Failure Analysis of Diesel Engine Inlet Valve

The inlet valve of diesel engine that made of one-piece forging and hard alloy surfacing welding broke during using process. In order to analyze the root failure cause and formulate the countermeasures, the analyses of macroscopic characteristics, microscopic morphology, metallographic structure, chemical composition, microhardness, and residual stress of the fractured intake valve were performed. The results indicate that the failure mode of the inlet valve is fatigue fracture. The hardness and residual tensile stress are high in the hard-facing layer. The intake valve is subjected to the superposition of mechanical shock load and high residual tensile stress in a complex working environment. Coupled with the high brittleness, all of these effects led to the appearance of the localized cracks in the surfacing area. And then, the cracks further expanded in a fatigue manner under repeated working loads until they finally broke. It is recommended to strictly control the heat treatment process after surfacing of the intake valve, in order to reduce the hardness and residual tensile stress, and avoid the recurrence of such failures.