Carbon restoration for decarburized layer in spring steel

Abstract

It is well known that decarburization has a bad effect on spring steel strength. This research presents a method to improve the product quality by means of recovering the decarburization layer. Unlike conventional methods, which usually use mechanical means, this method relies on a basic metallurgical principle, the process of diffusion. A carbon-rich layer is coated on the surface of the object. The object is then heat treated at conditions similar to the manufacturing process. To accomplish the objective, an experiment and a finite-element analysis (FEA) simulation were performed. The material chosen was a hypo-eutectoid steel with an excessive decarburization layer. The simulation was performed by digitizing the optical micrograph of decarburized raw materials and meshing the picture to get elements to start the analysis. Simple diffusion theory was then applied to the model. Various time parameters were used to simulate the redistribution of the carbon atoms. Comparable with the simulation, an experiment was also performed. The experiment began by coating a carbon-rich material onto decarburized raw material. The samples were then austenitized and subsequently either annealed or quenched. The state of the carbon restoration was then evaluated. The research concluded that the idea of carbon restoration can be implemented in the manufacturing process.