A working roll of 210 mm diam and 500 mm face length was examined because of shell-shaped fractures. The roll consisted of Fe-0.83C-1.6Cr steel. The chromium content was low for a roll of this diam. The crack origin was located about 10 mm under the roil face. Surface hardness (HV1) of 900 kp/sq mm was exceptionally high corresponding to the martensitic peripheral structure. An untempered piece with such a thick cross section and a hardened peripheral zone with such high hardness must have high residual stresses that culminate in the transition zone. Therefore it must be very sensitive against additional stresses, be these of a mechanical or thermal nature. This contributed to the fragmenting of the roll face.

The governor on an aircraft engine failed and upon disassembly of the unit, it was discovered that the retainer for the flyweight pivot pins was broken. The channel-shaped retainer was made of 0.8 mm (0.030 in.) thick 1018 or 1020 steel. The part was plated with copper, which acted as a stop-off during carburizing of the offset, circular thrust-bearing surface surrounding the 16-mm (0.637-in.) diam hole. The bearing surface was case hardened to a depth of 0.05 to 0.1 mm (0.002 to 0.005 in.), then austempered to obtain a minimum hardness of 600 Knoop (1-kg, or 2.2-lb, load). Considerable vibration was created in the installation because of the design of the mechanical device used to transmit power to the governor. The pins were permitted to slide axially a small distance. Analysis (visual inspection, microscopic examination, and ductility measurements) supported the conclusion that failure of the retainer was the result of fatigue caused by vibration in the flyweight assembly. Impact of the pivot pins on the retainer also contributed to failure. Recommendations included redesign of the flyweight assembly, and replacement of the channel-shaped retainer with a spring-clip type of pin retainer.