Causes Analysis on Cracking of an Engine Exhaust Valve

The head of engine exhaust valve cracked in radial direction during the durability test. The cracking causes of exhaust valve were analyzed by chemical compositions analysis, macroscopic inspection and metallographic inspection. The results show that the weld overlaying technology of cone area of exhaust valve was not optimum, and the stress relief treatment was not in-time and complete. As a result of that, high residual stress remained in weld overlaying cladding. Under the combined action of mechanical stress and thermal stress, cracks were formed in weld overlaying cladding near the cone area and then propagated on radial direction.