Embrittlement of 1.25 Ni-Cr Case Hardenable Steel Used for Gear Assembly

Abstract 1.25 Ni-1.0Cr-0.1Mo case hardenable steel of EN353 grade is used for manufacturing gears. One such gear assembly was used in the azimuth control gearbox of an antenna system. After about six months in operation, the gear failed with a big noise in the gearbox during operation. The gearbox when opened showed disintegrated teeth of both gear and pinion, which was found, crushed and resulted in multiple smaller pieces. Globular shaped metallic pieces were also found in the gearbox. Detailed metallurgical investigation indicated that the fracture of the gear teeth occurred under impact of extraneous globular shaped metallic pieces of plain carbon steel entrapped in the gearbox. Inter-granular mode of fracture developed could be attributed to embrittlement of material.