Effect of Induced Residual Stress and Its Contribution to the Failure of an IC Engine Valve Material

Abstract

The increasing engine demands such as high power, fuel efficiency and lesser emission have led to enormous modification in the intake and exhaust system of an engine. These improvements create additional loads on the valve train components as they have to cope with the increased speed as well as the efficiency and higher temperatures. Thus, engine valve materials must have high durability, high fatigue, wear resistance and temperature resistance. Intake valves generally made of martensitic steels will undergo high cyclic loads, and due to this higher stress in the material, chording of valve face occurs. Major cause for the failure of inlet valves is fatigue. A chorded inlet valve has been analyzed to see the root cause of the failure, and various factors contributed to the failure have been studied. Failure analysis has been done starting from the engine operating conditions to the production processes of the valve material to find out the failure initiation point. Metallurgical study of the chorded valve material through SEM reveals the microstructural details, composition and inclusions. Residual stress induced in the material during various points of production and operation has been observed to calculate the effect of inferring stress to failure. The amount of residual stress in induction-hardened valve material before and after stress relieving has been calculated to find out the contribution of stress relieving to remove the added tensile stress. Failure prevention modes are suggested based on the lowest possible residual stress value observed.