack in high chromium alloys are described briefly. Exposure to carbon monoxide at 1750 F was found to cause rapid simultaneous carburization and internal oxidation of some nickel-chromium alloys. The addition of iron and silicon to the alloys slowed the attack. The addition of 2 percent columbium or 2 percent titanium prevented the attack completely. Some comments are made about mechanism.
6.3.10
