The Research of Heat-Resistant Layer Defects Formed during the Surfacing of Nickel Alloy on the Exhaust Valve Chamfer

Abstract

The final set of properties of the exhaust valve is formed in the course of the entire set of processes, the most important is the build-up of the valve chamfer which is subjected to constant high temperatures, gas flow and thermal cycling, therefore strict adherence to the whole complex of properties is necessary. In the study two materials were investigated: the deformable part of the base material (steel grade 40X10C2M (EN steel grade X40CrSiMo10)) and surfacing (alloy EP616A), used to manufacture the exhaust valve of the internal-combustion engine.The study was carried out at different stages of valve manufacturing: after electro-forging during the formation of a valve head from a rod, subsequent heat treatment (quenching + high tempering), after surfacing a ring with the heat-resistant alloy. The chemical composition of phases, inclusions, and sections of EP616A alloy around the shrink-hole were determined by the method of micro-X-ray analysis. The results indicate a shortage of visual inspection, and that conducting a selective destructive method does not ensure the full probability of detecting internal defects. It is advisable instead of destructive control to introduce ultrasonic flaw detection.