Improving Surface Characteristics of Mold Steel using Electric Discharge Alloying

Abstract

Electric discharge alloying (EDA) is one of the evolving and promising techniques in the field of surface alloying. In EDA, deliberate transfer of tool material over the workpiece surface along with decomposed dielectric is anticipated to form a hard alloyed layer over the workpiece. The process mechanism of EDA lies in the basic concept of re-solidification of the melted tool and workpiece material which is resulted from electric discharge generated between them. This process could fmd its application in industrially important material, namely AISI P20 DIN 1.2311 SCM4, a low-alloy tool steel which is widely used as thermoplastic molds, extrusion dies, injection molds, and die-casting dies. It is essential to improve the surface characteristics of the dies and molds in terms of its hardness, wear, and corrosion resistance as it suffers from mechanical wear, corrosive environment during the casting process. Considering these aspects, electric discharge alloying is found to be economical and less time-consuming for surface modification, as the same set-up will be used for both the fabrication and repair of the molds. The main focus of the present work is to enhance the surface characteristics of AISI P20 mold steel in terms of its hardness, corrosion resistance, and wear resistance by using the electrical discharge alloying process. It was envisaged to achieve this by alloying titanium, aluminium, and nitrogen over AISI P20 mold steel by using a green compact powder metallurgy tool with a composition of 50 % titanium and 50 % aluminium compacted at a compaction pressure of 443 MPa. Three types of dielectric media, namely hydrocarbon oil, deionized water, and urea mixed deionized water, were considered. The present work investigates the EDA process both experimentally and numerically. The study was carried out to investigate the influence of the EDA processing conditions viz. discharge current, discharge duration, and the type of dielectric medium onto the alloyed layer thickness, material deposition rate, surfa