Manganese Steel Gear
Microstructural defects in a failed cast manganese steel gear from a coal mine excavator. Massive chromium carbides (A) formed due to an excessively high pouring temperature when the gear blank was cast. Carbide films (B) at the grain boundaries formed during heat treatment when the gear was not quenched quickly enough after coming out of the furnace. These conditions weakened the bond between grains, resulting in failure of the gear in service. Titanium carbonitrides (C) were intentionally produced to absorb nitrogen gas in the molten metal during the casting process.